Can anybody give their input on the following issue of LPT/DPT on Al-Bronze
casting:
One of our valve manufacturer has indicated inability to carry out Surface
flaw test and instead suggesting Radiography for Al-Bronze casting.
Following is the brief explanation that vendor has provided.
"....so far all (100%) of the castings we have made have been rejected by
the test house we are using. The reason is that every casting is exhibiting
very shallow linear surface 'flaws' along the lines of section change and
at the location of the joints on the patterns.
I understand from the lab that these superficial 'flaws' are common on
aluminium bronze castings and reference to another customer who uses this
technique backs this up. They can be easily removed by polishing the
surface of the casting in the affected areas. Unfortunately, without the
ability in house to find the flaws we cannot deal with the issue before the
laboratory tests them. Not only that but when they are rejected we have no
means of seeing the flaws ourselves.
While I'm confident that the castings are sound – we've had castings
x-rayed to prove it – we cannot overcome this dye penetrant issue.
Unfortunately, despite making a fair number of castings and having each
checked we are going to have to accept that we cannot make the castings
under the required specification. I appreciate that this is a major
inconvenience to you and for that I apologise. We cast a huge number of
castings in aluminium bronze with great success particularly in the fluid
handling industry. Therefore we never considered dye pen would present such
an obstacle. We still believe the castings to be of high quality and
integrity on a par with anything else we've made but I know that's no
consolation if there's a spec that has to be met."
Of course, I have no experience in Al-Bronze, I am not fully agreed with
the above explanation, and we are asking them to carry out the DPT only
(even after grinding or wire brushing if required to remove the surface
flaws). Your valuable input will be very useful for me.
Best regards,
Prasad
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