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Correct belt tension


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I have an old russian self contained hammer (similar to Beche and Anyang). Today when I started using it I noticed that it slowed down after couple of blows. It didn't stop completely, but went down to maybe half the normal speed under load. I haven't noticed the slowing down earlier. I guess them most logical explanation is that the belts have started to slip. I checked them and to me they seemed quite loose. Free distance for the belts between the pulleys is about 60 cm (24 inches). In the middle they move more or less freely about 3.5 cm (1.4 inches) sideways (from the center line). Tomorrow I'll put some spaces under the motor to get the belts tighter. How tight should they be so that they stop slipping, but wont put too much pressure on the bearings?

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I raised the motor so that the belts have now that one inch movement with moderate pushing force. The power of the blows is back to normal.:)



One thing you should do now that you have it back working well is throw an amp meter on the motor and see what the draw is.. You can tell alot about if the belts are where they need to be from the amp draw on the motor... When your working the hammer heavy (most work for the hammer is a long blow that does not quite land on the die) it should be within about 10% of what the motor tag says... If its more than 20% over your belts are two tight and you will put extra stress on the motor and motor bearings... If its under 20% or more your belts are too loose and your sacrificing performance... measurements taken at full load are the only ones that really matter...
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One thing you should do now that you have it back working well is throw an amp meter on the motor and see what the draw is..


Thanks, that's a good advice. I'll have an electrician coming to add a new switch to the hammer within next couple of weeks. I'll ask him to measure the amps at the same time.
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Never checked my Nazels, but I did check my 200lb Chambersburg and it drew way more current on light blows than full out. I figured it was having to stop the ram from coming down all the way, putting on the brakes as it were.



Yep... I think its harder on the motor to have to "catch" all that weight and suck it up rather than pick it up after a hit....
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  • 2 weeks later...
  • 1 month later...

The electrician came last weekend and we measured the currents. The plate on the motor says 5.5kW@380V, cos(phi)=0.86. The three phase voltage is 400V over here nowadays. So if I got it right then the max current would be
I=P/(sqrt(3)*U*cos(phi))=5500W/(sqrt(3)*400V*0.86)=9.23A
Here is what we measured:
start: 10.1A
idle (ram down): 5.3A
light blows: 8.6A
heavy hits: 9.7A --> sqrt(3)*400V*9.7A*0.86=5.78kW (*)
We also measured the currents with somewhat more loose belts and the results were more or less the same. I think the tightness on the belts should be ok now.

(*) As the voltage is higher the motor output is also probably higher. Can I simply calculate it like this 400V/380V*5.5kW=5.79kW?

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