Problem with a microhardness tester MHT-1,from japan

[lalie90]

Hi guys,

what do you think could be the problem with a micro hardness tester that i'm using because i seem to be getting wrong values(between 800 HV and 900 HV) compared to the calibrations that were done(which are from 695-705 HV).

any suggestion or solution to what the probllem might be will be appreciated.

 

[cloa]

What are you testing?

 

[lalie90]

I'm actually doing the callibration data again using a steel disc of (695-705 HV)to see if i will get the same values as the people that did it before,but the values that i'm getting are extremely high,and when people use it gives false readings too when comparing to the callibrations that were done before(between 695 and 705 HV)

 

[EdStainless]

What do you get at lower ranges?
Have you looked at the indenter under magnification? Make sure that it isn't chipped.
Double check the weights. If they are internal one may be caught and not loading.
Either of these will give you high readings.

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Plymouth Tube

 

[SteveHooker]

I have a Chinese microhardness tester, and it took a while to set it up for accurate readings. The greatest problem I found was due to the error in the magnification, and hence the accuracy of the measurement scale. I used a stage micrometer to recalculate the actual magnification, and used this factor in the software supplied to calculate true hardness. A check on the weights (at the indentor) found that the adjustable internal mass was also in error, causing greater errors at low loads.

 

[mrfailure]

First, you should be checking your microhardness using a certified calibration sample. You do not know if the earlier test results were incorrect and yours were actually correct. Our lab QA procedure requires NIST-traceble calibration checks within a tolerance band defined by ASTM E384 (currently 2% of the certified value in the hardness range you are looking at). It is important that your calibration specimen be certified at the load you are going to test at. Despite implications, load makes a difference. We have found higher hardness obtained on the same test specimens when we tested at a 100g load compared with 500g. This happened recently and we were performing our testing of steel with similar hardnes (i.e. >800 HV). While calibration hardness checks were within tolerance, we found increases of hardness of up to 75 HV when using the 100g load.

If you are out of the allowable tolerance range when you test a traceable calibration specimen, then you will need to recalibrate the optics of your system until you are in tolerance.

Aaron Tanzer

http://www.lehightesting.com