GB2100175A - Apparatus for use in moulding articles of foamed plastics material - Google Patents

Abstract

Apparatus for use in moulding articles from foamed plastics material comprises a mould (1) in which the constituents are placed, the mould (1) having an upper wall or lid provided with perforations (3) and a cover member (4) is in sealing contact with the upper wall or lid and defines therewith a chamber (5), which is connected via a conduit (9) and valve (10) to a piston and cylinder device (13) which is used to control the pressure in the chamber (5) and mould (1) to a predetermined valve during foaming so that the resultant product has desired characteristics. <IMAGE>

Description

SPECIFICATION Apparatus for use in moulding articles of foamed plastics material This invention relates to apparatus for use in moulding articles from foamed plastics material.

The apparatus and methods which have been used to produce products of polymers in the form of moulded flexible foams with a polyurethane base, present certain difficulties when attempting to obtain a final product with optimum characteristics, since consideration must be given to resolving the problem of controlling pressures in accordance with the necessary requirements to give the desired level of foaming to produce the required molecular density, cell size, grade of hardness or other qualities in the produced foam.

As is already known, the fundamental reason for the difficulty in the control is derived from the free outlet of gases emanating from the foaming due to the activity of the chemical components of the mixture, and it is precisely this difficulty which the present invention tends to overcome, obtaining at all times the necessary precision in pressure control in conformity with the parameters established and, therefore, the final characteristics of the product.

According to the present invention there is provided apparatus for use in moulding articles from foamed plastics material, comprising a mould in which the article is to be moulded, said mould having a perforated lid or upper wall, a cover member in sealing contact with the upper wall or lid and defining therewith a chamber in communication with the interior of the mould via said perforations, and means for regulating the pressure within the chamber during foaming of the material within the mould to provide a predetermined pressure in the mould.

The two elements are hermetically sealed together by pressure closures.

So that the desired pressure control will be effective and the whole process of manufacturing the polyurethane foam will be in accordance with the predetermined calculations, the said cover member of the mould is preferably provided with an instrument for indicating pressure and a valve to regulate the pressure, previously graduated so that any undesired excess pressure may be relieved, so that during the foaming process the desired predetermined levels of expansion are reached. The said pressure regulating valve will consist of an adjustable one-directional valve which only permits the escape of gases beyond the predetermined pressure, the valve closing at the moment this is reached.

An additional device is provided to carry out conjointly the constant control of the pressure in relation to the interior temperature so that the foaming process will be carried out in accordance with the pre-established plans, and this may consist of a dual directional pass valve which can assist in normalising optimum internal conditions in the mould and cover member.

For the development of the foaming process, once the mixture is placed in the mould, and the cover member hermetically closed on the mould, a valve provided in a conduit which communicates the interior space of the cover member with the cylinder of a piston and cylinder device is opened so that the piston and cylinder device serves as an adjustable expansion for the chamber defined by the cover member and mould, and in which the necessary pressure or vacuum may be previously created, either by moving the piston plunger or with the aid of an impelling aspirant pump, in order to regulate the pressure in the spaces of the mould and cover member to ensure that the characteristics of the foam correspond to the preestablished characteristics.

If during the foaming process it is desired to increase the pressure in the mould and cover member, the piston is moved forward, with the valve open, thus compressing the gases in the respective spaces by reducing the space which they occupy.

If, on the other hand, it is necessary with the valve in the open position, to effect an increase in the expansion chamber in order to lower the pressure, it is sufficient to invert the working of the said plunger, in this case making it withdraw to facilitate the necessary expansion of the gases.

With the said valve in the closed position, the cylindrical chamber of the piston can be used to make a prior increase in pressure, this increase being carried out by moving the plunger in a forward motion, and if it is necessary to use greater pressure in the common chamber of the mould and cover member, it is sufficient to open the valve so that the accumulated pressure in the piston and cylinder device is dispersed in the said mould, thus controlling the expansion process of the foam.

Similarly, a prior vacuum can be obtained in the cylindrical of the piston and cylinder device by moving the piston of the same in a backward movement, if it is necessary to diminish the pressure in the said common chamber of the mould and cover member, for which operation it is sufficient to open the valve so that the gases tend to also occupy the said vacuum of the cylinder, thus reducing the pressure in the said chamber.

If it were not sufficient to move the piston forward to obtain a prior pressure charge to be used, only if necessary, this can be increased efficiently with the aid of an aspirant-impulse pump fitted as an auxiliary device which allows the appropriate pressure increase, the said aspirant-impulse pump communicating with the cylinder chamber through the forward end thereof.

For the same reason, if what is required is an increase in the vacuum mentioned previously, this can also be obtained by working the aspirantimpulse pump in the aspiration direction, it being only necessary in either of these two cases to open the valve afterwards so that the pressure will increase or decrease in the chamber formed by the mould and cover member.

Obviously, the need for adequate pressure control is fundamental, in order to produce the desired qualities mentioned above during the foaming process such as molecular density, cell size, grade of hardness and others which may be required according to the intended use of the produced article, and it is therefore possible, with the said pressure control system, to control and adjust the pressure to the functional demands of the foam when it is solidified, which in each particular case will include the different characteristics which its application requires.

With the inclusion of the hermetically sealed cover member, it is obvious that a precise control of the foaming process will be possible, even accelerating or retarding at will the expansion of the foam, which as it grows gradually reaches the entire surface of the wails of the mould, which makes a fine layer or skin on contact, which point is also adjustable by the effect of the pressure of the gases within the pressurised chamber, duly controlled by the action of the devices which have been mentioned.

An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawing, in which the single figure is a section through the mould and control apparatus.

The drawing illustrates a section through a mould 1 in which the mixture is placed to carry out the foaming process, the mould 1 having a chamber 2 in which the mixture is placed, and a lid or upper wall provided with holes 3 for the inlet and outlet of gases in order to reach the ideal pressure gradient. A cover member is hermetically sealed to the mould 1 by pressure closures to carry out and control the pressurisation process through a chamber 5 formed between the lid or upper wall and the cover member 4. A manometer 6 is connected to the cover member 4 and used for measuring the pressure. A pressure regulating device 7 which can be graduated beforehand to open at the maximum permitted pressure is provided on the cover 4.A further device 8 is coupled to the cover 4 and which carries out the mentioned function of an additional constant control of the pressure in relation to internal temperature. A conduit 9 is connected to the cover 4 which communicates via a valve 10 with the cylinder 1 1 of a piston and cylinder device 1 3, in whose chamber 12 a predetermined pressure can be created as mentioned, so that when the said valve 10 is opened the said pressure is communicated to the chamber and then to the foam mould 1 through the communicating holes 3.

If the general pressure attains satisfactory results the foaming process will be carried out without other operations, but if a greater or lower pressure is desired this will be increased or decreased by the action of the piston of device 13 through the chamber 12 of the cylinder 11 and additionally with the aspirant-impulse pump 14.

From the above description it can be easily deduced that the desired pressure is reached within the mould 1 with absolute precision, since tq this effect all the elements have been foreseen which are indispensible for the correct working of the whole and the development of the foaming process to attain the pre-established characteristics for the product resulting from the solidified polyurethane foam.

Claims (14)

1. Apparatus for use in moulding articles from foamed plastics material, comprising a mould in which the article is to be moulded, said mould having a perforated lid or upper wall, a cover member in sealing contact with the upper wall or lid and defining therewith a chamber in communication with the interior of the mould via said perforations, and means for regulating the pressure within the chamber during foaming of the material within the mould to provide a predetermined pressure in the mould.

2. Apparatus as claimed in claim 1, in which the cover member adjusts itself to the mould hermetically by means of pressure closures.

3. Apparatus as claimed in claim 1 or claim 2, in which the said mould and cover constitute a common chamber in which the desired pressure can be built up to control the foaming process of the polymers.

4. Apparatus as claimed in any of claims 1 to 3, in which the cover member is provided with a monometer to give an indication of the interior pressure reached in the mould and chamber.

5. Apparatus as claimed in any of claims 1 to 4, in which the cover member is provided with a pressure relief valve so that the pressure will not exceed that calculated for the manufacturing process.

6. Apparatus as claimed in any of claims 1 to 5, in which the cover member is connected to means for effecting constant control of the pressure in relation to the interior temperature of the pressurised chamber, and by which as required gases can be introduced at the desired temperature to ensure that the foaming process is carried out in accordance with its planned phases.

7. Apparatus as claimed in any of claims 1 to 6, in which the chamber is connected to a piston and cylinder device via a conduit having a valve which when open ensures that the pressure in the mould and chamber is the same in the cylinder of the said piston and cylinder device which acts as an extension of the gas expansion chamber.

8. Apparatus as claimed in claim 7, in which when the valve is open and in order to duly control the development of the foaming process with an increase in pressure due to a lowering of the gas volume, the piston is caused to move with a forward motion compressing the said gases to the desired pressure.

9. Apparatus as claimed in claim 7, in which when the valve is open and it is necessary to cause a decrease in pressure by means of an increase in the volume of gases during the foaming process, the piston is moved in a backward direction to decrease the pressure to the desired valve.

10. Apparatus as claimed in claim 7, in which with the valve in the closed position, the piston and cylinder device can be used to provide a prior increase in pressure in the cylinder itself attained by advancing the piston, it then only being necessary to open the valve so that the said pressure increase enters the chamber common to the mould and cover member.

11. Apparatus as claimed in claim 7, in which a prior vacuum can be obtained in the piston and cylinder device through the backward movement of the piston so that if it is necessary to lower the pressure in the said common chamber of the mould, it is sufficient to open the valve so that the gases will tend to immediately occupy the said vacuum in the cylinder.

12. Apparatus as claimed in claim 10, in which the prior increase in pressure can be increased with the aid of an aspirant-impulse pump.

13. Apparatus as claimed in claim 11, in which the prior vacuum can also be increased using an aspiration-impulse pump.

14. Apparatus for use in moulding articles from foamed plastics material, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.