Dave Dickey Forum Moderator 291 Posts
Re: Input power of electromotor, power of gearbox and the safety factor21 February 2008 at 1:29pm
With the information provided, I do not get the same results for motor size and drive torque. To rotate the described anchor impeller at 60 rpm in 60,000 cp resin, the power required would be at least 90 KW or 14,000 N.m output torque, probably requiring a 100 KW motor and 15,500 N.m output torque. However, at 20 rpm, the power requirement would be about 9.6 KW but at 4,600 N.m torque.
Putting these results in terms of operating conditions, the mixer could run at up to 28 rpm in 60,000 cp resin fully loading a 20 KW motor but with 7,000 N.m output torque. Alternatively, the mixer could be run at 60 rpm and a 20 KW motor with 3,000 N.m output torque, but with only 10,000 cp resin.
However, since the impeller and drive design are more likely limited to a maximum torque of 3,000 N.m, the maximum resin viscosity that could be mixed at the minimum speed of 20 rpm would be 40,000 cp. To successfully mix 60,000 cp resin with a 3,000 N.m design, the rotational speed would have to be 13 rpm.
Conclusion, the anchor mixer design described is not suitable for 60,000 cp viscosity. At the minimum speed of 20 rpm, the maximum viscosity for the mixer would be only 40,000 cp. At the maximum speed of 60 rpm, the maximum viscosity would be only 10,000 cp. The impeller and drive design would have to be capable of at least 7,000 N.m output torque to handle 60,000 cp resin at the minimum speed of 20 rpm.
We are going to produce water base resins. These resins have an average viscosity of 60000 cp in a 6-ton industrial reactor, and an anchor mixer has been used for mixing the content of reactor (with the speed of 20-60 rpm). Therefore, we have made the impeller with proper dimensions (shown below). Now we must fix an electromotor and gearbox to the shaft and impeller system. What is your recommend about input power of electromotor, power of gearbox and the safety factor (the agitation system works continuously about 7 hours /day). My calculations show, M2(out put torque) is about 3000N.m and P(motor)= 20 KW and P(gearbox)=20*1.5=30KW, f=1.5 Characteristics of our anchor Impeller with two horizontal arm: D=1.75m, w (blade wide) =0.2 m, H=2m, t (thickness of blades)=0.02m blades are in 45 degree.
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