Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1996-12-13
1998-12-29
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
264323, 264327, 425384, 425407, B29C 4304
Patent
active
058536442
DESCRIPTION:
BRIEF SUMMARY
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 pressure thereto. This need often exists when wishing to obtain particularly fine surfaces on the workpiece, or when encapsulating electronics in screening or shielding laminates that are comprised of thermoplastic foils and metal foils and where 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 rigidity necessary to distribute a uniform pressure 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 alternatively 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 temperature 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 of the thermal resistances present in the construction, these resistances often being dominated by contact resistances 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.sup.2 is often in the order of thirty minutes. When pressing thermoplastic plates where the material 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 coated with a substance which reduces friction and increases thermal conductivity 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 such variations, and the joints between the thermostat-controlled device and the tool have low thermal resistance, and the thermostat-controlled device can be 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 manufacturing 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
REFERENCES:
International Search Report mailed on Sep. 23, 1995 corresponding to International Application No. PCT/SE95/00687.
Eashoo Mark
Silbaugh Jan H.
Telefonaktiebolaget LM Ericsson
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