External aluminum thread 1

[bjpil]

Hello,

I’ve been asked to replace a hydraulic filter fitting (external tap) with an aluminum cast in feature, part of the main housing, to reduce the number of parts. My concerns are the service life of the part and the wear of the aluminum threads due to changing the filter, cross-threading, nicked threads… Anyone have some experience with this?

BJP

 

[CoryPad]

Externally threaded aluminium parts are common. Aluminium and its alloys will have lower strength than steels, so thread damage (nicks) will be more common. Also, the friction coefficient will be higher, so galling (wear) may be a problem (as well as lower developed preload). A lubricant is recommended for this application. Cross-threading usually is a geometry problem, not a materials one, so it shouldn't be a factor.

Regards,

Cory

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

 

[bjpil]

Cory,

Thanks for your reply. You bring up a good point on galling. What I fear is that the part should have a service life of 10 years and in that time the filter will be replaced around 65 times. This is going to be a steel/aluminum mating condition. What I am worried about, probably unnecessarily, is that the first couple of treads could easily become deformed which would cause cross threading. I know that aluminum threads are common but I don't think it is common to have aluminum threads on a part that will be screwed on and off more than a few times.

Can anyone one point me in the right direct to similar products? Cockroach gave me a few good hints but my original thread disappeared and I had not check out his suggestions.

BJP

 

[griffengm]

bjpil,
At one time, we had a machine with a cast Al oil pan and tapped threads in a boss. After several years, the cross thread scenerio occurred. We then rebored the hole and installed a helicoil which was still in place when we sold the machine some years later.
This brings me to the point - can a steel or stainless steel insert be molded in? This would seem to carry enough positive value that the price can be adjusted to cover the cost.

Griffy

 

[bjpil]

Griffy,

Thanks for your reply. Somebody beat me to the star. Your oil pan description is a very good example of the problem I think I may have if I go to this design. Do you know if this design is still used today so that I may check it out? Prototyping something like this could be very expensive and I was hoping to do it on the cheap if possible.

A insert could be cast into the part but there are other drawbacks that need to be worked out such as the cycle time between parts will slow down due to inserting the part into the cavity, maintaining perpendicularity, and ensuring a good bond between the dissimilar metals. It’s a good suggestion but I think it will be hard to change the direction of the new design right now.

BJP