All posts by Louise Scott

Proud of the British Heritage in the vickers hardness test

This year the UK should be celebrating a very special milestone in the field of mechanical testing. It is 100 years since the development of the Vickers hardness tester by Robert L. Smith and George E. Sandland at the Vickers laboratory in Erith Kent.  

Vickers Ltd was founded in 1828 and had a long association with the North East of England from 1927 until the final closure of the Vickers Defence Systems factory on Scotswood Road at the end of 2013 which saw the end of the Vickers name in the North East of England. However, the name of Vickers lives on in the metallurgical world with the hardness test being accepted as one of the main methods of hardness testing.

The immediate acceptance of the importance of the test by the Institute of Mechanical Engineering, is a testimony to the astute judgement of engineering societies over 100 years ago. The Institute of Mechanical Engineering representatives believed the development had significantly improved hardness measurement and accordingly awarded a £20 prize each from the Sir Robert Hadfield prize committee (equivalent to £900 in 2021). Even in 1921 the importance of their development was recognised! 1,2.  The invention was granted patents in the UK and in the USA.3 4

Our laboratory located in the North East of England, Metaltech Services Ltd, has chosen to celebrate the centenary by the purchase of a fully automated Vickers hardness tester with a load cell loading mechanism combined with image processing software to measure the indent, which are two features known to eliminate many of the sources of measurement error. We have chosen the Future-Tech FLV-50ARS-F. This machine gives us the capability of micro, low load and macro-Vickers hardness scales.

MSL’s new acquisition, a Future-Tech FLV-50ARS-F

The Vickers hardness tester was initially developed to improve the reliability of testing of materials above 450HB where the existing Brinell test, developed in 1900, was found to be lacking due to the crushing of the steel ball indenter. The main change was the use of the diamond indenter shaped in the form of an equilateral diamond shaped pyramid with a plane angle of 136°.  The specific angle was chosen to try to give similar numerical values of hardness as the established Brinell method. The hardness number is determined by the load divided by the surface area of the indentation and not the area normal to the force which gives similar units to stress but they should not be confused since the calculations for stress and hardness differ. The concept and machine design were so good that the Vickers hardness test subsequently became one of the most universal and widely accepted hardness test method in the metallurgical world.

If Robert L. Smith and George E. Sandland were around today they would be totally amazed at the current generation of commercially available automatic Vickers hardness testers. They are a clear example of the impact of robotic technology on our working lives. Although an expensive investment they can carry out work previously not dreamt of as being a reasonable request for product development. For example, some weld configurations have required several hundred hardness indents across the weld metal and various heat affected zones to ensure that the weld procedure gives the appropriate level of integrity and durability for the subsequent service conditions.  To carry out this task with a manual machine would be expensive and a significant challenge for the operator.

Despite the fact that many commercial grades of material lack homogeneity of mechanical properties the improved test technology that now eliminates known errors in testing is a significant improvement. To be more confident on the demarcation between acceptable material and deficient material adds to industries confidence in product testing.

Unfortunately, for the UK, Vickers did such a good job on machine construction that some of their test machines have lasted over 60 years. This caused a commercial dilemma in that new sales did not warrant product improvement and Vickers lost the initiative and ability to finance further product development. The main manufacturers are now Austrian (Emco-Test Prufmaschinen GMBH), Dutch (Innovatest Europe BV), German (KB Prüftechnik GmbH and Zwick-Roell Ltd) and Japanese (Future-Tech Corporation).

A UK based Company that has carried out development work on the hardness measurement is, Spectrographic Limited of Leeds. They have developed a digital camera system and software, that can be retrofitted to the conventional Vickers hardness tester, to improve the accuracy of measurement of the hardness indents. This innovation will allow a further life extension of the traditional Vickers loading frame and mechanism allowing the iconic image of the traditional Vickers hardness tester to remain with us for many more years.

References

  1. R L Smith and G E Sandland, An accurate method of determining the hardness of metals, with particular reference to those of a high degree of hardness, Proc., Inst., Mech., Engr., 1 May 1922, page 623
  2. R L Smith and G E Sandland, Some notes on the use of a diamond pyramid for hardness testing, JISI,1925, Vol 109, Page285
  3. British patent 196962A dated 8th December 1921
  4. USA patent US1478621 dated 25th December 1923.

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MSL teams up with ITA Limited, a Czech-based company specialising in computer simulation of rolling, forming and heat treatment technologies.

MSL have had the pleasure of working closely with ITA Ltd, a Czech company founded in 1991 by research workers. One of ITA’s areas of expertise involves the development of metallurgial software, they also offer a range of existing products and services.

To find out more information about the products ITA offer, click here.