The Different Scales of Hardness Testing

Hardness testing systems provide a quick and economical method of testing mechanical properties; all materials can be tested for hardness provided the correct method of test is adopted. Hardness testing offers valuable information for research and production application where material properties are an important consideration.

The hardness test measures a materials resistance to indentation and is a good reference for properties such as resistance to abrasion. Typical applications are for automotive heat treatment studies, protective and hard coating applications in aerospace and weld inspection in advanced fabrications. In this article we intend to look at the five main types of hardness testing, their history and a brief description of their industrial applications.

Brinell

The Brinell hardness testing method is the first method invented for standardising hardness, from which other hardness measurement methods have since been derived. Originally invented by Dr. J. A. Brinell in Sweden in 1900, a steel or carbide ball is used of diameter 1mm to 10mm depending on the requirements for hardness test. The ball is loaded with upto 3000Kg to create an impression or indentation in the surface, the size of the indent is measured and converted to a hardness value.

Brinell testing is valuable in foundry applications where the testing of inhomogeneous material is required such as large cast iron castings. The advantage of the large ball is that the components hardness is measured across a range of microstructural features and this enables consistent hardness values to be achieved. While the Brinell test is considered to be less versatile than that of the Vickers or Rockwell, it is more effective at testing materials such as forgings and castings.

Vickers

The Vickers hardness test was originally developed in 1924 by Smith and Sandland at Vickers Ltd, as an alternative to the Brinnell test, which was considered to be rather inaccurate and limited in application. The resulting Vickers test on the other hand, retained the same process as the Brinell but by using a pyramid shaped diamond rather than a steel ball indenter, they were able to deliver a more consistent and versatile hardness test.

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Proceq manufactures quality nondestructive portable testing instruments for metal hardness, concrete properties and roll hardness tester. Proceq invented the Equotip portable metal hardness tester and the world’s first portable concrete test hammer, the Schmidt concrete test hammer.

The Parotester 2 roll hardness tester

The Parotester 2 roll hardness tester provides accurate and reliable evaluations of the roll hardness, hardness profile and hardness variation of paper, foil and film rolls. With Proceq’s roll hardness tester, unevenly wound reels can be spotted prior to interruption of operations and cause of quality problems in printing and converting operations.

By taking Leeb readings across the roll, uneven, too soft or too hard winding can be detected and the roll can be rejected. This minimizes the risk of complications e.g. during the printing process on paper.

Automatic loading and unloading of the impact body by pressing the impact device to the roll as implemented in the Parotester 2 roll hardness tester results in fast and repeatable tests of greater resolution than the commonly used Original Schmidt type L hammer tester.

APPLICATIONS

• This roll hardness tester is well suited for the paper industry
• Foils, films and other plastic sheet materials where a low impact energy is required
• Special metal applications (also see metal hardness tester Equotip 3)

FEATURES

• The Leeb hardness value (HL) immediately indicates the winding tightness. The measurement with the roll hardness tester is objective and precise
• The high resolution (1 LU) facilitates comparatively small differences in hardness to be revealed
• The large LCD display of the roll hardness tester enables an immediate visual assessment of the values
• The unit can be easily programmed for individual user requirements
• About 5’000 single measurements can be stored internally. The data can be retrieved via RS 232C for further processing on a PC (use Parolink 3 or Hyperterminal software) or directly printed
• Using the external barcode reader (accessory part), roll identifications can be quickly captured and accurately read from the barcode of rolls
• The paper roll hardness tester Parotester 2 is robusta and requires little maintenance

Please contact Proceq for more information on the roll hardness tester Parotester 2.