HIGH TENSION Who does it?

[1964GN]

Dude, that was a an amazingly great post!

[Dottonedan]

That IS an excellent post and I'm excited about every word of it.

This brings me to this question them.

Specs for mesh is given in its relaxed state not stretched.. So the open area is what it is at any tension.. Mesh that is stretched squared will provide best open area but the thread diameter does not get thinner so percentage of open area remains the same.

Now, I guess I am looking to hone in on this part. I know I've read many times that higher tension produces more open area. I see clearly that what you say here makes sense, but so does the idea that the open are becomes slightly larger. Like maybe 3-7% more open let's say.

Apparently that would only be in the case with one type of mesh scenario. (High elongation and low module).  So as a result of this, you need to assure that you stretch to perfect 90 degrees to get a good square opening since this mesh can be stretched more easily to non uniform warp and weft. Correct?  This produces good high tension...this closer off contact, thus faster and more accurate image reg.

So do you ever find this scenario to be a negetive?  Is a mesh that is more stretchable (high elongation and low module) ever a bad thing?

I would think the more rigid mesh type ( (Low elongation and high module) would be more prone to popping.

[Gilligan]

I'm sure there is a balance, but high elongation means to achieve high work hardened tensions means you will be getting farther away from spec mesh openings.

Obvious if it's TOO rigid then it wouldn't have much give and that would mean easier to pop.

[Dottonedan]

When I read it, I felt the lean towards the more rigid being the better or more accurate option of the two, I'm sure it's s preference but I thought I'd play devils advocate.

And father away from spec (may not be) a bad thing. That is of course, how they promoted high tension (in the past). I'm talking what I read 10 years ago, so as always, products change, processes change with time. I probably did hear of the differences way back then, but I seemed to have focused on obtaining the more open area.

[Gilligan]

Well... like I said there is a balance.

No one is suggesting to print with rubber bands, but not rigid plastic either.

The difference in what we are talking about is EXTREMELY subtle.  You want low elongation in what we have as options vs high elongation.

[starchild]

The offcontact is what supports image tolerance..  Tension only accomadate the offcontact distance therefore you do not need high tension to be within image tolerance.. What the tension does is prevent mesh lag (positive or negative) if this can be accomplished at 24n then good to go..

Yes S mesh will be way more rigid (less give) than T mesh so it needs less stretch to square the opening. T mesh also has thicker threads so no matter the tension level increasing the opening, the thicker thread will always handicap the ink flow (pressure drop) more than a S mesh..

Tension and speed just don't belong together.. (shear foce is achieved when the edge of the blade applies pressure to the ink as it moves across the screen- faster speeds promotes higher shear- and not the the downward force which is needed for the stencil to make contact with the shirt so tension and shearing don't go together) If we're discussing speed of ink delivery then address the passage's opening and distance to travel.

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[ScreenFoo]

A (mesh) material made to be resistant to deformation will produce high tensions with very little stretch so it has a low elongation tendency- it is high modulus.
A (mesh) material that is made to deform easily can be streched a lot and so will naturally produce very high tensions- It is low modulus.

A low elongation mesh, with a balanced SS curve, will produce a squared mesh opening with let's say a 5% stretch from relaxed position and 20n of tension.
A high elongation mesh, with an imbalanced SS curve, will have to be stretched to let's say 15% of it's relaxed position And tension in the 30n's to even begin to have the opening get to 90 degree angles and because the ss curve is imbalanced the amount of stretch in the warp and weft will need diffetent values..

Specs for mesh is given in its relaxed state not stretched.. So the open area is what it is at any tension.. Mesh that is stretched squared will provide best open area but the thread diameter does not get thinner so percentage of open area remains the same..


Tension (static) does not play a part in ink transfer..

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Most of this strikes me as reasonable, but a couple of things I have to ask:

First, you compare a thin thread mesh that is low elongation with a standard thread mesh that is high elongation.  It has been many years since I saw a real printing mesh being sold that was not 'low elongation'.  Why compare thin thread quality mesh to mesh used for filtration plants?   Is there a point I'm missing from this comparison?

Second, you say mesh parameters are measured while relaxed, but the paper I read long ago by the SPTF disagreed saying some measure tensioned, others relaxed--i.e. there was no standard, and goes on to say that if you want good numbers you need to measure them yourself.   Are you sure this is bad information?

Also:  If you stretch a mesh to 110% of it's original length along an axis, how can that NOT change the open area?  Not only are you changing the spacing between the perpendicular threads, you are making the threads thinner when you stretch them, are you not?

Third, you say static tension plays no part in ink transfer--isn't that kind of like saying a screen that isn't getting printed plays no part in ink transfer?
After all, the tension will change as the blade pushes the mesh to the substrate, will change again as it starts to pull across the screen, and the pressure on the substrate will be defined by not only the downward force on the blade and the footprint of it and by the force in the print direction, but also by the 'static tension' of the screen opposing it.

Also, FWIW, an average thickness of a mesh will be less than twice the thread thickness--IIRC, I believe it has something to do with how they heat set the knuckles.  If there are exceptions, it would be fun to know what they are and why. 

[ABuffington]

There is some great info here, but lets get down to production needs.

1. You want to print non-stop in perfect register?
2. You want your screens to last and not pop?
3. You want decent ink laydown for opacity?
4. You want good production yields per hour?

In all cases your mesh selection is critical. 
Your tension selection will preserve mesh, and if your mesh is low elongation with a balanced stress strain curve you don't need excessively high tensions.
Optimum lay down of ink needs good open area.
Good production yields will follow with mesh that holds register with sharp prints at an 'optimum' tension not the 'highest' tension.

Recipes:
Vector:
Base: 150/180/225S meshes at 22-25n
Overprint: 160T, 225/40, 250T at 25-30n (or the same as above in S mesh, higher tension helps spot colors peel on large print areas.)
My choice would depend on the details and size of solid areas in the art.

Sim Process
Base: 225/S at 22-25n
Overprints: 300T at 25n or 300HD at 30n,  or 350s at 22n.

All of these counts and tensions work extremely well. 
You can use S mesh open area for less squeegee pressure, great for bases.
S Mesh at 22-25n will peel fine as long as hot tack base plates aren't present.

If you have tack issues, or multiple wet on to wet prints and need better peel, move up to 300 HD at 35 newtons.

It is all art dependent.

High tension above 35n brings critical off contact to pallet needs in the corners.  All pallets must be in perfect level to each other.  If not you need more squeegee pressure to get it to print will deform image or laydown too much ink. 

The largest tonal range will come on S mesh, not high tension mesh.

In the high volume shops I deal with most are in the 22n-27n range to preserve meshes. Going for the highest tensions possible doesn't insure better print yields, it can yield good print yields on a well tuned press, but my experience is pallets go slightly out of level to each other in heavy production environments, changeovers, inertia of cycling, etc.  Quite often the mesh needed to get 35n+ will have very low open mesh areas that can eliminate finer details and halftones.  If your mesh doesn't lose tension or you hit a work hardened screen after a quick retension it can lower the labor needed.  This is why statics are gaining popularity.  Stretched to a cut out tension of 25n yields a work hardened 20-22n screen that holds register and prints well downline.  Of course I do promote Smartmesh since it has all the bells and whistles to print non stop more often than not.

PM me Dan and samples are on their way.  This goes for anyone else.  I have a ton of bolt end samples I can spare. 

Al

[Dottonedan]

There in lay the question.

What is "optimum" tension?  Not optimum for the mesh type, but optimum...to yield the highest efficiency, speed and quality.

I don't "need" optimum tension. I don't need 40-50, but rather (the most efficient).
So I had been looking at the Newmen high tension mesh -as I've read some guru articles that prefer higher tension to yield better overall results.

Now, I know you stand to pop more screens and who wants that...but the other option of even lower S mesh with thicker yet more spread out threads....still are known to pop frequently (even at its known lower tensions than compared to Newmans.

[Printficient]

This is all good info.  I'll throw out there the one constant that varies run to run.  Screen prep.  Quite a lot of issues that pop up on press can be traced back to improper mesh prep.  This is the issue most of the time but is discounted by rote of "Never had that happen before"  "The ink must be bad."  "The squeegee is dull"  "The platens are not level."  Most of the time if it is a "one off" issue you should look at what improper mesh prep coupled with a host of other variables from weather to power consumption.  Residue chemistry that is invisible to the naked eye is a monster that pops up a lot be is never held responsible.  Screens ARE the secret to great printing.  Yet we put the person with the least experience in charge of them and wonder why nothing prints profitably. 
Rant complete.

[ZooCity]

I tried high-ten years back- M3 rollers and Newman Roller Mesh at 40-65n/cm.  There are some cool sides to it that have been mentioned, repeatability being my favorite, but I would never introduce ultra high tension mesh into ours, or probably any, production environment.  Here's why:

Now, I'd hate to agree with Sonny , but he is correct that many of the common machines cannot hold the tolerances to reap the benefits of high tension which, as Starchild eloquently explained, lie primarily in reduced off contact.  All of the good stuff about high tension comes from that reduced off contact- better/easier reg, less pressure required to clear inks, repeatability.  I do not want to steer this great conversation wrong but it's fact to me that there's no way the presses in my shop would stay within tolerance to take advantage and we maintain them very well and regularly.  If I'm not mistaken, Stretch Devices ruffled some feathers with press mfg's when first introducing their frames and pre-reg system as the limiting factor was the build and design of the machines but that was before my time and could be hearsay.  In any case, it's not a knock on one brand or another, just a component of the current reality of this.  I see new presses and designs out there that might could handle ultra high tension and they all seem to be improving with every generation. 

To pile on reasons not to go high tension: you're adding a need for serious muscle on the roller master table as your torque values need to go up, you may also need to get into that "reverse curve" or whatever it's called method to keep the frames from bowing, corner softening becomes an elaborate process and tensioning and retensioning takes longer generally.   The mesh costs a lot on top of all that.

In a perfect world that high tension guru mesh is probably amazing.  In my world we use lower tension mesh with excellent stress/strain properties.   

If your world doesn't look friendly to delicate mesh (both thin and high ten screens will necessitate a change in handling for most shops) I'd start with the best T threads you can source and see how high you can go within reason on that tension.

*quick possible correction to Starchild's post, I believe the thread diameter of Newman Roller Mesh does indeed change (becomes thinner) when brought to it's recommended high tension and you need to watch out for a new issue called polymer necking at this point as it can mess with the consistency of the thread's diameter. 






 

[Gilligan]

We still just printing underwear right? 

[alan802]

When it comes to mesh tension, which is second in importance to mesh count selection, the Law Of Diminishing Returns applies to a higher degree than anything else in the shop...in my opinion.  It's not "supposedly" or anything of the sort, but properly tensioned screens (the manufacturers' suggested tension level), which means the highest tension level the manufacturer recommends for a given mesh count will outperform all other tension levels below that.  You can argue against that all you want but what you're really arguing is, what level of tension does it make sense to maintain to give you the desired print quality, production capacity, ink consumption, etc?  With that being said, I can produce a much better print, and print it much faster with a 150/48 at 18 newtons versus a Newman Roller mesh of 160/???"who knows what thread diameter really" stretched to 65 newtons because mesh count selection is more important than tension.  You have to set the parameters of this debate to get a clearer picture of what shop managers and/or owners should strive for when it comes to this subject.   

I used to be a high tension guy but that was before I discovered thin thread mesh and learned how to use it.  Without knowing about thin threads, I was working with what I had knowledge of at the time and without a doubt our high tension screens outperformed the low tensioned screens by a HUGE margin.  It wasn't easy getting screens up to 60-65 newtons and maintaining them, not to mention having to calibrate the pallets and print heads to a tolerance that would allow the usage of such high tensions.  I'm glad we were able to move in a different direction with better mesh counts but if we didn't have thin threads I'd no doubt be using high tensioned standard mesh.  I'd just be doing more work on the screens and press calibration. 

[ScreenFoo]

Oh well, I guess I'm not in on the joke.

FWIW Alan, you're still a high tension guy--'high tension' is just propotionally lower on S mesh.

[ABuffington]

A note on manufacturer's recommended tensions.  Let's look at 225/40 S mesh.  The chart in my catalog says tension range is 18-29.   29 is the point at which our tests have shown to be safe before the mesh pops.  Anything above this is not going to get much more tension without creating a ticking time bomb in your shop.  Then lets look at how it is tensioned.  Bar stretchers on static frames drag the mesh across the frame.  For S mesh this can cause it to pop with too high a tension. What kind of presses?  Graphics can get to the highest tension due to better shop handling, more forgiving press set ups, less squeegee pressure needed, better presses with smooth flat vacuum tables,etc.  Textile printers have gotten used to 110 mesh and handle all screens accordingly.  As mentioned, we give the most valuable tool to the least skilled person in the shop to handle and since reclaiming, ink removal of thick inks is often accomplished with brute force I recommend something in the middle of the range.  In this case 24n would be a safer stretch on 225/40 than 29.  For base plates this is plenty of tension, yet low enough to adjust during printing to pallet out of level issues, seams, pallet bumps etc.  Textile printers also tend to use more squeegee pressure, rarely round off the squeegee ends and also use a frame that causes the squeegee to be very close to the inside of the frame. 

A graphic frame is usually square and has ample distance between a rounded squeegee end and inside of the frame, often 4-6 inches.  Textile printers often never round their squeegees and will push the print image so much that they are lucky to have 1.5 inch clearance to the frame.  This creates high momentary tension during the print stroke. Even more momentary tension if higher off contact is used.  So to fix screen popping on S mesh we recommend lower tensions in the middle of the range.  If you have rounded corners, proper off contact you can push tension up, but after the upper number 29 in this case, you are just creating a fragile screen with threads at the breaking point.  You may be able to push a roller farther at max tension, but quite often the tension doesn't climb with the extra movement as much as it did in the beginning.  The mesh is staged and at it's max tension point.  The next sound you here will be a 20 dollar piece of mesh exploding.

There is no additional mesh opening gain with more tension due to knuckles that are welded.  It will print accurately at either 20 or 28n, hold good registration etc.  Its the peel factor where higher tension is a great help.  A 300/34 (T) is 18-28, and a 300/40 (HD) is 26-40.  Our statics can handle 30n, but a Newman would be needed to stretch above that.  A 300/40 at 35n would peel better and would be beneficial if the print had wet solid areas and halftones from previous wet onto wet prints.  Art may need to be curved on 300/40, and you may lose a few tonal values below 10% due to thread diameter blocking fine dots, but in a wet onto wet print of red/blue solid areas, then higher tension does have an advantage.  The press levelness and off contact needs still apply.

Al