Do we need to calibrate gauges on process equipment?

mjoakin

Involved In Discussions
#1
We have a machine we use to glue foam to leather (seat covers for GM), the foam has a special glue that melts to certain temperature. So we bought this machine (one of those used in a dry cleaning), so ... we installed a timer, a thermometer and a pressure gauge, but ... do we need to calibrate those gauges? the timer release the plate at 40 secs, the thermometer always keeps the plate at 140C and the preassure gauge is set to 80 lbs. We are a very small company and the lamination is not a safety issue, is there any way we can say we don't need to calibrate those gauges?
 
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Jeff Frost

#2
7.6 of TS 16949 does give guidance related to when measuring devices (timers, temp gauges and pressure gauges) must be calibrated. The items you list must be calibrated if they are used to meet a specified requirement or will be used to set the requirement. Also check your imposed customer requirements regarding calibration.

For general principle I would recommend that you calibrate this equipment to establish it accuracy and then using this calibrated equipment to monitor the process to assure uniformity of its output. You may find that room temperature or changes in air pressure has an effect on the quality of the product produced.

I worked for an organization that did ultrasonic welding of polyurethane and we discovered that changes in temperature of the room were the equipment was in operation did effected the quality of the weld and by charting the process we developed methods compensate for environmental effect on the welding equipment.
 
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Hershal

Metrologist-Auditor
Staff member
Super Moderator
#3
mjoakin said:
We have a machine we use to glue foam to leather (seat covers for GM), the foam has a special glue that melts to certain temperature. So we bought this machine (one of those used in a dry cleaning), so ... we installed a timer, a thermometer and a pressure gauge, but ... do we need to calibrate those gauges? the timer release the plate at 40 secs, the thermometer always keeps the plate at 140C and the preassure gauge is set to 80 lbs. We are a very small company and the lamination is not a safety issue, is there any way we can say we don't need to calibrate those gauges?
The real question is.....how do you know if something goes wrong?

If it is far enough out, it will likely be obvious.....but just enough out, maybe not.....

Phil Stein gave the best advice.....If the measurement matters, calibrate.....if the measurement does not matter, why is it being measured?

Hershal
 

Marc

Hunkered Down for the Duration with a Mask on...
Staff member
Admin
#4
Part of the point here is it is process equipment rather than for an inspection or test. Just because it is not used for measurement and test does not mean it isn't important. The more critical the process parameter(s), the more important calibration of the associated gage is.

But - I've seen lots of process equipment which had process parameters which weren't 'critical' and one or moe gages were essentially references.

So - Evaluate how critical the process parameter is and go from there.

Essentially I agree with Hershal and the others, but I do advise making an evaluation rather than blindly calibrating every gage on every machine in the house.
 

Miner

Forum Moderator
Staff member
Admin
#5
Marc said:
But - I've seen lots of process equipment which had process parameters which weren't 'critical' and one or moe gages were essentially references.

So - Evaluate how critical the process parameter is and go from there.

Essentially I agree with Hershal and the others, but I do advise making an evaluation rather than blindly calibrating every gage on every machine in the house.
Marc is right on target here. The best method would be to perform a DOE on these parameters. If one has a significant impact on the output, calibrate it. If it does not, tag if as Reference Only, and the DOE is your proof that you made a good decision.

Performing a DOE will be much less expensive than calibrating a gauge that does not require it.
 
J

jrcook5

#6
Is your question, do you need to calibrate the devices because you are trying to conform to a paticular standard or regluation or do the gauges provide some useful information? I think the answer depends on the question.
 

mjoakin

Involved In Discussions
#7
All we know is that we need to "set" our machine to those parameters to get the right lamination (glue the foam to the leather), if something goes wrong, simply the foam does not glue to the leather, will be an obvious defect. Now, the timer (just like any other regular timer) you set it to 40 secs and stops to 40 secs, the thermometer always keep the same temperature and the preassure gauge gives the sames lbs, if all this gauges make the machine "works" properly, my question is ... do I have to calibrate them? I mean, it is like when you re-heat food in your microwave, you need your food warm (or too hot), you only set the timer and the temperature, the microwave will do the rest. In our case, I just turn on the machine, it will reach the temperature needed and I can start laminating the leather. As I said before, it is not a safety issue, now, three time at day we do a destructive test to verify that the all the glue is being melted correctly, is that enough to control my process? Can I say to my registar that I chose not to calibrate those gages because I don't think it is necessary?
 

Jim Wynne

Staff member
Admin
#8
mjoakin said:
All we know is that we need to "set" our machine to those parameters to get the right lamination (glue the foam to the leather), if something goes wrong, simply the foam does not glue to the leather, will be an obvious defect.
Not necessarily. Do you have to do environmental testing (heat, humidity,etc.)? It's possible to have apparently good adhesion at the machine and failure under adverse conditions in end use.

mjoakin said:
As I said before, it is not a safety issue, now, three time at day we do a destructive test to verify that the all the glue is being melted correctly, is that enough to control my process? Can I say to my registar that I chose not to calibrate those gages because I don't think it is necessary?
Another factor is your control plan. Does it detail the machine settings and tell how they're verified? If not, it probably should. If your control plan says that your verification of correct temperatures, etc. is a destructive adhesion test, then you're probably not beholden to calibrate anything except the device used in the pull test.
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#9
There is an obvious solution.....if calibration of the heat and pressure measurements are not necessary, remove the instruments involved.

The timer is a control tool, not strictly a measurement item.

Just a thought.

Hershal
 

mjoakin

Involved In Discussions
#10
Well, the temperature and the preassure (analog) gauges show only the parameter which the machine was set, I can not remove them from the machine. If I'm making tests to verify the adhesion was succesful, and all of them are Ok, so I don't need to calibrate those gauges, is that correct? I don't use any special tool to pull them, as soon as the piece comes out the machine, the glue is really hot and the parts can be easily separated from each other (the foam can't be used again). So, with this test I can validate the process/product and I don't really need to calibrate the gauges, you know, may be I'm using the word "gauges" incorreclty (sorry for my english) they are indicators that show the current setting of the machine.
 
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