OT hydraulic press safety

[kamenges]

Originally posted by JeffKiper:

OSHA said it doesn't qualify as a hydraulic press because it is air powered.

Isn't that kind of like saying "You won't drown in that pool because it is only 8 feet deep, not 80 feet deep".

Is there a separate regulation covering air powered presses? If not, why not? Last I checked force is force. My hand really doesn't care how that force is generated.

As Dan said, I'm glad you are going beyond the requirement. It seems to make sense in this case regardless of what the regulatory agency seems to say.

Keith

 

[JeffKiper]

Will the ram drop if an air line is disconnected, or blows?

No the ram will creep down. What is an acceptable spped? OSHA ans ANSI haven't declared what a safe speed is for ram creep as of yet. ANSI has a proposal out but it hasn't been adopted yet.

Is the Solenoid that controls the valve driven directly from the PLC, or an interposing relay?

Yes from the PLC. The PLC is getting it's supply voltage from the Safety module. THe light Curtains are going to drive the Safety module.

What if the Relay gets welded closed?

It is a safety rated force guided relay so The system will not move.


I just talked to a guy that sits on the ANSI board. The current version of B11.2 is titled "Safety Requirements for Hydraulic Power Presses" The current revision of B11.2 is entitled "Safety Requirements for Hydraulic and Pneumatic Power Presses"

Like Keith said does you hand care what is casing the force? If the single non safety rated mechanical solenoid fails and the cylinder crushed my hand or the contacts weld do I really care?

 

[Peter Nachtwey]

I have worked in saw mills. They usually have a mechanical safety stop that keeps the two halves of the machine from coming together when working between the two halves. The cylinders must be retracted in a safe direction and then the pressure is off the hooks so they can be lifted. I have seen many presses but most rely too much on electronics. I would like to see more mechanical stops or hocks that extend and block the press and the mechanical stops need to be withdrawn. It seems to me a spring would do the job and the spring could be forced back with air when everything is working right.

As far as valves go. Again in the saw mill industry there are often blocking valves between the servo valve and the cylinder. These valves must be energized open. There are contacts and relays that must keep these valves energized open. If any relay or contact opens the valves close. However, this doesn't keep the cylinder from moving it just keeps the cylinder from moving quickly. The cylinder will probably drift slowly due to leakage. This is a problem because most of the time the press is applying force on the cap or blind side of the piston. As the pressure equalizes between the rod and cap side the cap side force will be higher and extend the rod. On top of that gravity is pulling the press down.

Also, check the electrical output to the valve. Make sure it can't possibly fail high ( energized ) or there is some way to detect when it does.

 

[Steve Etter]

My question is what type of valves do I need to be using?

Jeff - For mechanical presses, clutch and brake valves are known as press safety valves.

Please see THIS link.

While you are clearly not working with a mechanical press, what you seem to be wanting is a "control reliable" valve so this might be a good solution.

Steve