Hardening Of Aluminium Threads 3

[Speedy]

I have an application where an internal thread of 'M10 x 1.5 Metric Coarse Thread' is required. I have to use this size as it is standard for the application. Basically I want to increase the strength of the thread as much as possible.

How can I achieve this?

I opted for a high Shear Strength Aluminium (47900psi) as I would like to keep the component as light as possible. Would anodising increase the shear strength at the threads?
Are there any other surface treatments which could help?
How about other suitable materials?
What about helicoils, are these expensive to install?

Appreciate any comments,

Speedy

 

[CoryPad]

Anodizing will not improve the shear strength of the threads. There are no treatments that can be used to improve the aluminium material, so you should use the highest strength material possible.

Inserts are certainly a possibility. Helicoils are not difficult to install - you just screw them into tapped holes. I am unsure how to answer the question of "are these expensive to install?" - they are not terribly expensive components to buy, and they don't necessarily require expensive installation equipment. But, they are extra components requiring extra process steps. You will need to quantify the costs yourself.

 

[etch]

Im a bit lost by your answer cory that no process will improve Aluminium material, surely this depends on the material. Aluminium is readily heat treatable if containing anything Magnesium.

I might be missing a point , its late.

 

[Kenneth]

CoryPad is correct. If the strength of your heat treated aluminum does not provide adequate thread shear strength, a threaded insert would appear the most pratical solution. Take a look at thread404-11447 for a discussion on threaded inserts in aluminum.

 

[CoryPad]

etch,

There is no way to strengthen the aluminium other than by traditional bulk heat treatment. There are no coatings, selective small area hardening, radiation, etc. that will improve the thread shear strength.

 

[BrianR]

An additional point to remember is that aluminium to aluminium contact in a screw thread will sieze in service and you should always use an insert such as a helicoil. They are easy to install and commonly used.

 

[etch]

ah thanks cory, i misunderstood question, i though he wanted to treat full component.

cheers

 

[Woody1]

Guys, you are all on the right track but helicoils can and do pull out of aluminum.
I would use an item called a thread-sert. They are made just for such soft materials and do hold up much better. Woody Ebersold
Consulting Engineer
"AN EXPERT IS ALWAYS SOMEONE FROM OUT OF TOWN"

 

[diamondjim]

keenserts or helicoil inserts have
been successfully used to accomplish
higher strength and come in different
lengths ie 1, 1.5 or 2 times the diameter
for differenct stress levels. The lengths
required would depend on the grade bolts
being used. We have used these in machine
gun turrets which see a lot of vibration
at at times heavy loads. If you have
a very thick piece and can tap it 3 times
the bolt diameter in length, you may have
enough strength in the internal thread to
resist pulling out but you wound need to
coat the bolts with an anti galling paint
or coating.

 

[rhc]

We have an application which requires a device to be "permanently" fastened to an aluminium base with M10 coarse thread ss scocket head cap screws. If the screws get loose the device fails. In operation it is always underwater and subject to constant vibration and occaisional severe load. The best we have got so far is gooping the threads with epoxy during a new installation. It seems to spread the load and resist vibration better and yes the longer the available thread the better but sometimes all we can get is the diameter x 2

 

[CoryPad]

rhc,

Socket head cap screws are not a particularly good fastener if you are joining components with strengths lower than high-strength steels. The complete lack of bearing area, coupled with their usually large strengths, means that you exceed the allowable bearing strength of the joint components, which increases susceptibility to loosening. Their large strengths also require large thread engagements. If you are "gooping" adhesive, I recommend you ask your fastener supplier to provide fasteners with pre-applied adhesive. Lastly, thread adhesive does not spread the load, but rather it adheres to both external and internal threads and prevents relative motion between them, which is the cause of vibration loosening.

 

[rhc]

Thanks CoryPad I was not reccommending socket head cap screws only stating that we use them. We have space & streamlining issues that overide bearing area. The device is made of 316L stainless steel and fastened to aluminium with M10 316L socket head capscrews.
It is my experience that during a fixing installation where one surface has to slide a relatively long distance over another before reaching "home", applying solventless epoxy resin to both mating surfaces is better than applying to only one because it reduces the risk of progressively being wiped off as it is introduced to new dry surface. Between mating threads there are always tiny voids and mechanical load cannot transfer directly across a void so all mechanical load has to transfer around them. This in turn increases the risk of "point loading" or concentrating stress on specific rather than general areas of the threads.
In my opinion filling those voids with a solid nexus of incompressible solventless epoxy resin goes a long way to spreading the load.

 

[dwillms]

We have a similar difficulty strengthening the threads in a fairly thin-walled aluminum extrusion (wall thickness < thread dia). Helicoils require their full length to be seated in metal in order to prevent them backing out. They can be clipped shorter but this doesn't really work in a production environment.

Solid inserts can stick through the other side, but require a much larger diameter initial hole (M8 insert requires an M12 hole).

T-nuts, or equivalent on the inside of the extrusion would work, but if the extrusion is long, locating them halfway down is tricky.

Anyone else with this type of problem? Any suggestions?

Dave

 

[rhc]

Dave, this is way out of my area but could you punch the holes with a special forming punch - you might &quot;extrude&quot; a longer hole for more threads.