I am reposting this from a thread a couple of months ago...
I agree with Blueslal, if you do not pre wet the cloths in the morning your first plates will typically scratch. The money you think you are saving by not buying wash up clothes is probably being wasted in the time you are paying your press operator to wash them by hand. If you are not worried about time and your labor costs are low, then maybe it is less expensive than buying the cloths.
In my experience the plate that scratched the most was the 1st unit. This is because the paper dust and powder settles in the guard. When the guard is slammed shut or dropped it makes the dust fall onto the washup cloth and scratch the plate. Make sure to keep the inside of the 1st units guards clean.
I wrote this back in 2003 concerning scratches:
There are many things that can cause plate scratches, the most common being dirt. First, lets explain the mechanical items that could cause a scratch.
On the classic machines the vacuum unit in the first unit which is responsible for removing excess silicone is a culprit. This unit is difficult to remove at best, as a result it gets dinged up due to the fact it is made of aluminum. This unit will scratch the plate during the loading process if there are burrs or dried ink on it. When the plate loads it must release first, when this happens the plate material actually comes off of the plate cylinder 2 or 3 mm very briefly. At this moment it touches the vacuum unit and scratches the tail end 4 inches of the plate. This is an easy one to identify for 3 reasons:
1. The scratches are about 4 inches long on the tail.
2. They are always on the first unit.
3. They are always in the same place.
This problem does not happen on the Plus or the Pro machine as the vacuum units were redesigned, for easier removal and to move closer to the plate mechanically during the cleaning process.
The next mechanical issue is the plate wash cloths themselves. The early material Heidelberg originally used had short grain, it ran from side to side. Because of this it would stretch during the clean up process causing wrinkles in it. This wrinkles would come up high enough to drag on the plate while the press was running. This would scratch the plate during the press run. Also this plate wash cloth was notorious for having fibers come loose and drag on the plate causing the same problem. Once again this problem is easy to identify. Any time you have a plate scratch that is not apparent during make-ready and appears during the run it is due to something dragging on the plate. The location of the scratch will be random. We have not used this style of cloth since 1997, although it is still available through aftermarket companies and is used by quite a few QMDI shops. They may be a bit less expensive than the ones we sell, but that savings is offset by the plate re-burns they are responsible for. The way to tell the difference between the aftermarket ones and ours is that ours have dimples in them to reduce loose fibers and the grain runs long to stop stretching.
If the air pressure is too high for the plate cleaning pistons (these actually press the plate wash cloth against the plate). You will get scratches consistently on all units in random places. The adjustment for this next to the console by the delivery on the operator side (You will have to move the console). It should be set between 3 and 4.5 bars.
If the plate scratches look like Morse code (Dots and dashes) , you more than like have a problem with the black rubber covered shaft not spinning freely on the plate gap guard.
The last mechanical issue is the foam rubber strip on the plate wash mechanism itself. This strip gets damaged due to the pressman trying to save a buck. The plate wash material will run out, instead of changing it right away the pressman will reset the count knowing that there are about 4 more cleanings left. He forgets he did this and runs the unit free of cloth. Now instead of the cloth hitting the, plate the foam hits it and gets ripped off of the device. (I have seen the tail end of the cloth wrap around a plate cylinder by a pressman doing this and pull the whole mechanism out of the brackets. 25K repair tag on this mistake, all in the name of saving 2 dollars and some change.) When the press operator orders the new foam to install he needs to glue it to the bar. We recommend using Loctite 406 for this, as it is a type of superglue which dries sort of rubbery. Typically the operator uses superglue instead, some of it gets on the outside of the foam and hardens. This hardened glue now scratches the plate during wash up. These scratches are identified as being in the same place, going from gripper to tail and noticeable at make-ready. Usually they are very dark.
The main reason for plate scratches is the this… Dirt. All it takes is a piece of dried ink, powder, or dust to scratch a plate. The first unit is where 90% of the scratches happen. This is because there is typically powder and paper dust everywhere as the feeder is rarely ever vacuumed or cleaned on any regular basis. Take a look at the guard on this unit, when you open it you will see powder on it. If you accidentally drop the guard, all of that powder and dust comes free and settles on the plate wash cloth which is exposed. (The other cleaning units are in the press under the cylinders so they do not collect the amount of dust the first unit does.) This causes random light scratches at startup. If you keep the guard and feeder area clean it will reduce scratches dramatically.
Another thing most people notice, is that after the press sits for the weekend and the first job is burned on Monday, plate scratches are apparent on the first unit. This is because dust settled on the cloth over the weekend and the lines which supply the wash-up solution are dry. I recommend to prime the lines in special function 12 on each unit a couple of times and to advance the plate cloths by manually starting the plate cleaning mode and hitting the stop button as soon as it starts. You will hear the clothes advance three times after you hit the stop button. By doing this you will have a new cloth ready to go and solution in the lines.
I have been working on this machine since 1996. I have done countless shows with new and used machines, not too mention how many I have worked on in the field. Plate scratches are rarely an issue, if I had to place a number on them I would say 1 in every 20 plates will get scratched, as we cannot control every piece of dirt there is in a print shop. I have used the plate washers in every situation. The only time I suggest to turn them off is to hand wipe a large solid, then I start the wash up program to finish up (this prevents silicone from getting in the rollers causing hickeys.). I never use them to clean hickeys from the plate during a run, more than likely whatever is on the plate causing the hickey is something that will scratch the plate if you use the hickey cleaning mode (I affectionately call this the " Plate scratcher mode".). Just wipe it off by hand, it only takes a minute which is much less than having to re-burn a plate.
Hopefully this long winded explanation will help you get a handle on your scratches.
Paul Cavanaugh
DI Technical Support
