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Increasing the speed of a hydraulic cylinder
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Bernoulli
posted
I would appreciate listening in on a discussion regarding increasing the speed of a hydraulic cylinder for a defined work operation. In particular a cylinder;
(1)Extends 4 inches against little resistance.
(2)Extends 1/4 inch against a 15 ton work load.
(3)Return to starting position with little resistance.
This could be the work cycle for a cylinder closing a metal working die punching a 3/4" hole in 1/4" mild steel. The time period while
the cylinder rod is traveling to and from the work is "non productive time for the punch operator".
I have received advice to shorten the travel distance and to increase the volume of oil from the pump. Good suggestions, but in most applications the distance is needed and large pumps are undesirable.
I have read that regenerative cylinder circuits would increase extension speed of a cylinder, and also that a larger piston rod diameter increases the return speed. I hope to learn more about this.
A four inch dia. cylinder and a 3000 psi pump could punch the 3/4" hole, but the wasted time traveling to and from the work is the problem. The cycle time is the important item. (I dream of a cycle time of one second}.
 
Posts: 9 | Registered: 16 April 2012Reply With QuoteReport This Post
Bourdon
posted Hide Post
quote:
(I dream of a cycle time of one second}.

Ha ha, then you replace the entire press with a mechanical excentric-press.
Almost all the regenerative circuits are explained here: http://hydraulicspneumatics.co...egeneration-circuits


It is not untill you realize how little you know about the subject, that you have actually learned anything.
 
Posts: 615 | Location: Singapore | Registered: 05 July 2010Reply With QuoteReport This Post
New User
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This has been a really nice reply and but whatever has been posted and described has a meaning and so i must appreciate this.

homes for sale in las vegas
 
Posts: 1 | Location: 204 NE Kelly Ave, Gresham, OR 97030 | Registered: 21 April 2012Reply With QuoteReport This Post
Pascal
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This would be a viable concept.

Increasing the rod size would indeed assist with increasing the retract speed BUT at a cost of slowing down the Regen extend speed.

The load sense circuitry towards the right (in brown) will need to be added if the pump runs continuously. If the pump only runs when a cycle is activated, the load sense circuit is not required.

The limit switch is positioned to trigger about 1/4 inch from the workpiece. At that time it will activate valve C diverting the oil from Regen and sending it to tank. This will let the cylinder exert more force on the workpiece.
When the control is set to Retract, relay R1 will deactivate valve C. The oil will then use the Retract Valve path back to tank.
When Extend is chosen, the oil will follow the Regen circuit again until the limit switch is activated.


However, the 4" by 4" cylinder holds just under 2 pints of oil at the 4" extention point.
Doing the math, it will take quite a bit of flow to achieve the one second cycle time.
15gpm?

This message has been edited. Last edited by: Jim Rocco,

 
Posts: 309 | Location: Baltimore | Registered: 25 December 2009Reply With QuoteReport This Post
Pascal
posted Hide Post
I redrew this schematic with check valves instead for easier visualization.
Check valves will achieve the same results.

 
Posts: 309 | Location: Baltimore | Registered: 25 December 2009Reply With QuoteReport This Post
Bernoulli
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I appreciate the replies from Smedsgenbo & Rocco regarding "a one second work cycle for my cylinder". I have now accepted that "general hydraulic knowledge does not have a solution for my problem". However,(with all the humility of Donald Trump) I contend that perhaps I can contribute something on this subject.
Years ago I cobbled together a collection of scrap parts, called it a hydraulic press and took it to my friend Roscoe, a foreman at a manufacturing plant. He installed it along side of his flywheel presses and somehow he kept it operating for six weeks and said that production speed was not a problem. Plant management and their manufacturing engineers were less enthusiastic, but told some very good Robe Goldberg jokes.
I put my press in my junk grave yard, bought Roscoe a beer and we probably talked about the idiots that he had to work with. I thought that this adventure was dead but it reappeared some months later.
I don't know if my story fits in a forum discussion on hydraulics? Please advise me if I am out of line!
 
Posts: 9 | Registered: 16 April 2012Reply With QuoteReport This Post
Pascal
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quote:
general hydraulic knowledge does not have a solution for my problem". However



??
No, it can be done hydraulically, but probably more efficiently with mechanical press.
What is your goal for wanting a hydraulic press? Adjustable strokes, or force control or ?? Those are valid reasons, that a mechanical can't do, but also add complexity and possible position or force feedbacks and proportional/servo controls, and electronics.

Or is a simple ironworker type machine?

I would add that, to the circuits above, the system capacitance (compression of oil expansion of hoses) and acceleration and deceleration times start to affect the calculations. Not quite just stroke divided by time, as peter n will quickly point out, but the whole thing can be done hydraullically.
 
Posts: 489 | Location: Minneapolis MN USA | Registered: 02 November 2005Reply With QuoteReport This Post
Bernoulli
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Isn't this the place to use a two stage pump? High volume low pres on the first part of the stroke then when you contact the work piece the pressure rises, the unloader valve opens and you get high pressure from the small section of the pump.

Sounds just like the requirements for a log splitter.

C.O.
http://whatsintheshop.blogspot.com/
 
Posts: 6 | Location: Alaska | Registered: 25 April 2012Reply With QuoteReport This Post
Bourdon
posted Hide Post
quote:
Originally posted by COR:
Isn't this the place to use a two stage pump? High volume low pres on the first part of the stroke then when you contact the work piece the pressure rises, the unloader valve opens and you get high pressure from the small section of the pump.

Sounds just like the requirements for a log splitter.

C.O.

http://whatsintheshop.blogspot.com/


For a 3-4 second duty cycle, maybe yes. But it still have to be much better than average even to achieve a 3 second duty cycle. I think if one wants a cylinder to move 4 1/4" in less than half a second, change direction and move back to zero position in another .5 second, one needs to use some very big accumulators and some sophisticated control.


It is not untill you realize how little you know about the subject, that you have actually learned anything.
 
Posts: 615 | Location: Singapore | Registered: 05 July 2010Reply With QuoteReport This Post
Bernoulli
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Pursuing "my dream of a one second cycle time" for a hydraulic cylinder, here is an example with numbers. HARDWARE: cylinder 4" bore dia, piston rod 1 3/8" dia: two volume pump, 5 gpm to 500 psi, 1 gpm from 500 to 3000 psi, 2 hp electric motor. OPERATION CYCLE OF CYLINDER: extend mode, 4" with little resistance: work mode, 15 tons for 1/8": return mode, 4 1/8" with little resistance; cycle complete.
Calculating the time for each mode for: CONVENTIONAL CYLINDER(with 4-way control valve): extend mode 2.6 sec, work mode .4 sec, return mode 2.4 sec, total time per cycle 5.4 sec. REGENERATIVE CYLINDER (regenerative control for extend mode, then conventional cylinder for work and return modes): extend mode .3 sec, work mode .4 sec, return mode 2.4 sec, total time per cycle 3.1 seconds. The regenerative flow between cylinder ends is 8640 cubic inches per second (38 gallons per minuite).
The REGENERATIVE CYLINDER is encouraging except for; (1) the large regenerative oil flow, requiring large valves and plumbing, and (2) the long time period required for the return mode. Is there any hydraulic knowledge that can help with these two problems?
 
Posts: 9 | Registered: 16 April 2012Reply With QuoteReport This Post
Bourdon
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Kevin J has good post. Hope some others could give you some advise and more calculated facts. But definitely a simple hydraulic system won't give you desired cycle. The hydrsulic system that could make your desired output is like "trying to connect the power input directly to your work output". It has to be "rigid".
 
Posts: 805 | Registered: 12 November 2008Reply With QuoteReport This Post
Bourdon
posted Hide Post
quote:
Originally posted by LittleJohn31:
I would appreciate listening in on a discussion regarding increasing the speed of a hydraulic cylinder for a defined work operation. In particular a cylinder;
(1)Extends 4 inches against little resistance.

Is this distance required to get the work piece in and out?

quote:

(2)Extends 1/4 inch against a 15 ton work load.

It looks like you are using the force of the hydraulics alone to do the punching. How much mass are you moving? You should be able to compute how much work the punch needs to do to punch through 1/4 of mild steel. What if you used more of a kinetic energy approach? How fast would the punch need to be moving?

quote:

(3)Return to starting position with little resistance.
This could be the work cycle for a cylinder closing a metal working die punching a 3/4" hole in 1/4" mild steel. The time period while
the cylinder rod is traveling to and from the work is "non productive time for the punch operator".

Yes, that is why I asked if opening 4 inches is required to get the work piece in and out.

quote:

I have received advice to shorten the travel distance and to increase the volume of oil from the pump. Good suggestions, but in most applications the distance is needed and large pumps are undesirable.

It sounds like you need the large opening to get the work piece in and out. Instead of getting a larger pump an accumulator may help. The accumulator store energy during the dwell time if there is any. If not then you need to think about return on investment. Can you justify the bigger pump with increased production?

quote:

I have read that regenerative cylinder circuits would increase extension speed of a cylinder, and also that a larger piston rod diameter increases the return speed. I hope to learn more about this.

Using regeneration implies that you have system pressure on the rod side of the piston. That effectively cancels out the much of the area on the cap side. You are right to think in terms of getting a bigger diameter rod since that will increase the effect pushing area on the cap side. Making the rod too big may decrease the speed when retracting. This would happen because it is really force that makes the piston move. If you make the rod are too big there is less force to make the piston retract and yet the cap side has a lot of area to resist the retracting. When retracting the oil pushes the piston but it also must push out all that oil on the cap side.


quote:

A four inch dia. cylinder and a 3000 psi pump could punch the 3/4" hole, but the wasted time traveling to and from the work is the problem. The cycle time is the important item. (I dream of a cycle time of one second}.

[/quote]

Jim, is right about possibly reducing the extend speeds because there wouldn't be that much oil coming back from the rod side to the cap side. On the plus side there is less opposing force from the rod side.

This is where a little modeling will allow one to find the optimal solution. How much is a 1 second cycle time worth? How about a 3/4 second cycle time?


"Living is easy with eyes closed, misunderstanding all you see.." John Lennon, Strawberry Fields.
 
Posts: 628 | Location: Battle Ground, WA United Socialist States of America | Registered: 09 August 2006Reply With QuoteReport This Post
Bourdon
Picture of akkamaan
posted Hide Post
quote:
Originally posted by LittleJohn31:
Pursuing "my dream of a one second cycle time" for a hydraulic cylinder, here is an example with numbers. HARDWARE: cylinder 4" bore dia, piston rod 1 3/8" dia: two volume pump, 5 gpm to 500 psi, 1 gpm from 500 to 3000 psi, 2 hp electric motor. OPERATION CYCLE OF CYLINDER: extend mode, 4" with little resistance: work mode, 15 tons for 1/8": return mode, 4 1/8" with little resistance; cycle complete.
Calculating the time for each mode for: CONVENTIONAL CYLINDER(with 4-way control valve): extend mode 2.6 sec, work mode .4 sec, return mode 2.4 sec, total time per cycle 5.4 sec.

So far your numbers are OK
But your regen math seems off, unless you try to compare "apples with oranges"....
quote:

REGENERATIVE CYLINDER (regenerative control for extend mode, then conventional cylinder for work and return modes): extend mode .3 sec,

This 0.3 sec cycle number will only work with a 5 gpm pump, (3000psi), now you are talking about a almost 10hp power supply. To compare regen with 2-stage pump, isn't it fair to use the same power supply??
So I suggest you use the "1gpm" pump in the regen example, to stay within the power limits you have set, 2hp.
quote:

work mode .4 sec, return mode 2.4 sec, total time per cycle 3.1 seconds.

These numbers will increase a lot with the 1 gpm pump
quote:

The regenerative flow between cylinder ends is 8640 cubic inches per second (38 gallons per minuite).

I do not know how you calculated the "8640 cubic inches per second", that is 8640/231=37.4 USG per second Eeker You must mean 8640 cui per minute (5gpm pump)??!!
(There is 231 cui in a gallon, and 60 seconds in a minute)

quote:

The REGENERATIVE CYLINDER is encouraging except for; (1) the large regenerative oil flow, requiring large valves and plumbing, and (2) the long time period required for the return mode. Is there any hydraulic knowledge that can help with these two problems?

As others already pointed out, there is no way to change the total cycle time in regen, by changing rod diameter. The rod diameter will only affect the proportions in force and cycle time between extend and retract. The total cycle time will always stay the same as long as bore and stroke is constant.
Extreme difference between bore and rod diameters will always cause extreme increase in return flow or regen flow.
If you want as many "punches" per minute as possible, with a 2hp power supply, the mechanical options is the way to go. Any hydraulic solution will always waste power into heat. higher flow more heat.
1 sec cycle time IS a dream, with the power limitations you have set.


Per A
...ak kam aan...flow doesn't make motion, flow is motion....
 
Posts: 1231 | Location: Port Angeles WA USA | Registered: 24 September 2008Reply With QuoteReport This Post
New User
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How about decreasing the bore size and increasing the PSI to match the force? That will make it go faster!


MAG
 
Posts: 1 | Location: Iowa | Registered: 11 June 2012Reply With QuoteReport This Post
Bourdon
Picture of akkamaan
posted Hide Post
quote:
Originally posted by MAG:
How about decreasing the bore size and increasing the PSI to match the force? That will make it go faster!

If power supply is limited, 2hp, the flow will need to be lower if pressure is increased, status quo...


Per A
...ak kam aan...flow doesn't make motion, flow is motion....
 
Posts: 1231 | Location: Port Angeles WA USA | Registered: 24 September 2008Reply With QuoteReport This Post
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