Unwind Stand, Increase your production speed: Chapter 33
Analysing slitter rewinders piece by piece:I was called into a plant that was making counter rolls on one of their rewinders. These rolls varied in width from 6 inch wide to 18 inches wide. All finished rolls had about 600 lineal feet of paper. Each roll was rewound on an inch and half core. The machine in question was a 65 inch wide Cameron duplex slitter rewinder from the early fifties.
The plant manager was utterly frustrated with the number of rolls that were being produced per shift. My mission was to recommed any design changes that would increase production.
Conditions:
I had to work with what they had. They had no desire to buy a different machine. They loved this old clunker. I was quite amused by this, but I went along with what the boss-man wanted. The boss-man had rather modest goals. A 10% increase in production would be enough to make him happy.
Dr. Winder analyses this problem:
First of all, this was the wrong machine for the job. Secondly, this was an old clunker that had a top speed of about 300 feet a minute. Any faster and the machine may fall apart due to the vibrations. Third, they had very limited resources and didn't want to spend too much money. Keeping the above points in mind, I went to work.
The parent rolls coming into the plant were seconds. These were rolls that had been rejected by the mill for one reason or another. The plant could buy these rolls at scrap prices. However, the finished rolls fetched top dollar. The profit margin on these rolls was extremely high.
Rejected rolls from a mill are rejected for good reason. The rolls are either wound too tight or too loose. The cores may have gotten crushed or the roll was dropped and damaged. Water damage etc, there are quite a few reasons why these rolls are rejected. The point is that this is all good material. There is nothing wrong with the paper.
These rejected rolls weighed anywhere from 2,000 to 4,000 pounds each. The forklift operator would pick up a roll using a roll clamp and "steer" this into the unwind stand. This was pretty hairy . One wrong move and the forklift could easily do some serious damage to the winder. Roll-changes took about 20- 30 minutes from start to finish. This was not counting the crushed core repair or the "wet and damaged material" waste cycle removal times.
A simple overhead crane system was installed that took care of loading the rolls on to the unwind stand. This was easier, safer and much quicker than loading by forklift. Time to load the new roll was cut down to about 8 minutes versus 20 to 30 minutes using the forklift method. This simple retrofit boosted production by about 25%. The plant manager was beaming from ear to ear.
Production of these rolls could be increased 20 fold if they used the right equipment to begin with. Notice....no changes were made to the unwind stand or the winder.
Live long and prosper....till the next post
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