Method of Shaping Products made of HDPE or PA, particularly Spatial Shaping of HDPE or PA Tubes, and a Device for Performing it

Abstract

The invention relates to a method of shaping products made of HDPE or PA, particularly spatial shaping of HDPE or PA tubes, in which HDPE or PA semi-finished product is shaped. A semi-finished product from HDPE or PA is first heated to temperature T close to melting temperature T.sub.g of the material so that the material remains in a solid state, T the semi-finished product made of HDPE or PA is left at this temperature for time period t.sub.1 required to obtain plasticity and to disrupt completely or partially the crystalline or semi-crystalline structure of the HDPE or PA material and for relaxing the internal tension of the HDPE or PA material and for restoring the amorphous or partially amorphous state of the material, whereupon the HDPE or PA semi-finished product is inserted into a shaping fixture and the temperature of the HDPE or PA material gradually decreases to ambient temperature.

The invention also relates to a device for performing the method.

Claims

1. A method of shaping products made of HDPE or PA, particularly spatial shaping of HDPE or PA tubes, in which a semi-finished product from HDPE or PA is shaped, characterized in that the HDPE or PA semi-finished product is first heated to temperature T close to melting point T.sub.g of the material so that the material remains in a solid state, at this temperature T the HDPE or PA semi-finished product is left for the time t.sub.1 required to obtain plasticity and to completely or partially disrupt the crystalline or semi-crystalline structure of the HDPE or PA material and for restoring the amorphous or partially amorphous state of the material, whereupon the HDPE or PA semi-finished product is inserted into a shaping fixture and the temperature of the HDPE or PA material gradually decreases to ambient temperature.

2-8. (canceled)

Description

DESCRIPTION OF DRAWINGS

[0010] The invention is schematically represented in the drawings, wherein

[0011] FIG. 1 shows a diagram of the temperature and time dependence during the process according to the invention and

[0012] FIG. 2 shows a block diagram of an exemplary workstation according to the invention.

EXAMPLES OF EMBODIMENT

[0013] The invention will be further described on an exemplary embodiment of a method of shaping products made of HDPE or PA in which a pre-prepared product, in fact a semi-finished product, e.g., a straight tube or a multilayer tube, etc., is transformed into a desired final shapethe resulting product, e.g. spatially shaped (bent) tubes.

[0014] According to the first exemplary embodiment, a HDPE or PA semi-finished product is first heated to temperature T close to melting point Tg so that the polymer does not melt, i.e., the material remains in a solid state, and at that temperature T, the HDPE or PA semi-finished material is left for a time period t1 required to obtain plasticity and to disrupt completely or partially the crystalline or semi-crystalline structure of the HDPE or PA material, and to restore the amorphous or partially amorphous state of the material. This disruption of the crystalline (semi-crystalline) structure results in the loss of stiffness, or, in other words, increased plasticity of the HDPE or PA material. Subsequently, the thus prepared HDPE or PA semi-finished product is inserted, manually or mechanically, into a shaping fixture and the temperature of the HDPE or PA material is gradually decreased to tempering temperature TT at which the HDPE or PA material in the fixture is maintained for the time period tT of tempering, the period required to relax the internal stress and to completely or partially restore the crystalline or semi-crystalline structure of HDPE and PA material. Consequently, after the tempering the stiffness of the HDPE or PA material with reduced internal stress is increased again, whereby now it is already a product shaped by means of the shaping fixture into the desired shape. Subsequently, the product made from the re-shaped HDPE or PA material is cooled by air and optionally cooled by a cooling medium, e.g., water. Thereafter, HDPE or PA material is removed from the shaping fixture as a finished product made of re-shaped HDPE or PA. The temperature course over time for Example 1 is indicated in FIG. 1 by a solid line.

[0015] An example of the first embodiment of the described shaping method is the shaping of a HDPE tube having a diameter of 26 mm and a wall thickness of 2 mm into a spatially shaped bent tube. This tube is first heated to a temperature T near the melting point Tg=130 C. and maintained at temperature T for time period t1=40 min. Subsequently, the tube is inserted into a shaping fixture, e.g. a known shaping labyrinth, and the temperature is decreased to a temperature TT=90 C. at which the tube is maintained for a time period tT=20 min. Subsequently, the now re-shaped HDPE tube is cooled by air for 5 minutes. Thereafter, the tube is removed from the shaping fixture as a finished product with a stable new shape as defined by the shaping fixture.

[0016] According to a second exemplary embodiment, the HDPE or PA semi-finished product is first heated to temperature T close to melting point Tg so that the polymer does not melt, i.e., the material remains in the solid state at temperature T, the HDPE or PA semi-finished product is left for time period t1 required to obtain plasticity and to disrupt completely or partially the crystalline, semi-crystalline structure of the HDPE or PA material and to restore the amorphous or partially amorphous state of the material. This disruption of the crystalline (semi-crystalline) structure leads to loss of stiffness or increased plasticity of the HDPE or PA material. Subsequently, the thus prepared HDPE or PA semi-finished product is inserted manually or mechanically into the shaping fixture and is allowed to cool freely (in the air) or, if necessary, cool additionally by a cooling medium, e.g., water. Thereafter, the HDPE or PA material is left in the shaping fixture at normal room temperature TS for time period tS needed to obtain shape-stabilized HDPE or PA material. Free cooling, possibly additional cooling and subsequent shape stabilization of the HDPE or PA material in the shaping fixture are needed to restore or partially restore the crystalline or semi-crystalline structure of HDPE or PA material and to relax the internal stress, which means that the stiffness of the HDPE or PA material which has now been already shaped by the shaping fixture into the desired shape of the product is increased again. Subsequently, the product from the reshaped HDPE or PA material is now removed from the shaping fixture. The temperature course over time for example 2 is represented in FIG. 1 by the dashed line which in the initial phase overlaps with the solid line of example 1. An example of the second embodiment of the described shaping method is the shaping of a HDPE tube having a diameter of 26 mm and a wall thickness of 2 mm into a bent spatial tube. This tube is first heated to a temperature T close to the melting point Tg=130 C. the polymer does not melt, i.e. the material remains in the solid state, and maintained at temperature T for a time period t1=40 min. Subsequently, the tube is inserted into the shaping fixture, e.g. a known shaping labyrinth, and allowed to cool freely in air for 5 minutes. It is then cooled additionally with water at 10 C. for 0.5 min and afterwards left in the shaping fixture at normal room temperature TS for a time period tS=12 to 48 h. The tube is then removed from the shaping fixture as a finished product with required overbend 3 to 6 and a slightly unstable new shape defined by the shaping fixture.

[0017] The device for performing the method comprises a heating space 1, such as a furnace, with a thermostat 6 for setting and maintaining temperature T close to melting temperature Tg of the respective material, and with a timer 2 of the required time period t1 at temperature T. In the direction of the passage of the HDPE or PA material through the manufacturing process, downstream of the heater space 1 is disposed a station 3 of shaping fixtures, where the heated HDPE or PA material is inserted, manually or mechanically, into the shaping fixtures not shown, e.g., known shaping labyrinths (not shown). In the direction of the passage of the HDPE or PA material through the manufacturing process, a tempering space 4, such as a suitable tempering furnace, is arranged downstream of the station 3 of shaping fixtures and/or an air cooling station 8 is arranged there, downstream of which is arranged a station 9 for additional cooling by a cooling medium, e.g., water, downstream of which is arranged, if appropriate, a stabilizing station 10. The tempering space 4 is provided with a tempering thermostat 7 for setting and maintaining the temperature T.sub.T of the tempering and is further provided with a timer 5 of the time period t.sub.T of the tempering for setting the duration t.sub.T of the tempering. The stabilization station 10 is provided with a stabilization timer 11 for setting the stabilization time period t.sub.S.

INDUSTRIAL APPLICABILITY

[0018] The invention is applicable for mass production of HDPE or PA products by further shaping pre-shaped HDPE or PA semi-finished products, especially for the spatial shaping of HDPE or PA tubes or straight HDPE or PA tubes.