US2151233A - Lens blocking - Google Patents

Description

March 21, 1939. F ROWE 2,151,233

LENS BLOCKING Filed Jan. 21, 1937 INVENTCR 241/3 F Powe r mR N l-k Patented M... 21, 1939 UNITED STATES PATENT OFF-ICE Louis I. Rowe, Southbridge, American Optical Company,

Mass assign to Southbrldgtafisl a voluntary association of Massachuse Application January 21, 1937, Serial No. 121,808

. 3 Claims. (01. 51-216) This invention relates to repetitive blocking of lenses or lens blanks; and has for one of its objects an improved method of blocking lenses which makes it possible to repeatedly use the same lens block. a

A further object of the invention is to provide a block which is of such material as to be usable a large number of times without reshaping or replacement oi. any part of the block.

In the drawing that illustrates my invention" Fig. I is a central sectional view of a block composed substantially entirely of the novel material;

Figs. 1:! and III are similar views of blocks hav- 1; ing inserts of the novel material; and

Figs. IV and V are respectively a sectional view and a view in side elevation of a modification-of the block shown in Fig. I.

So far as shape and contour are concerned, the

blocks disclosed in the figures oi the drawing conform to conventional practice. In Fig. I the block has a body portion 4 provided with a plurality of spots 5 on which the lenses may be mounted. The body portion 4 is carried by a metal adapter 6 which may include anchoring means 1' and a baseplate la. The adapter has a key slot lb for securing the block on an actuating member, such as a spindle for rotation of the block' during a surfacing operation.

In Fig. H the block has ametal body Portion 8 with inserts 9 which take the place of the spots 5 on the form of block shown in Fig. I. The

. adapter for the body portion 8 is shown at ll.

In the form or block shown in Fig. III the body portion 12 is dished' and carries a plurality of.

inserts I! on which the lenses or lens blanks are to be mounted.

In the form of block shown in Figs. Iv and v there is a metal core l5 overlaid with .molded material it, the spots So being molded as an integral part of the latter, as indicated in Fig. The metal core 15 has the usual adapter, as shown at l6.

According to customary practice for surfacing 5 the second side of a lens after the first side has been already surfaced, a block is used having a core of metal oi substantially the character shown .at H in Fig. IV. To prepare for blocking, according to customary practice, this core isover- 50 laid with pitch, the spots on the pitch being; each molded to approximately the required shape of the side oi-the lens which has already been sur-' laced. In the process of actually blocking the lenses, the spots are sumciently softened by heat 5 to conform to the lens surfaces applied thereto.

According to my invention I deviatetrom the Y customary practice by employing a resinous material for the entire block, as in the form shown in Fig. I, or for inserts, such as shown at 9 and I3 in .Figs. II and III respectively, or for the 5 overlaid portion l6 shown in Figs. IV and V.

In general, the mat economical is the form of my invention shown in-Fig. I, in which the body portion I is molded of resinous material. The body portion] can conveniently be molded from 10 a mix which is plastic when formed; It is optional whether the mix be apermanently hardenable one or not. Non-polymerizing resins have the advantage that the blocks may be ground up and again molded to make new blocks as desired. Re- 15 sins which are permanently hardenable, such as synthetic resins of the phenol formaldehyde condensation products type, are usable with or without a filler or fillers for the body portion 4. The

synthetic resins of the phenol formaldehyde type 20 are customarily molded under heat and pressure, and under these conditions become permanently rigid and will then be substantially unafl'ected by heat below the charring point.

When such a permanently -material is employed as the body portion-l, it is usable for blocking lenses L by first painting thespotslwithathincoatingofanadheslve paint I. A block of this character is very durable so that blocking can be repeated almost indet- 30 initely without replacement oi the block becom- .ing necessary. '1

Iheresinousmaterialotthebodyportionl and of the spots I has a low rate of heat co ductivlty, sothattheadhesivepaint'l'readily dhe the warm lenses during blocking. This is a distinct advantage over the use of a metal block withadhesivepaint appliedasacoatingtothe spots, since the heat from the warm lenses flows into the cold metal of the body portion'of metal 40 blocks so rapidly as to render the coating of paint substantially non-adhesive to the glass.

'As above mentioned, the body portion 4 and thespotsSotizhebloclrmaybecozfnposedore-r filler and a resinous binder which does not become permanently hardened under heat treatment. Moreover, I have found such a composi hardened resinous 2 tion to be particularly advantageous for the inserts shownat 9 and I3 in Figs)! and III respectively. In this case the body portion 8 or It may be cast iron, or may be a composition including phenol formaldehyde synthetic resin --with or without a filter, or other suitable material.- It is not necessary to employ an adhesive 5,

paint, since the lenses will adhere to the resinous material 9 or II.

One composition'which- I have found suitable for my purpose is a mixture of 70 parts by weight of a filler, such as finely ground asbestos, and 30 parts by weight of commercial gum rosin. The relative proportions of the filler and rosin may be considerably varied. V The tackiness of the composition is increased by decreasing the proportion of filler, but the material is not so rigid nor so resistant to deformation when applying the hot lenses. On 7 the other hand, it is not desirable to reduce the V proportion of rosin below 25 parts in 100, as the mix is diflicult to handle. I find that a mix containing 25 parts or more of rosin in 100 produces a block sufliciently tacky.

- the-content of filler increases the rigidity of the resulting block.

Instead of the finely ground asbestos I may employ diatomaceous earth orother suitable filler. In place of commercial gum rosinI may employ V synthetic resins, and more particularly non Both the mixes containing rosin and the mixes .containing chlorinated diphenyl resin can be cold molded. The less tacky mixes require considerable molding pressure, and good results are obtained with hydraulic pressure. The need for pressure in molding is reduced if the mix is molded hot, for instance 150 F. The hot molding results in a more solidly molded material.

It is notable that these mixes require no appreciable allowance for shrinkage. This is contrary to experience with pitch compounds which require an allowance of as much as /4 diopter on a 6 base curve. Whenmolding these mixes, the molds are fashioned to the curve desired, and the molded block or insert retainsthe curve imparted by the mold. I

An alternative method for obtaining blocks or inserts is to machine the resinous material, to

the desired shape. I include within my invention the use of permanently hardenable resins and the use of nonpolymerizing resins. The latter type provide spots which become tacky when hot. In mounting a hot lens or lens blank 'on one of the spots, I apply pressure to' the hot lens or lens blank to cause it to adhere to the block. This may be "repeated as-often as there are spots on the block. The exposed surfaces of the lenses or lens blanks are then ground or polished, or both, after which the lenses are removed in the customary manner by chilling. The cycle is then renewed by replacing the removed lenses by hot lenses, each being applied to substantially the same position on a spot occupied by a removed lens;

My invention has the advantage. that the spots are remarkably durable. In spite of the pressure applied when the hot lenses are mounted on the spots such as the inserts 9 and l 3, these spots Thus increasing are not appreciably deformed, especially if a high content 6f filler is employed. The adhesive characteristics of the resinous material of the non-polymerizing type are ample for firmly holding the lenses or lens blanks during grinding and 5 polishing. Resinous materials which do not pro:

wise embodied and practicedwithin the scope or 15 the following claims.

I claim:

1. A device for supporting work pieces comprising a body portion having a preshaped attaching seat formed of a mixture of thermoplastic and discrete non-thermoplastic constituents in which portions of some of said discrete particles of the non-thermoplastic constituent, throughout the seat, lie in the plane of and retain the shape of the seat'and in which the thermoplastic constituent fills the voids between the discrete particles and, when subjected to heat as from a hot piece of work placed on said seat, is adapted to exude from between the discrete particles and provide means 'forretaining the work piece in secured relation with said seat with the portion of theparticles of the non-thermoplastic constituent in the plane of the seat providing a rela tively positive positioning rest for said .work piece.

2. A device for supporting work pieces com- 5 prising a body portion having a plurality of preshaped attaching seats thereon, thematerial of the portions having the preshaped attaching seats comprising a mixture of thermoplastic and discrete non-thermoplastic constituents in which 40 portions of some of said discrete particles of nonthermoplastic constituent, throughout each seat, lie in the plane of and retain the shape of said seat and in which the thermoplastic constituent fills the voids between the discrete=particles and, 5 when subjected to heat as from hot pieces of work placed on said seats, is adapted to exude from between the discrete particles and provide means for retaining the work pieces in secured relation with said seats with the portions of the 5 particles of the non-thermoplastic constituent in the plane of said seats providing a relatively positive positioning rest for said workpieces.

3. A lens blank support comprising a body portion having a raised preformed attaching seat thereon formed of a mixture of relatively solid particles which retaintheir shape under the'heat of a lens and an adhesive'ingredient,.said preformed seat having portions of said solid particles distributed throughout the area of said seat and lying in the plane of said seat with portions of the adhesive ingredient in said plane, the said adhesive having characteristics which will cause it to soften and exude from between said solid particles when subjected to heat, as from a 5 heated lens blank having a surface shaped'substantially to the shape of said seat, and placed on said seat, the saidadhesive, upon exusion, being adapted to adhere to the surfaceof the lens blank with the said surface engag n the solid 7 particles in the plane of said seat to position and hold the said lens blank on said seat.

LOUIS F. ROWE.

Images