Measuring hydraulic pull-back ram force

manoweb · Apr 28, 2021

An engineer asked to perform some rough testing on 6061 Aluminum parts I'm fabricating. The setup should be relatively simple, I have to pull this part apart and see how much force it takes to deform it and make it fail. My idea is to fabricate a rig with steel tubing and use a porta-power pull-back ram while filming the process from a couple of different angles, and measuring the pressure with a good quality digital gauge. This should make it easy to calculate the force applied at any given time. However this assumes I know very well the size of the hydraulic piston. This is a pull-back ram and it might be more complicated than just measuring a diameter. I have placed an order for one of these rams and it's going to take a couple of days before I get it.

Anybody has any advice on what I am getting into with this?

Any advice? Thanks!

atex57 · Apr 28, 2021

Ask the manufacturer?

Ed.

manoweb · Apr 28, 2021

I think it's a long shot to be able to get in touch with somebody that knows what I am even asking and is willing/authorized to help a random customer. Nowadays whoever sells this stuff does not even know what it is...

DDoug · Apr 28, 2021

manoweb said:
I think it's a long shot to be able to get in touch with somebody that knows what I am even asking and is willing/authorized to help a random customer. Nowadays whoever sells this stuff does not even know what it is...

If you purchased from Enerpac/OTC/Simplex I would expect an answer.

Using a hollow cylinder for tensioning application is popular, and they need
that information just like you doo.

jermfab · Apr 28, 2021

I would suggest putting a dynamometer inline and then there’s no question as to what force you’re exerting is.

Be safe

Jeremy

Edited because of stupid fingers

manoweb · Apr 28, 2021

That is also an option. Any suggestion on what dynamometer brand I should get?

manoweb · Apr 28, 2021

Eheh we are taking a "scrappy" approach here, this is possibly a one-off test and I'll have to do with much cheaper equipment.

boslab · Apr 28, 2021

You got any kind of load cell?, I’d be tempted to ring a local college with Engineering department, usually helpful, they probably have the latest all singing instronic tensile test machine sitting idle in case the sound of the sample breaking offends some minority group
You can fabricobble just about anything but trying to derive the force from the hydraulic pressure is always going to be troublesome, use the hydraulic to pull or push the load cell is easier, failing that stick on bridge strain gauges are cheap disposable parts, clean, stick and measure, any NDT firm could help
Mark

wheels17 · Apr 28, 2021

I don't know how much force you are talking about, but if it is a "few" off, Amazon sells a crane scale that goes up to 1000Kg for $140. A section of I-beam with a couple of lugs and a come-along would complete the tester. A 300Kg scale is under $35.

idacal · Apr 28, 2021

is it being tested to deform or to fail? that is a big difference it will start deforming before you can see it but most of those cylinders can be taken apart fairly easily and measured. I used a 4" cylinder filled with oil and pressure gauge with eyes on both ends for a juryrigged pull scale on a drill rig casing line so I knew my tonage that was hanging

john.k · Apr 28, 2021

All thats needed is to know the effective area of the cylinder......any brand name cylinder will have this information readily available .....if its a Chinese cheapie,the pull the ram to pieces and measure and calculate the effective area....then you need a pressure gauge....Force is pressure by area...simple.

john.k · Apr 28, 2021

OP says a scrappy approach for a one off......but hollow rams dont come cheap ,so some other approach is needed.....maybe make up a fixture so the loading can be done in the shop hydraulic press.

rbent · Apr 28, 2021

Pressure gage in line on the pressure side of the ram works just fine. Your force is area of the bore minus the rod area and multiply that times your pressure, should get you within ~5 percent.

Frame can be stupid simple, enough steel to not be a concern and away you go.

Crane scale load cells and readouts can be found reasonably priced on eBay if you want a readout. Just having a load cell doesn't do anything for you unless you have a readout and a way to calibrate it. Used dynamometers can be found too, for reasonably priced, but unless you have a way to check it, you don't know if it's accurate.

If you are asking this question, don't even worry about trying to use strain gages by themselves.

Fixturing is always the biggest PITA on doing small testing like this. If you've got a university with an engineering program nearby and you can already fixture it so it is either a straight pull or push, they might just do it for free. Pretty easy to get more time in fixturing than testing.

If you want an actual report, those cost money.

boslab · Apr 29, 2021

Problem with bourdon pressure gauges unless dead weight pressure test rig handy they are as much use as a chocolate saucepan, due to the linkage not even linear, you can tweak the things to get a straight bit around the pressure your at but most of them are wildly inaccurate unless you stump for certification and calibrated.
Electronic pressure gauges may be better I suppose
Mark

manoweb · Apr 29, 2021

boslab said:
You got any kind of load cell?, I’d be tempted to ring a local college with Engineering department, usually helpful, they probably have the latest all singing instronic tensile test machine sitting idle in case the sound of the sample breaking offends some minority group

Ahhaah that was unexpected and so even funnier

Yeah in theory - any other time in history I could ask at least two colleges with very well equipped labs. But during the coronavirus, it's all sealed up and closed, ont even the actual students get to use the equipment. I tried.

You can fabricobble just about anything but trying to derive the force from the hydraulic pressure is always going to be troublesome, use the hydraulic to pull or push the load cell is easier, failing that stick on bridge strain gauges are cheap disposable parts, clean, stick and measure, any NDT firm could help
Mark

manoweb · Apr 29, 2021

wheels17 said:
I don't know how much force you are talking about, but if it is a "few" off, Amazon sells a crane scale that goes up to 1000Kg for $140. A section of I-beam with a couple of lugs and a come-along would complete the tester. A 300Kg scale is under $35.

You are right, my bad I should have given some more details. It's a hexagonal connector made out of 1/4" 6061. The computer simulations say it should take few tens of kN before it fails (that is, few tons). I'm going to use a 10ton pull-back ram.

manoweb · Apr 29, 2021

idacal said:
is it being tested to deform or to fail? that is a big difference it will start deforming before you can see it but most of those cylinders can be taken apart fairly easily and measured. I used a 4" cylinder filled with oil and pressure gauge with eyes on both ends for a juryrigged pull scale on a drill rig casing line so I knew my tonage that was hanging

We are going in all the way

and deformation, cracks, rupture, are going to be filmed but we need to have an indicator of how much force we need to apply. What you are describing does not sound that different to what I was thinking.

manoweb · Apr 29, 2021

Yes the shop press could be used to do this, with a fixture to create tension, not a bad idea!

manoweb · Apr 29, 2021

boslab said:
Electronic pressure gauges may be better I suppose
Mark

Yeah nowadays it's easy to get digital pressure gauges that go up to 10000PSI and some even have USB output to capture with the computer, but the video will be sufficient.

manoweb · Apr 29, 2021

rbent said:
Pressure gage in line on the pressure side of the ram works just fine. Your force is area of the bore minus the rod area and multiply that times your pressure, should get you within ~5 percent.

That part is clear.

Frame can be stupid simple, enough steel to not be a concern and away you go.

Exactly, a little bit of band saw and welding and it should be done quick.

Crane scale load cells and readouts can be found reasonably priced on eBay if you want a readout. Just having a load cell doesn't do anything for you unless you have a readout and a way to calibrate it. Used dynamometers can be found too, for reasonably priced, but unless you have a way to check it, you don't know if it's accurate.

If you are asking this question, don't even worry about trying to use strain gages by themselves.

OK now you made me curious, now I'll check this out, I'm never shy to pull out the oscilloscope

Fixturing is always the biggest PITA on doing small testing like this. If you've got a university with an engineering program nearby and you can already fixture it so it is either a straight pull or push, they might just do it for free. Pretty easy to get more time in fixturing than testing.

If you want an actual report, those cost money.

Unfortunately - Colleges are off limits right now. Even students cannot access the labs.

I got word from the Engineer it will take several more days for the design to be ready to manufacture. In the meanwhile I'll try to come up with something, thanks to everybody for the ideas!

Measuring hydraulic pull-back ram force

Plastic

Stainless

Plastic

Diamond

Cast Iron

Plastic

Plastic

Titanium

Stainless

Hot Rolled

Diamond

Diamond

Stainless

Titanium

Plastic

Plastic

Plastic

Plastic

Plastic

Plastic

Similar threads