HK1022665B - Apparatus for calibrating extruded hollow plastic panels - Google Patents

Description

The invention relates to a device for calibrating hollow plate extruded strands of thermoplastic plastic and hollow plate produced on an extrusion system with a calibrating device according to the invention.

State of the art

DE-C 32 44 953 or EP-B 158 951 describe so-called vacuum forming channels used for calibrating hollow chamber profiles made of thermoplastic material. The hollow chamber profile is passed through a channel of two cooling plates covered with vacuum channels. A sacking of the hollow chamber profile by the action of gravity during the cooling phase is counteracted by the supporting force resulting from the pressure difference between the interior of the hollow chamber profile and the outside.

DE 3 526 752 describes a process and device for the manufacture of hollow-chamber plates of plastic, whereby the upper and lower bands are extruded and welded with prefabricated brackets. The upper and lower bands are sucked and cooled by means of vacuum calibrators.

DEU 9 014 968 describes a process and device for extruding hollow-chamber plates of thermoplastic material. The belts and rails of the profile are extruded separately and welded together while still in the thermoplastic state. The purpose of this process is to prevent the formation of bumps which may occur due to thermal contraction of the rails during the cooling phase, especially during the single extrusion. The hollow-chamber plate profile thus obtained is then passed directly through a calibrating device with a top and bottom endless band consisting of metal pre-filled with a metal bar. The heat transfer process is carried out by a calibrating plate located above or below the end of the end of the plate, which is inserted into the end of the plate by means of a calibrating plate, which is used to keep the end of the refrigerant in a vacuum, so that the end-profile is not exposed to any changes in the temperature, and the end-profile is not exposed to any changes in the temperature, which can be caused by the heat transfer process.

Common vacuum calibrators, which inevitably involve frictional forces between the extruded surface and the vacuum-opened, cooled metal plates of the calibrator, have a number of disadvantages.

The sliding of the extruder on the calibration leads to scratching of the extruder surface and, if necessary, further disturbances due to the accumulation of abrasion, especially in the case of scratch-sensitive plastics.

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The cooling-induced twisting of the rails as they pass through the plate by calibration and by pressing the upper and lower strap against the calibration surface may lead to the formation of impact points in the rails area, which are more pronounced the greater the temperature difference between the entry and exit of the rails, the lower the pressure and the thicker the rails.

High downpressure, which is desirable for a good heat transfer between the calibration and the belt surface and to avoid impact points, leads to high abrasion forces due to the frictional forces between the calibration and extrudate, which in extreme cases can lead to the rupture of the extrudate between the calibration and the extrudate.

The maximum temperature difference between the extruded material when it leaves the extrusion nozzle and the calibration is limited by the maximum possible extraction speed with vacuum dry calibration, as too large temperature differences lead to the formation of self-voltages in the extruded material.

Task and solution

The task was to provide an improved device for calibrating hollow plate extrusion threads made of thermoplastic plastic.

The problem is solved by a device for calibrating hollow-chamber plate extruded strands of thermoplastic composed of an evacuated housing (1) with a plate-shaped inlet area (2), support rolls (3) and a plate-shaped outlet area (4).

Figure 1 shows an arrangement according to the invention.

A hollow-chamber plate extrusion line of thermoplastic plastic (5) is ejected from an extrusion nozzle (6) and pulled through the plate inlet zone (2) between the support rolls (3) and through the plate outlet zone (4) with flexible seals (7) through the evacuated housing (1) of the calibrator by means of two retractor rollers (8).

The following is the text of the present invention:

The device of the invention is located a short distance behind the extruder-fed extrusion nozzle and consists of an evacuated housing (1) with a plate-shaped inlet (2), support rolls (3) and a plate-shaped outlet (4). The inlet (2), support rolls (3) and plate-shaped outlet (4) form a channel through which the extruded hollow chamber plate extrusion strand is passed, supported and cooled.

The plate-shaped inlet zone (2) is used to cool the surface of the extruded strand below the softening temperature of the plastic. For example, a polymethyl methacrylate plastic strand coming out of the extrusion nozzle at a temperature of 260 °C is cooled to about 110 °C. The inlet zone (1) is also used to seal the pressure in the housing against the environment.

The housing (1) must be evacuated at least at the top to prevent the hollow chamber plate profile, e.g. a double-plate, from falling under the weight of the upper belt and the rack, by applying a relatively low pressure, e.g. 10 to 100 Pa. The lower half facing the extruder side should also be evacuated if appropriate, to avoid the formation of deposits due to the contraction of the rack due to cooling.

The supporting rollers (3) are placed above and below the channel for the extruder string. They support the extruded hollow chamber plate string against the pressure applied to the housing. They are adjustable in height as appropriate. This has the advantage of allowing the supporting surface of the extruder to be adjusted precisely to the course of the rotation of the rails as they cool down.

The extruded surface is cooled by cooling the support rolls (3) by spray cooling the extruded surface or by flooding the entire housing (1) with water (wet calibration).

The plate-shaped outlet (4) and the inlet (2) are used to seal the calibrating device; the outlet may be height adjustable or may be fitted with flexible sealing strips (7), e.g. of polytetrafluoroethylene (PTFE) or other temperature-resistant plastics with good sliding properties.

On an extrusion system equipped with a calibrating device according to the invention, high-quality hollow-chamber plates of thermoplastic plastic can be produced.

The calibrating device according to the invention is in principle suitable for hollow chamber plates and plastics of all kinds. Special advantages are obtained in the case of multiple and double-jointed plates made of polymethyl methacrylate and polycarbonate or other transparent plastics. This results in a better visibility of the hollow chamber profiles by avoiding scratching of the surface of the profile. In addition, wavy thickness variations in the belt thickness, which may lead to undesirable deflection of the passing light rays due to the lens effect, are largely avoided. The calibrating device can be fitted to all extrusion systems and all hollow chamber extrusion plates in any dimension.

The low friction forces in the calibrating device also make the necessary pulling forces comparatively small, making it possible to produce brackets with few or very thin brackets that can withstand only low pulling forces.

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The overall low friction forces in the calibrating device make it possible to achieve a significantly longer time than the equipment normally used.

Claims (6)

1. Apparatus for calibrating extruded lengths of cellular sheet for web sheets made of thermoplastic synthetic material, consisting of an evacuatable housing (1) having a plate-shaped entry area (2), support rollers (3) and a plate-shaped exit area (4), wherein the plate-shaped entry area (2), the support rollers (3) and the plate-shaped exit area (4) form a channel through which an extruded length of cellular sheet can be drawn, supported and cooled, and wherein the support rollers (3) are arranged above and below the extruded length of cellular sheet in such a way that they support it against the vacuum applied to the housing (1).
2. Apparatus according to claim 1, characterised in that the support rollers are adjustable in height.
3. Apparatus characterised in that the support rollers are coolable.
4. Apparatus according to claim 1, characterised in that the support rollers are provided with a drive.
5. Apparatus according to claim 1, characterised in that the plate-shaped exit area (4) is provided with flexible sealing strips (7) of a highly heat resistant plastic.
6. Use of an apparatus according to one or more of claims 1 to 5 for calibrating extruded lengths of cellular sheet for web sheets.