Hardness Testers

Hardness Testers
Starrett Hardness Testers indicate the hardness of a material, usually by measuring the effect on its surface of a localized penetration by a standardized rounded or pointed indenter of diamond, carbide, or hard steel.
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.
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 several different test methods.

Starrett Hardness Testers utilize the following Hardness Testing Methods:

Benchtop Hardness Testers
• Rockwell
• Brinell
• Micro Vickers
• Macro Vickers

Rockwell Hardness Testing
The Rockwell hardness tester utilizes either a carbide ball or a conical diamond and indicates hardness by determining the depth of penetration of the indenter under a known load. This depth is relative to the position under a minor initial load; the corresponding hardness number is indicated on a dial or digital display. For hardened steel, Rockwell testers with diamond indenters are particularly suitable; they are widely used in metalworking plants. The Superficial Rockwell Tester is particularly suitable for use in hardness testing of thin components and layers, or with specimens whose calculated hardness value is outside the Regular Rockwell scale. Starrett offers regular, superficial and combination units available to operate in all Rockwell scales in regular and superficial Rockwell ranges.

Vickers Hardness Testing
The Vickers hardness tester uses a square-based diamond pyramid indenter, and the hardness number is equal to the load divided by the product of the lengths of the diagonals of the square impression. Vickers hardness is the most accurate for very hard materials and can be used on thin sheets. Micro Vickers: Microhardness testing of metals, ceramics, and composites is useful for a variety of applications: testing very thin materials like foils, measuring individual microstructures within a larger matrix, or measuring the hardness gradients of a part along the cross section. The actual indenters used are Vickers (more common; a square base diamond pyramid with an apical angle of 136°) or Knoop (a narrow rhombus shaped indenter). The result for either Vickers or Knoop microhardness is reported in kg/cm2 and is proportional to the load divided by the square of the diagonal of the indentation measured from the test. The load on the Vickers microhardness indenter usually ranges from a few grams to several kilograms.
Macro Vickers: In contrast, 'Macro' Vickers loads vary from 1 to 120 kg. The indentations should be as large as possible, within the confines of sample geometry, to minimize errors in measuring the indentation (hence the reported hardness). Vickers hardness is also sometimes called Diamond Pyramid Hardness (DPH) owing to the shape of the indenter.

Brinell Hardness Testing
Brinell hardness is determined by forcing a hardened steel or carbide ball of known diameter under a known load into a surface and measuring the diameter of the indentation with a microscope. The Brinell hardness number is obtained by dividing the load, in kilograms, by the spherical area of the indentation in square millimetres; this area is a function of the ball diameter and the depth of the indentation. The Brinell hardness test method as used to determine Brinell hardness, is defined in ASTM E10. Most commonly it is used to test materials that have a structure that is too coarse or that have a surface that is too rough to be tested using another test method, e.g., castings and forgings. Brinell testing often use a very high test load (3000 kgf) and a 10mm diameter indenter so that the resulting indentation averages out most surface and sub-surface inconsistencies.

Portable Hardness Testers
• Leeb
• Ultrasonic

Ultrasonic Testing
Ultrasonic Contact Impedance is based on a 136 degree diamond at the end of a vibrating rod being depressed into the test surface at a fixed load. The difference in Ultrasonic vibration frequency is then calculated into a hardness value. The UCI test procedure is slower than the Dynamic Impact style, however the “UCI” method of hardness testing is portable, easy and accurate. It also has its own advantages when utilized for certain testing applications. UCI testers are not restricted to large mass items like dynamic type testers. These units can test metals as thin as 1mm and at a hardness value as low as 20HRC (75HB). They also excel at performing hardness tests on larger, harder metals as well. Another reason for the rise in popularity is due to the fact that the UCI method is categorized as “Non-Destructive”. That translates into less scrap parts/ lower mfg costs due to necessary inspections.

Leeb Testing
The Leeb rebound hardness test method was developed in 1975 by Leeb and Brandestini to provide a portable hardness test for metals. It was developed as an alternative to the unwieldy and sometimes intricate traditional hardness measuring equipment. Very well suited for the hardness testing of ferrous and non ferrous materials. Measurements are made in the Leeb Scale and depending on the instrument can be converted to Vickers, Brinell, Rockwell C & B and Shore. Materials that can typically be tested include cast steel, alloy tool steel, stainless steel, aluminum, bronze, copper, cast irons etc.

LEEB / REBOUND testers are NOT suited for testing the hardness of very thin parts like sheet metal, thin walled or very light weight parts.

Parts down to 2mm (0.11") when very well supported/coupled to a heavier part and up to any thickness can be tested with an Ultrasonic Hardness Tester.

Test Blocks and Accessories for Hardness Testers
Starrett blocks can be used to test Rockwell, Brinell or Vickers scales. They are available in steel, brass and aluminum. Each block is serialized, with a certificate detailing the environmental conditions used to test the block.
Actual readings are given, with the averages of these readings: min. reading, max reading and a repeatability figure. The blocks are calibrated according to ASTM E-18 standards, ANSI (NCSL) Z540-1, (ISO) 10012-1, ISO/IEC 17025 and Mil-std 45662A.
Starrett hardness test blocks are manufactured from square steel or brass plates, as opposed to the more common round bar stock. The use of the plate gives a more accurate and consistent surface for inspection. Metallurgical tests have proven that during the production of round bar stock, suspended carbides in the mix migrate to the center of the rod. The scientific name for this condition is carbide segregation and results in different readings being found in the center of a rod rather than at its outer edges. Some manufacturers remedy this situation by removing the centers from their blocks.
Hardness test blocks are designed to be used only on one side and the indents should be more than .010" from the centers of two indents or no closer to the block's edge than .040".
Calibration kits are also available from Starrett. No facility with a hardness tester in use should be without a calibration kit. These kits come with from 3 to 20 calibrated test blocks and the serialized penetrator that was used to inspect each of the blocks in the set. When a discrepancy is detected in a tester, these kits allow you to determine the direction to proceed to resolve the issue.