Gear quality/manufacturing - How to judge?

[Extreme-Duty]

Finally we received the new gears for our Carraro planetary final drive (we had a locking pin failure). As expected, they are different from the genuine ones. Now the question is whether they are about the same quality or lesser/cheaper. Things I have noticed:

1. They got burrs at the edges.

2. The tooth surfaces show some mildly large diagonal machining marks. Hopefully, they are not "prepitted".

How to tell whether the teeth have been heat treated? Shouldn't there be signs of it at the edges? (The sides/edges of the old gears look semi melted in this area)

I'm so frustrated.

 

[Kestas]

The burrs and diagonal machining marks don't sound good.

You can't tell by looking if the gears were heat treated. You can simplistically check to see if it is file hard by dragging the flat of a file across an innocuous flat surface (top of tooth or gear side). If the file digs in, the gear is soft. If it skates over the surface, it's hard.

Are there signs of any shot peening? What is the country of origin?

 

[Extreme-Duty]

Thanks Kestas,

I don't see any signs of shot peening, it's more like the sides got machining marks too, like small parallel grooves all the way around, you know. The gears are sold by an Italian parts supplier. The bags only show the Case IH OEM number they are supposed to replace, as well as two bar codes.

My file tells me they are hardened to some degree.

As for the burrs, they are small and won't disturb gear meshing, but are dislikeable of course.

Just read some info online. The semi-melted areas on the side of the teeth of the old gears are likely from "gap by gap" or maybe "tooth by tooth" inductive hardening. The new gears are different.

What methods are being used for hardening, and shouldn't the machining mark change with any of them?

 

[Kestas]

Without destructive testing, there's no way to tell for sure how the gears were hardened. Ther superior way to harden a gear is to case carburize, then harden. Tooth by tooth hardening is usually reserved for very large gears.

The machining marks will not change with hardening. The gear is typically machined (cut) before hardening. After heat treat the part may be cleaned of scale by grit blasting or shot peening. Post heat treat machining is usually limited to grinding and honing to final dimensions, though some places now used hard machining.

 

[A_Harman]

If you can take the gear to a local testing lab that has hardness testing machines, you could have some measurements taken at the tips of the teeth without hurting anything. Fully-hardened gears should have hardness of ~60 Rockwell C, or 700 Vickers. (Since you're in Europe, Vickers is used more than Rockwell.) If the gears are tooth-to-tooth induction hardened, they might be soft at the center of the tips, but they would be hard on the teeth flanks or in the roots. If they are carburized, or single-shot induction hardened, they would be hard all over. How big are these gears; OD, number of teeth, width? If the gears have been hardened and then shot-peened, you would be able to see a slight change in color at the ends of the teeth where the peening has deformed the soft core material more than the case.

The large diagonal machining marks that you mention on the tooth surfaces make it sound like the gears were only hobbed, and not ground. How does the appearance of the teeth on the new gears compare to the teeth of the old gears? Do the old gears have similar diagonal marks in the areas that are not worn?

 

[Extreme-Duty]

Good info, thanks.

For now, I would say it's too early to throw away the new gears, just because they are different from Carraro's.

If the supplier is reputable, they deal with trustworthy manufacturers only. Unfortately, the supplier is relatively unknown on the internet.

Isn't there a likelihood of finding reasonable gears in India or Asia?

 

[Extreme-Duty]

Originally Posted By: A_Harman
If you can take the gear to a local testing lab that has hardness testing machines, you could have some measurements taken at the tips of the teeth without hurting anything. Fully-hardened gears should have hardness of ~60 Rockwell C, or 700 Vickers. (Since you're in Europe, Vickers is used more than Rockwell.) If the gears are tooth-to-tooth induction hardened, they might be soft at the center of the tips, but they would be hard on the teeth flanks or in the roots. If they are carburized, or single-shot induction hardened, they would be hard all over. How big are these gears; OD, number of teeth, width? If the gears have been hardened and then shot-peened, you would be able to see a slight change in color at the ends of the teeth where the peening has deformed the soft core material more than the case.

The large diagonal machining marks that you mention on the tooth surfaces make it sound like the gears were only hobbed, and not ground. How does the appearance of the teeth on the new gears compare to the teeth of the old gears? Do the old gears have similar diagonal marks in the areas that are not worn?


1. The sun gear has an O.D. of approx 2", a width of 1.38" and 15 teeth.
2. The 3 planet gears have an O.D. of approx 3.5", a width of 1.18" and 29 teeth.

The ends of the teeth actually show even machining marks and no signs of peening, by my understanding. That said, my experience with this is very limited.

Looking at the old tooth surfaces, I would say they are all shiny, but the gears have been destroyed by the needles that got in between because the planet gear shaft fell out when the locking pin failed. I only have one of the old gears at the office now, it's too damaged to tell a lot. Tomorrow, I will inspect the other planets (The sun is still in the temporarily reassembled axle).

It is to dark over here to take reasonable pictures, so that will have to wait as well.

 

[A_Harman]

Based on my experience, I don't think you have much chance of finding good gears from Asia, especially China. Issues that we take for granted in the west, such as how to harden steel, are still something they're learning over there. Maybe India would be better, but I think you have a much better chance of sourcing good gears in Europe or the US.

 

[Extreme-Duty]

Hopefully, the Italian supplier is able to control what the manufacturer is doing. The reason I brought up India is the tie rod end they sent us, it's made by Talbros, which is Indian. They might have facilities elswhere, though. I don't think we can return the gears, so we might have to swallow another wheel hub loss, who knows.

 

[onion]

Ever notice that you have a tendency to over-think things, ED?

If the parts fit, I'd put it together and use the thing. If you're really worried about it, it isn't THAT much work to take one of those planetary setups apart. Use it hard for a month, then take it apart and see how the parts are holding up. All you'll be out is and hour of tinkering and some sealant... maybe some gear oil.

 

[A_Harman]

Do you have a service manual for the planetary that gives limits on dimensions and clearances? If you're putting it together yourself, and can assure it is being assembled to the original tolerances, you'd have more chance of success.

If you could do a gentle break-in procedure after you get it back together: run the drive at medium speeds and low torque loads for a couple of hours, then drain and refill with fresh gear lube to get break-in debris out of the unit. If you really want to check your work, you could disassemble it and look at the tooth load patterns to see if they are uniformly distributed across the teeth, and with even patterns from tooth to tooth.

 

[unDummy]

I'd debur them with a file or fiber media wheel, or maybe give them a gentle run in a media tumbler, and get them cryo'd. Then, put them to work and cross your fingers. That'll probably double the cost of the gears. But, if there were no other suppliers, then you have to use what you got.

The other option is to use them 'til failure and slam the supplier.

http://www.procryo.com/RemGears.html
http://www.meta-lax.com/
http://www.osro-germany.de/en/products/research-and-development/

 

[Extreme-Duty]

Originally Posted By: onion
Ever notice that you have a tendency to over-think things, ED?

If the parts fit, I'd put it together and use the thing. If you're really worried about it, it isn't THAT much work to take one of those planetary setups apart. Use it hard for a month, then take it apart and see how the parts are holding up. All you'll be out is and hour of tinkering and some sealant... maybe some gear oil.


Over-thinking things? No! Just taking the responsibility for the work I do to the equipment, ensuring to get the best out of it. It is kind of a commitment that goes beyond any warranty by any shop, which is provided for how long? 90 days, 6 month or???

 

[Extreme-Duty]

Originally Posted By: A_Harman
Do you have a service manual for the planetary that gives limits on dimensions and clearances? If you're putting it together yourself, and can assure it is being assembled to the original tolerances, you'd have more chance of success.

If you could do a gentle break-in procedure after you get it back together: run the drive at medium speeds and low torque loads for a couple of hours, then drain and refill with fresh gear lube to get break-in debris out of the unit. If you really want to check your work, you could disassemble it and look at the tooth load patterns to see if they are uniformly distributed across the teeth, and with even patterns from tooth to tooth.


Unfortunately, the Carraro literature is not very informative on things like that. It's mostly like "check for wear" - "replace as required". I plan to break in the new gears at moderate loads and within a few months, I will be taking it apart anyway, because the sun shaft seal and bronze bushing are going to be replaced, as well as the U-joints.

 

[Extreme-Duty]

Originally Posted By: unDummy
I'd debur them with a file or fiber media wheel, or maybe give them a gentle run in a media tumbler, and get them cryo'd. Then, put them to work and cross your fingers. That'll probably double the cost of the gears. But, if there were no other suppliers, then you have to use what you got.

The other option is to use them 'til failure and slam the supplier.

http://www.procryo.com/RemGears.html
http://www.meta-lax.com/
http://www.osro-germany.de/en/products/research-and-development/


The supplier seems slightly unreachable and I can imagine they got some rather expensive lawyers, saying that I am over-thinking things if I am going to ask why the gears did not last 500 or so hrs.

These refining processes you are linking to look just as expensive as a lawsuit. We might just get us some genuine gears at a tenth of the cost. The genuine gears don't even cost much more than the replacements. At about 40 percent more, 2-3 days delivery time and without prepaying, we could have had genuine gears. Too bad I did not find the right Carraro dealer in time.

Needless to say, these replacements are no bargain at all, but we cannot afford not to make use of them.

Also, I would love to tell you about the "prepitted" bearing race they sent us. Maybe, I should just overlook instead of over-think them.

 

[Kestas]

Originally Posted By: Extreme-Duty
Also, I would love to tell you about the "prepitted" bearing race they sent us.

Oooh, please go on. (I'm not sarcastic). Include pictures.

 

[A_Harman]

Originally Posted By: Extreme-Duty


These refining processes you are linking to look just as expensive as a lawsuit. We might just get us some genuine gears at a tenth of the cost. The genuine gears don't even cost much more than the replacements. At about 40 percent more, 2-3 days delivery time and without prepaying, we could have had genuine gears. Too bad I did not find the right Carraro dealer in time.

Needless to say, these replacements are no bargain at all, but we cannot afford not to make use of them.



When it comes to something as highly engineered and difficult to manufacture as a gear, I think it's best to use OEM parts whenever possible. Maybe you can buy the OEM gears as a backup for the aftermarket gears and decide whether or not to use them when you disassemble the planetary in a couple of months. Since you have a concern about the quality, it sounds like you already have a plan to monitor the condition. This is much better than most other people do.

 

[Extreme-Duty]

Originally Posted By: Kestas
Originally Posted By: Extreme-Duty
Also, I would love to tell you about the "prepitted" bearing race they sent us.

Oooh, please go on. (I'm not sarcastic). Include pictures.


No problem:

I hope you enjoy this. I do not! It actually looks worse in reality. At one spot, I can easily feel the grooves with my nails and with a pen. The other bearing we got is not as bad as this one. Either they are poorly manufactured or it's the way they are shipped. They just threw the race and cone together into a bag.

These bearings say something like "FtT" or "F+T" on them, and PF6. Is this a manufacturer you know?

 

[Extreme-Duty]

Originally Posted By: A_Harman
Originally Posted By: Extreme-Duty


These refining processes you are linking to look just as expensive as a lawsuit. We might just get us some genuine gears at a tenth of the cost. The genuine gears don't even cost much more than the replacements. At about 40 percent more, 2-3 days delivery time and without prepaying, we could have had genuine gears. Too bad I did not find the right Carraro dealer in time.

Needless to say, these replacements are no bargain at all, but we cannot afford not to make use of them.



When it comes to something as highly engineered and difficult to manufacture as a gear, I think it's best to use OEM parts whenever possible. Maybe you can buy the OEM gears as a backup for the aftermarket gears and decide whether or not to use them when you disassemble the planetary in a couple of months. Since you have a concern about the quality, it sounds like you already have a plan to monitor the condition. This is much better than most other people do.


Lesson learned, I guess. Why is it I always get into situations like this? It seems I gotta double check myself and others all the time.

Originally Posted By: A_Harman
If you can take the gear to a local testing lab that has hardness testing machines, you could have some measurements taken at the tips of the teeth without hurting anything. Fully-hardened gears should have hardness of ~60 Rockwell C, or 700 Vickers. (Since you're in Europe, Vickers is used more than Rockwell.) If the gears are tooth-to-tooth induction hardened, they might be soft at the center of the tips, but they would be hard on the teeth flanks or in the roots. If they are carburized, or single-shot induction hardened, they would be hard all over. How big are these gears; OD, number of teeth, width? If the gears have been hardened and then shot-peened, you would be able to see a slight change in color at the ends of the teeth where the peening has deformed the soft core material more than the case.

The large diagonal machining marks that you mention on the tooth surfaces make it sound like the gears were only hobbed, and not ground. How does the appearance of the teeth on the new gears compare to the teeth of the old gears? Do the old gears have similar diagonal marks in the areas that are not worn?


One question: If these diagonal marks were from hobbing, shouldn't they all point in one direction?

No matter how I look at the gear, and how I turn and flip it around, if I follow the marks from the tip to the root, they always go from left to right.

 

[A_Harman]

If the machining marks on the teeth go from the tip to the root, then the gears were probably made using a milling cutter, and not a hob. This is not necessarily a problem, but it does mean that the tooth profiles will not be true involute forms closer to the tips and roots. What it does mean is that the gears should only be mated with ones that were made with the same cutters.

It's sad about those bearing races being pitted when you got them out of the box. It's like they've already failed.