US3541737A - Method and apparatus for polishing metallographic specimens - Google Patents

Description

NOV. 24, 1970 w F STUHRKE ETALl 3,541,737

METHOD AND APPARATUS FOR POLISHING METALLOGRAPHIC SPECIMENS Nov. 24, 1970 W F, STUHRKE ETAL y 3,541,737

METHOD AND APPARATUS FOR POLISHING METALLOGRAPHIC SPECIMENS Filed May 21, 196e V s sheets-snee?. 2

Fig-Q PUMP 3 l l////l// /z @MJ/Q??? Nov. 24; 1970 METHOD AND APPARATUS FOR POLISHING METALLOGRAPHIC SPECIMENS Filed May 21, 1968 W. F. STUHRKE I'AL s sheets-sheet s INVENTORS wuz/4M. A frz/fewe- United States Patent O 3 541 737 METHOD AND APPAR'IUS FOR POLISHING METALLOGRAPHIC SPECIMENS William F. Stuhrke and Charles R. Underwood, Dayton, Ohio, said Underwood assignor to the United States of America as represented by the Secretary of the Air Force Filed May 21, 1968, Ser. No. 730,831 Int. Cl. B24b 47/02 U.S. Cl. 51-151 6 Claims ABSTRACT OF THE DISCLOSURE A metallographic specimen is moved in a iigure-ofeight motion over a stiff paper supported by a hard backing surface on which the polishing compound is positioned at the crossover point of the iigure-of-eight motion. The specimen is rotated about its axis after each predetermined number of motions. Apparatus is provided to give a continuous range of selectable pressures between the specimen and paper.

BACKGROUND OF THE INVENTION In prior art polishing systems for metallographic speci mens, large amounts of expensive polishing compound have been required to obtain suitable specimens. When a 4 SUMMARY OF THE INVENTION According to this invention the specimen is moved in a Kiigure-of-eight pattern over a stiif sheet of paper which is supported on a hard backing surface. A small amount of the polishing compound, such as diamond dust or silicon carbide in oil, is placed in the normal path of movement of the specimen preferably at the crossover point in the iigure-of-eight pattern and is spread out by Patented Nov. 24, 1970 rice Reference is now made to FIG. l of the drawing which shows a metallographic specimen polishing apparatus 10, having a support structure 12 secured to a base member 14. The support structure 12 has a recess 16 therein. A hard support plate 18, of a material such as granite, is positioned in the recess 16 with a chamber 19 beneath the plate 18. A plurality of holes 20 are bored in the plate 18. A sheet of stiff paper 22 is positioned over plate 18 and is retained by means of a vacuum in space 19 acting through holes 20 and provided by means of a vacuum pump 24 and a flexible tube 25 interconnecting the pump 24 and chamber 19 to provide a vacuum in chamber 19 of about 25 microns of mercury. The vacuum level given is merely by way of example as the exact vacuum would be determined by the particular structure.

A specimen holder assembly 30 is held by a support arm 31 which, in turn, is supported by support structure 33. The support structure 33 is secured at 35 to a plat# form 37.

The platform 37 is positioned above an air bearing base member 38 which is secured to base member 14. The platform 37 has a recess 39 with a metal plate 41 of a material such as stainless steel closing the recess and providing a chamber 43 within the platform 37. The plate 41 has a plurality of holes 44 therein and may be secured to platform 37 by welding or with an adhesive. Air at a pressure of about 30 p.s.i. from supply 46 is supplied to chamber 43, through a iiexible tube member 47, to raise the platform .005 to :006 inch from member 38 and provide an air bearing between the platform 37 and the air bearing base member 38. The air pressure given is merely by way of example with the exact pressure being determined by the particular design of the air bearing and support structure.

The platform 37 is moved over the air bearing base member 38 by means of two crank members 49 and 50 driven by a motor 52 through gear boxes 54 and 55. The gear ratio of gear boxes 54 and 5S are selected so that crank 49 rotates at twice the speed of crank 50. Crank the motion of the specimen in a very thin layer over ,Y

the entire pattern on the sheet of paper. This requires about 1/500 of the amount of vcompound used in prior art devices and eliminates the agglomeration problem. By cleaning the specimen and discarding the sheet of paper used, contamination can be eliminated when changing from one grade of compound to the next. Means are provided to vary the pressure over a continuous range to include levels substantially below the capability of existing machines, so that improved results can be obtained in polishing metallographic specimens.

Vibration is substantially eliminated in the apparatus by the use of an air bearing and a massive support for the specimen holder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a specimen polishing apparatus according to the invention;

FIG. 2 is an enlarged left end view of the polishing apparatus of the device of FIG. l;

FIG. 3 is a sectional view of the device of FIG. 2 along the line 3 3;

FIG. 4 is an enlarged cutaway top view of the polishing arm for the device of FIG. 1; and

FIG. 5 is a sectional View of the polishing arm of FIG. 4 along the line 5 5.

49 drives the platform 37 by means of a pair of slider bars 61 and 62, secured to platform 37 by supports 63 and 64, a slider 65 and linkage 66. Crank 50 drives the platform 37 by means of a pair of slider bars 6,7 and 68, secured to platform 37, by supports 70 and 71, and slider 72 and a linkage 74. The crank member 49 runs at twice the speed of crank member 50. By the use of elongated sliders 65 and 72, and because of the low frictonal load of the air bearing, this drive arrangement was made to function without binding even though there is some torque on the sliders during operation.

The specimen holder assembly 30 is rotated in arm 31 by means of a pawl 76 which operates a ratchet wheel 77 on the assembly 30. The pawl is driven by a conventional air drive cylinder 78 to which air is supplied from supply 46 through tubular member 79,` pressure regulator 80 and a conventional rotary valve v81. The rotary valve 81 is driven by shaft 82 which also drives crank 50 so that the pawl 76 is operated after every predetermined number of revolutions of crank 50 in accordance with the ratio of pulleys 84 and 85, shown here to be 1 to l.

The metallographic specimen to be polished is held in a conventional specimen holder 86 such as the chuck shown. It is to be understood that other specimen holders than that shown may be used.

The pressure of the specimen against the paper is determined by the pressure of the air supplied to air cylinder 87 which is controlled by valve 89 and gage 90` connected in line 91 from air Supply 46. The pressure may 'be adjusted -between 0 and 100 p.s.i. The tube 92 from gage 90 3 isV secured against rotationV as ratchet wheel 78 is rotated by means of connection 93 to arm 31. A conventional seal 95 is provided around tube 92.

In the operation of the apparatus, vacuum pump 24 is turned on and a sheet of stiff paper 22, such as a le card, is positioned over support plate 18. The specimen is then secured in the specimen holder 86'and the desired pressure level is set by valve 89. A small amount of polishing compound is placed in the normal pathof movement of the specimen but preferably at the crossover point of the gure-of-eight pattern on paper 22. The motor 52 is then started to move the specimen over the paper in a figureof-eight pattern 97. After each revolution of shaft 82, an impulse is supplied to air cylinder 79 to rotate the specimen a portion of one turn about its vertical axis. When it is desired to change to a different grade of polishing compound, the machine is shut down, the paper 22 is replaced by another paper, the specimen is cleaned and replaced in the specimen holder, and the above described operation is repeated with the new grade of compound. There is thus provided an improved apparatus and method for polishing metallographic specimens.

4 continuous predetermined range; and a specimen polishing compound on said disposable material on at least a portion of the figure-of-eight pattern.

2. The device as recited in claim 1 wherein said means for holding said disposable material is a support member having a recess therein; said support surface being a closure member for said recess, whereby a chamber is provided in said support member; means for evacuating said chamber; said support surface having a plurality of holes therein, whereby the vacuum created within Said chamber by said evacuating means retains the disposable material in contact with the support member.

3. The device as recited in claim 2 wherein said means i for moving the specimen holder over the disposable ma- While a particular apparatus is shown and described, it

is obvious that other apparatus could be provided without departing from the general principles and scope of the invention.

Also, the method of the invention could be performed by manually moving the specimen in the gure-of-eight pattern over the paper.

While paper has been described as the material for holding the polishing material, a sheet of any disposable material having a mat surface, including plastic, cloth and even some metals and glass may be used. A mat surface for this purpose is to be considered to be any surface that is not too smooth or shiny to retain the polishing compound.

Many other changes also can be made without departing from the general principles and scope of the invention.

What is claimed is:

1. An apparatus for polishing a metallographc specimen comprising: a sheet of disposable material of predetermined dimension, having a mat surface; a rm support surface for said disposable material; means for holding the sheet of disposable material on said support surface; a specimen holder adapted to support a metallographic specimen in Contact with said disposable material; means for moving said specimen holder and the specimen in a gure-of-eight pattern over said disposable material; means for rotating the specimen holder a fraction of a turn after each predetermined number of cycles of the gure-of-eight motion; means for adjusting the pressure of the specimen against the disposable material over a terial is a platform and a support arm supported by said platform and means for moving the platform in a cyclic motion at a predetermined frequency and a predetermined distance in a rst direction; means for moving said platform in a cyclic motion at twice said predetermined frequency in a direction at right angle to said rst direction and a distance equal to one-half said predetermined distance; means for providing an air bearing surface beneath said platform and means for providing an air ilow between said platform and said bearing surface means to thereby provide an air bearing therebetween.

4. The device as recited in claim 3 wherein said disposable material is a stiif sheet of paper.

5. The device as recited in claim 1 wherein said means for moving the specimen holder over the disposable material is a platform and a support arm supported by said platform and means for moving the platform in a cyclic motion at a predetermined frequency and a predetermined distance in a rst direction; means for moving said platform in a cyclic motion at twice said predetermined frequency in a direction at right angle to said first direction and a distance equal to one-half said predetermined distance; means for providing an air bearing surface beneath said platform and means for providing an air flow between said platform and said bearing surface means to thereby provide an air bearing therebetween.

6. The device as recited in claim `5 wherein said disposable material is a stiff sheet of paper.-

References Cited UNITED STATES PATENTS 1,257,047 2/1918 VSuverkrop 51-64 3,305,976 2/1967 Koskie 51-151 OTHELL M. SIMPSON, Primary Examiner U.S. Cl. X.R. 51--231 y

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