vfd for power hammer

dian · Apr 18, 2020

a friend of mine is blacksmith. he has a power hammer and complains that its too fast. i thought of making him a present and install a vfd. would that work or is there more to it? i have no idea about these machines and how they function.

Phil in Montana · Apr 18, 2020

How hard it hits is a factor of speed, 1/2 as fast is 1/4 the hitting power...works on the sqr of the speed....Phil

CalG · Apr 18, 2020

Note too, that HP available from the electric motor drops off with rpm, unless increased amp draw (heating) is tolerated.

Depending on the hammer mechanism, the better solution may be in gearing. Same motor rpm, fewer bpm.

3t3d · Apr 18, 2020

A friend of mine put one on his power hammer.
He liked the results. Worked great.
He can run it slower or faster as needed.

gbent · Apr 18, 2020

Little Giant and others made the clutch so you could slip it as necessary from 1 single blow to full speed.

markz528 · Apr 18, 2020

CalG said:
Note too, that HP available from the electric motor drops off with rpm, unless increased amp draw (heating) is tolerated.

Depending on the hammer mechanism, the better solution may be in gearing. Same motor rpm, fewer bpm.

Torque is what is important here. Below base speed you are in constant torque range so not an issue. Want to run the drive in sensorless vector mode.

dian · Apr 18, 2020

Phil in Montana said:
How hard it hits is a factor of speed, 1/2 as fast is 1/4 the hitting power...works on the sqr of the speed....Phil

so does the hammer drop down (works by its weight) or is it forced down?

the motor is a monster, probably pretty slow, btw. i run several vfds, so i know how they work (sort of). i only saw the machine once, we dont go visiting now.

johansen · Apr 19, 2020

dian said:
so does the hammer drop down (works by its weight) or is it forced down?

the motor is a monster, probably pretty slow, btw. i run several vfds, so i know how they work (sort of). i only saw the machine once, we dont go visiting now.

depends on the mechanism but its usually a resonance between the hammer, a spring and the flywheel. a little bit slower is a lot less energy, but to my mind that is exactly what you want. a slower repetition with softer blow gives you more time to think about what you're doing.

most vfds allow for non linear input. a variable foot switch wired up for minimum operation being say, 30hz, max at 60hz may be what you want.

dian · Apr 19, 2020

if its really a lot less energy then its probably not what he would like. the problem is to give him time to turn the part to an acceptably precise angle.

Peter from Holland · Apr 19, 2020

Torque stays the same
With less speed you need less power

Peter

dian · Apr 19, 2020

i was talking about the hammer.

Peter from Holland · Apr 19, 2020

Oke
You cannot have it all

Peter

Rob F. · Apr 19, 2020

dian said:
a friend of mine is blacksmith. he has a power hammer and complains that its too fast. i thought of making him a present and install a vfd. would that work or is there more to it? i have no idea about these machines and how they function.

There are many types of power hammers, it would help to know what he has.
I have self contained, some are gear drive and some are belt drive.

dian · Apr 20, 2020

i will find out more about it, when this is over. all i know is that its not pneumatic. what do you mean by "self contained"?

Ries · Apr 20, 2020

A lot of the older self contained hammers had unusual, by today's standards, motors, with lower rpms than commonly available replacements. Its not uncommon to see 80 year old machines outlasting their 80 year old 1100 rpm motors, and having them replaced with 1725 rpm motors. Often this happens when high voltage large horsepower 3 phase motors are replaced with single phase motors when the shop doesnt have 3 phase.
There is a lot of info online about the major brands of power hammer, including original catalog pages, and you can usually find out what rpm and horsepower motor was original.
My guess is the current motor is a mismatched replacement, as this is very common.

For instance, this old Nazel catalog lists the original rpms of the motors as either 900 rpm or 1200 rpm, depending on model.
Both are prohibitively expensive to get these days.
Nazel - United - New England Blacksmiths

dian · Apr 20, 2020

o.k., i see, it doesnt need external air (or steam). the motor in question probably is 700 rpm (by he size of it).

trevj · Apr 20, 2020

I'd suggest a two pronged approach.

A gear or chain drive reduction of the (possibly) too fast motor, to bring the beats down to what is expected, and use a VFD for soft starts and speeding the motor up some, for the times it seems appropriate to increase the beats. A 1750 RPM motor on a machine that was supposed to have a 900 RPM motor, is going to be in a bit of a bad state after running at half speed and having to put out pretty close to full work running the hammer.

As I see it, slowing the motor well below the normal operating speed is more like to cause problems than slowing the beats of the hammer is, which is pretty subjective to the point of view of the operator. A guy can probably adapt pretty well if his 300 pound hammer strikes like a 200 pound one. Maybe less so, if he keeps frying motors!

There are several types of power hammers, the most common found in North American shops are the Little Giant type, which are purely mechanical, and very easy to change out the speeds they run, there are likely more electric/pneumatic types where the motor runs a large piston, which is in turn, running the piston attached to the hammer itself. Nazel and their like, which come in sizes that are far more 'industrial' than the Old Little Giant style.

Rob F. · Apr 20, 2020

dian said:
o.k., i see, it doesnt need external air (or steam). the motor in question probably is 700 rpm (by he size of it).

Does the motor run an internal piston, like the nazel catalog that Reis posted above? That is self contained because the hammer makes it own air pressure, not needing an external source of air (or steam). You could also have a mechanical hammer with any number of types of springs in the mechanism. Little giant and many others used something called a "dupont linkage" IIRC. Other companies had variations of it to avoid the dupont patent. Mechanical hammers need a spring in the blow to take up different thickness of material being worked.

dian · Apr 21, 2020

as mentioned the machine is mechanical. now, i realize that kinetic energy is 1/2mv^2, but if there was a spring that projects the hammer down and the motor only lifted it up the speed should not really matter. does little giant work on that principle?

(i only found a few books on it and a drawing, but didn understand the latter.)

trevj · Apr 21, 2020

dian said:
as mentioned the machine is mechanical. now, i realize that kinetic energy is 1/2mv^2, but if there was a spring that projects the hammer down and the motor only lifted it up the speed should not really matter. does little giant work on that principle?

(i only found a few books on it and a drawing, but didn understand the latter.)

The Little Giant uses a crankshaft to essentially 'fling' a spring loaded hammer assembly both up and down.
There is a foot clutch that is used to control the impact, and whether the operator wishes to get a solid hit or a lighter one, based on how he or she manipulates the clutch pedal.

This video shows the operation fairly well.

vfd for power hammer

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