The cure to all corrugator diseases


Élixir d'AnversWhen I was young, every time I felt a bit under the weather, my mom gave me “Elixir d’Anvers”. It was the cure to all illnesses. If it was a flu or an indigestion or whatever… “Elexir d’Anvers” took away the pain. I even heard that farmers where giving it to their horses when they had some stomach problems. (image courtesy Wikipedia)

It was nothing more than a herbal short alcoholic drink that was invented by a medical doctor as a simple and effective cure in 80 percent of the cases (and the alcohol in it was an additional advantage).

http://www.elixir-danvers.be/en/150-years-of-tradition

In exactly the simular way that “Elixir d’Anvers” was a cure to all illnesses, a cure to all Illnesses in the corrugating process is ‘less heat and less starch’

Let us some up some corrugating diseases and there cure:

Symptons:

  • Washboarding
  • Slinging (glue splashing)
  • Blisters
  • Honneycomb
  • Brittle bond
  • Steam bubbles opening layers (secret blowing)
  • Post warp
  • Bad slitting/ bad cut off
  • (and others)

Cure:

  • Less starch, less heat

For my job I do a lot of troubleshooting and problem solving and it is amazing how simple my job sometimes is (please do not tell this to my boss).

The very first thing I suggest, when confronted with a problem, is to reduce heat and starch to the minimum required, and in 80 percent of the cases the problem disappears, just like using Elixir d’Anvers.

I make it sound very easy, but to convince someone that is already using 30 years too much heat and too much starch is quite a challenge.

Some time ago I was at a company making heavy combinations for the fruit and vegetable market: the typical BC semi-chemical coated kraftliner and heavy paraffined brown kraft. They were complaining about honeycomb, wash boarding and bad bonding of the coated kraftliner.

Observing the double backer, I noticed that every time a certain combination came up with coated kraftliner, the operator put a 100% wrap around a small preheater just before the hotplates. I asked him: “Why do you put so much heat in this coated kraftliner?”. The answer I got was:  “Because someone told me to do so, and if I do not do it then we have a bad bond.”

I enquired if he understood the physics behind what he was doing, but even when explaining it to him; he didn’t want to change this behavior. It was just an automatism based on the trigger word “CKL” coated kraftliner. This resulted in a not so good looking board, I would even dear to call it plain waste.

I had to be in the same plant the next day. I was a bit devious and closed the valve at the drive side that fed the steam in to this small preheater. After a while it was around 40 degrees Celsius and was only brought to this temperature because of the preheating of the liner in the triple stack big preheaters. Nobody noticed me doing this.

The next day when the same “challenging” combination came up the same operator again put a 100 percent wrap around the small preheater. The board was looking better today then yesterday and the operator called me and explained to me that having that 100 percent wrap around is essential for having nice board. Proudly he showed me the 100 percent wrap around and the board that looked a lot better compared to yesterday.

I listened to his story and nodded from time to time. Then I took out my IR camera and showed him the fact that the small preheater was completely cold ( as I had closed the valve the day before). He panicked first a bit and then he suddenly made the link to the better board and the less heat combination. In the coming runs he even put the wrap around on 10 % since he realized that someone had given him the wrong explanation.

It was probably a lucky shot, thirty years ago, but the quality standards for making board have also changed drastically during that time.

I would like to challenge all of you that are running with a lot of starch and heat to try the following.

Let us say that you are running with the first hotplate on 6 bar (single wall, just to keep it simple).

Reduce it to 3 bar and see what happens. Most probably nothing… Reduce it to 1 bar. Remember that with thick hotplates it takes about 12 to 15 minutes before temperatures go down.

If it changes nothing to the final board, then the question is: “Why are you running with those high temperatures in the first section?”

Give your corrugator some “Elixir d Anvers”, less starch and heat, and you will be amazed how many problems it solves.

Koen

 

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S-warp


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A while ago a customer was constantly facing s-warp on his recent corrugator (2800 mm).

In the picture you see E-flute with s-warp. The s-warp was only noticeable when running E-flute.The s-warp was so extensive that certain jobs were considered as broke. This had for sure a cost.

At the beginning we thought the paper was the cause. After turning around reels end changing positions the s-warp remained in the drive side so it became clear that the problem was caused by the corrugator.

During several weeks we verified a lot on the corrugator.

A first thing we noticed was an accumulation of dirt on the first pressure rollers on the hotplates. This accumulation was especially at the dirve side. These rollers where cleaned but still the s-warp remained.

In the picture below you see the pressure rollers. At the left hand side you see the dirt accumulation, and on the right side you clearly can see the damage on the hotplates by the grinding action of the belt.

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I was convinced that it was a parallelism issue but the question was where did it happen in the corrugator?

So a big job was done by checking everything starting from the single facers up to the belt.

Step by step the glue-machines in the SF where checked and double checked. All the preheaters, and rap arms where double checked. All preheating cylinders wherechecked, as well on parallelism as on heat distribution.

Iodine images and also absolute humidity measurements, where helpful in this process.

Many times we found a difference between operator side and drive side. After readjustment, we still had the same s-warped board. It improved a bit but the problem was still not gone.

Same action was taken on the unwinders by checking the parallelism.

After a visit of the corrugator technicians (supplier), they suspected a different porosity of the upper belt between operator side and drive side.The different porosity could also explain the faster contamination of the first pressure rollers on the belt.

A brand new belt was installed but still the problem remained.

At this time we got a bit desperate because we thought we checked everything.

The hotplate positioning in height however and the belt pressure system was not yet checked….

We asked a belt supplier who uses an acupressure system to check this up. It took a while before we could organize this but at the end we were able to get the technicians to come and perform this mapping.

A pressure sensitive material is put between the cooled down hotplates and the belt, and then step by step the whole hotplate section was checked up.

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We first tried the pressure for EB and that gave a rather equal image. However, when we gave in the E-flute settings and about 50% of pressure, we recognized a big difference between operator side and drive side.

Picture10

We decided to do the measurement based on the E flute settings. We noticed a higher pressure at the operator side compared to the drive side. The pressure was higher on the operator side on both the pressure roler and the shoes throughout the whole hotplate section.

Picture11As the images where rather similar on each row of shoes we did two tests to make sure that the measuring tool was not faulty.

I came up with a very professional test which you can see in the following picture. It is the “ISO Samsung S3 test”.

Picture6On the pressure sensitive material I had put my mobile phone and then a can of 5kg lubricating oil was put on my phone. On the picture at the right you can see the readout on the computer. One can even recognize the rounded corners of my mobile.

As a second test we turned the complete measuring device around to make sure the pressure sensitive sensors weren’t invoking a difference. But the image we got was exactly the same. So it was clear that what we could see on the screen was the reality.

So it was very clear that or the pressure system or the hotplates needed to be re-adjusted.

After that re-adjustment the problem improved drastically. To be a 100% sure one should redo the acupressure measurement.

Picture1

The before and after picture…….

Another solution would have been to install a zonal moisturizing device, but it would be a bit strange to try to correct a problem with an investment

 

 

My corrugating philosophy


I have been doing customer trials in a 1000 places around the world.

After many years I can already tell after 5 seconds of contact with people if they want it to make it happen or not. Are they open for new ways of doing things or not…

Sometimes bosses enforce trials upon their people and they should know this will never work. New stuff brings operators – people – out of their comfort zone, so they are not always enthusiastically waiting for me.

As an example, I was in Russia and I needed to do a trial on the corrugator. They had massive hotplates that take about 20 minutes to cool down. I received a window on the corrugator of 5 minutes, so obviously the test failed.

But when the senior VP of Walmart wakes up one morning with a vision and says ‘I want to reduce packaging consumption with 20%’, then corrugating plants have to follow

In order to meet the new Walmart standards, corrugators will not only need to run their equipment in optimal states, they will need to adopt the state of mind of their operators as well.

One cannot make an omelet without breaking eggs. Change means disruption.

We may understand this, but the challenge is in transmitting this message to the operators who often consider us as the ‘bad guys’. We ask them to run faster, we ask them to run more difficult stuff, we ask them to have less cigarette breaks…

I strongly believe that we need to involve them a 100% in the change process, even the lady cleaning the floors should be involved as she is as important as the guy adapting the software of the million euro equipment. Training is the key; people have to feel confident in what they are doing.

In a well-organized project, there is special attention for change management. I can only plead to carefully plan the change management for your teams running the corrugators.

And when it comes to teams… Is your night shift running the same final quality as your day shift? Do you sometimes hear statements like ‘I hope that this combination is for the other shift’. Do your shifts communicate with each other? Do you create the opportunity to allow them to communicate? Do your shifts compete on waste and starch consumption?

Competition isn’t a bad thing, but should be positive. Your teams shouldn’t benchmark against each other but against achievable new standards. Sometimes it is just about changing your communication style and which graphs you post on the whiteboard. Don’t make them run against each other but provide them with a common enemy. Make sure people focus on achieving new quality levels instead of beating the other team.

Think positively.

 

Washboarding in all its aspects.


Time to post something new…

I have been in many countries since the last post and I am looking forward to my X-mass holiday. Spending some time with my family I have been neglecting so heavily the last years:-)

washboardIf i would have the cure to wash boarding i would be a rich guy……But unfortunately putting 250 grams liner on N  flute is not daily business…:-) This is apparently too expensive for some people.

Finding a flexo plate system that has a perfect solid print, and can go up to 70 lines per cm in the screened process colours, with no dot gain on the flute-tip compared to the valley, and still be able to print at 10000 sheets per hour, is an illusion.

So OK, I think we all agree. I am personally convinced that the cure to stripyness is understanding what is causing it in a print.

strypiness versus no stripiness

We could say that a certain amount of stripyness is acceptable, but please be aware that on flexo preprint one does not have any stripyness in the print.

Neither when one prints in offset on solid board etc….. Also inkjet has this problem less. So there is a need to control and minimize the stripyness to prevent losing business.

The stripes one observes on flexo post printed material is often named wash boarding. I prefer to call it stripyness in print. I think one needs to make a distinction on the different mechanisms of wash boarding.

One can have a sheet of corrugated board with no visual wash boarding or severe height differences between flute tip and valley, but still have stripyness in print .

This could be caused by a wrong plate/mounting system (too hard) in combination with a rough paper surface and a relatively low anilox volume printing on bad quality white test.

One also needs to make a difference in approach between solid areas and screened areas.

Without trying to be posh, i would like to introduce some terminology, so we all talk about the same thing and can immediately visualize it.

Mechanical wash boarding: height difference between flute tip and flute valley expressed in microns. (I also would recommend to read my earlier post on ‘a new device have been born’).

stripyness

Stripyness in print: uneven print on flute valleys compared to flute tips, this can be caused by mechanical wash boarding but also by other peripheral circumstances.

Typically one sees higher density (ink coverage) on flute tip then flute valley. In certain circumstances one can have negative stripyness, in these cases the ink coverage on the flute tip is lower than in the valley.

 

negative stripyness

This negative stripyness can have different causes.

 

 

 

 

2013-12-15 07.28.11

Cockling or honeycomb: too high moisture will cause the fibres to expand. This will happen in proportion a lot more in the width then in the length. The fibre direction of the liner is always perpendicular to the flutes.

As the fibre groups are already fixed on the flute tips, the fibre expansion will cause an unevenness, also known as honeycomb or cockling. A simple test to create honeycomb is to take a sponge and wet the surface of a piece of corrugated board. Wait for a while, you will see the honycomb appearing. Later, after penetration of the water in the fibres and the evaporation of the surface water, the surface will not return to its initial state, it is irreversibly damaged.

Crushed board/damaged board surface: in-feed-systems in flexo postprint presses can damage the sheets even before print and that damage will mostly be more severe on the flute tip then on the valley. Also this can cause a stripy structure in the print. In some cases I have seen this caused by a transport roller in the corrugator (i.e. MHI dry end) which has been roughened to have grip on the board. The surface of the roller looks a bit like sanding paper and will damage the coating on the flute tips.

stripyness

The in feed systems from flexo postprint presses mostly have a rough metal roller and a rubber roller. This rubber roller will lose its grip after many prints. To still have the sheets transported, the operators increase the pressure or reduce the gap and start to damage the flute tips. In these cases one should replace the rubber roller or interchange the rubber roller with the metal roller. (i.e. metal rough roller only touching the inner liner and not the coated top liner).

Banding stripyness: In double wall one can notice some repetitive bands on the board which are caused by the frequency differences between different flute types. i.e. BC flute.

BC banding

Please notice that the flutes are sometimes supporting each other (green in the image) and sometimes not (red). This happens with every flute combination that has not been mathematically sequenced. One solution is for instance to run EE. If the profile of the two E is identical no banding will occur. Another solution is to adapt the flute profiles so they are a mathematical multitude of each other.

banding  unadapted  flute profiles

adapted ratiobanded

Stripyness caused by post glazing: the corrugating process is a physically very rough process. Take a coated liner, moisten it, heat it and then drag it for about 15 meters under high pressure on metal heated plates. This can and will change the coating structure on the flute tips and will result in a different way how inks are settling or penetrating. You can compare post glazing with what happens if you iron the pants of your best suit too warm…your pants start to shine.

Stripyness in print can also be caused by too hard fluting. You can perform the following test. Make a composition with a high grammage semichemical fluting and one with a softer recycled fluting. Optimize printing pressure in the flexo press and compare the results.

Even the so called econoflutes (with lower take up factor) are not helping us as the flute tip starts to become a knife.

Mechanical wash boarding finds its root cause in the mechanism of the drying of the starch. When the starch dries it has the tendency to retract and it pulls down the liner. It is able to do so as the top liner is humidified by the condensation of the vapour on the backside of the top liner. Also the sheets in a pallet communicate with each other and the inner liner transfers moisture to the top liner of the next sheet.

So far the terminology lesson of the day.

Koen

Pictures of BC flute with conventional and adapted ratio: courtesy BHS.

A new device to measure washboarding is born!


About a year ago I was invited at Proflex to act as a speaker at the DFTA in Stuttgart.

I presented the mainly German Flexo audience with some philosophy about corrugating and advice on making good corrugated board for flexo postprint.

Proflex also hosts small booths to give people who are active in flexo the opportunity to show their novelties.

I passed by a combined booth of FAG and Peret, and my left eye fell on a USB device that could correctly measure braille and also creases in FBB (carton blanks produced on folding boxboard). So we started to talk, since I have been searching already for a long while for a device that can accurately measure washboarding. When I want to do corrugator settings optimization I have to depend on subjective assessments about the amount of washboarding. In the past I tested equipment that is used in the quality control of the production of metal parts, but it did not give me a perfect repeatability and the setup just didn’t fit my suitcase.

Objectivity versus subjectivity… What is perfect board? For one person the board is bad, for the other… I wanted to find a device that could give an objective, correct and repeatable measurement of mechanical washboarding.

The existing braille device has an accuracy of 3 microns and makes a topographic image of a surface. I asked Lukas and Philippe, “can you measure washboarding with it?”. As both are no corrugating experts, I went to look for a sheet of corrugated board to explain them what I had in mind.

Lukas was very interested and immediately started to develop ideas in his mind… I talked to my friend Daniel at Bobst and also he was immediately interested I such a device. One year later the CORRCHECK prototype was ready and I could show it to people in the industry.

The CORRCHECK measures washboarding by giving a value which is based on the average distance between the highest point and the lowest point on the surface. This value is based on the average of 5 measurements. A lower value relates to a lower washboarding amount.

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I was impressed by the repeatability of the measurements. The final version will even have a better accuracy than the prototype.

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As the device accuracy is 3 microns, it also measures the roughness of the paper surface. Hence, measuring a sheet of corrugated board with a cheap and rough recycled liner results in a value that would indicate heavy washboarding. My French colleague Hervé pointed out to me that it would usefull to calibrate the device on the medium itself.

Doing more tests with the CORRCHECK prototype, we figured out that the functionality available in one of the other devices was perfect for checking the flute profiles of single faced material.

This made us think further… The device would be ideal to monitor the mechanical wear of corrugator rollers over duration of time. By measuring the single faced material (coming out of the single facer) at the same positions on the web, on regular basis, and storing the dated measurements for later comparison, one can easily monitor the state of the mechanical wear of the corrugator rollers.

Many potential users are enthusiastic about this function.

O, G, N, F and E flute can be measured accurately with this small portable CORRCHECK device.

Last week I talked to a corrugating manager and one of his problems is that scores performed on the corrugator are good until a customer complains because the folding fails on the erecting/filling line. It is very painful and extremely costly to figure this out at the moment the customer has refused and returned your full lorry.

Measure the crease after you’ve replaced the scores, store the values somewhere and after feedback of the customer that the boxes worked perfectly, you can keep these measurements as a guideline. On regular intervals you retake an image when you are running the same box. Based on the saved values you can make for yourself a tolerance of when you need to replace the score line so you never get costly lorries returning back to your company anymore.

As an example you can find below a graph of the measurements of all the combinations of boards of our recently printed swatch book. The measurements reflect nicely the amount of wash boarding that is visible. The results are very logical and are confirming our thoughts: E flute is better than B flute, the higher the grammage the lower the wash boarding, the surface roughness (Brite uncoated versus Lite + coated ) has an influence, etc.

SnipImage

So about the CORRCHECK…
We expect to finalize the final version by the end of this calendar year. The device is small, USB connected, comes with a practical user interface for Windows, measures accurately and most importantly it fits my suitcase J. More information can be found here http://www.fag.ch/products/pdf/FAG_CORRCHECK_METSA.pdf

Just for the record… Lukas is the guy developing the device, Philippe from FAG is selling it and I’m there for testing in the field.

Did we now solve wash boarding? Not at all! The mechanical wash boarding value is only one small part of the jigsaw puzzle.

Keep up the good board!

I once was at a plant and I observed the older corrugating manager put his hand in a stack of fresh board. He thinks for a second and then decides that the board is too wet and takes actions based on these tactile sensations. I asked him if he is Spiderman. He smiles says ‘Why?’. I say, if you can feel the absolute humidity of board by just putting your hand in a stack then you need to have special sensors in your hand which feed via your nerve system in to your brain.

Even heat transfer


Today it was a terrible day to travel.  Due to an autumn storm I got rebooked and delayed. This prevented me from getting some work done on the corrugator this afternoon, so I’m using the time wisely to talk about another parallelism challenge or better put ‘controlled heat transfer’.

It is very important that an equal amount of heat transfer happens as well in machine direction as in cross direction.

A corrugator (“is not an evaporator”) has plenty places where heat is transferred to the liner fluting and corrugated board.  I already talked about the parallelism challenge from reel-stand towards the next stage in the unwinding in my first blog ‘parallelism’. That type of parallelism mostly prevents the forming of creases. Irregular tensions, however, can also cause irregular heat transfer. One only has heat transfer if there is a contact between paper and preheater, or hotplates, etc.

Once it comes to preheating, irregular web tension will result in irregular heating, causing warp at OS or DS depending where the irregular heating occurs.

IR_0126With a simple pyrometer (= an infra-red thermometer) one can check this.  Even a better tool is an IR camera, this can easily show differences between OS and DS in machine direction caused by irregular tensions. The rule here is to aim for only minor differences.

Online systems can also help us but their usefulness is as good as the correctness of the measurements. When using thermometers it is necessary to understand that one needs to adapt the sensitivity of the device depending on the materials that are measured (shiny steel, mat steel, coated liners, brown liners, white liners, etc.).

So lets now go in detail in to the double-backer.  We all are aware of the fact that the more shoes we apply – or rollers we engage – the more contact we are making, the more heat we are transferring. A key question is: do you know if the heat is equally transferred at OS and DS or even in MD?

I will gladly entertain you with some terribly disappointing (shocking?) images of irregular heat transfers on the double-backer.

Psi accupressure1

For these examples I am using real images I have ‘stolen’ from Alabany which is using a system called “Accu-pressure” to check the double-backer rollers, the shoes, the Shortt-press or combinations pressure towards the corrugated board.

The identification used is the following: dark colours show high pressure areas, light and yellow shades identify low pressure areas.

A special film is put under the belt and the shoes/rollers. Once the shoes/rollers are engaged, the amount of pressure à contact à heat transfer can be visualized in an image looking like the one underneath.

Accupressure-RT Norcro(4

 
Every red square represents a shoe. You don’t have to look close to see that on drive side there is no contact and in the middle there is an area with heavy contact that can cause scratches.Accupressure-RT Norcross (3)

In this way the whole double-backer section can be mapped and in this example above, one can clearly see that there is a difference between operating side and drive side.

On top of the previously mentioned pitfalls you also should take into account the simple mechanical system of siphons, valves that transport the steam in the cylinders and hotplates. All of this has to function correctly to make sure that we have no irregularities in heat amounts. Problems can easily be caused by corrosion, damage or failure.

I know, corrugating is complicated, so many things that can go wrong…  and yet also so many things that can work perfect.

It all starts with parallelism.


The ideal we want to get in corrugating are  flat sheets, no delamination, no wash-boarding and no honeycomb.

To obtain above one has to have a corrugator which is in a perfect state. And this has nothing to do with the age of a corrugator but all to do with maintenance.

People spend millions on a 2.8 or 3.3 meter corrugator, but seem to have no money left to spend on some simple and basic tools to maintain the state of their equipment. For instance, when I’m visiting corrugating plants, I often need to improvise to be able to make an iodine image. I some cases I even have to bring or buy my own iodine. A simple setup can make a big difference and allow you to save multiple thousands of Euros a month. Other affordable but indispensable tools around a corrugator are: a wet film glue metering gauche, and infrared thermometer, a device to measure absolute humidity, a tachometer, a digital microscope, etc.

In this article, and probably many times in the future, i will repeat the importance parallelism. With ‘parallelism’ I refer to both mechanical parallelism (such as reelstand splicers, incoming rollers, glue machine preheaters, etc.), thermal and glue application evenness.

Today there is the tendency to run lower board grammages compared to the past and in addition we run them on wider corrugators. This may lead to creases while unwinding.

Sometimes these creases can be invoked from the paper, either the creases are already in the reels, or the humidity and thickness profiles may cause the crease happening while unwiding. Do not forget that a mechanical chock on a reel, which makes the reel dancing (bouncing), can also be the cause of irregular tension resulting in.

thickness profile paper humidity profile paperGood profile (left: thickness, right: humidity)

A mill expert will be able to tell you based on the profiles if the paper is causing the creases. This can always be the case of course, but in most mills the paper has been wound and often been rewound, so the operators would have noticed if some PROFILES were bad. Winding and rewinding speeds in the mills are at least three times faster than on a corrugator….. the webs are also wider than on the corrugator.

Imagine you are the liner of the singlefaced C  that will end up as BC double wall board. At the start you will be unwound on the UNWINDING STAND that is furthest away of the take-off. Already here you have the option to be unwound on TWO DIFFERENT UNWINDERS.  PLENTY OF ROLLERS will guide towards the singlefacer. Some will be FORMED SPECIALLY to avoid wrinkles or creases (banana reels). You get PREHEATED a couple of time and then you MEET the C flute. Depending on the type of singlefacer you will be PRESSED to the C flute and in between there will be starch applied through the singlefacer GLUEMACHINE. Then you are pulled upstairs on the bridge and they fanfold you. Then you are put on the bridge after being fanfolded, awaiting the next stage in the process.

In the imaginary story above I placed the words in CAPITAL of the areas where parallelism is important.

I think we all agree that if you have two different UNWINDERS (let’s call them unwinder 1 and 2),   there should be no difference between the two. In reality I often see lots of difference. And when i say ‘lots’ then I refer to the fact that I see three corrugators a week by average and this for about 40 weeks (for a period of about 9 years now).  One corrugator a day keeps the doctor away 🙂

If you place your hand on a singlefacer, you will feel the vibration. This vibration is going on every second the machine is running and in the long run there is a risk that parts reposition and mess up parallelism.

The same thing happens to your equipment as to the glass of wine in the video. Centerlining or checking parallelism should be done every second year especially if you are running low grammages.

Other causes to destroy parallelism may be small accidents. For instance if one hits a reelstand with a reel truck or so. Things like this happen more often than they are revealed.

One easy trick if you have issues unwinding is to first unwind the reel on stand 1,  check where the creases are happening (OS or DS),  change the reel to stand 2 and check again.  When you change the reel to stand 2, make sure to follow the unwinding logic.  If the creases disappear it could be that there is something wrong with unwinder 1. If the creases remain in the same relative position toward the reel, then the chance that there is something wrong with the profile of the reel is big. If the creases are still there but at the same side, like when the reel was on reel unwinder 1, then most probably you need to look a bit further in the process to find the cause of the problem.

In this article I concentrated on the singlefacer and reel stands, but parallelism is important in many other area’s which I will discuss in future blogs.

It’s time for my sauna now.