US2494834A

US2494834A - Mounted specimen

Info

Publication number: US2494834A
Application number: US604280A
Authority: US
Inventors: Richard S Ringheim
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-07-10
Filing date: 1945-07-10
Publication date: 1950-01-17
Anticipated expiration: 1967-01-17

Description

Jan. 17, 1950 R. s. RINGHEIM' MOUNTED SPECIMEN Filed July 10, 1945 Fig.1

, Fig.4.

INVENTOR. RIOHAR D $.R IN GH EIM ATTORNEY Fig.5.

Patented Jan. 17, 1950 MOUNTED SPECIMEN Richard S. Ringheim, San Gabriel, Caliih, assignor to the United States of America as represented by the United States Atomic Energy Commission Application July 10, 1945, Serial No. 604,280

Claims. 1

This invention relates to microscopy and more particularly to an improved mounting for a specimen to be examined under the microscope and a novel method of preparing such a mounted specimen. The mounting of the present invention is particularly useful in cases where it is desired to examine a transverse section of a relatively thin sheet of material such as, for example, a metal alloy sheet or a composite metal sheet. However it will be understood that the present mounting is not limited to such applications.

In cases where it is desired to examine a transverse section of a thin sheet of material the specimen to be examined must be carefully mounted in order that the examination may accurately reveal the characteristics of the specimen that it is desired to determine. It has previously been proposed that such a specimen might be mounted in a molded plastic block and a face of the block perpendicular to the plane of the specimen finished on in such manner as to expose a transverse section of the specimen for examination. In using this technique, however, a number of difficulties arise which render the results obtained by microscopic examination somewhat misleading. In mounting the specimen, the piece of material to be examined may be enveloped in a suitable molding powder and pressure and heat applied to convert the molding powder into a solid block containing the specimen. During this molding operation there is a tendency for the specimen to tilt to a greater or lesser extent from the vertical position and thus when the face of the molded block is finished oil the section of the specimen exposed is not a true transverse section, 1. e. it is not precisely perpendicular to the plane of the specimen. Hence, if, for example, it is .ence to the accompanying drawing wherein desired to determine the relative dimensions of parts of the section these dimensions will be in error to the extent that the specimen has tilted during the molding operation.

A further dlfllculty arises due to distortion of the specimen under the pressure that is normally applied during the moldin operation. It is evident that such pressures may easily alter the physical character of the specimen to such a degree as to produce a misleading appearance under the microscope.

It is accordingly an object of the present invention to provide an improved mounting for a specimen of a relatively thin sheet of material wherein a transverse section of the specimen is exposed that is previseiy perpendicular to the plane or the specimen. I i

It is another object of the invention to provide 2 an improved method of mounting a specimen for microscopic examination of a transverse section thereof.

It is still another object of the invention to provide a method of mounting a specimen of a relatively thin sheet of material for microscopic examination of a transverse section thereof in such manner that the specimen is firmly held in the mounting and precisely aligned with respect to the face of the mounting that is to be examined.

Other objects of the invention will be in part obvious and in part pointed out hereinafter.

The many objects and advantages of the present invention may best be appreciated by refer- Fig. 1 is an isometric view of a specimen mounted between two supporting blanks of preferred construction Fig. 2 is an isometric view similar to Fig. 1 but showing an alternative supporting structure;

Fig. 3 is a vertical cross-sectional view of a mold showing a specimen in position for incorporation in a plastic block;

Fig. 4 is a view similar to Fig. 3, but showing the molding powder compressed around the spectmen;

Fig. 5 is a view similar to Fig. 4 but showing the specimen at the end of the molding operation embedded in a plastic block;

Fig. 6 is a transverse section taken on the line 6-6 of Fig. 5 and showing the relative positions of the exposed faces of the specimen and supporting blanks in the finished mounting; and

Fig. 7 is an isometric view of the finished plastic block with the specimen and its supporting pieces encased therein.

In one of its broader aspects the present mounting comprises the combination witha specimen of sheet material of a pair of reinforcing supporting members or blanks fixed to opposite faces of the specimen, the specimen and blanks being encased in a molded block of plastic that has one surface finished to expose a transverse section of the specimen for microscopic. examination. The manner in which the present mounting is made may be best understood by reference to the accompanying drawing. Referring to the drawing and particularly to Figs. 1, 2 and 3 the numeral Ill designates a cylindrical mold of well-known construction having a platen l2 on which the object to be molded may be placed and a plunger l4 that fits snugly into the cylindrical mold Ill and is adapted to be pressed downwardly to exert a desired pressure on the object to be molded. Re-

ferring particularly to Fig. 1 a rectangular specimen lt'oi' the sheet of material to be examined is mounted between a pair of U-shaped supporting pieces or blanks II and 20. The blank II (which may be identical with the blank 20) comprises a pair of vertical legs I! and I1 and a horizontal bridging member ii, the parts l5, l1 and. I9 being of square cross-section. The legs I! and I1 and bridging member l8 define a channel or milled out portion 2| through which the side of the specimen i6 is exposed. The blanks l8 and 20 may be affixed to opposite faces of the specimen in any suitable manner and the particular method used will depend to some extent upon the materials of which the specimen and blanks are constructed. It has been found that where the blanks l8 and 20 are made of brass and the specimen 18 of nickel or copper that a rubber cement may be desirably used for afiixing the blanks to the specimen.

Care should be taken to make sure that the lower edge of the specimen I6 is precisely aligned with the lower faces of the blanks Band 20. This alignment may be effected advantageously after the blanlm have been cemented to the specimen and before the cement has hardened by pressing the blanks andspecimen downwardly on a fiat surface. The blanks are then firmly clamped to the specimen to prevent relative movement thereof and the cement permitted to harden.

The clamps are then removed and the blanks and specimen placed on the platen E2 in the manner indicated in Fig. 3. A suitable molding powder such as a Bakelite powder 22 is poured into the mold ID in an amount sufi'lcient to cover and envelop the specimen I6 and associated blanks l8 and 20. The plunger M is pressed downwardly to force the molding powder 22 against the specimen IS in such manner that the powder completely fills the channel 2i of the blank l8 and the corresponding channel of blank 20. The relationship between the specimen and the molding powder at this stage of the process is illustrated in Fig. 4 of the drawing.

After the molding powder has been compressed around the mounted specimen the mold is heated to cause the molding powder to be converted into a solid block. The condition of the block and specimen at the end of the molding operation is illustrated in Fig. 5 of the drawing.

The preferred molding schedule comprises heating the mold to about 65 C. at a pressure of the order of atmospheric pressure; then increasing the pressure to about 3000 pounds per square inch and increasing the temperature to about 150 C. The temperature of 150 C. is maintained for approximately five minutes after which the molded product is permitted to cool under pressure to about 100 C. to 110 C. at which temperature the mounting may be removed from the mold and permitted to cool to room temperature in the atmosphere.

At this point in the process the blanks l8 and 20 in the specimen l6 are embedded in a solidified mass of plastic. The blanks and specimen are so positioned within the plastic block 22 that one edge of the specimen l6 and the lower faces of the legs l5 and ll of blank i8 and corresponding faces of the blank 20 are adjacent the lower surface 24 of the block 22. The surface 24 of block 22 is ground down to expose the transverse section of specimen I6 that it is desired to examine by any suitable method such as by utilizing well known grinding, lapping or polishing techniques.

The appearance of the ground surface 24 is indicated in Fig. 6 wherein it designates the specimen to be examined and more particularly an exposed transverse section of the specimen that is precisely perpendicular to the plane of the specimen. Abutting the specimen at its ends are exposed surfaces of the legs l5 and I! of the blank l8 and exposed surfaces of the legs H and I3 of the blank 20. As stated above the plastic during the molding operation passes throughthe channels in the blanks I8 and 20 into contact with the specimen so that the transverse section of the specimen I6 that is to be examined is bounded for most of its length by the plastic material of the block 22. The finished mounted specimen is illustrated in Fig. '7 of the drawing.

The channelled construction of the blanks I0 and 20 which permits the plastic to be molded into intimate contact with the sides of the specimen is an important feature of the present mounting. If the

blanks

18 and 20 were not milled out and the specimen I B were bounded by metal instead of plastic less satisfactory results would be obtained. It is difficult if not impossible to prevent small clearances between the metal of the specimen and the metal of the supporting blanks and these tiny crevices tend to become filled with finely divided material during the grinding operation. Furthermore such crevices may permit deformation of the specimen during the grinding operation. With the present construction, on the other hand, the plastic may be molded flush with the side faces of the specimen along most of its length in such manner that there is no clearance between the specimen and plastic.

The blanks l8 and 20 perform several functions in the present mounting. In the first place they retain the specimen in vertical position during the molding operation so that when the surface 24 of the block 22 is ground the exposed transverse section of the specimen I6 is precisely perpendicular to the plane of the specimen. This accurate alignment of the specimen with respect to the block 22 is particularly important where the specimen is a composite structure and it is desired to measure the relative and absolute thicknesses of the various strata of the specimen under the microscope, or in fact in any case where accurate micro-measurements of the specimen are desired.

In some cases the structure of the specimen I 6 may be relatively delicate and it is important to avoid distortion of the specimen during the molding operation in order that the examination of the specimen under the microscope may yield an accurate picture of the structure of the specimen. The blanks l8 and 20 are of substantial assistance in preventing such distortion. The principal stresses during molding are vertical stresses due to the downward pressure of the plunger I4 and these stresses are almost entirely sustained by the supporting blanks. Furthermore the blanks serve to markedly diminish the horizontal stresses that would otherwise be exerted on the specimen. Thus only a small fraction of the total molding stress is transmitted to the specimen with the result that distortion of the specimen due to such stresses is substantially reduced.

It is to be understood that the foregoing description is illustrative only and that many modifications may be made in the method of forming the present mounting and in the mounting itself. For example Fig.2 illustrates an alternative type of blank that may be used. In Fig. '2 the specimen 26 is formed in the shape of a semi-circle and supported by the blanks 28 and '30 which are in the form of half rings of rectangular crosssection Any suitable type of powdered polymeric material may be used in the mold l0 and either a thermosetting or thermoplastic resin may be used. The molding procedure will of course be modified slightly where other types of plastics are used but such modifications are commonly known in the molding art. Thus for example methyl methacrylate plastic known as Lucite has been successfully used in place of Bakelite but when Lucite is used it is desirable that the mounting be cooled to say about 50 C. before it is ejected from the mold. In some cases it may be desirable to etch the exposed section of the specimen before it is examined under the microscope and in cases where the specimen is to be etched before examination Bakelite is preferable to Lucite because of its greater resistance to acids. When, however, the nature of the examination is such that no etching is required, a less resistant plastic such as Lucite may be satisfactorily used.

Since many embodiments might be made of the present invention and since many changes might be made in the embodiment described, it is to be understood that the foregoing description is to be interpreted as illustrative only and not in a limiting sense.

I claim:

1. A mounted specimen of a relatively thin sheet material having a transverse section exposed for microscopic examination, comprising, in combination with said specimen, a pair of reinforcing blanks aflixed to opposite faces of said specimen and a molded block of plastic encasing said specimen and blanks, said block having one surface finished to expose a transverse section of said specimen for microscopic examination.

2. A mounted specimen of a relatively thin sheet material having a transverse section exposed for microscopic examination, comprising, in combination with said specimen, a pair of reinforcing blanks affixed to opposite faces of said specimen. said blanks being so affixed to said specimen that corresponding faces of said two blanks are flush with said transverse section, and a molded'block of plastic encasing said specimen and blanks, said block having one surface finished to expose a transverse section of said specimen for microscopic examination.

3. A mounted specimen sheet material having a transverse section exposed for microscopic examination, comprising, in combination with said specimen, a pair of channelled blanks affixed to opposite faces of said specimen and a molded block of plastic encasing said specimen and blanks, said block having one surface finished to expose a transverse section of said specimen and said plastic extending through said channels into contact with said specimen.

of a. relatively thin,

a 6 4. A mounted specimen of a relatively thin sheet material having a transverse section exposed for microscopic examination, comprising, in combination with said specimen, a pair of channelled reinforcing blanks affixed to opposite faces of said specimen, said reinforcing blanks being so aflixed to said specimen that said channels are adjacent said transverse section,'and a molded block of plastic encasing said specimen and blanks, said block having one surface thereof finished to expose said transverse section and said plastic extending through the channels in said blanksto points adjacent said transverse section;

5. A mounted specimen of a relatively thin sheet material having a transverse section exposed for microscopic examination, comprising, in combination with said specimen, a pair of U-shaped blanks aflixed to opposite faces of said specimen, said blanks being so aifixed to said specimen that the end surfaces of said blanks are flush with said transverse section, and a molded block of plastic encasing said specimen and blanks, said block having one surface finished to expose said transverse section for microscopic examination.

RICHARD S. RINGHEHMI.

REFERENCES CITED UNITED STATES PA'IENTS Number Name Date 239,770 Guild Apr. 5, 1881 553,533 Lord Jan. 28, 1890 1,308,330 Brown July 1, 1919 1,467,108 Hodgson Sept. 4, 1923 1,588,164 Brunner June 8, 1926 1,671,911 Tillyer May 29, 1928 1,956,527 De Groot Apr. 24, 1934 1,980,483 Hill Nov. 13, 1934 2,068,950 Hamilton Jan. 26, 1937 2,090,914 Porter Aug. 24, 1937 2,105,688 Fessenden Jan. 18, 1938 2,158,906 Netter May 16, 1939 2,264,003 Osenberg Nov. 25, 1941 2,268,529 Stiles Dec. 30, 1941 2,362,434 Fitch et a1. Nov. 7, 1944 2,383,465 Bradford Aug. 28, 1945 2,386,824 Tinnerman Oct. 16, 1945 FOREIGN PATENTS Number Country Date 197,784 Great Britain 1923 35,995 Austria 1909 OTHER REFERENCES The Metallograph and Heat Treatment of Iron and Steel, by A. Sauveur (4th edition, 1935, Mc- Graw-Hill Book Co.) pp. 490492.