I/R Temp Control...

[Disappointed]

Hi all,

this may already be in existance on some presses, but i dont know of any that have it. Is there any print related reason that Infrared temperature control should NOT be a closed-loop system. I.e. monitored and controlled automatically to give a preset stack/sheet temperature??

Do not concern yourself with the technical aspect, that is already covered. Likewise do not base your answer on cost-effectiveness as that is irrelelvant in this instance.

Purely, are there any reasons why it should not be closed-loop??

Thank

Dave

 

[CKL]

IR

IR

Output % will equal IR wave length.
We like 30 % --70% for a short wave length.

Some auto modes can be problematic with dirty sensors and sensors being out of calibration.

Good operators should be in tune with this.
Track your bulb burn hours if possible.

 

[Disappointed]

Ok,

Sensor cleanliness should not be a problem, it has it's own clean-air purge ring around its lens.

Lamps are halogen.

What we find by doing it manually is that the first 500-1000 of the run is under heated as the system has not warmed up, so we whack the heat up, then if it's forgotten, the rest of the stack is over heated.

Apart from manager, printer and various other tasks, I also do R&D stuff and have devised a simple way of making it closed loop, this should give us more consistent drying and less risk of overheat, plus if we use the air smoothers as well, the sheet comes out way hotter which is often overlooked resulting in a hot stack and wasted energy of course.

Tests with handheld measuring devices have shown that the first 500-1000 sheets need a lot more input than we are used to, but if it's given then the results are good. I aim for a stack temp of around 36c which I am told is optimum.

It's a pretty simple modification, I was just surveying any hidden reasons not to do so. It's one less thing for the operator to worry about as well.

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

Just curious. What make of press do you have? Do you have pre-heating function on the IR dryer?

 

[Disappointed]

Hi, it's a Ryobi and no pre-heat option.

I know it's not totally required but I haven't done any R&D for some time now and I'm getting itchy fingers

As I'm the operator, I see a need for something, then find a way to fill that need, it's very satisfying when you can pull most of it out of the junk box and make it do what you wanted

Dave

 

[turbotom1052]

Considering the ever increasing trend towards shorter and shorter sheetfed press runs it seems to me that to not have a preheating feature on an infared dryer is a serious oversight on the part of the dryers manufacturer. Please at least tell me that the press is older than 10 years old.
Just how many sheets is it taking the unit to come up to 36c now that you've installed your pile sensor?
Do you set the unit to full power and then use a controller to ramp it's output down as things heat up?
Curious to know!

 

[Disappointed]

Hi Turbotom,

Im afraid its only 4 years old, and is designed for short to medium run work! I won't name the model here though as its not relevant.

I am currently building the unit so i only have the data from the handheld tests i performed. Using it exactly as you say - almost full on then ramp down as it warms, i can get to temp in the first 100 sheets so its far better than it was. This is the type of control the automatic system will mimic when fitted. The existing control now becomes the maximum limit set-point.

I will also speak with the engineers to see if the timing for the drier can be altered or if its set code and fixed, bringing it on earlier would help even more.

Should have some results in the next few days depending on workload

Dave

 

[turbotom1052]

Sounds like your turning lemons into lemonade Dave. These are exactly the kind of challenges that continue to make the printing industry interesting to me after over 30 years. Good idea to trigger the unit earlier!!! It's likely that the timing to trigger the unit comes from something on or just before the first printing unit. If so this would make it impossible to trigger the unit earlier. However, if the unit is triggered further on down the press then perhaps by moving the trigger closer to the feeder end of the press you can accomplish your goals. Good luck Dave and keep us posted.

 

[Disappointed]

In some ways, luckily the machine is software controlled, i think it may be possible to alter but will need to have a chat with a friendly engineer next time they visit.

I went into print 32 years ago, mainly because i like machines and mechanical things and have a very inquiring mind. Over the years this has developed into the ability to look at a problem and find a way to improve or solve it, not always cost effectively but when there's no commercial way, needs must.

I created and operated the only automated start-up Solna 225 press in existance back in the 70's, it was a dream to use, no more starting the feed and puting her on impression at just the right moment Just press a button and away she went, and that was way before i discovered PLC's and computing

The machine i am on now has some minor software flaws but annoyingly, it is nigh on impossible to get any alterations made as the makers just dont listen, even with engineer backing, its a shame but thats life. I would like to re-create the front-end software myself but again there is no way into the system.

Ah well, back to work....

 

[Servicetech]

Pierry IR dryers use an automatic mode, there is an optical pyrometer that senses the sheet temperature, at the start of the run the dryer banks will come on at high intensity, as the run continues and heat builds up in the delivery the dryers turn down automatically to keep a consistent sheet temperature from start to finish.

Although there is an air line that blows over the surface of the sensor to help keep it clean, it does require cleaning, particularly if there is spray powder used when not coating / drying.

If ran in manual, you loose the ability to instantly adjust the IR lamp intensity to compensate for a variance in sheet temperature. I can think of no good reason why the lack of closed loop dryer control would be better.

 

[Disappointed]

Well it's working, not finished but working and I'm impressed so far.

It starts off at about 90% power and ramps down as the run progresses, generally to about 50% power on art paper. If we use the air-smoother, this tends to blow warm air and the added heat input makes the drier ramp even lower, this was not really thought of before.

Its interesting to note that the power applied now varies with press speed and paper thickness but the result is always the same - a stack core temperature of 36c +\- 1c. No changes have been made to the press at all apart from the original control being disconnected and an optical probe fitting in the delivery area. I have tested it with heavy spray powder usage and the air-purge keeps the lens spotless so it should maintain accuracy for a good period.

An interesting project and something that I feel should really be built-in at design time.

Its good to know I haven't lost the R&D ideas

Dave

 

[Disappointed]

Update

The unit is now fully tested and even running a mk2 version now with a custom interface circuit to the press i built. Control is very good, generally to within +/-1c, power usage is lower than manual control and warm-up is faster, overall a 100% success.

The controller with recently added power meter.


The stack sensor (front centre)



Now, what to build next ....