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.
Slitters: Increasing speed: myth; Chapter 36
Estimating production runs based on actual field tests versus pie-in-sky dreams:
In the last two posts we addressed the actual "run times" of a duplex slitter rewinder. The start-stop cycle time issues were calculated. In this post we will continue to explore these points in more detail.
This is the biggest mistake made by converting plants when bidding or estimating run times on any given converting job. A simple calculation mistake can lead to thousands of dollars in losses. This can also lead to future loss of business.
A client who was charged a dollar a roll for the last job is going to be extremely upset when you discover your mistake and now quote 2 dollars a roll for the same job. Had you done your homework the first time around, this mistake wouldn't have occured.
Knowing your production speeds, down to number of rolls produced per hour, on a given slitter rewinder is critical. We shall now continue with our time study.
Ramp speed:
How does one determine the best operating speed for any given grade of paper, film or foil?
This depends on several factors:
1) Lineral footage that has to be wound on the finished roll.
2) Properties of the material that is to be wound.
3) Grade of paper or film.
4) The thickness of the stock in question
5) Parent roll size and weight.
6) Other unique conditions.
These are not the only conditions, but this gives you an idea of what is involved.
Each grade of paper ( or plastic) has its' own unique properties. All these properties come into play during the rewinding cycle. The only way to determine the exact run times is an actual trial run. Ofcourse, if the plant has run a certain grade of paper in the past this becomes a moot point.
If you have never run a certain grade of paper before, don't assume that you can have the same production results.
The weight of the parent rolls will be different. The slitting knives will have to be readjusted for this new grade of paper. Core sizes may be different than what you are normally accustomed to. The job may call for a different rewind core diameter. You may not even have these different sized shafts in your plant.
The parent rolls may be seconds. They may be wound too tight or too loose. Crushed cores and other defects in the parent rolls may bring the plant to a complete stop. The job you thought was going to take 2 hours might end up being a 2 day nightmare.
If you, as the owner or the plant manager ignore all these points and go ahead and quote a price, you have to live with the results.
Standard operating procedures:
Every job that comes in has to have a master work sheet. This master work sheet doesn't have to look like the IRS tax return form. But try to address all the points listed above and then some. The form should be signed off by the estimator, the receiving manager and the machine operator before the quote is sent out to the customer.
This is Dr. Winder saying bye bye......Live long and prosper.
Slitters: Increased speed: Myth. Chapter 35
Increasing the slitter rewinder's speed:
...We will continue our discussion in this post. Plant managers and converting plant owners make the common mistake of equating speed with increased production. In the last example we had a roll with 500 lineal feet of paper. If your slitter rewinder has a top speed of 500 feet a minute, that doesn't mean you can wind this roll in one minute.
Imagine yourself sitting in a sports car with a top speed of 200 m.p.h. You are at a stop light waiting for the light to turn green. The next stop light is 500 feet away.
The sensible thing to do would be to start out real slow and then speed up. Once you are at a safe distance from the next stop light you start slowing down and then come to a full stop at the stop light.
Slitter rewinders have to be operated in the same way. The machine starts out real slow, picks up speed and then about a 100 feet from the end it ( the winder) starts to slow down. It comes to a dead stop at precicely 500 feet, because that is what the customer wants...a roll with 500 feet of paper on it.
In technical terms here is how it goes..... Machine has a "soft start" function built into the motor controls. The soft start assures that the machine cycle starts out smoothly without any sudden jerks. Any sudden jerking might break the web or introduce wrinkles or soft spots in the web. In addition this allows the operator to make sure that everthing is starting out as planned. In case of a problem, the machine can be shut down without too much waste.
Once the machine starts in the soft start mode, it takes a couple of seconds and then goes into the "acceleration" mode. Speed starts to pick up and then reaches the "ramp speed". Ramp speed is the optimum speed at which the winder can run, based on the stock being run and the actual lineal footage in question. Please note, "ramp speed" is not the "top speed". Ramp speed is simply the best speed for the job at hand.
Once the ramp speed is achieved, the "deacceleration mode" kicks in. This is the point at which the motor starts to slow down, smoothly. Just like the car driver starts to "slow down" before the next stop light. This slowing down is the "deacceleration mode". A good driver will do this without any jerking or "hitches". Controlled deacceleration plays a vital role in the quality of the finished product.
Let us look at this in slow motion.
1) Machine starts out real slow ( soft start). Paper starts to wind around the core. This cycle takes about 5-8 seconds. This can always vary depending on operator expertise.
2) Machine starts to accelerate slowly and then reaches ramp speed. The acceleration cycle may take another 3-8 seconds.
3) Machine reaches ramp speed. It continues to run at this speed till the signal to slow down is given.
4) Machine goes into the deacceleration mode. This takes about 5-10 seconds, depending on the ramp speed.
5)Machine comes to a full stop. The brake module had been activated at the deacceleration mode and now it applies the final brake.
We will examine each aspect of this cycle as a function of time and actual lineal footage wound.
This is Dr. Winder saying bye bye. Live long and prosper.
Winders, Increased speed: Myth: Chapter 34
Does increasing speed on a slitter winder translate into increased production?
Answer: Depends on the application and the product in question.
Billions of dollars are spent by the aeronautical industry on R&D, to increase the speed of its jets. As we approach the speed of sound, a different set of problems arise.
The same is true for the automobile industry. Billions are spent on car design and fuel efficiency. There are sports car on the road that boast 1,000 H.P engines and top speeds in excess of 200 m.p.h. If the legal speed limit on our highways is 55 to 65 m.p.h. all this extra horse power is a total waste. Yet people who have the means still buy these sports car.
Slitter rewinders are not in the same league as jets or cars. Yet increasing speed has become the holy grail of paper mills and converting plants. Let us look at this in some detail, with actual examples.
Counter rolls:
In the last post, I showed how the plant increased production by about 20% without retrofitting or touching the actual slitter rewinder. We will stick with counter rolls in this example.
We take a 12 inch wide counter roll, wound on an inch and half core, with 500 lineal feet per roll. On a 65 inch wide slitter rewinder you can get a maximum of 5 rolls per cycle (5 x 12= 60 inches). The top speed of this winder was about 250 feet per minute. To make calculations easy, it would take about 2 minutes per cycle to wind a 500 foot roll. Wrong!
Imagine that you are in your car waiting for the stop light to turn green. The distance to the next stop light is 500 feet. Assume there is no speed limit. But here is the catch. You must come to a full stop, without crossing the line at the next stop light.
If you start out by burning rubber and hit the pedal to the metal, you will need extra heavy duty brakes and a parachute to come to a full stop. This will be a short, violent
and brutal drive. The strain on the engine, burning tires and other stresses will take a heavy toll on the car.
In a slitting rewinding operation you can't start out like a bat out of hell. The web will break. Before the cycle begins, the web has to be threaded and wound on the core.
The operator has to check to make sure that everything is in perfect alignment. There are no wrinkles: the web path is true: The core is in perfect position: etc. This takes the operator anywhere from 10 -15 seconds or more. The operator also has to load the cores on the rewind shaft and set the shaft in position. This takes another 30-60 seconds. In this example we are using only one operator.
Once the cores are loaded and all inspection checks have been made, the process begins. If we add all the time so far, we have spent anywhere from a minute to two minutes and we haven't even started yet!!!
Soft Start:
The machine has to start out real slow. This slow start allows the operator time to see if everything is going as planned. In addition it allows the web to start in motion and overcome any inertia problems. If something goes wrong at this stage, the operator hits the stop button. This saves a lot of material from being wasted, if the cycle has to be restarted from scratch. Had you started full blast, you would have wasted several hundred feet of paper. The less waste you have the more profitable it is. Obvious.
The old time winders did not have this automatic slow start feature. Several different schemes were used for this "soft start" procedure. This was an art and it took the operators months of trial and error to learn. I am sure you can see the amount of waste during this training period not to mention the drop in production.
Learning this "soft start trick" actually took a lot longer than a few months. Each grade of paper had it's own unique properties. Hence, what worked on one grade of paper did not work on a different grade of paper.
So far we have seen that about 2 minutes have gone by and we haven't even started the operation. We shall continue to explore this in our next post.
Till then, live long and prosper.
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
The case of the pesky paint sticks: Chapter 32
Increasing Production. Simple Retrofits:
We have been talking about the survival of the converting industry in to-day's climate.
We have also established that we (American manufacturers) can not compete with the Third World countries based on wage rates, taxation structures and all the other handicaps.
That leaves us with only one option and that is to be more productive. We have to produce more per hour to reduce our manufacturing costs.
Let's be realistic:
I could start doing some arcane mathematical calculations to prove certain assumptions. However, we want to keep this as simple as we can. Let's say that a simple 'paint stick'
costs one cent a piece. These paint sticks are made in China or India. We ignore all transportation and shipping costs. The fact remains that these paint sticks cost a cent a piece in the USA. Most times , when you buy a can of paint you can pick up a few of these paint sticks for free. These paint sticks have a nice logo or the paint manufacturers name or the hardware store's name imprinted on them. This logo can be one color or two color or three colors.
There are certain standards that these paint sticks have to meet. They have to be nice and smooth with no sharp edges. Secondly, they have to have some structural integerity.
You can use only certain kind of woods to make these paint sticks. This in a nutshell shall serve as our first example.
Obviously, if these paint sticks are selling for a cent a piece, the manufacturing cost is even lowerer. Let's say that if you bought these paint sticks directly from China your net cost would be half a cent per piece.
You are an American manufacturer. One of the products that you make is paint sticks. Suddenly you notice that your buyers are not buying this product. It doesn't take you too long to find out why. You were selling these paint sticks for 5 cents a piece and barely making any profit on them. So you call an emergency staff meeting to discuss this disaster. After hashing this over for a week or two you still have no idea about what to do.
It is at this point that you realise that you need outside help. Dr. Winder is called in....
The Doctor is in:
When I showed up at the plant and sat down with the management team, I was presented with all kinds of pie charts, production figures, manufacturing methods....you get the picture....
After looking at these charts etc. I asked "what is the cost of your raw wood"? No-one at the plant had figured this out. Calculators came out and in a very short period it was determined that the cost of the raw material was almost 2 cents per piece!! Just to convert the raw logs into paint sticks cost 2 cents a piece. I looked at the boss man and told him he could not compete with China or India. That was it. I was done.
All cost figures etc given in the above example are all made up to illustrate a point. I don't look forward to some bean counter sending me e-mails to point this out.
We shall continue.....in future posts. Till then, live long and prosper.
Slitter rewinder : Chapter 31
How to increase production:
The utter lack of vision at some converting plants never ceases to amaze me. Wrong machines are used. The job could be run much easier and faster only if the right machine was used. When probed for answers as to why a certain job is being run on a particular machine, all kinds of nin-compoopish answers are given.
Rule number one:
Use the right piece of equipment for the job. You can limp along using the wrong machine for a while. Sooner or later, you are going to lose this segment of the business to someone else. Most of the time this blunder is made by the owner, however , there are times when this decision is made by the plant manager. No-one likes to be told that they are making a big mistake. The pesky "ego" factor comes into play.
Rule number two:
Don't be shy about getting an outside opinion.
If you do decide to call in an outside specialist, don't tie up his hands. Give him full rein to find all areas of weakness. Let him know that there are no sacred cows. If he sees a problem with management, so be it. Spare no-one. Allow the specialist to do his job unhindered.
Why call in outside help if you know all the answers? Don't wait until it is too late.
We shall continue with this in future posts. Till then live long and prosper.
