US2917919A - Hardness-testing device - Google Patents

Description

Dec. 22, 1959 i R SCHULZE ETAL HARDNESS-TESTING DEVICE Filed May 21. 1953 FIG. I

INVENTORS.

REINHART SCHULZE HEINRICH BROSCHKE BY v a W A M a,

ATTORNEYS.

2,917,919 Patented Dee. 22, 1959 United States Patent- "ice HARDNESS-TESTING DEVICE Keinliart Schulzeand Heinrich Broschke, wetz'lartLahn), Germany, assi'gnors to Ernst Leitz G.m.b.H;, Wetzlar,

' Ger-many V V Application May 21, .1953, Serial No. 356,518 Claims priority, application Germany May 24, 1 952 i 6 Claims. c1. 73- 81) 1' This invention relates to new and useful improvements in hardness-testing devices. 7

v The hardness of materials can be ascertained by measuring the size indentation produced therein .by means of embodiments ofthe invention are illustrated, by wayof example, in; the accompanyingdrawings in whichm Figure 1 is an elevational view showing a testing device in accordance withv the invention and which employs a bimetallic strip for applying the load to the indenter and specimen.

Figure 2 illustrates details of a modified form of the invention in which the linear expansion of an electrically heated wire is employedlfor loading the indenter, the device of Figure 2. 'abeing'otherwise similar to Figure 1.,

1 Figure 3 is a bottom plan view of the guide lever show- 7 ing its point and knife-edge bearing members.

As shown in Fig. 1, a base :plate 1-carries;two.separate supports or uprights 2, 3 and a specimen table 5. Reference. numeral 4 designates the specimen tobe tested. A supporting arm'6 is rotatable on sleeve 6a which isjvertically adjustable on, upright 2 by means of a rack and a vweighted indentor which usually consistsof a diamond point In order to avoid errors in measurement, it is important that during the formation of the indentation, the diamond point shall be lowered precisely linearly as it penetrates into the material to be tested. Devices are.known in which the indentor diamond ismounted on a guide lever whose fulcrum is located'at exactly the same. level as the diamond point.- A tangent drawn at this point to the arcofthepath described by thediarnond I 'J ventional means is perpendicular to the specimen tested. Inasmuch as the diamond. point, penetrates into the material but slightly, its movement maybe considered effectively linear. 1

Careful investigation has revealed that measurements After extensive research and experimentation, the cause of the error was discovered and a novel construction devised which obviates the shortcomings of the known devices. It was found that in these devices, the weights applied cau se a slight bending of the guide lever and the guide lever support. Subsequently, when the diamond pinion mechanism 2a. Sleeve 6a may be locked in posi tion bylocking or stop lever 2b which is provided with an eccentrically mounted cam element 20. Supporting arm 6 carriesith'e test arm orguide lever 7 having point and knife-edge. bearings 8, 8, respectively; (see Fig.3). Guide lever 7 is' provided with a horizontal sliding surface 9 which rests on a cooperating anti-friction element 10 such,as;a-ball or roller, the latter being disposed in a suitable recess or otherwise retained in position by con-1 The indentation forming element "or.

indentor 11,. which maybe provided with a diamond thus produced lacked the desired degree of accuraey. s

point,nfor instance, is mounted'on guide lever 7. Weights 12 are zsuspended, for instance, by means of a 'Wire or thread 12a from the free'end portion of a bimetallic strip 24. One end of the strip 24 is fixed in a supporting arm 30'which is preferably of adjustable length, conventional. means (not shown)- being'provided for this pur-. pose. Supporting arm 30,-like:the arm;6 previously described, is rotatablein a horizontal. plane on a sleeve 3a.-

The sleeve Sa is vertically adjustable on upright 3 by point,'in itsdownward movement, engages the test specimenand cuts into it, the bending stress isrelieved, caus ing. a; straightening of the guide lever. As a result, the

diamond .point is subjected to a component of lateral or horizontal motion, wherebythe. indentation produced is horizontally enlarged and the measurement falsified. This error is particularly noticeable in micro-hardness testing, when small loads are used. 1.-

An object of the invention is to I of error and provide a simple, yethighly accurate and reof thegwire when heated bythe electric current causes the-burden of the weights to be applied to the'indentor and test specimen.

According to a preferred form of construction, the guide,v lever and weight or load. applying element are separately supported. for rotationabout vertical axes and may 'be swung outwardly, away from the base plate on which they are mounted, so that large specimens, for instance machine parts, may readily be tested.

With these and other objects in view, as will become more apparent from the following specification, several eliminate this source means of a-rack and pinion meghanism 3b so that it raised or lowered at wilL. The weights 12 rest on theguide' lever 7 directly above the indentor 11. 1 f '1 In order .tobe able to test large pieces of machinery which can'notbe' accommodated on table 5, arm 6 is constructed of sufficient length and mounted rotatably on upright, 2 so that it may be swung out horizontally 'beyond the :basexplatein order to place indentor 11 in the desired positioni above the machine .part to be tested.

Supporting arm 30, whic'hcarries the bimetallic strip 24, may likewise be swung about and in order to position the weights directly aboveindentor 11-,1'arm 30 being of adjustableilength inwardly or outwardly with respect to upright i 3. -It will be-clear that insteadof making arm 6 and the weight supporting arm 30 rotatable on uprights 2, 3, the

latter-may be rotatably mounted on thebase 1. To provide-for adjustment of the lengths of the arms 6 and 30;.

a telescopic form of constructionjmay be employed.

.An electrical resistance element 24a :is disposed on the. 1

bimetallicfstrip 24. The resistance element 24a is connected in an,energiz ing circuit including a source (if ele'c-' trical energy indicated as a battery 22 and: a controlswitch 23.

The operation of theijtesting, device is as follows: Specimen 4 is placed on'the table '5. The arm 6'is'then lowered by means ,of rack and pinion mechanism 2a until the indenter 11 engages the Upper surface of the speci: men 4. and the horizontal surface 9 is clear of the ball or roller 10. Rack and pinion mechanism. 3b isthenmanipulated'so that with the switch23'open, the entire burden of the weights 12 is carried by the bimetallic strip 24 so that the load on the indenter 11 and specimen 4 is substantially zero, a slight clearance between the point of the indenter and the specimen being permissible,

24a heats the bimetallic strip 24 causing its free end portion to move downwardly. This, in turn, removes the support for the weights 12 so that their entire burden is transferred tothe indenter 11 and the specimen 4. Flexure of the upright 3 as the burden of the weights 12 is relieved produces no flexure of the other upright 2 and hence no tendency to cause horizontal movement of the indenter 11 as it penetrates into the specimen 4. The center of gravity of the weights 12 being directly above the point of the indenter 11, there is no force present which might tend to produce undesirable horizontal movement of the indenter 11 as it penetrates into the specimen 4. The pivots 8, 8' and the point of the indenter 11 lie in a common substantially horizontal plane so that the short path of downward movement of the indenter is further constrained by the guide le'ver 7 to be substantially precisely vertical, thus avoiding any error-producing horizontal enlargements of the indentation formed in the specimen 4 by the point of the indenter 11.

In the modified form of the invention shown in Fig. 2, the bimetallic strip 24 and heating resistor 24a have been replaced by a vertical wire 21. The constructionis otherwise the same as that shown in Fig. 1. When the switch 24 is closed, the wire 21 becomes heated and expands longitudinally so that the burden of the weights 12 is gradually transferred from the arm 30 and wire 21 to the indenter 11 and specimen 4. The method of operation is similar in all respects to that described above in connection with Fig. 1.

Various changes and modifications may be made with out departing from the spirit and scope of the presentinvention and it is intended that such obvious changes and modifications be embraced by the annexed claims.

We claim:

1. A hardness testingdevice producing indentations for microscopic evaluation, "comprising: a first supporting means, a guide lever pivoted to the latter, indenter means carried by .the free end portion of said guide lever, at least one Weight supported on said free end portion, second independent supporting means, a resistance wire connected to said second supporting means and tothe free end portion of said guide lever, to support the latter in suspended relationship with respect to said second supporting means, means for impressing an electric current f on said resistance wire to heat the same and produce an elongation thereof, to lower the end portion of said guide lever whereby said indenter, when it is lowered onto a test specimen and is unsupported by said resistance Wire, applies the burden of said weights to the test specimen and produces a test indentation therein solely by the burden of said Weight and free from any lateral deformations which would otherwise be caused by the production-of a bending moment in said guide lever or said first supf porting means.

' 2. A hardness testing device comprising: afirst'supporting means, a guide lever pivoted to the latter, indenter means carried by the free end portion of said guide lever, at least one weight supported on said free end portion, second supporting means, said second supporting means being independent of said first supporting means whereby a change in the loading of said second supporting means produces no stresses in said first supporting means or saidguide lever, a bi-metallic' element carried by the latter, connecting means secured to said bi metallic element and the free end portion of said guide lever to support the same in suspended relationship with respect to said bi-metallic element, controllable heating means associated with said bi-metallic element to heat the latter and cause the same to'ben d. to lower the'suspended end portion of said guide lever, whereby said indenter, when it is lowered onto a test specimen and is unsupported by said connecting means, applies the burden of said weights to the test specimen and produces an indentation therein, said indentation being formed solely by the burden of said weights, the independence of said second supporting means from said first supporting means preventing the formation of any lateral deformations in said indentation.

3. A device for testing the hardness of a specimen by producing indentations for microscopic evaluation, comprising supporting means, an electrically actuated element carred by said supporting means, weighted indentation forming means carried by said electrically actuated element and normally maintained above said specimen, and an electrical control circuit connected to said electrically actuated element for actuating the same, actuation of said electrically actuated element serving to lower said' weighted indentation forming means on to said specimen. I

4. A device for testing the hardness of a specimen by producing an'indentation therein for" subsequent microscopic evaluation, comprising supporting means, an elec- -i trio-ally actuable element supported by said supporting 1 tact with said specimen, thereby transferring the burden of said-Weight means on said guide lever to indentation forming means'and said specimen.

5. A device according to claim 4, in Which-said electricallyactuable element comprises a bimetallic strip and electrical heating means disposed in thermally conductive relationship with respect to said strip, said control circuit being connected to said heating means to cause warping of said strip.

Y 6. A device according to" claim 6, in which said electrically actuable element-comprises an electrical resist:

resistance wire.

ance wire which carries the burden of said weight means, said-wire being elongated upon passage of current there'- through, said control circuit being connected to said References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Broschke: A Hardness Tester for Small Load, Microtecnic, vol. V1,.No. 1, January-February 1952 (pp. 15 to -21).

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