TECHNICAL FIELD

The present invention relates to plastic pressing apparatus which includes a rapid heating and cooling facility.

TECHNICAL FIELD

There is often a need to heat and cool a plastic workpiece, particularly a thermoplastic workpiece, while applying pres¬ sure thereto. This need often exists when wishing to obtain particularly fine surfaces on the workpiece, or when encap- sulating electronics in screening or shielding laminates that are comprised of thermoplastic foils andmetal foils andwhere electrical contacting is desired, as described in Swedish Specification 9300966-0.

In the case of existing plastic pressing apparatus, the desired pressure is often generated with the aid of hydraulic piston-cylinder devices, where the force is distributed over the tool through the medium of a steel pressure plate. The pressure plate must be relatively thick, in order to have the rigiditynecessaryto distribute a uniformpressure force over the whole of the surface to be pressed, particularly when pressing workpieces of large surface areas.

In the case of present-day pressing apparatus, the whole of the pressure exerting plate, or at least a significant part of the plate, is thermostat-controlled so as to adjust the temperature to a desired level. The plate, which thus also transmits heat, is often provided with passageways through which attemperated liquid is flushed. The plate may alterna¬ tively be heated with the aid of electric heating elements placed in direct thermal contact with the pressure-exerting plate.

When the process is to be carried out at varying temperatures, existing apparatus have the limitation that the relatively large volumes of materials which make up the pressure and heat-transmitting plate, the tool and the workpiece require the input of large quantities of energy to change the tempera¬ ture of the material, and that this energy flow is limited to the energy that can be developed in electrical heating elements for instance, and also by the rate of the temperature change ofthe thermal resistances present in the construction, these resistances often being dominated by contact resistan¬ ces between various parts.

As a result, the total heating time and cooling time in a press for pressing a flat laminate at a pressure of 500 N/cm ² is often in the order of thirty minutes. When pressing thermoplasticplateswherethematerial itself affords a rapid working cycle, the slow temperature change constitutes a serious drawback from a production-economic aspect.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a plastic pressing apparatus which solves the aforesaid problem associated with the use of state-of-the-art techniques.

The apparatus is comprised of several thermostat-controlled- devices against which a pressing tool can be pressed by a tool holder, wherein the tool can be moved between the thermostat- controlled devices while maintaining a pressing force, and wherein a large part of the tool surface comes into contact with the thermostat-controlled device. The surfaces of the thermostat-controlled device and that part of the pressing tool that lies against said device are lubricated so as to reduce friction and the thermal resistance.

As a result of the construction of the inventive apparatus, only a minimum amount of material is subjected to temperature variations, meaning that only small quantities of energy are required to effect suchvariations, and the joints betweenthe thermostat-controlled device and the tool have low thermal resistance, and the thermostat-controlled device canbe given a large mass which functions as a thermal buffer.

The time taken to effect these variations in temperature is consequently very short and thus results in a speedy manufac- turing cycle, which solves a serious problem associated with present-day plastic pressing apparatus.

The invention will now be described in more detail with reference to a preferred exemplifying embodiment thereof and also with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a side view of one embodiment of an inventive apparatus.

Figure 2 is a side view of another embodiment of the inventive apparatus.

BEST MODES OF CARRYING OUT THE INVENTION

Two exemplifying embodiments of the invention are described below with reference to the accompanying drawing. The descri¬ bed embodiments can be varied in different ways and the invention is therefore restricted solely by the contents of the following Claims.

Figure 1 shows a stand 1 which has mounted in its upper part a thermostat-controlled cold device 2 and a thermostat- controlled hot device 3, said devices being affixed to the

stand 1 through the medium of heat-insulating material 4. The two thermostat-controlled devices 2, 3 are separated from one another by heat-insulating material 5. Mounted centrally on the frame 1, vertically above the thermostat-controlled devices 2, 3, is a pedestal 6 which forms a mounting for a hydraulic piston-cylinder apparatus 7 which functions to exert a pulling force on a tool holder 9 through the medium of a yoke 8.

The force applied by the hydraulic cylinder 7 presses a press tool 10 between the tool holder 9 and the thermostat-con¬ trolled devices 2, 3. The tool holder 9 is thermally insulated from the tool 10 by means of thermally insulating material 11. The tool holder 9 and the tool 10 carried thereby can be moved between the cold thermostat-controlled device 2 and the hot thermostat-controlleddevice 3 bymeans of a hydraulicpiston- cylinder apparatus 12, wherewith the tool 10 slides on a film of lubricant on the undersurfaces of the thermostat-control¬ led devices 2, 3, these surfaces being flat and parallel.

Energy is supplied to the hot thermostat-controlled device 3 from an electric heating element 13, whereas the cold thermos¬ tat-control device 2 is cooled with cold fluid circulated in a cooling channel 14, the energy flows being regulated so that an essentiallyuniformtemperaturewill prevail inthe devices 2, 3.

The yoke 8 and the hydraulic cylinder 7 form a pendulum, with the tool holder 9 attached to the outer end thereof. As the pendulum swings towards the flat thermostat-controlled devices 2, 3, the working length of the hydraulic cylinder 7 will change during the working cycle of the apparatus. In order to compensate for this change in length and also in order to maintain a constant pressure, the apparatus includes a hydraulic accumulator 15 between the hydraulic pump 16 supplying hydraulic fluids to the cylinder 7 and said cylin-

der. The oil pressure, and therewith the press pressure, between the tool holder and the thermostat-controlled devices 2, 3 can be read-off from a manometer 17.

In a typical working cycle of the apparatus, the pistons of the hydraulic piston-cylinder apparatus 12, 7 are initially in their respective extended positions. The tool 10 carrying the material to be worked is placed on top of the tool holder 9 and the hydraulic cylinder 7 is activated, wherewith pressure is exerted against the cold thermostat-controlled device. The tool holder 9 is then drawn over to the hot thermostat-controlled device 3, by means of the hydrau i piston-cylinder apparatus 12. When the temperature of the material carried by the tool 10 has risen to the level desired, the tool holder 9 and the tool 10 are moved back to thethermostat-controlled cold device 2, andwhenthetempera¬ ture in the material has fallen to the level desired, the hydraulic cylinder 7 is expanded and the tool holder 9 therewith lowered so that the tool 10 can be removed.

The tool 10 may be provided with a thermometer, to enable the temperature of the tool to be checked. The temperature of the thermostat-controlledhot device 3 may be considerablyhigher than the highest tool temperature, and the tool temperature is adjusted by moving the tool holder 9 back to the cold thermos¬ tat-controlled device 2 immediately the tool 10 is heated to a maximum temperature. This facility permits a considerably large difference in temperature between the thermostat- controlled devices 2, 3 and the tool 10, resulting in a larger heat flow and quicker temperature adjustment.

Figure 2 illustrates a variant of the apparatus in which the thermostat-controlled devices 2, 3, the tool holder 9, the tool 10 and the hydraulic piston-cylinder device 12 are arranged in the same manner as in the Figure 1 embodiment. In the Figure 2 embodiment, the pressing force is obtained

through the medium of a hydraulic piston-cylinder device 18 which acts between the bottom and the upper leg of the stand 24. The hydraulic piston-cylinder device 18 is mounted on a carriage 19 which runs on rollers 20 along guides 21. The upper and the lower leg of the stand 24 are held together by a draw bolt 22.

Minor variations in the volume of the hydraulic piston- cylinder device 18 caused by variations in the measurements between the guides 21 and the thermostat-controlled devices 2, 3 are compensated for with the aid of a hydraulic accumu¬ lator 23.

It will be understood that the invention is not restricted to the aforedescribed and illustrated exemplifying embodiments thereof and thatmodifications can bemade within the scope of the following Claims.