M14 Forum banner
1 - 9 of 9 Posts

·
Registered
Joined
·
15 Posts
Discussion Starter · #1 ·
ive got a somewhat stupid question. i have a sidemarked polytech receiver that im slightly curious about the hardness of. serial number 165xx.

at work the other day i noticed that we have an old school hardness tester that we use for checking crankshafts with. its the type that has the metal ball inside it -- you let it impact the part youre testing and you read the measurement on the side of the tool. obviously its non-destructive and its only going to test surface hardness.

would this be an acceptable way to see if my receiver is hard enough to trust? is it any more accurate than taking a file to it?

we use it on crankshafts that literally cost millions of dollars, but thats a different use and a different industry.

also, the tester has a current calibration sticker on it, if that matters to anyone.
 

·
Registered
Joined
·
288 Posts
I think Brinnel gage is not the right gage for a surface hardness. You probably want a Rockwell C tester. This will give you case depth but not depth of hardness or core hardness.

What kind of crankshafts? Natural gas engines?
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #4 ·
its a rockwell C gauge. does anyone know what sort of range i should look for?

the crankshafts are for large bore (700-1040mm) diesel engines. mostly container ships and whatnot. big stuff, usually 4-5 decks high, 120 feet long. 5 ton pistons, etc. when there is a major failure, the crankshafts are machined in place. with all the welding and grinding, hardness and finish tests are done pretty often (usually with more complex equipment than the drop tester i mentioned).
 

·
Eye Master
Joined
·
4,185 Posts
One of the issues you will deal with is that there is through hardness, and then there is surface hardness. Surface hardness will not usually affect the overall strength of the part very much, but is excellent to resist surface wear.

Your non-destructive tester can not tell if the hardness it sees on the surface is really just on the surface, or if it is through hardened. This is why hardness tests are usually destructive - you need to split the part open so you can measure hardness both on the surface and in the core of the metal.

Art
 

·
Registered
Joined
·
999 Posts
i think brinnel gage is not the right gage for a surface hardness. You probably want a rockwell c tester. This will give you case depth but not depth of hardness or core hardness.

What kind of crankshafts? Natural gas engines?
correct, with a "c" scale, none tell case depth have to cross section for that. "b" is for a lower range of hardness with ball. Diamond stylus is used for "c" scale. There is however a crossover range between the 2. Normally c is used for tool steels and such where the hardness tends to be complete not just case or pack hardened.
 

·
Registered
Joined
·
544 Posts
I believe the chinese receivers are around 47c to 50c rockwell. And they reharden them up to 52c rockwell.

Back in the 70's my new borgwarner super T-10 4 speed tranny blew 2 times. When i compared the hardness of the gears to the muncie 4spds the muncie gears were much harder. The degree of the Hardness can mean success or complete failure.
 
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top