Torque requirement for a sand mixer / motor selection 3

[caprock]

Hi everyone,

I am in the process of designing a sand mixer and could use some help with calculating the motor torque requirements.

Some details:

It is silica sand in a small mixing vessel that is inclined at 60 degrees from horizontal. The vessel is 11.2 inches in height and 8 inches in diameter and will be half filled with sand, it will have blades that rotate on the inside of the vessel that are similar to the ones in the image attached. I have calculated (also attached) the acceleration torque and the load torque (only from the drag on the blades due to the sand). I used the formula for drag force (F = 0.5 C ρ A V^2) (using the bulk density of silica) even though I know this is for drag force for fluids. For granular material should I try to calculate this a different way? At the end of my calculations I ended up with around 50 N.m as the required torque. Is this a reasonable value for the situation described? Is there a better way to figure this out for this situation?

Additionally, lets say that I do need about 50 N.m of torque with some uncertainty and I were to apply a safety factor of 2. So now my goal is to find a motor/gearbox assembly that will output 100 N.m of torque at an operating speed of 60 rpm (so 0.84 hp). What would the best kind of motor be for this application? Should I go for a DC/AC motor? Any suggestions for suppliers?

Thanks!

http://files.engineering.com/getfil...ee3a-426d-b820-491d0f249102&file=IMG_0723.JPG

http://files.engineering.com/getfil...85aa-4ae7-b490-87d84c7b0333&file=IMG_0722.JPG

http://files.engineering.com/getfil...2d06-4545-87bd-7a8d078cebec&file=2.Blades.jpg

 

[MintJulep]

As a sanity check, the smallest concrete mixer shown on HD website is 1/2 HP.

 

[geesamand]

I suspect your maximum torque will always be at startup, before it can even resemble a heavy fluid. Can you mock up your impeller assembly and use a torque wrench to estimate the startup torque?

Once that is known I would design for that load to be safe.

 

[EdStainless]

Is there a reason that you are not rotating the vessel (like cement mixers)?
We used to mix specialty foundry sands in one that also had a fixed blade that was inserted into the open end.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[moon161]

Is there any reason you're not using a cement mixer?

http://www.harborfreight.com/1-1-4-quarter-cubic-ft-compact-cement-mixer-91907.html

Just sayin, for less than what a day of head scratching will cost, you got it.

 

[arunmrao]

Practice is to empty start the mixer and then load with sand. Else, you will be burning your motor.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[BUGGAR]

Maybe unrelated but building codes require (used to require?) paddle mixers for mixing masonry mortar.