GB2227567A

GB2227567A - Controlling injection mould filling by galvanic cell action

Info

Publication number: GB2227567A
Application number: GB8922751A
Authority: GB
Inventors: Alan Harper
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-01-28
Filing date: 1989-10-10
Publication date: 1990-08-01
Also published as: GB8922751D0; GB8901927D0

Abstract

The process is applied in resin injection transfer moulding, in which a two component thermosetting resin is transferred at low pressure, into a closed mould (15, 16) containing a fibrous reinforcement (17) for the resin, and comprises locating in the mould (15, 16) at least one pair of galvanic cell components (24, 25) adapted to generate an electromotive force when immersed in an electrolyte; injecting the liquid resin into the mould so as to immerse at least a portion of each component of the pair in liquid resin to create a galvanic cell; detecting any electromotive force generated by the galvanic cell; and determining from a change in the electromotive force the operational status of the moulding process, which may comprise the arrival of liquid resin at the location of the cell, to indicate the rate of or completion of mould filling, or the onset of completed polymerisation when the resin ceases to act as an electrolyte. The described galvanic cell components are a copper and a zinc electrode. <IMAGE>

Description

METHOD OF, AND APPARATUS FOR, CONTROLLED MOULD FILLING This invention relates to a method of, and apparatus for, controlled mould filling. It is particularly concerned with the casting of plastics material which are injected in a liquid state but which subsequently harden to form a solid.

Among processes involving the casting of plastics materials is a resin transfer moulding ("RTM") process in which fibre reinforced articles are produced by transferring a two-component (catalysed) thermosetting resin at low pressure into a closed mould in which a fibre reinforcement has been placed. Such a process is described in my co-pending application 8623323. The process can be operated at a low pressure of about 150 pounds per square inch and as such is readily undertaken in a mould which is itself of plastics material. Such a mould provides a number of benefits as against a conventional high pressure metal mould including being substantially cheaper to manufacture and to use.In mould operations involving polymerization there would be operational benefits in knowing un-unequivocally the existence of one or more of the following events: the flow of liquid resin within the mould; the arrival of liquid resin at a region of the mould remote from the resin entry point; and the onset or completion of polymerization. Typically given this last event mould utilisation could be enhanced since it would enable the earliest moment to be established when the mould could be opened, and the moulded component removed, to enable the next moulding cycle to be started.

According to a first aspect of the present invention a method of moulding such as by a resin transfer moulding process into a mould comprises the steps of: 1 locating in the mould at least one pair of galvanic cell components adapted to generate an electromotive force when immersed in an electrolyte; 2 injecting liquid resin into the mould so as to immerse at least a portion of each component of the pair in liquid resin to create a galvanic cell; 3 detecting any electromotive force generated by the galvanic cell; and 4 determining from a change in the electromotive force the operational status of the moulding process.

Typically the change is used to regulate the process. In a first preferred form of the first aspect the location of the components is at a predetermined distance from an entry point for liquid resin into the mould. In a further preferred form of the first aspect or the first preferred form the determining step is used to establish the arrival of liquid resin at a given point in the mould. In yet a further preferred form of the first aspect or any previous preferred form thereof the determining step is used to establish the occurrence of polymerization by change of state of the resin from a liquid to a solid with the consequent substantial removal of a liquid electrolyte whereby the components are enabled to generate an electro-motive force.

According to a second aspect of the present invention there is provided an apparatus for a moulding process comprising: 1 a pair of galvanic cell components; 2 locating means for mounting the pair in a mould for the process in a working region accessible to an electrolyte; and 3 detection means for sensing an electro motive force generated by way of the components.

In a preferred form of the second aspect of the present invention the components are mounted in the working region in the form of points creating a galvanic cell of small area or in the form of extended electrodes providing a galvanic cell of linear form or other extended form. According to a third aspect of the present invention there is provided a mould system for the moulding of fibre reinforced articles to enable a two component (catalysed) thermosetting resin at low pressure to be injected into a closed mould characterised by: 1 a mould adapted to receive the resin; 2 an apparatus according to the second aspect or the preferred form thereof; 3 a supply system whereby prepared liquid resin can be injected into the mould by way of at least one inlet thereto; and 4 a control system whereby operation of the supply system can be regulated in dependence on the output of the detection means of the apparatus.

Typically the components of the apparatus are located in the mould at a given position relatil e to the inlet to establish at the position at least one of the following: 1 flow, or existence, of liquid resin; 2 occurrence of polymerization.

An exemplary embodiment of the invention will now be described with reference to the accompanying drawing which is a diagrammatic view of a resin transfer moulding system.

The system is made up of a mould 10 (shown only in part) fed by way of a resin supply unit 11. Mould operation is governed by a control system 12.

The mould 10 is shown in a closed position with upper shell 15 clamped to lower shell 16 to enclose a fibre insert 17 which is to be embedded in liquid resin which subsequently polymerizes to form a component in the form of a car bumper. The mould is fed polymerisable resin by way of a sprue 18 as will be described hereafter. The resin supply unit 11 is of a type known as a 'Hyperject'(RTM) unit. A dispensing tank 20 is fed the necessary resin mix components by way of lines 21 prior to the controlled dispensing of mixed resin components by way of dispensing line 22 which feeds sprue 18 by way of a thermal isolating means as described in my co-pending Application 8623323 referred to earlier. Flow along the line 22 into the sprue 18 is regulated by way of an inlet valve 23.

The control system 12 is used to regulate operation of the valve 23 and the supply of components to the tank 20 by way of lines 21. The upper shell 15 of the mould 10 incorporates a galvanic cell made up of two electrodes 24, 25 of different materials (metals, typically zinc and copper) disposed in a working region 26 to which liquid material in the mould in the vicinity of region 26 has ready access. The electrodes 24, 25 are coupled to circuit 27 which incorporates a galvanometer 28. The mould 10 is shown at the start of a casting cycle with insert 17 in place and the mould parts 15, 16 clamped in place but with no resin yet injected. A suitable resin mix is prepared in the tank 20 by feeding the necessary feed stocks into the tank by way of line 21.The pressurisation of the interior of tank 20 ensures that when valve 23 is opened the displacement of liquid resin into the mould occurs along line 22. Once injected resin enters the region 26 the resin serves as an electrolyte creating with the electrodes 24, 25 a galvanic cell which generates an e.m.f. in the circuit 27 whose existence is indicated by galvanometer 28.

The onset of an e.m.f. shows that resin has arrived at region 26. For as long as the resin remains liquified the galvanometer continues to indicates an e.m.f.. On the occurrence of polymerization the region 26 no longer contains an effective electrolyte and consequently the e.m.f. falls to vanishing point so providing sufficient indication that the mould shells 15, 16 can be released and the freshly moulded component removed prior to the insertion of a fresh fibre insert and the start of a new casting cycle. The exemplary embodiment makes use of a pair of electrodes 24, 25 which create a galvanic cell of small, effectively circular, form in the region 26. Alternative geometries for electrodes can be used. For example an extended form producing a galvanic cell of substantially greater length than width and located so as to extend away from the mould filling point.The output of such a 'long' cell will depend on the proportion of the entire length of the electrodes which is immersed. In use this will provide a measure of the extent to which a mould incorporating the 'long' cell is filled. It will be apparent that one or more of the proposed galvanic cell located in a mould can provide outputs representing several possible events. For example: the arrival of liquid resin at the cell (which can be disposed at the remotest point in the mould from the filling point to provide a check that the mould is fully filled); the rate at which the mould is filling and the onset of completed polymerization. The output of the galvanic cell provides an analogue signal representing the stages of casting from an empty mould, to one filled with liquid material, to the completion of casting. The output e.m.f.

can be either be used by an observer to ascertain whether the casting process is occurring correctly and/or to undertake controlling actions or to serve to control an automatic operating system; or a combination of these functions.

Claims

CLAIMS 1 A method of moulding involving a resin transfer moulding process comprising the steps of:

1 locating at a test position in a mould at least one pair of galvanic cell components adapted to generate an electromotive force when immersed in an electrolyte;

2 injecting liquid resin into the mould so as to immerse at least a portion of each component of the pair in liquid resin to create a galvanic cell;

3 detecting any electromotive force generated by the galvanic cell; and

4 determining from a change in the electromotive force the operational status of the moulding process.

2 A method of moulding as claimed in Claim 1 wherein the location of the test point is at a predetermined distance from an entry point for liquid resin into the mould.

3 A method of moulding as claimed in Claim 1 or Claim 2 wherein the determining step is used to establish one or more of the following events at the test point: the arrival of liquid resin; the onset, occurrence or completion of polymerization of the resin from a liquid electrolyte to a polymerised solid.

4 Apparatus for a moulding process utilising an initially liquid polymerisable material comprising:

1 a complimentary pair of galvanic cell components;

2 locating means for mounting the pair in a mould for use in the process at a test point accessible to the initially liquid material; and

3 detection means for sensing for the presence or absence or change in an electro motive force generated by way of the components at the test point while in contact with the liquid material.

5 Apparatus as claimed in Claim 4 wherein the components are mounted at the test point in the form of points creating a galvanic cell of small area or in the form of extended electrodes providing a galvanic cell of linear or other extended form.

6 A mould system for the moulding of fibre reinforced articles to enable a two component (catalysed) thermosetting resin at low pressure to be injected into a closed mould characterised by:

1 a mould adapted to receive the resin;

2 an apparatus as claimed in Claim 4 or Claim 5;

3 a supply system whereby prepared liquid resin can be injected into the mould by way of at least one inlet thereto; and

4 a control system whereby operation of the supply system can be regulated in dependence on the output of the detection means of the apparatus.

7 A mould system as claimed in Claim 6 wherein the components of the apparatus are located in the mould at a given position relative to the inlet to establish at the position at least one of the following:

1 flow, or existence, of liquid resin;

2 onset, development or completion of polymerization.

8 A mould system as hereinbefore described with reference to and as illustrated in the accompanying drawings.