Billet de-scaling before forging 3

[arash66]

Hi all,

we are looking for an effective method of billet de-scaling or protecting coating to minimise the scaling of the billets before forging.
our forging temp is normally around 1200C (steel). currently we are using rotary de-scaler which same as the coatings we use is not very efficient.
has anyone have any experience to share?

Thank you in advance.

 

[TVP]

How are you heating the billets? How long are the billets at temperature before forging? Acheson (Henkel) and Renite supply very good billet coatings for hot forging:

http://www.henkelna.com/us/content_data/176842_LT5703_Forging_Lubricant_SS395657.pdf

http://www.renite.com/metal-sum.htm

 

[Wrenchbender]

I've seen high pressure air blast used for descaling steel billets in both open-die and closed-die press-forgings.

 

[arash66]

thanks for the reply guys, the heating mechanism is gas furnace, the time is different as we forge diameters as small as 90 mm to diameters as big as 450 mm.

Wrenchbender, our billets are not necessarily big to maintain the heat loss due to the air blast, do you probably know how much is the temperature drop?

 

[Wrenchbender]

I don't exactly know. For relatively small parts, I would dare say the convective temperature drop of the workpiece from a momentary blast of air is no more that of conduction loss to the die pot or the ram. (Speaking for closed die forgings.) I think pyrometer measurements and experimentation would be the best approach.

 

[BMKR]

Why exactly is the scale an issue? Once you press the billet the scale should break off, I am just having a hard time figuring out why you would need to descale it. We Forge everything from 1020 to Incos and we do not descale, then again we do open-die forging.

 

[redpicker]

Scale can be a very serious issue with closed die forgings where you need tight dimensional control. With closed-die upsetting operations, it can also lower the friction between the die and metal needed to prevent surface defects from forming.

I have seen lots of methods proposed and used. Most of them employing a air blast. A previous employer looked at a high-pressure/low volume water (2-4 KSI) system, but did not purchase it. The two most common methods I've seen are either the "do nothing method", where you do nothing and just deal with the result by adding extra material to the forging dimensions, or the "bump and blast method" where the material is given a brief upset by the press accompanied by a high pressure air blast prior to the forging operation. The loss in temperature is kept to a minimum by limiting the duration of the air blast.

I have also heard of protective atmospheres and other techniques that I guess have been successful for some materials, but I believe their cost is prohibitive for steel forgings. It's just cheaper to deal with the consequences.

rp

 

[EdStainless]

In flat rolling the billets are high pressure water descaled entering the first rolling stand. There is no measurable impact on the slab temperature.
It works because you force water under the scale and then let the steam blow it off.

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Plymouth Tube

 

[rmw]

The only forging operation I ever had experience with used air. But then again we forged the same size billet every time and many times per hour so the air blast set up and mechanism never had to change.

rmw