Rockwell Hardness Tester Operation, Technical InformationRockwell Test Method, Part 1The Rockwell test method is defined in ASTM E-18 and is the most commonly used harrdness test method since it is generally faster/easier to perform and less operator dependant for accuracy than other types of hardness testing. Rockwell hardness testers can be used on all metals except in conditions where the test metal structure or surface conditions (roughness, shallow surface hardnening, etc) would introduce too much variation, where the indentations would be too large for the application or where the sample size or shape prohibits its use. For

an

in-depth education on hardness testing see the ASM websiteThe test method measures the permanent depth of indentation produced by a force on an indenter. First, a preliminary test force (A), also called pre-load or minor load, is applied to a sample using a diamond indenter. This is the zero or reference position that breaks through the surface to reduce the effects of surface finish. Then, an additional test force or major load (B) is applied to reach the total required test force. This force is held for a predetermined amount of time to allow for elastic recovery of the metal (C). The additional test force is then released and the final position (D) is measured against the preliminary position and converted to a Rockwell hardness number.

Rockwell-Scale Hardness Tester Indentations

The Rockwell Hardness Test Method, Part 2As a general guide to selecting a Rockwell scale, the operator should select the scale that specifies the largest load and smallest indenter possible to do the job without exceeding defined operating conditions and accounting for conditions that influence the test result. These influencing conditions include test specimens which are below the minimum thickness for the depth of indentation (see chart); a test impression that falls too close to the edge of a specimen or another impression (indentations should be spaced greater than 3x indentation diameter and greater than 2-1/2x diameter from the edge of the specimen); or testing on cylindrical test specimens (see chart).

Hardness Testing Information GuideThis brief guide is intended to be a refresher for those a ready involved in hardness as well as a reference for first time users of hardness testers. Hardness is a characteristic of a material, not a fundamental physical property. It is defined as the resistance to indentation, and it is determined by measuring the permanent depth of the indentation. More simply put, when using a fixed force (load)* and a given indenter, the smaller the indentation, the harder the material. Indentation hardness value is obtained by measuring the depth or the area of the indentation using one of over 12 different test methods.

Rockwell, Brinell & Microhardness Testers Section 1: General Considerations for Hardness Testing.LARGE PARTS - Parts that either overhang the anvil or are not easily supported on the anvil should be clamped into place or properly supported. SMALL PARTS - The smaller the part the lighter the load needed. Be sure to meet minimum thickness requirements and properly space indentations away from inside and outside edges.

CYLINDRICAL TESTING (See at right) - A correction to a test result is needed when testing on small diameters cylinder shapes due to a difference between axial and radial material flow. (Refer to ASTM round correction charts for Rockwell scale testing). SPACE INDENTATIONS - Maintain a spacing equal to 2~1/2 times the indentation's diameter from an edge or another indentation.

THICKNESS REQUIREMENTS (See at right) - Maintain material thickness at least 10 times the indentation depth. (Refer to ASTM minimum thickness charts for Rockwell scale testing ). SPACE INDENTATIONS - Maintain a spacing equal to 2~1/2 times the indentation's diameter from an edge or another indentation. SCALE CONVERSIONS - Sometimes it is necessary to test in one scale and report in another scale. Conversions have been established that have some validity, but it is important to note that unless an actual correlation has been completed by testing in different scales, established conversions may or may not provide reliable information. (Refer to ASTM scale conversion charts for non-austenitic metals in the high hardness range and low hardness range.) Also refer to ASTM standard E140 for more scale conversion information. GAGE R&R STUDIES. - Gage Repeatability and Reproducibility Studies were developed to calculate the ability of operators and their instruments to test according within the tolerances of a given test piece. In hardness testing there are inherent variables that preclude using standard gage R&R procedures and formulas with actual test pieces. Material variation and the inability to retest the same area on depth measuring testers are two significant factors that affect GR&R results. In order to minimize these effects, it is best to do the study on highly consistent test blocks in order to minimize these built-in variations. Newage Testing Instruments hardness testers operate very well in these studies. Unfortunately, since these studies can only be effectively done on test blocks, their value does not necessarily translate into actual testing operations. there are a host of factors that can be introduced when testing under real conditions. Some Newage testers excel at testing in real-world conditions by reducing the effects of vibration, operator influence, part deflection due to dirt, scale, a specimen flexing under load.

Some important operating conditions are: the axis of test must be within 2 degrees of perpendicular; there should be no deflection of the test sample or tester during the load application (from conditions such as dirt under the test specimen or on the elevating screw; surface finish should be kept ; surface conditions such as decarburization from heat treatment should be removed.

Hardness TestingThe Test Methodology Guide, Part 2This brief guide is intended to be a refresher for those a ready involved in hardness testing as well as a reference for beginning users of hardness testers. Hardness is a characteristic of a material, not a fundamental physical property. It is defined simply as the resistance to indentation, and it is determined by measuring the permanent depth or width of a testindentation. When using a fixed force (load)* and a given indenter, the smaller the indentation, the harder the material. While the the concept is ectremely simple, the indentation hardness value is obtained by using one of over 12 different test methods.

Also see our recent article in ASM's Heat Treat Progress Magazine: Common Problems in Hardness Testing as well as the follow up: Common Problems in Microhardness Testing

Section 2: Test Method Principlesor navigate to: Part 3, or Part 1

ROCKWELL HARDNESSThe Rockwell test method measures a permanent depth of indentation produced by the preliminary and total test forces. First, a preliminary test force (pre-load or minor load) is applied. This is the zero or reference position. Then, an additional test force (or major load) is applied to reach the total required test force. This additional force is held for a predetermined amount of time and then released, but with the preliminary test force still applied. The indenter reaches the final position at the preliminary force and the distance traveled from the major load position is measured and converted to a value into one of the many scales for Rockwell hardness. A. Depth reached by indenter after application Preliminary test forces range from 3 (superficial Rockwell) to 10 kilograms (regular Rockwell) to 200 of preliminary test force (minor load). kilograms (macro Rockwell scale). Total test forces range from 500 grams (micro) to 15 through 150 B. Position of indenter under total test force. kilograms (superficial & regular) to 500 through 3000 kilograms (macro). To see a more complete description of the Test method for Rockwell Hardness.

C. Final position reached by indenter after elastic recovery of the material.

D. Position at which measurement is taken.

BRINELL HARDNESSWidely used on castings and forgings, the Brinell method applies a predetermined test force (F) to a carbide ball of fixed diameter (D) which is held for a predetermined time and then removed. The resulting indentation is measured across at at least two diameters - usually at right angles to each other and averaged (d). A chart is then used to convert the averaged diameter measurements to a Brinell hardness number. Test forces range from 500 to 3000 kilograms. For a more complete description of the Brinell test method and related Newage Brinell testers see Test method for Brinell Hardness.

Brinell Measurement Calculation D = ball diameter d = impression diameter F = load HB = Brinell Result

VICKERS HARDNESS (Micro and Macrohardness) and KnoopMostly used for small parts, thin sections, or case depth work, Vickers and Knoop methods are based on an optical measurement system. The new Computer Assisted Measurement System (C.A.M.S.), now available from Newage Testing Instruments, Inc., has improved productivity, accuracy and repeatability of these labor intensive methods. (See pages 14 and 15). To perform a test, a predetermined test force is applied with a pyramidal shaped diamond indenter. After a dwelt time, the force is removed. Then, in the Vickers method, the indentation length of vertical and horizontal axis is measured and averaged. In the Knoop method, only the tong axis is measured (Figure 5). A chart is used to convert the measurements to corresponding Vickers or Knoop hardness numbers, Test forces range from 1 to 2000 grams, Vickers does offer higher force capabilities - up to 150 kgs - but are not used frequently in North America. Link to a more complete description of the Test method for Vickers Hardness.

Vickers Test Opposing indenter faces are set at a 136 degree angle to each other

Knoop Test Long side faces are set at a 172 degree, 30 minute angle to each other. Short side faces are set at a 130 degree angle to each other

DUROMETER & IRHD HARDNESS

Widely used in the plastics and rubber industries, the Durometer method (sometimes erroneously referred to as the Shore method after the company that originally developed the test.) has evolved from a coarse handheld measurement to today's repeatable test method. Bench model testers can now read to a tenth of a point with good repeatability. The Durometer method applies a predetermined test force to a spherical or conical shaped indenter. The depth of indentation is translated into a hardness value by means of a dial gage or electronically. Test forces range from 822 grams (A scale) to 4550 grams (D scale). Non-standardized "micro" scales are also available from many manufacturers. These scales permit testing on thinner and more narrow specimens. The use of IRHD, or International Rubber Hardness Degrees, has increased considerably in North America since its origin in Europe. It provides a very repeatable result on rubber parts of all shapes and sizes. It is especially important in the determination of the hardness of rubber O-rings. The method employs a preliminary test force that is applied to the specimen through the indenter. The test is zeroed at this position, then the total test force is applied. The distance between the these two forces is then measured and converted to an IRHD hardness value. Preliminary test forces are 8.46 grams for micro scales and 295.74 grams for regular scales. Total test forces are 15.7g for micro and 597 for regular scales.Shore is a registered trademark of Instron Corporation

How to Read a Hardness Number Scale Name Example Rockwell 60 HRC ExplanationHardness Rockwell "C" scale with a "60" test value

Hardness value in Rockwell "15T" scale with a "80.5" test value using a "W" or Tungsten carbide ball indenter. (Rockwell test results in scales using a ball indenter must indicate either "W" for carbide or "S" for steel indenter on all results (Steel balls are no longer 80.5 HR15TW permitted as of June 2007Brinell 200 "200" test value using a 10 mm diameter carbide ball, a 300 kg load and HB10/3000/15 a 15 second dwell 500 HBS An old report of a "500" test value using a no-longer-valid steel (HBS) 1/30/20 ball of 1mm diameter with 30 kg load and 20 second dwell An informal report assuming the most common parameters - 10 mm HB 200 carbide ball, 3000 kg load and "200" test result value

Microhardness 200 HV 500/15"200" test value with Vickers 500 g load, 15 seconds duration 200 HK 500/15"200" test value with Knoop 500 g load, 15 seconds duration Durometer A/50/15 D/50/15 Durometer type A with "50" test value result and 15 second duration Durometer type D with "50" test value result and 15 second duration

Section 3: How to Select a Hardness TesterFundamental to reliable hardness testing are several factors. 1. Choose the correct test method based on the application. Plan to use the highest test force and largest indenter possible. Consider the effects of the shape and dimensions of your test sample. Refer to Section 1

2. Many questions may need to be answered in order to determine the scale and tester to be used:

Is there a hardness scale specified? What is the materials being tested and is it suitable for a a particular test? How large are the parts? Is the test point difficult to reach? What volume of testing is to be done? How accurate do the results need to be? What is the budget? What are the problems that have occurred in the past

3. Verify that the test results meet your needs for accuracy and repeatability. You may want to conduct a Gage R&R study to see how much error the operator and measurement system contribute. There are significant differences between levels of performance within each classification of tester. A difficult job on one tester could be very simple and fast on another. So, although often hardness testers within a test method and classification look alike, there are many features that can significantly affect productivity and accuracy. A good example of features affecting performance is demonstrated in bench Rockwell hardness testing systems. All can handle moderately long parts using larger anvils or jack rests, however the Versitron can usually test large parts more quickly and accurately, when compared to other bench testers which require external support stands or fixtures. The Indentron, on the other hand, is much easier to use on small, awkward parts. If you need assistance with your application, contact a Newage Testing Instruments sales representative. Also the reader can follow this link for "Choosing the Right Hardness Tester"

TEST SPECIFICATIONS

TEST Rockwell

TEST METHOD Regular Superficial Light Load Micro Macro

TEST FORCE INDENTER TYPES RANGE 60, 100, 150 kgs 15, 30, 45 kgs 3, 5, 7 kgs 500, 100 grams 500 to 3000 kgs 5 to 2000 grams 5 to 2000 grams 500, 3000 grams .01 to 200 grams 500 to 3000 kgs Conical Diamond & Small Ball Conical Diamond & Small Ball Truncated Cone Diamond Small Truncated Cone Diamond 5, 10 mm Ball 136 Pyramid Diamond 1300 x 1720 Diamond Truncated Cone Diamond Triangular Diamond 5mm, 10 mm Ball

ASTM TEST METHOD E 18 E 18 Informal Informal E 103 E 384 E 384 Informal Informal E 10

MEASURE METHOD Depth Depth Depth Depth Depth Area Area Depth Depth Area

MicroHardness

Vickers Knoop Rockwell Type Dynamic

Brinell

Optical

Depth Durometer Regular Micro IRHD Regular Micro

500 to 3000 kgs 822 (A), 4550 (D) grams 257 (A), 1135 (D) grams 597 grams 15.7 grams

5mm, 10 mm Ball 35 Cone (A) 30 Cone (D) 35 Cone (A) 30 Cone (D) 2.5 mm Ball .395 mm Ball

E 103 D 2240 Informal D 1415 D 1415

Depth Depth Depth Depth Depth