Hardness test using a hand grinder 8

[frankiee]

I read this from:

http://www.marineengineering.org.uk/Default.htm

under the heading of repair and main engine

"hardness testing of the journal indicated results far in excess of maximums. Spot grinding using a hand grinder to 1.6mm indicated that hardness was still unacceptably high. As this was approaching maximum allowable decision taken to replace crankshaft"

I wish to know how to do a hardness test with hand grinder.

 

[patdaly]

I believe they are referring to hardness at a specified depth, I.E. case depth.

If I am wrong, someone kindly explain the hand grinder hardness check!

 

[metengr]

A hand grinder hardness check means nothing. It is not a qualified or acceptable test for metal hardness.

You might as well use the "metal file test" instead of thje hand grinder; take a standard metal file, which is hardened, and file the edge of the sample to see if it is as hard or softer than the file.

 

[swall]

If the crank were carburized, the grinder could function as an in situ spark tester. By grinding to successive depths and observing the spark stream, one could get an idea as to case depth.Perhaps the concern was excessive case depth for the application?

 

[redpicker]

I believe the link refers to evaluation of a diesel crankshaft that had experienced a loss of lubrication and, consequently, local overheating (and subsequent hardening) of a connecting rod journal. The hand grinder was apparently used, not to determine the acutal hardness, just to indicate the hardening (damage caused by the overheating) exceeded 1.6mm (0.064"), which apparently was close enough to the service limit for rework that the engineer made the decision to replace the crankshaft rather than rework it.

Certianly not an approved method of determining the hardness of a steel crankshaft, but it does illustrate how common tools can be used to evaluate the metallurgical condition of a damaged component. I certianly would not ues this method to qualify a material for use, but would have no problem using it to reject suspect material (as was done here).

 

[unclesyd]

You just have to use the right file.
I have several sets of these files. I seen some people that were good with a grinder in determining whether a part was hardened or not.
It wasn’t too long ago that I was in a local fab shop when a older fitter while prepping some flat bar by grinding called attention to some CR CS that was to hard. It turned out the material was heat treated 4140 that had been marked wrong by the service center. I spark tested all the material for them and separated the 4140.

http://www.hardnesstesters.com/test-block.htm#yamafiles

 

[Carburize]

There is a set of files available form TSUOSAN which have calibrated hardness between 40 and 65 Rc for somewhat more accurate checks.

 

[limct]

The file test is only good for checking the surface hardness.
grinder test is good to confirm (to certain extent) the carburised depth, the rule of thumb is, the higher the carbon content, the more spark is seen,
high carbon steel will exhibit "x" shape spark as compare to mostly single line spark on low carbon steel.

Best regards,
ct

 

[tripleZ]

With regards to the sparking, I seem to remember my grandfather explaining to me that checking the sparks thrown by a certain type of grinding wheel was one method they used to look for excess elements in steel bars (in addition to hardness). Certain elements not only threw a certain shape of spark, but a certain color as well. And before I get flamed for making stupid comments, please understand that this had to do with steelmaking in the late 1930s/1940s.

 

[BrianBT]

Please note that redpicker has it correct. Unfortunately the article was badly worded. The journal was obviously badly damaged. However due to the cost involved in replacemetn it had to be proved irreperable. This may be done by checking how deep you have to grind before the hardness reduces to an acceptable level, and then compare this to the manufacturers allowable grinding limit.

WHere it is suspected that this will be some depth spot grinding either using a small air driven pencil grinder, or in extreme cases ( as was the fact with this failure) by light application of a hand held grinder.

 

[met20]

I have just become a member when I read your problem. There are several manufacturers of portable hardness testers out there that would be able to accurately give you the hardness of the surface. The unit I am familiar with was the size of a flashlight with a probe attached to a cord the size of an ink pen. Go on the internet and type in the words portable hardness testers and you will find what works best for you.

 

[ornerynorsk]

Bad science. Plain and simple. There are numerous grades and hardnesses of grinding stones, all of which will "feel" different.

 

[BrianBT]

Please note that hardness measurement was taken using an appropriate meter.

The use of a hand grinder was only to remove material to find out how much material would have to be machined before hardness reduced to acceptable methods.

The hand grinder was not used in any way to detect hardness