304 MAG welding issue--black layer (slag)

Date 11-13-2012 16:18

Hi, Everyone,

A thin black layer (like Slag) on stainless steel 304 MAG weld face, sometimes, is difficult to prevent. But, this will endanger the fuction of our product. I have to get rid of it from welding quality control side or mechanical cleaning afte welding. The process employed is MAG pulse welding, Mixed gas+wire.

Questions:
1, I changed the Mixed Gas, but it did not work. Should I also check the Wire?
2, How to remove the black layer? It is very difficult to remove it thoroughly by wire brush, is there any other good power tool to remove it? How about Needle Scaler?

Waiting for your suggestion.

Many thanks.

By jd369

Date 11-14-2012 12:40

Hello

By jd369

Date 11-14-2012 12:45

Hello
I do a fair bit of GMAW on 316 and 304 ss at my shop. The black scale on top is normal. It usually comes off with a ss wire wheel on an angle grinder. I also use smaller wire wheels on my die grinders without any issues. I'm currently using a 98/2 gas mix of Argon/CO2 at a flow of 35-40 CFH. The wire speed is between 425-475 and voltage is 24-25 depending on brand of wire. I'm running 0.035 diameter. I'll attach a before and after picture of the results. You can see the black scale along the center of the weld in the before pic.Hope this helps.
Regards
Jim

Attachment: 316sselbowaswelded.JPG (169k)

Attachment: 316ssElbowWireBrushed.JPG (194k)

By 46.00

Date 11-14-2012 13:26

allenliao, is jd369's pictures showing what you are trying to describe?

By allenliao (*)

Date 11-14-2012 15:27

Hi My friend,

I think the scale in picture is due to oxidation reaction of weld metal?

But the scale on my welds is a bit different from this picture. Mine looks like GTAW weld scale, which is thicker and very hard to remove after weld metal cooled.

I will get the pictures from my supervisor to asist to explain this.

Thanks.

Attachment: QQ20121116125111.gif - Pictures of MAG "slag" on weld surface (84k)

Attachment: QQ20121116125032.gif - Pictures of MAG "slag" on weld surface (79k)

By allenliao (*)

Date 11-16-2012 05:28

Hi, Jd369,

Please refer to the attachments of MAG "slag". The result we want to achieve is a very thorough cleanliness before pickling,which our product "clean air system" demands.

Two options we can use to hit the aim:
1). Prevent this defect by improving welding procedure/process.
2). Or using special tools to clean this defect effictively at hard-to-reach area, like corners.

Needle or Chipper Scaler are considered to use, but the unwanted consequence is a rough profile it will produce.

Thanks.

By ssbn727 (*****)

Date 11-16-2012 06:53 Edited 11-16-2012 07:07

Hi allenliao!

Could you please explain what is the procedure you use to prep the product prior to welding?

I ask this because it seems like the residue is originating somewhere within the weld prep of the joint with respect to the treating of the material during/after pickling/passivation or visa versa... There may also be a need to improve on your weld parameters for GMAW-P (MAG) and, what gas mix will work best for your application.

Could you also give us more details regarding both materials thicknesses and weld parameters and then we may be able to give you better recommendations to help you with your problem... We cannot help you in any precise manner without more information allenliao.

Respectfully,
Henry

By jd369

Date 11-16-2012 18:43

Hi Allenliao
I would have to agree with Henry that more information is required to make suggestions. I have given you my parameters for GMAW of stainless steel, if you could share yours we may be able to make some suggestions. I would like to see your wire speed, voltage, type of gas and flow rate as well as the manufacturer of the weld wire and diameter. As a side note I would recommend to remove the scale while the material is still hot after welding, it does come off much easier.
Regards
Jim

By 99205

Date 11-16-2012 18:49

I tend to think it may be a gas issue, also.