Screen Tensions....???

[starchild]

I wish one day these thread discussions about mesh will be all about the mesh's spec (dia, open area, ink volume etc etc) and the fluid pressure required to feed the stencil based on the type of ink and squeegee (profile, angle, speed, pressure) used to accomplish a maximum effective transfer to the substrate. Then tension will be a "goes without saying" after thought type a deal because the tension used was in direct relation to the mesh specs. But alas I won't be the one to start this type of discussion because I'm here to learn. I do however appreciate that if a mesh is required to be stretched to 18 newtons to be in spec, I don't go to 26 newtons because I will only be introducing new variables into the transfer process that I will then have to address.

[Rocfrog]

Nick.. all of this is happening because you let it happen. In your quest to be the 'good' intern, you let this guy walk all over you thinking if you do this for him, he'll do that for you and my guess.. they haven't done a single thing for you but make your life more difficult as you work harder and harder to solve their problems.

 This is a dose of truth, it will never get better at that shop and the best thing you can do is walk away with the info you have gained and let them sort out their own problems.

Being in Colorado.. you have Graphic Elephants in Elizabeth, Lon and Jason are a couple of world class consultants.

I agree, unfortunetly I try and do the best at evrything I do and tend to hope that others will appreciate the outcome I produce, but unfortunetly this is one of those situations that I just get used and abused. The "unpaid intern" comment was just a "what I feel like I get paid" comment, I am an actual full time employee of this company.

I showed my wife this thread last night and she completely agrees with all of you on the current situation, but even with that said Ihave been looking for a new gigg for some time now with no real results and I can't just up and leave....so I just bide my time here and us it as a complete learning experiance and take my knowledge else where later. Sadly in the mean time I can't just sit back and watch this happen, I mean after all when I see the shirts out in public I want to be able to say "Hey look I designed and printed that shirt!" and be proud to say it!


I definetly think I'm going to have to do a little more research into this Graphic Elephants company and see if I can get up there and check it out....

Nick

[Printficient]

I wish one day these thread discussions about mesh will be all about the mesh's spec (dia, open area, ink volume etc etc) and the fluid pressure required to feed the stencil based on the type of ink and squeegee (profile, angle, speed, pressure) used to accomplish a maximum effective transfer to the substrate. Then tension will be a "goes without saying" after thought type a deal because the tension used was in direct relation to the mesh specs. But alas I won't be the one to start this type of discussion because I'm here to learn. I do however appreciate that if a mesh is required to be stretched to 18 newtons to be in spec, I don't go to 26 newtons because I will only be introducing new variables into the transfer process that I will then have to address.

This is a continuation of another post. When I was taught this the whole process was much harder.  The inks were stiff, the screens were stapled, and the presses were all air.  As improvement came down the line it was this and other gems from Joe that helped me know what issues were going to pop up from the latest fix.  The following list helped me try things that were unconventional but had a good chance of success.  It is important to know why something happens not just that it happens.  What I learned the most was that my fixes at first were the exact opposite of what actually worked.  Poor ink coverage more likely than not was caused by pushing the ink into the substrate instead of on top of the substrate.  So lowering the mesh count and multi hitting were the exact wrong things to do.  Calibrating the press to proper settings gave me a much better chance at getting the ink lay down that I wanted with a higher mesh count less squeegee pressure and faster print stroke. However in those days most equipment wouldn't hold the calibrations for very long. I learned to set and him and our challenger to 57,000's of an inch off contact in five places on the platen. These settings would usually last for 1 to 2 shifts before they were out again. This was due mainly to people touching knobs they should not touch.

1.    “Pressure” equals force divided by area [F/A]

2.    The ideal pressure on the T-Shirt platen [or press bed] is zero

3.    The goal therefore is equilibrium between blade pressure [F/A] and mesh tension AT ZERO GAP

4.    Rough estimate ~2N/cm² gain for every 16” of off-contact gap

5.    So a 110/80 mesh at 25N/cm² screen at 1/8” gap prints around 29N/cm²

6.    The ideal blade edge during the stroke ~250m and 16” in length = 0.16in²

7.    This mesh uses 231pL [picoliters] of ink [not including the garment]

8.    More ink delivery causes wet artifacts, less causes dry artifacts

9.    Therefore buckling is inadvisable – causes image drag and pressure on platen

10.  Multiply dynamic N/cm² by 1.4503 to find PSI = 29N/cm² * 1.4503 = 42PSI

11.  The ideal force on that blade = 42 * 0.16 = 6.7lbs of force

12.  Mechanical “pressure” does not transfer ink, after zero gap it only causes blade buckling and drag

13.  Speed and entrapment cause a [fluid] pressure head [~as the ink climbs up the blade]

14.  Ink transfers when the speed & entrapment increase FLUID pressure causing the ink to escape [into the mesh]

15.  Shear is the direction of force applied to the ink parallel to the mesh

16.  Very high shearing force is needed to cause matte-down and a smooth surface

17.  High shear is ONLY possible with high stroke speed

18.  High speed is ONLY possible with minimum angle [or broadcasting and wet artifacts occur]

19.  Minimum angle permits minimum [mechanical] pressure, maximum [fluid] pressure, optimal edge & minimum drag

20.  The mesh defines the wet-film-thickness [WFT] but it filters or restricts the VOLUME of ink.

21.  The blade must deliver sufficient volume to fill the garment [if first down] PLUS the mesh.

22.  At 60N/cm² the increase from static to dynamic tension is ~7N/cm² at the center

23.  At the ends of a single-axis blade the increase is >25N/cm² ~ 85N/cm² [dynamic] tension

24.  They can’t calibrate the press accurately enough to achieve platen-to-platen consistency

25.  If their gap is slightly off, the cylinders won’t deliver the force needed to bring the stencil into contact

I do not know why there are lines through the last points.  Sorry.  Happy New Year

[jsheridan]

I agree, unfortunetley I try and do the best at everything I do and tend to hope that others will appreciate the outcome I produce, but unfortunetly this is one of those situations that I just get used and abused.

I spent a better part of my life doing that, it's called a convert contract and all it got me was a head full of resentment when they didn't live up to their part of our self imposed bargain. So you try harder with the same results and things get worse. It's a cycle that once you learn to break it.. you find out that when you work,

YOU do it for YOU and your self worth, not theirs.

I don't work for others in the sense that the only person i'm trying to be better than, is the person who I was yesterday. I love screenprinting, have a deep passion for it  because it makes ME happy. Screw with  my happiness and we have a problem.


From my past experience, your type of owner is so wrapped up in his business trying to get new orders that any and all changes will require zero expenditure and will require a strenuous approach from you to make it all happen, then the second you're not there, will revert back to the way he knew how way back when before you were there. in other words, all your hard work to 'fix' the place will never stick cause once your gone, the new guy has to do exactly what you did.. fix the place to his way to make things work.

my solution for your problem..
just go to work and stop caring about making him happy and start using his tools to the best you can to make your job as happy as you can make it. 

[jsheridan]

I wish one day these thread discussions about mesh will be all about the mesh's spec (dia, open area, ink volume etc etc) and the fluid pressure required to feed the stencil based on the type of ink and squeegee (profile, angle, speed, pressure) used to accomplish a maximum effective transfer to the substrate. Then tension will be a "goes without saying" after thought type a deal because the tension used was in direct relation to the mesh specs. But alas I won't be the one to start this type of discussion because I'm here to learn. I do however appreciate that if a mesh is required to be stretched to 18 newtons to be in spec, I don't go to 26 newtons because I will only be introducing new variables into the transfer process that I will then have to address.

They do talk about it, they want to know how to make all that work on static frames because right now, the ability to tension mesh to a specific target point that will achieve the mesh specs that lead to maximum transfer abilities are not in their level of abilities or the budget for getting some roller frames is on the 'to do' list for next year.

The removal of variables is vastly important from the steps of film output through screen set up and print. At any point in this line is a multitude of problems that can go wrong. As you remove those variable you are less likely to think about what could go wrong and more time thinking about how it's going to work. The longer those steps stay in place and people aren't allowed to drift from them, the level of accuracy remains. Introduce a new set like over tension or skipped re-tension and things like coating microns can change which will effect burns times of fine dots that leads to press registration and color shifting issues, that can only be corrected by using a correctly tensioned screen in the first place.

[Rocfrog]

Here is a perfect example of what we run into here.....

100pcs brown in color printing white on front and back....

Here's a screen shot of the art work....


Here's a few shots of the film....




Here is the 1st hit on the press....on a 230 screen 2 swipes...


And here is the shirts after the second hit (2 swipes) and they've been thru the dryer...




and this took about 1.75hrs on the auto......and the backs still aren't done....

This is typical and acceptable for our shop...

**EDIT** Sorry for the crappy cellphone pics**

Nick

[ZooCity]

Hoooeee, that's some epic dot gain.  Good screens, not even great screens, just decent, would make that a one hit and you would have crisp edges and a print that actually resembled the art.  That halftone fill is totally closed in after the 2nd hit (probably 4 strokes at this point?).

For a quick fix, talk to your art dept and get them to start comping for the extreme dot gain on art like this, either by linearizing the film output (this can be done by eye) or just plain pulling back the % fills.

Also, your run times are obviously waaaay long on this, slower than our times manual printing for an identical job.  On a job like this we're at around 75 pcs/hr print/flash/print or 100-150/hr single hit, sorted, counted, boxed and ready to go.

[alan802]

That's a perfect job for a "one hit white" at our shop.  I just did one earlier today and I'll get the video up later.  That type of artwork is absolutely perfect for a one hit.  I did our last job on a 100/55 at 25 newtons with a 50 micron stencil.  23-24 psi on the printhead and 10"/second print stroke.  A special fill blade and a special squeegee blade played a large role but I'll get more into that stuff later in another thread.  So, like Zoo said, a little better screen, perhaps the right stencil thickness and off contact, better mesh count selection and you'll get rid of at least 2 of those 4 strokes and possibly 3 of them.

[Rocfrog]

For a quick fix, talk to your art dept and get them to start comping for the extreme dot gain on art like this, either by linearizing the film output (this can be done by eye) or just plain pulling back the % fills.

Umm....I am the "art department".....

**EDIT** we are a two and half person shop.....Me = art, reclaiming, burning, auto press operator, etc.... The other full time person is the manual press operator and she can run the auto but doesn't like it and then we have a part-time new person that has ZERO experience and he is just supposed to be "general shop labor".....

That's a perfect job for a "one hit white" at our shop.  I just did one earlier today and I'll get the video up later.  That type of artwork is absolutely perfect for a one hit.  I did our last job on a 100/55 at 25 newtons with a 50 micron stencil.  23-24 psi on the printhead and 10"/second print stroke.  A special fill blade and a special squeegee blade played a large role but I'll get more into that stuff later in another thread.  So, like Zoo said, a little better screen, perhaps the right stencil thickness and off contact, better mesh count selection and you'll get rid of at least 2 of those 4 strokes and possibly 3 of them.

I would love for something like this to be a one hit wonder, but everything we do light on dark "has to be hit twice" kind of an unwritten rule around here so the white "is nice and bright". Our manual press person is running the auto and I know for a fact if she was to print this on the manual it would go 10x's faster but for our shop those "counts" mean they go on the auto. But at the same time I think she would still do a hit/flash/hit on the manual as well and not be concerned about the "halftone" "filling in" just that the white is "bright".....

Nick

Nick

[ZooCity]

Well, for now, pull back the fill % to accommodate for the gain. 

Try, try, try, to get better screens in there.  You can't build without that foundation, it's the heart of the process. 

[Rocfrog]

Well, for now, pull back the fill % to accommodate for the gain. 

Try, try, try, to get better screens in there.  You can't build without that foundation, it's the heart of the process.

Are you meaning turn everything into a halftone....presay....

Nick

[ZooCity]

Well, for now, pull back the fill % to accommodate for the gain. 

Try, try, try, to get better screens in there.  You can't build without that foundation, it's the heart of the process.

Are you meaning turn everything into a halftone....presay....

Nick

Haha! I guess you could, you are printing totally solid at what, 50% fill there?

Glad you have a sense of humor about it, that's the only way to go.   

[Rocfrog]

Haha! I guess you could, you are printing totally solid at what, 50% fill there?

Glad you have a sense of humor about it, that's the only way to go.

Ya the word basketball is at 55%....

It's about the only thing keeping me sane here.....

Nick

[alan802]

Here's a poorly done video of what I was talking about earlier.  This art is much like the one you showed except no halftones and a little thicker lines in the font on our print but you get the picture. 

One Hit White/Plastisol ink

[islandtees]

Alan,
Are you using Miami Screen Supply white? Which version if you are? Did you reduce it? You mentioned special squeege, whats special about it?