×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Strange Requirements

Strange Requirements

Strange Requirements

(OP)
I have been in gear engineering for a long time but every now and then a customer comes up with a requirement that I cannot understand! A recent request requires that the gear MUST NOT exceed 300 BHN and the pinion 350 BHN hardness.
Does anybody know the origin of these curious numbers and why a user would be concerned?

RE: Strange Requirements

300 BHN and 350 BHN are 32 RC and 38 RC respectively which is the limit for gear machining (hobbing).

This also the hardness that is not yet sensitive to hydrogen embrittlement according to the MIL-STD's.

What is the designed use for these gears?

RE: Strange Requirements

(OP)
Don't know what the intended use is yet - but does it matter for an enclosed gear box?
As for the hobbing issue, that may once have been true but with current machines we are hobbing gears up to 415BHN with no problem.

RE: Strange Requirements

About the hobbing, I know that for fine pitch gears the 38 RC used to be a limit. If this is not the case any more then this is an important issue for me.

I believe that if the gear box is subjected to inpact loads or is very critical it is better to have a high ductility material and suffer some tooth distorsion than having a brittle fracture of tooth.

RE: Strange Requirements

I would assume that the 300 BHN and 350 BHN would be used for concernes with tensile and yield strength of the gear teeth.

Many enclosed drives are designed for a specific application. Getting the teeth any harder may make them too brittle for this particualr application and cause premature failure in the drive.

Another reason that many designers specify a MAX BHN is to cause a failure in a particular area of the equipment. This acts as a fuse to protect more costley repair items.

RE: Strange Requirements

The expression of max hardness smacks of failure analysis experience. Could be that your contact had bad experience with failed parts with high hardness.

I worked on an interesting project where we hushed down gear noise by a helical combination of soft pinions and gears with high internal damping. We also used extended addendum on pinions. However, the upper stages were heat treated. You couldn't hear any gear noise after that.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources