JPH04167948A - Manufacture of metallic mold for forming tire - Google Patents

Abstract

PURPOSE:To manufacture a metallic mold for forming a tire having high dimen sional accuracy by manufacturing a molding plate with a low thermal expansion alloy specifying average coefficient of thermal expansion at the time of casting the metallic mold for forming the tire by arranging plural pieces of gypsum molds as annular-state on the molding plate. CONSTITUTION:In the molding plate 1 for arrangement composed of a disk part 1a and a cylinder part 1b, plural pieces of the gypsum mold 2 are arranged as annular-state through lining material 3 on the disk part 1a so as to surround the cylinder part 1b. This is set in a molding flask 2 providing heat insulating material 6 and secondary drying is applied at the max. temp. of about 150-250 deg.C and molten alloy obtd. by melting Al alloy is poured from a sprue 7 to cast the metallic mold for forming the tire. Then, the molding plate 1 for arrangement is manufactured with the low thermal expansion alloy having <=6X10<-4>/ deg.C the average coefficient of thermal expansion at the room temp. to 250 deg.C. By this method, the dimensional accuracy and roundness of the metallic mold for forming the tire in as-cast can be restrained to small value of about 0.3mm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a tire mold by a precision casting method using a plaster mold.

(Prior Art) Tire molds are generally manufactured by precision casting aluminum alloy using a plaster mold.

Specifically, a mold is first made with a rubber mold, a gypsum slurry is poured along the rubber mold, the gypsum is hardened and released from the mold, a gypsum mold is prepared, and this is then dried. Then, the dried gypsum molds are arranged on an arrangement plate so as to form an annular shape as a whole.

- Since the plaster mold after drying absorbs moisture from the atmosphere, it is generally kept at a maximum temperature of 150°C until immediately before aluminum alloy casting.
Redrying (secondary drying) is performed at ~250°C.

Then, a casting space is formed by surrounding the outer periphery of the plaster molds arranged in an annular shape on the arrangement surface plate with a casting frame, and molten aluminum alloy is poured into this casting space to manufacture a tire molding mold. .

(Problem to be Solved by the Invention) However, when gypsum molds are arranged in a ring shape and subjected to secondary drying, it is found that when aluminum alloy is cast, the gypsum molds arranged in a ring shape on the arranging surface plate are The overall arrangement dimensions and roundness varied, and the dimensional accuracy of the tire molding mold sometimes deteriorated.

The object of the present invention is to prevent fluctuations in the array dimensions and roundness of the entire annularly arranged plaster mold in the secondary drying stage,
It is an object of the present invention to provide a method for manufacturing a tire molding die that can always maintain good dimensional accuracy of the tire molding die.

(Means for Solving the Problems) The present invention is a process of producing a plurality of plaster molds; arranging these plurality of plaster molds in a ring shape as a whole on an arrangement plate; Manufacturing a tire molding mold by a precision casting method, the method comprising: drying the plaster mold; and casting a tire molding mold by casting molten metal along the annularly arranged plaster mold. In this method, the average coefficient of thermal expansion from room temperature to 250°C is 6
The present invention relates to a method of manufacturing a tire molding die, characterized in that the arraying surface plate is made of a low thermal expansion alloy of /''C or less.

(Example) First, the precision casting method to which the present invention is applied will be explained in more detail.

First, a predetermined rubber mold is made, a gypsum slurry is poured into the mold, the mold is hardened, the mold is released, and the mold is dried to obtain a gypsum mold 2 as shown in FIG. Next, the disk-shaped part 1a and the columnar part 1b
As shown in FIGS. 1 and 2, gypsum molds 2 are arranged in an annular manner on a disc-shaped portion la so as to surround a columnar portion 1b. Plaster mold 2 and columnar part 1
A lining material 3 is provided between the Here, the columnar part 1b
This is effective in terms of improving workability in setting the casting frame 4 and saving on the backing material 3, which will be described later. From this point, the disc-shaped part 1 without the cylindrical part 1b
The purpose of the present invention can also be achieved even if the arrangement surface plate 1 has only a structure. (However, in that case, the lining material 3 will be provided on the entire inner periphery of the annularly arranged gypsum molds 2.) In Fig. 1, for ease of understanding,
It shows a state in which only three plaster molds 2 are arranged, and the backing material 3
is not shown. In this way, multiple plaster molds 2
The dimensions and circularity of this annular array are precisely defined when they are arranged in an annular shape at room temperature in the atmosphere. Since these plaster molds 2 absorb moisture from the atmosphere, it is necessary to dry them (secondary drying) immediately before casting the molten metal.

For this purpose, as shown in FIG. 3, the arrangement plate 1 on which the plaster molds 2 are arranged in an annular shape as a whole is set in the casting frame 4, and in this state, the plaster molds 2 is subjected to secondary drying at a maximum temperature of 150 to 250"C. In Fig. 3, 6 indicates a heat insulating material. Then, the molten alloy obtained by melting the aluminum alloy is poured from the hot water lower, and an annular shape is formed. A tire mold is cast by pouring molten metal along plaster molds arranged in a row.

Here, according to the present invention, it is important that the material of the array surface plate 1 is limited.

That is, as a result of studying the cause of deviations in the roundness and arrangement dimensions of the annularly arranged plaster molds 2 during the secondary drying process, the inventor found that this is due to thermal expansion of the arrangement surface plate l. It was found that this was caused by

The material of this array surface plate 1 is 25°C from room temperature.
By using a low thermal expansion alloy with an average thermal expansion coefficient of 6xlO-'/''C or less up to 0°C, the dimensions of the annular arrangement of the plaster molds 2 due to the thermal expansion of the arrangement surface l during secondary drying, This made it possible to suppress fluctuations in roundness.

To explain this point in more detail, up to 2
Under secondary drying conditions of up to 50゛, when the material of the array surface plate is a material with an average coefficient of thermal expansion exceeding 6xlO-6/℃, sufficient dimensional accuracy can be obtained for the tire molding mold. do not have. Specifically, for tire molds whose roundness in the as-cast state is worse than 0.3,
Since it is necessary to straighten the distortion of the casting, if a roundness of 0.3 mm can be ensured for the casting (tire mold) in the as-cast state, the number of man-hours will be reduced, which will be a great advantage.

As shown in 2, the upper limit of the coefficient of thermal expansion of the material of the arrangement surface plate 1 that can obtain roundness in the order of 0.3 for as-cast castings is about 6X10-6/"C, and from this point on, It is more preferable to use a material with a smaller thermal expansion coefficient. Note that the roundness here refers to the difference between the maximum diameter and the minimum diameter of the casting.

A more specific experimental example will be described.

As a surface plate 1 for arranging plaster molds 2, from room temperature to approximately 250℃
Each alloy material having an average coefficient of thermal expansion in the range shown below was used.

Jin Jinlin carbon steel, average coefficient of thermal expansion 12X10-6/'C Alloy cup low thermal expansion cast iron Average coefficient of thermal expansion 6X10-6/'C Composition: Fe-2IC2χ5i-32X Ni SχC
Jinjinryodan low thermal expansion cast iron, average coefficient of thermal expansion 3xlO-6/'C Composition: Fe-1χC-1χ5i-28χNi-12χC
o -0,3χNb Using each of the above arraying surface plates 1, arranging the plaster molds 2 on it, then performing secondary drying of the plaster molds for each surface plate, casting aluminum alloy, and then The roundness of aluminum alloy castings in the as-cast state was compared.

That is, using each of the array surface plates 1 described above, as shown in FIGS. 1 and 2, plaster molds 2 of the same type were arranged with the same precision on each surface plate 1 (the maximum array diameter was approximately 600 plates, Roundness 0.05
mm or less). Then, hot air drying (secondary drying) is performed for each arraying surface plate 1 at 200° C. for 3 hours, and immediately after that, as shown in FIG. 3, a casting frame 4 is placed on the arraying surface plate 1, Molten aluminum alloy was injected from the hot water lower and casting was performed. The casting conditions were the same for each array surface plate.

(Aluminum alloy i equivalent to JIS ACdC, casting temperature 650°C).

As a result of measuring the roundness of the aluminum alloy casting in the as-cast state after solidification of the molten aluminum alloy, it was found that when using a normal carbon steel surface plate (average coefficient of thermal expansion 12xlO-6/"C), the radial dimension The difference between the maximum and minimum values was 0.8 mm, while the average thermal expansion coefficient was 6
When using a 13X10-'/''C low thermal expansion cast iron array plate, the diameters are 0.3 mm and 0.15 mm, respectively, and when using a low thermal expansion cast iron array plate, the aluminum It was confirmed that the roundness of the alloy casting was good.

(Effect of the invention) According to the method for manufacturing a tire molding die according to the present invention, the average coefficient of thermal expansion from room temperature to 250 degrees is 6xlO-6/
Since the arraying surface plate was formed of a low thermal expansion alloy of less than Fluctuations and deterioration can be prevented.

Therefore, the dimensional accuracy of the tire molding die in the as-cast state,
The roundness can be suppressed to about 0.3 mm, and therefore there is no need to correct the distortion of the metal casting.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing a state in which plaster molds are arranged on an arrangement plate (only a portion of the gypsum molds are shown), and Figure 2 is a cross-sectional view showing a state in which plaster molds are arranged on an arrangement plate. FIG. 3 is a sectional view showing a state in which an arrangement plate on which plaster molds are arranged is set in a casting frame.

Claims (1)

[Claims] 1. Step of producing a plurality of gypsum molds; arranging the plurality of gypsum molds in a ring shape as a whole on an arrangement plate, and drying the gypsum molds in this arrayed state. and a step of casting a tire mold by casting molten metal along the annularly arranged plaster molds, the method includes the step of manufacturing a tire mold by precision casting, the method comprising: The average coefficient of thermal expansion from to 250℃ is 6 x 10^-
A method for manufacturing a tire molding die, characterized in that the array surface plate is made of a low thermal expansion alloy of ^6/°C or less.