Long/short grain effect on machine built

[gufs_place]

Hi,

two questions that are bugging me
1.) why does the paper cut (short vs. long grain paper) have an effect on weboffset machine built?

On the Goss website for example, the same machine Sunday 4000 has different speeds for long grain (up to 45,000iph) and short grain (up to 60,000 iph)

http://www.gossinternational.com/clientuploads/pdf/Datasheets_English/Sunday_4000_datasheet.pdf

2.) also why is the distinction short vs. long grain only made in commercial but not in newspaper? I gather that in commercial some things are better printed in long grain (posters?), others better in short grain (CD covers).
does it not matter in newspaper what grain direction is being used or is it always a certain grain?

thanks!!!
Guf

 

[jlind]

Guf:
What do you mean by web offset machine built?
Any time you run a roll of paper into a machine, it's grain short, news or commercial. It can only be grain long if it is sheeted. The web cut off could lead to a fold with or against the grain, is that maybe what you mean? If you feed a roll of paper into a sheetfed press, (roll sheeter, Millers, MAN Roland) you print grain short. Seems to me that if it's a multicolor press, the long or short grain arguement doesn't mean as much unless you need the imposition in a certain grain direction for binding or folding.
John Lind
Cranberry Township, PA
724-776-4718

 

[gufs_place]

Hi John,
thanks for the quick response;

my question about offset machine built arose from looking at the data sheet of the Goss Sunday 4000 commercial press, where different specifications for long and short grain are mentioned (please see below for more detail) Given that I was curious how the difference in iph arises and why this distinction is mentioned in the commercial section of their machines but not offered in the newspaper section (where they dont mention grains at all...)

based on your explanation, would that then mean that the machine, (both long or short grain 'option') is still run grain short and then the binding and folding section of the grain long machine is different? (which in turn requires different construction?)

- - -

for example it says they offer "Long and short grain presses from 32 to 80 pages"
Sunday 4000 Long Grain up to 45.000 iph Web widths 980 mm (35.6 inches)
Sunday 4000 Short Grain Up to 60.000 iph Web widths 1260 mm (49.6 inches)
see http://www.gossinternational.com/clientuploads/pdf/Datasheets_English/Sunday_4000_datasheet.pdf

 

[RGPW17100]

most sheet fed presses the grain is parallel to the gripper. This allows the sheet to conform better to the impression and transfer cylinders and is mainly a problem on cover and board stocks. Tail slap and total sheet registration are what we notice when we run short grain on our SM 52

 

[HKafeman]

Guf

John is right that the paper is always run the same way through a web press - with the grain parallel to the direction of movement.

The difference is in the orientation of the printing plates/pages on the press.

For Long Grain the long dimension is around the cylinders and for Short Grain the long dimension is along the cylinders. So Short Grain cylinders are smaller. Short Grain Folders also have to be different to match the change of page orientation by 90 degrees.

Long Grain means with the grain parallel to the longer dimension of the sheet or page.

The maximum surface speed of a press is usually what limits production, so a Short Grain press with smaller cylinders produces more impressions per hour for a given surface speed - hence your observation about Goss 4000 Sunday presses.

Some years ago I worked for Baker Perkins Ltd. here in the UK on Commercial Presses. Short Grain was seen as a strong market trend and the "G44" range of Short/Cross Grain units and Folder was developed (in the late 1980's early 1990's). The benefit was increased productivity from the Printing Presses as above. One downside was that when standing products (magazines or newspapers) upright on a shelf though because Short Grain tends to flop over whereas Long Grain stands up! Another possible downside was the requirement for wider paper reels.

However, the market trend never really took off and not many presses were ordered!

Let me know if I can be of any more assistance.

Regards
Henry Kafeman

 

[jlind]

Henry:
Thanks for a most informative reply. You nailed that one.
John Lind
Cranberry Township, PA
724-776-4718

 

[gufs_place]

Thanks a lot for those thorough explanations!

Henry, does that mean that the matter of short/long grain is not mentioned for Goss newspaper presses (like the colorliner) as these are all printed long grain? (based on the difficulties with paper reels you mention...)

 

[HKafeman]

Guf

Actually, I am not up to date with this subject but that is probably the case.

As I said, I was involved some time ago and in commercial printing. But I suspect because this did not take off in that market, that it did not happen in the newspaper market as well.

Maybe somebody out there is more up to date?

The big move at the moment seems to be to change over to narrower web widths to save paper!

I am pleased that I could be of assistance.

Regards
Henry