Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D5/00—Bonded abrasive wheels, or wheels with inserted abrasive blocks, designed for acting only by their periphery; Bushings or mountings therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B9/00—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor
  • B24B9/02—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor characterised by a special design with respect to properties of materials specific to articles to be ground
  • B24B9/06—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor characterised by a special design with respect to properties of materials specific to articles to be ground of non-metallic inorganic material, e.g. stone, ceramics, porcelain
  • B24B9/08—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor characterised by a special design with respect to properties of materials specific to articles to be ground of non-metallic inorganic material, e.g. stone, ceramics, porcelain of glass
  • B24B9/14—Machines or devices designed for grinding edges or bevels on work or for removing burrs; Accessories therefor characterised by a special design with respect to properties of materials specific to articles to be ground of non-metallic inorganic material, e.g. stone, ceramics, porcelain of glass of optical work, e.g. lenses, prisms

Definitions

• the present invention relates to a grinding wheel for grinding ophthalmic lenses, of the type comprising a disc-shaped core which carries on its periphery a diamond abrasive layer.
• a grinding wheel is intended to equip a grinding machine, in particular automatic, usable for trimming blanks of spectacle lenses.
• the trimming of ophthalmic lenses is carried out on an automatic grinding machine.
• This machine has one or more abrasive wheels driven in rotation at high speed and used as tools for cutting the edge of spectacle lenses.
• the grinding glasses are mineral glasses, the grinding wheel must have a diamond abrasive layer, and this abrasive layer is carried by a rigid metallic core in the shape of a disc.
• Automatic grinding machines generally comprise a grinding wheel shaft provided with means for driving in rotation at high speed, means for supporting a glass blank suitable for rotating this blank with a slow rotation speed according to a support axis parallel to the support shaft grinding wheel, and means for varying the distance between the two axes as a function of the angular position of the blank around the support axis.
• the invention aims to extend the life of the grinding wheel relatively economically. To this end, it relates to a grinding wheel of the aforementioned type, characterized in that the abrasive layer has a convex profile over at least part of its length.
• the grinding wheel according to the invention may include one or more of the characteristics described in claims 2 to 9.
• the invention also relates to a machine for grinding ophthalmic lenses according to claim 10, comprising a grinding wheel as defined above.
• Figure 1 is an axial sectional view of a grinding wheel according to the invention, this view schematically showing the associated parts d 'an automatic grinding machine;
• Figure 2 shows larger scale region II of Figure 1;
• Figures 3 and 4 are views similar to Figure 2 of two variants.
• the grinding wheel 1 shown in Figures 1 and 2 consists of a body or core 2 and an abrasive layer 3.
• the body 2 is a metal disc of axis X-X delimited by two radial planar faces 4, 5 and by a cylindrical peripheral surface 6 with circular 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. It consists of grains of synthetic diamond coated in a binder and has a homogeneous composition. Over the length L, the abrasive layer 3 is subdivided into three sections: in the middle, a section 8 of relatively high constant thickness el + e2, and, on either side of this section 8, two sections 9, 10 having a progressively decreasing thickness from el + e2 to el, this value being reached at each axial end of the grinding wheel. For example, one can choose el of the order of 2 mm and e2 of the order of 0.5 mm.
• the meridian section of layer 3 thus has a profile made up of three straight segments: a central segment 3A parallel to the axis X-X, framed by two inclined segments 3B and 3C.
• the length E of the section 8 can be between 1/5 and 4/5 of the total length L, and is generally between 1/3 and 2/3 of this length.
• the grinding wheel 1 is fixed by its orifice 7, by means of appropriate wedging means, to a drive shaft 11 of an automatic grinding machine, the shaft 11 being connected to a motor 12 for driving high speed around axis XX, which is fixed relative to the machine frame.
• the machine also comprises removable fixing means 13, for example of the suction cup type, which make it possible to position a blank 14, for example initially circular, of ophthalmic glass, in particular mineral glass, and to rotate the latter at low speed around of a support axis YY parallel to the axis XX .
• the axis YY may be the axis of the blank 14, or may be slightly offset from it.
• the length L of the grinding wheel of the order of 2 cm, is slightly greater than the edge of the thickest blank 14 of divergent or concave type which one may have to grind.
• the machine also includes means making it possible to bring the YY axis closer to or further away from the XX axis, along the double arrow F of, FIG. 1.
• FIG. 1 These means are shown diagrammatically in FIG. 1 by a radial arm 15 for supporting the gripping means 13, articulated on a fixed shaft 16 parallel to the axes XX and YY and situated outside the plane which they define (which is the plane of Figure 1).
• the blank is fixed by means 13, in an appropriate position relative to the center thereof, and it is rotated slowly around the YY axis, while positioning the latter at a predetermined distance from the axis XX, variable as a function of the angular position of the blank around the YY axis.
• the blank thus attacks the peripheral surface of the abrasive layer 3 and is brought to the desired configuration.
• the blank is substantially centered relative to the length of the grinding wheel. It can be seen that, after trimming a large number of blanks of different types, it is the middle region of the wheel that wears out the most.
• the thick section 8 is centered on the length of the grinding wheel, so that it is essentially this section 8 which is stressed. This results, at the cost of a small increase in the volume of abrasive material and therefore at a moderate cost, a substantial lengthening of the life of the grinding wheel, which retains, throughout this lifetime, a peripheral surface. whose shape is close to a cylinder.
• the shape of the additional thickness of the layer 3 compared to the conventional cylindrical shape of constant thickness el, is roughly symmetrical with a curve C corresponding to the shape that the layer 3 would take, after wear, in the absence of this extra thickness.
• the wear curve C can have a deeper U shape and extend from one end to the other of the grinding wheel ( Figure 3).
• FIG. 3 which is substantially symmetrical with this form of wear for the outer profile of the layer 3.
• the theoretical curve is approximated by a succession of line segments, five in number in the example shown, where the middle segment 3A is parallel to the axis XX.
• the adjacent segments 3B, 3C being slightly inclined relative to this axis, it can be considered that the segments 3A to 3G together define a median section 8 of approximately constant thickness and of length E bordered by two sections 9, 10 d ' markedly variable thickness.
• the meridian section of the blank 14 ( Figure 1), we see that, compared to the middle of its peripheral edge, it has more material on one side (the left side in Figure 1) than the other, and it is the same with a convergent or convex glass with a thin edge.
• the actual wear of the abrasive layer 3 is in fact slightly shifted to the left with respect to the middle of the length L.
• the section 8 of the layer 3 of maximum thickness may be slightly offset in the same direction relative to the middle of the length L, as illustrated in the variant of Figure 4.
• the allowance is new symmetrical with respect to the wear curve C, which in this case has practically only a substantial deflection over the length E above.
• the section 8 is then framed by two sections 9, 10 of thickness substantially equal to el.
• the convex profile of the section 8, with its adjacent concave connections 17, 18, is a curve without angular point.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Inorganic Chemistry (AREA)
• Grinding And Polishing Of Tertiary Curved Surfaces And Surfaces With Complex Shapes (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9484871

Family Applications (1)

Country Status (4)

Families Citing this family (8)

Family Cites Families (13)

• 1995
  • 1995-11-23 FR FR9513960A patent/FR2741560B1/fr not_active Expired - Fee Related
• 1996
  • 1996-11-25 WO PCT/FR1996/001861 patent/WO1997018922A1/fr not_active Application Discontinuation
  • 1996-11-25 US US08/875,089 patent/US5951381A/en not_active Expired - Fee Related
  • 1996-11-25 EP EP96941067A patent/EP0805734A1/de not_active Withdrawn

Non-Patent Citations (1)

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