Converting pressure to torque

[craigclick]

In the manufacture of laminated timber structures the pressure should be 0.6-1.0 N/mm². In attempting to convert to 'foot pounds', I'm just all over the place with ridiculously high figures (325 ft pd) to incredibly low (4.7). The latter coming from 1 N/mm2 = 1 MPa.

Can anyone shed some light? Thanks

 

[jayrod12]

Well you are correct that N/mm^2 is MPA. However this would in no way convert to a ft-lbs without way more information and math than a simple conversion. Look at the units, how do you go from a force per unit area to a force*length. It's not possible to do a straight conversion.

 

[rb1957]

Agree with previous, don't see how/why to convert pressure to torque?? Unless there's something you're not telling us ...
waht calc are you doing (to come up with 325 ft.lb from 4.7MPa) ?

I think you need psi (1 MPa = 145 psi).

another day in paradise, or is paradise one day closer ?

 

[klaus.]

Pressure and torque are two different things

For conversion of torque see here

 

[JoelTXCive]

I'm confused too.

To get a pressure to turn into a torque, you would need to apply the pressure to an area, which would give you a force. Then multiply that force by a moment arm to get to a torque.

 

[dik]

Are you applying a torque, ie, to a clamp, that is exerting a pressure?

Dik

 

[craigclick]

Exactly Dik, applying torque to a clamp, as in the attached photo. To get it right we want to use a torque wrench.

 

[jayrod12]

Depending how precise you want to be, that's not the best way to do this. A series of load cells at each clamp would be the only accurate way.

Using torque in an instance like this will not be precise as it will depend heavily on friction between the screw and the clamp etc.

 

[rb1957]

um, I don't think that's what dik was referring to.

what you have the a pressure (N/mm2) applied over an area (mm2) via some clamps (compressing the wood, force P)

so P = p*A; the force you have to apply to the area to get your pressure.

now to apply P you (admittedly) torque the clamps. Torque = F*d (F is the force applied to the handle (on both sides of the handle circle, as a couple) and d is the diameter. Now the screw pitch on the clamp causes the compression (one turn of the handle causes the clamp to contact); typical assumption is T = PD/5 where D is the diameter of the clamp thread.

I'd still be interested in how you calculated your result ?

another day in paradise, or is paradise one day closer ?

 

[rb1957]

oh, and don't base load on the number of surfaces being compressed. You apply load to one face and it transmitted through the stack.

another day in paradise, or is paradise one day closer ?

 

[BridgeSmith]

Neglecting friction on the clamp screw threads (which you can't do and still get an answer that is even close), you can convert torque to force using the thread pitch of the clamp screws. Torque on the clamp screw multiplied by pi, divided by the thread pitch will give you the force the clamp exerts. Greasing the clamp threads will get you closer, but even then the applied torque will be much higher than the effective torque.

The only way I know of to get a somewhat accurate estimate of the force being exerted by the clamp is to test one of them under the same conditions (lubrication, etc. where they will be used. From what I have found, the only good way to do this is with a clamp force gauge. To be really accurate, you'd have to insert one of those gauges in your clamping system.

If this is something to be used over and over, fitting it with hydraulic jacks, pressurized from a single pump with a gauge on it would be a wise investment. Then, you would know what force you were applying, and you'd be applying the same force to all the clamp locations (if you need different forces at some locations, use jacks with different sized cylinders).

 

[dhengr]

Craigclick:
Is this a student project or an experimental/research project? That seems like very clean, and very complicated pressing equipment for a GluLam production operation. And, the question doesn’t suggest that there is much experience involved in this process. Manufacturing stds. will dictate some pressing pressure for glue-up of these GluLam members. that is your “.6-1.0 N/mm²,” I would assume. That value should be a well studied value based on ply stiffness, glue squeeze-out, etc. so as to bring the plies into intimate contact, but still will have sufficient glue in the joint so it is not starved of glue. Then, think in terms of N or pounds force per unit of length, or unit area per length, and that will be a function of the width of the beam you are laminating, 2x4, 2x6, 2x8, etc., for a total area per unit length, or a total force needed per unit length.

Except in very well controlled conditions, with much testing to set torque values with the equipment and screws used, torque on a screw or C-clamp, or some such, is a poor way to set or measure clamping force, there are just too many indeterminate variables to deal with. I would much rather use hydraulics or pneumatics cylinders, with pressure gage readings to set those forces per unit length. Then, wedges, spacers, or some adjustment means locks things in place during the curing period, so pressure leakage is not an issue.

 

[oldestguy]

I suspect the poster wants to know the force or grip of bolts by measuring the torque during installation. This ought to be calculated with the scoop on threads and making some assumptions for friction. A statics calculation. This also applies to wheel lug nuts and torque you run it up to.

 

[craigclick]

Thanks all for taking the time to respond. While we are laminating only 1" boards for non-structural purposes, we wanted an idea of the clamping pressure involved and the only info available was for structural glu-lam.

The 325 ft-lb number was mis-understanding my associate; the number was what he came up with using a conversion table and was actually N/m, and not ft-lbs.

I concur that hydraulics or pneumatics are the only accurate way to set/measure the force.

Regards

 

[klaus.]

must be Nm and not N/m
Torque is Force times distance = N times m = Nm

 

[dik]

Should look at some other means of measuring pressure... torque is such an unreliable means of measurement. I never allow the use of a calibrated torque wrench for structural steel bolts.

Dik

 

[BridgeSmith]

"I never allow the use of a calibrated torque wrench for structural steel bolts."

We don't either. We specify a rotation of the nut past a snug-tight condition for most anchor bolt nuts. We check them using our hydraulic torque wrench that can generate up to 6000 lb-ft of torque. It's fun to watch. For fully tensioned bolts we most often see twist-off bolts used, although we allow tension-indicating washers, also.

 

[klaus.]

you can use torque wrench ...but it need to be calibrated before word starts...and in between....

 

[dik]

klaus: you may want to re-consider the use of a calibrated torque wrench.

Dik

 

[rb1957]

really ? for the purpose intended ?? This is not a structural installation, but a manufacturing process. I'd've thought the process was well enough understood to appreciate the potential effects of under (and over) pressure, outside the tolerance band.

If you really want to control the process, simply include a test specimen in the stack. I suspect "turn of nut" is probably the best way to control the applied load.

another day in paradise, or is paradise one day closer ?