Dear all,
I work in a stainless steel company.we have a contineous Annealing and Pickling line.It consist of furnace section, Shotblasting section and sofftning section.

In shotblasting section we have eight 75HP,1440rpm AC motors.there motors are used to blast the steel shot(about 0.5 mm dia.)on the steel coil.

Now my problem is that, due to excesive shot leakage,the shots get entered into the motor and resulting into earthing of that.the line run for 24 hour.A motor run on an average 16-18 hours a day.On avarge after 10 days one motor get earth.
The shots entered into the motor from top.Please suggest me what should do for that.Suggest me if there is any equipement that can be use to protect the motor from earthing?I really need your valuable opinion.

Abhishek Puri.

 

I would suggest better shielding (some form of enclosure) for the motors to keep the shot out. Are there any guards currently installed? Were any of the existing guards removed? Steel shot may bounce quite a bit, so they may be getting into the motors indirectly. Any shielding however must not obstruct the air flow which cools the motor.

Another alternative might be a totally enclosed fan cooled motor, but I don't know what is available in 75HP size, or how much this may cost when compared to shielding the existing motors.

I imagine that dealing with shot is analogous to dealing with dust, in the sense that both would tend to get into everything.

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Michael Griffin
London, Ont. Canada
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Consider a Totally-Enclosed-Fan-Cooled motor!

Regards,
Phil Corso, PE
Boca Raton, FL
[[email protected]] ([email protected]) {[email protected]}

 

Usually these damages start to increase because of people trying to shorten the downtime by using cheaper methods.
If you fix the motors properly, this situation will not happen. Train your electricians on how to fix the motor properly. The life of the newly replaced motor will be short if they use shortcut methods to fix it. Of course the motor is very heavy, the place is very cramped and dirty but you can not compromise on workmanship.

You will need to check against any small holes etc through which the shots enter. Use rigid motor covers and DO not use sealents like silicone, epoxy to seal small holes. The motor terminal cover should be fitted with all screws if not re-tap the holes and fix with new screws. If the TB had a rubber seal, fix it back properly. Put proper cable glands and if the cables are short replace with new cable, new cable gland and shrouds. Keep enough spares like cable glands, etc. so that in event it happens on a night shift, the motor is fixed properly. Do not allow the motor to run if it is not fixed right the first time.

regards,
Sekar

 

TEFC motors or motor enclosures are the norm for shot blasting.

Regards

cww

 

Abhishek,

A good first step would be to use TEFC motors. They are totally enclosed so nothing from the outside gets inside. If this solves your problem there won't have to be a second step.

 

Well, there's a lot of things that can cause motor to have earth fault, some to mention
1. foreign object
2. insulation failure because of heat
3. improper use (class intermintent use in continous).

Responds to TEFC motor you could get 75 kw above.
If you already use TEFC motor then placing additinal guard or enclosures,
or consult with the motor manufacturer, but you need to have second opinion about what thw mfr sales suggestion.

good luck

 

From working in a foundry, I can tell you that shot blasters are very high maintenance machines anyway. They consume themselves through shot erosion. But motors shouldn't be a problem if they are properly shielded and enclosed. The shot is fairly big and there shouldn't be any openings in the motor case that will admit shot.

Regards

cww