Bursting Plastic Tubing

Hi gfwhell,

Tubing is generally rated for pressure and temperature. What is the tubing pressure and temp rating? What is the max temperature that the tubing "sees"? Is there a point where the tubing is rubbing against something?

There's a solution to this, but we need more info.

Mike

Hum, a 4kW cutting laser and random pipe bursts. I would suspect that you are getting some scattering of your infrared laser beam. Remember it is the invisible infrared laser light not your alignment pilot laser light that is doing the cutting. You might be able to detect this infrared scattering with a CCD camera monitoring your cutting area. Was any guards removed from the cutting area?

I once bought a 500 foot roll of 1/4 air line. On this particular type of hose and a lot of other hose the outer jacket is perforated. The outer jacket just being a wear protection it is not designed to hold air pressure. Well on this lot the machine that does the perforation also perforated the inner tube which does hold the pressure. Maybe you just got a bad run of hose.

My first question is , how old is the machine?

My second question is How many hours or shifts a day does it operate?

My third question is when was the last major/heavy maintenance service done?

The reason for my questions are that the nylon tube has a limited service life, actually on a cutting laser everything has a limited service life. If your management has been trying to maximise on profit/and throughput at the expense of maintenance then you will get this sort of disruption to production eventually.

I have been involved with a firm that had a 6kW Bystronic laser. It had been operating 2x 8 hrs 5 day shifts and 1 x8 hr shift on the Saturday for pretty much 6 years. In the 6th year all manner of "maintenance" issues popped up due to risk management maintenance scheduling. In the end the machine collapsed progressively till the company closed the doors (due to other financial issues). Rather sad really.

We also had airlines in other parts of the factory, that were popping, after 8 years service in part due to environmental factors.

The Bystronic manuals which were very comprehensive (if you could read German) had tables which referred to expected MTBF of various systems and schedules for replacing things.

p.s. nothing scarier than having a DI coolant line burst in the exciter cabinet.....

All the obviouse reasons have been fully explored.

The tubing pressure and temprature ratings are twice the duty imposed.

Burst pipes occur within the shielded cavities of the machine and certainly are not exposed to laser energy, they are fully supported mechanically and do not rattle about. The lift master is some distance from the laser operation and fully shielded.

The Trumpf/Liftmaster is 4 years old.

Both water and air lines are bursting.

The common factor is "FESTO", the tube manufacturer, who has refused to offer any assistance.

GF

Now we all know that Festo brand pipes/tubing should not be bought ever again!!!!

Vote with your feet guys!!!!

Maybe, what if this model of Festo tubing is rated to not degrade for two years and the hoses were installed eight years ago, or were discontinued four years ago while also rated for just two years. If I was a Festo representative dealing with an inconsolable irate customer demanding flawless use years after the expected service life then I might not help, too. There are many things here not evident here.

Surely such hoses/tubing need to be replaced at regular intervals, say every 4 years for example, as the others appear to have lasted 8 years......50% of the achieved life?

Well, I'm glad that you've brought some follow up information on your pipe bursting problem. I brought up the idea of the laser light being a possible hidden culprit with the idea that you came to us for ideas on easy to overlook possibilities. Well if you now suspect the hoses themselves, I'd try to find a spare length of old hose and test its burst pressure and compare it to a length of new hose. I would also try to get some optical microscope to examine the burst locations for some indication of a cause. Look for tell tale oxidation signs in the plastic layer that may show you cracking prior to bursting. I would also recommend some simple flexibility measurements of the hoses (old vs. new) to see if vibration might be a problem.

You need to look at this first as a failure analysis project. I seriously doubt that you could keep one of these cutters off line while you study it for a failure analysis. I'd recommend first replacing all of the failed hoses with identical hoses to get it back to operations. Save the failed hoses. If you have another machine that did not fail yet, replace the identical hoses from that machine with new and save these older hoses, too. This will permit you to make a real comparison of component wear and fatigue.

Good luck.

Besides the common factor of "Same Manufacturer" I have noted a descrepancy in the wall thickness The inside bore not being co-axialy disposed making one side thicker than the other. Im not talking about much of a differance, only a 0.001" or 2.

However, When cycling the presssure this small discrepancy could cause un-even stress on the wall in the thinner sections.

What are the "oxidization " signs and what causes them?

GF

I would install data acquisition equipment to record operating pressures and temperatures, looking for spikes in either that may contribute to premature failure. You don't need to spend a bunch of money on it, either. Several good, low cost DAQ units have come on the market in the past few years.

If laser scattering could be the problem AND if the hoses that are popping could be "seen" by the laser, how about putting some thin plastic sheeting or even paper (watch out for fires!) around the pipes and look for burns once a job has run.....

On reflection (no pun intended!), paper sounds too dangerous, use something else.....

You need to protect the pipes AND see if that is the problem at the same time.....preferably white to reduce possible heating........white plastic carrier bags?

Polyethelene tubing?

Try Nylon tubing.Very tough, but will get brittle if exposed to long-term high temperatures.If you must use poly tubing, try another brand, like Eastman.

Use strain reliefs at all connections that bend or flex.

Also,is there a possiblilty of Ozone getting to the tubing?Not sure about poly, but it can wreck some plastics.It sounds like your tubing is being attacked from the outside since both air and water lines are being affected.