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Trouble Shooting on Hardness Testing

Issue 01

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Problem
The results from the Rockwell hardness are several points higher from the designated test reference blocks.

Diagnosis
If you are testing using a diamond indenter, then the chances are that the indenter is ‘chipped’ or has suffered damage. You will need to check if the indenter scratches glass – if it does, then this needs to changed, but it is worth both checking the form on a shadowgraph or a magnifier.

Solution
The indenter is a 120° cone with a 2µ radii.
If you are using a ball for indentation, then the chances are that this has ‘flatted’ and should be changed, but do not forget to ‘bed in’ with either a piece of Aluminium or an soft, old and clean test reference block.

Issue 02

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Problem
The Vickers’ results from the test reference blocks are too high/too low from what is expected and the reference indentation is also reading too high/too low as well.

Diagnosis
The chances are that the optical measuring system has not been zeroed. However, it may be that the load has changed or has been tampered with.

Solution
Please then check against the reference block, but if the problem still persists after the setting of the zeroing of the ocular, then please call the manufacturers’ service department or the servicing agent.

Issue 03

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Problem
We have just moved the Rockwell and the results from the test reference block is erratic.

Diagnosis
The chances are that the weights have become out of line or simply come off their correct position.

Solution
Ensure that these weights are correctly installed and test several times against the reference block. If the problem persists, then please call the supplier or the service agent.

Issue 04

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Problem
Our Quality Standard/ Supplier require us to have our hardness testing machine accredited to UKAS standards and to both the ISO and the ASTM standard.

Solution
The indenter needs to be accredited and the machine itself needs to be directly and then indirectly verified. The indenter will remain in service for a maximum (currently) of 2 years if there is no damage in between this time schedule. The test reference block (currently) will be valid for a maximum of 5 years before re-accreditation, if this is possible. All the certificates (for the indenters and the machine) must be given to the calibration engineer after the initial calibration for the engineer then to add the data from both the machine and the indenters, into the uncertainty of measurement calculation. The Direct calibration lasts for 12 years or until the machine is moved and an indirect calibration must be done as a minimum on an annual basis (please note that some specifications call for the ball indenter holder to be accredited and also a reduction in the calibration schedule).

Issue 05

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Problem
The results are very erratic on our hardness tester since this has been moved.

Diagnosis
It may well be that the machine has dislodged the weights, or the machine is not set correctly, or it is not level, it has lost its calibration or the indenter has been damaged.

Solution
Check the hardness tester for all the above possible problems and rectify, but remember that if you wish to maintain the UKAS accreditation, then you must get the machine DIRECTLY calibrated and if the indenter is replaced, then this will need to be accredited.

Issue 06

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Problem
The certificate of accreditation for the ball is in excess of the permitted 2 years allowable.

Solution
This is because the ball accreditation is done on a batch quantity, with certain percentages going for different Physical and Mechanical tests (all of these parameters will be recorded on the certificate of accreditation). If you require an official letter from the manufacturer to support this, then ask (please note that there may well be a charge for this service).