Can steel shaft be replaced by oversized Al shaft?

[Rinsuke]

We are designing a small portable winch with a 2t (metric) pull capacity. Weight is the number one factor and must be decreased from 24 kg at present to under 20 kg. The engine weight and size cannot be changed as well as the wire length, size and weight and therefore all weight savings have to come from the internal gearbox, winch drum, shaft and gears... Sounds fairly easy but gearbox wall thickness, bearing casings and just about everything else has been shaved to its minimum so we are left with the shaft + drum assembly and I suggested getting rid of the drum and instead attaching the wire directly to the shaft only the shaft would have to be a lot bigger to allow for proper wire bending calculations. The steel shaft is 20mm diameter stainless steel at the moment, could that be replaced by an oversized aluminium shaft?

regards


Stephan

 

[arunmrao]

You will be playing it safe if you could consider using a high strength steel hollow shaft instead of considering an over sized Aluminium alloy shaft. This would again entail design changes to accomodate the over sizedshaft.My intution is that Al alloy shaft will be too soft for the application and would nedd frequent replacement too.

 

[Merlinz]

In normal gearbox design, it is found that using better materials can greatly reduce the size and therefore weight of the whole product.
e.g. 2 gearboxes I've seen... one weighed 480 kg, and the other weighed 46 kg. they had similar specs. so look into the strongest materials, to reduce weight, not the lightest materials.

 

[stanweld]

You state that the current shaft is stainless steel. What grade and what strength? Is it necessary that the part be stainless steel to prevent corrosion? There are number of high strength steels available to save weight. The key to the proper selection is your service/design requirements.

 

[Rinsuke]

To all who took time to respond. Sorry for the very belated reply. We are still making slow progress on the project as posted on the gear thread and have eliminated certain options in favor of others , mostly through failures...

The AL shaft seemed to have been but a cruel joke in my mind and we are now using a 22 mm SCM 435 with no key but rather four machined splined. Not an ideal solution if we were to manufacture this thing in great numbers but it worked for the demonstration prototype and after three damaged shafts (bent, bent, twisted) we had to do something drastic. However, the amount of waste is not acceptable

The original stainless steel shaft was put in for no other reason, in my mind, that the previous machine shop cut corners and used what they had on hand instead of what was needed, hoping I would not notice ... yup , it happens...

step1

 

[EdDanzer]

You will save money by doing finite element analysis on this type of design. When designing something like this, high strength heat treated steel will give you the most strength per pound. One thing to watch is deflection. When doing FEA look at the amount of deflection as well as stress in the design, the deflection may cause gear damage or other problems.
Good luck we worked on a similar problem, but wanted 200 pounds pull at 300 ft per minute, and found the market to small to justify the design expense.