Tech Showcase: Which Hardness Test Works?
Used to check material uniformity or processing treatment, most hardness tests employed in quality control applications yield numerical values based on a material’s resistance to indentation under the conditions imposed by the particular test. Resistance to scratching and the measurement of the amount of energy absorbed by a material when struck by a falling object also are measures of hardness. Because they indicate characteristics more than properties of materials, hardness numbers have practical significance only when correlated with service experience or a particular material property.
On a macroscale, the hardness of a material as a whole is used for comparison with service experience or a general property. One way of determining a material’s hardness on a macroscale is through indentation testing, a measurement of a material’s resistance to permanent deformation. Applicable methods of indentation testing are the Brinell, Rockwell and Vickers hardness tests. Indentation testing is used for applications on a microscale as well, testing constituents or grains of metal to provide the most useful method for data correlation. Hardness tests that must be carried out on a microscale may be thought of as measurements of a particle’s hardness; the Knoop and microcharacter hardness tests can be used for this purpose. In general, there is no simple relationship between the results of the different indentation tests, although conversion tables for hard steels do exist.
Another type of testing at a macroscale is rebound hardness testing, or dynamic hardness testing, in which a scleroscope is used to measure hardness by tracking the height of rebound of a steel hammer after falling on a specimen from a fixed height.
The Brinell test is widely used on large parts such as castings and forgings of low to medium hardness. The Rockwell and Vickers tests are mainly used on small parts and those of low, medium or high hardness. The scleroscope, which leaves no depression on the test specimen, is used in quick, routine inspection and shop tests. Tests performed on a microscale, such as the Knoop and microcharacter, are used for measuring the hardness of very small parts, thin sections, thin cases and individual grains of particles.
When deciding on a hardness test, the thickness of the specimen tested must be considered. The thickness must be such that the backing material or anvil on which the specimen rests has no effect on the testing machine’s penetrator; an imprint on the specimen’s undersurface after a test is an indication that the specimen was too thin. When such an imprint occurs, a test using a lighter load or a larger indentor should be performed.
Some types of hardness testers are available in both manual and motorized models. Motorized models are well suited to production testing of simply shaped, small pieces that can be fed or placed into a test quickly. For heavier and more complicated pieces, a motorized tester can lessen operator fatigue.
What follows is an offering to quality professionals of today’s hardness testing equipment.
The AMH43 from Leco (www.leco.com) features a patented visual method for sample reconstruction, along with advanced image-recognition technology that allows for analyses not available with limited threshold-based methods. Features include an optional advanced analysis module with complete impression coverage of the analysis sample, an available color hardness/contour map and pattern support for welding studies. Designed for a number of applications, the AMH43 measures impressions of various surface conditions and supports both microindentation and macro/Vickers hardness testing.
Reply 700
Qualitest (www.WorldofTest.com) presents the Handy Esatest portable hardness tester for hardness measuring of samples with flat surface or hard-to-reach areas. This portable hardness tester was designed as a response to problems inherent to hardness testing, such as inaccessible testing points and thin or lightweight samples. With this unit there are no minimum thickness or weight requirements. It also can test metals of any hardness and leaves minimal indentation marks on samples. The unit’s system of impression reading requires neither optical reading of the impression nor measuring of penetration depth. It can perform testing in all positions with minimum difficulty and without special stability. This solution is useful for testing superficially treated specimens, allowing an evaluation of the depth of the superficial treatment and possible alteration of ground parts. In addition, readings can be provided on the display in Vickers, Rockwell C and other scales.
Wilson Instruments (www.wilsoninstruments.com) introduces the Minuteman ELT Series of semi and fully automatic systems for Knoop, Vickers and Rockwell hardness testing. Available in four different versions, the series is for use in microindentation and Rockwell scale testing. The entry-level ELT1, the intermediate ELT2 and the fully automatic ELT3 are options for the Tukon microindentation testers, while the ELT4 version is for Rockwell and MicroRockwell testers.
Electro Arc (www.electroarc.com) presents its family of Ames analog testers. Each tester is manufactured following the ASTM guidelines and guarantees a ±1 Rockwell point accuracy. The testers are lightweight and handheld. The typical test only takes about 6 to 8 seconds. Standard Ames testers read in 15 direct standard Rockwell scales and four models work in the superficial (N & T) ranges. Conversion charts for Brinell, Vickers and Knoop are included in the tester package.
Following the ASTM procedures for testing in Rockwell, the indicator is initialized then a minor load is established with a known hardness force. This eliminates surface variations before setting the tester to a zero point. Next, the major load is applied. After reaching the major load, it is removed to measure the difference between the major load point and the minor load point. This distance is calculated into a Rockwell number. The standard Ames tester includes everything needed for testing in the A, B, C, D, F and G Rockwell scales. Three certified and traceable test blocks are included. Additional balls and special anvils are available. The testers are available in 10 configurations.
The No. 3817 Automated Digital Hardness Testing System from The L.S. Starrett Co. (www.starrett.com) is capable of measuring all Rockwell, Rockwell Superficial, Vickers and Brinell Scales, and meets or exceeds all major industry standard requirements including those for ASTM, ISO and direct NIST traceability.
The system offers a one-touch automated testing operation that requires minimal operator involvement. 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. Built-in electronic conversion charts for cross-referencing hardness scales and approximating tensile strength eliminate the need for mechanical or electronic adjustments.
The system includes closed-loop NTEP load cell technology that improves repeatability and efficiency, and removes the need to use the conventional weights method. The system also has 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. Additional features include upper and lower limits alarms and a fitted tray for indentors and anvils. The system supports minor loads of 10 kilograms, superficial minor loads of 3 kilograms, major loads of 60/100/150 kilograms and superficial major loads of 15/30/45 kilograms. Maximum test height is 10 inches.
The Versitron wall-mount Rockwell system from Newage Testing Instruments (www.hardnesstesters.com) enables companies to test very large pieces that could previously only be tested using portable testers. The unit has virtually unlimited vertical capacity and a horizontal capacity range from 8.5 inches to 20 inches, depending on the position of the head and configuration of the test piece. The Versitron wall mount has a built-in clamping capability and the test head has a unique test surface referencing feature that enables the tester-both of which help prevent and compensate for deflection under load.
To raise and lower the test head automatically, the test stand has a motor drive with hand controls connected to the tester by cable, so the test head can be raised to provide more room for samples or lowered into position for testing. The clamping shield protects the indenter from impact against the test piece while being lowered onto the piece, so operators need not worry about positioning at an exact height and breaking diamond indenters. The test cycle can either be motorized or have the standard lever-pull activation.
The tester mounts to sound structures such as steel columns in a factory. The test pieces can be placed on the floor or on a raised base. Potential applications include testing large diameter pipe, large forgings and automotive parts that cannot be lifted by hand.
Reply 705
The OmniMet MHT System from Buehler (www.buehler.com) allows automation of the hardness measurement process from start to finish: indent placement, measurement, case-depth calculation and report generation all in compliance with ASTM and DIN/ISO standards. The system provides a number of options to accommodate various automation levels, tester types, stage sizes and applications. Click a button to add a sample or samples to the measurement queue. The required indentation pattern of indentation positions can be generated with the Profile Wizard and aligned in any direction for automated implementation. The system is calibrated to traceable standards and the software provides several levels of operator access for added security. Measured data is securely saved in the provided database and can be retrieved using built-in search tools. Via standardized report templates, the operator can generate diagrams and reports on current or previous samples in the database. The database also may be accessed over the company network using the included Sample Viewer Tool for remote report generation.
Model No. MET-UD is a portable ultrasonic hardness tester from Phase II (www.phase2plus.com). The handheld device includes both an ultrasonic probe and a Leeb impact device that allows the measure of hardness of metals from as thin as 1 millimeter to the largest assembled parts or castings. The nondestructive feature allows testing without physical or structural damage to the operator’s part. The gage can easily convert and be calibrated to all the popular hardness scales such as HRC, HRB, HB and HV. The unit outputs to a PC via USB interface.
Micro Photonics (www.microphotonics.com) announces the Nanovea Micro/Nano Scratch and Hardness tester. The tester is a completely integrated mechanical testing instrument for high-resolution scratch, mar and fracture toughness indentation testing. Hardness testing features include a motorized Z approach, integrated IBIS nano-indentation head with exclusive multi-frequency indentation technology and a force range of 0 to 500 meganewtons. Capabilities include fatigue and fracture toughness tests and dynamic mechanical analysis for visco-elastic deformation studies. Real-time display of frictional force, depth of curve and automated optical microscope inspection before and after the test are standard.
Precise control of the indentation process is ensured through the closed-loop force feedback system found in the IBIS Nano-indentation module. The module also offers exclusive multi-frequency indentation testing for those researching MEMS or visco-elastic deformation of plastic and polymer materials as a function of frequency. The scratch tester operates with the force range of 0.1 to 50 newtons and is suitable for coatings on a range of applications including plasma-processed layers, pharmacological applications and optical components.
Reply 708
On a macroscale, the hardness of a material as a whole is used for comparison with service experience or a general property. One way of determining a material’s hardness on a macroscale is through indentation testing, a measurement of a material’s resistance to permanent deformation. Applicable methods of indentation testing are the Brinell, Rockwell and Vickers hardness tests. Indentation testing is used for applications on a microscale as well, testing constituents or grains of metal to provide the most useful method for data correlation. Hardness tests that must be carried out on a microscale may be thought of as measurements of a particle’s hardness; the Knoop and microcharacter hardness tests can be used for this purpose. In general, there is no simple relationship between the results of the different indentation tests, although conversion tables for hard steels do exist.
Another type of testing at a macroscale is rebound hardness testing, or dynamic hardness testing, in which a scleroscope is used to measure hardness by tracking the height of rebound of a steel hammer after falling on a specimen from a fixed height.
The Brinell test is widely used on large parts such as castings and forgings of low to medium hardness. The Rockwell and Vickers tests are mainly used on small parts and those of low, medium or high hardness. The scleroscope, which leaves no depression on the test specimen, is used in quick, routine inspection and shop tests. Tests performed on a microscale, such as the Knoop and microcharacter, are used for measuring the hardness of very small parts, thin sections, thin cases and individual grains of particles.
When deciding on a hardness test, the thickness of the specimen tested must be considered. The thickness must be such that the backing material or anvil on which the specimen rests has no effect on the testing machine’s penetrator; an imprint on the specimen’s undersurface after a test is an indication that the specimen was too thin. When such an imprint occurs, a test using a lighter load or a larger indentor should be performed.
Some types of hardness testers are available in both manual and motorized models. Motorized models are well suited to production testing of simply shaped, small pieces that can be fed or placed into a test quickly. For heavier and more complicated pieces, a motorized tester can lessen operator fatigue.
What follows is an offering to quality professionals of today’s hardness testing equipment.
The AMH43 from Leco features a patented visual method for sample reconstruction. Source: Leco Corp.
Reply 700
The Handy Esatest portable hardness tester has no minimum thickness or weight requirements. Source: Qualitest
Reply 701
The Minuteman ELT Series of semi and fully automatic systems for Knoop, Vickers and Rockwell hardness testing are available in four different versions. Source: Wilson Instruments
When used on a microindentation tester, the Minuteman ELT Series is an upgradeable system that allows the operator to start with a basic system and progress to a fully automatic version as needs and budget change. The entry-level ELT1 is a video filar system for measuring the indents on the computer’s monitor using a virtual joystick for easy, on-screen operation. The ELT1 has all of the report writing capability of the higher-level systems, such as multiple graphing, MS Excel export, statistics and case depth plotting.
The ELT2 option adds image analysis capabilities to the software to automatically measure the size of the indent, eliminating the need for manual measurement by the operator. The Minuteman’s image analysis indent software program provides high indent measurement accuracy on a range of surface conditions.
The fully automatic Minuteman ELT3 and ELT4 versions have a large motorized stage, which can accommodate multiple samples. The stage has an integrated controller that eliminates bulky hardware. Jominy tests and any other repetitive operations can be automated using this fully automatic system. All of the Minuteman ELT systems have complete computer control of the tester for hands-off operations.
Reply 702
Ames hardness testers are available in 10 configurations. Source: Electro Arc
Following the ASTM procedures for testing in Rockwell, the indicator is initialized then a minor load is established with a known hardness force. This eliminates surface variations before setting the tester to a zero point. Next, the major load is applied. After reaching the major load, it is removed to measure the difference between the major load point and the minor load point. This distance is calculated into a Rockwell number. The standard Ames tester includes everything needed for testing in the A, B, C, D, F and G Rockwell scales. Three certified and traceable test blocks are included. Additional balls and special anvils are available. The testers are available in 10 configurations.
Reply 703
The No. 3817 Automated Digital Hardness Testing System is capable of measuring all Rockwell, Rockwell Superficial, Vickers and Brinell Scales. Source: The L.S. Starrett Co.
The system offers a one-touch automated testing operation that requires minimal operator involvement. 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. Built-in electronic conversion charts for cross-referencing hardness scales and approximating tensile strength eliminate the need for mechanical or electronic adjustments.
The system includes closed-loop NTEP load cell technology that improves repeatability and efficiency, and removes the need to use the conventional weights method. The system also has 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. Additional features include upper and lower limits alarms and a fitted tray for indentors and anvils. The system supports minor loads of 10 kilograms, superficial minor loads of 3 kilograms, major loads of 60/100/150 kilograms and superficial major loads of 15/30/45 kilograms. Maximum test height is 10 inches.
Reply 704
The Versitron wall-mount Rockwell system enables the testing of very large test pieces that could previously only be tested using portable testers. Source: Newage Testing Instruments
To raise and lower the test head automatically, the test stand has a motor drive with hand controls connected to the tester by cable, so the test head can be raised to provide more room for samples or lowered into position for testing. The clamping shield protects the indenter from impact against the test piece while being lowered onto the piece, so operators need not worry about positioning at an exact height and breaking diamond indenters. The test cycle can either be motorized or have the standard lever-pull activation.
The tester mounts to sound structures such as steel columns in a factory. The test pieces can be placed on the floor or on a raised base. Potential applications include testing large diameter pipe, large forgings and automotive parts that cannot be lifted by hand.
Reply 705
The OmniMet MHT allows automation of the hardness measurement process from start to finish. Source: Buehler
Reply 706
Model No. MET-UD includes both an ultrasonic probe and a Leeb impact device. Source: Phase II
Reply 707
The Nanovea Micro/Nano Scratch and Hardness Tester is an integrated mechanical testing instrument for ultra high-resolution scratch, mar and fracture toughness indentation testing. Source: Micro Photonics
Precise control of the indentation process is ensured through the closed-loop force feedback system found in the IBIS Nano-indentation module. The module also offers exclusive multi-frequency indentation testing for those researching MEMS or visco-elastic deformation of plastic and polymer materials as a function of frequency. The scratch tester operates with the force range of 0.1 to 50 newtons and is suitable for coatings on a range of applications including plasma-processed layers, pharmacological applications and optical components.
Reply 708
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