Thread: Translating the manual
Put it all back together with clean relays, fixed the broken solenoid connection, checked LED b20 now lit when I closed the guard and it all looked hopeful.
I switched on the motor, pressed "Close mould" and the platen zoomed forwards, I pressed "Open mould" and it zoomed back, I pressed "Advance ejectors" and heard the ram go, couldn't see it because the guards were shut. Didn't dare press anything else because the screw was cold and I haven't checked the interlocks that would prevent me testing the screw shear pin for functionality at the same time.
Jubilation, shouts of "Yeehar etc.
Next I need to put together the water cooling, check for leaks and descale the pipework. The cooling does the oil, the mould and puts a thermal break in the screw which is in hot plastic at one end and connected to a hydralic motor at t'other. Don't want to cook the seals.
For cooling I have a 1/4 hp suds pump, the cheapest new car radiator I could find on e-bay, 10 yards of 3/4" hose, a nice quiet fan and lots of sulphamic acid for the descaling.
Sounds fun! But why are you doing this (oh to have so much time on my hands :) )
My logic went like this... I can get 2 new moulds made for around £8k, but for the same money I can make around 15 moulds and buy an old injection moulder to boot.
My experience has not been good. It takes time to set up an injection moulder and you pay for it, plus you have to buy lots of parts to justify the setting expense. My original UK supplier made me wait weeks while he sent my parts off to a home for the disabled to be de-sprued, they couldn't be arsed to cut and simply ripped the sprues off. When I suggested I cut the sprues off myself he shrugged and said "No". Eventually a shedload would arrive as a fait accompli and if there was something wrong I had to grin and bear it because the alternative was to send it all back and wait another month or two. Eventually I gave up and sent the moulds to China but they are now having problems.
The only way to get quality control is either to have a supplier you can rely on or do it yourself... for the volumes it seems the latter is the better option for you, if you can stand the setup costs and have the time to get it working. Mind you, once you have got it running you have another string to your bow, mould production and low-volume prototype mouldings as a service?
I had to make 2 new hose connectors before I could try pumping water into it's cooling system. Nothing would go through the oil cooler, turns out it has a thermostatic valve so I won't know if it leaks until 32 gallons of hydraulic oil get hot.
Nothing came back down the screw cooler return pipe either, but it did a pretty good impersonation of the "Mannequin Pis" so it would seem I have blown a gasket. Don't think that circuit has a thermostat, seems unlikely, probably just gunged up. Hopefully things will become obvious when I split the gasket seal. It's in a bit of a tricky place to get at, but that has never stopped me before.
Opened the leaky gasket and found a sump full of rust gunge. Just waiting for the top to dry out before I remove the last of the old gasket and make with the gasket compound. Type blue I think.
No obvious blockages, no thermostat, the water goes over the top. I can only presume the rust gunge blocked the pipe, it is certainly the gasket eating culprit.
I sat there for 20 minutes stabbing a screwdriver up in to the top cavity until no more great lumps fell out. If it blocks again I should be able to dislodge it with compressed air and let it drop into the sump. Well, it's nice to have a plan
HOW INJECTION MOULDERS WORK
We are looking below where the raw plastic granules enter the screw. In front of the screw is a pool of molten plastic. To inject you advance the nozzle to touch the mould, drive the screw forwards to nearly fill it and then start spinning the screw. The screw winds new plastic forwards out of the hopper, forcing it up hard against the heated barrel and squeezing the air out. As this new plastic moves forwards and melts, the plastic in the mould is cooling and shrinking. It can't take all the new melt arriving in front of the screw so the screw is driven backwards inside the heated barrel building up a new pool for the next shot. By adjusting the rpm of the screw and it's resistance to moving backwards you try to maintain the mould filling pressure and get the perfect fill. They call this notion "backpressure". The plastic entering the mould cavity is about the consistency of treacle. Where it touches the mould walls it thickens so the main flow is as far away from them as it can get, ie: up the middle. The exception to that are the "gates", narrow constrictions where the flow is fast enough to stay molten. Injection ends when the flow stops and the gates freeze. I haven't figured out how to size gates yet.
I suppose it is vaguely possible that someone might have similar problems and find my pictures useful, so here are some buzz words for the search engines to pick up on... Arburg Allrounder 221 221-55-250
Last edited by Robin Hewitt; 15-07-2012 at 03:18 PM.
Through a search for a problem (almost exactly what you describe) I found your posts on MYCNCUK...
I have just obtained an Arburg very similar to yours (221-75-350) with what appears to be the same problem. I cannot get the moving platen to move forward. It will move back (if I adjust the stops b44 etc.), but it seems to me that the hydraulic interruptor is not allowing the platen to move forward. I traced my connections, and I have the b20 lit (safety gate switches). I am able to move the ejectors forward and back, but when I press the mold close button, I hear the machine trying to deliver pressure, but no movement. Any suggestions you have would greatly be appreciated.
I am no expert. If it sounds like it's trying then we assume the solenoid valve is okay? That leaves the clamp closing speed knob on the front panel and the hydraulic interruptor. You have checked the knob isn't set to zero?
If b20 lights the interruptor roller must be dropping into the notch on the rod. It has a perspex window in the front, you should be able to see the switch operate when you open and close the guard.
If it was me I'd probably divert the interruptors return to reservoir connection in to a bottle and see if it filled up. If it did, I'd disassemble, look for a blown seal, then consider bypassing the blessed thing if faulty, it looks kind of expensive to replace. Rather depends on your H&S constraints.
Would a movie of it opening and closing help? There might be clues in the sound track.
First off - Thank you so much for the prompt reply...I do appreciate your time and advise. It is a reassured feeling that one is not alone in their struggles.
I'm actually not sure what this problem could be. Since sending the first post, I disassembled the interruptor valve and looked closely at the switch - nothing seemed damaged or faulty. The switch contactors are doing their job (as I witnessed LED's inside the control cabinet). Since the hydraulic ejectors are the only thing working normally at this point, I decided to take the plug off of Eject Forward side valve and connect it to the Mold Closing side valve (to see if there was any blockage or some other physical problem inside the lines that prevented the platen from moving forward)...The platen moved forward when I pressed the Eject Forward button (only a short distance - but still forward)...I used this opportunity to double check my b44, b25, and b20 switching. I then returned the plugs to their intended homes to try manual movements (the way they were intended)...back to the same problem. The pump gives me the pressure up "sound" but no movement. Platen can move backward, ejectors move forward and return, but still no platen forward. At this point I'd rather just bypass the thing anyway...I'm just not sure how or if to jump out the switch. I can make up a block similar to what they have to allow the fluid passage un-interrupted...beyond that I'm stuck. Any suggestions are greatly appreciated. I'm also going to try calling Arburg service...
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