Hi permibility metal for dynamometer

[S3ssion]

What type of metal is suitable for the dynamometer?
I have a "self" designed dynamometer for testing our motors; it allows me to load up to 36 in-lb torques. Currently, the metal disc used in the dynamometer is a low carbon steel 1018 and it might too soft. As a new requirement of 48 in-lb torques applied, the dynamometer gets hot and the disc starts to deform. I need to find a metal which can withstand the temp. and get better performance. Some one suggested to used 430 steel which has Hi permeability; I have not tried it yet.

 

[CoryPad]

What is the heat source for your dynamometer disc? What is the actual temperature of the part?

What is your definition of permeability?



Regards,

Cory

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

 

[S3ssion]

Hi Cory;

The heat is generated by magnetic force. I did not measure the heat temp. but by touching the body of dynamometer which has a coil installed in the metal case.

In general, soft magnetic alloys are materials that can be easily magnetized - thus exhibiting high permeability - and just as easily demagnetized. Permeability is a ratio of the magnetic induction output (B) to the magnetic field strength input (H) that produced the induction. The higher the permeability, the better the magnetic performance. This permeability allows to generate force on disc or toeque to simulate a load on motor.

Thanks

Harry

 

[StoneCold]

Lot's of exercise equipment is designed with this type of system. My guess is that the thickness of the disk is the problem and not the metalurgy. How thick is the disk? How far out on the radius of the disk is the magnetic force applied?

Regards
StoneCold

 

[S3ssion]

Hello Stone;

The thickness of disc is 1/8" with 7" dia. It is a flat disc. Compare with other dynamometer, the inner portion of disc should be thicker than outer portion to prevent the deformation. Since this is an old self designed machine, there is no room for the changes and there is no drawing for the information. I just hope that I can find a different type metal to improve the performance.

Thanks

Harry

 

[sreid]

How about forced air cooling with a blower?

 

[redpicker]

I'm not sure exactly how your dyno is designed, but it really doesn't matter. I'm guessing that it operates by putting a load on the motor and measuring the force on the disk and correlating that force into a power value. The power produced has to be turned into heat (I guess this is the point I am trying to make). If you are trying to increase the power it can measure, it will have to make more heat. Changing permeability may change the amount of power it is capable of measuring, but if you are measuring more power, you will be producing more heat. To correct that problem, you will have to get better heat transfer (as has been mentioned, forced air cooling, maybe adding fins or ribs to the disk, or other methods. Keep in mind that making these modifications may alter the calibration characteristics.

rp

 

[S3ssion]

I do have a external air blower for cooling but it not enough. The speed of motor is about 14000 rpm max. With load, it is about 6000 rmp. Thanks

Harry

 

[S3ssion]

It is true that to enforce disc by adding additional material might help to reduce deformation. I might have to open it and make a measurement for changes. A force air cooling is probably a good choice. Thanks a lot for information.

Harry

 

[MagMike]

I admit I don't know how your dynamometer is constructed, but would it be possible to use thin permanent magnets (1/8" thick) embedded into the steel disc? They might provide additional flux which should increase the torque.

Just my $.02

Mike

 

[S3ssion]

Thank you for the suggestion. However, our torque requirement reflects the weight load on the next level product and it related to the current limit and speed requirement per Acceptance Test Procedure. Increase in torque will increase current and reduce motor speed. It has to be balanced.

Thanks,

Harry