RU1808720C - Method for blow-molding of spherical article from thermoplastic sheet - Google Patents

Abstract

Usage: processing of sheet blanks from thermoplastics heated to a temperature of a highly elastic state by pneumatic vacuum molding. SUMMARY OF THE INVENTION: a method of pneumoforming a spherical product from a sheet of thermoplastic includes laying the preform in a arm-shaped form with sealing the mold, heating the preform and mold in the convection chamber to the temperature of the highly elastic state of the thermoplastic, deforming the preform due to the temperature expansion of the air enclosed inside the mold , and cooling the product with a naturally cooling heating chamber, 2 ill., 1 table.

Description

The invention relates to a technique for processing thermoplastic sheet billets heated to a temperature of a highly elastic state by the method of o-vacuum molding and can be used & any industry engineering.

The aim of the invention is to increase "(the quality of a spherical product by eliminating residual internal stresses.

HJa of Fig. 1 shows a arm-shaped form after laying a workpiece in it, side view; figure 2 is a arm-shaped form with a spherical product, side view.

The primitive shape consists of a chamber 1 with a clamping frame 2 and a long ring 3 - having a round hole 4 with a diameter D. A sealing rubber 5 is glued to the upper (working) surface of the clamping frame 2.

The method of pneumoforming a spherical product from a thermoplastic sheet by free blowing is carried out as follows.

The blank b from the thermoplastic sheet is laid on the clamping frame 2 of chamber 1. On the outer surface of the workpiece 6, a long ring 3 is laid. The armhole-shaped form is sealed. To do this, the gasket 5 is pressed between the clamping frame

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2 and the workpiece 6 by creating compressive forces between the frame 2 and the draw ring 3, for example, by means of screw clamps (not shown in the drawing) or by any other known method. Then, the arm-shaped form with the preform 6 is placed in a heating chamber with forced air circulation (not shown in the drawing) and it is heated together with the preform 6 to a temperature of high elastic state of the thermoplastic. During the heating period of the mold, the air enclosed inside the sealed chamber 1 is also heated to the temperature of the highly elastic state of the thermoplastic and undergoes thermal expansion, due to which excess air pressure is created in the chamber 1 and the workpiece 6 is deformed. The workpiece b deformation is automatically combined with the beginning of its heating to a temperature of a highly elastic state, and the moment of completion of deformation coincides with the moment of completion of heating of the workpiece 6. Product 7 and a rammed inside the yoke is cooled naturally cooling the heating chamber to 50-60 ° C, Then an appropriate product 7 is extracted from proymoobraznoy form. Next, the cycle repeats. The height of the spherical product 7 depends on the internal volume of the chamber 1; the diameter D of the round hole 4, the thickness of the preform, the thermophysical characteristics of the processed thermoplastic and is determined empirically.

Example. A test of the known (prototype) and proposed methods for pneumoforming a spherical product from a polymethacacrylate sheet by free blowing was carried out. According to GOST 10667-90, a spherical product 7 was made of flat organic glass of the СО-120 brand with a diameter of 150 mm and a round hole 4 of a long ring 3. The linear dimensions of the blanks were 220x220 mm, thickness 5 mm, and the required product height was 40 mm

When testing the known method, the preform 6 was heated in a convective chamber preheated to 150 ° C, i.e. to the temperature of the highly elastic state of polymethylmethacrylate, the heating time of the workpieces is 3 minutes for each millimeter of their thickness. The heated blank 6 was laid in a arm-shaped form, the mold was sealed by compressing the heated blank 6 between the clamping frame 2 and the draw ring 3 using eccentric clamps. Then the workpiece 6 was deformed, feeding compressed air from the workshop line into the chamber 1 of a arm-shaped shape. When the required height of the article 7 was reached, the supply of compressed air to the chamber 1 was stopped. The required height of the article 7 was visually checked by a string stretched over the center of the round hole 4 of the extension ring 3. The article 7 was cooled with ambient air to 50-60 ° C. During cooling in

0, chamber 1 was periodically supplied with compressed air to prevent a decrease in the height of the article 7. After cooling, the article 7 was removed from the mold.

To test the proposed method

5 made a arm-shaped form with

linear dimensions of the camera 1160x160x170 mm. To the working (upper) surface of the clamping frame 2 was glued

sealing gasket 5 of sheet

0 rubber with a thickness of 3 mm. The blank b was laid in a arm-shaped shape. The mold was sealed by compressing the gasket 5 between the frame 2 and the draw ring 3 using screw clamps until the air inside the chamber 1 was completely exhausted from the surrounding air. The preform 6 was placed in a convection chamber (oven) heated to 150 ° C. Heated mold and blank 6 with this

0 temperature for 15 minutes (at the rate of 3 minutes for each millimeter of workpiece thickness 6). -Then product 7 and the mold were cooled inside a naturally cooling heating chamber to 50-60 ° C. - After cooling5, no product 7 was removed from the arm-shaped form.

Products 7 made by the compared pneumoforming methods were examined in polarized light to

0 determination of internal residual stresses in them. The study noted the presence or absence of internal residual stresses without determining their quantitative value.

5 the achieved height of the article 7 with the help of the bracket with the indicator MCH according to GOST 577-68.

The test results of the methods are given in the table.

From the experimental

From the data it follows that the proposed method of pneumoforming, in comparison with the known methods, provides for the manufacture of a spherical product without internal residual stresses, which increases the quality of the product. Products made by the proposed method have deviations from the required height within 2 mm; products made by a known method (prototype) have a deviation from the required height within ± 0.15 mm

The proposed method ensures the automatic achievement of the required height of the product and for its implementation does not require a workshop line of compressed air or a compressor. Formulas of the invention Method for pneumoforming a spherical product from a thermoplastic sheet by free blowing, including heating the workpiece to a highly elastic state, laying the workpiece on arm-shaped form with hermetic sealing of her cavity, deformation of the workpiece at a temperature

the juice-elastic state of the thermoplastic and the cooling of the product, characterized in that, in order to improve the quality of the product by eliminating residual internal stresses, the preform is heated after it is laid on the mold at the same time as the mold is heated in the chamber, and heated after deformation of the preform due to thermal expansion air1 located in the mold cavity maintains the mold and the product until they are cooled inside the heating chamber when it is naturally cooled. ,

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