US3404861A - Optical casting gasket - Google Patents

Description

Oct. 8, 1968 R. w. EWER OPTICAL CASTING GASKET Filed Feb. 16. 1966 United States Patent 3,404,861 OPTICAL CASTING GASKET Ronald W. Ewer, Torrens Park, South Australia, Australia, assignor to Optics Australia Pty. Ltd., Adelaide, South Australia, Australia Filed Feb. 16, 1966, Ser. No. 527,907

Claims priority, application Australia, Feb. 22, 1965,

55,409/65 4 Claims. (Cl. 249187) ABSTRACT OF THE DISCLOSURE An optical casting gasket for interpositioning between the optical surfaces of a pair of dies during the casting of lenses from monomer material, wherein the gasket has an outwardly directed portion extending substantially radially outwardly beyond the peripheries of the dies, and upstanding projections on the outwardly directed portion to engage the peripheries of the dies and thereby position the gasket without the formation of pockets which would allow the monomer to set and adhere to the outer edges of the dies.

This invention relates to a gasket of improved shape which can be used between dies employed for optical castmg.

Many lenses are cast from synthetic resin based monomer material (usually allyl diglycol carbamate), and these are usually cast between glass dies which have been polished and which are retained in a spaced relationship by means of a T section gasket. The material used for casting tends to adhere to the die around its edge where the material has been confined, and the dies are therefore damaged by removal of this material, and to limit the damage the dies are bevelled. This bevel allows a certain amount of feather edge of material being cast to form between the inwardly projecting flange of the T section gasket usually employed and the die itself, since the monomer is confined at this locality and can therefore, solidify, and consequently there is :a cleaning operation which requires substantial labor. It is a characteristic of allyl diglycol carbamate that it will not cure in the presence of air.

One of the objects of this invention therefore is to provide a gasket which will be less likely to form a feather edge with the casting material, and this is achieved by the use of an optical casting gasket which is characterized by the cross-sectional shape of the gasket which includes an inwardly directed portion having opposite side surfaces of a shape substantially complementary to the shapes of the respective optical surfaces adjacent their peripheries, and an outwardly directed portion extending substantially radially outwardly from respective peripheries.

By having the opposite side surfaces of the gasket extending outwardly in a substantially radial direction from the peripheries of the optical surfaces of the dies, there will be no confined space around the outside surfaces of the dies to entrap the monomer, so that it will not cure at this locality. This enables easy removal of the cast lens from the dies. Furthermore, by having the inwardly directed portion of the gasket substantially complementary to the shape of the optical surfaces, formation of flash is substantially reduced or eliminated.

Cleanliness of course is one of the prime considerations when optical lenses are being cast between glass dies, and the presence of any foreign substance is very deleterious. Even when considerable efforts are made to clean the dies after a lens has been cast, the presence of partly or wholly cured particles of monomer is often sufficient to damage the surface of a subsequently cast lens. When the dies are moved apart from a T section gasket, a suction frequently exists which upon being broken allows a sudden inrush of air which carries with it some particles, and

.these are deposited on the die surfaces. A further object of the invention is to reduce this particle collector on the die surface, and this again is achieved by avoiding the use of an annular flange surrounding the gasket.

Although an annular flange is not utilized in this invention, it is nevertheless desirable to have some centering device for positioning the dies relative to each other, and according to this invention this is achieved by having a plurality of projections circumferentially spaced around the gasket. These projections touch the dies at localized points only, so that the flexibility of the gasket is not interfered with.

The invention is further described below in some detail with reference to an illustrated embodiment in the attached drawing, in which:

FIG. 1 illustrates the casting of a lens between the optical surfaces of dies,

FIG. 2 is a central section through the gasket used, and

FIG. 3 is an elevation of the gasket.

According to this embodiment a gasket 10 is formed from a flexible resin based material (for example polyethylene) the gasket having an outwardly directed radially extending planar portion 11 and an inwardly directed frusto conical portion 12, the two opposite side surfaces of the frusto conical portion being positioned between the dies 13 so that upon clamping together of the dies 13 these opposite side surfaces become of complementary shape to the shape of dies 13 near their peripheries, at which locality they approximate a frusto conical shape.

The planar portion 11 of the ring has a plurality of projections 14 arranged circumferentially, and in this embodiment the projections 14 are of circular shape so that they engage the edge surfaces 15 of the complementary dies 13 over very small areas. These however fully locate the complementary dies relative to one another and relative to the gasket.

As shown in FIG. 1 the dies are clamped together with a spring clip 17, a projection 14 is aligned with a pin 18, an outwardly extending tab 19 is deflected by a finger 20, and the allyl diglycol carbamate is fed through a conduit 21 into the space between the dies 13.

Although the above embodiment is a very simple example of the invention, it will nevertheless be seen that the gasket in being flexible is easy to strip off after a lens has been moulded between dies, the gasket readily follows the contour of the dies, and the dies are more easily cleaned than in other methods since the monomer tends less to adhere to the dies at the locality of the gasket, remaining in liquid form where it is exposed to the air.

While one complete embodiment of the invention has been disclosed herein, it will be appreciated that modification of this particular embodiment of the invention may be resorted to without departing from the scope of the invention as defined in the appended claims.

What I claim is:

1. An optical casting gasket interposable between the optical surfaces of a pair of dies, during the casting of lenses, to space said dies, said gasket having a cross-sectional shape including an inwardly directed portion with opposite side surfaces of a shape substantially complementary to the shapes of the respective optical surfaces of the dies adjacent their peripheries, and an outwardly directed portion extending substantially radially outwardly beyond the peripheral edge surfaces of the dies, and a plurality of circumferentially spaced projections on the outwardly directed portion, said projections extending in a direction normal to the outwardly directed portion and being engageable against the edge surfaces of the dies to thereby position the dies relative to the gasket.

2. An optical casting gasket according to claim 1 where- 3 in'said projections are circular in section and have outer cylindrical surfaces tangentially engageable with the edge surfaces of the dies.

3. An optical casting gasket for interpositioning between and thereby spacing the optical surfaces of a pair of dies during the casting of lenses, the cross-sectional shape of the gasket including an inwardly directed portion having opposite side surfaces of shape substantially complementary to the shapes of respective of said optical surfaces adjacent their peripheries, an outwardly directed portion extending substantially radially outwardly from respective peripheries, and a plurality of circumferentially spaced projections on the outwardly directed portion, the projections being engageable against the edge surfaces of the dies to thereby position the dies relative to the gasket, the gasket being formed of a thermo-plastic material sufficiently yieldable that its inwardly directed portion conforms to the shape of the optical surfaces when clamped between the dies during casting.

4. An optical casting gasket for interpositioning between and thereby spacing the optical surfaces of a pair 7 of dies during the casting of lenses, the cross-sectional shape of the gasket including an inwardly directed portion having opposite side surfaces of shape substantially complementary to the shapes of respective of said optical surfaces adjacent their peripheries, an outwardly directed portion extending substantially radially outwardly from respective peripheries, and a plurality of circumferentially spaced projections being engageable against the surfaces of the dies to thereby position the dies relative to the gasket, the outwardly directed portion having a tab extending radially outwardly from its periphery.

References Cited UNITED STATES PATENTS 3,056,166 10/1962 Weinberg. 3,136,000 6/1964 Slyk. 3,331,102 7/1967 Mignen.

WILLIAM J. STEPHENSON, Primary Examiner.

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