RU2577280C2 - Production of thick-wall casts and polymers - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: claimed process consists in that the polymer material melt is transformed in the injection mould into the cast to be withdrawn therefrom and cooled down. After the cast withdrawal from the mould and at its cooling it is subjected to reduction from the side of its mid surfaces.

EFFECT: higher efficiency of polymer cast fabrication, ruled out pulls and pipes.

2 cl, 8 dwg

Description

The invention relates to foundry for the production of products, mainly from a thermoplastic polymer by injection molding, mainly thick-walled products. The technical solution of the invention can also extend to the receipt of products from other materials. A known method of producing thick-walled castings from polymers [1], which consists in the fact that the molten polymer material is converted into a casting, which is removed from there and solidifies. The method is based on the operation of an injection molding machine with an injection mold containing a movable part with a casting trimmer mechanism, a middle rotary part with a casting push mechanism and a fixed part.

However, this method is not effective due to the fact that in the finished casting relatively many shrinkage shells are formed and the internal cavities of the casting are obtained with a flake, which must then be cut by using additional equipment after removing the casting from the mold.

A more efficient method for producing thick-walled castings from a polymeric material is known [2], which consists in the fact that the molten polymer material is converted into a casting mold that is removed from there and solidifies. In this case, an injection mold is used that contains the mechanism for trimming the casting, the mechanism for pushing the casting, and the mechanism for flashing the internal cavities of the casting.

This prototype method [2] allows you to get castings without burr in their internal cavities and with fewer shrinkage shells inside the material of the castings. However, it is still not sufficiently effective, since the presence of these shells is undesirable, their presence reduces the quality of the castings.

Therefore, the objective of the invention is to obtain a technical result to increase the efficiency of the method of producing thick-walled castings from a polymer material by preventing or reducing the formation of shrinkage shells in them.

The problem is solved in that the method of producing thick-walled polymer castings, which consists in the fact that the molten polymer material is converted into a casting, which is removed from it and cools down, has a distinctive feature: after extraction from the mold, during cooling, it is exposed compression.

Compression of the casting, during its cooling, will increase the flexibility of the solidifying layer of the material and direct it to the center of the casting in the direction of action of the shrink forces in order to prevent a gap between the cold and warm zone or minimize the growth rate of the cavity that has arisen. Castings made by this method will have a homogeneous structure, stable mass, have predictable properties, symmetry of the structure with respect to any plane or axis passing through the center of the casting, which will eliminate or significantly reduce the formation of shrinkage cavities in the material of polymer castings, increasing the efficiency of the method for their preparation .

Embodiments of the invention:

- the casting is subjected to compression from its end surfaces;

- the casting is subjected to compression from its non-end surfaces;

- the casting is subjected to compression from all its surfaces.

The invention is illustrated by illustrations, where in FIG. 1 shows a general diagram of an injection mold before starting to implement a method for producing thick-walled castings from a polymeric material; in FIG. 2 is the same as in FIG. 1, but when injected into the injection mold of the melt (intermediate position of the piston); in FIG. 3 is the same as in FIG. 2, but when pushing the casting; in FIG. 4 is the same as in FIG. 3, but upon release of the casting from the sign of the mold; in FIG. 5 shows an example of a cooling process scheme for a casting extracted from an injection mold with four stages of its transformation; in FIG. 6 - the proposed casting form with compensating end protrusions; in FIG. 7 shows an example of a circuit for applying additional forces to a non-end surface of a casting using a clamp; in FIG. 8 shows an example of a circuit for applying additional forces to all surfaces of a casting using a pressure medium in an airtight vessel.

To implement the method, an injection mold is used, made, for example, in the form of a mold for injection molding (Fig. 1). It contains a fixed detachable part 7 and a movable detachable part 2, made with the possibility of its forward and reverse motion, and, with a variable-volume forming cavity 3 located in it, in which there is a sign in the form of a piston 4, mating with its surface and equipped as at least one rod 5, which may be integral with the piston 4. More than one rod 5, the sign may contain (not shown) in the case, for example, of strengthening its structure or in the case of injection molding of products with a central hole.

For better extraction of the casting from the mold, the surface of the piston 4 and the surface of the forming cavity 3 mating with it are different from the cylindrical shape.

The surface of the piston 4 and the mating surface of the forming cavity 3 may be different from a cylindrical shape. For example, they can be made (not shown) rectilinear or with curved mating surfaces of complex shape.

The piston is made with the possibility of its direct stroke x (in Fig. 2 - in the direction of the arrow to the left) under the action of the melt 7 injected under pressure p (in Fig. 2 - in the direction of the arrow in the right) through the fixed part 7 into the forming cavity 3 of the movable part 2, and with the possibility of pushing out the casting 8 (Fig. 3, 4) from the forward stroke Y (in Fig. 3 - in the direction to the left).

For injection of the melt 7 (Fig. 2), the fixed part 1 is provided with a nozzle 9, to which the output part of the injection machine (not shown) is supplied for feeding the melt 7.

The rod 5 is movably in the guide 10, sandwiched between the insert 11 and the cover 12 of the detachable part 1. The insert 77 therein is enclosed by a housing 73 and provided with a cooling jacket 14 where coolant (not shown) is supplied.

The detachable part 7 is made with the possibility of its movement using the closing-opening unit of the injection machine (only its fixed and movable plates 15 and 76 are shown). Between the end of the sign and the nozzle 9, a feature of the device (not shown) of the movable plate 16, a guaranteed gap Δ (Fig. 1) is formed as an element of the hydraulic resistance "nozzle-damper".

In the process of cooling the casting 8 (Fig. 5), extracted from the injection mold, four stages of its transformation (A-D) can be observed. Stage A - without exposure from outside to the hot casting 8, with the same temperature throughout its material structure; stage B - with the action of additional forces f on the end surfaces 17 of the cooling casting 8, which has a pronounced central zone 18 with a warmer temperature than the peripheral part; stage C - as in stage B, but the said central zone is reduced and a significant portion of the end surfaces 19 has acquired a funnel shape; stage D - completely cooled casting 8.

The ends of the piston 4 (Fig. 1) and the guide 10 of the injection molding mold, facing the inside of the forming cavity 3, can have a special shape, with the help of which a casting 8 (Fig.6) with protrusions 20 is obtained.

A variant of the scheme for applying additional forces f to the periphery of the casting 8 is possible, for example, by using its clamp 21, or (not shown) a cartridge with special cams, using a collet and other means of girth.

A variant of the scheme of simultaneous action of force on all surfaces of the casting is possible. This may be a symbiosis (not shown) of any of the above methods, or the placement of the casting 8 in an airtight vessel 22, where a working medium 23 is supplied through a valve (not shown) under pressure P, for example, gas or liquid.

Injection molding is carried out using the above-described mold as follows.

In the initial position (Fig. 1) of the plates 15 and 16 of the injection molding machine, the releasable parts 7 and 2 of the mold are closed and under pressure, and the rod 5 together with the piston 4 are in the extreme right position.

Then (Fig. 2), an injection unit of the injection machine (not shown) is brought to the inlet of the mold, with the help of which the melt 7 is fed through the nozzle 9 under pressure p. Overcoming the hydraulic resistance created by the mutual arrangement with a guaranteed gap Δ of the nozzle 9 and the piston 4, the laminar jet of the melt 7, entering the gap Δ, hits the end face of the piston 4, sharply changing its direction along this end. Therefore, together with the movement of the X piston 4 with its rod 5 under the pressure of the melt 7, the particles of this melt mix (its turbulent movement), which helps to eliminate the negative effects of the “free stream”, “cold junctions” when filling with melt 7, the forming cavity 3 in the boundary flows of the melt 7, close to the surface of the forming cavity 3.

In this case, the thermal casting is controlled by the supply of coolant (not shown) to the cooling jacket 14, and, if necessary, around the stationary part 2 (not shown).

Under the influence of the pressure of the melt 7, the rod 5 will move to the leftmost position. The piston 4 also occupies the extreme left position, forming the necessary volume of the forming cavity 3, in which the hot melt will be located.

After that, the flow of melt 7 through the nozzle 9 is stopped. The melt 7 cools down, hardening and forming in the forming cavity a specific shape defined by the contour of the forming cavity 3. Due to the previously obtained turbulence effect of the flow of melt 7, which eliminates the above-mentioned negative effects, inside the obtained casting cold junctions are not formed, gas and shrinkage porosities, shells are significantly reduced, and on its surface, as well as on the surface of the forming cavity 3, it is not formed soot.

To extract the molded casting 8 (Fig. 3) carry out a direct stroke Y of the movable detachable part 2.

After removing the casting 8 from the mold, the detachable parts 1 and 2 are closed by the injection molding machine and are under pressure, according to FIG. 1. Next, the mold cycle is repeated.

There is also a way to extract the casting 8 using special pushers (not shown), passed through the piston 4 or through the piston rod 5 of the piston 4 and the piston 4. When the movable part 2 of the press-form is retracted to the left when opened (Fig. 3), such pushers its drive mechanism (not shown) is pushed by the casting 8.

After removing the hot casting 8 from the mold immediately, the entire structure of its material has the same temperature (stage B of FIG. 5).

Then, at the beginning of cooling (stage B in Fig. 5), when a pronounced central zone 18 with a warmer temperature than the peripheral part appears in the casting, additional forces f are applied to the end surfaces 17 of the cooling casting 8. This causes the cooler outer layers to quickly cooling material tend to the center of the casting 8, not allowing them to stop. As a result, the warmer central zone decreases in size (step C of FIG. 5). In this case, a significant portion of the end surfaces 19 acquires a funnel shape 19. After the temperature is equalized over the entire structure of the material of the casting 8 and the pronounced central zone 18 disappears, the additional effect of f on the casting 8 is stopped.

The result is a completely cooled casting 8 (stage D in Fig. 5) without shrinkage cavities or shells in its material, as is the case with traditional casting methods, or with small sizes of these cavities or shells.

When this funnel-shaped shape 19 of the end surfaces 17, if necessary, can be removed by machining or compensated by the initially cast protrusions 20 (Fig. 6), which are eliminated by cooling under the action of shrink forces and additional forces f.

A variant of the scheme of simultaneous action of force on all surfaces of the casting is possible 8. This may be a symbiosis (not shown) of any of the above methods, or pi placement of the casting 8 in a sealed vessel 22, where a working medium 23 is supplied through a valve (not shown) under pressure P, for example gas or liquid.

The ends of the piston 4 (Fig. 1) and the guide 10 of the injection molding mold, facing the inside of the forming cavity 3, can have a special shape, with the help of which a casting 8 (Fig. 6) with protrusions 20 is obtained.

This scheme (Fig. 5) can be implemented (not shown), for example, on presses, clamps, squeezing devices, spring mechanisms, using weights, as well as any of their options, allowing to compress the casting 8 from both ends simultaneously or from one of them focusing on another.

A variant is possible (Fig. 7) of applying additional forces f to the periphery of the casting 8, for example, using the clamp 21 gripped by it with forces F, or (not shown) a cartridge with special cams, using a collet and other means of girth.

It is also possible (Fig. 7) to simultaneously apply force to all surfaces of the casting 8. This may be a symbiosis (not shown) of any of the above methods, or placement of the casting 8 in a sealed vessel 22, where a working medium 23 is supplied through a valve (not shown) under pressure P, for example gas or liquid.

Due to the methods described above (Fig. 5, 7, 8), additional forces f are applied to the casting 8, unlike castings obtained traditionally [1, 2], 8 voids (shrinkage shells) are not formed or are insignificant in the casting. Therefore, the quality of the casting is greatly improved.

Information sources

1. USSR author's certificate N 161555, cl. B22D 17/10, 1988.

2. Patent RU 2010667 C1, IPC B22D 17/22, priority from 1990.12.13, published 1994.04.15 / prototype /.

Claims (2)

1. The method of producing thick-walled castings from polymers, which consists in the fact that the molten polymer material is converted into a casting, which is removed from it and cools down, while after being removed from the casting mold, during cooling, it undergoes compression, characterized in that that the casting is subjected to compression from its non-end surfaces. 2. The method according to p. 1, characterized in that during compression of the casting from the side of its non-end surfaces, additional compression is also carried out from the side of its other surfaces.

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