US3524343A

US3524343A - Hardness testers

Info

Publication number: US3524343A
Application number: US708212A
Authority: US
Inventors: Arthur W Sear
Original assignee: ARTHUR W SEAR
Current assignee: ARTHUR W SEAR
Priority date: 1968-02-26
Filing date: 1968-02-26
Publication date: 1970-08-18
Anticipated expiration: 1987-08-18

Description

Aug. A. W. SEAR HARDNESS TESTERS I Filed Feb. 26, 1968 2 Sheets-Sheet l Inventor fi my;

1970 v A. w. SEAR 3,524,343

HARDNESS TESTERS Filed 26. 1968 2 Sheets-Sheet z lnventbr United States Patent US. Cl. 73-83 4 Claims ABSTRACT OF THE DISCLOSURE An apparatus for measuring the hardness of solid materials in which a relative rotation is established between the test element and the indentor so as to overcome static friction and provide greater accuracy.

BRIEF SUMMARY OF THE INVENTION An important use for the invention will be to measure the hardness of metal alloys used in casting bullets. Many users of firearms load the ammunition they use in hunting or target shooting. The cost of reloading can be minimized by casting bullets from scrap lead obtained from various sources. The composition and hardness of the resulting alloys usually vary over a wide range. Although a wide range of bullet hardness can be tolerated without malfunctions, uniform performance and consistent accuracy is enhanced if the hardness of bullets used in reloading is kept close to a predetermined value. Both the behavior of the bullet as it goes through the barrel and the firmness with which the bullet is crimped into the cartridge into the cartridge case during the loading process are affected by bullet hardness. These factors, in turn, influence bullet velocity and point of impact and therefore bullet hardness is an important factor in producing ammunition having good effective accuracy.

By checking the hardness of sample slugs cast from the molten alloy, the hardness of the alloy can be corrected by adding a portion of soft lead, such as sheet lead, if the mixture is too hard, or adding a portion of solder, or other hard alloy, if the mixture is too soft. My invention provides a hardness tester in which the test sample is rotated with respect to the indenter so as to overcome static friction and provide greater accuracy. Also my invention lends itself to light, compact, and simple construction in which hardness tests can be made quickly and accurately. Since hardness tests can be made quickly with the device herein described, several adjustments can be quickly made and the hardness of the alloy can thus be made to conform to a predetermined standard.

BRIEF DESCRIPTION OF THE DRAWINGS The operation of a portable embodiment of my invention for measuring hardness can best be described by referring to the accompanying drawings which show the invention in approximately full size. FIG. 1 is a longitudinal section through a first embodiment of the tester, FIG. 2 is a top view of FIG. 1, and FIG. 3 shows the left end of FIG. 1. FIG. 4 is a cross section of the side view of a second embodiment of the hardness tester. FIG. 5 is a left end view of FIG. 4. FIG. 6 is a top view of the load yoke and FIG. 7 shows the top view of the transfer beam. FIG. 8 is an enlarged section of the spindle that shows the spring clip used to hold the indenter in place.

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DESCRIPTION OF INVENTION In FIG. 1 a bullet, or test specimen 1 is shown in position on an anvil 2 with an indenter 3 having a smooth conical surface with a rounded point piercing the specimen under the force of a spring 4. The frame of the tester consists of a shell 5 and the members '6, 7, and 8, which are rigidly attached to the shell. In alternate construction these members may be formed as integral parts of the frame. Frame member 6 supports spring 4 and guides the rear end of indenter 3 which passes through it. Frame member 7 guides a sleeve 9 and indenter 3, with these parts sliding freely in longitudinal relative motion. Frame member 8 is threaded to receive a screw 10 which in turn supports anvil 2.

With screw 10 retracted a test specimen can be placed through the open side of shell 5 onto the recessed face of anvil 2 where it is centrally located. Relatively fine threads are used in engaging screw 10 and frame member 8 and a close fit is maintained so that anvil 2 is accurately centered as it rotates to slowly advance test specimen 1 against indenter 3.

I found experimentally that more consistent measurements are obtained if there is relative rotation between the specimen and indenter as the force is increased. This discovery is an important feature of my invention.

In the operation of the prior art hardness testers the indenter is forced against the specimen without relative rotation and as the force increases, the metal under the unyielding indenter is deformed, allowing the indenter to penetrate the surface of the specimen. Penetration of the specimen by the relatively smooth and polished indenter is resisted by friction between the engaging surfaces in addition to the work done in deforming the material. Because static friction is greater than dynamic friction, penetration does not occur in a smooth flow but by increments of motion as the indenter sinks into the specimen. Thus the measured depth of penetration can vary depending on whether an increment of motion has just occurred or is impending.

In my invention the continuous relative rotation between the indenter and specimen, as the force between them is increasing, serves to break down static friction. With static friction eliminated at the interface between specimen and indenter the depth of penetration is determined by the shape of the indenter, the magnitude of the force acting, and yielding of the test material through its plastic deformation which is a function of the hardness of the specimen, thus allowing hardness measurements to be made with greater precision.

In the present embodiment the specimen rotates and the indenter is prevented from turning. Alternate construction would permit the specimen to be held stationary and the indenter caused to rotate as the force is increased.

The body of indenter 3 is threaded and screwed into a bracket 11 and held in place with a locknut 12. Bracket 11 is rigidly attached to a tray 13. Tray 13 also carries a pivoted pointer 14 as a part of the tray assembly. Indenter 3 extends through and is guided by frame member 6. Thus tray assembly 13 is constrained vertically but can move longitudinally between the flanges of shell 5 as better seen in FIG. 3. The tray assembly is biased in a forward position by spring 4 but is limited in forward motion by sleeve 9 and frame member 7. A spring 15 biases sleeve 9 in a forward position and because a final turn 16 of this spring is hooked over a downward bent tab 17 of pointer 14, spring 15 also keeps tab 17 in contact with a flange 18 of sleeve 9 and the pointer biased in a counterclockwise position, as viewed in FIG. 2.

The components of the tester are proportioned so that when there is no pressure exerted on a specimen, indenter 3 is approximately flush with a nose 19 of sleeve 9, flange 18 of the sleeve 9 is in contact with frame member 7, pointer 14 is biased to the top of scale 20, and spring 4 is under a tight compressive force.

Important features of my invention as applied to a portable hardness tester lie in the manner of applying the force between the indenter and test specimen and the method used for determining the depth of penetration. In the described portable hardness tester the load is applied by advancing the test specimen against an indenter that is attached to a spring loaded sliding tray. As the tray slides relative to the frame the spring is compressed until a predetermined force between the specimen and indenter is indicated by the position of tray with respect to the frame. The depth of penetration of indenter 3 is indicated by a pointer mounted on the moving tray because indenter 3 determines the position of tray 13 and the position of pointer 14 is determined by the undistorted surface of test specimen 1. Thus, penetration is referred to the surface presented to the indenter rather than measured with respect to the anvil supporting the specimen as is done with the prior art hardness tester.

Two benefits result from this innovation. First, a relatively simple and low cost indicating mechanism can be employed. And second, neither distortion of lightweight frame of a portable device, or the yielding at the surface of the specimen in contact with the anvil can affect the accuracy of measurements.

With a specimen in place of anvil 2, screw is turned to advance the specimen against the pentetrator 3 and to increase the pressure on spring 4. As screw 10 is advanced tray assembly 13 is forced to the left until a gauge mark 21 on tray 13 precisely coincides with a gauge mark 22 on the shell of frame 5. At this point, the force on spring 4 reaches a magnitude that is equal to the force used in calibrating the device. Calibration is accomplished by selecting a suitable spring force, which in the described tester is approximately forty pounds, and determining the penetration of the indenter in standard alloys when the selected force is applied. The position of indenter 3 in tray number 11 and the position of pointer tab 17 are then adjusted to produce the proper pointer position when the standard alloys are tested.

As spring 4 is compressed its full force, except for the insignificant force of spring is exerted by the penetrater on the surface of the specimen causing the penetrater to enter the specimen to a depth determined by the hardness of the specimen. Because the nose 19 of sleeve 9' has a relatively large surface compared to the penetrater, it does not penetrate the specimen and because spring 15 exerts a light force, the sleeve 9 and pointer tab 17 are pushed farther to the left in the drawing than is tray assembly 13. As a result, pointer 14' when viewed in FIG. 2, rotates in a clockwise direction proportional to the depth the penetrater sinks into the specimen.

The shape of the penetrater point, the multiplying factor of pointed length and tab position, the stiffness of the main spring, and many other design details can be chosen to provide a tester to cover various ranges of material hardness. Furthermore the configuration of the tester and the design of the components can be modified without changing the spirit or scope of my invention.

The hardness tester as described was made to cover the hardness of lead alloys ranging from pure lead to Linotype metal, and the scale is so marked. The lowest scale mark is for a hardness equal to that of pure lead.

The other marks indicate a hardness equivalent to that of an alloy containing one part tin to 20 parts lead, one part tin to 10 parts lead, and Linotype metal respectively.

The embodiment of the invention in a tester suitable for mounting on a bench is shown in FIG. 4 to FIG. 7, inclusive. This instrument is intended for measuring the hardness of a wide range of material from the relative soft alloys of aluminum to the hard alloys of steel, and is of sturdy construction capable of withstanding the large forces utilized. This embodiment includes a sensitive dial indicator to measure the small pentration of the indenter in the hard alloys.

FIGS. 4 and 5 show a test specimen 1 supported on an anvil 2 in contact withan indenter 3. The shank 4 of indenter 3 fits into a concentric hole in a spindle 5 and is prevented from falling out by friction due to pressure of a spring clip 6, better seen in FIG. 8.

Hardness testers are usually provided with interchangeable indenters because indenters having different radii of curvature are needed to measure the hardness of materials ranging from the hardness of soft alloys to that of hardened steel. In prior art, changeable indenters have been held in place with a thumscrew bearing against a flat side of the indenter shank. The force applied to the indenter is transmitted through a flange at the base of the shank so that the indenters need only to be retained against the force of gravity. The use of a spring clip to provide the friction for retaining the indenter allows easy interchange in indenters. This is particularly useful in my inventon because rotation of the spindle may cause the thumbscrew to be oriented at an awkward position.

Spindle 5 turns freely and can slide vertically in bearings where it passes through a frame 8 and a frame member 9. The downward motion of spindle 5 is limited as a spur gear 10 that is fixed to spindle 5 makes contact with a boss on frame 8. A race 11 of a thrust ball bearing 12 bears against a shoulder of spindle 5. A race 14 of thrust ball bearing 12 has V grooves on either side of a central hole that is larger in diameter than spindle 5 at this point. The V grooves of race 14 of the thrust ball bearing mate with corresponding knife-edges of a load-yoke 15 also shown in FIG. 6. The left end of load yoke 15 in FIG. 4 is attached to frame 8 by a pair of swinging links 16. The right end, in FIG. 4, of load-yoke 15 is attached to a load transfer lever 17 by a pair of swinging links 18. Load-yoke 15 is biased downwardly by a spring 19 that bears against frame number 9. The bias force of spring 19 serves to maintain a firm contact between the load-yoke 15, the components of thrust ball bearing 12, and to bias the spindle 5 in a downward position. The lower holes in links 18 are slotted to permit load transfer lever 17 to be raised without removing the downward bias of load-yoke 15.

The upper end of spindle 5 terminates in a ball-point that engages a mating ball-socket 20 in a transfer beam 21 also shown in FIG. 7. The position of transfer beam 21 in FIG. 4 is established by its contacts with spindle 5 and a bracket 23. Lateral stability of transfer beam 21 is maintained by the contact of its long knife-edge 22 with the flat undersurface of a bracket 23 that is attached to frame number 9. The left end of transfer beam 21, in FIG. 4, presents a flat surface to a spring biased plunger 24 of a dial indicator 25. A bias spring 26 overpowers the bias of plunger 24 of a dial indicator 25. A bias spring 26 overpowers the bias of plunger 24 and maintains a firm contact at ball-socket 20 and knife-edge 22 so that dial indicator 25 correctly shows the precise elevation of spindle 5 with respect to frame member 9 of frame 8. Spur gear 10 meshes with a spur gear 27 that is afiixed to a bevel gear 28 so that the combined gears revolve about a shaft 29. A mating bevel gear 30 is mounted on a shaft 31 that is driven through a miter gear pair 32 which in turn is driven from a gear train 33 within a gear box 34. Gear box 34 also has an output shaft 35 that carries a face plate 36. A pin 37 located off-center in face plate 36 carries a connecting link 38 as the face plate turns through a complete revolution. The lower end of connecting link 38 has a slotted hole 39 that contains a pin 40 that is fixed in load transfer lever 17.

When an electric motor 41 through gear train 33 turns face plate 36, the load transfer lever 17 is lowered and the load of an adjustable weight 42 is transferred from link 38 to links 18 and to load-yoke 15. The load is thus applied through thrust ball bearing 12 to spindle 5, and so to indenter 3. As the face plate continues through its turn link 38 picks up the load transfer lever 17 and removes the force of weights 42 from indenter 3. As connecting link 38 reaches the top of its motion a projection 43 operates a switch 44 to open the electric circuit to motor 41 and stops it at this position. Switch 44 is a normally closed switch which is connected in parallel to a starting switch 45 which is normally open.

The home positions for link 38 is at the top of its travel so that switch 44 is open and the motor 41 is stopped. To start the cycle of operation, switch 45 is operated for a moment. This starts motor 41 and turns the face plate 36 enough to allow switch 44 to maintain the circuit closed until face plate returns to home position to open switch 44. As motor 41 drives the gear train, miter gears 32 and gears 30, 28, 27, and 10 cause the spindle and indenter 3 to slowly rotate including the period which pressure is applied between indenter 3 and test specimen 1. The relative rotation between indenter and test specimen breaks down the static friction at the interface between the two surfaces with the resulting benefits described in the description of the portable embodiment of this invention.

Anvil 2, which carries and supports test specimen 1, is mounted on an elevator screw 46 which is kept from turning by a keyway 47 and a key 48. A handwheel 49' has an internally threaded hub that engages threads of elevator screw 14 so that rotation of handwheel 49 serves to position test specimen 1 vertically for correct contact with indenter 3.

A know 50 is attached to the scale of dial indicator 25 is used to rotate a scale 51 through a narrow range to permit precise alignment of a pointer 52 with a fiducial mark 53 before the main force is applied during a hardness text.

The procedure for performing a hardness test is outlined below. With elevator screw 46 lowered, a test specimen 1 is placed on anvil 2. A suitable indenter 3 is plugged into the end of a spindle 5 and hand wheel 49 is turned to bring test specimen 1 in contact with indenter 3. The specimen is then raised further to position pointer 52 of dial indicator 25 at the top of the scale. This motion raises spindle 5 so that the hub of gear is no longer in contact with case 8. Raising spindle 5 causes thrust ball bearing 12 to left load-yoke and increase the pressure of spring 19. Raising spindle 5 also raises transfer beam 21 and elongates spring 26. Precise alignment of pointer 52 with fiducial mark 53 is accomplished by slight adjustment of knob 50. When the correct fertical position of test specimen 1 is established the combined bias force of spring 19 and spring 26 together with the weight of the components, serve to bring a firm contact between anvil, specimen, and indenter which constitutes the minor load of the test. Starting switch 45 is then pressed and held momentarily to permit motor 41 to turn face place 36 and move projection 43 of link 38 away from switch 44. This action maintains the circuit throughout the cycle and stops the motor when face plate 36 returns to its home position. As face plate 36 turns, load transfer lever 17 is lowered by link 38 until link 18 supports lever 17 and the major load is applied through load-yoke 15, thrust ball bearing 12, to spindle 5, to force indenter 3 into the surface of specimen 1. During the loading process the gear train is rotating indenter 3 to eliminate the effect of static friction. Links 18 may be constructed of a semi-resilient material, such as nylon, to reduce shock as the load is transferred to the indenter. When the major load is lifted from the indenter the minor load remains to hold the indenter firmly at the point of maximum penetration. The magnitude of penetration is indicated by the dial indicator scale to provide a hardness number for the material tested.

The shape of the indenter point, the magnitude of the major load, and the markings of the indicator scale are proportioned so that the hardness numbers obtained in tests correspond closely to established number for the various materials.

From the foregoing description I believe it is evident that I have invented a device for measuring the hardness of materials and that the device is simple to manufacture and convenient to use. Many obvious modifications of the disclosed devices will occur to those skilled in the art and I do not desire to be limited by the specific design utilized in the described embodiments.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A hardness testing device comprising: an indenter having a relatively smooth and non-cutting end, a sleeve surrounding acid indentor, first bias means to resist regression of said indenter, movable means for supporting a test specimen, means for advancing said movable means and said test specimen in a turning motion to eliminate static friction between said indenter and said test specimen, means for gauging compression of said first bias means, second bias means operable to maintain said sleeve in contact with the advancing surface of said test specimen, a linkage responsive to relative longitudinal motion of said indenter and sleeve as said indenter penetrates into surface of said test specimen, and indicating means connected to said linkage to indicate depth of penetration and thus the hardness of said test specimen.

2. A hardness testing device comprising: an indenter and spindle assembly, movable means for supporting a test specimen in contact with said indenter, means for rotating said spindle and said indenter to eliminate static friction between said indenter and said test specimen, thrust bearing means for applying longitudinal force to said indenter and spindle assembly, yoke means for applying longitudinal force to said indenter and spindle assem- -bly, yoke means for applying longitudinal force to said thrust bearing, first bias means for applying a minor load to said yoke, linkage means for applying a major load to said yoke and removing the major load from said yoke, second biased linkage means for sensing longitudinal motion of said spindle, indicator means for displaying said longitudinal motion and thus the penetration of said indenter due to said major load.

3. A hardness testing device comprising: an indenter and spindle assembly, movable means for supporting a test specimen in contact with said indenter, thrust bearing means for applying longitudinal force to said indenter and spindle assembly, yoke means of applying said longitudinal force to said thrust bearing, first bias means for applying a minor load to said yoke, cyclic means for applying and removing a major load to said yoke, gear train and motor means for producing cyclic motion of said cyclic means, second gear means for producing relative rotation between said indenter and said test specimen to eliminate static friction between said indenter and said test specimen, a first motor control switch for initiating the cyclic motion, a second motor control switch to terminate the cyclic motion, second biased linkage means for sensing longitudinal displacement of said indenter and spindle assembly, indicator means for displaying longitudinal displacement and penetration of said indenter into the test specimen due to application of said major load thus testing the hardness of said test specimen.

4. A hardness testing device comprising: an indenter having a relatively smooth non-cutting end, a sleeve slidably supporting said indenter, movable means supporting a test specimen so that said test specimen may be moved into engagement with said indenter with a predetermined force, movable means to provide relative rotation between said test specimen and said indenter to eliminate'static 2,333,747 9/1943 Sklar 73-83 friction and allow the depth of penetration of said indenter to be determined by the hardness of the material, and FOREIGN PATENTS movable means connected to said indenter to indicate the 1,004,186 3/1952 Francedepth of penetration of said indenter into said test specimen at the predetermined force 5 RICHARD C. QUEISSER, Prlmary Examiner C. E. SNEE III, Assistant Examiner References Cited UNITED STATES PATENTS -R.

7381 710,116 9/1902 Osterman et al 27976 X 10 1,661,718 3/1928 Davis 73-81