Synchronize Cylinder Movement

A narrative description might help; I don't see how this scheme works.

Furball, your schematic will produce the opposite of a synchronous setup. You're not taking into account fluid volume which is a fundemental consideration when designing such systems. I took your picture and added an example with numbers to illustrate. True synchro hydraulic systems use flow dividers, LVDTs, and PLC's, to not only ensure the same amount of fluid is sent to the cylinder, but also to measure travel and provide compensation if there is a detected difference in extension / retraction. This is because all hydraulic systems leak a small amount and you need to compensate. Are you a student by any chance because everyone new to hydraulics tries to connect the rod side of Cyl A to the ram side of Cyl B to achieve synchronous extension. It can't work that way.

In my example I used a 4" bore cylinder with a 1" rod. When cylinder A moves 1", cylinder B" will move .9375".

Hi,

As the gentlemen said, and as a result, may be this arrangement will not work properly due to the followings:

1. Different speed of cylinders (due to difference between the area of the cylinder and the annuals area).

2. The PRV should be drained to the tank.

3. I have some doubts about the middle valve? Is it for isolating the two cylinders?

4. I recommend using one throttle for speed control.

As Tornado said, description of the operation will help and a schematic diagram of the mechanism as well.

Good Luck

As Tornado said, a description of operation is required. I think I know, but you may have something entirely different in mind. It appears to me that you have redundant flow controls or, at least, one of them is shown backwards. Also, I suspect you have reverse flow through the pressure regulator during the return stroke. How will this work? What's the purpose of the pressure regulator?

As TerraMan pointed out, if you are after synchronized cylinder movement, the areas on both sides of the pistons must be the same. This can be accomplished with double-ended cylinders.

As I understand the circuit - these are 2 cylinders connected in a row (not parallel!)

Could you epxlain how the cylinder are attached to your Casting machine?

Someone gave you a GA but there's something off in your schematic (...I think).

"...the pressure relief valves perform this function. If one cylinder bottoms first, the absence of flow from that side will stop the flow splitter from turning, thus locking some fluid in the full bore end of the other cylinder. The pressure in this cylinder will increase and operate the relief valve so that it will also bottom"

This statement would be true for the return stroke only and...only if the loads pushing down on the cylinders are free to travel independently. So...what happens if one cylinder is stopped (while the two are slightly out of sync) by an object or bottoms out during the power stroke (filling up the full bore end) ? According to your schematic, the flow divider would stop running and not provide anymore flow to the cylinder that has not yet bottmed out or come into contact with anythiing. Therefore, they will continue to remain out of sync.

Please correct me if I'm wrong.

The rod ends of the tilt cylinders on a gravity die caster are mechanically tied together by the structure of the platen frame. Any twist in the frame caused by the cylinders getting out of sync can damage the expensive die head, so the OP wants a circuit to prevent this. The circuit I have shown only syncs the cylinders in the home (down) position and relies on the flow splitter to keep the cylinders aligned during the extend and retract cycle. Typically he will be controlling 40-80mm bore cylinders over a 800-1000mm stroke. A flow splitter should be able to keep the cylinders synchronised to within 0.2 to 0.5mm (depending on the rigidity of the linkages) which is well within what he requires. There is probably a bigger tolerance than this in his clevis pins. Also, because the fluid is metered out of as well as into the cylinders, any metering discrepancy is balanced out over the whole cycle. The relief valves are mainly there to compensate for leaks, which in a well maintained machine should not be present. The splitter is connected to the full bore end because this is less likely to leak than the annular end which has the rod seals. But if one side was impeded on the extend when the die is closed, the splitter would prevent the other cylinder from continuing and causing twist damage. On the retract the die head is often opened to reduce cycle time, so twist damage is less of a problem.

if you dont mind, can i use this circuit for my assignment? looks legit

I have no problem with that. You might want to improve the speed control by adding another flow control valve, each with a parallel non return valve so that you can control extend and retract independently. In this instance, extend is opposing gravity, retract is gravity assisted. That tells you which way round to mount your cylinders. Work out if you want to restrict flow entering the cylinder or leaving the cylinder, and explain why in your assignment write-up.

General tips on hydraulics.

Always give the fluid somewhere to go. Hydraulic pumps build up enough pressure to kill people, always include a relief valve.

All joints are potential leak points, the fewer the better.

Most hydraulic pipe joints bite the olive or swage the pipe, if they are made wrong you cannot remake, you have throw it away and start again. Always check your measurements more than once.

If it vibrates, moves, or you don't know exactly where it is, connect it with a flexible hose. I once designed a 40' trailer for testing and cleaning transformer oil using only hoses. It saved £'000s in drawing and design time, routeing around equipment squeezed into a small space, making up pipes, pipe fitting, catering for vibration, reducing the number of joints, and ongoing maintenance.

As with most engineering, a little knowledge is dangerous. If you don't fully understand it, don't build it.

okay cool.. thx by the way.

If the main operation is accomplished during the pushing stroke, I prefer to locate the throttle valve on the outgoing line(the line connecting the two cylinders, rod side and the valve). This will avoid any additional drag due to mechanism arrangement.

Remember: When you are in doubt, meter out.

Good luck

Hi..

You have a good schematic there. Though, i think it will cost you a bit. You also have to carefully select your gear divider. Wrong sizing will reduce the cylinder speed coz you already put a flow control before the divider. As for replacement, a simple flow divider cartridge valve should do the work. Or maybe two flow divider cartridge on both side of the cylinders(depending on usage). Plus, you can skip the relief valves. Let say you need 120 bar working pressure for the cylinders, at least you have to set the relief valve to 130 bar. For that, your destroke movement will go past the relieves to either your gears or cylinders, made it no use at all (not dumping). For two synchronize cylinders, one double pilot check will do. It only for holding the cylinders at load side.

Feel free to comment on my thought...cheers mate.

Using schematic symbols that show rod side and blind side would make this more clear, as would a verbal description of what you are trying to accomplish. The circuit appears needlessly complicated.

Hey, thx everyone for the reply. hadnt check this forum for quite awhile and i wonder if you guys are still following this. First of all, im a bad mechatronics engineer, the college doesnt teach me all the things i need so im gonna have to try to research on my own. Next, what do i need to consider when building a hydraulics circuit? Is there a step-by-step instructions? What formulaes n concepts that i need to know? seriously, i cant just depend on my lecturers, they left out all the important details. thx in advance.

Dear adlfurball

The best instruction is how to choose the Hydraulic unit;

1)Work required;by evaluating the mass and speed of the whole unit

2)Piston size;by evaluating Force (from Paragraph:1) and Piston course

The best solution -will be to approach Hydraulic Unit Producers with this info!!

(proffesional producers-will add their knowledge performance too!!)

Ofcourse the whole tilting unit has to be installed on a stiff frame!!

-This to insure Pistons synchronization

Here's the Gravity Die Casting Machine simulation that i have made using v.basic. Thx for all your advices. I shall keep in mind!

http://jumbofiles.com/n4hnnt8i2wju