MANUFACTURING MOULDS FOR USE IN INJECTION MOULDING OF GLASS

Abstract: A method and apparatus for machining a cast mould half (3) for use in injection moulding of glass. The method is characterised by the following steps: (a) positioning the cast mould half (3) in a first jig (19), (b) turning the section of an outer surface (13) of the cast mould half (3) to the required dimensions measured with respect to a reference point on the first jig (19), (c) positioning the cast mould half (3) in a second jig (51), and (d) milling another section of the cast mould half (3) with respect to the turned outer surface (13) of the cast mould half (3) to form a planar surface (7). The apparatus comprises the first (19) and second (51) jigs for use in the method.

Description: MANUFACTURING MOULDS FOR USE IN INJECTION MOULDING OF GLASS . __ The present invention relates to the manufacture of mould halves for use in the injection moulding of glass. It is known to manufacture glass bottles by injection moulding techniques in which molten glass is gravity fed into the mould. It is an important requirement that the moulds are manufactured to close tolerances in order to ensure that good quality products are manufactured. However, molten glass is an extremely volatile and corrosive material, and even with careful selection of materials for the moulds it is generally the case that the moulds have a relative short working life varying from 2 hours to 2 weeks. The moulds for the manufacture of the neck region of glass bottles (hereinafter referred to as "neck rings") are generally cylindrical and comprise a male and a female mould half in which are formed the respective mould cavities that define, when combined together to form the mould, the shape of the product to be moulded. The mould halves have nlanar surfaces that contact along the longitudinal centre nlane of the mould. It is an important requirement that the mould halves are manufactured to close tolerances. In the case of the planar surfaces the close tolerances are necessary so that there is substantial contact over the surface area of the planar surfaces in order to ensure that there is no leakage of molten glass from the mould. Furthermore, the mould halves are constructed to interlock thereby to ensure that the mould halves are correctly positioned when brought together to form the mould. In this regard, the mould halves are constructed so that the outer marginal sections of the male mould half project beyond the plane of the planar surfaces and the outer marginal sections of the f-male mould half are rccccccd with respect to the plane of the planar surfaces so as to receive the outer marginal sections of the male mould half. It is known to manufacture the mould halves from rods having the required outer diameter. However, the interlock feature of the male and female mould halves means that it is not possible to manufacture male and female mould halves each having a unit length from a unit length of the rod. Two unit lengths of the rod are required, and as a consequence there is a significant amount of waste. Attempts have been made to rough cast the mould halves and to machine the castings to the required dimensions. However, the preferred material for the mould, namely a nickel-aluminium special alloy, is relatively volatile and therefore difficult to cast without the resultant mould half having unacceptable levels of porosity. Furthermore, since the dimensions of the rough castings will vary from casting to casting, it is necessary to reset the lathe and milling machines for each casting. In view of the relatively large number of such castings required, the foregoing practice is both an inefficient and expensive method of manufacturing the castings. It is an object of the present invention to or vide* a method of manufacturing mould halves which alleviates the disadvantages described in t >- preceding paragraphs. According to the present invention there is provided a method of manufacturing a mould half Cor use in injection moulding of glass, said mould half havincr a mould cavity and comprising a planar surface adapted to contact a corresponding planar surface of another mould half along the longitudinal centre plane of a mould formed from the two mould halves, said method comprising: (a) casting the mould half, (b) positioning the cast mould half in the first jig, (c) turning a section of an outer surface of the mould half to the required dimensions measured with -.' s αc Lo -t J. L -_-J.v liUC J—>J. n »— J . I v.u J ι~ j f (d) positioning the cast mould half in a second jig, and (e) milling the planar surface of the mould half to the required dimensions measured with respect to the turned outer surface of the mould half. It is preferred that the mould half forms part of the neck ring for the injection moulding of bottles. In particular, it is preferred that a plurality of mould halves are positioned in the first and second jigs and are machined simultaneously. According to the present invention there is also provided an apparatus for machining a mould half for use in injection moulding of glass, the mould half comprising a planar surface adapted to contact a corresponding planar surface of another mould half along the longitudinal centre plane of a mould formed from the two mould halves, said apparatus comprising: N rs half so that a section of an outer surface of the mould half can be machined to the required dimensions measured with respect to a reference point on th~ first jig, and (b) a second jig to receive and support the partly machined mould half so that the olanar surface of the mould half can be machined to εhe required dimensions measured with respect to the section of the outer surface of the mould half. It is preferred that the first jig comprises a plurality of compartments, each of which is adapted to receive and support a respective said mould half. In this re ard, it is preferred that the first jig comprises an elongate body having a flat upper surface and the compartments are defined by a plurality of plates extending from and spaced along the length of the upper surface. With such an arrangement it is preferred that the fiat upper surface defines the reference point. It is preferred that the first jig further c m rises a plurality of spacer olates each ?.ss nf,; a-<= *-Hi-h nnr* nf said compartments and positioned on the flat upper surface, whereby in use the planar surfaces of the mould halves contact the spacer plates. It is particularly preferred that the spacer plates comprise projections that in use extend into the mould cavities of the mould halves to so retain the mould halves in position on the spacer plates. It is particularly preferred that the first jig further comprises a plurality of securinσ members to secure the respective said mould halves to the first jig. It is particularly preferred that each securing member comprises a clamp pivotally mounted on one side to the upper surface of the first jig and movable from an open to a closed position at which the clamp extends around a section of the outer surface of the mould half and is releasably pinned on to the other side to the upper surface of the first jig. ur er e a e es p on o embodiment of the method and apparatus of the present invention is now provided with reference to the accompanying drawings, in which: Figures 1 and 2 are perspective views of as-cast male and female mould halves of a neck ring; Figure 3 is an end view of the mould halves shown in Figures 1 and 2 positioned together to form the neck ring; Figure 4 is a perspective view of a first jiq for receiving and supporting a plurality of the mould halves shown in Figures 1 to 3 for partial machining; Figure 5 is a section along the line 5-5 in Figure 4; Figure 5 is a section along the line 6-6 in Figure 5; Figure 7 is a perspective view of a second jig having a plurality of holders for receiving and supporting mould halves partially machined in the first jig for further machining; Figure 8 is a section of one side of one of the holders of the second jig showing in detail the location of a male mould half for machining; and Figure 9 is a section of one side of one of the holders of the second jig showing in detail the location of a female mould half for machining. In Figures 1 and 2 are shown the respective male and female mould halves 3a, 3b of a cylindrical neck ring for use in the injection moulding of glass bottles. The mould halves 3a, 3b are in a rough as-cast form prior to machining, and each mould half 3 comprises a curved outer surface 5, a planar surface 7, and a mould cavity 9. The outer surface 5 is formed with a central semi-circular groove 11 which separates two outer semi-circular sections 13. It is an important requirement for the neck ring that the planar surfaces 7 are machined to close tolerances so that when corresponding planar surfaces 7 of two mould halves 3 are brought together to form the longitudinal centre plane P (Figure 3) of the neck ring there is substantial contact between the planar surfaces 7 to prevent leakage of molten glass from the mould cavity 9. In order to facilitate proper alignment., the mould halves 3 are formed to interlock. In this regard, the outer sections 15 of the male mould halve 3a shown in Figure 1 project beyond the plane of the planar surface 7 and the outer sections I 7 of the female mould half 3b shown in Figure 2 are recessed with respect to the plane of the planar surface 7, thereby to receive the projecting outer sections 15 of the male mould half 3a. In Figures 4 to 6 is shown a first jig 19 for use in machining the rough as-cast mould halves 3. The firs jig 19 comprises an elonqate body 21 having a flat upper surface 23 and a series of plates 25 extending from and spaced along the length of the flat upper surface 23 to define therebetween compartments 27 to receive the rough cast mould halves 3. The first jig 19 further comprises a plurality of spacer plates 31 each positioned on the flat upper surface 23 of a respective compartment 27. The length and the width of the spacer plates 31 are selected to correspond closely with that of the planar surface 7 of the mould halves 3 so that in use the projecting outer sections 15 of the male mould members 3a extend part way down the sides 33 of the spacer plates 31. As can best be seen in Figure 5, the thickness of the spacer plates 31 is selected so that the projecting outer sections 15 of the male mould halves 3a terminate short of the flat upper surface 23 of the first jig 19. Each spacer plate 31 further comprises a pair of pins 37 and a plate 39 which, when a mould half 3 is positioned on the spacer plate 31, extend into the mould cavity 9 of the mould half 3. As can best be seen in Figure 6 the pins 37 and the plate 39 act to securely position the mould halves 3 onto the spacer plates 31. The first jig 19 further comprises a plurality of clamps 29 to secure the mould halves 3 and spacer plates 31 to the flat upper surface 23 of the first jig 19. Each clamp 29 s p vote on one s e o e rs g or mov m n from one open position (not shown) to a closed position at which, as can be best be seen in Figure 5, the clamp 29 extends in the groove 11 of the mould half 3 and is pinned on the other side 43 of the first jig 19. In use, a plurality of the as-cast mould halves shown in Figures 1 and 2 are positioned on the first jig 19 as described above with the planar surfaces 7 of the mould halves 3 contacting the spacer plates 31. The clamps 29 are moved to the closed position to secure the mould halves 3 and spacer plates 31 to the first jig 19, and the first jig is then positioned on a lathe (not shown) for machining. As can best be seen in Figure 6, when positioned on the jig 19 as described above, the two semi-circular sections 13 of the outer surface 5 of each of the mould halves 3 extend above the first jig 19 and are conveniently turned on the lathe to the required dimensions. In this regard, the calculation of the required dimensions is based on the spacing from the flat upper surface 23 on th~ fi ct jig 19 and therefore is independent of the other dimensions of the mould halves 3. Thus, the first jig 19 positions each of the mould halves 3 so that the semi-circular sections 13 on the outer surface 5 of the mould halves 3 are turned on the lathe to the same spacing from a reference point on the first jig 19. In Figures 7 to 10 is shown a second jig 51 for machining the planar surfaces 7 of the as-cast mould halves 3 partially machined in the first jig 19. The jig 51 comprises a plurality of holders 53 spaced along the length of an elongate base 55. The base 55 is formed to be positioned on a milling machine (not shown) . Each holder 53 comprises a semi-circular cut-out section that is adapted to receive and support a mould half 3 and is defined by semi-circular surfaces 57. The dimensions of the semi-circular surfaces 57 are selected to correspond closely with the dimensions of the machined sections of the outer surfaces 13 of the mould halves 3 so that the mould halves 3 are snuggly supported by the second jig 51. The second jig 51 further comprises a plurality of slide members 59 to correctly position the mould halves 3 in the holders 53. The slide members 59 are positioned in grooves 61 formed in one side wall of the holders 53, and the end of each slide member 59 which is arranged to extend into the cut-out section is stepoed and comprises a first surface 63 and a second surface 65. In use, when a male mould half 3a is positioned in the second jig 51 with the machined sections of the outer surface 13 positioned on the respective semi-circular surfaces 57 of the holder 53 the slide member 59 is moved to project partially across the cut-out section and the position of the male mould half 3a is then adjusted, as required, so that the projecting section 15 of the male mould half 3a on the same side of the holder 53 as the slide member 59 contacts the first surface 03 of the slide member 59 ec show in Figure ~ . The male mould half 3a so positioned is correctly aligned and the planar surfaces 7 can then be milled with the dimensions measured using the machined sections 13 of the outer surface 5 of the mould half 3 as the reference point. Similarly, when a female mould half 3b is positioned in the second jig 51 with the machined sections of the outer surface 13 positioned on the respective semi-circular surfaces 57 of a holder 53 the slide member 59 is moved to project partially across the cut-out section and then the position of the female mould member 3b is readjusted as required, so that the recessed section 17 of the female mould member 3b which is on the same side as the slide member 59 contacts the second surface 65 of the slide member 59 as shown in Figure 9. The female mould half 3b is then correctly positioned and the planar surface 13 can be milled to the required dimensions measured with respect to the machined sections 13 of the outer surface 5 of the female mould half 3b. Once the planar surfaces of the mould halves 3 have been machined in the first and second jigs 19, 51 respective pairs of male and female mould halves can be clamped together to form nack rings which are then positioned in a lathe for final turning of the mould cavity 9 and the remaining as-cast sections of the outer surface 5 of the mould halves. One of the features of the method and apparatus described above is that the measurement of the dimensions to which the planar surfaces 7 of the mould halves 3 must be machined in order to meet the tolerances required for the neck rings is independent of the initial dimensions of the as-cast mould halves 3 and thus the accuracy of the castings in terms of the initial dimensions is not as critical. As is described above, this is accomplished by using a fixed reference point on the first jig 19 as the basis for the measurement of the dimensions to which sections of the outer surface 5 of the mould halves 3 have to be machined, rather than using a given point on the mould halves 3. Once machined, as described above, L e outer surface 5 of the mould halves in effect becomes the reference point for the measurement of dimensions for the machining of the planar surfaces 7 and other sections of the mould halves 3. As a consequence it is possible with the method described above to produce a plurality of mould halves machined to the same tolerances from rough castings, notwithstanding that there are variations in the initial dimensions of the rough castings. Furthermore, by constructing the first and second jigs 19, 51 to receive and support a plurality of mould halves 3, not only can a plurality of identically dimensioned mould halves 3 be reproduced but also the rate of production can be increased. In this regard, it has been found that 200 neck rings can be manufactured in an 8 hour shift using the five compartment jigs shown in the drawings. Furthermore, the first and second jigs allow a single rough cast mould half to be machined without difficulty to a range of sizes and mould cavity configurations, with the variations in size only requiring minor recalculations of the basic dimensions and the use of sleeves to vary the dimensions of the cut-out sections of the second jig. Many modifications to the method and apparatus described above may be made without departing from the snirit and scope of the present invention.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A method of manufacturing a mould half for use in injection moulding of glass, said mould half having a mould cavity and comprising a planar surface adapted to contact a corresponding planar surface of another mould half along the longitudinal centre plane of a mould formed from the two mould halves, said method comprising: (a) casting the mould half, (b) positioning the cast mould half in the first jig, (c) turning a section of an outer surface of the mould half to the required dimensions measured with respect to a reference point on the jig, (d) positioning the cast mould half in a second jig, and (e) milling the planar surface of the mould hall to the required dimensions measured with respect to the turned outer surface of the mould half. 2. The metho fin in ^laim 1 wherein the (-, jr na '' section is semi-circular. 3. The method defined in claim 1 or claim 2, wherein the mould half forms part of a neck ring for the injection moulding of bottles. 4. The method defined in any one of the preceding claims, comprising positioning a plurality of mould halves in the first and second jigs for machining. 5. An apparatus for machining a mould half for use in injection moulding of glass, the mould half comprising a planar surface adapted to contact a corresponding planar surface of another mould half along the longitudinal centre plane of a mould formed from the two mould halves, said apparatus comprising: (a) a first jig to receive and support the mould half so that a section of an outer surface of the mould half can be machined to the required dimensions measured with respect to a reference point on the first jig, and a secon g o rece ve an suppor p r y machined mould half so that the planar surface of the mould h alf can be machined to the required dimensions measured with resp / ect to the section of the outer surface of the mould half. 6. The apparatus defined in claim 5, wherein the first jig comprises a plurality of compartments, each of which is adapted to receive and support a respective said mould half. 7. The apparatus defined in claim 6, wherein the first jig comprises an elongate body having a flat upper surface, and the compartments are defined by a plurality of transverse plates extending from and spaced along the length of the upoer surface. 8. The apparatus defined in claim 7, wherein the flat upper surface defines the reference point. 9. The apparatus defined in claim 8, wherein the first jig further comprises a plurality of spacer plates each associated with one of said compartments and positioned on th« flat upper surface, whereby in us a the planar surfaces of the mould halves contact the spacer olates. 10. The apparatus defined in claim 9, wherein the spacer plates comprise projections that in use extend into the mould cavities of the mould haves to so retain the mould halves in position on the spacer olates. 11. The apparatus defined in any one of claims 5 to 10, wherein the first jig further comprises a plurality of securing members to releasably secure the respective said mould halves to the first jig. 12. The apparatus defined in claim 11, wherein each securing member comprises a clamp pivotally mounted on one side to the upper surface of the first jig and movable from an open to a closed position at which the clamp extends around a section of the outer surface of the mould half and is releasably pinned on to the other side to the upper surface of the first jig. . e apparatus e ne n any one o c a ms o , wherein the second jig comprises a cradle to receive and support the mould half by direct contact of the turned section of the outer surface of the mould half. 14. The apparatus defined in. claim 13, wherein the second jig comprises means to align the mould half in the correct position. 15. A method of manufacturing a mould half for use in injection moulding of glass substantially as hereinbefore described with reference to the accompanying drawings. 16. An apparatus for machining a mould half for use in injection moulding of glass substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: MATASKA JOHN ROMAN, MATASKA, JOHN, ROMAN
Applicants: INT MOULDING ALLOYS PTY LTD, INTERNATIONAL MOULDING ALLOYS PTY. LTD.
Application year: 1987
Main classification: B23P15
IPC codes: B23P15, B23Q3, C03B40