Most offset printing presses differ in the way they balance ink and water, but there's a simple way to measure your window in your pressroom.
In my printing experience, the ink and water balance measurement has always been a feel thing. It wasn't hard to tell if an ink was behaving properly just based on my experience and instinct.
I was soon introduced to a method of actually measuring the window that gave me a tangible number. This allowed our pressroom in a number of ways:
This method, I can assure you will work for any press, web or sheetfed. So here it is:
1. At a specific running speed, get a water reading at the bottom of the window. This means, run the absolute minimum amount of water until the product is about to scum. At that point take a reading on the dial you use to adjust your water. Or it could be a reading on the motor itself. It's not really important where you take it from. The main thing is that the number represents a reading from the water motor speed. We'll call this number Y.
2. Now bring the water up until the point where you are just about to start losing density. That is, up to it's maximum. That's right, the top of the window. Again, take a measurement. We'll call it X.
3. Do the math. Take X-Y and divide it by X+Y. This will give you a fraction. Multiply it by 100 and you have your number. Make a record of it and use it to compare.
Thought there have been many articles that speak about what makes an ink water balance stable, as of yet, I still have not seen anything more practical to use in the pressroom from GATF or anyone else, so if you are looking for something simple and easy to compare, this formula may work for you. If you have better ideas, leave your comment below.
In my printing experience, the ink and water balance measurement has always been a feel thing. It wasn't hard to tell if an ink was behaving properly just based on my experience and instinct.
I was soon introduced to a method of actually measuring the window that gave me a tangible number. This allowed our pressroom in a number of ways:
- comparing different ink brands
- keeping historical accounts of the same brand
- tracking quality
This method, I can assure you will work for any press, web or sheetfed. So here it is:
1. At a specific running speed, get a water reading at the bottom of the window. This means, run the absolute minimum amount of water until the product is about to scum. At that point take a reading on the dial you use to adjust your water. Or it could be a reading on the motor itself. It's not really important where you take it from. The main thing is that the number represents a reading from the water motor speed. We'll call this number Y.
2. Now bring the water up until the point where you are just about to start losing density. That is, up to it's maximum. That's right, the top of the window. Again, take a measurement. We'll call it X.
3. Do the math. Take X-Y and divide it by X+Y. This will give you a fraction. Multiply it by 100 and you have your number. Make a record of it and use it to compare.
Thought there have been many articles that speak about what makes an ink water balance stable, as of yet, I still have not seen anything more practical to use in the pressroom from GATF or anyone else, so if you are looking for something simple and easy to compare, this formula may work for you. If you have better ideas, leave your comment below.
Hi Bill,
ReplyDeleteOne of my favourite topics is density control and ink water balance. I am an engineer and view it a bit differently. I will comment on what I know.
Density variation related to ink and water balancing is actually a simple problem to understand and to correct in offset presses. This view is not accepted by press operators and even the industry in general but it is and will be shown to be true.
The problem with density control on even modern offset presses is due to the inconsistent ink transfer at the ductor. This inconsistent ink transfer condition is aggravated by changes in water, temperature, press speed and other variables. Ink keys do not set the ink feed rate into the press because of this inconsistent ink transfer feed rate condition.
That is the simple explanation. The simple solution is to have an ink feed that feeds ink in a positive way, directly into the roller train, that is independent of those other variables.
This can be done with any positive displacement ink pumping device that is properly configured. I have a patented, simple and low cost concept that basically transforms a normal open ink fountain into a constant displacement pump for each ink key.
This concept has been tested on three different presses. The first prototype was tested almost twenty years ago on a 40" web press running EB inks. The second prototype was tested on a small multi sheetfed press with conventional inks.
The third prototype was tested at Drent Goebel in Holland on their test press and it stayed on that press for four years. The initial tests there were done with UV inks and printed on coated, uncoated and plastic coated substrate.
In all tests, the density window was very large. Basically the density was consistent and independent of changes in water setting and press speed. In all tests, the operators could not wash out the print even when greatly increasing the water feed and having soaking wet plates. Although, printing on plastic did result in poor quality print but not a loss in printed ink.
My point here is that ink water balance is basically a press design issue and is ultimately corrected by correcting the ink feed method, which can potentially be done on any offset press. This should be good news to printers but for some reason they have not been happy to hear this.
Hi i was checking this formula and my max is 35 but my min is 30 so the right figure should be more than 30. But base on calc is not... how to explaine this
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