US 1798639 A
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Description (OCR text may contain errors)
March 31, 1931. R. TVESTMANN 1,798,639
Filed Oct. 10, 1928 33%; 1M) Jm Mia/M Patented Mar. 31, 3931 uairno srArss PATENT OFFICE BUDOIJF TVESTMANN, OF NEW YORK, N. Y., ASSIGNOR TO E. LEITZ INCQA. GOBPORA- TION on NEW YORK roLI snme MAC INE Application filed October' lO, 1928. Serial No. 311,449.
This invention relates to improvements in polishing machines of the type used in. lab-.'-
oratories for grinding and polishing speci mens for test purposes. .More particularly this invention relates to polishing machines of the type disclosed in the U. S. Patent No. 1,636,557 dated July 19th, 1927, in which the specimen or work is held in a workholder in contact with a polishing disk .byv means of an electromagnet, and suitable mechanism. is
provided for oscillating the work on the Tig. 1 is a plan view of a polishing machine embodying the inventionwith certain parts omitted.
Fig. 2 is a side viewof the machine with parts omitted and arts in section.
Fig. 3 is a detail view showing how the specimens are mounted in the work holder.
The specimen or work to be olished is mounted in a suitable work holder. Heretofore it has been the practice to use a short I section of iron pipe and mount the specimen in one end thereof by means of wax or cement. This requires quite some time and skill and it is not always feasible to mount a small specimen in'this manner.
One object of this invention is therefore to provide a work holder of novel construction and means for quickly mounting the work therein. The work holder comprises a barrel 5 and two cooperating semi-circular jaws 6, 6 having a pivotal edge '7 which divides each jaw into a larger upper portion 8 and a smaller lower portion 9.
The jaws are cut angularly as at 10 to enable them to seize the work, and a screw 11 is operated to force the upper ends of the jaws apart, and the lower ends of the jaws together to seize the specimen or work.
In mounting a specimen 12, Figure 3,, use is made of a stage 13 having an annular ,14- and the two jaws placed .When thescrew is operated, the jaws are means o'f a pulley 19 to which plied" Thework holder is held in positionflange 14 and a shallow socket or depression 15. The specimen l2- isplaced on the latter, the rrel put on the stage within the flange inside the barrel.
moved around their pivots 7 ..to seize and clamp the work and at the same time the aws are selflockmg within thebarrel as is obvious. lVhen the screw is screwed outward, the parts of the workholder come apart and the work is released.
After mounting the work, the work holder is placed on a polishing disk 16 fast on a shaTt 17 suitably mounted in a general framewonklS. The shaft and disk are rotated by power is ap on the disk by an arm 20 having an adjustable entension 21 the end of which is shaped like a fork to engage the holder. The extension is adjusted by means of a slot 22 and bolt 23..
The arm :20 is pivoted at 24 on an oscillating bearing 25 on a stud 26 on the framework 18. The :arm 20 is oscillated to move the work over' the disk by means of a cam 27 fast on the shaft 17 The cam engages an arm 28 securediat 29 in the oscillating bearing 28. The frame is cut out as at 30 to permit swinging on the arm. A spring 31 keeps the arm 28 in contact with the cam. The work holder arm 5-30 rests by gravity on 3. lug 32 which is a part of the bearing A s :rew 33 serves to adjust the height of the arm.
The numeral 35 denotes a stationary 'electromagnet having a head or pole 36 large enough to reach from the shaft 17 to the periphery of the disk. Electric current is supplied to the inagnet in any well known manner. I
When the work holder is placed on the disk 16 and the current is turned on to the magnet, it will be: seen, that inasmuch as the frame and bearing 23 as well as the arm 20 and the work ;holder are of iron or other magnetic material, these elements together with the core of the magnet form a horseshoe magnet with the lines of force or strongest attraction passing through a disk 16 at the point where the work 12 is held.
Consequently the work holder is attracted pulled down on or against the disk 16. The latter will therefore be rotated and turn rapidly under the work polishing the same. During the operation the work is being oscillated on the disk by the arm 20.
In polishing specimens, a fine abrasive or polishing powder is used on the disk 10 and because of the even steady pressure of the specimen on the disk, particles of this powder and fine particles of the material of the specimen works into the surface of the specimen and produces what is known as incrustation in the surface thereof. The incrustation is very common when magnesium oxide is used as a polishing powder, and alumina will also )roduce this condition at times. It
will also e seen, that with a construction as hereinbefore described, the specimen is held in the same position all the time and this fact also hinders or is disadvantageous for a perfect polishing.
In order, therefore, to provide an improved polishingmachine and eliminate the objections referred to, it is an object of this invention to provide a nonhomogeneous pol ishing disk consisting of both magnetic and nonmagnetic material. This has the advantage of interrupting, as it were, the steady downward pressure on the work and it also provides for automatic rotation of the work during the operation.
The object may be accomplished in several ways, but it has been found that by providing the disk 16 which is of nonmagnetic material with soft iron or other magnetic inserts 40 in the form of' round small disks the objects are attained in an inexpensive'practical manner. By referring to the drawing it will be seen that the magnetic inserts 40 are graded in size and arranged in accord ance with a regular pattern. This is mostly for convenience in manufacture. The same result may be obtained by scattering the inserts irregularly. The inserts are of magnetic material and simply forced into corresponding openings in the disk, no other securing means being needed.
It will be apparent, therefore, that as thework is being oscillated on the disk and the latter rotated, the magnetic pull, that is the pressure on the specimen or work, is interrupted every time a nonmagnetic portion of the disk passes under the work, and the pressure is put on or increased when a magnetic portion, that is an insert, passes under the work. Again, it will be seen, that as the work is moved from one insert to another across the disk, there will be a greater or lesser pull on the work holder at the edges thereof due to the different sizes of the inserts. Consequently the work holder and the specimen are rotated slightly or moved or shaken during the operation. As a result, incrustation in the surface of the specimen or work is prevented and it is polished and provided with a straight surface clear to the edges thereof.
If the inserts 40 are arranged as shown in the drawing, the work will be rotated in a clockwise direction because as the larger inserts -10 pass under thework holder, a correspondingly greater pull will be exerted at the edge of the holder. 1f the inserts are arranged dill'ercntlv or otherwise graded, the work may be rotated anticlockwise or even oscillated regularly or irregularly.
1. T he combination of a work holder adapted to hold the work therein, a polishing disk, magnetic means for keeping the work in contact with the disk, means for operating the latter and means-for varying the magnetic lines of force between the magnetic means and the work to vary the pressure of contact between the work and the polishing disk.
2. The combination of a work holder adapted to hold the work-therein, a polishing disk for polishing said work, means forrotating. said disk, means for keeping the Work in frictional contact with the disk-'andmagnetic means for varying the pressure between the work and the disk.
3. The combination of a Work holder adapted to hold the work therein, a polishim disk, magnetic means for keeping the WOIC in contact with the disk, meansfor operating the latter and means for varying the magnetic lines of force between the magnetic means and the work to vary the pressure of contactbetween the work and the polishing diskand to cause rotation of the work.
- BUDOLF TVESTMANN.