Busting Screens On Press

[alan802]

We made it the 1st 8+ years without ever busting a screen on press during a run, and now we've had 3 bust in the last 6 weeks, 2 in the last 2 days.  I'm fairly certain they've all been on the same print head, number 6, right next to the 2nd flash unit.  They've all 3 busted at different locations, one on the left side, one right down the middle and the other on the right side closest to the flash.  Also, 2 have been bolt mesh and the one today was a brand new, never before used S Mesh Shurloc panel stretched to 28 newtons, max tension for that mesh is 35 so I feel good about it not being because I'm tensioning them too high.  We've had one 225/40 and two 180/48's.  We've been using thin thread mesh for going on 4 years now so it's nothing new to us.  One thing I find interesting is it's started around the time I got the latest crop (a whopping 2) of new employees.  My printer is dead set on it being something wrong with the print head and I've watched it off and on for 3-4 hours today and have used it on every job and I have not seen anything that would cause a busted screen.  Flood bars are polished well, most mesh is below max tension and corners are good and softened.  We print next to the 1st flash all the time, but it's usually a lower mesh, but a more delicate mesh than a 180 or 225.

Does anyone have an idea where all I need to be looking?  I've covered a lot but want to make sure I don't overlook something.  I noticed my screen guy has started using the sharp edge of the scoop coater and he started using it on Wednesday of last week.  And I specifically told him to not use the sharp edge because it was scuffed up but he said he polished it really good before he used it.  I'm thinking that maybe the one 6 weeks ago was an anomaly and the last 2 were related but I'm all ears/eyes on this one.  I have my suspicions, and I also am very good at finding issues like this but I'd like some help from the gallery here because I think I'm too biased in what I think is causing it and want to get some outside perspectives.

[jsheridan]

it's like chasing a pig.. when you finally catch it, was it worth the chase.

[ZooCity]

Look at all the other places screens rest.  It could be coincidence they are breaking on that head. 

[alan802]

I think we're still within the tolerance of it being coincidence given a lot of the other factors that exist that are hazardous to mesh, 2 new guys being the biggest concern of mine.  And one of the new guys has skillets for hands, a bit on the clumsy side.

[brandon]

Same print head? What is your ceiling made of? I'm serious

[Colin]

Also:

Where within the mesh area, did the tears start?

That will give us a good starting place

[AntonySharples]

I never busted one in 3 years, but since we got the auto we have busted at least 15 in the last 8 months.  Different printheads.  Pressure is not too high.  It busts right at the edge where the flood bar wing is.  Thought we figured it out that it was a bent flood bar, but still does it now and then.  Haven't quite figured it out yet though.

[Doug S]

I've only had it happen a couple of times but it's always the worst time.  My culprit was very dry days with the back door open and vehicles traveling back and forth across the dusty alley in back.  Needless to say a little dirt managed to get in the ink.  At first I noticed a little unusual single streak in the ink during the flood and then next was contastrophy.

[ABuffington]

Some things to watch out for.

Avoid laying any tools on the mesh during set up.  This can be a hard habit to break for workers used to laying the flood bar, squeegee and clips on the mesh. 
Avoid very aggressive wash pads.  If they are soft, no problem, if they can scrape the back of your hand they are too harsh and could nick the threads that may not pop until frames are degreased and put in sun, or as a print run starts.
Avoid dry wall spatulas with sharp edges to remove ink.
Round off the corners of your squeegees and polish them smooth.
Check all flood bars for nicks.  Place tape on the inside of the screen where they and the squeegee land to absorb the impact.  Check flood bar and squeegee pressure.  With S mesh less is better.
If screen is next to the flash aim an infrared thermometer gun at the frame after the flash has turned off.  If the frame heats up a lot it can expand and increase tension.  Try protecting the frame with a heat barrier so frame doesn't heat up.
Check off contact and pallet level.  overtime pallets can go out of level on some machines.  balance off contact front to back and side to side.
As mentioned watch other areas of the shop.  Are frame corners resting on mesh?  Are frame corners dragging across mesh when pulled out of a dip tank.  Try putting only one at a time in a dip tank when reclaiming.  The time to blast out a screen allows enough time for one in the dip tank to be soft enough to reclaim.
Have you switched tape recently?  Sometimes tape becomes so bonded to the emulsion it can rip mesh on removal.
Check squeegee pressure and durometer.  Avoid high durometer squeegees set vertically.  70 duro at 5 degress more angle than 'normal' angle of 10 degrees helps.  Think about the squeegee action and pinch the ink rather than attacking it with a high vertical angle, especially at high squeegee speeds.

Quite often the reason for the popping of mesh isn't present when it does.  You can nick mesh, abrade mesh with long runs, scrape with tools or scrub pads and not notice a popping of the mesh until later downline, usually after reclaiming when it is drying.  Your tension seems correct, but I have found that with most of the S meshes a mid point tension works better in harsh handling that is typical in textile shops.

If you stretch on your own avoid super glue type glues.  They create knives out of the mesh.  Any flexing over the glue can cause it to cut the mesh.  We use a 2 part Poly glue that is softer for this reason.  If you must use super glue, (cyanolates) keep glue within frame width.  Avoid glue on the mesh to the inside of the frame.  Again this will be a knife that will cut the mesh.

For plastisol, especially white, it can help to wipe down the inside of the stencil area with some curable reducer so that the squeegee has a lubricated surface to begin printing on.  White can be very viscous and need some working to soften up.  Fresh white can cause a lot of friction until it is softened in the screen.  Use a turn about to keep white bases soft.  In the morning the ink in the screen can really get stiff.  Remove most and add some that has been worked with a spatula or in a turn about.  Especially on long runs since the printing process will pick up a lot of fibers that accelerate thickening of the ink.

Send some photos so I can check out location, this helps.

Alan

[ScreenFoo]

I've had issues with the sharp side of the squeegee not being 'dressed' properly by the supply house.

Funny edit:  I don't know why I said squeegee, I hope you figured I meant scoop coater. 

If it's one of those types, you may want to check that the edge is flush with the end caps.


Does sound weird to me though, screens here pop after reclaim or after retension, *almost without fail.

*What, like I never mishandle one? 

[balloonguy]

I would make sure that print head is level. We had one that was so far out the flood bar was not touching in the back of the screen and pushing .125" in to the screen at the other end.

[alan802]

Here's the one from yesterday.  The one that busted the day before was about 6" to the right, and the one from 6 weeks ago was about 2-3" to the left of the pictured rupture.  We've had a floodbar wear a hole in a screen on a few occasions by coming down at an angle when using a hard fill, but having a huge failure like the ones we've seen is new on press.  Over the years I've found many in the dark room that have busted after a retension or after a coating but having it happen on press concerns me even more.



If the rupture wasn't so far to the middle I could see it being something within the print head, a bad floodbar or way out of calibration.  It's been about 4 weeks since I checked calibration of the press and it wasn't far out at all.  It's actually in tighter tolerance than some of my first attempts at press calibration so I think we're good there.  I checked the floodbars for imperfections and didn't find anything.  I double check Alan's list and make sure we're good on all of those but first read through looks like all the precautions we do but it's easy to get complacent with some of those.

I don't have a pic of the other 2, we've already stripped them and the frame are waiting in line for stretching.  They are identical in length and direction to the one pictured, but just more to the side closer to the edges of sq and fb, but they DID NOT bust right in line with edge/end the sq and fb and were about 1/2"-1" towards the inside of the edges. 

[jvanick]

stupid questions... (sorry if you answered them before/already)

1. when was the last time you retensioned the screens?

2. how much tension are you running.

3. when was the last time your tension meter was calibrated?

I've only had them pop in the middle of the screen like that when we were running too much tension.

[ScreenFoo]

^^If it's random like that I'd tend to agree--it would point to excessive tension, or the 'crap in the ink' theory.

Had one of the part timers shatter a glass mug and got glass in the white.  That was a fun month.
In retrospect, I would have saved money just tossing the whole gallon. 

[3Deep]

I maybe reaching here put to me that screen looks like to gave way in the middle from maybe a very small hole and high tension and not really over tension just high...look right at the left of the I on Kids about a 1/2 inch down that's where the rip looks like it started to me.