aluminum gears and coatings 1

[robojerry]

In order to reduce weight in a machine, I am converting a rack & pinion system from steel to aluminum.
The original rack is made from Boston stock, 14.5 PA 12 DP, 3/4" square rack, 716mm long. The original pinion is a stock 14.5 PA 12 DP 18T, with 3/4" face. Both are coated with IonBond 7-24 CrN and MoST. I will probably leave the pinion as steel with the CrN & MoST coating, since there is not much weight to be saved. The gear-rack, I plan to change to aluminum 6061-T6511 with Bodycote/Ionbond TC40-41 Tungsten DLC. The loading is very light, the unit will run without lubricant, and is subject to occasional caustic washdown. Runs 24/7. Making things physically smaller is not an option due to structual and mounting constraints. Can anyone offer suggestions or warnings regarding these combinations?

 

[TVP]

Make sure the roughness is as low as possible both prior to coating and after coating for both parts. Definitely keep the MoST coating if no lubricant will be used.

 

[CoryPad]

Is the loading on the aluminium teeth mostly sliding? The base metal is not hard enough to support much contact stress in the normal direction, even with a hard coating.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Philrock]

AL 7075-T6511 has almost twice the strength of 6061-T6511.

Have generous fillets between teeth. Smooth finish is important on fillets as well as on working flanks.

 

[strokersix]

Caustic washdown may be detrimental to the aluminum.

 

[unclesyd]

If you use a caustic wash make sure it is inhibited specifically for Aluminum.

Anytime we had any rubbing contact on Al we would use the Hardtuf process by Tiodize.

For occasional contact we would use a thermosetting resin coating with Teflon, MS2, or WS2.

Look to bottom of the page.

http://www.tiodize.com/anodizing.html