Guhan S K - Ink Mileage

Maths and me @ Ink Mileage

Project : Ink mileage calculation (For Newspaper production).
Aim : To create best ink mileage calculation based on image coverage for Newspaper industry.
Time line : 2016-2017
Project detail posted in WAN-IFRA forums Printing>>Ink ; Print-planet forums printplanet.com/threads/

What is Ink mileage?

We can represent ink mileage in pages per kilogram, such as 94,500 pg/kg of ink, in a manner similar to how reel mileage is computed in newspaper printing. This means that printing 94,500 pages requires one kilogram of ink. Here, the result of translating pages to square meters per kilogram is 94500 pages * 0.190008 m² (product size) = 17955 m²/kg of ink. Since 1 kilogram is equivalent to 1000 grams, we can simplify this to 17.955 m²/grams of ink for our convenience. We can easily recall and communicate this little number, which rounds to 18 m²/g. The maximum and minimum tolerance parameters can be readily adjusted with the target, and changes can now be readily noted as 18.00, 17.75, and 17.50 (in m²/g).

For example, the average ink mileage data is => C - 18.02, M - 15.61, Y - 13.12, and K - 7.15 (m²/g).

Why mileage unit is m²/g and not g/m² :

In case of Ink testing sq.meter of paper hold some 'x' quantity gram of ink layer to check ink yield, here paper is in fixed size for calculation. But in newspaper production, ink coverage as said above pages (sq.m) / kg consumption is proper manner to calculate mileage of INK.

Let 94500 pages printed in 1kg or1000g of ink, then

GSM - gram per sq.meter >> 1000g/ (94500 * 0.190008)m² => 0.0556 g/m², - here - 'x' gram of ink per 1 sq.meter of paper
SMG - Sq.meter per gram >>(94500 * 0.190008)m² /1000g => 17.955 m²/g or 18 m²/g - here - 'x' sq.meter of paper per 1 gram of ink.

Square meter of Newsprint in which gram of ink is spread - based on total consumption (pg/kg method), an integer number as square meter per gram (Example; Black ink mileage = 7.15 m²/g as average) then,

Let average pages per day production = 6,05,262 pages

Total m² coverage = 605262 total page printed * 0.190008 product size = 115004.622 m²
Total consumption = 115004.622 m²/ 7.15 (m²/g mileage) => gives consumption 16085 g (16 kg - per day * 31 = 496 ~ 500 kg per month)

SMG - Square meter per gram method is a perfect solution to consider as unit of Ink mileage calculation for Newspaper production. This help us to easily communicate, remember and compare ink mileage.

Factor that influences ink-mileage :

Pigment strength and content of the ink-formulation.
Stock quality that used for printing (Newsprint).
Ink feeding style of the production plant.
Water / ink balance behaviour in production.
Pre-press adjustment or settings like UCR/GCR etc. TIC % standards may reduce or increase the consumption of ink.
Press (machine) condition settings like ink duct roller gap, pressure setting of ink roller train etc.. may affect consumption pattern.

How to get ink consumption?

Machines have automatic ink filling systems now a days, making it challenging to track ink usage in certain situations for a specific production. Let's go into more depth about the alternative methods we need to practice in order to obtain consumed ink before calculating mileage.

My mom says 50 ml of milk is short today, by observing the bottle of milk purchased from the vendor. How this is possible? - By percentage method level of milk daily purchased is compare with the day of shortage; from 1000 ml (1 L) of milk it is possible to find 50 ml shortage that is 5%. Yes we can do so, then apply same concept of percentage method to find ink consumption is also possible.

Ink duct picture shows percentage method to calculate consumed ink. 20 * 70% = 14 so consumption of ink is 20-14 = 6 kg like that we are able to find following duct 20 * 50% = 10 >> 20-10 =10 kg and other one 20 * 15% = 3 >> 20-3 =17 kg .

By using measuring scale or percentage method as discussed above we can calculate ink consumption in tank on daily basis. For example if we have ink tank @ full capacity (on open) is 1500mm (100%) and empty cane is @ 20mm (0%), mark top and bottom end. Now centre mark is >>(1500-20)/2 = 740mm (50%), then rest of readings can be marked in scale and used to calculate remaining ink (balance) in tank.

Can a worksheet will hep to calculate consumption?

Yes, in our style we prepared worksheet to do this calculation for ink mileage;

This image is an excel sheet snap short that hold data of physical picture of opening balance and closing balance of ink with percentage method. The out put we get from here is variant- m² of paper per gram ink covered and we combine average image value per page on that day with this data.

So with help of worksheet we are able to calculate ink mileage in daily basis based on actual consumption. To get consumed ink for example C 17.95 m²/g - then expanding 17.95 * 1000 / 0.190008 = 94470 pages/kg ; divide this by total production pages 43,10,526 / 94470- we get total consumption as 45.62 kg of Cyan ink finally.

In this case fixing tolerance and monitor the deviations is not so difficult -Example 18 ± 1 give deviation to ± 10,000 pages approx. If we feel that more deviations, then we reset the tolerance as ± 0.5 (~ ± 5000 pages) as our customs settings. If my ink mileage for cyan comes between 92105 to 97368 pages - it is safe and we say with in tolerance (18.5 to 17.5 m²/ g).

Can we compare ink mileage?

Yes we can compare easily ink brands or batch by average data collected like below ;

INK A (D** *NK)-> C - 18.2 ; M - 15.6 ; Y- 13.12 and K - 10.5 (m²/g)

INK B (SA**T* *NK)-> C - 19.11 ; M - 11.50 ; Y- 9.44 and K - 7.47 (m²/g)

INK C (HU*** *NK)-> C - 15.5 ; M - 14.50 ; Y- 13.54 and K - 5.11 (m²/g)

Now can we say the difference between these two company's / batch INK - A has more mileage in Magenta, Yellow ,K-Black compared to INK B. Is this correct? - Yes, when calculated as average for more than a month ( mostly 1 quarterly period). Total square meter of paper for 3 months / consumption of ink in grams for 3 months will be near to target.

When INK A & B covers equal % of image in single day production when consolidation, then we say in this case mileage is true. For ink mileage we have to consider the image ratio into account for correct comparison. Some time average (image ratio/month may be approx. equal) data per month in 3 to 6 cycle can be graphed and monitor to get conclusion as said in above example.

Ink key setting;

To calculate volume of ink in each zone is based on key opening, from the image ink layer area is calculated by following formula;

Area = π(h²+2rh),

when we are able to calculate area of each zone with time and speed of machine then, it is possible to derive consumption of ink based on this formula. The thickness of ink layer is said to be ink profile, this is based on image coverage in that particular zone. We can say ink profile is area (A) that cover the image area of plate and reproduce on substrate, if output is heavy or low inking has to be adjusted using key opening that is decided by manual (production staff) or Auto correction (PID).

Here graph show that when ink key opening is more then area (profile) also get increased, but not in linearity manner.

What is Average image value or Average ink coverage (AIC)?

It is a integer value of every column of Image usually calculated by imaging software for individual color, Full image is divided into columns for example I have 700 mm image width, it is divided by 50 mm of each column 700/50 = 14. So I have 14 column as Zone 1-14.

There are number of software companies that provide this image coverage calculation, you can check out free version also available (like APFill, printcal etc..). Image coverage value differ from company to company full solid coverage in a column may be 60 and another may be 80 it depends upon software in-account of TIC (total image coverage).

Four color image CMYK - separated with 14 column and weight of ink / image is summed and average is taken. Let us consider average value for a page as 15 for K (so n = 105 then, n / 7 = 15), sum of all column in every pages and compute average (average image/page), then total image/page >> and divide by number of pages we get average image value per production. With this single integer number start to calculate ink consumption, when average image value / average ink coverage increase ▲there will be drop ▼in ink mileage number of pages per kg or sq.m/g. - More image value - more ink consumption << result >> less mileage

Ink consumption based on AIC - average ink coverage In web-offset Newspaper production;

Set parameters;

Fill total gross pages for an average of 3 months example here (38,400,500 pages)
Actual Ink consumption for an average 3 months (C450, M600, Y600,K950)
and Average image/page for an average of 3 months can fill as shown in the calculator (C50;M55;Y60;K85).

You can change this setting as in your press, Now Click Pre-set button; actual sqm/g according to the month total pages is calculated and parameters were protected.

This condition set the running density reading of a press.

Change the Gross pages for a day or month enter current day image/page and Click Submit button >> you will get the consumption for a day or month

Try your hand for some other values - get ink consumption based on average image/pages. Higher the image part lower the mileage sq.m/g and increase the ink consumption.

Example;

Let gross pages = 899706 (per day);
C50 img.value >> 16.21 sq.m/g ; 10.55 kg
M50 img.value >> 13.38 sq.m/g ; 12.78 kg
Y50 Img.value >> 14.59 sq.m/g ; 11.72 kg
K90 Img.value >>7.25 sqm/g ; 23.57 kg

Here Image/page value is XML data output from INK software.

[Note: To reset the Pre-set value refresh the page and start from first]

Ink consumption based on AIC - calculation worksheet;

In this case, the input values are random integers generated for illustrative purposes in this worksheet. Let 'x' be the integer for the image value or image/page, or pre-set value. As we add more images to the plate, this integer increases, and vice versa, much like in a worksheet. In this case, each row (production) must be processed separately for ink consumption before we can obtain the outcome.

As we know higher image value may run for shorter pages so taking average of image/page is meaningless here for cumulative production calculation.

Above said is a sample program to show the power of mathematical calculation. Provided values are example settings trial basics we have to find the actual consumption and ink factor value, that has to be fed in set-value parameters of this program to calculate such mileage.

INK pre-set value or screw opening calculation;

Image value - number based on image zone coverage generated by ink value software. This can be convert to pre-set ink value (key opening) - ink screw value calculation with single formula in excel - FORECAST, below image is an example for calculation using (x,y) coordination and linear interpolation formula [ (y2-y1)/(x2-x1)*(x-x1) ]. We can generate pre-set (key opening) ink screw value for our press standard as below.

Ink pre-set value is based on curve settings (custom), that we do with trial and error method. If we feel image more dark with pre-set value then, we can control by adjusting the curve value. We tried this concept with Excel worksheet and displayed images here. Based on external ink coverage software and curve settings >> image-ratio vs key opening we can convert values by above said manner.

Google Sites

Report abuse