Off topic - Hyundai Hit 8 lathe

[Johnny Rotten]

Its been awhile, but does anyone have experience on these Korean made units?

Every time the foot pedal for the chuck is pressed (which is a flip-flop), the hydraulic motor trips out on overload. If you cap the hydraulic lines going into the chuck cylinder, it runs.

Motor draws 3.4 amps at 208V, 3 phase, but every time you hit the pedal it goes to 11.0 amps.

The hydraulic unit is made by LG Electronics, and we've swapped that with another (including motor) and just about everything else less the chuck cylinder assembly.

Thanks for any info.

John

 

[Singapore_Mats]

is it a new machine? I believe korea have 220v (400V?).

 

[milldrone]

If you cap the hydraulic lines going into the chuck cylinder, it runs.

Does this mean when you stop the flow of hydraulc fluid to the chuck and activate the switch the pump does not trip on overload?

 

[Johnny Rotten]

Exactly! It seems very odd. I think the LG Electronics Pump must be a 2 stage and plugging the chuck cylinder hydraulic lines must keep it in high pressure therefore it returns fluid to the tank properly??? I'm not a mechanical tech, but do know the basics of hydraulics.

The mechanics spend some time on it today, tryed a new chuck cylinder and it still trips the motor out.

My only guess would be the flow of hydraulic oil is causing something to plug the return?

Any other ideas?

Thanks for the replies, john.

 

[milldrone]

I'm not a hydraulic specialist, but being a sparky always involves trouble shooting mechanical problems as well as electrical.

One of my trouble shooting tools is a set of fittings that I can insert into the hydraulic line and test. The set up has in order from the pressure side a gauge, flow control valve, flow meter, gauge. This allows me to shut off flow and check pressures on both sides of the flow control valve. Or allow some flow and observe pressure on both sides of the flow control valve. Also in a case like yours it allows me to see the flow going to a cylinder via the flow meter. What I would expect to see in the case of a cylinder is flow as the piston moves then no flow when it stops. In some cases you may need to have a second test setup to monitor the other side of the cylinder. This would be when there is some leakage past the seals that is too small for the flow meter to register. In this case you simply close the valve on the side that is currently going back to tank, If you see any significant pressure after the piston has stopped then the seals are bad.

Just like electical trouble shooting you need to have meters and test instruments for hydraulics and some idea of how to use them.

 

[OkiePC]

Just a WAG...

With the line plugged you should get a crisp, sharp pressure rise that abruptly operates a relief valve or pressure switch or both.

With the cylinder connected, its motion and/or leakage should result in a more gradual rise in pressure which may cause the relieving device(s) to operate at a different timing with regard to the motor load.

It may be a simple adjustment to a relief valve or pressure switch, or a faulty device that needs replacement.

Again, this is just a WAG...food for thought.

I 2nd what Mildrone advise about testing with gauges. Sometimes the simplest test fixtures will clarify exactly what is happening within the branches of the circuit, whether it's fluid power or electrical...

It's an interesting problem, so please do give us the details when you get it solved!

Good Luck!
Paul

 

[Peter Nachtwey]

Power=flow x pressure. Adding the extra cylinder can mean the pump must supply extra flow to the cylinders. Have you tried reducing the pressure? It doesn't sound like the pump is sized to run at max flow and max pressure at the same time. You should look at the HP rating.

HP=GPM*PSI/(1714*.Eff)

Eff is the efficiency of the pump which is about .95.
Now see if you are expecting more from the pump than what it can give.

 

[Johnny Rotten]

Just a quick history from my one day trouble shoot.

The other 6 lathes seem to do fine with that motor. Putting in a big bad assed North American motor has crossed my mind a time or two.

Hyundai no longer supports their equipment. The plant manager was Korean and 'gave up' when I asked him to call their office in Korea. He said they were 'sold'.

The mechanic had 'ZERO' pressure gauges. So I 'toughed it out' using intuition. It got me nowhere.

The motor would ramp up slowly to 7 amps very slowly. I watched the curve. After that it hit 11.0 amps just before it would have stalled. We goofed around with the valves and had it stable (as stated before) many times.

It is a very complex machine, and very few stump me. Your ideas from above are perfect.

The mechanic had some good basic ideas, was fast with a metric wrench.

We need to know how to contact a pro on Hyundai lathes, simple as that.

John

 

[milldrone]

After that it hit 11.0 amps just before it would have stalled. We goofed around with the valves and had it stable John

Any chance you can post a hydraulic schematic? And some observed operating conditions ie. does the hyd pump run all the time, or just when closing and holding a part?

We need to know how to contact a pro on Hyundai lathes, simple as that. John

Does this mean you no longer want any help from us/me?