Calculating safe operating load on a hydraulic press

[imagineers]

I would like to calculate the safe operating load on a hydraulic press we have. There is no operating label or load label on it. Is there a way to calculate this ? I attached a pic

 

[desertfox]

Hi

Are there any labels on the cylinder itself? if you can find the safe working pressure of the cylinder and its full bore diameter it would be a start, if you manage to get the safe working pressure it's still not the answer because the weakest part of the press might be lower than the maximum force you can get from the cylinder.

Without any information it's going to be very difficult because for example I could calculate the maximum load in the cylinder that would generate say the yield stress in the bolts attaching it to the frame as being the weakest point, however that load would depend on the size and grade of the bolts and in addition to achieve that load I might have already exceeded the safe working pressure of the cylinder without knowing it.

 

[3DDave]

Just analyze joint by joint to see what the load capacity is. I suggest a safety factor of at least 2:1. The big problem is the material; assume most of it is 36ksi steel. You'll have to check the bolts to see what grade they are to be sure of their strength. It looks like simple shear, tension, and simply supported bending for the various components.

Other failures include rupture of the hoses or the hydraulic cylinder.

The biggest concern is that it doesn't look to be bolted to the floor or a wall and has short feet; It's not a huge falling hazard, but that depends on whether the area is prone to earthquakes or being nudged by a fork truck. 99% of such items will still be standing 100 years from now, but that 1% can be painful.

 

[imagineers]

Well thanks guys...Not sure if there are any labels on the cylinder as I haven't taken a close look at it yet. I can find out bore diameter. So what should I do first , go take measurements of the parts ? Get as much detail on the motor and piston? Should I try to simulate this in say... SOLIDWORKS ?

 

[desertfox]

Hi

If it's easy to get the cylinder bore size and wall thickness of the cylinder that's a good place to start.
If you know the working pressure for the cylinder and we get the bore diameter we can establish the maximum working force of the cylinder.

 

[imagineers]

Where can I get the working pressure for the cylinder? Getting measurements is easy, getting working pressure of the cylinder I am not sure. Also, I have not looked at the system in person but it looks like it is controlled by a motor, how does this fit into the equation with rpm speed etc?

 

[imagineers]

are you talking also about the strength of these bolts?

 

[MintJulep]

The simplest starting point would be go shopping.

http://www.dakecorp.com/products-detail.asp?section=models&page=Elec-Draulic II

And other manufacturers.

Find one that matches all the important dimensional parameters, and then you'll have a pretty good idea of its original rating.

 

[imagineers]

MintJulep,

most of the specs they call out are very close. the horsepower, rpm etc are exact same, what factor is influencing the rating to double on these ie 25, 50, 75 tons??

 

[MintJulep]

What factors do you think are important? Why?

 

[imagineers]

I am not 100% sure, I am assuming bore diamter, and working pressure are important, but how do I compare these models to the one I have? they are almos identical looking except a few spec differences namely the C minimum ram to table
D maximum ram to table, and ram speed press and return values. there is no mention of piston diameter or anything

 

[desertfox]

Hi imagineers

The bolts I was referring too was those that you have marked number 2 on your upload.
The main factors in deciding the hydraulic force will be the cylinder bore size and the working pressure, I assume the electric motor is for pump operation which may also have a bearing on the hydraulic force.

If your getting dimensions and as I mentioned earlier if we can get a measurement of the cylinder bore and outside diameter we can estimate the working pressure from the cylinder wall thickness.
Once we have the maximum working load we can then check the other bolted joints for suitability.

Final question have you any idea what you want to use the press for? if we know what its going to do we could possible workout the required force from that.

 

[imagineers]

I will get the measurements and will respond with an update

 

[imagineers]

and the press is mainly used for pushing bearings and straightening bent parts

 

[imagineers]

Also is there on online calculator to determine this if you do have the cylinder and dimensions?

 

[desertfox]

Hi imagineers

There might well be online calculators for working out the force of a cylinder made of a known grade of material for a given working pressure but the situation your in is slightly different because we don't know the grade of material the cylinder is made from.
To explain further the cylinder is basically a pressure vessel and should be made to some design code which would limit the working pressure for that particular cylinder, if we get the measurements I was going to use the least strength grade of steel I could find and work out what the maximum pressure would be, this would be conservative and give a safe value of pressure and ultimately a force for the press assuming of course the bolts and other structural parts hold up.
However we need a starting point which frankly at the moment we haven't got.

 

[Compositepro]

You have a commercially built hydraulic press, in good shape. It should be fairly simple to find the manufacturer. The pressure gage may be marked with a safety limit, and there is almost certainly a relief valve in the hydraulic circuit that will open if the safe working pressure is exceeded. Just looking at it, I would guess that it is a 50 ton press.

 

[JStephen]

I'm not sure how you'd actually specify a "safe" working load for something like that. If it's all the complete unit as manufactured, then the beams and bolts and all that should be adequate for the full force of the cylinder. If it's a replacement pump or larger cylinder or something like that, then you may have problems determining proper load. If you want the "rate load" rather than a "safe" load, then manufacturer's info or maximum pressure (if available) times cylinder area would be the numbers.

 

[imagineers]

The whole setup was build by hand, and was not commercially built, which is why there is no spec on the unit. The pump I might be able to find information on, but the rest, like bolts and steel they used etc, I am not sure. I would have to assume the lowest. When I get a chance to run by the place I will get as much info on the unit as I can.

 

[imagineers]

Also, can I assume the maximum force from looking at the pressure gauge to use in the calcualtion, or since it is not a commercially purchased press, can I assume the gauge may not be suitable, thus have to calculate maximum pressure using the measurements of the cylinder?