Isolating a Power hammer slab.

[nonjic]

This issue seems to raise its head time and again, and I have helped seveal IFI members out by PM when installing hammers.

Firstly, There is no one size fits all solution to isolating the vibration from a hammer. I am not an expert on vibration attenutation, and there is a lot about it I dont understand.

As far as I understand it in order to stop the transmition of vibration the frequency of the hammers vibration has to be matched to the frequency of the isolators, which effectivly cancels it out. (not enough isolators and it will bounce, to many and it will transmit the vibrations still)

So, .... Whilst I am far from an expert in this somewhat specialised field I have over the last 15 years put quite a few hammers onto isolated inertia blocks (up to 6000lb ram weight).

We have used the method outlined below with measured 98% attenuation from inertia block to surrounding ground. It is, in my opinion the simplest method of isolating a slab, that works.

I can not answer specific questions about your individual hammer install, and I can not accept (nor my company) any responsability for how the information here is used.

There are several companies that can supply the synthetic cork and void filler, two that spring to mind are James Walkers, who supply the TICO S pads, and Fabreeka.

So, In a nutshell. Decide (or calculate!) how big an inertia block you want (generally bigger is better, mass is the best isolator!).

1) Dig a hole in your floor. Shutter it off and pour your concrete. you now have a smooth walled, and floor 'pit'

2) Glue the isolators into the pit. Line the pit with plastic sheet. (Any ingress of concrete between inertia block and surrounding ground will transmit the vibrations.)

3) Drop cage of re-bar into the hole, with your hold down bolts secured in place, again, DONT TOUCH THE SIDES!!!!

4) Fill hole with concrete. Leave a month or so. install hammer and have fun without upsetting the neighbours, VMC's CMM's etc!

If you study the sketch (done in BiroCAD v-1 ! you will see that the top 'capping' strips end up sitting on a ledge of concrete, so can not disapear down the sides of the inertia block. When I do the install I additionally put a 1" sq piece of pine over the top of the TICO pad, at what will be floor level.

When the concrete has gone off, remove the pine strip (which will leave 25mm channel all round the top of the Inertia block, and then fill this channel with a liquid rubber to keep debris from the Tico Pad. I have used 'Thioflex 600 PG' with good success. (this is a 2 part polysulphide rubber used for expansion joints on concrete floors etc, available from builders yards etc.


There are lots of other ways to do the job, If you know a better proven way, or have experience in isolating slabs please post in this thread, hopefully it can become a usefull resource in the future!


Please click on the thumbnail to a larger version of sketch. Please ignore the dimensions for the inertia block. These were for a specific machine.

Edited October 6, 2009 by John N
info & thubmnail added.

[pkrankow]

This is a more advanced method that was discussed in class. For clay earth there was no sleeve, just poured straight onto the undisturbed earth with an expansion strip between the new slab and existing slab.

Did your company evaluate that case, and how much of a performance difference was seen?

Phil

[farmer12888]

Thanks for the great information. Few questions: how thick should the walls and floor be poured? is thickness some ratio to inertia block? rebar in walls and floor or can rebar affect isolation? You are alternating strips of isolator pad and void filler for 50% each coverage on the floor only of the pit?

Do you have any experience with air isolators such as Firestone Airmount Isolators (airbags) which are apparently used under some commerical forging hammers and supposedly allow the reduction in the size of the inertia block? (Maybe eliminate inertia block for smaller hammer?)

[nonjic]

I cant answer to specifically on the thickness of the 'underslab' or walls, other than to say they are there only to support the mass of the hammer and inertia block, NOT vibration if the system is working well! Local ground conditions will vary.

There is little point in just having an expansion gap between the hammer slab and the floor, with the inertia block resting on the sub soil. That is not an isolated foundation. it is an expansion gap. I say this as many of the problems of ground borne vibration are not seen next to the hammer, but some distance away. The vibration is transmitted a considerable distance, and can show in neighbouring properties, when there is seemingly no vibration next to the hammer.

We re-installed a hammer at a plant in London as the vibration was showing up in an office block several hundred feet from the hammer due to a chalk seam (with no vibration around the hammer itself). Vibration will also travel through groundwater etc.

On the hammer foundations I have payed to be designed they always seemed to come up with approx 50% of the pit floor as isolating material, the rest void (especially with the Tico s pads), hence that is what I have shown in my sketch. Of course the mass of the hammer and inertia block, and the frequency of the matting will dictate the exact % covering you need. Perhaps someone will post post how to calculate this.

The sketch above is just to show the principle, as I have installed them in the past. It is not a plan as there are to many variables for me to say 100% this is what you do. If I was installing my own, small, 1 piece frame hammer I would go with the sketch as above.

If you were paying me to install a hammer, and isolate it, and I had to guarantee it would work I would pay a specialist to run the numbers for me, and I would pay a civil engineer to do all the calcs on load bearing etc.

The foundation as sketched is the most ecconomical way I personally know of isolating a slab.

You could just bolt your hammer to a 3" steel plate to eliminate the inertia block, and put the isolating pads under the steel plate. Thats not an isolated slab, its just machine mounts.

If you are considering using commercial air isolators / spring & damper units get a price for them before you spend to long designing the install, and be sitting down when they give you the price. However...... when you pay full whack from a specialsit supplier they will advise you what you need, and you wont have to rely on possibly sketchy advice from some bloke on the internet you have NO comeback against. your call :D

[farmer12888]

Thanks for the answers to the questions. I really appreciate the technical approach and information. It makes sense that a chunk of concrete with an expansion joint in a hole in the slab just setting on the sub-soil may stop the slab from cracking from impact but will do little if anything to control or reduce vibration in the soil and, thus, in the walls of nearby foundations. An actual isolated foundation/inertia block must be used to achieve vibration control.

[JNewman]

While John's information is excellent I think you have to remember that the hammer installations he is speaking about are for huge hammers with tup weights weighing as much as your whole hammer. These installations are in the 10s or even 100s of thousands of dollars. You are installing a small hammer that if you are concerned about shaking from the hammer, just pour an extra yard of concrete in your foundation. That is about an extra 2000 lb of mass of inertia block for around $100. The extra weight makes a big difference. Put a 1lb block of steel on the floor, hit the side of it as hard as you can with a sledge hammer, now do the same with an anvil. My 600lb hammer with a proper foundation (that I bought the plans for from John N) shakes the floor far less than my homebuilt hammer does with a 100lb head and no foundation but the floor sawcut around it.

[nonjic]

Hi John, Hope the Massey is starting to earn its keep!

Mass is a great isolator, and im in full agreement about the extra yard of concrete.

The synthetic cork isolating system Ive described above works great for hammers of all sizes (although as you point out, most of my installs have been on 250kg +

If you think about the system its only really less than 1sq mtr of 'proper' isolating material for a small hammer (polystyrene sheet will work for the void filler). Though there is a lot of extra hours in doing the job.

Ive really posted it here as I get lots of people who ask me about lining pits with conveyor belting / timber etc, then doing a second pour for the slab. (ie, the same amount of work as doing it as described above)

[myloh67]

John N, thanks for all your time and input, very much appreciated!
Today I managed to lift my hammer 31.5 inches over its anvil using gantry that was self built (and non creaking) and laid it to rest on the block. The block of 40 newton vibrated concrete 2.5cubic meter sits on the the dirt. It is then has an outer layer of 40mm polystyrene sheet for sides 3mm hardboard and backfilled to the vertical dirt with compacted sand.
I used 600 polysulphide thioflex on the floor of the anvil socket in which i attached 50mm fabreeka pads. Sat the anvil in and wedged with oak slips. Everything at the moment looks ticketyboo! (funny word that), will wedge anvil to foot casting apeture, all that remains to do is excavate and pour shallow foundation for motor 300m deep, aquire star delta switch fie up and destroy an innocent hard boiled egg, why because I'm not much good at forging hard boiled eggs.:D

[JNewman]

Yes John the hammer is starting to earn its keep. I have been working a lot of 3" 4340 taking it down to a feather edge. I am actually using full power occasionally.

[MadHatter]

John N, thanks for posting the info. I am just in the process of setting up my new (new to me) 50k SayHa, and have been wondering how to minimize the vibration so the neighbors don't have a reason to shut me down. Not quite ready to cut a hole in my slab yet, since I'm going to experiment with shop layout now that I have the Hammer. But at least I have some direction, and will be looking into this Tico S stuff and Fabreeka.
BIG help! You answered a lot of questions.
Thanks
Chad