OT hydraulic press safety

[JeffKiper]

I am quoting a retrofit for a small air over oil press. This small 5 ton press is now being used as a hand in die operation. The press controls are simple in this application.
My question is what type of valves do I need to be using? I was thinking a simple 4 way 4 port valve. This is a machine where someone will be putting their hand in it every 20 seconds or so 16 hours a day.

 

[leitmotif]

Jeff

Is this a simple hand operated valve OR electric controlled valve?

What is actuation speed of dies? I think this may be the critical question.

If a similar setup to the presses used to press on or remove bearings then I would think all you need is a simple hand operated valve. This is a bit different than hands in dies and even more different if a high speed unit.

Dan Bentler

 

[JeffKiper]

No Dan it is a electric solenoid. 4" stroke in 5 seconds.
It is currently a 2 stage system with a low force fast advance then a high force slow speed advance. Then both return. So there is the potential for serious personal damage. I am going to use Light Curtains and two hand controls. I know from the years of doing stamping presses that we still had to have self monitoring valves in the mechanical press world. Every other machine I have built over the years have always been on turn tables or shuttles. So the point of hazards was the loading station. I haven't done a machine that was a hand in die operation that wan't a full blown mechanical power press. So you see where the problem is?

 

[leitmotif]

I have read enough accident reports on presses to last for a long long time. Two years ago a lady I knew sawed off a hand. Harborview (Seattle) was able to put it back on and were pretty sure she would regain 80%.
20 years in health and safety field.
The speed of advance and electrical controls are main issues in my mind. I could easily agree with two hand control or a curtain and not blink an eye at the cost. I think you are correct.

Quick war story In about 1991 at Boeing where I was Health and Safety another safety guy brought me a diagram for controls on a sheet metal shear. I could see the motor and contactor normal 3 phase and teh light curtain. BUT all the control wires went to this box on the print that said AB xxxx.
So we went to the equipment engineer and I asked him what this AB xxxx gizmo was and why all the controls are going to it. He says its a PLC kinda like a computer and does all the controls. I worked with the guy and knew I could trust him so I said I know nothing about it - can we really trust it. He said yes BUT we will test to ensure - think you should be there anyway. It worked trouble free for at least five years that I know of.

When I learned a little on PLC I started wondering if I had made the right decision.

Dan Bentler

 

[JeffKiper]

I still have trouble second guessing myself years later as well. I built this machine about 10 years ago. It had a indexing table and light curtains on it. The hand where not in the die so I wasn't concerned about it.

No this same machine comes FULL CIRCLE for AUTOMATION (hint hint). I keep thinking what the H*LL was I thinking when I made this machine the first time. I do things so much different now.
I am going to talk to KY OSHA in the morning and see what they say. I just wanted a few others Ideas just in case I over looked something.

Thanks Dan have a good night

 

[leitmotif]

Yeah that is the big drawback with knowledge gained over time ie experience. Let us not talk about some of the things we did at 19 or 20.

Dan Bentler

 

[JeffKiper]

funny you should say 19 or 20. I think I was about 21 or 22 when I build this machine. a lot has changed since then.

 

[Doug_Adam]

Hi Jeff,

Both Pilz and Allen Bradley (Guardmaster) have standard PLC fits and safety curcuits for what you want to do. I would suggest having a look on their web sites for this. Generally, I would consider this to be a CAT4/PLe/SIL3 type job. The person is placing themselves into constant danger with only the control system preventing a serious, possibly irriversible injury.

Also, if go to this site:
http://www.dguv.de/ifa/en/pub/rep/rep07/index.jsp

and look up this report:
Functional safety of machine controls (BGIA Report 2/2008e)

It has a lot of safety circuits that could possibly be useful.
I know it is European, not US, but a lot of the safety principles are similar.

Hope this helps,

Doug

 

[bce123]

also look at using a special relay for the two hand switch many mfg make them. is there a way the operator could load this press with tongs or other device as this would elimitate the need to have ones hands under the dies. hard wire as much of the saftey stuff as you can and let the plc just do what you need it to. as for the valve ?.. lots of them out there just make sure your vendor knows what it is being used for and get their advice. you should make sure they know the application and understand it .

 

[flowdam]

I still have trouble second guessing myself years later as well. I built this machine about 10 years ago. It had a indexing table and light curtains on it. The hand where not in the die so I wasn't concerned about it.

No this same machine comes FULL CIRCLE for AUTOMATION (hint hint). I keep thinking what the H*LL was I thinking when I made this machine the first time. I do things so much different now.
I am going to talk to KY OSHA in the morning and see what they say. I just wanted a few others Ideas just in case I over looked something.

Thanks Dan have a good night

Jeff- your OSHA contact will probably point you here:

http://www.amtonline.org/TechnologyandStandards/ANSIB11SafetyStandards/ansib11-2-1995r2010safetyrequirementsforhydraulicpowerpresses.htm


Most of our presses are quite a bit larger than 5 ton, but we've added some safety/blocking valves to our circuits to help control any hydraulic energy. We've done a good job in the past of controlling the electrical energy with light curtains, redundant e-stop circuits, but you also have to make sure that you take into account what could happen if a line breaks or a valve sticks.

 

[sjohnson]

X2

Jeff- your OSHA contact will probably point you here:

http://www.amtonline.org/Technology...afetyrequirementsforhydraulicpowerpresses.htm


Most of our presses are quite a bit larger than 5 ton, but we've added some safety/blocking valves to our circuits to help control any hydraulic energy. We've done a good job in the past of controlling the electrical energy with light curtains, redundant e-stop circuits, but you also have to make sure that you take into account what could happen if a line breaks or a valve sticks.

 

[JeffKiper]

OSHA said it doesn't qualify as a hydraulic press because it is air powered. I still have to protect the operator from the hazard (pinch point ) two hand controls handles that for me.
Guys thanks for your help.

 

[leitmotif]

Jeff

I like your going above and beyond the call of duty and not merely staying with what OSHA requires. I fully support your decision. I wish more employers - including several I worked for including the one where the lady sawed off her hand BTW - would do this.

Maybe your effort will not prevent an accident BUT one thing is for sure you did not succeed for lack of trying. Well done.

Dan Bentler

 

[JeffKiper]

Thanks Dan.
My dad still works for that company. He is at another plant, who knows he may be the one working on this system in a year or so.

 

[gbradley]

Will the ram drop if an air line is disconnected, or blows?
Is the Solenoid that controls the valve driven directly from the PLC, or an interposing relay?
What if the Relay gets welded closed?