Tech Showcase: Hardness Testing Options

June 8, 2009
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The breadth of hardness tester offerings means there is nothing hard about finding the best solution.

Hardness tests are commonly used to check material uniformity or processing treatment. Most hardness tests yield results based on a material’s ability to resist indentation while under test. A material’s ability to resist scratching also is considered a hardness test, as is the measurement of the amount of energy absorbed by a material when struck by a falling object.

Macroscale hardness testing determines the hardness of a material as a whole. The Brinell, Rockwell, scleroscope and Vickers hardness tests are examples of such measurement. On the other hand, microscale hardness testing functions on a very small scale and can be thought of as determining particle hardness. The Knoop hardness test is an example.

Specimen thickness must be considered when selecting a hardness test method. The tester’s anvil, on which the specimen rests, must not affect the indentation made by the indenter. If there is an imprint on the underside of a specimen after a test has been performed, the specimen was too thin for the test method.

The Brinell test is applicable for large parts such as castings and forgings of low to medium hardness. A Brinell test applies a known load for a specified length of time to the specimen under test. The diameter of the mark left by the indenter-a hardened-steel or carbide ball-is measured and usually converted to a Brinell hardness number.

Rockwell and Vickers tests are used for small parts, as well as parts of low, medium or high hardness. The Rockwell test makes two indentations; the indenter applies a minor (initial) and major (final) load to the specimen. The different depths affected by each load are then compared. The Vickers test is very similar to the Brinell test, except that it uses a pyramid-shaped diamond indenter.

Scleroscopes are portable hardness testers used for routine inspection and shop tests. The test is based on the height of rebound a steel hammer experiences after colliding with the specimen from a fixed height. The hammer falls through a graduated glass tube, and the rebound is measured by eye or an indicator.

A Knoop test applies a known load for a specified length of time to the specimen under test. The indenter is a diamond having unequal longitudinal and transverse included angles. In addition to determining particle hardness, the Knoop test can be applied to very small as well as very thin specimens.

Hardness testers are made as both handheld and motorized devices. Motorized testers are advantageous for high-volume testing and can help eliminate operator fatigue when heavy parts require testing.

What follows are hardness testing products available today.

GE Sensing & Inspection Technologies (www.gesensing.com) introduce the MIC 20, a two-in-one tester combining the ultrasonic contact impedance (UCI) and rebound test methods. The UCI method tests small and complex shaped parts composed of fine-grained metals, while the rebound method is preferred for larger, coarse-grained forgings and castings. The tester has automatic scale conversion to HV, HB, HRC, HRB, HS, HL and N/mm2. The tester can store approximately 5,000 measurements, and calibration data are saved and can be recalled. A large color TFT display shows all necessary information during measurement, such as average, single value and statistical data.

Zwick/Roell Testing Systems (www.zwick.com) introduces the ZHU/zwicki-Line for classical and instrumented hardness testing. This fully automatic universal hardness testing system covers the Vickers, Knoop, Brinell, Rockwell, ball indentation and instrumented indentation methods.

The tester’s instrumented indentation testing in the macro range covers a range of applications and has hardware and electronics made to the requirements of hardness testing. In addition to instrumented indentation tests to determine hardness and other material parameters, the tester can perform all the classical hardness testing methods used for metals.

Whichever method is used, the testing system records the load-indentation depth curve to provide additional material assessment. The instrumented indentation test includes elastic and plastic deformations in order to obtain the elastic and plastic material characteristic values.

The core of the testing system is a hardness measuring head, into which the measuring systems for test load and indentation depth, plus an indentor with hold-down device, are integrated. For optically based hardness testing methods to Vickers, Knoop and Brinell, an add-on unit with measuring microscope is available. Indentation setting, microscope positioning and optical measurement of the indentation are all performed automatically.

Nanovea (www.nanovea.com) introduces the Micro/Macro module, which handles loads from the millinewton range to 200 newtons, allowing micrometer-scale indentation testing, scratch testing and wear testing of thicker coatings and substrate materials.

The higher loads are well suited for testing hard coatings, such as those used in the tooling industry. However, the more sensitive loads of the micro range are ideal for the characterization of industrial coatings, ranging from plasma processed layers used in semiconductor and optical technology, to decorative and protective coatings used for automobile parts and consumer goods. The module uses independent force and depth sensors to obtain depth vs. load curves used in instrumented indentation. True load feedback control ensures stable scratch and wear testing.

The module uses a noncontact white light sensor directly connected to the diamond mounting, which enables direct measurements of the depth of the diamond. This technique allows quick tests and eliminates depth errors caused by surface roughness or sinking of the reference on soft materials when a physical reference is used to determine the height of the surface.

The company’s micro technology also provides true depth measurements during scratch testing or wear testing. The light sensor performs as a full 3-D noncontact profiling tool that gives 3-D images of scratch tests, indentation tests or wear tests and can be used for other types of profiling work, such as measuring surface roughness or height of steps.

Leco (www.leco.com) introduces the AMH43 hardness tester. Its patented visual method automatically traces a sample edge to easily position indents and patterns directly onto the overview image of a part.

The tester has an optional advanced analysis module with complete impression coverage of a sample, as well as pattern support for welding studies. An available color hardness/contour map displays sample hardness and location with a color representation of hardness variances. The tester includes case-depth analysis, surface analysis, weld profiles, decarburization and coating hardness. The tester supports both microindentation and macro/Vickers hardness testing in fully automatic and semi-automatic configurations.

The L.S. Starrett Co. (www.starrett.com) introduces the No. 3817 automated digital hardness testing system. The system measures Rockwell, Rockwell superficial, Vickers and Brinell scales and meets or exceeds major industry standard requirements including those for ASTM, ISO and NIST.

Hardness numbers are displayed from 1 to 1/100th point on an illuminated digital control. To comply with ASTM E-18 tolerances, the system provides preset dwell times and automatic cylindrical correction. The system has built-in electronic conversion charts for cross-referencing hardness scales and approximating tensile strength, eliminating the need for mechanical or electronic adjustments.

The tester includes closed-loop NTEP load cell technology that removes the need to use the conventional weights method. The system includes a rigid, modular base assembly, RS232 output and a detachable clamping device for oversized or irregular parts. A self-contained head assembly is adaptable for special applications. The tester also includes upper and lower limit alarms and a fitted tray for indentors and anvils.

Qualitest (www.worldoftest.com) introduces the HTD 4000 case depth hardness tester, which allows for case depths of up to 2.8 millimeters to be measured by a single indentation. The tester is capable of verifying case depths ranging from 0.4 millimeter to a maximum of 2.8 millimeters.

The system uses a principle based on the continuous measurement of the electrical resistance in relation to the working load applied. The stand enables the testing of large work pieces with overall dimensions up to 550 millimeters in height and 350 millimeters in depth.

Affri (www.affri.com) introduces the 3332 MRSA hardness tester. The tester conforms to the Rockwell standard ASTM E-18 and performs tests in three seconds. The tester can be used on unstable surfaces and is resistant to vibration. It has a large amount of area to support special fixtures for small and heavy parts.

Phase II (www.phase2plus.com) introduces the Model PHT-1800, a handheld, multi-function hardness tester able to convert to hardness scales such as HRC, HRB, HB, HS and HV. The tester offers the operator the opportunity to store a large amount of test data printable to a PC or mini-printer via a USB output. The tester comes with a five-year warranty and is supplied as a complete turnkey package with base instrument, impact device “D,” calibrated test block, software, USB output cable, carrying case and operation manual. The tester is appropriate for field, shop and laboratory use. A special support ring kit is available for convex and concave surfaces. Optional impact devices are available for testing rough surfaces, inside grooves and case hardened material.

Electro Arc Manufacturing Co. (www.electroarc.com) introduces the Ames portable hardness tester, a handheld instrument that requires no electricity and gives a true Rockwell reading conforming to ASTM E-18. The “slingshot” configuration holds the specimen between the penetrator and anvil, allowing positive contact for the minor and major loads to be applied. It comes in eight sizes, each guaranteed accurate to within ±1 point, but still portable enough to carry around the shop.

Each model comes with a set of anvils, penetrators and certified, serialized test blocks for confirming the tester’s continued accuracy. Most models read directly in all standard and superficial Rockwell scales. Charts are provided to convert the readings into other Rockwell scales or Brinell, Vickers or Knoop equivalents.

Wilson Instruments (www.wilsoninstruments.com) introduces the 400 Series Knoop/Vickers tester with optional Minuteman ELT automatic traversing and reading. The tester is an automatic microhardness solution for fully- or semi-automatic Knoop and Vickers testing of metals, ceramics and other nonmetallic materials.

The tester has a standard automatic turret and eight dial-selectable test forces ranging from 10 grams to 1,000 grams, with an optional 2,000-gram test force available.

Having optics with a magnification of 100X and 400X, measurements are automatically made through the high-resolution USB digital video camera system. The fully automatic stage provides 100-millimeter by 100-millimeter travel for multi-sample testing. The tester is ASTM and ISO compliant.

WESTport Corp. (www.westportcorp.com) introduces the Big Hardness Test Block Series. The Brinell Big Block provides a testing area of 6 inches by 2½ inches.

The manufacture of these hardness test blocks includes the stability of closed-loop load cell technology. Brinell test blocks are calibrated with tungsten carbide ball indenters. Each test block comes with NIST-traceable certification and is compliant to American and international standards. WESTport is accredited to ISO/IEC 17025, ISO 9001, ISO 6506 and ISO 6508.

Proceq (www.proceq.com) introduces the Equotip Piccolo 2 and Equotip Bambino 2. The testers come with an accessory kit that allows testing in confined spaces, on recessed surfaces or with local target precision. The flexibility to switch between two different probes ensures a high usability.

Because of the single loading/release mechanism, metal hardness testing can be done in less than two seconds. To simplify the testing of metal hardness, the testers come with an automatic compensation for impact directions.

The Equotip Bambino 2 is particularly suitable for on-site hardness checks. It has all the measurement capability of the Equotip Piccolo 2, but the Equotip Piccolo 2 additionally offers real-time monitoring and operator-defined hardness conversion curves, and comes with Piccolink software, which allows analysis of recorded data and the ability to edit and export data to reports.

Sun-Tec Corp. (www.sunteccorp.com) introduces measured Rockwell diamond indenters that meet ASTM E-18 standards. Indenter geometry is measured on a high-accuracy vision system then performance tested in the company’s laboratory. This ensures that geometry and performance meet or exceed specified tolerances. These directly measured indenters provide traceability and accuracy.

Buehler (www.buehler.com) introduces the OmniMet MHT microindentation hardness testing system. The tester provides automated hardness and case depth, fast operation, report and trace generation, and easy-to-use controls. The tracing function allows the operator to outline the exterior of a specimen, rapidly set multiple indent paths, document the placement of hardness profiles and create a visual record of the entire measurement.

Shimadzu Scientific Instruments Inc. (www.ssi.shimadzu.com) introduces the DUH-201/201S hardness tester. The tester is well suited for measuring the strength properties of material surfaces and microscopic materials such as thin films, plastics, metals and fibers.

The tester has a wide test force range-0.1 to 1,961 millinewtons full scale-and a low test force with measurement resolution of 0.196 micronewton, allowing measurement of material strength properties in micro regions and in the outermost surfaces of specimens. Specimen indentation depth can be measured in units of 0.0001 micrometer for depths up to 10 micrometers, and operators can perform precise evaluation of the elastic modulus using correction based on instrument rigidity and the shape of the indenter tip.

The tester supports a range of testing methods, such as depth setting, unload and load processes, cyclic and step load/unload tests and the Vickers hardness test. Numerous data processing functions enable the display of test force, displacement and strength for graphical comparison and analysis. Optional accessories include a length measurement kit and slender specimen holder.

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