Hi all...
I have been working on a Heidelberg SM-72V cpc machine...I continue facing problem of % dot screen not transferred to substrate ...specially for dot % between 25% to 80%..on printing the dots illustration become solid.
what will be the possible reasons, is it happen due to excess dot gain only..???
What is the reason for the same from machine end...???
Please help...!!!!!
Thanks in advance for your support.
don't really understand your problem are you saying that the screens from 25% to 80% are printing as a solid?.
A 25% dot printing solid would be indicating something disastrous or catastrophic had happened on press.
There is no way a press, even a HD Speedmaster 72 could print a 25% dot as a solid caused by machine induced Dot Gain. On a well set press in the 25% area I would be expecting quite a lot less than 1% mechanical gain.
So what else is going on.
Check the machine out check all of the settings packing and so on.
Check the blankets are they installed properly ( I have seen them installed sideways on to the cylinder axis) are they packed properly and so on. Eliminate the press if you can
How old are the inking rollers? Do you use proper wash up techniques and good quality washes? When was the last time they were deglazed?
Is this problem just happening on one press or all of them.
What is the mixture of the dampening fluid like? Do you use alcohol as a wetting agent or are you running alcohol free? Is the tank working properly?
I once saw a situation where an operator was using a tank with an old type Alcohol system. Not being allowed to use alcohol in there location they had just stuck the pick up tube, that had once been used for alcohol, into the container of alcohol substitute. The system being unable to measure any specific gravity of the solution just sucked the entire contents of the container into the water tank. The results were amazing and it took a whole day and several hundred gallons of water to flush the mess out.
Check the press over, check your inks ( are they suitable for lithography even) check the dampening system. Check the inking rollers, they should be dull looking and not shiny at all. When it's all done you might want to call the local Heidelberg Agency and schedule a visit from one of their technicians.
Look for the simplest things first. It is often something simple that fixes what at first appeared to be a huge problem.
