[MW:8841] MW:8825- what is TRAILING SHIELD ?

Dear Aslam,

Training shield is required for GATW of reactive materials such as Titanium, Zirconium. The purpose is to shield the cooling weld and HAZ from hydrogen and other gas related embrttlement. For these materials weld and HAZ are quite reactive till 400 deg C, hence use of trialing shields are necessary. Usually it consists of the same gas or may be a  different  mixed gas (as proposed in the WPS) to protect the weld and HAZ as stated above.

You don’t require such devices for other materials , both ferrous  and other common  non ferrous materials. See below the illustrations from QW-256 on the trialing shields/gases.

You may engage multiple welders  for SMAW, such as welding of large diameter pipes. However two welders feeding electrodes on the same (common) weld pool would be difficult to implement, due to inconveniences to the welders and the difficulty in separation of slag and weld metal ,this would cause heavy slag entrapment.

Thanks.


Pradip Goswami,P.Eng.,IWE.
Welding & Metallurgical Specialist & Consultant
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net

     

-----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of aslam khan
Sent: Sunday, December 19, 2010 11:20 PM
To: materials-welding@googlegroups.com
Subject: [MW:8825] what is TRAILING SHIELD ?

HI FRIENDS,
GOOD MORNING !
IN WPS  GAS (QW-408) IT IS WRITTEN TRAILING SHIELD, CAN YOU SHARE YOUR KNOWLEDGE ,WHAT IS TRAILING SHIELD ?AND TECHNIQUE (QW-410 ),IT IS ALSO BE WRITTEN MULTIPLE OR SINGLE ELECTRODE, IS THERE ANY TECHNIQUE BY WHICH WE CAN DO WELDING OF SMAW AS MULTIPLE ELECTRODES?

THANKS IN ADVANCE
REGARDS
ASLAM

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