JP2002283004A - Coating material of metallic mold for casting iron shape memory alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent burning in and pin hole on a cast surface and to improve a shape memory effect. SOLUTION: A coating material (b) is applied on the inner surface of a mold when a pipe is produced from an iron shape memory alloy by a centrifugal casting, wherein the component weight ratio of water:zircon base aggregate is binder=100:3050:1.0-3.0 and the coated layer thickness is 50-800 μm. Since this zircon based coating material as the aggregate, has good thermal conductivity, a speed from molten state to solidification, is quick and the burning-on and the pin hole on the cast surface are difficult to occur, and a unidirectional solidified structure is easily generated, and the shape memory characteristic is improved by this structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner coating material for a metal mold and a coating structure used when a product is cast by metal mold using iron-based shape memory alloy as a raw material.

[0002]

2. Description of the Related Art For example, a new tunnel method (WBR method)
The production of a pipe joint made of an iron-based shape memory alloy by a centrifugal casting method, which is applied to the invention, is disclosed in Japanese Patent Application Laid-Open No. 10-280061 and the like. As shown in FIG. And the molten metal a is cast from the melting furnace 3 through the triangular ladle 4 and the casting trough 5 on the inner surface of the mold 1 to form a cylindrical molten metal layer (tubular body) c having a required thickness. By doing.

At this time, in order to protect the inner surface of the mold 1 from the high-temperature molten metal a, a coating layer is formed on the inner surface of the mold 1 by spraying a coating material b or the like, and then the above-described molten metal a is cast. Conventionally, as the coating material b, a material obtained by blending a binder and water with an aggregate containing about 80 to 90% by weight of a silicic acid (SiO ₂ ) component such as silica powder or diatomaceous earth is used.

[0004]

However, when a pipe is manufactured by centrifugal casting with an iron-based shape memory alloy, a sound casting surface is hardly obtained due to seizure on the casting surface of the coating material b, and the appearance is impaired. Casting defects (pinhole defects) were generated (see Comparative Examples described later), and the pinholes sometimes cracked when trying to exert shape memory performance.

[0005] It is an object of the present invention to prevent defects from occurring on a casting surface when a product is manufactured from an iron-based shape memory alloy by casting under the above-mentioned circumstances.

[0006]

In order to achieve the above object, the present invention provides a coating material whose main component is a zirconia-based aggregate. That is, first, when a molten metal of an iron-based shape memory alloy is cast, a basic oxide is likely to be generated on the surface layer, and when a coating material containing an aggregate containing a silicate component of the acidic oxide is used, Reacts easily to cause chemical burning and gas defects. Therefore, coating materials used for iron-based shape memory alloys include zirconia (ZrO ₂ ), magnesia (MgO), and chromite (Cr ₂ O ₃ ) based materials that have a high melting point and are less likely to chemically react with the molten metal. Aggregates that exhibit basic or neutral oxide properties must be used.

Next, among the basic and neutral oxide zirconia (ZrO ₂ ) -based, magnesia (MgO) -based, and chromite (Cr ₂ O ₃ ) -based aggregates, the magnesia-based aggregate has a large moisturizing effect and is used in molds. It is difficult to remove water when used, and pinhole defects are generated due to residual water. Further, in the case of chromite, it is difficult to form the coating layer, and the strength of the coating is low, so that the protective function of the mold is impaired. On the other hand, the zirconia type does not have such a problem. For this reason, a zirconia-based material is preferably used as the die coating material for casting an iron-based shape memory alloy. However, among the zirconia-based materials, zirconia (ZrO ₂ ) has high purity and is expensive, so that naturally produced and relatively inexpensive zircon (ZrSiO ₄ ) aggregate is more preferable. At this time, the zircon aggregate contains a silicic acid component, but there is no problem because the amount is small.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As an embodiment of the present invention, when a product is manufactured by die casting using an iron-based shape memory alloy as a raw material, a zirconia-based aggregate is mainly used to protect the inner surface of the die. Apply a coating material. The casting means include sand mold, lost wax, centrifugal casting, etc.For mass production with simple shapes such as pipe joints and pipes,
It is preferable to adopt a centrifugal mold casting method. The component weight ratio of the coating material in this centrifugal casting is water: aggregate: binder =
It is good to set it as 100: 30-50: 1.0-3.0. If the weight of the aggregate is less than 30 with respect to 100 of water, the thickness of the coating layer is small and the protection performance of the mold is small. Further, spray coating must be repeatedly performed to obtain an appropriate film thickness, which is a problem in productivity.
On the other hand, if it exceeds 50, it becomes difficult to spray the coating material. If the weight ratio of the binder is less than 1.0 with respect to 100 of water, the bonding strength of the aggregate is weak and the coating film is easily peeled off, so that the mold cannot be protected. On the other hand, if it exceeds 3.0, the amount of water of crystallization contained in the binder increases and pinhole defects increase.

Various well-known techniques such as brush coating and spray coating can be used for applying the coating material. In the case of centrifugal casting, a spray method is preferable. In the case of the spray coating, the coating material is used. The coating material may be ejected from the nozzle onto the inner surface of the mold while the ejection nozzle and the mold are relatively moved in the cylinder axis direction and the mold is rotated. By doing so, the layer thickness can be made uniform and the workability is good. In the case where the trough moves, the coating operation can be performed by attaching a nozzle to the trough.

[0010] The coating layer thickness is 20 to 1000
μm, preferably 50 to 800 μm. If it is less than 20 μm, the following cooling rate may exceed a preferable range. In addition, since seizure occurs between the shape memory alloy melt and the mold from the viewpoint of manufacturing, the function of protecting the mold is lost. Further, casting defects such as casting cracks and hot spots occur. On the other hand, if it exceeds 1000 μm, casting defects (gas defects) occur on the outer surface, and from the viewpoint of production efficiency, it takes time to repeat the coating operation and to remove the coating material remaining in the mold after casting.

In centrifugal casting using a shape memory alloy, the casting trough and the mold may be relatively moved in the cylinder axis direction. Is the casting temperature, casting speed,
It is preferable to control the cooling rate and the mold rotation speed to obtain their optimum values.

The relative movement between the trough and the mold is as follows.
You can move either one, but moving the trough is
The driving force and equipment are small. In this case, the trough becomes a long gutter, and the casting portion (casting point) moves by relative movement. Therefore, the unit casting amount is reduced because only the casting portion is sufficient, and the molten metal is gently poured into the mold. Casting can be performed, and the occurrence (involving) of dross defects on the inner surface of the tubular body can be reduced. For this reason, the cutting allowance for removing the defect can be reduced, which is advantageous in terms of cost.

The casting temperature is 1400 ° C. or higher. If it is less than this, the flow of the molten metal becomes worse, and it is difficult to obtain a uniform thickness over the entire length of the pipe. The higher the temperature, the better the flowability of the molten metal. However, if the temperature exceeds 1600 ° C, the oxidation of the molten metal proceeds, and a large temperature drop occurs when the molten metal is discharged from the melting furnace to the ladle. And it is not economical. Therefore, the upper limit is preferably set to 1600 ° C.

The casting speed is appropriately set in accordance with the thickness of the tubular body formed on the inner surface of the mold, and can be set by controlling the tilting speed of the pouring ladle and the relative speed between the trough and the mold. According to the present invention, the flow rate of the molten metal from the ladle is 3.0 to 10.0 kg / sec, and the relative speed is 50 to 150 mm / sec. Thus, a tubular body having a thickness of 5 to 20 mm can be easily manufactured.

The molten metal (tubular body) is cooled by air cooling or water cooling inside or outside the mold. In general, the solidification structure becomes chill crystal, columnar crystal, equiaxed crystal from the quenching side depending on the cooling condition, and the shape memory is obtained. With regard to properties, columnar crystals are preferred. An appropriate cooling rate is required to obtain a columnar structure exhibiting its shape memory performance, which is governed by the cooling conditions of the tubular body (mold material and thickness, rotation speed, coating conditions, etc.). , Cooling rate is 1-30 ° C / sec
c. Further, a range of 3 to 20 ° C./sec is preferable. When the temperature exceeds 30 ° C./sec, the chill layer increases in the solidified structure of the obtained tubular body, and the shape memory characteristics are deteriorated.
On the other hand, when the temperature is lower than 1 ° C./sec, the number of equiaxed crystals increases, and the shape memory characteristics similarly decrease. Incidentally, the rotation speed has no effect on the growth of columnar crystals.

The mold rotation speed (GNo.) Is 50 to 15
It is good to be 0G. Beyond this value, it becomes difficult to cast the molten metal normally. Here, GNo. = Acceleration of centrifugal force / Acceleration of gravity = rω ² / g (...), And this relationship is expressed by the diameter D (cm) of the tube and the number of rotations N (rp).
m), r = D / 2, ω ² = (2πN) ²
/ 60 becomes ² (...). Substituting into
No. = (D / 2g) · ( 2πN) 2/60 2 ( where,
g = 980 (cm / sec ² ), π = 3.14). = DN ^2/17900, and the finally, knowing the diameter of the tube (D) and rotational speed (N) is, GN
o. , And conversely, this GNo. The rotation speed (N) can be specified from the specification of.

[0017] The iron-based shape memory alloy tube manufactured by the centrifugal casting method under this condition has a macrostructure in cross section of 80%.
% Or more of the columnar crystal, the shape recovery rate can be obtained from near 3.0% or more, and the yield strength becomes 300 MPa or more.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An iron-based shape memory alloy (Fe-0.05% C-28% Mn-6% Si-5
% Cr). First, as a coating material b, bentonite was used as an aggregate and binder shown in Table 1, and the mixing ratio was water: aggregate: binder = 100: 30.
-50: 1.0 to 3.0 (weight ratio) was used.

[0019]

[Table 1]

The coating material b is sent from the pump 6 to the nozzle 8 via the hose 6a, the carriage 7 is moved back and forth, the mold 1 is rotated, and the coating material b is ejected from the nozzle 8 to the inner surface of the mold 1 (spray). Thus, a coating layer was formed to a thickness of about 600 μm. At this time, the mold 1 was preheated to 150 to 250 ° C. before spraying.

Next, from the high-frequency melting furnace 3, the triangular ladle 4
And the ladle 4 is moved on the rail 9 to a required position with respect to the mold 1.
Thereafter, the ladle 4 is tilted as indicated by the arrow, and the bogie 7 is moved back and forth as indicated by the arrow to cast about 70 kg of molten metal a from the trough 5 into the inner surface of the mold 1.
A pipe with a length of 50 mm, a length of 1000 and a wall thickness of 8/13 mm was produced. The manufacturing conditions were such that the above-mentioned casting temperature and the like were within the optimum values.

Under these manufacturing conditions, the coating material b
Table 2 below shows an experimental example of the mixing ratio of
FIG. 8 (b)
Shows photographs of the casting surface when a silica diameter coating material was used under the same conditions. FIG. 8 shows a photograph of the metal structure.

[0023]

[Table 2]

According to the experimental results shown in Table 2, when the bentonite (binder) deviates from 1.0 to 3.0% by weight based on the water, the casting surface has defects regardless of the amount of the aggregate. I can understand that it comes out. Also, it can be understood that when the aggregate is close to 30% by weight of water, casting surface defects are likely to occur. For this reason, it can be understood that the amount of the aggregate is 30% by weight or more, and preferably about 50% by weight or more. 60 aggregate
When the weight is close to 50% by weight, spray coating becomes impossible.
The following is assumed. The upper and lower limits and the optimal values may be selected optimally through experiments and the like. When not spray-coated, it may exceed 50% by weight, but from experience it is preferably 50% by weight or less.

2 (a) and 2 (b), the former shows a uniform dot pattern over the entire casting surface, whereas the latter shows defects such as seizure and pinholes. Can be Thus, it can be understood that the device according to the present invention is excellent. In addition, as shown in Table 3 below, a zircon-based coating material has a higher thermal conductivity and a higher rate of solidification from a molten state than a silica-based coating material. The directionally solidified structure required for the above is easily generated. By obtaining this unidirectionally solidified structure, as shown in FIG.
Compared with the silica-based coating material, the material of the present invention obtained the same or better performance.

[0026]

[Table 3]

From these experimental results, it was confirmed that the zirconia-based coating material was excellent for casting an iron-based shape memory alloy. In particular, in centrifugal casting, the weight ratio of the components was water: bone Material: Binder = 100: 3
It can be understood that the range is preferably 0 to 50: 1.0 to 3.0.

In this example, the centrifugal casting method was used. However, from the experimental examples, it can be inferred that the coating material of the present invention is effective also in other casting methods. The heating layer thickness is appropriately determined by experiments and actual operations according to the casting method.

[0029]

According to the present invention, by using a zirconia-based material as described above, it is possible to obtain a casting having a good casting surface without defects such as seizure and pinholes. In addition, it is easy to obtain a unidirectional solidified structure required for the expression of shape memory characteristics,
The shape memory effect is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a centrifugal casting machine.

FIG. 2 (a) is a photograph of a casting surface according to one embodiment.

FIG. 2 (b) is a photograph of a casting surface of a comparative example.

FIG. 3 is a photograph of a metal structure of a casting according to the example.

FIG. 4 is a diagram showing a shape memory effect recovery rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical type (mold) 2 Roller for rotation 3 High frequency melting furnace 4 Triangular ladle 5 Casting tray 6 Coating pump 7 Moving trolley 8 Coating nozzle 9 Rail a Iron-based shape memory alloy b Coating material

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroshi Kubo No. 35, Kawachimoto Hasekura, Aoba-ku, Sendai-shi 11-204 Kawauchi Housing F-term (reference) 4E093 NA04 NB08 NB10

Claims (4)

[Claims] 1. A coating material used for protecting an inner surface of a mold when a product is manufactured by mold casting using an iron-based shape memory alloy as a raw material, wherein a main component is a zirconia-based aggregate. Characteristic mold coating material for iron-based shape memory alloy casting. 2. The coating material according to claim 1, wherein the casting is a centrifugal die casting method. 3. The weight ratio of water: aggregate: binder = 10
The mold coating material for casting an iron-based shape memory alloy according to claim 2, wherein the ratio is 0:30 to 50: 1.0 to 3.0. 4. Spraying the coating material according to claim 3 on the inner surface of the centrifugal casting mold to form a coating of 20 to 100.
A coating structure on an inner surface of a centrifugal casting mold, wherein a layer having a thickness of 0 μm is formed.