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?
Does anybody know the origin of these curious numbers and why a user would be concerned?





RE: Strange Requirements
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
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
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
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
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.