Summary for scale minimization Discussion
Scale minimization is the central issue in this stainless steel thread: Bhupendra Jha of Ahmedabad asks how to reduce heavy scale loss during reheating slabs to 1280–1300 °C before hot rolling, whether a protective coating could survive those temperatures, and whether any chemical could make the scale easier to break and remove with a 150 bar descaling system. In reply, Manikkavasagam Elangovan says that in his earlier plant in India, smearing the billet surface with normal lime before charging gave better results and may help reduce scale loss. Kunal Juyal adds another practical option: grind the whole billet before furnace charging so the primary casting scale loosens its grip and is easier to remove. The thread does not offer a proven coating or chemical solution, but it does suggest simple preheating surface preparation methods to improve descaling and reduce embedded scale defects.
2003
Q. Dear Sir,
We are the 2nd largest producer of Stainless Steel in India.
We cast Billets – 140 * 140 sq. mm in 6/11 radius billet caster and slabs of 160 * 1050 – 1810 * Lengths in 7 mm radius Slab Caster.
The slabs are ground to remove oscillation marks or any surface imperfection prior to Hot rolling operation.
Slabs are heated to 1280 °C in an oil fired pusher type reheating furnace prior to rolling in a 4 High Plate Mill.
During heating, excessive scale formation takes place. We have online high pressure (150 bar) descaling system.
Stainless Steel scale, being very rigid type, does not come out completely and during subsequent rolling passes gets embedded, causing severe surface imperfections.
Now, my question to you is:
(a)How to minimize scaling loss during heating.
(i) Is there any protective coating which can be applied on the surface to overcome the problem?
(ii) If yes, will the effect of coating remain at 1280 – 1300 °C
(iii) From where it can be procured?
(b) Is there any method or chemical which can help in changing the nature of scale, making it easily breakable/removable by High Pressure Water Jet System.
I will be highly obliged to get reply from you.
Looking forward to your mail at the earliest.
BHUPENDRA JHA
– AHMEDABAD, GUJARAT, INDIA
A. Mr. Bhupender, Regarding your query, I wish to pass on this small bit of information. In my earlier plant in India, where we used various size of billets from 125 x 125 to 250 x 325 (for structural rolling and normal grade billets), once we adopted a practice to reduce scale loss.
Prior to charge, we smeared the billet surface with normal lime and a better result was observed.
See if this could be of any use. Thanks.
Manikkavasagam Elangovan
– Abu Dhabi, UAE
2003
A. Or, one other option is to grind the whole billet before charging in furnace. This helps a lot because primary scale layer which has been generated during casting will loosen its grip.
kunal juyal
– Punjab, India
August 29, 2014