Hardness punches

[padams8888]

Were hardness punches conducted on new production commercial rifles before they went out the door? Is this known? Was it at random? This D I received has flippen single clean punches on all parts of the weapon and is obviously not a refurb......I can put some pics up after work.......just curious.

[running-man]

Hey Pat,

I don't think we can even begin to know all the proof testing, acceptance testing, and general non destructive / destructive testing that China did on their firearms before they were approved for shipment.  Having said that, nowadays you'd generally run a certain percentage of parts/raw material from a specific heat treat batch through all forms of testing before you even began to use the stock from that batch.  Anymore, you almost never see a hardness divot on a finished part, it's just bad form and usually indicates something went really wrong somewhere in the process and someone had to double check something. 

Seeing hardness divots on multiple parts would indicate to me that maybe

a) the Chinese weren't all that good at their bookkeeping (performing unnecessary testing that didn't need to be done).
b) they were using suspect excess material or material treated in a suspect process.
c) they were reusing various components machined back when the processes weren't quite as well developed or weren't followed very well.

Hard to say.  Maybe they were just giving Han loads and loads of practice using the Brinell indenter too... 

[Loose}{Cannon]

Good stuff..  Was hoping you posted on this matter.  I dont know much about this punching method of testing hardness.  And more info as to how the procedure is done?

[carls sks]

thanks for sharing. 

[XXXSKS]

Unless someone notices a pattern. This could be a random rifle pulled from the production line for the very purpose of QC testing.

.............Joe

[running-man]

Unless someone notices a pattern. This could be a random rifle pulled from the production line for the very purpose of QC testing.

.............Joe

That's a good thought Joe.  I hadn't considered that maybe they pulled an entire unit for QC and went through it with a fine toothed comb to look for issues.  With the "waste not, want not" mentality of combloc countries, I could easily see them taking the final rifle and stuffing it in a crate along with all the others for sale.  It would work just as well as the others, just wouldn't look a nice.

And more info as to how the procedure is done?

The procedure depends a bit on what method they are using.  The two big ones these days are Brinell & Rockwell. (there are also others like Vickers & Knoop testing, but those don't use ball indenters) 

Brinell uses a standard size carbide indenter (think of a ball bearing made of carbide) anywhere from 1mm to 10mm in diameter.  A known force anywhere from 500kgf to 3000kgf is applied to one end of the ball and the ball creates a divot in the material being measured.  The indentation is then measured and the hardness is backed out using the std Brinell hardness equation:



Brinell is suspect to operator error as it's sometimes very difficult to accurately measure the diameter of the indentation, especially if the surface isn't well prepared.

Rockwell testing is performed in a similar manner, but the indenter doesn't have to be a ball, it can be a a spherical diamond-tipped cone of 120° angle and 0.2 mm tip radius (called a Brale).  The type and size of indenter used determines what scale output is given as Rockwell testing covers something like 30 different scales from soft materials like plastics all the way up to ridiculously hard materials like ceramics.  A preliminary minor load of 10kgf is applied to break the 'skin' of the material.  This first step helps to eliminate surface effects that can skew the final results.  The dial indicator on the machine is zeroed out and then the test is performed by implementing a major load to dig the indenter into the material.  The major load is held for a specified time until the indicator stops moving and then the major load is removed, leaving only the 10kgf minor load.  This pulls out all the elastic effect and only the plastic deformation is measured.  The dial indicator is then read, and using a formula the final Rockwell number from a particular scale (dependent on the indenter shape, size, and force applied) is the result. 

[Loose}{Cannon]

Very nice...  So is it the Rockwell method we see on the sks?

[firstchoice]

  I see several of mine with the little ping marks on the usual components. What I do notice is that some parts have more than one ping mark. This receiver cover lever has two ping marks:



  Most of the time I see only one mark but I've seen up to three, usually in a row. I'll try to dig up some pics of the varieties. These are the one-ping levers of several of my late "Tickler"-hand guard rifles.





  I've seen these marks on the FSB, (both on the front of the FSB and just above the Bayo Lug), RSB, Trigger Group Housing, Bolt, Bolt Carrier, (just forward of the charging handle), and Gas Block. I can't remember seeing them on the magazine or Receiver Cover, but that doesn't mean it's not there. I just haven't taken note of them as much, nor have I taken pics of them for the sake of the ping marks. I'll look through some of them and see if I can find more.

  Is there a chance that these were a part of the refurb process? Sort of a manual "check list"? Might explain the multiple ping marks? Just guessing.

firstchoice

[running-man]

  Is there a chance that these were a part of the refurb process? Sort of a manual "check list"? Might explain the multiple ping marks? Just guessing.

firstchoice

That's certainly a plausible explanation as well.  A guy with a simple punch tracking something or another on XYZ gun. It would be interesting to see more multiple marked parts and see if the indents are identical (which would point to hardness testing performed multiple times) or if they are different which would maybe point to a guy and a punch.

[armedhippie]

This is very interesting fellas.  RM, I have at least 1 receiver with at least 3 or more indents in a circular pattern going below the stock line. Might take me a bit, but I'll get some pics.

I've always wondered why more than 1 hardness test per part would be required. Keep up the good work guys.