Grinding wheel for ophthalmic glasses and corresponding grinding

Details Grinding wheel for ophthalmic glasses and corresponding grinding Grinding wheel for ophthalmic glasses and corresponding grinding

1997-07-22

1999-09-14

Rose, Robert A.

Abrading

Machine

Rotary tool

451 42, 451 43, 451540, 451542, 451547, 451544, 451240, B24B 500

Patent

active

059513810

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a grinding wheel for the grinding of ophthalmic glass blanks, of the type comprising a disc-shaped core which carries a diamond-charged abrasive layer on its periphery.
Such a grinding wheel is intended for equipping a grinding machine, in particular an automatic one, which can be used for routing the blanks of spectacles or glasses.
To fit an ophthalmic glass in the circle or surround of a spectacle frame, a generally circular glass blank is taken as a starting point, and then this blank is routed to the contour of the frame circle. The blank routed in this manner is subsequently passed to a finishing station.
The routing of ophthalmic lenses is usually carried out on an automatic grinding machine. This machine possesses one or more abrasive grinding wheels which are driven in rotation at high speeds and serve as tools for cutting the edge of the spectacle glasses.
When the lenses to be ground are mineral glasses, the grinding wheel must comprise a diamond-charged abrasive layer, and this abrasive layer is carried out by a disc-shaped rigid metal core.
Automatic grinding machines generally comprise a wheel-holding shaft provided with means for driving in rotation at high speeds, and means for supporting a glass blank, which is designed to cause the blank to rotate at a slow rotational speed along a supporting axis parallel to the wheel-holding shaft. The machine also includes means for varying the distance between the two axes as a function of angular position of the blank about the supporting axis.
During the use of the grinding wheel, it has been discovered that a middle part of the length of the grinding wheel undergoes more rapid wear. It is therefore necessary to change the grinding wheel well before the entire abrasive layer is worn. This is particularly troublesome in view of the high costs of diamond-charged products.


SUMMARY OF THE INVENTION

The object of the present invention is to extend the life of the grinding wheel relatively economically. For this purpose, the subject of the invention is a grinding wheel of the abovementioned type, wherein the abrasive layer has a convex profile over at least part of its length.
Another subject of the invention is a machine for the grinding of ophthalmic lenses comprising a grinding wheel, as defined above.


BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described with reference to the accompanying drawing in which:
FIG. 1 is a view in axial section of a grinding wheel according to the present invention, this view diagrammatically illustrates associated parts of an automatic grinding machine;
FIG. 2 shows region II of FIG. 1 on a larger scale; and
FIGS. 3-4 are views, similar to that of FIG. 2, of two variants of the present invention.


DETAILED DESCRIPTION OF THE INVENTION

A grinding wheel 1 is illustrated in FIGS. 1 and 2 consists of body or core 2 and of an abrasive layer 3.
The body 2 is a metal disc having a central axis X--X. The body 2 is delimited by two radial planar faces 4, 5 and by a cylindrical peripheral surface 6 having a circular cross-section. The body 2 is pierced with an axial orifice 7.
The abrasive layer 3 extends axially over the entire length L of the body 2. The abrasive layer 3 consists of grains of synthetic diamond which are coated in a binder, and it has a homogeneous composition.
The abrasive layer 3 is subdivided over the length L into three portions: in the middle, a portion having a relatively high constant thickness e1+e2 and, on either side of portion 8, two portions 9, 10 having a thickness which decreases progressively from e1+e2 to e1. The e1 value is reached at each axial end of the grinding wheel. As an example, e1 may be selected as being of the order of 2 mm and e2 of the order of 0.5 mm.
The meridian cross-section of the layer 3 thus has a profile consisting of three segments of a straight line: a central segment 3A, parallel to the axis X-X-, which is framed by two inclined segments 3B and 3C.
The length E of

REFERENCES:
patent: 3599377 (1971-08-01), Dartnell
patent: 3802130 (1974-04-01), Lindenbeck
patent: 4151685 (1979-05-01), Frangipane
patent: 4720942 (1988-01-01), Miller
patent: 5218948 (1993-06-01), Mazaki
patent: 5321915 (1994-06-01), Lecert et al.
patent: 5406929 (1995-04-01), Uderf et al.
patent: 5441033 (1995-08-01), Chiuminatta et al.

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