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Impact Force of a JackHammer
3

Impact Force of a JackHammer

Impact Force of a JackHammer

(OP)
What is the best way to calculate Impact Force per Blow given a jackhammer's weight, BPM (Blows per Minute), and Stroke Length? For ,example Ingersoll Rand JH40C3 has a Stroke Length of 67mm, BPM of 2000, and a weight of 27.7 kg.
I was thinking to use F=(0.5MV^2)/2 or F=(MV)/T ,but I am curious to see answers from others. Ingersoll Rand stated this is not information that they provide.

RE: Impact Force of a JackHammer

You would need to know the weight of the reciprocating, impacting piston and its velocity just before impact. Then you could apply the energy equation. Impact velocity and return velocity are not equal.
We would use an impact test machine to measure the impact output of a breaker.

Ted

RE: Impact Force of a JackHammer

What do you really want to know? What does "impact force" mean? Place the same jackhammer on a load cell on a steel plate vs a pile of gravel and your reading (if it were capable of sampling that fast and not being destroyed) would be significantly different.

RE: Impact Force of a JackHammer

If you don't mind I'm curious about what the value to knowing the impact force per stroke is? If the consideration is the amount of work the hammer is expected to do than the numbers you're using refer to a new tool and it's all down hill from there determined by many different variables. Also with respect to the work getting done wouldn't the primary consideration be the bit and bit condition along with the amount of pressure\force being applied by the hammers operator whether manual or mechanized?

This highlights information IR at one time issued with impact wrenches used in production with various torque sensing devices being translated to hammers.

RE: Impact Force of a JackHammer

https://www.eng-tips.com/viewthread.cfm?qid=328481

I think whatever force number you have will be meaningless. Even a 27 kg hammer will bounce around all over the place without the 120 kg "fatboy" leaning on it.

Bit size and area of the bit will have a huge impact on the number as will whatever you're trying to break up.

Far too many variables to get any answer worth having.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Impact Force of a JackHammer

All you will really know is how much energy is delivered to the shank of the drill rod.

Ted

RE: Impact Force of a JackHammer

This rockdrill has a 2.5in. bore and 2.63in. stroke. The rifle bar diameter is around .75in. diameter. If the air pressure was constant 90psi for the full stroke, the work done = energy would be at best about 88ft-lb. The piston will not use the full stroke before impact. The air pressure will not be constant for the full stroke. Some energy is used turning the rifle bar ratchet.

Ted

RE: Impact Force of a JackHammer

The value by hytools provided constant pressure in the chamber will be higher because on the downward travel of the stroke, the input energy has to overcome the springs compression unless the jack hammer is two stroke which I doubt. The springs are needed to return the stroke back up.
on my behalf this is the way I would estimate. Your Ingersol Rand manual should list the air consumption at various air pressure so the input power to the jack hammer will be the air pressure times rate of air consumption. The input power input is equivalent to the rate of work which equals to force time average velocity of the shank. The only problem is to be able to get cycle speed of the shank to determine the average velocity. Once average shank speed is available the force will be the impact force. But again the surface which you are trying to break up MAY have a bearing on the speed of the shank.
Before you get too involved there is a trade magazine "Equipment Today" which compare construction equipment and which provide comparison information of such equipment. Do a search and you may be fortunate to come across more details about jack hammers. Also Ingersol Rand was bought out by Atlas Capco and there is a booklet of their pneumatic equipment which they provide to their sales force. If you are a good customer you may be fortunate to get one of those booklets. I had one but one of my former ACAD student never returned it.

RE: Impact Force of a JackHammer

My first pass on thinking about a jack hammer operating vertically - it seems like the point would be that the hammer body is raised pneumatically and free falls until the body impacts on the chisel. (Let the tool do the work.) So the potential energy between the body at top of stroke and the chisel on pavement would be the amount of energy available (maybe the belly of the operator raises and falls also). As far as force - W = f x d, so how far does the chisel penetrate the pavement per impact to get force as a function of potential energy (mgh) and penetration depth?

RE: Impact Force of a JackHammer

The springs on the steel retainer do not return the hammer. The springs keep the steel retainer in place under the drill steel collar. The valve in the backhead is pilot operated by the hammer position and directs compressed air to the underside of the hammer to return it. At approximately midstroke the piston head portion of the hammer passes the exhast port in the side of the body.

There is generally a double impact on the drill steel. One by direct impact of the hammer, the second by the body when it returns down against the drill steel collar.

In a previous career life I worked for Gardner Denver in their mining and construction division which designed and manufactured pneumatic tools. They were a competitor to IR, Joy, Atlas Copco.

Ted

RE: Impact Force of a JackHammer

Propelling the hammer downward lessens the body impact? I guess the operator provides the resistance/reaction and not acceleration of the body away from the pavement. Interesting to think about.

RE: Impact Force of a JackHammer

Sharpy Impact force to shear concrete or rock, go from there

RE: Impact Force of a JackHammer

2
This topic of impact force comes up regularly here and it seems the discussion is always the same, and off-track. A hammer blow supplies only energy, not force. The force is created by the resistance of what is being hit. An infinite resistance would theoretically create infinite force. In the real world something has to give. Rock may crack or pulverize or the impactor will deform elasticly or plasticly. There is no simple way to calculate impact force accurately without using FEA on a microscopic level, and with detailed knowledge of the material properties of the impactor and what is being impacted. The geometry of the contact area is also critical. The only thing that can be accurately calculated is impact energy or absorbed impact energy, as with a Charpy impactor

RE: Impact Force of a JackHammer

That is all the OP asked. How to calculate energy.

Ted

RE: Impact Force of a JackHammer

Errrr "What is the best way to calculate Impact Force per Blow..~"

Looks like the force question to me.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Impact Force of a JackHammer

Actually he asked about "calculating impact force" using the specs of the hammer. As many have questioned, what's the value of any information calculated using the limited information given? It wouldn't translate to anything having to do with actually using the hammer. It's like someone giving the HP and torque specs for an engine and then asking for someone to tell them how fast will their car go with just this information.

RE: Impact Force of a JackHammer

Littleinch, you are correct. I was reading it as I often heard a customer question with my interpretation of what they were actually asking.
Thanks for clarity.

Ted

RE: Impact Force of a JackHammer

Also my post wording should have been
Charpy impact test

RE: Impact Force of a JackHammer

"I was thinking to use F=(0.5MV^2)/2 or F=(MV)/T"

The first equation is 1/2 kinetic energy.
The second equation is impulse-momentum.

Was not sure how to answer. Chose energy.

Ted

RE: Impact Force of a JackHammer

The stroke of the chisel would be the distance.
Shouldn't this also apply for an impact wrench?
My suggestion would be to reverse engineer
A jack hammer.

RE: Impact Force of a JackHammer

mfgenggear, the links you are posting are not very relevant to answering the OP's question. You are getting distracted about details of how jackhammers are designed rather than understanding the concept of how impact force is created at the tip of a chisel when hit by a hammer. This is a very important concept to clearly understand, in many fields of engineering and everyday life. It seems a simple concept at first, but it is pretty complicated to understand the the first time one tries to figure it out. This is why this question keeps coming up. If one takes the effort and time to figure it out once it will save time and effort many times in the future, and make one a better engineer. In most cases, true impact force is a function of time during the impact event and almost impossible to calculate theoretically. Impact energy is much easier to quantify.

RE: Impact Force of a JackHammer

,@compositepro
Thank you for the explanation
Much respect a star for you

RE: Impact Force of a JackHammer

I am stubborn. It does seem simple.
But nothing is as it looks.
Time to move on

RE: Impact Force of a JackHammer

Well as the OP appears not to have even bothered logging in to look at the replies since he posted the question it all seems a bit moot. But I'll remember this one if it comes up again.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Impact Force of a JackHammer

Almost the same discussion 8 years ago.

Ted

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