The Riehle hardness tester is a portable unit that is designed for making Rockwell tests comparable to the bench-type machine. The instrument is quite universal in its application, being readily adjustable to a wide range of sizes and shapes that would be difficult, or impossible, to test on a bench-type tester.

Figure 1-28 shows the tester and its proper use. It may be noted that the adjusting screws and the penetration indicator are set back some distance from the penetrator end of the clamps. This makes it practicable to use the tester on either the outside or inside surface of tubing, as well as on many other applications where the clearance above the penetrator or below the anvil is limited. The indicator brackets are arranged so that it is possible to turn the indicators to any angle for greater convenience in a specific application, or to facilitate its use by a left-handed operator. Adjustment of the lower clamp is made by the small knurled knob below the clamp. The larger diameter knob, extending through the slot in the side of the clamp, is used for actual clamping.

Each Riehle tester is supplied with a diamond pene-trator and a 1/16-inch ball penetrator. The ball penetrator should not be used on materials harder than B-100 nor on a load heavier than 100 kilograms. This is to avoid the danger of flattening the ball.

The diamond penetrator, when used with a 150-kilogram load, may be used on materials from the hardest down to those giving a reading of C-20. When the expected hardness of a material is completely unknown to the operator, it is advisable to take a preliminary reading on the A scale as a guide in selecting the proper scale to be used.

The basic procedures for making a test with the Riehle tester are as follows:

3. Apply a major load of 60, 100, or 150 kilograms (depending on the scale), and then reduce the load back to the initial 10-kilogram load.

4. Read the hardness directly on the penetration indicator.

The hardness reading is based on the measurement of the additional increment of penetration produced by applying a major load after an initial penetration has been produced by the minor load. In reporting a hardness number, the number must be prefixed by the letter indicating the scale on which the reading was obtained.

the upper clamp. To remove a penetrator, there should beat least 2 or 3 inches of space between the upper and lower clamps so that one hand can be placed underneath the upper clamp to catch the penetrator when it is released. Two or three turns of the clamp screw will release the penetrator. The two contact pins that extend through the penetrator on either side of the point are retained in the tester when the penetrator is removed.

To replace a penetrator, it must be turned so that the flat side faces the clamp screw, and the locating pin on the penetrator is in line with the slot provided to take the pin. The contact pins should be guided into their respective holes through the penetrator. With the penetrator in place, it should then be clamped securely by turning the clamp screw. Before you make an actual test, one or two preliminary tests should be made to properly seat the penetrator.

The Barcol hardness tester, shown in figure 1-29, is a portable unit designed for testing aluminum alloys, copper, brass, and other relatively soft materials. Approximate range of the tester is 25 to 100 Brinell. The unit can be used in any position and in any space that will allow for the operators hand. The hardness is indicated on a dial conveniently divided in 100 graduations.

Figure 1-30 is a cutaway drawing of the tester, showing the internal parts and their general arrangement within the case.

The lower plunger guide and point are accurately ground so that attention need be given only to the proper position of the lower plunger guide within the frame to obtain accurate operation when a point is replaced. The frame, into which the lower plunger guide and spring-tensioned plunger are screwed, holds the point in the proper position. Adjustment of the plunger upper guide nut, which regulates the spring tension, is made when the instrument is calibrated at the factory.

The position of this nut should not be changed. Any adjustment made to the plunger upper guide nut will void the calibrated settings made at the factory.

The leg is set for testing surfaces that permit the lower plunger guide and the leg plate to be on the same plane. For testing rivets or other raised objects, a block may be placed under the leg plate to raise it to the same plane. For permanent testing of this type, the leg maybe removed and washers inserted, as shown in the drawing. The point should always be perpendicular to the surface being tested.

The design of the Barcol tester is such that operating experience is not necessary. It is only necessary to exert a light pressure against the instrument to drive the spring-loaded indenter into the material to be tested. The

Table 1-5.-Typical Barcol Readings for Aluminum Alloys