Aq coating issues.

On CD74 with short delivery, have issues with coating setting up. Try to run heat down around 98F but sheet feels cold, wet and sticky in delivery. Run higher heat and sheet feels dryer and warm but still have picking probs. Any ideas?

 

Not a lot of info to go on.

Has it been running okay until recently?
The only time I feel the sheets are a bit cold/tacky is upon start-up, but running the press at high speed on start-up with the dryer on, whilst I go off and search for paper, helps get it up to temps for the first job.

As a go to method, run temps in manual mode, hot air knife 100% and set IR % to get to desired temp, start it at 100% also, and reduce once temp is reached.
I always leave the air knife on 100% as this is what evaporates the water and ammonia out of the coating solution, leaving just the coating, so it will cure faster.
Short deliveries can be a pain with high ink coverage and coating not drying fast enough, but is helped by slowing the press down a little to give it slightly more time to cure, when required.
Also ensure the extractor is turned on correctly.

If it's a recent problem, then something's wrong with your hot air knife!
(I tend to aim for 40c 1st pass then 36c on 2nd pass.) Temps in new money

Hope this helps in some way.

 

Thank you Steve. Here's a bit of history. I've recently returned to printing after a several year hiatus. In the past I would keep air knives at100% and adjust temp with IR as I was trained to do. Upon my return, to the same shop and machine, that method creates to much heat in delivery. Now we have a new blower motor for knives, new air diffuser, and new bulbs. Problem is if I run dryer on manual with knives at 100% and IR at 10-15% temp gets into 115-120+F. Run on auto set at 98F both go down to 10% settings especially on a longer run. Evacuation at 100% also.

 

Are you certain that even though evacuation is set at 100% that your actually getting the gases out of the delivery??? Have you checked filters? Have all components in the exhaust system been checked for proper operation? The short deliveries can be a bit problematic, but if all is working as it should safe coating should be possible. You are right in trying to maximize the use of the air knives and to just use the IR to arrive at the desired final temps. Perhaps you need to bypass the use of the auto set and arrive at the desired temps, in the desired way by going with a manual over ride of the controller.
The biggest problem ive encountered with the short deliveries are that a much more precise control is required, because the freshly printed sheet has a lot less time in the delivery. Using the automatic settings on your controller will have the drying unit scrambling to find its desired levels. This becomes even more of an issue on shorter runs!!! At least on a long run if everything is working as it should the system has time to come into proper balance. Drying systems ,just like ink water balance, need a little time to stabilize.

 

Further to what Tom mentions above re checking and cleaning filters/cooling vanes inside the dryer cabinet, what pressure is the gauge next to the expansion tank reading? I have had one of them go U/S before, although I think you'd get a Guide Plate Hot error if it was faulty. Checked on an XL at work today and it was reading 0.6 in operation.

Going back to the extractor itself, on XLs after press power up, there are two sources of extraction, intermediate and lateral, and only the intermediate one turns on automatically. To turn the other one on, press the Paper Feed sub menu then Dryer, and press the extractor menu button (think it's right hand side at the top). You'll see the two extractor systems side-by-side, the left one (intermediate) will be on, and the one on the right (lateral) probably won't be. To turn it on you'll have to press the + sign to 100% and press the button above it. Visually it's not a very clear way to see if it's actually on.

Another thought, once you've set the air knife to 100% there is another setting to watch out for. The "blower output of the hot air zone". I think it's adjustable 40%-100%. To see what it is, go back onto the dryer screen, and check the two yellow figures. The top one is what you've set the air knife to, so probably 100%, and the yellow figure below it is the blower output value. A normal setting for that in my experience is 60-70%. If that's at 100% then your temps are going to be too high, which is what you have been experiencing (also, if it is at 100% you'd find lighter stocks trying to skip over the sheet brakes and be kicking out in the delivery)

To maintain desired temps, with air knife at 100% I don't think I've ever had to turn the IR down below 50%, so with your temps you're either generating to much heat/blast air from somewhere or the heat just isn't getting taken away very well.

Hopefully some of this info transfers from XL to CD. I haven't run a SM/CD with an air dryer, just IR.

 

Thank you both, Tom and Steve. The evacuation seems to be working but haven't been able to check helper fan on roof of building. I perform cleaning and maintenance regularly of the filters and air cabinets. The sheet guide pan cooling system runs between .5 and .8. It does seem to need charging quite often though, just charged it today. The point about the air blast setting is a possibility however. It's set at 100% and I don't/ haven't played with it to test if it makes a difference. I will experiment with that. Thanx.

 

Pierry dryer system? Have you checked the thermostat for the cooling system, and/or the coolant pump?

 

It's a CAN dryer. Not aware of a thermostat to check. Pump it turning. Recently replaced a pressure valve however.

 

Sorry, could actually be a pressure valve, it regulates coolant flow in the system. Sounds like you’ve already addressed the problem but I still wonder about the pump working correctly. Part of what you are describing sounds like a coolant issue that I’ve seen before. The manufacturer recommended replacing the valve (which we did) but it actually ended up being the pump.

I wanna say that even when the technician arrived, he couldn’t be sure if it was the pump until he physically replaced it.

 

Yeah, talked with Heidelberg tech via phone about pump. He says if it's turning it's working. It's turning so.... management doesn't really want to pay for onsite service. Also that pump was replaced once already according to manager.

 

Could be cooling issue however, getting low pressure error every few weeks or so. Don't remember having to charge the unit that often. Thank you for your feed back.

 

As an aside, I remembered over the weekend, that a couple of years ago one of the changes in a software update we received, was that in auto heating mode the air knife will never go below 50% heating output regardless of whether the temp in the delivery was actually above what has been set as the desired delivery temp.
Not using auto mode though, I've not seen it in action.

 

Thanx but we apparently don't have that update. That's the problem on auto though, air knives and IR go down to 10% to maintain set temp of 98F. Coating is cold and wet in delivery at those settings, obviously. Will try lowering air blast setting next coating job. Let you know how it works.

 

I appreciate that Quig, it was more just to say that H'Berg obviously realised that allowing the air knife output to drop that low wasn't good
Fingers crossed.

 

Hey Steve, thanks for the tip on blast air setting. Set at 60% and was able run air knives up at 85-90% on 1st pass with matte aqueous, and 70-75% on 2nd pass and maintained pile temp of 100F and 95F respectively. Also using temp probe in pile instead of relying on press sensor in delivery, that seems to read at least 5 degrees higher than probe. I will keep experimenting though. Thanx again.

 

Ive found that a hand held infrared thermometer is a better tool than the temp probe. Hand held gives an instant readout, and is not influenced by how long you leave it in the pile. Of course you want to avoid a cheapo Harbor Freight unit, and spring for something of decent quality that measures in the appropriate range.

 

Yes, I agree Tom. Unfortunately the three places I looked are sold out due to people who believe it will work for body temperature. Probe was all I could find. Even Graingers is on back order. Thank you for your advice though

 

Hi all, another on going issue with my machine. Feeder keeps getting out of time even though I reset it. Any ideas what the problem is.?

 

feeder drive chain tensioner doing its job? For the best chance of feedback on the timing issue you should start another thread.

 

Not sure where that is. Encoder replaced is past according to manager. Can reset timing by loosening bolt in feeder head and adjust but doesn't hold for long. Especially at high speeds.