Intermittant duct control - good or bad idea???

[Disappointed]

Hi all,

On all of our previous machines the ink vibrator roller contacted the duct roller once for every sheet on a fixed cycle, nice and simple and has work for countless years.

We now have a Presstek 52DI which has the default option of intermittant ink vibrator control based on a set of figures that can be adjusted. It is broken into three bands of ink coverage - 0-20% will get 4 out of 10 contacts, 21-50% will get 7 out of 10 and 51-100% will get 10 out of 10 as in the older machines.

What i am tryng to find out is if this is a sound idea or not. What we are seeing is that because the roller on ly contacts maybe 4 out of every 10 sheets, any duct key adjustment takes a long while to have effect on the sheet. Is anyone familiar with this or could it be better to just switch it off and go for 10/10 as in older machines?

Does an SM52 have this feature or is it a Ryobi quirk?

Dave

 

[Cornishpastythighs]

This feature is also on our new Komori press. In another life I had these retrofitted onto 3 older Komoris. On very low coverage jobs it allows the operator to have his ink keys open a bit more and ink duct a little less instead of trying to grind metal on metal (figuratively speaking). When you get the hang of them they work fine, if they serve no purpose to you then hit the off button.

 

[Deleted member 16349]

This feature is also on our new Komori press. In another life I had these retrofitted onto 3 older Komoris. On very low coverage jobs it allows the operator to have his ink keys open a bit more and ink duct a little less instead of trying to grind metal on metal (figuratively speaking). When you get the hang of them they work fine, if they serve no purpose to you then hit the off button.

Yes, the advantage is with very low coverage but this again is a solution that is only half way effective. If one has a job that has both high coverage in one location and low coverage in other areas on the same plate, this method is not effective.

My view is that the press should be designed so that it will provide accurate ink feed for all conditions. This can be done with different and better technical approaches.

 

[Ironside]

You have to adjust the speed of the ink fountain roller.

You have to adjust the speed of the ink fountain roller.

We run a Ryobi GX and for low ink coverage this is a great solution. The key to understanding how to use it effectively is to understand how the ink moves down the ink train. Theoretically, on a specific stock the thickness of the ink film should be exactly the same no matter what the coverage is, the difference is how fast the ink moves from the fountain to the plate. The advantage of the intermediate ink ducting is an operator is able to run the speed of the ink fountain roller much faster which will facilitate a larger swath of ink being introduced into the ink train, not more, but spread thinner and thus faster to distribute down the distributor rollers to the plate.

This is the advantage, by running the speed of the ball faster if you want to increase or decrease the overall amount of ink being fed into to ink train you have a more precise incremental steps both ways. For example if you are running your ink fountain roller at 25 (on a scale of 1-100) you can drop that to 24 and you have a 4% reduction in ink flow into the press. On the other hand if you did not have skip ducting you would have to drop the roll of your ink fountain to 5 and this means that if you want to reduce ink using the fountain roller speed you would have to drop it by 20% increments.

In summary, by using the skip ducting function you are able to keep the roll of your ink fountain roller faster to start with giving you smaller incremental moves to achieve optimal ink flow.

hope this helps

 

[Disappointed]

Thanks all,

i think i have it sussed now.

As the press is 90% computerised, even the ink adjustment from a scanned sheet to feedback to the ink ducts, it does have a limitation in that the computer does not compensate for very low coverage jobs, it will always over adjust.

I have found a good reult by not using the auto system on low cover jobs, just use the brain and fingers on the ink keys and leave the intermittant way down on 2 or 3/10. Once you realise that nay adjustment will not be visible for 200 or 300 sheets, it get easy, if you need to get colour up fast then just spin the duct roller as in the old days.

Sometimes computers and A/I really suck

 

[Ironside]

Thats right, the lower ink coverage means the ink is moving down the ink train at a much slower speed thus taking longer for any changes to reach the sheet. There is an adjustment within the computers which will reduce the amount of automatic changes in the key opening, I believe it is called density feedback, however, it will it is only perfect for certain total ink coverages, it will be too small for high coverages and too high for low coverages. So your strategy of manually adjusting keys is good, however, I recommend you first use the roll of the ink fountain roller up and down to adjust gross density to get close then use the keys to fine tune across the sheet.

 

[Disappointed]

Yep, thats what i've been doing. You need to find the balance betweeen duct opening and spin speed. Sometimes the jobs are so tricky even one notch on the duct opening is too much and the difference needs to be made on the speed, its far easier to run solids than low jobs!