GB2451066A

GB2451066A - Compressibility measuring

Info

Publication number: GB2451066A
Application number: GB0713724A
Authority: GB
Inventors: Alan Harper
Original assignee: GSSC Inc
Current assignee: GSSC Inc
Priority date: 2007-07-14
Filing date: 2007-07-14
Publication date: 2009-01-21
Also published as: GB0713724D0

Abstract

A method of determining the compressibility of a layer 11 of a flexible material, such as fibre matting used in the production of reinforced plastic mouldings, the method comprising applying a predetermined pressure to the layer 11 of flexible material, and measuring the thickness of the layer 11 when subjected to the predetermined pressure. Also disclosed is a device for determining the compressibility of the layer 11, the device optionally comprising a weight block 13 of predetermined mass, which is placed on top of the layer 11 of flexible material. According to one embodiment the weight block 13 has a lower surface formed with a downwardly projecting rim 14 that engages the layer 11 of flexible material.

Description

COMPRESSIBILITY MEASURING

Field of the Invention

This invention relates to the measuring of compressibility and is of particular application to the measuring of the compressibility of fibre matting used in the production of reinforced plastic mouldings.

In the production of reinforced plastic components, two mould faces are normally employed to mould the component to the required configuration and the dry fibrous reinforcement is placed upon one mould face and is trimmed to fit the defined cavity. The contra matching mould face is then closed upon the first mould face, thus sandwiching the fibrous reinforcement between the two mould faces.

The cavity is then normally sealed and, in some cases, the pressure within the sealed mould cavity is reduced to below atmospheric pressure by operation of a vacuum pump. Once the cavity has been closed and sealed, a catalysed thermosetting resin is injected into the mould cavity so as to fill the voids between the closed mould faces and the gaps within the fibrous reinforcement material.

The pressure applied to bring the two mould faces into their closing positions so as to achieve the required mould design thickness can be resisted by the voluminous nature of the dry fibrous reinforcement, which can initially be of a significantly greater thickness than the mould design thickness.

A degree of experience and knowledge is accordingly required for the operator to choose a dry fibrous reinforcement of suitable thickness and density and, at the same time, obtain a moulded component having the required strength and flexibility characteristics.

It is accordingly an object of the present invention to provide an improved method of measuring the compressibility of a compressible material, such as a fibrous mat or cloth used in the reinforced plastics industry, though the method may also be applicable in other industries in which defined compressibility characteristics may be required.

It is also an object of the present invention to provide a device for measuring the compressibility of a compressible material, such as a fibrous mat or cloth used in the reinforced plastics industry, though the device may again also be applicable in other industries in which defined compressibility characteristics are required.

Summary of the Invention

According to a first aspect of the present invention there is provided a method of determining the compressibility of a layer of a flexible material, said method comprising applying a predetermined pressure to the flexible material and measuring the thickness of the layer when subjected to said predetermined pressure.

The layer of flexible material is preferably placed on a flat support surface and a weight of predetermined mass then placed on top of the layer of flexible material prior to measurement of the thickness of the layer.

The lower surface of the weight preferably has a projecting rim that engages the layer of flexible material.

According to a second aspect of the present invention there is provided a device

Brief Description of the Drawings

Figure 1 shows the first stage of a measuring operation, Figure 2 shows the second stage of the measuring operation, and Figure 3 shows the third stage of the measuring operation.

Description of the Preferred Embodiment

The device shown in the drawings includes a base 10 having a flat upwardly presented support surface on which a fibrous layer 11 can be placed. A vertical column 12 extends upwardly from the centre of the base 10 and the vertical column 12 fits within a central bore formed in a weight block 13. There is an integral annular rim 14 projecting downwardly from the lower surface of the weight block 13 and this annular rim 14 has a known surface area. The weight block 13 (together with any items attached to the weight block 13) has a known mass so that, when the fibrous layer 11 is placed on the base and the weight block 13 is placed on position on top of the fibrous layer 11, a known pressure is applied to the part of the fibrous layer 11 engaged by the annular rim 14.

When carrying out light RTM and film infusion moulding techniques, the closing force of the mould is the atmospheric pressure provided when the closed and sealed mould is placed under sub-atmospheric pressure. For example, if a mould is closed with an internal vacuum level of minus 500 millibars, the pressure applied to a fibrous layer within the mould will be no more than 500 glcm2. The mass of the weight block 13 and the surface area of the rim 14 will thus typically be such as to obtain an applied pressure of the order of 500 g/cm2. If, for any reason, a greater applied pressure is required, one or more weights can be added to the weight block 13.

A scale 15 over which a pointer 16 is movable is carried by a stand 17 mounted on the weight block 13 and the mechanism for moving the pointer 16 over the scale 15 is connected to a transfer element 18 that includes a part 19 that, in use, rests on the top of the vertical column 12.

Figure 1 shows the weight block 13 resting directly on the base 10 without anything between the downwardly presented surface of the annular rim 14 and the upwardly presented surface of the base 10. The pointer 16 is set accurately in line with the zero point of the scale 15 by operation of an adjustment element 20 mounted on the stand 17.

Figure 2 shows the weight block 13 in a raised position. The fibrous layer 11 rests on the base 10 and the column 12 passes through the centre of the fibre layer 11.

Figure 3 shows the weight block 13 in its lowered position with the fibre layer 11 sandwiched between the upper surface of the base and the lower surface of the annular rim 14. The distance indicated by the position of the pointer 16 relative to the scale 15 indicates the thickness of that part of the fibre layer 11 that has been subjected to the predetermined pressure.

The measured thickness will give an indication of the resistance to compression of the fibre layer 11 and, assuming that a consistent weight of fibre layer is measured, the greater the measured thickness the greater the resistance to compression.

The device can be used to measure the compressibility of not only dry fibre layers but also of fibre layer samples saturated with a resin. It is thus possible to establish and test the final compression figures within the mould. The flat presented upper face of the base can very easily be cleaned, as can the lower face of the weight block 13.

The use of a weight block 13, which is merely placed in position, rather than a mechanical compression device using, for example, compressed air or a hydraulic supply, permits the provision of a simple and low cost solution to the need to provide a known force acting over a given contact area.

Although the device has been described above with reference to the determination of the compressibility of a fibrous mat or cloth used for the reinforced plastics industry, the device may also be used in other industries requiring defined compressibility characterisation of flexible fibrous or foamed materials.

Claims

Claims:- 1. A method of determining the compressibility of a layer of a flexible material, said method comprising applying a predetermined pressure to the flexible material and measuring the thickness of the layer when subjected to said predetermined pressure.
2. A method as claimed in Claim 1, in which the layer of flexible material is placed on a flat support surface and a weight of predetermined mass is placed on top of the layer of flexible material prior to measurement of the thickness of the layer.
3. A method as claimed in Claim 2, in which the lower surface of the weight has a projecting rim that engages the layer of flexible material.
4. A method of determining the compressibility of a layer of a flexible material, said method being carried out substantially as hereinbefore described with reference to the accompanying drawings.
5. A device for use in determining the compressibility of a layer of a flexible material, said device comprising means for applying a predetermined pressure to the flexible material and means for measuring the thickness of the layer when subjected to said predetermined pressure.
6. A device as claimed in Claim 5, which includes a flat support surface on which the layer of flexible material is placed and a weight of predetermined mass, which is placed on top of the layer of flexible material prior to measurement of the thickness of the layer.
7. A device as claimed in Claim 6, in which the weight has a lower surface formed with a downwardly projecting rim that engages the layer of flexible material.
8. A device for use in determining the compressibility of a layer of a flexible material, said device being constructed and arranged to operate substantially as hereinbefore described with reference to and as shown in the accompanying drawings.