JPH1158402A - Mold for molding rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mold for molding rubber which has good contamination resistance. SOLUTION: In a mold for molding rubber in which an alumina membrane is formed on the surface of the mold which is brought into contact with rubber, the alumina membrane is obtained by heating an alloy comprising 20-60 wt.% of Cu, 3-12 wt.% of Al, 4-11 wt.% of Cr, and as required 8-24 wt. % of Ni, 0.2-1.8 wt. % of Mo, 0.01-0.1 wt.% of rare earth elements, and the rest of Fe and inevitable impurity elements. In this way, the alloy for molds has good cutting properties and improved contamination resistance, improving productivity remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber mold having excellent corrosion resistance and releasability used for molding natural rubber and synthetic rubber.

[0002]

2. Description of the Related Art Various rubbers such as natural rubber and synthetic rubber are
It is widely used in all industrial fields, including automotive parts such as hoses, sealing materials, power belts and tires. As a mold material for molding rubber parts, S45C,
Alloy steel for machine structure such as SCr, SCM, SNCM and S
Although stainless steel such as US304 is used, the mold is contaminated during the rubber molding process, and the releasability is deteriorated. For this reason, a complicated method such as solvent washing or mechanical removal of deposits such as non-rubber components in the polymer and the polymer adhering to the inner surface of the mold at a certain number of moldings is performed.

[0003] Conventionally, as a method for preventing contamination and accumulation of rubber components and ensuring releasability, a die surface is subjected to Cr plating or a Ni alloy film (for example, Ni-P, Ni-P).
Sn) or by applying a fluorine-based release agent in the mold surface in the molding step.

[0004]

However, in the Cr plating method, the mold is easily corroded due to minute defects inherent in the plating phase, and the plating layer is easily peeled off. This method is not sufficient in durability. Absent.

The Ni-based coating is usually formed into two or three layers by an ion plating method, so that the thickness is reduced to several μm or less in order to increase the cost and to avoid peeling of the coating layer. Needed, which also had durability issues. In particular, when molding ethylene / propylene / diene / methylene rubber (EPDM), sufficient performance cannot be obtained in terms of corrosion resistance, releasability, and the like. If the corrosion resistance is low, rust or scum is generated due to corrosion, and the releasability is deteriorated due to contamination by accumulation of compounding chemicals, non-rubber components in the polymer, and the like. Since these are factors that directly affect the quality and productivity of rubber products, their solutions are strongly desired.

[0006] In addition, when applying a release agent, the types of rubber that can be applied are limited, and even if the effect of the application is obtained, it takes time and effort to lower productivity and increase the defective rate. There is.

[0007]

Means for Solving the Problems In view of such circumstances, the present inventors considered that it is necessary to improve the corrosion resistance and mold releasability of rubber molds based on the alloy composition of the mold material, and made various studies. As a result, they found that a mold having an alumina film formed on its surface was excellent in terms of corrosion resistance and mold release properties against rubber molding. The present invention has been made based on the above findings.

In order to form an alumina film on the mold surface, a conventional mold material, that is, S4, which is a steel for machine structural use, is used.
It is also possible to use a PVD method after cutting 5C or the like. However, these methods have problems in that they are not satisfied from the viewpoint of cost, that the adhesion between the base material and the film is low, and that the film peels off during use.

The present invention is characterized in that a rubber mold has a strong alumina film at a portion where the rubber comes into contact, and the alumina film is a film spontaneously formed by diffusion of Al in an alloy component. This is a rubber molding die. That is, an alloy having characteristics such as high strength, good machinability, and high thermal conductivity, which are requirements for a rubber molding die,
Further, the surface of the alloy mold is covered with an alumina film by performing an oxidizing heat treatment, thereby providing a mold having corrosion resistance, mold release property, and abrasion resistance.

According to the study by the present inventors, the following alloy components exhibit the most suitable characteristics as a rubber molding die. That is, by weight ratio, Cu: 2
0-60%, Al: 2-12%, Cr: 4-11%, the balance being Fe and an unavoidable impurity element,
Ni: 2 to 24%, Mo: 0.2 to 1.8%,
A mold containing 0.01 to 0.1% of rare earth element.

Next, the role of the alloy component for a mold of the present invention and the limitation of the composition range will be described in detail. Al: Aluminum is an important element for forming an alumina film on the surface of the mold, preventing adhesion of the rubber component to the mold, and exhibiting releasability. When the content is less than 3% by weight, the film formation is unstable.
Β-phase appears in the phase, and the embrittlement becomes severe.
% By weight.

Cu: Cu is an element that does not alloy with Fe, and makes a Cu phase appear so that Fe
The phases were separated to improve the machinability of the Al-added steel. Also, C
u is an element that promotes formation of an alumina film by causing a fine Cu phase to appear in the Fe phase. Content is 20% by weight
If the amount is less than 60%, the machinability deteriorates. If the amount is more than 60% by weight, the hardness as a mold is insufficient. Therefore, the appropriate range is 20 to 6
0% by weight. Cr: Cr is an element that forms a solid solution only in the Fe phase and is useful for improving the corrosion resistance of the Fe phase. Content is 4-11% by weight
In order to exhibit this effect, the appropriate range was set to 4 to 11% by weight.

Although the use of a mold having the above-mentioned elements as a composition makes it possible to achieve contamination resistance,
Further, various characteristics can be improved by adding the following elements. Ni: Ni is an element that forms a solid solution also in the Fe and Cu phases and contributes to improving the corrosion resistance of the Fe phase and improving the hardness of the Cu phase. These effects are maximized when the content is 2 to 24% by weight.

Mo: Mo is an element that forms a solid solution with the Fe phase and improves pitting corrosion resistance, and the appropriate range is 0.2 to 1.8%. Rare earth element: An element that further strengthens the adhesion between the alumina film spontaneously formed by the oxidation treatment and the base material. If the content is less than 0.01%, the effect is small, and if it is 0.1% or more, the effect is saturated. The composition of these elements described above is determined according to the purpose of molding the rubber product.

In the production of the mold alloy of the present invention, the ingot can be easily prepared by adjusting the components in a high-frequency melting furnace or the like and melting it.

The alumina film forming treatment in the alloy mold of the present invention can be obtained by heating the mold in an oxidizing atmosphere. That is, after the mold alloy of the present invention is subjected to cutting in the shape of the mold, the alloy is subjected to 80
By heating at a temperature of 0 to 950 ° C. for 1 hour or more, preferably for about 4 hours, a strong film having high adhesion and a thickness of 1 μm or less is formed on the mold surface.

The alloy mold of the present invention in which the alumina film is formed on the surface of the mold as described above has excellent contamination resistance as compared with the conventional mold, and can greatly increase the cleaning process interval.
In addition, when the present alloy mold is used for a long time and a contaminant adheres, the alumina film is not damaged at all even through the immersion step in an alkaline solution which is a conventional method for removing adhered substances. Also, even if the alumina film may be damaged due to physical causes,
If the film formation process is performed again, the film is regenerated at the damaged part,
It is an excellent mold from the viewpoint of maintenance, for example, the effect can be easily recovered.

[0018]

EXAMPLE An alloy having the composition shown in Table 1 was melted in a 100 kg high-frequency melting furnace to prepare an ingot. Next, a weather strip molding die for producing a rubber product for a window seal such as a front and a rear of an automobile was manufactured by cutting. The alumina film formation treatment on the mold surface was performed by using an electric furnace at 920 ° C. for 4 hours in an oxidizing atmosphere, and then cooled to room temperature in the furnace. S45C was used as a comparative material, and after cutting, industrial chrome plating having a thickness of 3 μm was applied to the surface of the mold to obtain a mold of the comparative material.

[0019]

[Table 1]

The evaluation of the machinability of the mold material was made based on the maximum moving speed at which the cutting tool was not subjected to excessive force when performing plane cutting at a cutting depth of 3 mm using a vertical milling machine.
The results are shown in Table 2. In Table 2, ◎ indicates that the maximum moving speed is high, ○ indicates medium, and Δ indicates low.

For the evaluation of the releasability, a weatherstrip was molded from a mold using EPDM and natural rubber, and the number of continuous times until contaminant adhesion was observed was measured. The measurement test was performed on five samples, and the average value is shown in Table 2.

As is evident from Table 2, the moldability of the present invention moldability is better than that of S45C, and the stain resistance is EP.
Both DM and natural rubber are 4 ~ compared to the conventional mold with Cr plating.
5 times better.

[0023]

[Table 2]

[0024]

The rubber molding die of the present invention is excellent in the machinability of the material, the contamination resistance is greatly improved as compared with the conventional die, and the defect rate is greatly improved as well as the productivity. It greatly contributes to the rubber molding field.

Claims (4)

[Claims] 1. A rubber molding die, characterized in that an alumina film is formed on the surface of the die in contact with the rubber to be molded. 2. The composition of the mold is Cu: 20 to 6 by weight.
0%, Al: 3 to 12%, Cr: 4 to 11%, balance Fe
2. The rubber molding die according to claim 1, comprising an unavoidable impurity element. 3. The composition of the rubber mold according to claim 2, further comprising 2 to 24% by weight of Ni and 0.2 to 1% of Mo.
The rubber mold according to claim 1, wherein 8% by weight is added. 4. The composition of the rubber mold according to claim 2 or 3, further comprising a rare earth element: 0.01 to 0.1.
The rubber molding die according to claim 1, wherein the weight% is added.