CN1120067C - Bimetallic plate - Google Patents

Abstract

Bimetallic plate is produced by providing a substrate (S) of a first metal and, with the preheated substrate (S) positioned in a mould cavity (34) with a major surface of the substrate (S) facing upwardly and to fill a portion of the depth of the cavity (34), a second metal is cast against that surface to form a cladding component and, with the substrate (S), to form the bimetallic plate. Prior to the cladding being cast, the major surface is rendered substantially oxide-free and is protected against oxidation. The cladding is cast by a melt, of a composition required for it, being poured at a superheated temperature whereby, with the preheating of the substrate (S), an overall heat energy balance is achieved between the substrate (S) and the cladding. The heat energy balance causes a diffusion bond to be achieved between the major surface of the substrate (S) and the cladding, and attainment of the energy balance is facilitated by causing the melt to enter the mould cavity (34) through a series of gates (44) which provide communication between at least one runner (40) and the mould cavity (34). The series of gates (44) is disposed laterally with respect to flow of the melt therethrough whereby the melt forms a laterally extending melt front. Attainment of the heat energy balance is further facilitated by causing the melt front to advance away from the gates (44), over the substrate (S) surface, at a rate which is substantially uniform across the lateral extent of the front.

Description

Method and forming apparatus for producing bimetallic sheets

technical field

The present invention relates to a method and forming apparatus for producing composite metal articles comprising bimetallic plates.

Background technique

Various prior art solutions for making composite metal articles are discussed in US Patent No. 4,953,612 (Application No. PCT, AU84/00123) to Sare et al. These schemes have many shortcomings and limitations, at least some of which are overcome by the technology of USP 4953612. The scheme proposed by USP 4953612 is very suitable for producing composite metal products which include a cast part which is bonded to a base part. However, this solution is less suitable for the production of composite metal products comprising bimetallic sheets, especially bimetallic sheets which are thinner and/or have a larger surface area. Therefore, in the production of bimetallic plates of large dimensions, such as bimetallic plates of approximately 300 x 300 mm or larger, having a thickness of less than approximately 30 mm and a thickness ratio of cast metal to substrate of approximately 1.1 or less, the proposal of USP 4953612 Certain difficulties are encountered, such as uneven bonding.

The present invention seeks to provide a method and forming apparatus capable of producing thinner bimetallic sheets. However, while enabling such production, the invention can also be adapted to produce thicker plates. In either case, the present invention is capable of producing bimetallic panels of relatively large dimensions, for example up to and exceeding 1800 x 1000 mm, while indications are that the present invention can produce bimetallic panels of at least up to 3000 x 1500 mm.

In the method of the present invention, a plate formed of a first metal (hereinafter referred to as "substrate") has a portion formed of a second metal cast thereon (hereinafter referred to as "cladding") to form a bimetallic plate. The first metal used as the substrate may be titanium, nickel or cobalt, an iron-based alloy, or a titanium-, nickel- or cobalt-based alloy. The second metal used as the coating may be copper, nickel or cobalt, an iron-based alloy, or a copper-, nickel- or cobalt-based alloy. Although this is not required, the compositions of the first and second metals are usually different. However, when the first and second metals are the same or similar, i.e. their components are close, different properties can be obtained based on the microstructure, for example, because the substrate is made by hot or cold then have an as-cast microstructure.

As described in USP 4953612, the surface of the substrate on which the molten alloy is to be cast to form the coating should be substantially free of oxides. At the same time, the substrate is preheated and protected with an appropriate coating to prevent oxidation. The coating can be formed with a flux applied to the surface of the substrate and melted into a protective film during the preheating process. However, other protective coatings may also be used, such as deposits of suitable metals, for example by electroless or electroplating nickel or other metals, or non-metallic coatings, such as colloids with silicate binders graphite. Depending on the protective coating employed, it is displaced or alloyed with the alloy cast into the coating to facilitate the wetting of the substrate surface by the cast alloy.

Also, as described in USP 4953612, pouring the molten metal used to form the cladding at superheated temperature, combined with preheating of the substrate, can be beneficial to achieve an overall thermal energy balance, thereby obtaining a diffusion bond between the cladding and the substrate . Diffusion bonding is preferably obtained in the substantial absence of melting of the substrate surface onto which the cladding is cast.

When producing bimetallic sheets, it can be difficult to achieve a sufficient thermal energy balance for a good bond between cladding and base body. This is especially the case when the area of the plate is large and/or the plate is thin and/or the thickness of the cladding and the substrate is relatively small. Under these conditions, it was found that the loss of thermal energy to the mold becomes an important factor in preventing this energy balance, and this loss comes from the preheated matrix and the molten alloy flowing through the matrix. This loss is exacerbated by the delay between preheating the substrate and pouring the molten alloy to provide the cladding and/or by excessive pouring of the molten alloy. It has also been found that loss of uniformity in thermal energy balance, and thus non-uniformity in bonding, can be caused by uncontrolled or irregular flow of molten metal over the substrate, which can result, for example, in excessively long runners and/or Reduced alloy flow rate.

Contents of the invention

We have found that by controlling the casting of the molten metal forming the cladding, significantly improved bimetallic sheets can be produced. In the method of the invention, the cast alloy is caused to flow over the surface of the substrate along a controlled melt front which advances in the manner described below, i.e., taking into account the predetermined The heat temperature, and the superheat temperature of the molten alloy, provide a balance of thermal energy over substantially the entire surface of the substrate and within limits sufficient to obtain a diffusion bond between the coating and the substrate.

Although not required, the bimetallic plates may be square or otherwise rectangular in shape. For the convenience of further description, it is assumed below that the base body and the fabricated plate are rectangular. In addition, for ease of description, the direction in which the melt front advances through the substrate is defined as the longitudinal direction, and the direction in which the melt front expands laterally relative to its advancing direction is defined as the transverse direction. However, while the base body and resulting panel may have a longitudinal dimension greater than its transverse dimension, the situation may be reversed, or the longitudinal and transverse dimensions may be substantially equal. Furthermore, while the longitudinal direction of advance of the melt front may be substantially between longitudinally opposite edges of the substrate, the advancement of the longitudinal melt may cover a portion of the longitudinal extent of the substrate. Furthermore, the transverse dimension of the melt front and thus also the width of the coating in this direction can overlap almost the entire transverse dimension of the base body or a part of this dimension.

In the method of the present invention, the controlled melt front is advanced in a manner that provides the desired thermal energy balance for bonding by virtue of at least one of the following features:

(a) The molten alloy enters a cavity in which the matrix is disposed through a set of laterally disposed gates forming communication between the runner and the cavity, in which the molten alloy forms a laterally extending melt leading edge; and

(b) advancing the melt front longitudinally across the substrate at a substantially uniform velocity across the transverse extent of the melt front.

The method of the invention preferably utilizes each of features (a) and (b).

Thus, according to the present invention, there is provided a method for producing a composite metal product comprising a bimetallic sheet, wherein the method comprises the step of pre- Heat, at the same time, place the preheated substrate in the cavity of a mold with the main surface of the substrate facing upwards. In order to fill a part of the depth of the cavity, a part made of a second metal (hereinafter referred to as is cast onto said major surface of the substrate to form said bimetallic plate together with the substrate; the method also includes, prior to the step of casting the cladding, substantially freeing said major surface from oxidation material and coat the main surface with a suitable coating so that it does not become oxidized; the step of casting said coating is to cast a melt of the components required for the coating at a superheated temperature so that together with the preheating of the substrate , to achieve an overall thermal energy balance between the substrate and the cladding, and to allow diffusion bonding between the main surface of the substrate and the cladding; while completing the above step of casting the cladding also includes passing the melt through a set of at least one runner communicating with the cavity enters the cavity, and the set of gates is positioned transversely with respect to the flow of the melt therethrough, whereby the melt forms a transversely extending melt front , and cause the melt front to advance away from the gate on the surface of the substrate at a substantially uniform velocity across the entire lateral extent of the melt front. This makes it easier to achieve the desired thermal energy balance.

The present invention also provides a forming apparatus for the production of bimetallic plates having a plate formed from a first metal (hereinafter referred to as a "base") and a second plate cast on the base. a metal forming part (hereinafter referred to as "cladding"); wherein said apparatus comprises a mold having a lower mold part and a cope part; Cavity in which a substrate can be placed with its main surface facing upwards; the cope portion defines a portion of the cavity whereby the components required to form the cladding can be poured while the mold is in its closed state of the melt to fill the portion of the cavity above the base to form a cladding; each portion of the mold defines a set of gates that communicate between at least one runner and the cavity; The flow of their melt is arranged transversely so as to form a transversely extending melt front; wherein the mold is adapted to position said base body relative to said set of gates, whereby the melt front is free from the gates on the base body The main surface is advanced at a substantially uniform speed in the lateral extent of the leading edge, thereby obtaining an appropriate thermal energy balance between the substrate and the cladding through preheating of the substrate and superheating of the melt. Diffusion bonding is enabled between the main surface and the cladding.

In order to obtain feature (a), the molding apparatus according to the invention comprises a casting mold defining a cavity in which a matrix can be arranged and a molten alloy can be cast on the upper surface of the matrix. The mold defines at least one feed sprue receivable for molten metal, the feed sprue communicating with at least one transverse runner whereby molten metal enters each of the gate groups from the feed sprue gate. At least where the cladding extends from a lateral edge of the upper surface of the base adjacent the gate set, the cavity may have a rectangular dial-like portion at which the gate communicates with the cavity.

In a casting operation using a mold providing feature (a), molten metal flows into the cavity through each gate, and sequentially the streams of molten metal from each gate merge into a melt front of molten metal , the melt front passes longitudinally across the upper surface of the substrate. Where the cavity has a rectangular pan section, the confluence of the streams preferably takes place within the pan section before the melt front reaches the substrate.

To achieve feature (b), the transverse runners can be shaped such that the metal pressure is substantially equal at each gate in the gate set. For this purpose, the cross-section of the runner can be reduced after each successive gate in a direction transversely away from the feed sprue, for example by giving the runner a gradually decreasing depth. Additionally, or alternatively, feature (b) is conveniently obtained by a mold having a configuration such that when the substrate is placed in the cavity, the upper surface of the substrate is directed upwards from the feed sprue Slope, that is, slope upward along the direction of progress of the melt front. Thus, under the influence of gravity, the direction along the transverse dimension of the melt front constrains the melt front to progress substantially uniformly.

While it is generally preferred to have the upper surface of the substrate substantially horizontal or slope upward from the feed sprue, there are certain advantages when the upper surface of the substrate is sloped slightly downward from the feed sprue. That is, the upper surface may slope downwards in the direction in which the melt front advances. The advantage of the downward slope is that the flow rate of the metal can be increased. The extent to which the inclination may be made depends on the viscosity of the melt, while the magnitude of the inclination must be limited in order to ensure a substantially uniform rate of advancement of the melt front over the entire transverse extent of the front.

Although metal molds can be used, sand molds have been found to work well in the present invention. The mold is designed into two main parts, namely a drag part and a cope part. The drag part and cope part are preferably accommodated in a steel mold support, by means of which the parts of the mold can be clamped together, for example hydraulically. The drag portion has a cavity in which the substrate can be placed, while the cavity forms at least part of the cavity. The drag portion may have a sprue cup in which the molten alloy is received from the feed sprue, and it may also have at least one transverse sprue. The cope section has the bottom of the feed sprue, while it may also have a cavity which forms part of the mold cavity and into which the cladding can be cast. In addition, the cope section may also have a set of transverse gates, and at the bottom and gate remote from the feed sprue, the cope section may have a transverse cavity for receiving excess cladding alloy.

The parts of the mold can preferably be clamped together by means of a clamping force which, in combination with the design of the mold, ensures that the mold is adequately sealed. Thus, recourse to sealing means provided between opposing or mating surfaces of parts of the mold can be avoided, saving time between preheating the substrate and closing the mold in preparation for casting the cladding alloy.

In one suitable construction, the drag and cope portions of the mold are formed within their respective supports with molding sand and a binder such as a sodium silicate binder. Quartz sand is suitable although other molding sands such as olivine sand and zircon sand can be used. To reduce attack by molten alloys, runners and critical parts of the gate system can be made of bonded sand such as water glass sand selected from olivine sand, zircon sand or chromite sand, or if it is made of quartz sand, these parts can be protected with refractory casting coatings. At the same time, in order to improve the surface finish of the casting cladding, the cavity surface of the upper mold box part can be coated with a refractory casting coating. The support for each section may be constructed of fully welded mild steel channels, preferably the drag section support consists of a steel rod passing under the sprue cup to support the sand against the forces generated by the pouring molten alloy .

In a mold of this construction, the dimensions of the cavities in the drag portion, especially in the transverse and longitudinal directions, are sufficient to allow thermal expansion of the matrix. However, when the base body is placed in the cavity, its upper surface is preferably flush with an opposite circumferential upper surface of the drag portion which is flush with the circumferential lower surface of the cope portion. The surfaces are joined. As will be described in detail hereinafter, the cope portion preferably provides a grip to the edge of the base when clamped to the drag portion.

As mentioned above, the substrate is preheated prior to casting the cladding alloy. It is highly desirable that the delay between the completion of preheating and the start of casting be minimized, and it is most practical to preheat the substrate after it has been placed in the cavity of the drag section. In fact, it is impossible to preheat the substrate completely uniformly, so that the substrate deforms or bends, usually with upward arching in the central area, but also very prone to a certain degree of upward warping at the edges. Casting the cladding alloy on the substrate in this fashion would exacerbate the deformation or bending and further make it more difficult to produce useful bimetallic sheets. At the same time, deformation or bending may, for example, make it difficult to achieve feature (b) described above. It is therefore desirable to minimize or eliminate deformation or bending of the substrate.

Metal bolts welded to the lower surface of the substrate and fastened to the drag mold support with nuts can be used to compensate or prevent deformation or bending of the substrate. Alternatively, the force clamping the drag and cope portions of the mold together can be used to create a compressive load to press the substrate into a nearly flat state, thereby counteracting deformation or bending of the substrate. In one suitable process, a plurality of transversely spaced apart and longitudinally extending metal strips are tack welded to the upper surface of the substrate to form longitudinal channels in the substrate along which the cast alloy can flow. In another suitable process, a plurality of metal studs are spot welded to the upper surface of the base body in a suitably arranged array. The metal strip is dimensioned to form a channel having a depth substantially corresponding to the desired coating thickness, the metal strip may be of composition similar to that of the cast alloy and is bonded to the coating as part of the coating. layer. A stud whose thickness corresponds substantially to that of the desired cladding may also have a similar composition and be incorporated in the cladding.

By closing the mold and clamping the drag and coping sections together, the clamping force causes the coping to engage the metal straps or studs, thereby forcing the substrate down against the resulting compressive force Lower box part. The base can be forced into a nearly flat state, but slightly arched between adjacent metal strips or studs. This compressive force makes it possible to maintain the substrate substantially in this state during casting of the cladding.

The use of longitudinal metal strips or studs on the central region of the substrate to achieve this nearly flattened state causes the edges of the substrate to be pushed down within the cavity of the drag section. Thus, the molten alloy used to form the coating can be substantially prevented from flowing below the base body. However, it is advantageous to firmly press the base body at the longitudinal side edges. To achieve the latter purpose, for each of these edges of the base body, a corresponding longitudinal refractory rod can be cast into the cope part of the mould, these refractory rods being located such that when the drag part When clamped together with the cope section, the corresponding refractory rod engages and presses against one edge of the substrate. Alternatively, when the drag and drag sections are clamped together, the respective refractory rods described above may cover and clamp the longitudinal edges of the substrate where the molding sand of the cope section has sufficient strength.

When the mold sections are clamped together, the mold sections abut against opposing circumferential surfaces over a contact area sufficient to allow the mold sand in the mold sections to withstand the clamping force. At the same time, the area of the cope sand directly on each lateral edge of the matrix, for example 25 to 30 mm, can withstand the compressive forces acting on it from the bending forces generated on the edges of the matrix due to thermal stress. However, at the longitudinal bands or core stays used to flatten the substrate, the compressive force per unit area can reach such a level that damage to the molding sand in the cope section occurs. To avoid this, the cope section may include ceramic pins, metal pins with ceramic covered tips, longitudinal refractory rods or the like, which transfer the compressive forces to the metal straps or mandrels. Various pins, rods or the like may be secured to or engaged with brackets in the upper form section to transmit compressive forces from the upper bracket through the pins, rods or similar and via metal straps or studs to the base .

In the immediate vicinity of the gate, it may be difficult to hold down adjacent lateral edges of the substrate. Thus, during casting there is a risk that this edge of the base body lifts and molten metal penetrates below the base body. This danger is great due to the temperature gradient from the upper surface to the lower surface of the substrate caused by the superheated molten metal and its rapid flow velocity and the resulting bending forces within the substrate. However, if a mandrel is used to hold down the lateral edges of the substrate near the gate, they are likely to be rapidly melted by the fast-flowing molten metal unless they are sufficiently large and/or located in the direct line of discharge from the gate. outside of metal flow. A similar situation occurs if metal straps are used to hold down the substrate instead of corbels. Unless the strips are positioned out of direct alignment with any gates, there is little or no turbulence in the metal flow and there is little chance of the strips melting too quickly. Therefore, it would be desirable to have an alternative method to eliminate deformation or bowing of the substrate which would cause the lateral edges near the gate to lift.

A suitable method of suppressing the lifting of the lateral edges of the substrate is to bend the substrate so that the lateral edges are forced down onto the molding sand of the drag box. Another way of restraining the transverse edge is to weld a steel strip on the underside of the substrate along this edge. A convenient steel strip, such as mild steel strip, may have a cross-section of eg 25 x 6 mm and is welded to the edge of a substrate about 10 mm thick. The steel strip is accommodated in a correspondingly arranged transverse groove in the drag part, where the depth of the cavity of the drag part is increased. During the casting process, the steel belt positioned in the trough prevents molten metal from penetrating under the edge of the matrix.

In order to carry out the invention, there may be provided a casting section which provides firm support for the drag portion of the mould, means for conveniently manipulating the preheating furnace, and means for relative to the drag when the preheating cycle of the substrate is completed. The device that places the box part precisely and clamps the cope box part. In the casting section, there may be a support structure mounted to a firm support surface, and the drag part is placed or fixed on the support structure by means of its brackets. In the vicinity of the supporting structure, there are means for pouring molten alloy for casting the cladding. The apparatus may be a ladle in which the alloy is received from a nearby melting furnace. Preferably, however, the melting furnace is close to the support structure and adapted to pour the molten alloy into the mould. The melting furnace can be, for example, a tilting induction furnace.

The cope portion of the mold may be supported or mounted so as to be raised or lowered from a position to which the drag portion may be clamped as required. Such movement of the cope section may be accomplished by any suitable means such as overhead winches, telescoping hydraulic actuators and the like. The support of the cope part is preferably provided with rollers supported on the columns of the support structure so as to guide the cope part during its movement.

In its raised position, the cope section may be spaced a sufficient distance above the drag section for the preheating furnace to be disposed therebetween. The support structure may comprise horizontally arranged tracks along which a carriage forming part of or supporting the preheating furnace may travel between a retracted position and an advanced position in which the preheating The furnace is located above the drag box section.

Preheaters can take many different forms, such as gas fired preheaters, induction preheaters or electric preheaters. For testing a substrate 10 mm thick, approximately 1950 mm long and 1050 mm wide, a suitable preheating furnace has a downwardly open stainless steel shell and is insulated from the interior top and side surfaces with 125 mm thick low heat capacity insulation. Thermally insulated with helical nichrome resistance wire elements supported by ceramic tubes. Make this preheating furnace link with a three-phase 415V control box and its maximum output power is 150KW.

Description of drawings

In order to understand the present invention more easily, now describe with reference to accompanying drawing, wherein:

Figure 1 is a schematic side view of the casting apparatus used for the tests according to the invention;

Fig. 2 is the top view of equipment shown in Fig. 1;

Figure 3 is a partial end/section view of the apparatus shown in Figure 1;

Fig. 4 is a side view of another optional component in the device shown in Fig. 1;

Fig. 5 is a top view of another optional part shown in Fig. 4;

Fig. 6 is the top view of the lower mold box casting mold support of equipment shown in Fig. 1;

Figure 7 is a side view of the bracket shown in Figure 6;

Figure 8 is an end view of the bracket shown in Figure 6;

Figures 9 to 11 are similar to Figures 6 to 8 but show cope boxes;

Figure 12 is a schematic top view of a common form of casting mold for the apparatus shown in Figure 1;

Figure 13 is an end view of the mold shown in Figure 12;

Fig. 14 is a sectional view taken along line A-A of Fig. 12;

Figure 15 schematically represents an end view of the runner and gate system of the mold of the apparatus shown in Figure 1;

Figure 16 is a schematic plan view of the system shown in Figure 15;

Fig. 17 corresponds to Fig. 12, but represents the details of the molds used in the tests performed with the apparatus shown in Fig. 1;

Figure 18 is a cross-sectional view taken along line X-X of Figure 17; and

Fig. 19 is a sectional view taken along line Y-Y of Fig. 17 .

Detailed ways

Referring to FIG. 1 , a casting facility 10 has a support structure 12 made of welded steel members bolted to a concrete foundation 14 . In the casting section 16, the structure 12 has a drag portion 18 of a mold 19 secured therein. Above the casting part 16 , the structure 12 also engages a cope part 20 of the mold 19 , while close to the casting part 16 of the structure 12 the apparatus 10 includes a melting furnace 22 . The drag section 18 is placed on the structure 12 at a fixed location. However, the cope section 20 is supported by a chain system (not shown) of an overhead crane (not shown) so that the cope section 20 can move between a raised position shown in FIG. In the lowered position, the cope part can be clamped onto the drag part 18 to close the mold 19 for the casting operation. During this movement, the cope part 20 is guided by rollers (not shown) provided which run on rail parts of the columns (also not shown) of the structure 12 .

Apparatus 10 also includes a preheat oven 24 adjustably mounted on support structure 12 . For this mounting, the structure 12 has a pair of transversely spaced longitudinal rails 12b which extend beyond the drag portion 18 in a direction away from the melting furnace 22 from each side thereof. The preheating furnace 24 is installed on a carriage 28 by means of a hydraulic actuator 29, and the carriage 28 has rollers 30, by means of the rollers 30, the carriage 28 can travel on the track 12b, so that the preheating furnace 24 can be moved from Fig. The retreat position shown by the solid line in 1 moves to the position shown by the double-dashed line in Fig. 1, at the latter position the preheating furnace is between the mold parts 18 and 20, and is immediately above the lower mold box part 18 (assuming cope section 20 is in its raised position).

As best shown in FIG. 3, the preheating furnace 24 has an outer shell 24a which is an inverted trough so that it is open downwardly. The housing is preferably made of stainless steel and has transverse and longitudinal dimensions greater than those of the base S. The inner surface of the housing 24a is lined with a low heat capacity insulating material 24b, and within the housing 24a is housed a longitudinal array of transversely extending resistive heating elements 24c. Heating element 24c may, for example, comprise a helical nichrome resistance wire supported on a ceramic tube and adapted to be heated by energy from a suitable power source (not shown).

As shown in FIGS. 12 to 14 , the mold has respective sand portions 18 a and 20 a of a drag portion 18 and a cope portion 20 . Sections 18a and 20a are formed within a welded steel drag frame 18b (see Figures 6-8) and welded steel cope frame 20b (see Figures 9-11), respectively. As can be seen most clearly in Figures 12 to 14, the drag mold portion 18a has a large rectangular cavity 34 in which the substrate S can be placed. The cavity 34 has a depth corresponding to the thickness of the substrate, has longitudinal and transverse dimensions sufficient to accommodate the substrate S, and has a void 36 allowing the substrate S to expand thermally.

At the end closer to the melting furnace 22 and adjacent to one end of the cavity 34, the drag mold portion 18a has a sprue cup 38 with a corresponding transverse gate on each side of the sprue cup 38. Track 40 (also shown in Figures 15 and 16). At the same end of the cope mold portion 20a, there is a bottom feed sprue portion 42 which is vertically aligned with the sprue cup 38 and has four sprue portions on each side of the sprue portion 42. Gate 44. Portion 20a also has a large rectangular cavity 46, the depth of which may be approximately the same as that of cavity 34, depending on the desired coating thickness for substrate S. FIG. However, the transverse width of the cavity 46 is smaller than the transverse width of the cavity 34, and at its end closer to the melting furnace 22, the cavity 46 protrudes out of the cavity 34 to form a rectangular dial-like portion and Realization can communicate with each gate 44 . At the other end of the cavity 46, the part 20a has an enlarged overflow containment chamber 47 above the end of the base body S. As shown in FIG.

The drag portion 18 of the mold is mounted or fixed on the support structure 12 so that its upper surface, and thus the base S, is at a slight angle to the horizontal. Specifically, as clearly shown in FIG. 1 , it is arranged in such a way that the substrate S is inclined upward at an angle of several degrees, such as at most about 5°, such as upward, from its end near the melting furnace 22 to its distal end. Tilt about 3°. The cope section 20 may likewise be inclined, or it may be substantially horizontal but adjustable as it is lowered onto section 18, thereby inclining in a similar manner to section 18 to facilitate closing the mould. In addition, the actuator 29 supporting the preheating furnace 24 above the carriage 28 is capable of maintaining the preheating furnace 24 at an angle to the horizontal so that the preheating furnace 24 is substantially parallel to the substrate S, and the actuator 29 The height of the preheating furnace 24 above the carriage 28 can be changed when necessary, for example, the preheating furnace 24 can be lowered to a desired distance above the substrate S.

As described above, the drag portion 18 of the mold 19 and the sand portions 18a and 20a of the cope portion 20 are formed on corresponding welded steel supports 18b and 20b. As shown in Figures 6 to 8, the bracket 18b has a set of transversely spaced and longitudinally extending lower channels 48a having a C-shaped cross-section, the webs of which are uppermost. On the channel 48a, the bracket 18b has a set of longitudinally spaced and transversely extending upper channels 48b of C-shaped cross-section, the webs of which are also uppermost. Surrounding the rectangular grid formed by the channels 48a and 48b, the bracket 18b has a rectangular perimeter provided by the C-section channel 48c. These channels are firmly welded together at their junctions, while the upper flange of each channel 48c has openings formed thereon at intervals along its length.

As shown in Figures 9 to 11, cope frame 20b is somewhat similar to drag frame 18b, and upper channel 49a and lower channel 49b correspond to channels 48a and 48b, respectively, and peripheral channel 49c corresponds to Channel steel 48c.

As mentioned above, when closing the mold, the drag portion 18 and cope portion 20 need to be firmly clamped together in order to seal the interface between the portions 18 and 20 to prevent leakage of the molten metal, while quickly Clamping can be realized in order to reduce heat loss to a minimum. To this end, various forms of clamping devices can be used. However, the preferred form is the means 70 shown in Figure 9, with a corresponding means 70 being provided at each of a number of locations around the periphery of the mould. Each device is mounted on a corresponding bracket 71 welded at intervals along each channel 49c of the bracket 20b. Each device 70 includes a hydraulic rotary clamp, such as the SU(L/R)S201 type commercially available under the trade mark ENERPAC, which provides a clamp of approximately 18.8 KN at an oil pressure of approximately 35 MPa. Tight force. These devices have a cylinder 72 mounted on the bracket 20b of the cope part 20, and an associated piston rod 74 protruding from the cylinder 72. Hydraulic lines (not shown) supply oil to the cylinder 72 to enable extension and retraction of the rod 74 relative to the cylinder 72 . The engagement between the rod 74 and its cylinder 72 is such that when the rod is extended or retracted it rotates in one direction or the other.

Below each device 70, the bracket 18b of the drag section 18 has a corresponding one of the aforementioned openings (not shown) cut in the upper flange of the corresponding channel 48c. Each opening is dimensioned such that the rod 74 and an eccentric ring 75 secured to the rod 74 pass through the opening when the cope part 20 is lowered onto the drag part 18 and the rod 74 is extended. The rod 74 can then be retracted and, in synchronous rotation, its ring 75 engages under the flange in which said opening is cut. Thus, under the simultaneous action of several devices 70, the drag portion 18 and cope portion 20 can be securely clamped together.

When the mold is closed, it is required that parts 18 and 20 be clamped together so as to obtain a seal between opposing surfaces surrounding cavities 34 and 46 to substantially prevent leakage of molten metal therebetween. Said clamping can preferably be obtained by sand-to-sand surface contact between the mold parts 18 and 20 without the use of sealing means.

By raising the mold part 20 , the base body S is positioned in the cavity 34 . Prior to this, at least the upper surface of the substrate S is treated in order to remove all oxides. This can be done, for example, by sandblasting or shot blasting, using wheel or belt grinders or pickling. When the cleaned substrate S is placed in the cavity 34, its upper surface is protected by a flux coating, for example formed of a flux comprising flux powder, liquid flux or flux powder in liquid suspension. The flux can substantially prevent the re-oxidation of the substrate S, and other means described in detail in this specification can also be used instead of the flux, if desired. The preheating furnace 24 is then moved along the track 12b to its position above the drag portion 18 in order to heat the substrate S to a sufficient preheating temperature.

It will be appreciated that the preheating furnace 24 utilizes thermal energy to raise the temperature of the substrate S to a sufficient degree to, in combination with the superheating of the molten alloy within the melting furnace 22, achieve the desired bond with the cast cladding alloy. Although the preheat furnace 24 may be preferably an electric heater as described above, it may also be a gas heater or an induction furnace.

Before describing in detail the cyclic operation of the cast cladding, it should be understood that preheating the substrate by the preheating furnace 24, for example to about 750° C., will induce thermal stresses in the substrate S and cause it to deform. In addition, casting molten alloy onto substrate S by pouring the alloy into the mold cavity including cavities 34 and 46 increases thermal stress and deformation. In structures as described so far, deformations can significantly prevent the production of useful bimetallic plates. In order to produce such a product, a number of further features need to be employed, combined with the inclination of the drag portion 18 and the substrate S and the configuration of the runner 40 and the gate 44 .

As shown, the bottom 40 a of each runner 40 is stepped upwardly after each gate 44 so that the cross-section of each runner 40 decreases transversely of the sprue cup 38 . In particular, each runner is shaped such that molten metal flows to and through each gate 44 at substantially the same pressure and flow rate in the pouring state described in detail below. The separate streams of molten metal passing through gate 44 form a single stream of molten metal very rapidly without creating uneven longitudinal flow of molten metal along the substrate S. It is also advantageous to avoid this uneven flow by tilting the substrate S, since the flow of molten metal along the substrate is against the force of gravity. Contrary to the situation where an inhomogeneous flow would occur, a melt front will in fact be generated which is preferably substantially uniform in the transverse direction of the substrate S and proceeds in this manner substantially longitudinally of the substrate S.

In order to compensate for thermal stress effects at the lateral edge of the substrate S closer to the melting furnace 22, at this edge a steel strip 50 (for example with a cross-section of approximately 25×6 mm) is welded across the lower surface of the substrate S on the edge. A corresponding transverse channel 52 is formed in the drag mold portion 18a and at the corresponding end of the cavity 34 so that when the substrate S is placed in the cavity 34, the steel strip 50 is neatly received within the channel 52. By providing the steel strip 50, deformation of the substrate S immediately adjacent to the gate 44 is substantially prevented, while leakage of molten alloy below the substrate S at this edge is also substantially prevented. This leakage can be further suppressed by providing a ceramic fiber seal or the like in the channel 52 below the steel strip 50 . In addition, if the capacity of the preheating furnace is low, it is also possible to place a layer of ceramic fiber paper in the cavity 34 and under almost the entire area of the substrate S, because this insulating material under the substrate can help shorten the preheating substrate S. the time required.

As will be understood, the provision of the steel strip 50 is merely a suitable arrangement to prevent deformation or bending of the substrate S at its lateral edges closer to the melting furnace 22 . Other ways of achieving this include using coring or longitudinal steel strips on the upper surface of the base S, or welding metal bolts to the underside of the base S, as detailed above. Alternatively, a suitable mold design can be used so that the lateral edges of the substrate S can be forcibly pressed against the drag mold by the sand of the cope mold.

As previously stated, the transverse dimension of the cavity 46 in the cope mold portion 20a is smaller than the transverse dimension of the cavity 34 in the drag mold portion 18a. This difference in size is greater than the thermal expansion gap 36, so that when the mold is closed, the longitudinal border S' of the substrate S is joined by the overlapping region of the cope mold portion 20a. Portion 20a may be provided with a refractory ceramic insert 54, at least for a substantial portion of this overlap. The insert strips 54 are structured such that each strip 54 is forced downward against a respective substrate boundary S' when the drag and cope sections are clamped together. The force necessary to close the mold to seal against leakage of molten metal is sufficient for the insert strips 54 to hold the boundaries S' substantially flat and thereby prevent molten metal from appreciably leaking below the substrate S through these boundaries . However, it is not necessary to provide ceramic strips 54 since they can be performed with coping sand covering boundary S' provided the strength of the coping sand is sufficient to keep boundary S' substantially flat.

Controlling the deformation of the substrate S so as to prevent leakage of molten metal below the edges of the substrate is very important for the production of useful bimetallic sheets. However, it is also very important for the coating to have a good uniformity of thickness, especially in the central region of the base body, since in this area the arching of the base body is often very severe. In order to reduce this deformation at least in the central region, suitable spacers made of a suitable alloy are provided on the upper surface of the base body and fixed, for example by tack welding. In the illustrated construction, the device comprises an array of circular studs or discs 56, each of which has a thickness corresponding to the desired thickness of the cladding. When the drag and cope portions are clamped together, the compressive force on the disc 56 acts to press the substrate downwardly into the cavity 34 so that the substrate assumes a slightly flattened condition. Between adjacent disks 56 , the base S still has upward arching, but this arching is relatively small, and its range can be controlled by means of the distance between the disks 56 . As shown, the disc 56 may be employed over the entire central region of the substrate S, as well as along its lateral edges remote from the furnace 22 .

To form a cast cladding on a preheated substrate S to make a bimetallic sheet, molten alloy at a suitable superheated temperature is poured from the furnace 22 into the mold to fill the cavity 46 . It is highly desirable to fill cavity 46 quickly. This will ensure that the overall thermal energy balance brought about by the preheated substrate S and the superheated alloy is maintained at a suitable level until the filling of the cavity 46 is completed, thereby obtaining between the cladding and the substrate S with almost Desired binding across the interface. In order to be able to fill the cavity 46 quickly, a pool-shaped outgate is mounted on the cope part 20 .

A pool-shaped outgate 58 is shown in FIG. 1, which was used in initial experiments to produce a bimetallic plate of approximately 600 x 600 mm with a substrate and cladding thickness of 10 mm each. The outer gate 58 is mounted relative to the cope section 20 by means of an upper feed sprue section 59 which brings the interior of the outer gate 58 into contact with the bottom of the cope section 20 . The material straight gate part 42 is connected. The outer gate 58 and the upper sprue portion 59 rise and fall together with the cope portion. As the portion 20 is lowered and clamped onto the drag portion 18, the outer sprue 58 is configured to receive heat from the melting furnace 22 as the melting furnace 22 tilts forward, i.e., over the outer sprue 58. molten alloy.

The operation using the outer gate 58 and the sprue portion 59 can generally meet the requirements of producing bimetallic plates with dimensions as large as 600×600 mm. However, for this type of plate it has been found that the construction shown in Figures 4 and 5 is preferred and necessary for the production of bimetallic plates of larger dimensions. The structure shown in Fig. 4 and Fig. 5 includes a pool-shaped outer gate 58' and an upper feed straight gate portion 59'. The important differences between the outgate 58' and sprue section 59' shown in Figures 4 and 5 and the outgate 58 and section 59 shown in Figure 1 are:

(i) the height of portion 59' is reduced, and the height and internal volume of outer gate 58' is correspondingly increased;

(ii) the outlet position of the outer gate 58' is closer to the center relative to the sprue portion 59'; and

(iii) Provide a roof over the outer sprue 58' so that the outer sprue 58' is closed substantially around the outlet of the melting furnace 22 when the melting furnace 22 is tilted to pour molten alloy into the outer sprue 58'.

Because of these differences, substantially sufficient molten alloy may be poured into the outer gate 58' to form a casting cladding of an appropriately sized bimetallic plate. In addition, since a more direct through-flow can be achieved to a large extent with the gate 58', the molten alloy can flow from the gate 59' into the mold 19 at a higher flow rate. Thus, the melt front of the molten alloy formed on the substrate S in the mold 19 can advance through the substrate S at a faster rate, thereby completing the casting within a period consistent with maintaining thermal energy balance and uniform bonding.

It will be appreciated that pouring molten alloy into the outer gate 58' can rapidly create a melt front within the mold 19. Furthermore, the melt front can start advancing through the substrate S quickly. Thus, the shortest time between the start of pouring and the creation of a suitable flow of molten alloy through the substrate S, and thus the loss of thermal energy, is minimized. This advantage can be combined with the following other features that can be achieved by the equipment 10, that is, after the substrate S is preheated by the preheating furnace 24, the preheating furnace can be quickly withdrawn along the track 12b, and then the molding The box part 20 can be lowered and clamped onto the drag box part with very short delay times. Thus, the loss of heat energy from the completion of preheating to the completion of casting can be minimized.

As shown in FIGS. 4 and 5, the pool-shaped outgate 58' has the shape of a rectangular block. It has an outer shell 60 made of sheet steel and an inner lining 61 of refractory material. In its lower half, the inner surface of the liner 61 converges towards an outlet leading to the sprue portion 59', the outer gate 58' having an interior somewhat resembling a funnel of rectangular cross-section.

The melting furnace 22 is an induction furnace for melting the cladding alloy, and it can be tilted so that the molten alloy charge can be poured into the outer sprue 58'. In use, molten charge is poured into the outer sprue 58' so that the head of molten metal therein provides a steady but strong driving force for filling the cavity 46. In the case of the structure shown in FIG. 1, the outer gate 58 has an elongated rectangular open top 64 for defining a cavity 66 between the sprue portion 42a and the melting furnace 22, which The cavity is separated from the sprue portion 59 by a transverse ridge 68 . The melt is poured rather than poured into the gate 58 at the cavity 66, while the melt flows to fill the sprue portions 59 and 42 and as the height of the melt rises to the ridge 68 in the gate 58 When up, the ridges 68 act to prevent excessive turbulence in the melt.

In Figures 17 to 19 there is shown a detail of the mold 119 due to the test in which a bimetal plate of 1800 x 1000 x 10 mm plus 10 mm thick was produced, using the apparatus shown in Figure 1, That is, the panel has an area of 1800 x 1000 mm, with a 10 mm cast cladding bonded to a 10 mm thick substrate. In FIGS. 17 to 19, parts corresponding to those shown in FIGS. 12 to 14 have the same reference numerals, but 100 is added to the numerals. However, the description is mainly limited to the differences of the mold 119 from the mold 19 shown in FIGS. 12 to 14 .

The mold 119 has a drag mold portion 118a and a cope mold portion 120a made of bonded molding sand. Although not shown in Figures 17 to 19, each section 118a and 120a is formed within a corresponding steel bracket, as shown in Figures 6 to 8 for section 118a and as shown in Figures 6 to 8 for section 120a. The brackets are shown in Figures 9 to 11.

The cavity 134 of the molded portion 118a has a transverse dimension of approximately 1120mm, which is approximately 20mm greater than the initial transverse dimension of the substrate S, thereby leaving an expansion gap 136 on each side of the substrate S of approximately 10mm. Likewise, the base S has an initial longitudinal dimension of approximately 1950 mm, while the cavity 134 has a longitudinal dimension of approximately 1970 mm, thereby providing approximately The gap 136 is 20 mm. Additionally, portions 118a and 120a are clamped together by sand-to-sand contact therebetween to achieve a seal. For this purpose and in order to prevent the lifting of the substrate S at its edges, the transverse width of the cavity 146 of the cope mold part 120a is about 1050 mm, so that the lateral borders S' of the substrate S, which is about 25 mm wide initially, are covered. The overlapping surface areas of the cope mold portion 120a press down. Furthermore, no mandrel is provided along the end of the substrate S remote from the melting furnace 22, but one end boundary S" of the substrate S is similarly pressed by the overlapping surface area of the cope mold portion 120a. The boundary S" is also about 25mm wide initially, which is due to the fact that the longitudinal dimension of the cavity 146 is about 1925mm, while the initial dimension of the substrate S is about 1950mm (and, and in the drag mold portion 118a The cavity 134 has a longitudinal dimension of about 1970mm compared to an end gap 136).

As shown in FIGS. 17 to 18, on each side of the sprue 142 there are two gates 144 through which molten alloy can flow from each runner 140. Likewise, each runner 140 gradually decreases in depth after each gate 144 so that the melt pressure and flow rate through each gate 144 are substantially equal.

At the end of the mold 119 remote from the furnace 22, the cope mold portion 120a also defines a flood containment chamber 147 above the corresponding end of the base S. However, after comparing FIGS. 14 and 19 it can be seen that there is a difference between mold 19 and mold 119 . In the mold 19 the cavity 47 is located astride the end edge of the base body S. As shown in FIG. In contrast, in mold 119, cavity 147 is located above substrate S and is separated from the edge by boundary S″. In FIG. The transverse channel of downward opening, but needs to be ventilated through part 20a.In Fig. 19, cavity 147 is also a transverse channel of downward opening equally, for example in the sectional view of Fig. 19 about 115 * 115mm, but cavity 147 communicates with the cope mold portion 120a by providing three vents 147a along its length.

As mentioned above, the mold 119 presses the substrate S at two boundaries S′ and another boundary S″. At the same time, as shown in the figure, the substrate S is provided with a lateral edge adjacent to the melting furnace 22 and the sprue 142. Transverse band 150, it is positioned in the transverse channel 152 that forms in drag mold part 118a.Although not shown in the figure, need be provided with the device that prevents substrate S from deforming to its edge, this device can comprise as front Alloy strips or studs described in detail.

The tests were carried out with the apparatus shown in Figure 1, wherein the mold shown in Figures 17 to 19 was used, which was mounted in the frame shown in Figures 6 to 8 and in the frame shown in Figures 9 to 11. In these tests, the mold was arranged so that it was inclined upwardly from the melting furnace 22 by approximately 3°. The substrate is a 10mm thick wrought 250 low carbon steel plate with initial dimensions of 1050mm wide and 1950mm long. The alloy used to form the 10 mm thick cladding on each substrate was 15/3 Cr-Mo high chromium white iron with the closest eutectic composition, which is suitable for forming a wear resistant cladding material.

The substrates were prepared by blast cleaning the upper surface of each substrate, that is, the surface to which the coating was to be bonded. The grit-blasted surface of each substrate was substantially free of oxides, and the grit-blasted surface was then coated with a suspension of commercial copper and brass fluxes available from CIGWELD to protect the substrates from being damaged during the preheating process. Oxidizes and promotes the formation of diffusion bonds. In addition, a zirconia-based mold coating was applied to the underside of each substrate to prevent bonding between the substrate and any cast alloy that penetrated beneath the substrate.

Before the substrates were subjected to blast cleaning, a 25 x 6 mm steel strip was welded to the edge of the bottom surface of each substrate across its front edge, ie the lateral edge closer to the furnace 22 . This is to reduce the risk of molten metal penetrating below the matrix during casting. In addition, bending control means are provided on the upper surface of each base. In the case of the first set of substrates, the control means consisted of three 10 x 3mm steel strips which were tack welded on the upper surface of each substrate to form four different longitudinal channels with the same transverse width, cast and melted Alloys can flow along these channels. In the second group of substrates, this steel band is not used; however, the control means for each substrate consists of 24 disc-shaped high-chromium white cast iron studs, 25 mm in diameter and 10 mm thick, in the form of A uniform array is spot welded to the substrate. In each case, the control device ensures that the bending of the substrate is suppressed so that it does not interfere with the flow of the molten alloy to a certain extent, whereby all the molten alloy will flow through one area of the substrate without wetting other areas .

For each test, approximately 260 kg of hypereutectic high-chromium white cast iron was melted and heated to between 1600°C and 1650°C in a tilting induction furnace. This represents approximately 350°C superheat. During the melting cycle the melt composition was adjusted to the proper composition and a final spectroscopic sample was taken just before casting.

During melting, a substrate is placed in the drag portion of the mold and preheated to approximately 750°C. At this preheat temperature the flux is liquid, wets the substrate and greatly reduces oxidation, but the time the substrate is held at this temperature should be kept to a minimum before casting white cast iron. Since it is physically impossible to make the temperature of the entire substrate completely uniform during the preheating process, and the edge part is cooler than the central part of the substrate, and the top surface is warmer than the bottom surface, the substrate will be slightly arched and bowed upwards . Therefore, after reaching the preheat temperature, the substrate should be soaked for about 10 minutes, which makes the temperature tend to be uniform and reduces doming. The preheat cycle is timed such that when the substrate is fully preheated, the liquid metal is at the correct superheat temperature and ready for casting.

When preheating is complete, turn off the preheating oven, lift it up and move it aside. The mold is closed by lowering the cope and hydraulically clamping the parts of the mold. The liquid metal is then immediately injected and flowed over the substrate. The entire operation of removing the preheating furnace, closing the mold and pouring needs to be done fairly quickly in order to minimize heat loss. These operations preferably take less than a minute and a half, so that the temperature drop of both the preheated substrate and the melt is relatively small. The pouring of 260 kg of metal is done in only a few seconds in order to ensure a fast flow rate of liquid metal on the surface of the substrate.

After casting, the mold was left clamped for about 30 minutes to allow sufficient solidification in the runner and overflow cavity. Then, the cope is removed and the casting is allowed to cool further. When cool, the bimetallic plate is removed from the mold, the sprue and excess metal behind the plate are cut off and the plate is cleaned. In addition, since the substrate is clamped between the parts of the mold at the boundary, so that the coating cannot extend to the boundary of the substrate, this boundary is also cut away, thereby providing a substrate with an area of 1800 x 1000 mm and a thickness of 10 mm. The steel plate has a bimetallic plate with a 10 mm thick white iron cladding.

When forming the cope section of the mold for initial testing, fast-response Type R and K-type exposed-tip thermocouples were mounted in the cope mold so that they protruded through the sand into the cladding void. cavity. The R-type thermocouple is used to measure the temperature of the cast metal above the substrate after casting, and the K-type thermocouple is used to measure the flow rate and flow distribution of the cast metal. During the course of the test procedure it was found that the response time of the R-type thermocouple was almost equal to that of the K-type thermocouple, so only R-type thermocouples were used in subsequent tests.

It has been found that the quality of the bimetallic panels produced by these tests is excellent. Although some boards warp slightly as they cool, these warps can be removed. It was also found that the white iron cladding was substantially free of defects and had good uniformity in thickness. It was also found that the coating had achieved a flawless diffusion bond to the substrate, characterized in that it had a very narrow bonding zone which showed substantially no trace of melting of the substrate. Furthermore, control devices are likewise incorporated in the layers of the cladding.

These tests have shown that in order to produce bimetallic panels of good quality, it is necessary to:

(a) In the case of providing a cladding of high chromium white cast iron on a steel substrate, in order to obtain good bonding at all locations, when the melt flows through the substrate, at any one position in the mold, the temperature of the melt Neither should be lowered below about 1400°C, and the substrate is at an appropriate preheat temperature.

(b) The cast metal must flow substantially evenly across the entire surface of the substrate.

(c) In order to avoid using too high superheat temperature in the melt, pouring must be fast.

(d) Removal of the preheating furnace and clamping of the mold must be performed extremely quickly in order to minimize heat loss from the preheated substrate and melt.

(e) In order to save time, the sealing of the mold must be obtained without the use of external seals.

Finally, it should be understood that various changes, modifications and/or supplements can be made to the construction and arrangement of the above-described parts without departing from the spirit and scope of the present invention.

Claims (24)

1. A method for producing a composite metal product comprising a bimetallic plate, wherein the method comprises the steps of: preheating a plate made of a first metal as a substrate, and simultaneously placing the preheated substrate in a into the cavity of the mold with the main surface of the base facing upwards, casting a part made of a second metal as cladding onto said main surface of the base in order to fill part of the depth of the cavity, to form said bimetallic plate together with a substrate; the method further comprising, prior to the step of casting the cladding, rendering said major surface substantially free of oxides and coating said major surface with a suitable coating so that it is not oxidized The step of casting said cladding is to pour the melt of the required components of the cladding at a superheated temperature so that, together with the preheating of the substrate, an overall thermal energy balance is achieved between the substrate and the cladding, and such that Diffusion bonding can be achieved between the major surface of the substrate and the cladding; while performing the above step of casting the cladding also includes allowing the melt to enter through a set of gates communicating between the at least one runner and the cavity cavity, and said gate set is arranged transversely with respect to the flow of the melt therethrough, whereby the melt forms a transversely extending melt front and causes the melt front to leave the gate on the surface of the substrate in a A substantially uniform velocity advance over the entire lateral extent of the melt front. This makes it easier to achieve the desired thermal energy balance. 2. The method of claim 1, wherein the first metal forming the matrix is selected from the group consisting of titanium, nickel, cobalt, iron-based alloys, titanium-based alloys, nickel-based alloys and cobalt-based alloys. 3. A method as claimed in claim 1 or 2, characterized in that the second metal forming the coating is selected from the group consisting of copper, nickel, cobalt, iron-based alloys, copper-based alloys, nickel-based alloys and cobalt-based alloys. 4. The method of claim 1, wherein the compositions of the first and second metals are different. 5. The method of claim 1, wherein the first and second metals are substantially the same or closely related in composition. 6. The method of claim 1, wherein diffusion bonding is obtained in the substantial absence of melting on said major surface of the substrate. 7. The method of claim 1, wherein the step of substantially removing oxide from said major surface of the substrate comprises a method selected from the group consisting of grit blasting, shot blasting, shot blasting, wheeled Or belt grinder polishing or pickling treatment. 8. The method of claim 1, wherein the step of providing a suitable coating to the major surface of the substrate comprises applying a flux to the major surface while melting the flux during preheating to form a protective film . 9. A method as claimed in claim 1, characterized in that the step of providing a suitable coating to said major surface of said substrate comprises depositing a suitable metal on said surface. 10. A method as claimed in claim 9, characterized in that the suitable metal is deposited by electroless or electroplating. 11. The method of claim 1, wherein the step of providing the major surface of the substrate with a suitable coating comprises applying a coating of colloidal graphite comprising a silicate binder on the surface . 12. The method of claim 1, wherein the substrate is rectangular and a melt front is formed adjacent to and along an edge of the substrate, the melt front oriented opposite to the one edge The substrate edge advances. 13. The method of claim 1, wherein the lateral extent of the melt front extends substantially the entire lateral extent of the substrate. 14. The method of claim 1, wherein the melt is introduced into the cavity in such a manner that the melt pressure is substantially equal at each gate. 15. The method of claim 14, wherein the equalization of the melt pressure is achieved at least in part by placing the substrate in the cavity in such a way that the main surface of the substrate is along the front of the melt The direction of advance is inclined upwards, whereby the influence of gravity constrains the melt front to advance substantially uniformly over the entire lateral extent of the melt front. 16. The method of claim 1, wherein the step of preheating the substrate is performed after placing the substrate in the cavity. 17. The method of claim 1, further comprising the step of constraining the substrate within the cavity in a manner that at least partially eliminates bending or deformation due to thermal effects. 18. The method of claim 17, wherein the step of constraining the substrate includes providing a set of bolts welded to the underside of the substrate and securely restrained by nuts to drag mold supports of the mould. 19. The method of claim 17, wherein the step of constraining the matrix includes utilizing a clamping force that clamps the cope and drag portions of the mold together, thereby creating a compressive load , this load acts to press the substrate into a nearly flat state. 20. The method of claim 19, wherein a set of transversely spaced and longitudinally extending metal strips are tack welded to the major surface of the substrate and are sized to form a plurality of depths thereof. The passage substantially corresponds to the thickness of the cladding required, and the clamping force compresses the base body through the cope portion resting on the metal strip. 21. The method of claim 17, wherein the step of constraining the substrate includes tack welding a plurality of metal studs to a major surface of the substrate, and the studs have a thickness corresponding to the desired cladding Thickness whereby the clamping force clamping the cope and drag portions of the mold together compresses the substrate through the cope portion resting on the mandrel stay. 22. A forming apparatus for the production of bimetallic plates having a plate formed of a first metal as a base and a plate formed of a second metal cast on the base as a cladding wherein the apparatus comprises a mold having a lower mold portion and an upper mold portion; the lower mold portion defines a cavity formed in part by the mold, wherein the main surface of the substrate can be brought upwardly Place the substrate in the same way; the upper mold part defines a part of the cavity, whereby, when the mold is in the closed state, the melt of the composition required to form the cladding can be poured to fill the part of the cavity above the substrate, The cladding is thereby formed; the portions of the mold define a set of gates forming communication between at least one runner and the cavity; the sets of gates are arranged transversely with respect to the flow of the melt passing through them, thereby enabling the formation of a a transversely extending melt front; wherein the mold is adapted to position said substrate relative to said set of gates, whereby the melt front is accessible away from the gates on a major surface of the substrate to be substantially uniform across the lateral extent of the front The speed is advanced, whereby diffusion bonding can be achieved between the main surface of the substrate and the cladding while obtaining an appropriate thermal energy balance between the substrate and the cladding by preheating the substrate and superheating the melt. 23. The apparatus of claim 22, further comprising means for vertically moving the cope portion between a lowered position and a raised position, in which the cope portion and drag The parts may be clamped together to close the mold, and in said raised position the substrate may be positioned within the cavity part defined by the drag part. 24. Apparatus as claimed in claim 22 or 23, further comprising heating means movable over the drag portion from a retracted position to an advanced position as the cope portion of the mold moves away from the drag portion position, whereby the heating device is able to preheat the substrate placed in the drag section.

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