Who teaches the teachers?

[Mark H]

So in presses with positive ink feed which as you say are open systems, what happens to the ink that does not go onto the substrate?

Al,

I don't know where the ink goes, and frankly I don't care. My statement was addressed to Erik in reply to his insistence that the law of conservation of mass could be applied to an open system (a positive ink feed press) which it cannot.

However, what seems to apply would be Pascal's principle of fluid mechanics - "Pressure applied to a confined fluid is transmitted undiminished throughout the confining vessel of the system." Please note that proper interpretation and application would require both a confining vessel (not to be confused with a closed system as used with the law of conservation of mass) and a homogeneous fluid.

Mark H

 

[Deleted member 16349]

Erik,

I don't believe that you are interpreting and applying the principle of mass/matter conservation correctly in this discussion. While it is true that that the mass of a closed/completely isolated system will remain constant over time, mass is not conserved in "open" systems when forms of energy are allowed into or out of the system. This is especially true in systems where work, or motion, are in progress or where chemical reactions or chain reactions are occurring.

A press, even a very well maintained one under laboratory conditions, would still be an open system and therefore not fall within the law of Conservation of Mass.

Mark H

Mark, I am sorry but you do not understand physics very well. Energy has no affect on the amount of mass and even chemical reactions do not affect the amount of mass. Conservation of Mass is used often in analyzing open systems.

 

[Mark H]

Mark, I am sorry but you do not understand physics very well. Energy has no affect on the amount of mass and even chemical reactions do not affect the amount of mass. Conservation of Mass is used often in analyzing open systems.

If I have a stick of wood weighting 5lbs and burn it the chemical reaction converts a portion of the wood's mass into heat and another portion into particles which are removed as smoke along with the rising heat. At the end of the reaction I have ash. When weighted, this ash will not weight 5lbs.

While crude, this example demonstrates a simple open system where what comes out is not what went it. Why? Because I cannot accurately account for the transfer of mass into heat or the chemical conversion of wood into other by products.

Your assertion that I am wrong, simply because you want me to be, doesn't stand up to even the most basic of reviews.

Mark H

 

[Deleted member 16349]

If I have a stick of wood weighting 5lbs and burn it the chemical reaction converts a portion of the wood's mass into heat and another portion into particles which are removed as smoke along with the rising heat. At the end of the reaction I have ash. When weighted, this ash will not weight 5lbs.

While crude, this example demonstrates a simple open system where what comes out is not what went it. Why? Because I cannot accurately account for the transfer of mass into heat or the chemical conversion of wood into other by products.

Your assertion that I am wrong, simply because you want me to be, doesn't stand up to even the most basic of reviews.

Mark H

Mark, you are more than wrong. Sorry.

 

[LoneGoose]

Yeah, I don't think that 'mass' can turn into 'heat'...

 

[J]

'A little learning is a dangerous thing' A small amount of knowledge can cause people to think they are more expert than they really are.
For example:
theflatearthsociety.org - Index

J

 

[meddington]

A small amount of knowledge can cause people to think they are more expert than they really are.
For example:
theflatearthsociety.org - IndexJ

Wow.. I am speechless.
I suppose given enough free time, one could come up with theories that "Prove" or "disprove" about anything...and find a following.

 

[Harvey Levenson]

To Al's questions.

Positive ink feed as described in this discussion is theoretical as pointed out by Erik. I believe he noted that it was tried in three companies and one went out of business. Hence, this does not apply to the many presses I have worked on.

I haven't organized my data, but would have had I anticipated this discussion. My observations include when I worked for GATF (now PIA) and I traveled the country and world doing audits of printing press procedures and troubleshooting press problems.

I do recognize the five categories of ink transfer that you've noted with the effect of water eliminated from only the first. I agree with you on that point. The remaining four can be variable regardless of the inking system.

Harvey

 

[Deleted member 16349]

Wow.. I am speechless.
I suppose given enough free time, one could come up with theories that "Prove" or "disprove" about anything...and find a following.

Just a comment on theories. Theories do not prove or disprove anything. Theories are explanations for how something works. If one disproves the theory then it is no longer a theory. The more a theory can withstand against attacks, the more it becomes validated.

It is never fully validated because it is always subject to attack and if an attack is successful, the theory becomes invalidated or at least in some specific situations. But if the theory is validated, it is then very practical because of its predictable properties. That's when it can help build the future without direct experience.

 

[gordo]

Just a comment on theories. Theories do not prove or disprove anything. Theories are explanations for how something works. If one disproves the theory then it is no longer a theory. The more a theory can withstand against attacks, the more it becomes validated.

Ah Erik, you make me homesick for my days working with the engineers at Creo/Kodak. Your comment perfectly reflects lesson #4 that I learned from them. Printshop folks might find it, and the other lessons, quite useful:
Quality In Print: Some things I learned from engineers (that printshop folks might find useful)

best, gordon p

 

[meddington]

Just a comment on theories. Theories do not prove or disprove anything.

Of course your right (which is why I placed "prove and disprove" in quotations). Perhaps "support" and "weaken" would be more appropriate. In any event, we could continue to squabble over ink feed issues, or join the real debate...flat or round!

 

[Cornishpastythighs]

Hands up who has actually seen what happens at the milisecond moment of printing. I've been Litho printing for 40 years man and boy and it still amazes me, If a new way of looking at our process is presented to us we should maybe invest as much time in seekng its benefits as we seem to do in shooting it out of the sky. This is just my .2c worth folks

 

[Mark H]

Yeah, I don't think that 'mass' can turn into 'heat'...

Seriously? Did you not pass High School chemistry?

Mass is loosely defined as the property of a body which causes it to have weight in a gravitational field. The rapid oxidation, or decomposition of a fuel material, such as the wood used in my example, when in the presence of both oxygen and heat is referred to as fire.

When there is enough heat the fuel's compound molecules break apart, and the atoms recombine with the oxygen to form water, carbon dioxide and other products. In other words, they burn. A side effect of these chemical reactions is a lot of heat. The fact that the chemical reactions in a fire generates a lot of new heat is what sustains the fire.

Hence, a result of burning is the reduction of the original body's mass. We are not talking the mass within the entire system, only the mass of the specific body.

Again, a simplistic example, but a useful one when discussing the application of the Law of Conservation of Mass.

Mark H

 

[Al Ferrari]

Thank you for the response Professor Levenson,

In your post of 11:05 AM Sunday, you stated:

"I’ll address (1) the “positive ink feed” theory " and then proceeded to mention your extensive experience as a consultant, etc.

But if none of your field tests involved presses with positive ink feed, then they do not in fact address the issue. This is not to cast any doubt at all in the validity of your data, but rather to point out that it does not shed any light at all, pro or con, on the “positive ink feed” theory.

But let's try to move forward. The problem so far has been that a press modification is required to test the theory, and no one has stepped up to the plate. But what if we could device a very close substitute situation that would replicate the conditions we would expect to find in a press outfitted with positive ink feed? An experiment simple enough that it could be performed by any seriously interested practitioner of lithographic printing? One that could be performed by readers in this forum, with simply the investment of time, a plate and at most a few thousand sheets of stock?

Would there be interest in such a test?

Erik and I have been discussing a test of this kind and when we have the details worked out, it will be posted as a new thread.

Al Ferrari

 

[Deleted member 16349]

Hence, a result of burning is the reduction of the original body's mass. We are not talking the mass within the entire system, only the mass of the specific body.

Again, a simplistic example, but a useful one when discussing the application of the Law of Conservation of Mass.

Mark H

Mark, Conservation of Mass applies to the entire system otherwise there is no point in having such a law. In analyzing an open system, one has to draw a boundary around that system and account for the mass going in and out and what changes in mass are in that system.

Yes, in your example with burning wood, the wood is reduced to ash but the Law of Conservation of Mass has never stated that the mass of the wood and the ash would be the same. But the ash and all the gasses supplied and coming off the combustion conform to the Law of Conservation of Mass. Burning the wood has not changed the total mass of the entire system which includes the carbon in the wood and the oxygen in that air that combined with the carbon during combustion and the products of combustion.

 

[Lukas Engqvist]

On the conservation of mass. I will try to raise a question, you may have raised it before and therefore have an answer. Ink in and ink out are equal, but is the ink out where it intended to be. Look at the printing and non printing areas. is it that all the ink ends up where it should (print areas) and all non-print areas are free from ink? Is there no places that accumulate ink? May be stupid prepress questions from merely observing a press and not actually using one.

 

[Deleted member 16349]

On the conservation of mass. I will try to raise a question, you may have raised it before and therefore have an answer. Ink in and ink out are equal, but is the ink out where it intended to be. Look at the printing and non printing areas. is it that all the ink ends up where it should (print areas) and all non-print areas are free from ink? Is there no places that accumulate ink? May be stupid prepress questions from merely observing a press and not actually using one.

It is not a stupid question. One person at another site commented on misting as one path out. This is true but it is not significant. If it would be significant then one has a hell of a misting problem.

One could have possibly be dripping ink onto the press frame at some point. Is this normal or abnormal? If this does not normally happen then I would say for practical considerations, it is not an issue.

If a press is working normally, the path out is in the image area. If one is scumming, then that affects the path out and when the scumming is corrected, the system will self correct to the proper conditions if there is a positive ink feed.

There may be shifts between the amount of ink going out in solids when compared to screens. This is an issue but I expect that when the ink feed is positive this issue can be looked into more carefully. I am curious about this. But right now there are global changes in the ink going out of the system with conventional ink feeds that needs to be corrected first.

 

[Deleted member 16349]

But let's try to move forward. The problem so far has been that a press modification is required to test the theory, and no one has stepped up to the plate. But what if we could devise a very close substitute situation that would replicate the conditions we would expect to find in a press outfitted with positive ink feed? An experiment simple enough that it could be performed by any seriously interested practitioner of lithographic printing? One that could be performed by readers in this forum, with simply the investment of time, a plate and at most a few thousand sheets of stock?

Would there be interest in such a test?

Erik and I have been discussing a test of this kind and when we have the details worked out, it will be posted as a new thread.

Al Ferrari

As Al has said, we will present a simple test method that any printer can try. It is a method that we think will demonstrate in a simulated way, how a positive ink feed will make the density control much more consistent, even when large changes in water are made. No modifications to your press are required.

It will be presented as a new topic post. I hope those interested will look for it and try the test. The feedback could be very interesting for all.

Erik

 

[vik la luna]

why not just take water out of the equation and go waterless?
develop a better water less process than what is currently available
water is by far the worst culprit in density consistency and it takes a pressman who understands ink water balance to produce the best results

 

[Deleted member 16349]

why not just take water out of the equation and go waterless?
develop a better water less process than what is currently available
water is by far the worst culprit in density consistency and it takes a pressman who understands ink water balance to produce the best results

I am hoping that the test results will change the way you view the problem.

If I had thought of this test method years ago instead of coming up with it now, it would have saved me a lot of grief because anyone could easily do the test and see the difference. But that is the way science works. It is not nice and orderly but it is a bit messy and takes unexpected jumps.

Hopefully it will not take too long to present the test method. Al is bringing the pressman's point of view into the presentation which I am sure should help.