GB2079665A - Mould for casting eyeglass frames - Google Patents

Abstract

A casting mould M for eyeglass frames comprises mould halves, 10, 10a including backing supports 28, 26 to which are fitted replaceable parts 32, 30, each part having a moulding cavity therein supplied with casting material via a runner in at least one of the mould halves. <IMAGE>

Description

SPECIFICATION Mould for casting eyeglass frames This invention relates to the casting of articles such as eyeglass frames and has particular reference to improvements in casting mould construction.

Present processes for casting liquid epoxy materials to produce eyeglass frames use rubber moulds consisting of two opposing halves which, when mated, provide a runner system and multiple cavities in which eyeglass fronts and/or temples are formed. These moulds, however, have a limited production life due to attack of their effective casting surfaces by the epoxy precursors and/or damage in handling. Accordingly, the complete mould structure must be replaced at the end of useful life of its casting surface with the result of high tooling and product cost.

An object of the present invention is to reduce equipment and end product cost in the manufacture of cast epoxy articles such as eyeglass frames.

According to one aspect of the present invention we provide a mould for casting eyeglass frames comprising two mating mould halves each including a permanent backer and an expendable blanket fitted upon said backer, each blanket having a casting surface with an article moulding cavity therein and a runner in at least one of said mould halves for directing a casting precursor into said cavities when said mould halves are tightly mated, said outer casting surfaces of said blankets providing wear surfaces of said mould which are renewable at end-of-service life by removal, discarding and replacement of said blankets on said permanent backers.

According to another aspect of the invention we provide a method of making wear surface blankets for article casting moulds comprising: providing a rigid master having the shape of articles to be cast and adders for process and shrinkage changes; embedding said master into a surface of a forming member with said surface arranged to simulate a parting line of the ultimate article casting mould; casting a replica of non-embedded portions of said article over said forming member; transferring said master into said cast replica and casting a second replica over said master and first replica, separating said cast replicas and removing said master therefrom; casting over each replica a first rigid blanket former; applying to each first rigid blanket former a coating of a thickness approximating that desired of a wear surface blanket intended to be produced;; casting a second rigid blanket former over said coating in each case of each first rigid blanket former; and casting blankets between corresponding pairs of said first and second blanket formers without said coatings.

Reference is now made to the accompanying drawings; in which Figure 1 illustrates a master used to form casting mould cavities according to the invention, the master being shown in the form of an eyeglass frame front for purposes of illustration only; Figure 2 is a plan view of a casting mould depicted as having casting cavities of shapes and sizes similar to those of the master in Figure 1, the upper half of the mould has been removed for purposes of illustrating the casting cavities with greater clarity; Figure 3 is a cross-sectional view of the mould taken generally along line 3-3 of Figure 2 including the upper half of the mould not shown in Figure 2; Figure 4 illustrates an initial step in a preferred procedure for making the mould shown in Figure 2 and 3; Figures 5- 14 are illustrations of further steps of the procedure for making the mould; and Figures 15-18 are illustrations in cross-section of blanket and backer components of the Figures 2 and 3 mould; and Figure 19 is a fragmentary cross-sectional view of a modification of the invention.

Articles such as eyeglass frames are cast of epoxy compositions between opposing mould halves which, when mated, define a filling well, runner system and one or more cavities used to form the articles, e.g. eyeglass frame fronts and or temples.

One such mould half 10 is illustrated in Figure 2 as having filling well 12, runner system 14with vents 16 and casting cavities 18. Cavities 18 correspond precisely in shape to master 20 Figure 1) from which they are formed as will be described shortly.

Mould half 10, being the lowermost one-half of the two part casting mould M shown in Figure 3, is provided with locating projections 22 which fit into correspondingly shaped receiving recesses 24 of the second half 10a of mould M. Mould halves 10 and 10a are separated in Figure 3 for clarity of illustration of details. During an article casting operation, however, they are brought tightly together with projections 22 fitted into recesses 24 and cavities 18 tightly closed. The casting precursor is poured into well 12 and enters cavities 18 through runners 14.

The filled mould is then subjected to an elevated temperature for curing of the castings.

Those interested in suitable casting compositions and article curing cycles may refer to U.S. Patent No.

4,034,955. While dealing with centrifugal casting apparatus and method, this reference discloses casting precursor compositions and curing cycles which are adaptable to the present system of static casting.

In the present case, halves 10 and 10a of mould M comprise permanent backers 26, 28 and disposable blankets 30, 32 providing expendable wear surfaces between which articles are cast in cavities 18.

A method of making the above two-part mould halves is illustrated in Figures 4-14 and involves the following: A pair of masters 20 which have been compensated by adders for process and shrinkage changes are embedded in a forming member 34 of clay. As it will become apparent from subsequent Figures of the drawings, upper surface 36 of former 34 establishes the location of a parting line between mould halves 10 and 1 Oa, i.e. the plane of separation of upper and lower halves of casting cavities 18. Also embedded in former 34 are balls 38 and rods 40 of sizes and shapes desired of mould M projections 22, recesses 24, runners 14 and vents 16. While not shown, but easily understood by the artisan, filling well 12 is similarly formed.

With the above master components so embedded in the clay former 34, a silicone rubber casting 42 (Figure 5) is made against surface 36. Master components 20, 38 and 40 are then transferred to casting 42 and a second side silicone rubber casting 44 is formed thereover (Figure 5).

First and second side rubber castings 42 and 44 are separated and all master components are removed.

Rubber castings 42 and 44 are next used as formers over which first rigid epoxy castings 46 and 48 are produced as illustrated in Figures 7 and 8.

Thin layers 50 and 52 of clay or wax (e.g. 1/8 inch thick) are next built up over epoxy castings 46,48 (Figures 9 and 10) and second rigid epoxy castings 54, 56 are formed over the layers of clay or wax 50, 52 (Figures 11 and 12).

First and second epoxy castings 46,54 (Figure 11) and 48,56 (Figure 12) with clay layers 50,52 removed thereby provide forming mandrels between which disposable flexible blankets 30, 32 (Figures 15 and 16) are formed by casting and vulcanizing or injection moulding and curing. Figures 13 and 14 illustrate cavities 58,60 which are used to form blankets 30 and 32 of Figures 3, 15 and 16.

Permanent mould backers 26 and 28 (Figures 3, 17 and 18) are preferably but not necessarily formed of silicone rubber. They are produced by casting directly over surfaces 62, 64 of rigid epoxy castings 54 and 58 of Figures 11,12 and 13,14.

The above mentioning of materials used for the casting or otherwise forming of various parts of casting mould M is to be taken as a generalization, there being many well-known and available substances in the field. The following, however, will identify presently preferred materials; Blankets 30 and 32 are preferably formed of a flexible polymer such as room temperature vulcanizing (RTV) silicone rubber, an injection moulding type polymer or a vulcanizable silicone gum rubber. A desirable commercially available RTV rubber is GE-662, supplied in the U.S.A. by General Electric.

GE-LIM 2500 A and B is the commercial identification of a liquid injection-type polymer and hardener which is curable under temperatures ranging from 1 40"F to 400oF. A temperature of approximately 350 F for a period of approximately 1 minute will produce desirable results. The liquid polymer is also available in the U.S.A. from General Electric.

Also available from General Electric is a gum rubber requiring vulcanization under heat of from 150'to 4000F, preferably about 330 F for a period of about 15 minutes.

The above-mentioned rigid mould making components 46,48, 54 and 56 are preferably formed of any of the variously filled epoxys, e.g. epoxys filled with aluminium bits or powder for strength and rigidity.

Iron, steel, brass, copper, fibreglass and otherfillers may be used. Epoxy resins and hardeners are commercially available from Hysol Division, Dexter Corporation, Olean, New York, U.S.A.

The clay used to construct former 34 (Figures 4 and 5) may comprise any of various modelling clay compositions, a preferred form of which is known commercially as P24 Polyform marketed in the U.S.A. by Polyform Products, Inc., Scheller Park, ~.

Illinois.

While the above modelling clay or an equivalent may be used as layers 50, 52 (Figures 9-12), it is presently preferred to use wax in sheet form, e.g. 1/8 inch thick wax sheets which may be purchased from Hapco Manufacturing Co., Hanover, Massachusetts, U.S.A.

In Figure 19 there is illustrated a modification of the invention wherein the expendable mould wear surfaces (blankets) may be provided in the form of inserts 60 in permanent mould backers 62, e.g.

mould backers 26 and/or 28 may be provided with recesses 64 (Figure 19) for receiving removable inserts 60 having casting surfaces 66 similar to those of blankets 30,32. The inserts 60 may replace only the wear surfaces of casting cavities 18 leaving runners 14, vents 16 and other portions of mould halves 10, 10a as permanent parts of backers 26,28.

From the foregoing, it can be seen that the present invention provides an article casting mould having expendable wear surfaces (Blankets 30, 32) on permanent mould backers 26, 28. At end-of-service life of the casting surfaces due to attack by article casting precursor and/or other damage, simple removal of blankets 30 and 32 from backers 26 and 28, discarding and replacement thereof renders the casting mould ready for continued service.

It has been determined that the above wear surface replacement can be accomplished for much less than one-third the cost of complete mould replacement and in considerably less time.

Claims (14)

1. A mould for casting eyeglass frames comprising two mating mould halves each including a permanent backer and an expendable blanket fitted upon said backer, each blanket having a casting surface with an article moulding cavity therein and a runner in at least one of said mould halves for directing a casting precursor into said cavities when said mould halves are tightly mated, said outer casting surfaces of said blankets providing wear surfaces of said mould which are renewable at end-of-service life by removal, discarding and replacement of said blankets on said permanent backers.

2. A mould according to claim 1 wherein said t blankets are inserted into said permanent backers

3. A mould according to claim 1 wherein said blankets are fitted over said backers and sides thereof oppositely of said wear surfaces are of irregular configurations interfittable with corresponding irregularities on said backers for secureness against relative displacement during use of said mould.

4. A mould according to any of claims 1 to 3 wherein said backers and blankets are formed of flexible polymers.

5. A mould according to any of claims 1 to 3 wherein said blankets are formed of a liquid injection moulded polymer.

6. A mould according to any of claims 1 to 3 wherein said blankets are formed of a heat vulcanized gum rubber.

7. A mould according to any of claims 1 to 3 wherein said blankets are formed of room temperature vulcanized rubber.

8. A mould for casting eyeglass frames substantially as herein described with reference to the accompanying drawings.

9. A method of making wear surface blankets for article casting moulds comprising: providing a rigid master having the shape of articles to be cast and adders for process and shrinkage changes; embedding said master into a surface of a forming member with said surface arranged to simulate a parting line of the ultimate article casting mould; casting a replica of non-embedded portions of said article over said forming member; transferring said master into said cast replica and casting a second replica over said master and first replica, separating said cast replicas and removing said master therefrom; casting over each replica a first rigid blanket former; applying to each first rigid blanket former a coating of a thickness approximating that desired of a wear surface blanket intended to be produced; ; casting a second rigid blanketformer over said coating in each case of each first rigid blanket former; and casting blankets between corresponding pairs of said first and second blanket formers without said coatings.

10. A method according to claim 9 wherein said coating over each of said first rigid blankets formers is clay.

11. A method according to claim 9 wherein said coating over each of said first rigid blanket formers is wax.

12. A method according to any of claims 9 to 11 wherein said first and second blanket formers are constructed of metal-filled epoxys.

13. A method according to any of claims 9 to 12 wherein said blankets are cast of a flexible polymer.

14. A method of making wear surface blankets for casting moulds substantially as herein described.