Build up welding of a gear tooth. 1

[0theblacksmith0]

Following a tragedy inside my Hino truck gearbox,and a fruitless hunt for parts, I have decided I have no option but to build up-weld the chipped/missing teeth. I was planning to tig weld(after a pre heat) with a filler rod for dissimilar steel that work hardens and is machinable. As welded tensile strength is around 180,000psi. Not sure if gear is case-hardened or fully hardened as one entity. The repairs are quite small and can be welded up in a relatively short time,but Id rather weld a small layer and leave for a while just to keep interpass temps down.
I saw one great idea in another forum regarding machining the teeth to the right profile-he made a 3 sided mold against a healthy part of the gear and poured molten lead in there which gave him a perfect copy of the teeth he needed to match.I can see this part of the job taking a bit of time and engineers blue.
If any of you guys can share any experiences or other suggestions Id love to hear from you.Thanks in advance.

 

[metengr]

Why don't you have the damaged gear reverse engineered? Weld repair is a poor decision and requires an understanding of the gear material chemistry and heat treatment. Without this information you might as well use coat hanger wire to weld the missing tooth. There are plenty of gear shops that can easily reverse engineer it.

 

[connectegr]

You may want to find a machinist to make a new gear. If the material is quenched and tempered, the welding will make the material brittle in the HAZ. Cosmetically your welded solution will work, but repair may not be adequate for the stresses.

http://www.FerrellEngineering.com

 

[0theblacksmith0]

I have priced up making a new gear and it was more than a second hand gear box and the cheapest of them I could find was NZ$2000 + gst(with NO warranty).A new gear alone from Hino $1462+tax.Welding it is not a problem-or profiling it-but the HAZ as you guys mentioned is.Maybe I should look into heat treatment after welding.I have made several tools in the past and quenched and tempered them and they are still strong today.I came accross some really good tempering charts on the internet a while back- I will have a rummage through my bookmarks folder as well.Thanks for the input.

 

[MiketheEngineer]

Spend a lot of money welding it and re-installing only to have it fail two days later.

Somehow - get a NEW gear. Find it or have re-made.

BTW - what is a Hino?? A neutered Rhino??

 

[gtaw]

Try it. What have you got to lose? The gear is scrape as it is. The vehicle can't move without the gear. The worst that can happen is that when you put it back together, the gear will shatter and destroy the entire transmission.

Best regards - Al

 

[cloa]

http://www.hino.com/

Hino Trucks part of Toyota.

 

[dinjin]

I know you are going to go ahead and do it but do keep us posted as to the resulting life. This is the kind of data that is lacking. Farmers in the past did a lot of welding and building up parts in their own shops. Lots of luck.

 

[0theblacksmith0]

I will dinjin. As you said -lots of farmers and quarry/mine fitters have welded stuff like this. I used to be a rep for Strata - Repair and Maintenance Alloys, and have demonstrated their product to many a fitter and engineer, with great results.
I'll keep you posted how it all goes,thanks.

 

[swall]

There are some welders that specialize in TIG welding of broken/worn dies. You might seek one out and see what he might be able to do with a weld build up using a tool steel filler rod. Then re-heat treat the gear after final machining.

 

[Guest102023]

Get some new gears, or better, an entire gearbox from a recycler.

Disregard all of the internet blacksmiths amd self-styled metallurgists who may claim there is a miracle cure for damaged gears.

 

[0theblacksmith0]

Welded the 3 teeth that were damaged(preheated gear and kept heat low during welding and a little post heat),die grind-ed them to shape(only option)then filed and used a fine abrasive slipstone to finish off..Changed all bearings in the gearbox and seals and after assembly made sure teeth were meshing properly and finally got the gearbox back in the truck around 4 pm today. Then went for a 70 km drive with a 3 tonne excavator on the back. No problems.No one has a gearbox in the country. Truck is an used Japanese import.The welding rod I used was an Euroweld 507.(Formerly Strata 507)120,000psi tensile strength as welded. easy to machine.
Thanks for all your input,Im a happy camper.

 

[Guest102023]

Congratulations, but post back here in 6 months.

 

[Tmoose]

What gear was busted? second, third or ??

 

[0theblacksmith0]

Third gear and the matching gear on layshaft(countershaft).

 

[dinjin]

I hope you also used dye pentrant or some method of checking for cracks. Glad you got it off the ground and on the road.

 

[MiketheEngineer]

I too want to know how long this lasts!!

 

[Tmoose]

I wouldn't use much throttle while in 3rd gear, or spend much time there. It won't take but a couple of hours to accumulate 1,000,000 load cycles on that tooth

 

[BillPSU]

Welding the gear is an extreme welding process. You will distort the remainder of the gear and have to deal with this distortion in the bore of the gear. The gear is made of 8620 or 4140 or material similar. Preheat to 350-400 degrees before you weld.

Now say you get past this now you have to machine the involute in a helical gear. You could take the gear to a gear shop and have them grind the involute.

Go ahead try your best and then either have a gear made or find a used transmission overseas or just scrap the truck.

Gear shops invest millions of dollars for gear hobs, gear shavers, gear shapers, ID and OD grinders and inspection equipment.

I am sure you can hand produce a usable gear without any equipment.

 

[chicopee]

I hope he picked up all the pieces within the gear box.