SU761518A1 - Method of moulding polytetrafluoroethylene articles - Google Patents

Description

The invention relates to the field of obtaining products from polytetrafluoroethylene for the electrical, electronic, instrument-making, radio engineering, aviation industry, etc. 5

A known method of producing products from polytetrafluoroethylene billets, which includes preheating the billet to 380 ° C, stamping in a mold having a temperature of 25 ° C, under pressure of 350–700 kgf / cm ² , cooling the product in a mold under this pressure up to 30–40 ° С [1].

The process of obtaining products from polytetrafluoroethylene by this method is carried out at 15 temperatures above the melting point (327 ° C), when the polymer is in a highly elastic state. Products, due to the relaxation processes of recovery, have a low dimensional accuracy. Dimensional accuracy, however, is often the basic requirement for polytetrafluoroethylene products.

The process of stamping products made from poly- 25 tetrafluoroethylene is carried out in stationary molds at high-speed presses and, therefore, the molding time takes up a small part in the overall technological cycle for producing products. Major faq 3 0

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The tori that limit further increase in the productivity of the process of obtaining products in this way are the heating time of the billet and the cooling time of the products in the mold. Therefore, it is necessary to strive to reduce this time.

Heating a polytetrafluoroethylene billet to a temperature close to the decomposition temperature of this polymer (415 ° C) leads to destructive processes at high speed. Reducing the level of destructive processes in the polymer improves the physicomechanical and other characteristics of the products.

The purpose of the invention is to obtain products from polytetrafluoroethylene with high dimensional accuracy.

This goal is achieved by the fact that the method of obtaining products from polytetrafluoroethylene includes preheating the billet, punching in a mold under pressure and cooling under this pressure, and the polytetrafluoroethylene billet is heated to 300-320 ° C, and punching is carried out in a mold having a temperature of 20— 60 ° С, under pressure of 1500–200 kgf / cm ^{1 2} .

The use of high pressures during stamping leads to an increase in the dimensional accuracy of polytetrafluoroethylene products.

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The drawing shows the curve of change of technological shrinkage of products of the type "insulator" depending on the pressure of stamping.

According to the proposed method, a polytetrafluoroethylene billet is stamped into the product at temperatures below the melting point (327 ° C), i.e. in a solid state of aggregation. Processing of polymers in the solid state has a number of technical and economic advantages compared with traditional methods. One of them is the production of products with enhanced physico-mechanical parameters. For example, indicators such as impact strength and durability, which determine the performance of parts made of polymers, are 2-3 times higher, on average, for articles molded by the proposed method than for products obtained by known methods.

Example. A product is molded in the form of a cylinder with protrusions along a generatrix and with a blind hole at one end of polytetrafluoroethylene (TU6-05-810-71). The billet cylindrical form of polytetrafluoroethylene is heated in a heating cabinet to a temperature of 320 ° C. In a mold preheated to 60 ° C and thermostatically controlled at this temperature during the molding process, a heated billet is placed.

Next, make the closure of the mold at a speed of 60 mm / min and molded product under pressure of 2000 kgf / cm ² . The product is cooled at this pressure to 40 ° C. Then relieve pressure, open the mold and remove the finished product.

Technological shrinkage of the obtained products on the outer diameter of the protrusions is 0.2–0.3%. At the same time, the technological cycles of product manufacturing are significantly reduced and the productivity of the process is increased approximately 1.5 times.

The best effect is achieved when stamping on a high-speed press in order to avoid

the cooling of the workpiece material. Moreover, the temperature of the mold should not exceed 60 ° C.

The use of the proposed method of forming articles from polytetrafluoroethylene by stamping in the solid state, in comparison with the existing methods for obtaining products, provides the following advantages:

- obtaining products with high dimensional accuracy;

- reducing the time of the technological cycle of manufacturing products by reducing the heating time of the workpiece and the cooling time of products in the form;

- improvement of physical and mechanical properties of the product.

The proposed method does not require special equipment, for its implementation can be applied conventional serial hydraulic, mechanical or hydro-mechanical presses.

The proposed method allows to intensify the production of products from polytetrafluoroethylene, while products are obtained with high dimensional accuracy and improved physico-mechanical characteristics.

Claims (1)

Claim The method of molding articles from polytetrafluoroethylene, including preheating the workpiece, punching in a press mold under pressure and cooling under this pressure, characterized in that, in order to increase the dimensional accuracy of the products, the workpiece is heated to 300-320 ° C, and punching is carried out at mold temperature 20-60 ° C under a pressure of 1500-2000 kgf / cm ² .