The authoritative public forum
  for Metal Finishing since 1989
-----

After Vibratory finishing - surface blisters on steel parts - why?

2004

We have a cold-extruded steel bush which is subjected to Vibratory polishing to remove sharp edges and scale formation. We have noticed abnormality on the steel external surface of the steel bush. i.e. Blister kind of formation at random noticed. Generally,Blister are hollow in nature and will have air passage, but in this case it is not hollow, instead "solid form" / "Embossed or raised dots" and have no cavity or dimple formation inside the tube.

During the extrusion process there is no surface abnormality. Only after the vibratory-polishing this surface defect occurs. From your experience, Could any one advise us the reason?

Regards,

Sivaraj Dhandapani
engineering products exports - Chennai, Tamil Nadu, India

---

Well this is new. Never seen or heard of a situation like this before and it is unlikely a cause attributed to a mass finishing system. More than likely it is either a problem with the composition of the material or the chemical being used with the mass finishing media. I'm leaning to some kind of chemical reaction.

AF Kenton
retired business owner - Hatboro, Pennsylvania
2004

---

Maybe the problem isn't a surface problem, have you ever cut one in half right where the dimple is? A cross section right in the middle of the dimple might help you I.D. the problem.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
2004

Mr Dhandapani

It may be possible there are differing areas of different hardness values which do not deburr and polish uniformly.

The bumps are probably harder than the smooth areas. If there is a Drawing operation there may be localised hot spots due to bad lubrication which on quench may lead to localised hard spots.

This above please note is speculation on what may be the possible cause..

Regards

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
2004