PAPER INDUSTRY WEB (PIW)

INERTIA


In the scheme of things, the winder is a VERY small part of the overall picture. In a greenfield mill, the winder probably represents about one half of one percent of the total project investment but has a VERY dramatic effect on the finished product out the door.

Paper Machine

DYNAMICS have a great impact in the winder operation and how it effects the winder's ability to keep production parity with paper machine production. 


Regardless if the the winder follows a newsprint machine operating at 4000 FPM or a 69# linerboard machine operating at 1750 FPM, the job is nearly impossible in a 24 hour-7 day a week duty cycle. The winder duty is difficult on either end of the production spectrum-light or heavy weights.

69# LINERBOARD/1750 FPM MACHINE SPEED

 

This chart shows a production analysis of a 69# linerboard machine operating at 1750 FPM making a 4 set, 50" diameter jumbo. Under these operating conditions the machine will produce 1883 tons of board in 24 hours, making 291 sets off the winder. Not an easy operating condition for a single two drum winder.

30# NEWSPRINT/4000 FPM PAPER MACHINE SPEED

Looking at the same kind of analysis for a newsprint machine operating at 4000 FPM, producing 30#/3000 sq. ft. news, making 42" diameter 5 set jumbo, using a 30" diameter reel spool with a single two drum winder. 

THE JUMBO-IS IT BIGGER THAN LIFE?

The jumbo being produced on our newsprint machine is HUGH. There is no other way to describe it! Just resting on the floor, Magic Johnson could barely reach the top of the reel. (Let him try to make a jump shot with this one!) If you parked your Cadillac Coupe de Ville along side the jumbo, it would still take another one to span the length of the jumbo and spool. (you could buy a Coupe de Ville with a couple of these babies).

 

Now to really appreciate what we're up against! The combined weight of the paper and reel spool that supports the jumbo is equivalent to about 21 Chevy Blazer utility cars. Just think of the inertia when this mass is rotating at high speed in the winder unwind stand: Or think about the horse power it takes to start and stop this mass. The regenerative motor and braking system at the back of the unwind in some cases appears to be almost as large as the jumbo itself. (and Don -"Big Daddy" Garalitus doesn't get off the line much faster).

CONVERTING THE JUMBOS AT THE WINDER

Our newsprint winder, in a normal day will process over 29 of these big monsters-an average of one every 49 minutes. That includes the bad reels (contrary to what the papermakers may say), winder breaks, drum splices, cores that don't match and the need for , unscheduled maintenance. For openers-this is the scenario if things are going smoothly. 
The business of the winder (beside having to produce high quality shipping rolls) is to cut down that enormous jumbo into package sizes convenient to ship and as specified by the printer. This can be anything from a range of 36" to 50" diameter, at varying widths. The more sets we can wind off a jumbo, the better the efficiency of the winder. A practical jumbo size when winding 42" shipping rolls is a 5 set reel about 8 feet in diameter. 
After all's said and done, our winder will produce a LOT of shipping rolls in 24 hours. Each of the jumbos will be converted to 5 sets of rolls off the winder, each set slit into six individual rolls weighing about a ton each. We will send 876 rolls to the roll wrapper and the shipping and receiving department. Not a bad days work.

PAPER MACHINE Vs. WINDER DUTY CYCLE

PM/Winder Duty Cycle Comparison

The paper machine operates at a constant speed 24 hours a day unless there is a sheet break. Comparing the paper machine duty cycle chart in the graphic above, to the batch operation of the winder in the graphic below, the differences in duty cycles are apparent.

 

Here's why! This chart shows a typical winder cycle for each of the 29.2 jumbos coming to the winder. It takes 4 minutes to load and thread the winder, 7 minutes to wind each set, and 45 seconds to make a set change. The time for splicing and slitter resetting is averaged in the times. This chart shows that at 7000 FPM, (the speed the winder must average to stay up with the machine at 4000 FPM), there will be 4 minutes between reels providing there are no unexpected events like serious unplanned maintenance, running out of cores, paper machine breaks, etc. It's obvious the crew has to maintain a steady rhythm to keep up.

THE MAGICIAN DOES HIS ROPE TRICKS

To get a better understanding of the balanced operation required of the winder, think back to the day you tried to tow a car down the street. How many times did you drive over a slack tow rope or snap it off? Unless the tow car and car being towed kept careful good control it was-to say the very least-a rough ride. This is exactly the same condition at the winder operation-visualize the winder towing the jumbo.

We're trying to pull paper off a 29 ton jumbo with a very thin, fragile tow rope (a .003" inch thick sheet of paper) and do it at speeds to 80 MPH. Our unwind has a regenerative brake motor or combination motor and mechanical brake that accelerates the jumbo until it arrives at speed. If the jumbo tends to over-speed due to rotational inertia, the control system makes adjustments. The tension of the rope is constantly monitored by a control system.

Again to emphasize what is demanded of the winder, try this one. Get your neighborhood tow service to make a tow of 3 buses (hitch load 35 tons) with a 450# test tow line from 0 to 80 MPH in 1.5 minutes. Don't be surprised if he can't do it, (or what his tow charge for the road call might be).

TRUCKIN' ON DOWN

USA MapOne of the best comparisons of the duty cycle of a winder is that of a tractor trailer. We all, at one time or another, have been passed by a large tractor trailer barreling down the Interstate. Think of the abuse that truck takes, traveling the highways, day and night. If you think that's bad-consider this scenario.

Just imagine you are a tractor trailer driver and have to do the same duty cycle as our newsprint winder. You load up a set of rolls in a mill in New England  in 45 seconds. Immediately take off and accelerate the tractor to 80 MPH in 1.5 minutes. Drive at a constant 80 MPH speed for 4 minutes. Slam on the brakes to decelerate to a full stop in 1.3 minutes. Now jump off the cab, unload the set of rolls and load on another set in 45 seconds and away you go again. Further, do this with out damage to the cargo and in a safe manner so no one is injured. Do this 146 times and you'll find yourself in Brunswick, GA, 24 hours and 1,360 miles later. During this 24 hour trip you are only allowed a total of 2 hours for fuel and service, stop for meals or make emergency repairs.

When you arrive at Brunswick, GA, you better have your relief driver and helper ready because you're not staying! You have to turn around and head right back to Maine. The paper machine doesn't stop kicking out rolls and the southbound truck is just leaving, headed our way. Now that's what you call tough duty! (and all the time you are doing this, you better keep an eye peeled for bears taking pictures) 

The Bottom Line

It is obvious after reviewing the paper machine and winder processes illustrated, that a single two drum winder can be hard pressed to stay up with machine production. The productivity in this article is based on normal operating conditions. It does not take much to go wrong to get the winder behind. There are instances when making newsprint, 2 two drum winders are required. When considering machines producing LWC (light weight coated) grades, normal operation is to use 2 duplex winders.

Luigi Bagnato-Paper Industry Web