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[MW:5564] Re: POAK MRKS ON SAW WELDING

By Materials & Welding

Hello Mr. Masthan,

Te correct word is "Pock Mark". It's commonly found with high Mn-silicate low basicity fluxes.Lincolnweld- 865 is a general purpose flux,with basicity of 1.0-1.3

High quality, and highly basic fluxes (Basicity 2.7 and above) will hardly produce this defect, unless  they are properly baked,or  reused or recycled.Recycled fluxes will have too many fine particles which will hinder the passage of gases on the flux layer. Ideally the gas pockets should all be entrapped in SAW flux layer. Following is the illustration from ASM Metals Handbook on this problem.

The SAW slag must be fluid enough so that it flows and covers the molten weld pool but must be viscous enough so that it does not run away from the molten metal and flow in front of the arc, leading to possible overlapping by the weld metal. It has been reported that if the manganese silicate flux viscosity at 1450 °C (2640 °F) is above 0.7 Pa · s (7 P), a definite increase in weld surface pocking will occur. Pock marks have been associated with easily reducible oxides in the flux, which contribute oxygen to the weld pool. The weld pool reacts with carbon to form carbon monoxide, which cannot be transported through a high-viscosity flux and is trapped at the liquid-metal/flux interface. The result is a weld metal surface blemished by surface defects or pocks. Because viscosity is sensitive to temperature and thus heat input, pocking can be the evidence that a flux formulated for high-current welding is being used at too low a current or too great a travel speed.

A few suggestions to reduce this problem:-

  • Reduce travel speed, to allow more time for solidification and gas entrapment at the same operating current. You may need a few trials to get the correct operating parameters.
  • Remove surface scales or dirt, because they also generate gases.
  • Check the condition of fluxes, if it's too old with a lot of fines, sieve, and get rid of the fines.If fluxes have too many fines, talk to manufacturer.
  • Last of all, if all solutions fail, change to basic fluxes (which generally have more deoxidizers). However welding productivity may be hampered, because basic fluxes are not high speed fluxes.

I attached a few illustrations to the above problem.Hope this would help you.

Thanks

Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of sreevalsan sreedharan
Sent: Saturday, June 12, 2010 1:12 AM
To: materials-welding@googlegroups.com
Cc: lakshmankumar4@gmail.com
Subject: Re: [MW:5548] Re: POAK MRKS ON SAW WELDING

HI
 
POCK MARKING OR SLAG STICKING
FOR MORE DETAILES PLS CHECK ATTACHMENT
 
S.SREEVALSAN
ABUDHABI


 
On 10 June 2010 20:49, lakshman <lakshmankumar4@gmail.com> wrote:
hi,
dear all,

shall i know what is a poak mark,
anybody having the photo of the same.

Thanks & Regards,
Lakshman

On Jun 9, 11:18 pm, "masthan" <sabreenbah...@hotmail.com> wrote:
Hi

We are continuously facing problem of Poak marks on the SAW Welding surface.   Welding Consumable L-61 (wire) with 865 (flux) combinations. Any body has    idea to prevent this. Please share.

Best Regards
M.Masthan

K.S.A

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