Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Patent
1986-11-04
1988-11-08
Lowe, James
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
264230, 264249, 264322, 26433117, 264510, 264523, 264573, B29C 4900, B29C 6502
Patent
active
047833033
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method of processing semifinished products made of thermoelastic cross-linked plastic material.
BACKGROUND OF INVENTION
Semifinished products, particularly tubes made of cross-linked polyolefins are obtained using, for example, an extrusion method, see German Pat. No. 1,679,826 and European Pat. No. 0,003,587. Processing of such material is relatively difficult due to its high stiffness. Thus it has been proposed, see, for example, European Patent Application No. 82,100,466.0, to shape semifinished products made of tubes by stretching the tube during its production and subsequently heating the tube to a temperature above the crystallite melting point for the shaping operation. During this operation the tube re-assumesits original nonstretched form and thereby is able to adapt to suitable respectively presented molds. Since the cross-linked material is difficult to process there existed hitherto the tendency of carrying out the cross-linking during or after shaping. Consequently, the advantageous properties of the cross-linked material could only be utilized for the limited number of products which could be produced in this manner.
DISCLOSURE OF THE INVENTION
Surprisingly it has now been found that semifinished products made of thermoelastic cross-linked plastic materials like polyolefins can be relatively readily shaped in the softened state using conventional shaping methods but retains, even through long service periods, the shape which has been impressed at the higher temperature, after cooling below the softening range of the cross-linked plastic material. It has further been found that this shape is stable over wide ranges of temperature so that articles formed, for example, from cross-linked polyethylene are dimensionally stable in the temperature range of -100.degree. C. to +130.degree. C. On reheating through the softening range of the cross-linked plastic material, the shaped product looses its impressed shape because the material which is heated to such high temperature, tends to re-assume the original shape of the semifinished product due to its rubber elasticity.
It is the object of the present invention to indicate methods of shaping semifinished products made of thermoelastic cross-linked plastic materials.
According to the invention this object is achieved by heating up the semifinished product to the softened state of the cross-linked plastic material, shaping the semifinished product in the heated state and cooling the semifinished product while retaining the thus formed shape to a temperature below the softening range.
Semifinished products made of cross-linked polyolefin are heatedfor shaping to a temperature above the crystallite melting point and, after shaping, cooled to a temperature below the crystallite melting point.
Shaping can be effected by blow molding, deep-drawing, pressing, rolling or calendering or also by stretching or orienting in one or more axes. Particularly and according to the inventive method, for example, the flexibility of tubes made of cross-linked polyolefins can be significantly increased. For this purpose, a predetermined section of the tube is shaped in the softened state in a blowing mold such that annular beads are formed in this section which annular beads increase the flexibility of the tube in this section.
Furthermore, the product which is obtained from the semifinished product by blow molding, can be provided by further mechanical processing with openings such as holes or slots in those regions which have been widened by the blow molding operation. In such shaped and further processed products the changes caused by the blow molding operation and thus also the changes produced by the further processing can be entirely or partially reversed by reheating the further processed product to a temperature range in the softening range of the cross-linked plastic material. The processing of the material thereby can be effected under more favorable conditions considering the properties of the processing tools.
Pl
REFERENCES:
patent: 2232475 (1941-02-01), Renfrew et al.
patent: 3418409 (1968-12-01), Hesse et al.
patent: 3576933 (1971-04-01), Batis et al.
patent: 4135961 (1979-01-01), Yoshizawa et al.
patent: 4156710 (1979-05-01), Carroll et al.
patent: 4332767 (1982-06-01), Kitanoha et al.
Lowe James
Wirsbo Pex Platzer Schwedenbau GmbH
LandOfFree
Method of processing semifinished products made of cross-linked does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of processing semifinished products made of cross-linked , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of processing semifinished products made of cross-linked will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-463032