Welding question (underwater)

[Lucy's Driver]

I need to figure out what welder to buy for work. Basically I need a cheap DC output only stick welder. This is going to be for underwater cutting rods (Broco). Most commercial diving outfits use a high end DC only unit since they use the welder for both welding and cutting, we only need it for cutting. Basically its just like stick welding but you strike the arc and then the stick burns by itself without the electricity, so you tell topside to shut down the power once the arc is lit, then you burn down the rod, put a new rod in, and power it back up just to light that new rod, and cut the electricity again. The rods are basically magnesium straws that you blow pressurized 100% O2 through to keep lit. It needs to be DC only so the diver doesn't get electrocuted (you still get shocked with DC power sometimes but it doesn't kill you). I am told you can just about get the right result using 2 car batteries but it doesn't light as well as with a real welding machine. The cheap buzz boxes I've been looking at seem to output only AC power, am I missing something?

[jasonmt]

I was curious enough to look up Broco and got this out of a little bit of reading:

"6. 150-200 amp 100% duty cycle DC welding power source or 12v or 24v battery."

"Ultrathermic Cutting Rods may be used with a maximum of 150 amps to assist in the burning process but have no electrical requirement."

I would be looking for an inverter machine as they are small and work well on generator power and due to their efficiency also require less input power for the same output power. If you only need 150 amps for short periods to light the rods you could probably get by with a Maxstar 150S (30% duty cycle @ 150A) but if you want to run the rods with the 150A assist a CST 280 (100% duty cycle @ 150A on single phase 230V) would be more appropriate.

I am all for buying more machine than you think you need so I would personally go with a CST 280 as it also allows you to use 3 phase input power as well.

[Lucy's Driver]

Thanks, that's perfect.

Now the only question is can I convince my boss to spend more money and buy one of those combo stick/TIG units.

[Murph]

How much more is the combo unit? If it can be used topside, and you don't have another welder, it should be an easy sell...Even nowadays.

Did you ever take delivery of that International CXT?



Andy

[Lucy's Driver]

Except I'm the only one who knows how to weld, so maybe my superiors would rather farm out jobs to real welders, but I'll work on it.

We ended up taking delivery of a Ford F-750. Not a 4x4, but still a pretty kick ass tow rig. It pulls around a 18,000 pound boat and trailer combo no problem, even with 30 scuba tanks, a compressor, and other heavy gear in the bed. Its got the self leveling airbags in the rear.

Basically picture a semi truck with one rear dually axle built under a one ton pickup truck body. Air brakes, 18 wheeler size tires, huge Cummins engine feeding power into an Allison trans. Pretty cool truck.

Only problem as it came from the factory with a pintle and we had to have a shop cut that off the sub frame and fab up a mount for a pintle ball combo. We also need to put an air over electric trailer brake controller in it to be able to tow the box trailer, which has electric brakes.

[Murph]

Except I'm the only one who knows how to weld, so maybe my superiors would rather farm out jobs to real welders, but I'll work on it.

We ended up taking delivery of a Ford F-750. Not a 4x4, but still a pretty kick ass tow rig. It pulls around a 18,000 pound boat and trailer combo no problem, even with 30 scuba tanks, a compressor, and other heavy gear in the bed. Its got the self leveling airbags in the rear.

Basically picture a semi truck with one rear dually axle built under a one ton pickup truck body. Air brakes, 18 wheeler size tires, huge Cummins engine feeding power into an Allison trans. Pretty cool truck.

Only problem as it came from the factory with a pintle and we had to have a shop cut that off the sub frame and fab up a mount for a pintle ball combo. We also need to put an air over electric trailer brake controller in it to be able to tow the box trailer, which has electric brakes.

One of my neighbors brings home a 4x4 F750 once in a while, and it takes up a LOT of his 6 car driveway :laughing:.


Andy

[scubaman]

Out of curiosity what do you do and what will you be cutting? I recently finished up commercial dive school here in Santa Barbara and had some fun with the broco's. One reason I ask what you are cutting is because there is a significant difference between burning while hot and burning while cold with those rods. They are far less efficient when you kill the power while cutting. I assume you already know that though. As for the power source I would say go for as nice of a unit you can get the boss to spring for and have it for double duty down the line as a topside welder or perhaps to use as an underwater welder if you guys end up doing that stuff. Oh and also remember not to skimp on a good knife switch.

[Lucy's Driver]

I don't think we'll usually be able to cut hot because we will be unable to make a circuit through the work. The work piece will usually be f'ed up. We'll be using a strike plate on a ground line C clamp to get it burning. The rods I burned with when we got trained (forgot type/brand but have records, they were green) let me cut a straight line of maybe a foot or more through 5/16ths steel before they burned down. I also was able to cut part of a heavy vehicle frame underwater that was a good half inch thick no problem. We cut concrete with them but its inefficient.

Basically the cutting will be through destroyed vehicles and collapsed structures - everything from sheetmetal and aluminum skin to rebar and concrete, etc. We have jackhammers and all but its way easier to get the stuff for a Broco unit on site and in the water than a hydraulic power unit.

I know the Santa Barbara school you were at, I was there for a short stretch a year or so ago.

I work for the government. Picture disaster scenes.