IL32668A - Device for forming articles of thermoplastic material - Google Patents

Description

A device for forming articles of thermoplastic material CEBAL 30729 The present invention concerns a method of heating moulds for thermoplastic and a mould for carrying out the Heating moulds for moulding or deformation under pressure and in the hot state of theremoplastic materials raises difficult owing to the fact that these materials are generally bad heat conductors so that the transmission of heat through their mass requires that walls of the mould should be raised to a temperature which rises in proportion as the thickness of the material to be heated increases and the time allowed for the manufacturing cycle is In the temperature of the mass of material must be as there is the danger that the regions are at an excessively low temperature will be in an insufficiently plastic state and the regions at an excessively high ature will suffer changes in their characteristics and It is known that these moulds may be heated either by resistances incorporated into them or by resistances surrounding them more by induction at the frequency of the Resistance heating suffers from the disadvantage owing to the automatic regulation of the mould it gives rise on the one hand to a sawtooth resulting in alternate overheating and underheating of the and on the other hand due to the mass of the it gives rise to excessively long heating and cooling times which oppose the high speed of manufacturing Heating by induction at the frequency of the ives rise to heat being given off in the material of the mould itself but it suffers from the disadvantage that it requires large resulting in an increase in the mass of the mould and consequently in heat The subject of the invention is a method of heating moulds for thermoplastic which permits the production in a region located in the immediate vicinity of the internal wall of the mould of the necessary amount of heat at a suitable temperature in a very short Invention also concerns a mould for carrying out the According to the present there is provided a device for forming articles of thermoplastic synthetic resin material using a two piece mold of an electrically conductive the two halves of the mold being electrically insulated from each other and adapted to be to an electric source having a frequency in the range from to 10 and conducting meana for electricall connecting the mold halves together connection points that are aa close as possible to each other and as remote as possible from the points of connection of the mold halves to the electric By reason of the frequency used and the mutual tion between the mold the flow of current therein is fined to a region surrounding the cavity in each half thereby supplying heat to the precise region of the mold required to provide optimum heatfag thermoplastic erial in An embodiment of the invention is illustrated by way example in the accompanying 1 shows a diagrammatic of a mould according to the and Figure 2 is a part of 1 showing the region in the induced currents In these the same elements are denoted by the same The mold in the drawings comprises two mold halves magnetic for example magnetic or less They are connected by the shortest possible conductor connected at points and which are as close together as Two adjacent points and on the mold halves are respectively located opposite the o points and but as remote as possible and serve to supply the mould with current through the intermediary of conductors and The current passes through the mould half the conductor and the mould half it cannot pass from one mould half to the other by any other Owing to the high frequency used and the mutual induction between the two mould the current is confined to a narrow region in the vicinity of the internal walls surrounding the space in which the thermoplastic material is cast in the case of or in which a blank intended to be deformed in the plastic state is disposed in the case of hot The operation is the material to be moulded or the blank is placed in the mould is closed and then a current is applied between the conductors and An induced current circulates in the region and gives of heat by heats the material contained in the space The current is cut and then the mould is The voltage of the current and the frequency depend on the size of the article to be produced and on the mass of the By way of the applicant produces toric joints by applying to the mould shown in Figure 1 a voltage of volts at a frequency of The frequency generally ranges from 100 kHz to 10 The invention also concerns the articles produced by means of the mould insufficientOCRQuality

Claims (1)

1. CLAIMS A device for of thermoplastic synthetic resin material using a mold of an electrically conductive the two halves of the mold being electrically insulated from each other a d adapted to be connected respectively to an electric source having a frequency from 100 to 10 and conducting means for electrically connecting the mold halves gether between connection points that are as close as possible to each other and as remote as possible from the points of connection of the mold halves to the electric A device according to Claim wherein the mold is shaped and the conducting means is located diametrically opposite to said A device according to Claim 1 or 2 wherein said mold halves are formed of a conductive and preferably magnetic A device for the forming of articles of a plastics synthetic resin material substantially as hereinbefore described by of example and with reference to the ing For the Applicants DE COM AID insufficientOCRQuality