Increasing winder speed; Facts versus fiction: Ch. 37
Calculating actual run time cycles:Before you bid on a job, it is best to determine if your plant has the right equipment to do the job. For example, if the counter roll customer specifies half inch cores on the finished rolls, you cannot run this job on your Cameron duplex slitter rewinder. it will not work.
To run small core diameter rolls you need a machine designed for the job. We will cover small core production in some future posts. For now we will continue with our counter roll project.
How to determine ramp speed:
Ramp speed is computed by the operator based on actual trial runs. It is almost impossible to hit this number right on the head based on paper calculations. Let us not split hairs. One can figure things out without an actual trial run by estimating line speeds. The accuracy of these calculations will be directly proportional to the operator's experience.
Golden rule of estimating:
If you have to bid on a job, it is best to be on the cautious side. I always advise my clients to bid a job based on your slowest ramp speed. If you have run this stock in the past then you have precise figures to work with. Any new material that you have not run before , must be carefully evaluated.
Load times:
Determine the number of cycles for loading the unwind stand. If each parent roll of paper is 50,000 feet, at 500 feet per finished roll, you will have to change this roll every 100 cycles. This is just to give you an idea. Ofcourse the footage will vary depending on the job.
In actual practice, here is what you can expect. Once the parent roll is loaded on the unwind stand, the operator threads the paper through the winder. He cuts off several hundred feet of this paper in setting the machine. Setting tension control, setting the slitting knives, adjusting the web etc.
Towards the end of the cycle, the operator will stop the machine before the roll has run out of paper. These "stub" rolls can be salvaged, but that is another subject. In other words, you cannot calculate 100 cycles for this project. 98 or in the best case situation 99 cycles is what you can expect.
If you do not allow for this "waste" factor, you are building an error in your bid that will hurt the bottom line.
Secondly, the time it takes to load the parent roll on to the unwind stand has to kept in mind. The length of time it takes to pick up a parent roll, bring it to the winder, load the unwind shaft, position the roll onto the stand, "square" the roll and finally thread the web has to be calculated. In addition the setting of the slitting knives, setting the tension control, the brake tension and the nip roll pressure also has to be taken into account.
Don't forget the time it takes the operator to load the rewind shafts with the cores and pick up these rewind shafts and lock them on the rewind arms. It may surprise you to know that this loading and unloading can take more time than the actual rewinding cycle!
This is Dr. Winder saying bye bye for now....Live long and prosper.
