Doubling on SM72

[aqazi81]

What can be the cause of doubling in lateral direction? It's same amount from lead to tail edge.

 

[Paul Cavanaugh]

Which unit? Is there a perfector. Lateral is from Left to Right (O.S. to D.S.), circumferential is from gripper to tail.

 

[Jruff]

we usually check for loose blanket, stuck grippers, bad blanket release and tight brush wheels at the feeder

 

[aqazi81]

Its a 6 color sm 72 and perfector between 1st and 2nd unit. Doubling is in 3rd and 4th unit and its lateral. Can it be thrust bearings?

 

[Paul Cavanaugh]

If the cylinder is moving due to the thrust bearings you should be able to see doubling by printing on one unit only (3 or 4 if that is the ones that are moving.) Keep in mind a moving cylinder can also produce a slur effect like you would see with a loose blanket. It depends on how aggressively the cylinder is moving.

To determine if it is the gripper bars you will have to print on both units at the same time. Although gripper bars rarely produce lateral doubling.

 

[aqazi81]

Thank you Paul for the input, I'll test print the problematic units and will update. Can I just tighten the threaded rings to overcome the problem?

 

[junker1984]

Not wise to simply tighten, Asif. If image is doubling uniformly across whole sheet, its almost surely thrust assemblies. Suggest you remove cover (or swing open if it's a later model) and check the appearance of of the oil weep channels or the bottom side of the adjusting ring. If you see plenty of dark matter coming from any (sometimes difficult to see anything behind cams on impression cylinder journals), it's absolutely necessary to inspect. If, upon removal, you see the race surface is scraped, replacement is needed. A shortcut by simply tightening a worn thrust could be catastrophic.

 

[aqazi81]

Decided to replace thrust bearings....

 

[exheidmech]

Typically thrust bearings will not produce a double or slur that is straight lateral movement. A thrust bearing will produce more of a diagonal movement due to the helical cut of the drive gears. If it is straight sideways movement likely the issue is coming from the plate cylinder. If it is diagonal movement, than yes thrust bearing. Also important to know if its on the lead or tail of the sheet. This will help you narrow down which cylinder. An improperly adjusted thrust bearing will also double.

 

[aqazi81]

@exheidemech... So you say it can be a plate cylinder movement, should I check for the lateral register mechanism on the plate cylinder or something else?

 

[junker1984]

I'm thinking that if it were the plate cylinder, the shift would be of a clean image only. If appearance of image doubling laterally across the sheet is uniform, at least do a visual check of thrusts. You might even consider using an indicator and pry bar to check cylinder end play.

 

[exheidmech]

It would not be the register system that would produce a double. The plate cylinder drive gear is actually 2 gears. The main drive gear drives the plate cylinder indirectly via a drive pin. Its this drive pin or the bushing in the outer gear that can become worn. This will produce a double image on the sheet that is straight sideways. First confirm it is sideways not diagonal.

 

[aqazi81]

Its sideways 100%...not diagonal.

 

[exheidmech]

Check plate cylinder gear

 

[aqazi81]

OK Thank You.

 

[junker1984]

If the alignment bushing and pin are worn or sticking in the plate cylinder double gear assembly, you'll only see the image wander in a circumferential (up-down) direction, causing you to chase it at CPC. Still sounds like thrust bearings to me.

 

[aqazi81]

I'll check both as soon as machine stops for maintenance work. Thank you all for your inputs.

 

[exheidmech]

Thrust bearings are definitely more common to fail than plate cylinder gears however for it to be a thrust bearing there would have to be a circumferential component to the sideways movement making it look diagonal because of the cut of the gears. If it is a true lateral double the only thing it can be is the plate cylinder gear. Sheets should be checked on all 4 corners to confirm 100% lateral movement without any circumferential movement. Once that is confirmed simply remove the plate cylinder gear and reinstall without the 4 springs. The main drive gear should slide on inner gear smoothly. May be easier to also remove inner gear. If the inner hub is sticky or drive pin is worn or sticky this will most definitely cause a lateral double without any circumferential component to the double. This is not too uncommon on very old machines especially MO because of the grease lubrication. Its also very common on machines that have never had the lubrication zerk lubed on the plate cylinder gears.

 

[Lynden]

need to contact

attention exheidmech, my email is lbalderamos@santiagocastilloltd.com. please contact as I need to establish more assistance. thanks.
sorry but I just cant seem to find out how to PM contacts.