Milling macine problem

[mrmatt]

Hi all

Had a phone call today asking if I would have a look at a milling machine that had been switched off last night and wouldnt power back up this morning.

Its a 3 phase machine with 3 main circits

1. motor
2. slurry pump
3. traverse

Checked power at isolater all fine
checked power in at transformer seems fine
checked out of transformer seems fine. The control gear is 24v

If the machine is powered on the tungsten filament light comes on.
None of the 3 starters for the above do anything. The emergency stop button seemed a bit dodgy so checked that out and it works ok.

If i push in the contactors manually and hold in place each part functions correctly. but there is no latching

I didnt have much time to look today so I said I would go back tomorrow to have a better look

any tips on this appreciated as the wiring diagram is lost, and I am still learning thanks

 

[Guest123]

Did you check for voltage on the coil terminals....A1 & A2....this coil pulls in the contactor to make the machine start.

Does sound like a simple fault if it was working fine yesterday.

Are there any other remote EM stops anywhere that could have been pressed???

 

[johnboy6083]

sounds like the control wiring matey. have you checked all the MCB's /fuses, thereshould be one that protects the control circuit. i would then start to test piont to point from there mate. good luck, and let us know how you get on.


PS, just thought, a lot opf machines have safety cam switches/ interlocks that stop the machine in the event of any of the gaurds/ covers of moving parts are removed. check all these too.

 

[lewlec]

hi

check each overload on the contactors, maybe one has gone out on overload therefore cutting the control voltage. check continuity across 95 & 96 on the overloads.

regards
gary

 

[davelerave]

the 24v is prob grounded- should be able to trace control circuit with voltage tester to earth

 

[mrmatt]

Thanks for the fast replies guys

Did you check for voltage on the coil terminals....A1 & A2....this coil pulls in the contactor to make the machine start.

Does sound like a simple fault if it was working fine yesterday.

Are there any other remote EM stops anywhere that could have been pressed???

I did check and I think there was voltage will recheck tomorrow

sounds like the control wiring matey. have you checked all the MCB's /fuses, thereshould be one that protects the control circuit. i would then start to test piont to point from there mate. good luck, and let us know how you get on.


PS, just thought, a lot opf machines have safety cam switches/ interlocks that stop the machine in the event of any of the gaurds/ covers of moving parts are removed. check all these too.

There is only 6 fuses inside the panel and all 6 test ok. Its a really old machine and I dont think there are any guards or covers that have switches built in, I did ask the operator and they said there wasnt, but ill recheck

hi

check each overload on the contactors, maybe one has gone out on overload therefore cutting the control voltage. check continuity across 95 & 96 on the overloads.

regards
gary

I could only see 1 overload inside the panel ill check it tomorrow didnt have enough time tonight

the 24v is prob grounded- should be able to trace control circuit with voltage tester to earth

it is managed to trace some of it back but will need more time and hopefully the diagram may turn up if they can find it.

 

[caddy]

I usually ask by asking the operator exactly what is supposed to happen when they start the machine, if they say this motor is supposed to start then i start by looking at what makes that part of the machine run if power is getting that far when the start button is pressed. If not then follow the A1 and A2 cables back.

It sounds like a fault in the stop circuit which will probably include any guard switches / locks see if you can find both ends of this circuit check if you have continuity from one end to the other or possibly a fault in one of the limit switches.

you could start by looking at the start circuit, do you have voltage at the start button ? if yes then do you get voltage back to whichever contactor pulls in first. If you have voltage but dont get any voltage back

 

[UNG]

Are any of the control buttons on moving parts of the machine ( table, saddle or pendant control station) cables are prone to fatigue on these parts and very often break down with multiple breaks making it difficult to find the faults when you are only looking for one

 

[mrmatt]

Are any of the control buttons on moving parts of the machine ( table, saddle or pendant control station) cables are prone to fatigue on these parts and very often break down with multiple breaks making it difficult to find the faults when you are only looking for one

its in a fixed enclosure that cannot be moved

 

[UNG]

its in a fixed enclosure that cannot be moved

The fault could be caused by the cutting oil / fluid getting into limit switches or cable insulation failing after contact with cutting oil / fluid

 

[silva.foxx]

Limit switches?

Are there start and stop push buttons or on/off switch?

Stop button jammed in?

Is there a safety relay or just latched safety circuit?

Start or Reset button not pressed or non-op?

Lost neutral?

I worked with a guy who diagnosed faults by testing between line and earth only. He diagnosed a faulty transformer once instead of a two pole toggle switch with a failed contact in the neutral. T i t.

Any foot-stops?

Safety switch on the belt-drive cover?

Asked how they last stopped it?

Lamp blown?

/.

 

[davelerave]

ya- but you can do a lot of fault diagnosis between L-E and 24v-grnd

generally

drawings are vital though

 

[mrmatt]

Went back in today to have a look to see if I could find the fault and again had no luck.

There is 24v out of the transformer for the control gear traced this to the start buttons. There are 3 start buttons, one for each contactor, and 4 stop buttons one for each contactor and and Emg stop. The emg stop functions correctly I have double checked this.

One contactor at the top has an overload attached this is the contactor for the main milling motor. If i push the contactor in manually it works untill I release it

The second and third contactors also work when pushed in

I couldnt see marked on the contactor A1 or A2 but I checked all the teminations at the contactor for voltage and there was no 24V on any just 230V to earth on each phase

Ive attached a picture showing the only overload on the machine. I am not 100% sure how it should be set. It apears to have popped out tried pushing it in but nothing happened and as i wasnt sure didnt mess with this anymore.

There are no guards or deadman switches remote stop buttons or anything similar on this machime. Once its back up and running they need to be fitted as it was picked up on a recent factory inspector visit

Any tips appreciated especially around the overload.

Thanks

 

[johnstantine]

Sounds very much like a break in the stop circuit to me.
You can check the overload is ok by checking for a circuit across 95 and 96 with power off. You should find the circuit opens whilst you have the reset button pushed in then makes again as you take your finger off.
How did you test stop buttons exactly?

 

[DEAN VOLT]

Hi does the slurry pump have to be started first,ie the start circuit for the main contactor may go through the normally open auxillary contact on the slurry pump before the start circuit is energised for the main contactor. Sounds something simple if it was running the day before....

 

[johnstantine]

I'm sure the A2 contacts are on the bottom right of the contractors looking at you photo's, just under and behind the no contact. And I would bet the A1 contact is on the top left, at the back behind L 1 contacts.

 

[mrmatt]

Sounds very much like a break in the stop circuit to me.
You can check the overload is ok by checking for a circuit across 95 and 96 with power off. You should find the circuit opens whilst you have the reset button pushed in then makes again as you take your finger off.
How did you test stop buttons exactly?

ill check the overload tomorrow

I cheched continuity across the emg stop button when the stop button is pressed the circuit is open

The user seemed to think you can operate the mill without the slurry pump on

 

[johnstantine]

ill check the overload tomorrow

I cheched continuity across the emg stop button when the stop button is pressed the circuit is open

The user seemed to think you can operate the mill without the slurry pump on

Ok. Did you check that when the stop button is reset that the circuit is closed?

 

[mrmatt]

Ok. Did you check that when the stop button is reset that the circuit is closed?

Yes it is closed once the button is reset. I initially thought it was this as the button was sticking - it isnt sticking now tho

Thanks for your imput thus far I really appreciate the help guys

 

[johnstantine]

Ok. Looking at your third photo I'm willing to hazard a guess that 0 and 2 on that terminal rail is your 24 v control. If so there's a good chance that you will have either 0 or 2 wires at the A1 terminals on the contactors behind the L 1 terminals. If there are wires numbered 0 at these A1 terminals then check for continuity between there and the 0 terminal at the terminal rail. If the wires are numbered 1 then check for continuity to the 1 terminal on the rail. This should more or less confirm that you have a common to the contactors and suggest that there is a break in the stop circuit.