Repair or replace cracked boom???

[Tugger2]

This technique of doing a small weld fill on the run out ends worked well for me on reinforcing plates and thumb mount bases. We would gring and polish the ends of the weld without digging into the base metal. I always used plug welds ,oval or round in the centre of the boom with assumtion you were welding in the neutral axis of the box. The idea came to me from the method Hitachi used on Cyl lugs and reinforcing cover plates. We cut up brand new machines and made them into high walker log loaders,back in the days of UH16 s and 181s. John deere guys came to our shop and said it wouldnt work so well. Look at them now. All that said i would not be afraid of repairing that Case boom.Ive repaired much worse when loggers i worked for started road building with 245 Cats

 

[skyking1]

That was the first broken boom I saw a 245 cat. When it broke off and flopped into the terex, it broke all hydraulic lines and sprayed oil all over too.

 

[terex herder]

Another snippet is that Cat booms are manufactured from A572M steel and have been for around the last 20 years to my knowledge.

Nige, there should be a grade number after the A572 to define the strength of the steel. Any idea of the grade?

 

[Nige]

Nige, there should be a grade number after the A572 to define the strength of the steel. Any idea of the grade?

I agree, but I would need to go looking to find it.

 

[Nige]

OK, so I went digging into the specs. It's a low-carbon steel, 0.22% or less for rolled plate. (Slightly different carbon % for bars & other structural sections).
Steels meeting ASTM A572 or A572M specification of either Grade 42 or Grade 50 are an acceptable replacement for the OEM material.
The minimum yield strength requirement is 290mPa (42k psi) which I would imagine would be the equivalent of the Grade 42.

 

[John C.]

Cheap stuff. Mild back in the day was 60K yield. So basically use any steel you want on a Cat boom. I know for a fact that you can use any mild steel you want on Sumitomo booms and sticks.

 

[terex herder]

Thanks Nige. Here in the States Grade 42 would be the next step up from A36 (36K psi yield strength). No special welding fillers or post weld heat treating should be necessary.

 

[Tugger2]

Always figured on 50000 yield. Those 245 s introduced me to broken boom ends, broken boom foot ears and a torn off rotec . As a yougster i managed to bushwack them all back into operating condition

 

[Welder Dave]

Thanks Nige. Here in the States Grade 42 would be the next step up from A36 (36K psi yield strength). No special welding fillers or post weld heat treating should be necessary.

With the heating and cooling and stress from such an extensive repair stress relieving would never be bad idea. Not all pressure vessels are stress relieved but critical ones are and it's the 516-70 boiler plate.

 

[Welder Dave]

Should say same boiler plate and depends on thickness. Some booms are stress relieved from the factory. I would think current booms use thinner but stronger steel than older machines to save on weight and weld size, etc.

 

[Pettiboner]

Take advice at face value from Welder Dave. He knows his stuff. He helped me along with repairing my broken yoke on my old beast. Still going strong without any issues.

 

[Willie B]

When machinery manufacturers use high strength steel & sophisticated welding & normalizing procedures it makes it more difficult to repair. It also makes the probability of a re break greater.

 

[John C.]

This stuff isn't rocket science and there are no exotic materials being used for mass produced machines that have to be competitively priced. 36 or 42 thousand PSI tensile is not high strength steel. There is nothing fancy in any manufactures' booms and sticks on excavators. Their strength is in their design and workmanship and not in the materials they build them from. I have yet to hear of any manufacturer state any kind of welding rod other than 7018 or similar for repairing booms or sticks. The only preheat used is to drive out moisture before welding and I've never seen a specification for post heat.

 

[Tugger2]

The Case backhoe booms that are made from ductile iron are the only ones out there ive seen that are a problem to weld. Im not sure why they would go with throw away stuff like that.

 

[John C.]

Cheap, and built to stay that way!

 

[Bluox]

This stuff isn't rocket science and there are no exotic materials being used for mass produced machines that have to be competitively priced. 36 or 42 thousand PSI tensile is not high strength steel. There is nothing fancy in any manufactures' booms and sticks on excavators. Their strength is in their design and workmanship and not in the materials they build them from. I have yet to hear of any manufacturer state any kind of welding rod other than 7018 or similar for repairing booms or sticks. The only preheat used is to drive out moisture before welding and I've never seen a specification for post heat.

I'll bet you even know what a whale tail is. Kinda obvious you are one of the few people on this thread who has actually welded on a boom. I'll bet a couple of these sexual intellects has never even struck a arc on one.
Bob

 

[Willie B]

I'll bet you even know what a whale tail is. Kinda obvious you are one of the few people on this thread who has actually welded on a boom. I'll bet a couple of these sexual intellects has never even struck a arc on one.
Bob

That'd be me. I never said I did. That doesn't mean I don't want to know. I'm not in a place where I'll ever have that opportunity. I see so many machines rendered useless by some hammer head with a stick welder, no grinder, no gouge. They step up with 6011 and gobber over the crack. In what world will that work?

I don't pretend to know how, but observation has shown me how not to do it.

 

[Pettiboner]

This stuff isn't rocket science and there are no exotic materials being used for mass produced machines that have to be competitively priced. 36 or 42 thousand PSI tensile is not high strength steel. There is nothing fancy in any manufactures' booms and sticks on excavators. Their strength is in their design and workmanship and not in the materials they build them from. I have yet to hear of any manufacturer state any kind of welding rod other than 7018 or similar for repairing booms or sticks. The only preheat used is to drive out moisture before welding and I've never seen a specification for post heat.

Pre heat has never been easier with the price of infrared thermometers at $50. Pre Heating the surrounding steel to slow the cooling of the weld immediately after laying the bead is the cheapest insurance you can buy against cracking. Throw some insulation over it when your done to further slow the cooling. These are cheap and easy precautions. It makes no sense NOT to do them.

I would repair that boom. But then again, I do a lot of stuff others wouldnt!

 

[Welder Dave]

Maybe someone can explain why booms on mining excavators are stress relieved? Taking extra steps to ensure a good repair is never a bad idea. All the welding has to put stress in the boom. Stress relieving makes the grain structure as close to if it was 1 piece as possible. Repairing it similar to if were a critical pressure vessel is the best way. Price out a new boom for giggles.

 

[Welder Dave]

Take advice at face value from Welder Dave. He knows his stuff. He helped me along with repairing my broken yoke on my old beast. Still going strong without any issues.

Lucky guess according to some I suppose but what do I know. First picked up a stinger in 1980.