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Small pores at the surface SF20T

(-----) 2006

Recently, our product is facing a serious appearance problem. After the tumbling process, the surface of is full of small pores which look like dented and scratch scrawl.
Therefore, I would like to seek for the help whether any solution/suggestion/root cause here.
Thank you.

Leonard Yong
precision hardware - Singapore

First of two simultaneous responses -- 2006

Lots of questions for you before answer. What is the material you are working with? How Big? What are you doing now and what have you tried? What happens to the part next? Are you using any media or liquids? If they are castings, what process is used to make them?

tony kenton
AF Kenton
retired business owner - Hatboro, Pennsylvania

Second of two simultaneous responses -- 2006

Maybe segregation or corrosion of the free-machining constituents (lead, sulfide, telluride).
Is this a wet tumbling processing?

SF20T is a free-machining, ferritic stainless steel rarely seen in the USA:
Carbon 0.05% max
Manganese 2.00 max
Phosphorous 0.05 max
Sulfur 0.15 max
Silicon 1.00 max
Chromium 19.00/21.00
Molybdenum 1.50/2.50
Lead 0.10/0.30
Tellurium 0.03 min
Iron -- balance.

Ken Vlach [dec]
- Goleta, California

contributor of the year Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.



It surface is round with the diameter about 9mm. It is produce by CNC cutting and after the tumbling process, the part will go to DI wash and visual inspection.
After the CNC cutting, no such problem is found.
During the tumbling process, we use media, compound and DI water for the process. The barrel is coated with rubber.

Leonard Yong
- Singapore


Hmmmmm. After reviewing you info, I am still leaning toward a problem with your material. If you are using a small media a 3 or 4mm abrasive ceramic media, you should be able to improve the surface finish significantly provided you are using a compatible liquid compound that does not react to the metal.

tony kenton
AF Kenton
retired business owner - Hatboro, Pennsylvania

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