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A new semi-automatic grinding and polishing machine
325
METALLOGRAPHY 17:325-329 (1984)
A New Semi-Automatic Grinding and Polishing Machine
T. KJER
The Technical University of Denmark, 2800 Lyn£by, Denmark
Introduction Most automatic rotating metallographic grinding and polishing machines on the market today have two motors: one for the disk and one for the specimen or specimen holder. Lapping machines, on the other hand, are generally equipped with only one motor, which drives the disk. The specimen holder is confined in a metal ring which rotates on the disk. Like lapping machines, the machine described here employs a disk-driven specimen holder but with the specimens fixed in the holder and with nothing but the specimens in contact with the disk. The specimen holder is mounted on a manual machine.
Description Figures 1 and 2 show the specimen holder mounted on a manual metallographic grinding machine, specifically a Knuth Rotor, made by Struers. The specimen holder is a 120 mm diameter disk, 12.5 mm thick, with holes in which the specimens are fixed by Allen screws. In the center a ball bearing is sunk with a loose fit. The bearing is held by a single screw which makes it easy to replace if necessary. The dimensions of the bearing are 10 mm ID, 26 mm OD and 8 mm width. The specimen holder is held by an arm which can be loaded with different weights. With the weight shown in Figs. 1 and 2 the total load on the specimens is 50 N. The maximum load for this machine, which runs at 300 RPM, is about 75 N. (The lower the RPM the higher the maximum load for a given p o w e r of the motor.) The arm is adjustable so that the specimen holder can be placed on the disk near the rim and so that the rod in the ball bearing is perpendicular to the specimen holder. © Elsevier Science Publishing Co., Inc., 1984 52 Vanderbilt Ave., New York, NY 10017
0026-0800/84/$1)3.00
T. Kjer
326
F1G. 1.
Specimen holder mounted on manual machine.
FIG. 2.
The arm and weight in upper position.
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FIG. 3.
327
Section through connection between arm and specimen holder.
The connection between the arm and the specimen holder is shown in detail in Fig. 3. In the vertical rod is pressed a small pin which rests on the inner ring of the ball bearing. Where it fits into the bearing the rod is a few tenths o f a mm smaller in diameter than the ID of the bearing, which allows for some wobbling of the specimen holder when it rotates. When mounting the specimens, the specimen holder is placed in a disk as shown in Fig. 4 so that the specimens extend about 2 mm from the holder. The design of the arm and specimen holder is flexible. The dimensions of the various parts could be different from those shown here and the specimen holder could be made to hold more than three specimens.
Operation When the specimen holder is placed on the grinding/polishing disk it is free to rotate. When loaded in the center, calculations and experiments show that the specimen holder will attain the same rate of rotation as the disk, irrespective of the diameter of the specimen holder and its position.
FIG. 4.
Section through specimen holder placed in device for mounting specimens.
328
T. Kjer
FIG. 5. Relative motion of a specimen on the disk when specimen holder and disk rotate at the same rate. The specimen moves at a constant velocity in a circle, once along the circular path for each revolution of the disk.
When the specimen holder and disk rotate at the same rate, the relative motion of a specimen on the disk is a translation in a circle, as shown in Fig. 5. The specimen moves at a constant velocity in this circle, once along the circular path for each revolution of the disk. The direction of grinding or polishing will thus change through 360 ° for each revolution. The velocity of the specimens relative to the disk is about 1 m/sec for the machine shown in Figs. 1 and 2. When the specimen holder and disk rotate at the same rate three specimens will move in the same three circles all the time. This is obviously inefficient. T o avoid this the specimen holder is loaded off-center. The pin by which the load is transferred to the inner ring of the ball bearing can be turned either toward or away from the center of the driving disk,
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329
causing slower or faster rotation, respectively. (The effect of changing the rate of rotation would be more p r o n o u n c e d if a bearing with a greater inner diameter were chosen.) The path of a specimen on the disk will then be displaced for each revolution, so that it wilt eventually cover all of the disk. The coverage will not be even, however. A wet grinding paper will be used up faster near the center and the rim than it will in between.
Practical Use of the Machine Preparation of metallographic specimens on the machine is carried out using standard procedures, that is, using the same grinding papers, polishing cloths, polishing medium, load, etc., as usual. When polishing, an automatic lubricant dispenser can be mounted. It is advantageous to have arms for the specimen holder mounted on several machines, so that the specimen holder can be transferred from one machine to another, as this is faster than changing disks.
Received July 1983; accepted February 1984.
METALLOGRAPHY 17:325-329 (1984)
A New Semi-Automatic Grinding and Polishing Machine
T. KJER
The Technical University of Denmark, 2800 Lyn£by, Denmark
Introduction Most automatic rotating metallographic grinding and polishing machines on the market today have two motors: one for the disk and one for the specimen or specimen holder. Lapping machines, on the other hand, are generally equipped with only one motor, which drives the disk. The specimen holder is confined in a metal ring which rotates on the disk. Like lapping machines, the machine described here employs a disk-driven specimen holder but with the specimens fixed in the holder and with nothing but the specimens in contact with the disk. The specimen holder is mounted on a manual machine.
Description Figures 1 and 2 show the specimen holder mounted on a manual metallographic grinding machine, specifically a Knuth Rotor, made by Struers. The specimen holder is a 120 mm diameter disk, 12.5 mm thick, with holes in which the specimens are fixed by Allen screws. In the center a ball bearing is sunk with a loose fit. The bearing is held by a single screw which makes it easy to replace if necessary. The dimensions of the bearing are 10 mm ID, 26 mm OD and 8 mm width. The specimen holder is held by an arm which can be loaded with different weights. With the weight shown in Figs. 1 and 2 the total load on the specimens is 50 N. The maximum load for this machine, which runs at 300 RPM, is about 75 N. (The lower the RPM the higher the maximum load for a given p o w e r of the motor.) The arm is adjustable so that the specimen holder can be placed on the disk near the rim and so that the rod in the ball bearing is perpendicular to the specimen holder. © Elsevier Science Publishing Co., Inc., 1984 52 Vanderbilt Ave., New York, NY 10017
0026-0800/84/$1)3.00
T. Kjer
326
F1G. 1.
Specimen holder mounted on manual machine.
FIG. 2.
The arm and weight in upper position.
New Products
FIG. 3.
327
Section through connection between arm and specimen holder.
The connection between the arm and the specimen holder is shown in detail in Fig. 3. In the vertical rod is pressed a small pin which rests on the inner ring of the ball bearing. Where it fits into the bearing the rod is a few tenths o f a mm smaller in diameter than the ID of the bearing, which allows for some wobbling of the specimen holder when it rotates. When mounting the specimens, the specimen holder is placed in a disk as shown in Fig. 4 so that the specimens extend about 2 mm from the holder. The design of the arm and specimen holder is flexible. The dimensions of the various parts could be different from those shown here and the specimen holder could be made to hold more than three specimens.
Operation When the specimen holder is placed on the grinding/polishing disk it is free to rotate. When loaded in the center, calculations and experiments show that the specimen holder will attain the same rate of rotation as the disk, irrespective of the diameter of the specimen holder and its position.
FIG. 4.
Section through specimen holder placed in device for mounting specimens.
328
T. Kjer
FIG. 5. Relative motion of a specimen on the disk when specimen holder and disk rotate at the same rate. The specimen moves at a constant velocity in a circle, once along the circular path for each revolution of the disk.
When the specimen holder and disk rotate at the same rate, the relative motion of a specimen on the disk is a translation in a circle, as shown in Fig. 5. The specimen moves at a constant velocity in this circle, once along the circular path for each revolution of the disk. The direction of grinding or polishing will thus change through 360 ° for each revolution. The velocity of the specimens relative to the disk is about 1 m/sec for the machine shown in Figs. 1 and 2. When the specimen holder and disk rotate at the same rate three specimens will move in the same three circles all the time. This is obviously inefficient. T o avoid this the specimen holder is loaded off-center. The pin by which the load is transferred to the inner ring of the ball bearing can be turned either toward or away from the center of the driving disk,
New Products
329
causing slower or faster rotation, respectively. (The effect of changing the rate of rotation would be more p r o n o u n c e d if a bearing with a greater inner diameter were chosen.) The path of a specimen on the disk will then be displaced for each revolution, so that it wilt eventually cover all of the disk. The coverage will not be even, however. A wet grinding paper will be used up faster near the center and the rim than it will in between.
Practical Use of the Machine Preparation of metallographic specimens on the machine is carried out using standard procedures, that is, using the same grinding papers, polishing cloths, polishing medium, load, etc., as usual. When polishing, an automatic lubricant dispenser can be mounted. It is advantageous to have arms for the specimen holder mounted on several machines, so that the specimen holder can be transferred from one machine to another, as this is faster than changing disks.
Received July 1983; accepted February 1984.