GB2342311A - A plastics moulding process - Google Patents

Abstract

A low frequency vibrating device is used in a moulding process. Preferably, low frequency vibrations from a vibrating device (1, figure 1) produce compression moulding forces directed towards a thermoset plastic. Preferably, one of the moulding tool assemblies (5, figure 2) is moved towards the other (6, figure 2), which is fixed in position, by using a simple electro-mechanical device such as a scissor jack (3, figure 2). The frequency and amplitude of the vibrations may be adjustable. Low frequency vibrations may also be used in other moulding processes, such as the assisted removal of moulded parts from an injection moulding tool, or the assisted parting of the two mould halves in an injection moulding tool.

Description

A PLASTICS MOULDING PROCESS.

This invention relates to a method for moulding thermoset plastic compounds Moulding of thermoset compounds by compression, transfer or injection is well established and the advantages and disadvantages are well documented. This invention has been developed to overcome the main disadvantage of high capital cost which is normally required due to the high grade tooling used. This new method uses the principle of low frequency vibrations to urge the moulding compounds to flow rather than high tonnage forces and hence enables lower cost tooling to be utilised. Vibration has been used in other industries such as concrete to cause consolidation and flow but this invention has adapted vibration as the moulding force for use in moulding glass reinforced thermoset plastics. Since there is no need for additional high tonnage forces which are normally supplied by hydraulic rams, this invention has also enabled the use of simple electrically driven screw devices, pneumatic rams, low pressure hydraulics or scissor jacks to be used to bring the moulding tools together.

According to the present invention there is provided a method of designing and manufacturing matched metal punch and die tooling, a method of mounting such tooling in a manner whereby the vibrational moulding forces are directed to the fixed tool half, a method of raising and lowering the mobile half of the tool to bring it into close proximity of the upper tool and a method of applying a low frequency vibration to the system whereby moulding of the thermoset compound placed between the two halves of the tool takes place.

In the case of the present invention, the thermosetting compounds shall be of types glass reinforced polyesters, phenolic moulding compounds and also various grades of thermosetting rubber compounds.

In a preferred embodiment, this moulding apparatus can comprise of a plurality of moulding cavities such that the apparatus be employed in a substantially continuous moulding system.

Typically, the moulding cavities are arranged on a conveyor belt or similar transfer surface.

A specific embodiment of the invention will now be described by way of example, but without limit to the scope of the invention, with reference to the accompanying drawings in which: Figure 1 shows a typical method whereby the upper tooling is floating to encapsulate the vibrational forces and direct them towards the moulding compound ; Figure 2 shows the moulding press in its open position ; Figure 3 shows the moulding press in its closed position and illustrates a typical electromechanical device which is used to raise the lower tool.

Referring to Figure 1, it has been shown that the tool is aligned in its moulding position by means of side bolts which, in turn are secured through a framework which is suspended by a series of springs or the like which are compressible. The exact position, frequency, amplitude and number of the vibrators required to perform the moulding operation is determined by an initial series of trials using the tool which is to be moulded and the particular compound from which the component is to be produced. The drawing which is Figure 2 shows the equipment in its initial stage with a charge of moulding compound placed on the lower tool which is mounted on a movable platform which, by way of this example can be raised and lowered by a scissor jack which is powered by a linear actuator. In order to perform a moulding operation, this lower tool is raised swiftly to a point just before the two halves of the tool are in contact and an electronic switch energises the vibrator. The vertical movement may be assisted by the incorporation of a series of guide bearings located at suitable positions on the edge of the tool. The lower tool continues its upward motion while the vibration is being applied until a point at which a small degree of pressure is developed between the two halves of the tool. This operation has now caused the moulding material to flow throughout the cavity formed by the tooling and the machine stays in this position for a period of time to allow for the chemical curing reaction to take place.

At the end of this time, the actuator is reversed to lower the tool and simultaneously there is a short burst of vibration before the scissor jack lowers the tool back to its initial position as shown by Figure 3. The moulded product is then removed and the machine is ready to perform another cycle.

It was discovered during trials that the short'burst'of vibration while simultaneously opening the tool assisted the breaking of the'seal'between the two halves of the tool. This also helped loosen the moulded product from the surface of the tool enabling easy removal.

This particular use of vibration has therefore extended its application to other areas of plastic moulding such as the assisted removal of moulded parts, from injection moulding tools, which have been produced from either thermosetting or thermoplastic compounds.

In certain cases, it may be preferable to mount the lower tool as the fixed half and rearrange the lifting device as to be above the upper tool and hence raise and lower this upper tool.

Where it is desirable to increase the opening daylight between the two halves of the tool, a series of scissor levers may be employed.

In another example of the machine it may be advantageous to arrange the raising and lowering of the moveable platen by means of a simple screw system in place of the scissor arrangement.

In all cases, it is normal to attach the vibrating device to the stationery half of the moulding tool.

In the instances where vibration is being used to assist removal of moulded parts, the vibrating source is mounted on the half of the tool in which the moulded part predominately resides, usually, but not exclusively, the female cavity.

Claims (7)

1. CLAIMS 1. A process for the moulding of thermoset plastics comprising of an electro-mechanical transport device for moving the tooling, a means of performing the moulding by use of low frequency vibrations and a method of mounting the tooling so that the vibrations are directed towards the moulding compounds.
2. 2. Any moulding process in general on which a low frequency vibrating device is attached to assist in the moulding of plastic compounds.
3. 3. Any moulding process in general on which a low frequency vibrating device is attached to assist in the parting of the two halves of a moulding tool.
4. 4. Any moulding process in general on which a low frequency vibrating device is attached to assist in the removal of moulded parts from the tooling.
5. 5. A moulding process as claimed in Claims 1, 2,3 and 4 wherein the vibrational forces are produced by electrically driven vibrators or pneumatic type vibrators.
6. 6. A moulding process as claimed in Claims 1, 2, 3 and 4 wherein the frequency of the vibrational forces and amplitude are adjustable to give the optimum force for any particular moulding compound.
7. 7. A moulding process as claimed in Claim 1 wherein either the upper tool or the lower tool, to which the vibrating device is attached, can be in the fixed position and the opposing tool is arranged to be raised or lowered.