thrumming in harness MIG / GMAW

Hello all
Upgraded torch / gun from some "Crapomatic" to Tweco #4 Classic.
Tweco doesn vastly better than the "Crapomatic", but still sometimes get this very characteristic problem - the torch and harness vibrate, and the wire "judders" coming out of the torch. What are the likely causes?
What do you do to avoid this happening?
Rich Smith
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Wire 1.2mm, which is .045".
The nozzle is quite small - something like 5/8inch. The copper has gone a dark chestnut colour. Not perceiving nozzle as being a / the problem - but could be mistaken.
BTW - like the Tweco nozzle mounting, where can slide the nozzle up to get contactor tip level / protruding for dip-transfer, then slide it out to recess contactor tip for spray.
Gas is Ar-20%CO2-2%O2. Suspect that need more voltage than you'd otherwise use, to get a spray-ish transfer.
Currently running most of the time at around 290A to 300A.
Anything else you'd find useful to know?
Thanks in advance, Rich
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I'll take a guess at the copper tranish has something to do with your problem. You can get little pads that slip over the wire just before the drive rolls and wet them with wire lube.
I normally spray transfer with .045 wire and my machine maxes out at 250A your current seems high to me. I use 92% Ar - 8% CO2 mix maybe that explains it.
Keep the cable as straight as possible from machine to gun and see if that helps.
Not nozzle size, but check wire and contact tip size.
Remove 333 to reply. Randy
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Could it be a drive motor issue or a mechanical issue in the rollers. Can you zero in on when it happens?
ie: Could it happen when you are near the maximum duty cycle or near max capacity? Is there a bad bearing that doesn't like a particular wire speed?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sure it's none of these.
I think the gas is the main culprit. As I mentioned elsewhere, they are forced to stay with Ar-20%CO2-2%O2 because this is the only type "the dippy weavers" can use.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Like Randy said the current may be too high. The wire can burn back to the contact tip, then it has to touch the work again in order to establish an arc and so on. There could also be dirt in the whip, you didn't say if you replaced that also. A couple years ago I got a new auto dark hood and it was so much easier for me to see through than my existing hoods that I was able to see the spray transfer happening in the arc for the first time. The end of the wire would enter the arc and vanish while at the other end of the arc I could see the bead forming on the work. Can you see the arc well enough to see whether the wire is doing this? Eric
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@whidbey.com writes:

Hi Eric, all
Sorry slow back to you all - family around and peak of summer heat-wave (always of short duration) here - my apologies for swimming in the sea all the time (!)
"... could also be dirt in the whip, you didn't say if you replaced that also. ..."
"whip" - that's a North American term. Which part of the setup is that? I must know it, but by some different name or it has no specific name at all here.
Current matches job - correct flowing-in / wetting-in of weld to plate. Getting pretty neat 45deg mitres. Wire feed isn't perfect, and sometimes get burn-back when stop - so won't easily restart. Or there is a pause then the wire pops-out with a lump of spatter which had build-up on the tip of the contactor tip.
The exasperation has been this gas is totally unsuitable yet the company would not change it. They had to provide for "the dippy weavers" who are the predominant category of welder here. Reckon it's disappearance of Trade training here - what remains is people passing on bad historical habits, where if you had colleges they could teach both old and new techniques, with in general people moving on with the times. So it might be that no sense will ever be found.
I'm moving jobs - new start on Monday. They use a gas which supports spray.
You never (??!) see clean spray with 20%CO2 argomix. The well-formed spray-cone is beautiful to see, I'll agree with that.
I so wish I could use 92%Ar-8%CO2.
The contactor tip size matches wire size, as does the guide-tube, etc.
I've been driven mad by spatter with the setup including 20%CO2. The worst problem is at around 6mm (1/4-inch) thickness. Dip is not energetic enough, especially is you simply was to melt-out / burn-out the mill oxide - yet spray with 20%CO2, at the lowest current giving a spray-ish transfer, throws out huge molten globs (vision of a volcano spewing out lava-bombs!) - which causes far too much trouble. So you have to grind to silver and dip - agonising slow and completely stupid for these low-value rough-and-ready fabrications.
At lower than 6mm thk., dip is fine. At great than 6mm thk., you can get into a fairly clean spray. But right on 6mm - it's enough to make you turn green and grow to some improbable height ("the Incredible Hulk") with your exasperation and rage.
Anyway, out of it now.
Regards, Rich Smith
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Keeping the harness / cable as straight as possible / one smooth curve is vital or it won't work, that's for sure.
I got the thrumming to more-or-less disappear. Don't know which attention to detail was the magic one - or whether it all worked together.
* more shielding gas flow for more torch cooling * change contactor tips more often * clean everything and try to make everything work as well as it can
As explained elsewhere, out of that employer now.
Regards, Rich Smith
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.