Horse power calculations for an AC induction Motor

I want to use an Induction AC motor to rotate a steel disc at about 100 RPM as a minimum speed. This steel disc is about 65.7cm in diameter, 2.5 cm thick, and weighs about 65Kg. this disc is going to be used as a fly cutter for cutting Plaster/gypsum and termite mound material (mainly silica, and termite saliva).

obvioulsy the power will be transmitted from the motor to the disc using a pollyes pair, bevel gears, or a warm and warm gear (open for suggestions). to increase the output ratio so that the torque can be maintained or increased at such a low speed (100 RPM)

if any one dose know a site or link that gives guidlines to selecting the HP/KW for an induction AC motors for the described purpose, please let me know. Do you think that the Induction AC motor will do the Job?

cheers

haythame78 said:

I want to use an Induction AC motor to rotate a steel disc at about 100 RPM as a minimum speed. This steel disc is about 65.7cm in diameter, 2.5 cm thick, and weighs about 65Kg. this disc is going to be used as a fly cutter for cutting Plaster/gypsum and termite mound material (mainly silica, and termite saliva).

obvioulsy the power will be transmitted from the motor to the disc using a pollyes pair, bevel gears, or a warm and warm gear (open for suggestions). to increase the output ratio so that the torque can be maintained or increased at such a low speed (100 RPM)

if any one dose know a site or link that gives guidlines to selecting the HP/KW for an induction AC motors for the described purpose, please let me know. Do you think that the Induction AC motor will do the Job?

cheers

Click to expand...

Talk to drive manufacturers like AB, Siemans, or Toshiba. The vector drives(AC) can regulate torque down to near zero speed. Twenty years ago I would use a DC motor for your application. If speed is not important concern then a series DC motor delivers very starting torque. A DC shunt motor can be regulated according to k@I. Where k is a constant @ is field strength, and I is armature current. In a shunt motor the torque is nearly proportional to armature current. Of course output is given by HP=TS/5250 where T is torque and S is speed.

The horsepower is determined by the load, not the motor. You need to know the load horsepower (or better, torque and speed requirements) and then choose a power train and motor to cover the load requirements.

Sounds like you could use a little outside help on this. Have you considered getting some engineering support to help you with this?

haythame78,

The Motor HP will be determined by the load placed on the motor. The choice of the "drive" depends on the size of the motor and what you want to do with it all..

The question is how much power will it take to cut the material? Tough guess without being able to see it. So considering that you have a 65 cm dia wheel..you might be cutting through maybe 20-25 cm of material. Figuring the material is like the consistancy of gypsum my simple wild guess would be 4 to 5 hp using a gear motor of some type to multiply the torgue and slow the wheel to the desired 100 rpm.

Now for the drive...If you do not need to vary the speed of the blade then maybe a soft start, or just a contactor/overload would be a whole lot less expensive and simpler to use..

Just a few thoughts...but you really dont have enough info to make a good selection as of yet...

Hi again

Thanks to everyone who replied it is appreciated and it was helpful

It is my mistake not to give you enough detailed info

I had to mention that this disk is going to be like a fly cutter, and that our slicing will be destructive incremental slicing with increments of 1mm and the total length to be sliced is about 3.5 meters ( the total length of the Termite mound) we need this to get a resolution small enough to capture the diameter of the smallest channels in these mounds which is about 1 mm. That means the mound will be sliced by removing 1mm layers using the fly cutter untill the whole mound is destroyed (sliced). i guess may be that means not alot of cutting forces are needed in this case.

so the machine should slice the first layer off (destroyed) take a picture of the sliced surface then decrement 1 mm and repeat the same action again.

it is worth mentioning too that the diameter at the base of the mound will be around 2.5 meters

so if we to use a steel cutting disc with 650 mm diameter and 25 mm (1 in) thickness that may need a high horsepower motor that is why we wanted to use an AC motor that can give high horsepower possibly 1 Hp and yet cheap.

the band saw is a good idea but i am afraid that while cutting across this big diameter and the 1 mm thickness the 3 meter saw (for example) may buckle or bend slightly which is gonna cause a problem for us.

Please let me know if you think using an AC motor (may be with a transmission agent from your discussion) would be good enough for this application.

one more thing we need the motor to be variable speed so i guess we will need to use an AC motor drive (correct me if i am wrong)

cheers

I can't think of a reason the AC motor and drive wouldn't work. However, positoning the cutter disk to cut 1 mm increments sounds like another issue. How do you intend to position it? Or maybe it isn't an issue with you? Are you using some sort of positioning system or is it done manually?

sorry for the delay in the reply

but i will come back to u soon Ken

This is ABB software for sizing motors and drives

here

A direct on line starter is good up to 5kW if you dont need speed control. A 4 pole 3 phase motor with a 10:1 reduction gearbox would give you about 140 rpm. As the final torque is a function of the gear ration the motor torque will need to be 1/10 (not including losses) of the final drive torque. To feed the cutting head, the easiest way would be a lead screw arrangement with a suitably sized stepper motor like a CNC machine. Don't forget that even if you are building this for your own use you have to comply with the PUWER.

I have just had a thought, if this machine is going to operate like a circular saw, then you probably cannot build it yourself as you will fall foul of the Health and Safety requirements. Get a machine builder to do it for you. I am assuming that a machine builder would not be asking this question.


I have just tried teh link and it doesn't work go to abb.co.uk and look under ac motor downloads

At some point even the kazi in england will have a special safety order regulation .
As this thing is a one off , surely if the guarding and electrical safety etc complies with HSAWA then there is no problem . Just out of interest is this thing going to have an edged cutter , or just use a plain disk ?
Re postitioning , use a lead screw with an escapment type gear that can be operated a fixed number of times by solonoid or small pneumatic cylinder to create the correct rate of advance at the end of each stroke - no need for clever postioners , keep it cheap

JohnW said:

This is ABB software for sizing motors and drives

here

A direct on line starter is good up to 5kW if you dont need speed control. A 4 pole 3 phase motor with a 10:1 reduction gearbox would give you about 140 rpm. As the final torque is a function of the gear ration the motor torque will need to be 1/10 (not including losses) of the final drive torque. To feed the cutting head, the easiest way would be a lead screw arrangement with a suitably sized stepper motor like a CNC machine. Don't forget that even if you are building this for your own use you have to comply with the PUWER.

I have just had a thought, if this machine is going to operate like a circular saw, then you probably cannot build it yourself as you will fall foul of the Health and Safety requirements. Get a machine builder to do it for you. I am assuming that a machine builder would not be asking this question.


I have just tried teh link and it doesn't work go to abb.co.uk and look under ac motor downloads

Click to expand...

thanks John

i am not buildiong this on my own, it is actually a part of a University project. There is a technician who already have some experience in machine building but not in mechatronics where i come to play

the idea for the cutter is that is it is going to be a disc with 4 or 8 lathe cutting tools evenly destributed along the disc which i think may be the best for the job needed. what you said regarding the lead screw idea is right. We are going to use the lead screw idea for the movement of the cutting head because it is accurate with no slipping or backlash.

I do not understand the application and or some of the terminology being used. Please explain these:
Termite mound
Fly cutter
Will the disc edge (2.5cm) be where the cutting tools are mounted?

The disc weight, surface area used, position of disc (flywheel effects), force applied to cut all are used to determine torque required.