Tuesday, June 19, 2012

Does SAE 841 have a Heat #?

As most of you know, for some time I was in charge of processing and distributing the Material Test Reports (MTR) here at Atlas Bronze. When I first took on the job I was a bit apprehensive.  The importance of the job and the accuracy of the documents was drilled into my head.  After all, I had heard the stories about those people who went to jail for falsifying Certs (see my post , Who knew you could go to jail! )

But, since I have no intention of falsifying any documents in my life... I'm safe. There is much to say about Material Test Reports...(and by no means am I an expert). But I did see a common thread of confusion surrounding one type of material - SAE 841, Sintered Bronze. 

Here's the story....

Recently, I had a customer who purchased some SAE 841 Sintered Bronze material from us and requested Certs with this material.  Happily I sent over the Certs and then she came back to me, puzzled, asking...."On your paperwork, do you have anything that indicates the lot #?".  I then replied with my standard reply.  After I did this I decided....I must post this on the blog, I get this question so often with Sintered products, hopefully it will help.

MATERIAL: SAE 841, Sintered Bronze
QUESTION: "On your paperwork (Certs), do you have anything that indicates the lot #?"
ANSWER: Unlike other bronze materials, Powdered Metal (841 Sintered Bronze), is not melted nor heat traceable, so therefore there will be not be a LOT# or HEAT#      
Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape (compacting), and then heating the compressed material in a controlled atmosphere to bond the material (sintering). The powder metallurgy process generally consists of five steps: 

(1) Blending - The part-specific powder is created by mixing the correct amounts of metals and lubricants to produce the physical and mechanical properties of the finished product.

(2) Molding - the powder is compacted into the desired shape using compressive forces. The part shape is created by compressing the correct blend of materials inside of the part-specific tools.

(3) Sintering - Through the application of heat, sintering permanently bonds the individual metal particles that have been compacted together through the molding stage.  This process is instrumental in providing the majority of the mechanical properties of the final product.

(4) Sizing - Sizing, sometimes referred to as "coining," is the final pressing of the fully sintered part.

(5) Oil Impregnation - Under vacuum, customer-specific oil products are impregnated into the remaining porosity of the completed part.

So looking at the five steps you can see just in Step 1 alone that maintaining a Heat / Lot # is not possible.   The metal is never melted. 

(PS:  I got your feedback that some of you were unable to leave a comment in the Comments section.  It is now fixed, so feel free to add your thoughts.)