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Chris Parks
1st Sep 2007, 08:55 AM
I was at tech the other night doing a 6 run downhand butt weld (MIG) when the clear perspex front lens on the helmet melted, in fact I had three of them melt. The old ones were a lot thicker than the new ones and I wonder if anyone else has had the same problem. BOC Wollongong reckon I am not the first too complain about this. I suspect it is a MIG only problem as you have to get very close to the weld to see what is going on, where as with stick you don't.

Big Shed
1st Sep 2007, 09:25 AM
What number lens are you using? If you have to get that close it sounds to me that the lens is too dark. Not a welding expert by any means, but I seem to remember that stick needs a darker lens than MIG, 11 vs 13?

Perhaps you are using a stick lens for MIG?

Where is Graeme Collins when you need him?

Wood Butcher
1st Sep 2007, 09:43 AM
Big Shed is Right. If you have to get your face that close to the weld that it is melting your lens then get a lighter lense. I use a no 11 as a general rule and only go for no 13 if doing high amp arc welding.

Also ask if you can get a glass lens if it really bothers you. I don't use them much but especially when doing overhead welding the glass lens doesn't get ruined from the shower of sparks that come down on you.

Chris Parks
1st Sep 2007, 10:05 AM
This is where everyone falls down with mig. If you have the angle right and if you want a good even sized weld you have to get in close, half the time unless you are looking across the weld you can't see it because the torch has such a short arc and covers the weld pool. Doing multi run welds of this nature you have to be very close to see how the welds are overlapping. With stick the welds tend to be wider and the flux flow gives a better indication of weld pool size. If you use a lens that is to light there is no contrast only glare. Believe me when I say that you have to be close you really do need to be, this is structural welding tested by breaking the welds to monitor penentration, not stick it together and it looks alright stuff.

wheelinround
1st Sep 2007, 11:02 AM
Unless MIG has changed since I last used it some 15 years ago I can't recall having to get that close to the weld.

All the years of welding bus frames with MIG standing on floor frames while reaching up at arms length :no: never melted a Glass shield. Maybe thats it we used to use Glass not plastic spater does stick but at least it wont melt.:o:oo:

I will admit you have to get close and personal with mig its like trying to hang on to an unco-operative child compared to hanging on to or letting a snake wrap around your arm like with stick

Grahame Collins
1st Sep 2007, 01:35 PM
I was at tech the other night doing a 6 run downhand butt weld (MIG) when the clear perspex front lens on the helmet melted,

is. I suspect it is a MIG only problem as you have to get very close to the weld to see what is going on, where as with stick you don't.

Hello Mini and everyone


A run D/Hand Butt
Yikes! Usually 16mm thick plate and up requires that number of runs to fill. In turn that means a lot of heat is generated. That heat could indeed melt your clear cover lens if you are close .I have seen it in a couple of guys who later fixed the problem via the optometrist

With respect ! I strongly suspect that you are far too close to the arc because you may need a change in script for your glasses.
Problems in clearly seeing the arc comes to most welders at around 40 years or so. My script changes with my B pressure.

I sneaky way around it that I have used is grab some of the reading glasses at the chemist.They are marked 2.00,3.00 3.5 power and try reading some text at your normal focal length for welding. Also a diopter lens helmet insert is available in those various powers through the welding supplies people.
I am not suggesting it takes the place of an eye test and script, but it sure gives one a perspective on the problem.

I feel that will go a long way towards improving your problem.
Have a great week end.
Grahame

Chris Parks
1st Sep 2007, 08:07 PM
This is on about 10mm plate using 6 runs and a big V prep. Now if you weld at the correct angle (which most don't) to contain spatter, the torch is held at about 80 degrees. This means the torch on a short arc covers the weld pool as seen from above so you have to get down and look into the weld pool under the torch. When you start doing multi runs you have to place the weld metal in the correct place, so yes, it is necessary to get in close. Remember also you are welding right to left not left to right as in ARC and you cannot see anywhere near as much as ARC. This is the technique taught these days. When I did a short MIG course 25 years ago they were not even advocating out of position welding at all, new machines were just being introduced at that time so pulse techniques could be used to overcome this.

Grahame Collins
1st Sep 2007, 10:39 PM
Mini,
I think you may be misunderstanding what I am trying to point out.
I believe that your lenses could be melting as your helmet is too far close too the welding arc, because the focal length that you currently view the weld with is too short in distance.

The focal length of the average height welder would run somewhere between 450 to 600mm, visor to weld arc, with bench height also as a consideration.

Those people that have problems with seeing the arc clearly ,tend to stoop and move their head in close in and in some instances melt the welding helmet or lenses.

I had thirteen years as a Tafe welding and Metalfab instructor,teaching all processes of welding to As 1796 levelIn that time I taught many hundreds of students to weld,so I saw the problem fairly regularly.

What level of GMAW course are you doing? It was that six passes seemed excessive.I am just curious , not trying to stir up trouble. Are the cap beads 4 passes wide?

Grahame

Chris Parks
1st Sep 2007, 10:59 PM
The exercise is six passes as laid down by the syllabus. I and my son both attend this course and it is a certificate course over 6 months. Believe me when I say that MIG is taught totally differently to the way it was in the 70's which is roughly when I last did it. The method now is how I described it, get low and look across the weld pool as it is impossible to see it any other way doing it with an upright torch, you just can't see the weldpool and you need to be spot on with the covering runs. The reason for the very upright torch is to contain spatter and to combat that you need a very short arc to the extent that the torch is just about dragging on the parent metal. It is totally different to what I knew and this is being taught by a person who is currently working in the industry and knows what is needed. To do all this you absolutely have to stoop over the job, there is no other way. Stick can be welded at arms length in total comfort, this stuff is hot and not nice.