AGMA 8 Manufacturing of helical gears 3

[jarimasen]

Greetings gear people,

I am asking a gear vendor to provide me with a set of helical gears. And although I am not specialized in gears I seem to remember that the pinion and gear shouldn't be from the same material (I also consulted Mark's Handbook) and I asked the manufacturer to comply with a manufacturing standard for this type of gear and he mentioned AGMA 8.

I have been trying to find this standard and couldn't find relevant information about it (visited AGMA page). So I have several questions that I think the forum, with the infinite wisdom it possess, could answer me:

What is the Std for helical gear manufacturing (150 HP, for mining)?

Does the Std AGMA 8 exists?

Should the material be different in pinion and gear?

What should be the steel strength for both gears (vendor says is the same for both 45 to 50 RB)?

Is there a hardening treatment used for tooth surface? (I seem to remember there is)

Do you know where can I find useful information on this matter?

 

[gearcutter]

AGMA 8 is a quality rating.
It comes from the, now obsolete, AGMA2000 quality rating standard.

The questions you are asking suggests that you are new at transmission design.
If the transmission you are attempting to design is for a mining application then I would highly recommend you employ the services of a Gear Design Consultant.
There are several listed on the AGMA website.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[PeteDB]

The pinion and gear can be the same hardness but often the pinion is made harder than the gear because it is usually smaller and sees more cycles than the gear and making it harder help to balance rating between the pinion and gear.

You did not describe what mining application you are getting your gears for so I will mention some standards that may apply.

AGMA 2001 is the general standard for rating gears. AGMA 6013 is the "Standard for Industrial Enclosed Gear Drives" and AGMA 6014 is use for "Gear Power Rating for Cylindrical Shell and Trunnion Supported Equipment". One of these latter two may be what you want your gears to be rated to. They both reference 2001 and other AGMA standards.

 

[jarimasen]

Thanks gearcutter and PeteDB... You are right I am not familiar with transmission design at all (I had hoped it wasn't that evident...) That is why I am asking a company who designs and manufactures gears to help me with this.

I am a plant engineer and I have a real old gearbox that is used for a overhead bucket crane. The pinion and gear in the gearbox are very worn, and I want to have it made. The problem is that the gearbox doesn't have a part number (I doubt if it is original) and the equipment is very old. So I am asking the gear manufacturers to take the samples (I have a spare) and make the gears from there. But I do not know what material should I use or what standard should I ask them to look into.

They should know this already (the gear manufacturers), but I want to make sure...

 

[mfgenggear]

jarimasen

it would be simple to reverse engineer the gears.

Have the gear shop do an unknow gear test, then document
the gear data/attributes.
The shop can tell by the Inspected attributes of the gear what AGMA quality class it is.
do a full detail inspection of the parts. then record the findings.

You can hold them to a tighter AGMA class but it will cost more.
yet it would be well worth the expense.

The tougher question is the material & process required for heat treat. I would suggest to take one of the scraped gears and do
met lab full analysis. The Met lab well will get you the chemical elements, physical properties,and if any case hardening & what type.
expect to pay good money for their expertise.
But it is well worth it for the piece of mind.

This may be a good gear shop , To trust but the full part analysis would be peace of mind.

or do as Gear Cutter recommends & hire competent consultant.

Regards
Mfgenggear

 

[dinjin]

I would recommend that you send the extra gear to
a reputable gear manufacturer and they should be
able to examine that and determine the answers to
your questions. You should also specify the operating
temperatures and atmosphere of where the gears will
be operating. Is it a cold temperature application.
You are lucky to have a spare. Normally the pinion is
specified to be of a higher agma quality and also harder
than the gear. You should also be able to test the
hardness of the gear and by visual inspection determnine
if either have been surface case hardened. There were
recommendations in order to prevent micro welding to
have a harness differential of the two parts but both
could be of the same material. It would also help to
know the maintenance schedule of those gears that have
excessive wear. I am surprised that you cannot find
product or serial numbers for the gears that you have
so you can trace it back to the OEM.

 

[tbuelna]

jarimasen,

Since you don't have much experience with gear design, I'd take gearcutter's advice and pay a gear expert to design your gears. A good gear consultant should be able to do the gear tooth profile optimization and provide recommendations on material and heat treat for a reasonable cost. You'll find that this money will be well spent when you consider that it is likely a fraction of the cost a premature gearbox failure will cost your company in downtime.

Gear design is much more complex than most people appreciate. Besides AGMA quality class, you must consider lubrication conditions, fatigue life speeds and loads, mounting structure effects, load distribution at the mesh, etc. Experienced gear designers also understand what gear tooth profile and geometry modifications to make, which can significantly improve gear life.

Rather than just try to simply duplicate an old part, take the opportunity to have a qualified gear designer incorporate some improvements using modern materials and analysis tools. It shouldn't cost much.

Good luck.
Terry

 

[geesamand]

Our company does this type of work but primarily for mixer drives.

Some things to keep in mind:
- Through-hardened gears may be an option if you need the gears fast. But they won't go to high AGMA quality levels
- AGMA quality levels (8, 10, 12, etc) are no longer the preferred way to specify accuracy but many of our customers are familiar with this terminology and that's sufficiently specific for most applications.
- If you have more time, you could get carburized and ground gearing made and those will usually achieve AGMA 10/12 quality due to the fact they are finish ground. They also have very high strength ratings.
- Determine the AGMA service factor you need. This is the best way to ensure the new design will provide long trouble-free life.
- Because you have very small quantities, I encourage you to require full gear inspection reports for the finished parts.
- While having a spare set helps to allow them to measure and determine the original gear parameters, that doesn't mean it's the best design. So if downtime of this unit has caused your operations difficulty, I recommend doing a root cause failure analysis of the gearing to determine which aspects of the design (lubrication, tooth form, tooth count, vibration, etc) might be worth modifying.