Holding Force of Sleeve

I don't think it's clear from the drawing what part is holding onto what... if you delete all but the two relevant parts, it may be more clear.
I expect it's all down to the tolerance, finish and material of the two relevant part.
Mind, what do I know? I jus a cat.
Del

The holding force is 22,308.6262 kg

It depends on the clearance between the sleeve and the internal part when no grease pressure is applied. The higher the clearance the lower the torque/force the sleeve can hold.

Thank you all for replying to my post.

The fit between sleeve and the internal part is H7/g6 fit. Please can you suggest which websites or books i need to look in to do my calculation's. I google it but i couldn't find much info.

Thank you for your time

I don't know what you are googling, but what you describe is a standard press (interference) fit and almost any machine design or even solid mechanics textbook will have good information on how to calculate.

I do not like when wrong indications are given. H7/g6 is a fit with 10 to 50 µ clearance.

The problem is that before you press the internal part you have to deform the sleeve and bring it into contact with the fastened part. The contact pressure depends of the sleeve stiffness and of the part stiffness. The problem is not as trivial as the other comment says. It depends also of the surface quality and of its "lubrication". It depends of the fact that the sleeve has a continuous surface or some groves to eliminate possible oil or other fluids present at assembly.

H7/g6 is a precison - Normal running/ sliding fit.

At dia 120 g6 (Shaft) is 12 to -34 microns and H7 (Bore) is +0 to +35 microns

It is just a bit worse that the standard precision H7/h6 that we more commonly use for precision fits.

Since it is a clearance fit, the holding force by itself would be theoretically zero (practically it would exist due to surface roughnesses and imperfections as well as the loading patterns)

Something else I don't understand is

OD112mmxID106mmx39mm (Thickness=1mm). ?

Thickness = (112-106)/2 = 3mm isn't it?

The whole configuration looks complicated- the actuating piston what does it do? The way it looks like that the grease is getting compressed and then creating an elastic/ plastic deformation on the sleeve (brown) and that is holding the member with the piston (pink) and the center (Darkish yellow ) Is it corerct presumption?

In that case the whole lot would depend on the pressure that you are applying through the grease on the two sleeves. Then that (axial) had to be converted to radial pressure and it would give you the torque carrying capacity.

The sleeve would seem to be 3 mm thick, not 1mm.

Is the outer surface of the sleeve subject to grease pressure, applied via the piston? Is the piston the small blue item? What is the material of the sleeve? Is the sleeve sealed at its ends to retain the grease pressure? What is the device expected to do? It looks as if the device could hold the center to the tailstock, but the center already has a taper for that purpose.

A clearer drawing with all parts called out would help.

I am sincerely surprised by the comments made. The device is a very common centering and holding device which uses a hydrostatic pressure to generate a holding force in axial direction and a torque.

Above sketch will explain its function. The bushing is usually made from a high strength steel and is sealed in its holder. The small piston moved by a screw with an O-ring presses the grease so that the wall deforms as in the bottom part of the sketch. It makes contact with the part to be hold and if pressure increases further then it is applied (part of it function of sleeve stiffness) to the contact surface generating the force which due to friction builds up the axial holding force and the holding torque. The deformation of the sleeve can be ONLY elastic since when pressure is released the sleeve comes back to its initial position and gives the part free as it is in the upper part of the sketch.

I hope that with this sketch it will be clear why I wrote that the force and torque depend on several factors as listed in previous comments.

Pressure can be important several hundred bar.

The device is also used in centering since its effect is very precise.

Hi Nick,

Nick, You are the best in the industry. You are the only person understood the concept. Even my customer don't know how it works , even after sending 3D model.

So please can anybody tell how to proceed with calculations.

Thank you for your time

Thank you for the compliment but as you see even if it such an enthusiastic comment your side it is not considered as a good answer since there is only 1 vote.

I suggested several times that a vote from the OP should be considered as double since the answer satisfies his request. It seems that changing the program to recognize the OP vote is too complex. We are not very "client oriented".

Now with respect to computations, what do you want to compute ?

There are 2 possibilities:

- FEA model but then you need a quite high level FEA soft since you have to simulate the contact (do not forget that its stiffness is playing a role in the results)

- a classical approach with equations and solving the system to obtain the unknown, it takes quite a lot of time and also is not easy.

You have the choice.

It seems odd that you are the supplier, but do not know how to calculate holding force. It also seems odd that your customer would request a 3D model, but does not understand what he might be buying.

The effect of sleeve deformation on reducing clamping force would be taken into account in the engineering of this device. Likewise, the effect of the "kink" that develops at the edges of the sleeve at high clamping forces would be taken into account, typically by using FEA. Will there be fatigue here? How much is the effective clamping area reduced by this effect? In doing this engineering, the clamping force will have been calculated. I'd say the easiest, most accurate means to get holding force vs pressurizing screw torque is to talk with your engineering department.

The effective area times the grease pressure will give you a clamping force. This, times the coefficient of friction will give you an axial holding force. Using the radius, the holding torque is easily calculated. The relationship between pressurizing screw torque and grease pressure is a simple calculation based on the screw type and size, the cylinder size, etc. How did you come to be a vendor of this but not have the engineering details?

K-Fry

First you didnt understand concept

I would say you are copycat, you just copied what Nick said.

If you are so intelligent, there is flaw in the Design. You didint point out.

So..................... ...

If see the picture properly, there is no outlet. Ä

I would say you are copycat, you just copied what Nick said.

Revealing. You seem to have a sensitivity to copying.

Actually, I am glad to see that my response and Nick's are similar, but in fact, I didn't copy him. Any engineer would say that there are essentially two approaches: using FEA or doing the calculations manually.

You've missed the subtle differences in his post and mine. I was implying that there is a third route: You can (if all you want is an estimate) ignore the stiffness of the part of the center that gets clamped, and that of the outer portion of the clamp that must resist clamping force. You can even ignore the stiffness of the thinned portion of the sleeve if the clearances are very small relative to the overall diameter of the piece being clamped. Then you can consider the effective area of the sleeve to be about 80% of the thinned area, and just consider grease pressure over that area. Typically, the clamping force will be in tons (metric or English).

However, as I said, your engineering dept should have this data. You are not, I assume, the designer, because designers do not ordinarily design things backwards: You need to know the forces involved before you design the parts -- that goes without saying, right?

If you are so intelligent, there is flaw in the Design. You didint point out.

The flaws in the design are independent of my intelligence or lack thereof: your statement makes no logical sense. Your statement suggests: if I were stupid, there would be no flaw in the design. I didn't do the design.

I am not here to point out design flaws. If you were looking for criticism, then you should have asked, and should have provided a detailed, clear design drawing.

rka9b- You are new to the forum hence please take this as an advice. This type of addressing copycat is not one we prefer in this forum. In case you have taken the pain to go through the post of K-Fry you would have found certain differences that won't have taken place had one copied and pasted.

In a post one might overlook what a previous post had said and there may be overlaps, detailed explanations and even entirely opposite interpretations and all would be correct to certain extent depending upon what the OP had deigned to provide as input.

The factors that are in play here are quite complex and need a rigorous exercise and that would include the temperature (especially in view of its differencial effect on grease).

I feel that you should calculate the maximum holding force which would be quite easy to calculate based on mechanical calculations based on the pressure or even better is the go for what is required multiply by the factor of safety and look for the grease pressure required to achieve the torque carrying capacity.

You mention effects (differential) of temperature on grease behavior. Please elaborate since the device is for a machine tool working in a plant. The only temperature rise could come from the tool itself and as far as I know it does not affect the compressibilty of grease. In this application any fluid could be used since it is a hydrostatic pressure transmission but grease is preferred for its high viscosity which makes sealing better.

With respect to other remarks made. The sleeve and part stiffness play a decisive role in the building up of the holding pressure. The sleeve wall thickness influences at power 3 and not at power 2 as in the stress computations. As well the ratio t/d has a big role so that a recipe (X% of projected area) is not to recommend. What I would recommend is to contact the MANUFACTURER of the holding device which is not the OP since I presume he is ONLY the re-seller of an imported machine. I doubt that his company is the producer of the device so that I believe his engineering dpt. does not know more than he on the subject. It is also possible but I do not think it is the case that his company made a copy of an existing device on a known machine. I did not look further for flaws or errors since the information is not sufficient for it.

Your comment is NOT out of range! On the contrary for the correct computation this MUST be considered. The pressure rise estimated with usual values for the expansion coefficient and bulk modulus for mineral oils is around 1.6 MPa/°C ≈ 130 psi/°F. It has not to be neglected. As far as I know the tightening torque limits the pressures but one can be very strong and then a very high pre-load + a temperature increase can make problems especially at the sealing level and then if it leaks other problems can appear in process.

It was good as well for the OP to be informed so he can be aware of the torquing limitations. I also have the feeling that his country is quite warm so that the problem can be even more acute.

The only temperature rise could come from the tool itself and as far as I know it does not affect the compressibilty of grease.

The drawing, crude though it is, shows a live center held primarily by the locking taper of the center/tailstock, and secondarily by the diaphragm chuck. It is reasonable to assume, as anonymous #2 did, that the workpiece will heat up and transfer heat to the live center and into the chuck. CNC machines have features to deal with dimensional changes from such heat transfer, so it is reasonable, I think, to believe that they occur. You have probably been around machine tools, and have witnessed workpieces becoming warm. In manual machining, I have had to deal with such temperature changes all the time.

With respect to other remarks made. The sleeve and part stiffness play a decisive role in the building up of the holding pressure.

If you do the math, I think you will find that the role is not particularly decisive, if by that you mean major. Certainly, from the drawing, which appears roughly to scale, you can see that the chuck housing and the center are of very heavy construction as compared to the diaphragm portion of the sleeve. Because large differences in thickness, the relative differences in stretch and compression of the pieces involved is huge. The diaphragm is stretchy; the center and chuck housing are not.

However, even if the center and chuck housing were made of relatively low modulus material, the effect would be to compress and stretch those pieces slightly more but this would only affect dimension, not holding force. Going to extremes, the chuck housing and center could be of aluminum, and the only effect would be to require that the screw be turned in slightly further to compensate for the larger volume cause by microscopic distortion of those pieces. The grease pressure would not need to be higher for a particular holding force (other than at the very low holding forces where deforming the diaphragm is a significant part of the problem).

What I would recommend is to contact the MANUFACTURER of the holding device which is not the OP since I presume he is ONLY the re-seller of an imported machine.

I had assumed that the OP was from the manufacturer*, but you might be right. There could be communication difficulties with the manufacturer, perhaps. Or perhaps this is a used piece, and the manufacturer is no longer in business. Of course an alternative to calculating (and more accurate) would be to simply put the chuck in a press, with the center pulled out a few mm from bottomed, and measure the force required to push it in (that last few mm) at various screw torques.

* and certainly wondered if this might be a copy, thus explaining the lack of knowledge on the part of the OP.