Blog RSS Feed http://parkinsontechnologies.com/ en BLundgren@parkinsontechnologies.com Copyright 2017 2017-08-15T15:45:00+00:00 <![CDATA[Value of Independent Pilot Lab Trials Part 2]]> https://www.parkinsontechnologies.com/blog/value-of-independent-pilot-lab-trials-part-2 https://www.parkinsontechnologies.com/blog/value-of-independent-pilot-lab-trials-part-2#When:14:47:00Z Why you should consider using the services of an OEM pilot lab facility instead of conducting trials on your production equipment.



By Ken Forziati

Director of Business Development & Product Management

In the first installment of this article, we reviewed how the material cost savings realized by running trials on a pilot scale line vs. production line can more than offset the expense of using an external facility like our Biax Lab. Beyond that, however, conducting trials on a dedicated external pilot line can provide additional advantages that improve the chances of successfully running an R&D project to completion.

The first and perhaps best reason for running development trials on a dedicated external pilot line is that it will likely be staffed by professional technicians who run these kinds of trials day in and day out. The skillsets and mindsets of production line operators are quite different from those of pilot lab technicians. Production personnel are normally focused on optimizing the throughput and quality of a limited number of formulations. They make small adjustments in processing conditions to achieve these goals.

When running trials, however, the goals are usually quite different. One typical goal is to define a process window for new materials, where key process conditions like temperatures or stretching conditions (draw ratio, stretch rate, etc.) will be varied from one bound of process-ability to another, collecting numerous samples and documenting process conditions for each along the way. Another goal is to vary the concentration or composition of one or more ingredients, over a specified range. In this case, each formulation must be accurately fed into the system, process conditions may need to be adjusted significantly and recorded, and samples will need to be collected. In either of these trial scenarios, throughput and fine tuning of quality are usually not a priority, as small quantities of samples of sufficient quality for properties testing are usually the desired outcome.

Our pilot line technicians do this on a daily basis and are accustomed to stretching the limits of the equipment in the process to achieve customers’ goals, which is their primary concern. Production staff, on the other hand, often are hesitant to “mess with the settings” for fear that they will not be able to “dial in” their next production run, and helping the researcher achieve his/her goals is not their highest priority.

One other benefit to working with experienced pilot line technicians is that by working side-by-side with them, researchers can gain significant insight into the process. Because they have run a wide range of materials for many applications, they will have insight that any production operator would never have an opportunity to learn in a typical manufacturing environment. This process knowledge also helps pilot line operators to run trials more efficiently, by quickly focusing on the critical process parameters to achieve a desired outcome. They are therefore able to run trials much more efficiently providing greater value in the time and effort spent running trials.

In addition to benefiting from working with experienced technicians, an OEM pilot line will likely provide much greater process flexibility with a wider range of capabilities than would a production line, which is optimized to manufacture a limited number of products highly efficiently.

For example, a commercial biaxial orientation line, will be designed for a specified base material (e.g. PP, PET, PETG, or PS) design throughput, line speed, finished thickness, and end application (e.g. heat stable packaging/specialty film, OPS sheet for thermoforming, microporous membrane for batter separator, shrink label film, etc.) Attempting to run trials on a different material and/or different application on a production line for which it was not designed would be much less likely to succeed. A versatile pilot line, however, should have the flexibility to vary setup configurations (dies, feedblocks, and auxiliary equipment such as blenders, feeders, dryers) to handle a broad range of materials and layer structures, as well as run a wide range of process conditions such as temperature, stretch ratios, stretch rates, and line speeds. While it will not be as efficient at cranking out a handful of large volume, high-quality products, it will certainly be more efficient at conducting trials over a wide range of applications and process conditions, with good correlation to scalability for eventual production.

A unique benefit to working with an OEM is that we also have the ability in-house to provide custom-built equipment to lab customers, allowing us to adapt and modify our pilot line as required to respond to their specific R&D needs, and to explore novel processes.

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2017-10-12T14:47:00+00:00
<![CDATA[Value of Independent Pilot Lab Trials Part 1]]> https://www.parkinsontechnologies.com/blog/value-of-independent-pilot-lab-trials https://www.parkinsontechnologies.com/blog/value-of-independent-pilot-lab-trials#When:14:56:00Z Why you should consider using the services of an OEM pilot lab facility instead of conducting trials on your production equipment.



By Ken Forziati

Director of Business Development & Product Management

When considering whether to conduct product/process development trials in an independent facility like our Biax Lab, initially customers often are caught off guard by the cost for that external capability. After running their trials here, however, they realize that there is tremendous value in working in a facility dedicated to such R&D efforts, and many become long term partners in ongoing product development initiatives.

In the development cycle for new film and sheet products, there comes a point where production processes need to be explored, samples need to be manufactured for properties testing and market development, and refinements in formulation need to be perfected. Researchers typically have one of two choices to accomplish this; schedule time on a production asset to run the experiments or run on a dedicated pilot line, whether company owned or independent.

Often the first and most obvious choice is to run on a production asset. Assuming capacity exists – which may not be the case – this can seem like a cost-effective solution as there are no outside fees to use the equipment, production operators can be used to run the trials, scale-up of a successful trial is automatic, and travel expenses are possibly avoided. However, there are some obvious (and other less obvious) downsides to running trials on a production line.

First, the throughput of a production line can be at least an order of magnitude greater than that of a pilot line. Given this, material cost alone can justify the expense of running on a dedicated pilot line. Take this example into consideration:

Let’s assume that the polymer resin costs $1 per pound. A pilot line running at 100 pounds per hour will nominally use $800 of material per day over the duration of the trial. Running the same trial on a production line running at 2,500 pounds per hour, would use $20,000 of material per day, and that doesn’t factor in any higher-cost minor ingredients/additives which would only tip the scales further against the production line option. Considering that a biaxial orientation production line could be running at throughput of three or four times that amount, the cost of running trials on a dedicated pilot line should seem like a bargain.

The savings on material cost alone should be enough to realize the benefits of using a dedicated pilot line rather than a production line with some open time. However, there are additional considerations to be taken into account, such as benefiting from the experience of pilot line technicians and the added versatility that an OEM pilot line can provide. Learn more about these topics in the upcoming follow-up article.

Please post any questions or comments below or email Ken Forziati at kforziati@parkinsontechnologies.com

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2017-09-28T14:56:00+00:00
<![CDATA[Advantages of a Linearly-acting Lay-on Roller]]> https://www.parkinsontechnologies.com/blog/advantages-of-a-linearly-acting-lay-on-roller https://www.parkinsontechnologies.com/blog/advantages-of-a-linearly-acting-lay-on-roller#When:15:45:00Z By Joe Connelly

Product Manager – Winding and Slitting


In two previous articles, lay-on rollers were discussed. From the evolution of the lay-on roller to the advantages of the more modern linearly-acting lay-on roller and minimum gap configurations to improve winding and web handling performance. Now the discussion will focus on the advantages of having predictable web tension and lay-on nip controls within this type of lay-on roller system.

You may recall that when tensile forces are applied to a piece of material, the resulting change in length, divided by its initial length, is the definition of strain, a non-dimensional measurement of how much the material has been stretched. Research has shown that maintaining a uniform strain in a web as it is being conveyed in a machine can lead to improved web control. The forces acting on the web must be predictable and uniform to ensure finished roll quality. In the case of a slitter rewinder, this uniformity applies to each slit strand and wound package, which requires both mechanical and electrical accuracy and robustness. Maintaining a constant relationship between a lay-on roller’s position with respect to its mating winding roll achieves more predictable winding results.

Converting operations that must constantly change the setup of their slitter equipment to meet their ever-changing production schedules cannot afford the time and material needed to establish proper operating conditions for the next run. There usually isn’t enough time or material to experiment with various settings and adjustments to establish the correct lay-on roller conditions to process the new material. Knowing what settings should be run is one thing that an experienced operator provides. But what if the experienced operator isn’t around to setup the machine? This is where having predictable web tension and lay-on nip controls can be a huge advantage.

Having a machine that is fundamentally easier to setup and run, and is not as dependent on the finesse or skill level of the operator to produce quality product can go a long way in reducing waste and improving overall productivity. The challenges that today’s materials present to the converter can more easily be overcome by processing them on equipment that allows materials with slight variation to be processed at higher speeds into high quality finished rolls, in larger sizes, with features that promote consistent web tracking and uniform finished roll formation.

In an upcoming series, we’ll discuss how the combination of uniform web path that maintains a constant winding geometry within the machine, along with modern controls technology, can lead to more predictable web handling results over a broader range of materials and operating conditions.

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2017-08-15T15:45:00+00:00
<![CDATA[Linearly-acting Lay-on Roller]]> https://www.parkinsontechnologies.com/blog/linearly-acting-lay-on-roller https://www.parkinsontechnologies.com/blog/linearly-acting-lay-on-roller#When:17:56:00Z By Joe Connelly

Product Manager – Winding and Slitting


In a  previous article, it was discussed how today’s web converters are challenged with the technology of their older slitter rewinder equipment and that one area where we have seen gains being made is the development of improved lay-on roller systems. Over time lay-on roller technology evolved from simple pivoting support arms, to pneumatically loaded, and then the individual lay-on roller system was introduced. However, these individual lay-on rollers added complexity and room for error due to the difficulty of not knowing how much lay-on nip force to apply. Thus, linearly-acting lay-on roller systems were developed to provide better nip force control.

Linearly-acting lay-on rollers have the benefit of maintaining a constant nip force for a given air pressure by the nature of their constant geometry. Although contact stress does change as roll diameter increases due to a larger contact area at the nip point, much more predictable winding results are realized without complicated calculations. If the desired starting and ending nip forces, along with the length of the lay-on rollers installed in the slitter machine are entered by the operator as set points, then the desired nip profile could now be accurately applied by the machine without empirical testing. For converting operations that must change setups frequently due to processing a variety of materials of various widths and thicknesses, these benefits can go a long way in reducing waste and setup time.

Being able to accurately impart the amount of nip load that ensures the required finished roll quality is one benefit of a direct or linearly-acting lay-on roller system. But how can these systems help when the material being processed responds better when it is not nipped at all?


Minimum Gap Mode: Lay-On Roller Benefits Without Nipping

This non-contact mode is used for nip-sensitive materials such as tapes and label stock with exposed adhesive, materials with high coefficient of friction, or materials with extreme gauge variation. Materials with these characteristics tend to wind better when wound softer, or with less wound-in tension. However, winding soft rolls with a large entry span can produce less than desirable edge profile results. It is therefore beneficial to convey the web as close as possible to the winding point without physically nipping the incoming web to the winding roll. Maintaining a small gap between the lay-on roller and the winding package throughout the roll build is, by definition, winding in minimum gap mode.

There are various ways to accomplish minimum gap, and  slitter rewinders with this capability generally use a motorized carriage to track the lay-on assembly away from the building roll as it increases in diameter to maintain the pre-determined gap. Positioning the carriage requires either an accurate real-time diameter calculation or measurement sensor. However, winding multiple lanes of slit material with slight thickness variations on a common shaft makes physical measurement of the diameter impractical. Thus, diameter calculation rather than measurement becomes the preferred method. To ensure accuracy, keeping web lengths and roller geometries constant throughout the roll build allows more precise diameter and length calculations. The advantage is improved winding and web handling performance.

Fundamentally a good lay-on system like the linearly-acting lay-on roller will ensure predictable web tension and lay-on nip controls, whether in contact or minimum gap mode, but are there other advantages?


NEXT ARTICLE IN THE SERIES: Learn more about the advantages of having predictable web tension and lay-on nip controls. 

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2017-07-26T17:56:00+00:00
<![CDATA[Evolution of the Lay-on Roller]]> https://www.parkinsontechnologies.com/blog/evolution-of-the-lay-on-roller https://www.parkinsontechnologies.com/blog/evolution-of-the-lay-on-roller#When:15:49:00Z By Joe Connelly

Product Manager - Winding and Slitting


Today’s web converters are challenged with production requirements that are becoming increasingly difficult to satisfy with the technology of their older  slitter rewinder equipment. Roll quality standards are harder to achieve as materials being processed are thinner, have lower modulus and have either very high or very low coefficients of friction, or when production speeds and finished roll sizes continue to increase. Modern slitters with improved web handling technologies can make these challenges more manageable. One area where we have seen gains being made is the development of improved lay-on roller systems that help address these process challenges.

As a point of reference, a lay-on roller is a nip, typically non-driven, that remains in contact with a winding package throughout the roll build. They are also referred to as touch, pack, or top riding rollers, and are primarily used to control roll hardness. They do this by metering the amount of air that is entrained into the building roll – pressing harder to squeeze out the air, thus producing a harder finished roll, or pressing lightly to let more air become trapped between the wound layers to yield a softer roll. Today’s lay-on rollers are rather sophisticated but they weren’t always that way. In the beginning, they were quite simple. Let’s look at how this type of equipment evolved over the years.


Pivoting Support Arms

Early versions of lay-on roller systems consisted of a pair of pivoting support arms that simply relied on gravity to apply a nip force based on the weight of the lay-on roller assembly against the winding package. The lay-on roller would start on top of and ride along the outer surface of the roll being wound (hence the name top riding roller) and as the roll’s diameter increased, the lay-on assembly pivoted upwards. As the roller pivots, the angle begins to increase between the vertical force vector from the roller’s weight and the applied nip force, causing the resultant nip force to decrease by the cosine of the angle. Also, the width of the contact patch at the nip point begins to increase as the winding package grows, which results in a decreased contact stress. These natural effects of a gravity-loaded lay-on roller are not always desirable for good wound roll formation. In many cases the applied nip load must increase during the winding cycle to yield the desired roll structure.


Pivoting Support Arms with Springs

One way to accomplish a good wound roll formation was to attach springs to the support arms to increase the applied nip force as the arms moved through their pivoting path. However, the nip force in either gravity or spring-loaded systems cannot be changed by the operator during the winding cycle without stopping the machine.


Pneumatically Loaded

The advent of pneumatically loaded lay-on roller systems made it possible to make changes on the fly. Not only could the force be changed remotely by the operator, but electro-pneumatic pressure regulators could be programmed to adjust the supply pressure dynamically to give a desired nip load profile based on wound roll diameter. Most machines today are supplied with pneumatically loaded lay-on rollers that offer greater process flexibility than simple gravity or spring-loaded designs. More sophisticated control logic became necessary to control the pneumatic systems in real time. Proprietary control systems used calculations to predict winding roll diameter and based on the mechanical geometry of the machine, were used to predict lay-on nip force during the winding sequence.


Individual Lay-on Roller Systems

As individual lay-on roller systems evolved from their full width predecessors, it was necessary to compensate for the changing weight of these lay-on assemblies as the roller lengths changed and this created added complexity and room for error. In a more conventional pivot arm configuration it becomes very difficult to know precisely how much lay-on nip force is being applied.


Introduction of the Linearly-acting Lay-on Roller

Because of the difficulty of not knowing how much lay-on nip force to apply, linearly-acting lay-on roller systems were developed to provide better nip force control. These designs have the benefit of maintaining a constant nip force for a given air pressure by the nature of their constant geometry.


NEXT ARTICLE IN THE SERIES: Learn more about linearly-acting lay-on roller systems and minimum gap configuration.

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2017-07-17T15:49:00+00:00
<![CDATA[Screen Changer; Screen Usage in a Timed Cycle Mode]]> https://www.parkinsontechnologies.com/blog/screen-changer-screen-usage-in-a-timed-cycle-mode https://www.parkinsontechnologies.com/blog/screen-changer-screen-usage-in-a-timed-cycle-mode#When:15:43:00Z By John Whaley

Product Manager - Extrusion & Orientation

In a previous article, I discussed pressure change vs. timed movements when setting up the control mode on a continuous belt screen changer. It was determined that timed cycle should be used as the primary screen advance command with a pressure override as a backup. The ideal settings are such that the timed sequence is long enough to generate an occasional pressure override but short enough that the screen doesn’t get pinned to the breaker plate. However, since the screen is advancing more frequently under this control scheme compared to a simple pressure setting, is it possible to use too much screen?

The short answer mentioned in the previous article is that screen cost is a pretty low number so screen usage shouldn’t be a concern. Here is why:

We frequently justify the screen roll cost against the standard square mesh filter packs used in slide plate machines. When a roll of screen can cost $1,000 or more depending on the size, it inevitably attracts the attention of purchasing departments. But when you break down the screen cost as a function of the pounds of product processed through the filter, it becomes clear that screen cost is insignificant.

Calculation Example:

Production: 4.5 in. production line extruding 800 lbs./hr. with a timed screen advance cycle setting of 0.5 in./hr.

Screen Roll Cost: 120 linear foot roll = $1,050, ($1,050/120 ft.) = $8.75/ft. or $0.73/in. or on an hourly basis $0.36/hr.

Calculations: (800 lbs./hr.)/(0.5 in./hr.) = 1,600 lbs./in. of screen. At a screen cost of $0.73/in. yields a screen cost per pound of production of $0.000456/lb. ($0.73/1,600 Ibs.) or $0.91 ($0.000456 x 2,000 Ibs.) per ton of production.

Total: 2,194 lbs. (2,000 Ibs./$0.91) of product for every $1.00 of screen consumed.

No matter which accounting model is used - conversion cost/hr. or conversion cost/lb. - screen cost is a pretty low number. The cost associated with the added risk of unplanned production shutdowns resulting from attempts to minimize screen consumption are much greater. Screen usage, therefore, should not be the primary concern when determining screen advance command settings.

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2017-06-05T15:43:00+00:00
<![CDATA[Screen Changer; Timed vs Pressure Control Screen Movements]]> https://www.parkinsontechnologies.com/blog/screen-changer-timed-vs-pressure-control-screen-movements https://www.parkinsontechnologies.com/blog/screen-changer-timed-vs-pressure-control-screen-movements#When:12:26:00Z By John Whaley 

Product Manager - Extrusion & Orientation

Pressure change vs. timed movements. In the world of continuous belt screen changers, this has long been a topic for discussion. Many processors just set the machine up in pressure control mode and let it do its thing. But that isn’t the best way to run this style of machine. Here’s why.

In pressure control mode, the screen changer will advance the screen automatically upon reaching a predetermined extrusion melt pressure. Setting the machine up to run in only pressure control mode means that the operator must be keenly aware of what the “clean screen pressure” (CSP) is for a given extrusion condition and, more importantly, what increase from CSP the machine can handle while still functioning normally. Not knowing and understanding these two data points will lead to an incorrect pressure control set point.

Why?

If the pressure set point is too high above the CSP, there is a good chance that the screen will eventually be pinned to the breaker plate. This causes erratic screen movements and annoying alarms that frequently get reset and/or ignored. This will eventually result in an unplanned shutdown. Many times, particularly in refit installations where operators had previously used a slide plate machine, they are accustomed to shifting the plate only when the pressure increase over CSP has reached several hundred or even a thousand psi. This leads to the belief that continuous belt-style machines should be operated similarly. This is never the case.

What happens if the pressure set point is set too low? (I.e. at or below the CSP)

In this case the machine will function normally, but it will advance the screen as often as the screen changer is capable and will consume excessive amounts of screen (more on screen use later). It is perfectly fine to run in this condition. It’s just not very efficient. The ideal pressure set point is normally 100-200 psi above the CSP.

So how do time controlled screen movements affect performance?

Very simply, once the main control timer is set, the machine advances the screen at that fixed time interval. Very much like in pressure control, the cycle time set point can be improperly set, but the operating window is much larger. At the low end, there is a minimum cycle time where the screen will advance as often as the machine is capable. This advances the screen as frequently as an incorrectly low pressure setting, but the length of screen that is advanced is typically different. If the cycle time is set excessively long, the machine will suffer the same fate as an excessively high pressure set point and will start functioning erratically, causing alarms and eventually stop working altogether, resulting in an unplanned shutdown. The window between these two set points could be hours.

What about screen usage? Am I using too much screen?

The short answer is that screen cost is a pretty low number so screen usage shouldn’t be a primary concern. We’ll continue this discussion in detail in one of our follow-up articles.

What is best?

At Key Filters we instruct our customers that the best practice is to setup the screen changer using a timed cycle as the primary screen advance command with a pressure override as a backup. Our controls are designed to enable operators to program independent screen advance lengths for timed and pressure control commands. Some operator intellect is required to set these conditions but once determined, the machine will run automatically for the life of the screen belt. The ideal settings have the timed sequence long enough to generate an occasional pressure override but short enough that the screen doesn’t get pinned to the breaker plate. This can be anywhere from 15-60 minutes. The ideal pressure control set point is normally 100-200 psi above the CSP and the pressure control screen advance length is twice that of the timed cycle.

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2017-03-23T12:26:00+00:00
<![CDATA[3 Key Specs to Communicate to Your Machine Builder]]> https://www.parkinsontechnologies.com/blog/3-key-specs-to-communicate-to-your-machine-builder https://www.parkinsontechnologies.com/blog/3-key-specs-to-communicate-to-your-machine-builder#When:21:49:00Z You’ve chosen a manufacturer for your new web handling equipment, and you’re eager to get started with the process. But, before you move forward, there’s one important part of the project that cannot be overlooked: communicating exactly how your machine will be used, and your expectations of its performance.

There are three types of specifications your machine builder must know before they can accurately build a custom-engineered or even a standard machine:

Operational. How will the machine be operated once it’s installed? For example, how often and what method do you intend to use for threading-up the machine? It is often found that operational practices that have been used for decades are no longer permitted due to current machine safety regulations. Alternative methods must be considered that ensure operator safety, and meet your production goals.

Handling. In the case of a winder, it’s important to know how the finished rolls of material will be handled (e.g. overhead hoist, forklift, cart, or other). This can dictate the design of the machine; not only with respect to accommodating the preferred handling method within the confines of the machine, but also with respect to planning the space requirements surrounding the machine upon installation in your facility.

Materials. This is probably the most mission-critical specification. Your machine builder will need to know all of the materials that will be run on the machine. If the builder is under the impression that only a few types of materials will be used, they will build a machine to handle only those types of materials and may overlook some important design requirements.

Ideally, samples of all materials to be processed in their finished form should be provided to the manufacturer for evaluation before the machine is even quoted. Providing the specifications of the cores is just as important, including the core materials and sizes. For example, if you require the core to extend from each end of the finished roll for subsequent handling or packaging, this needs to be communicated to the manufacturer as it may impact the overall size of the machine.

The bottom line: up-front communication with your equipment manufacturer is absolutely essential. Given complete and accurate specs, your manufacturer can design and build a piece of equipment that lives up to your performance expectations and becomes an asset to your business. 

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2017-02-01T21:49:00+00:00
<![CDATA[A Good Winder Won’t Necessarily Fix a Bad Web]]> https://www.parkinsontechnologies.com/blog/a-good-winder-wont-necessarily-fix-a-bad-web https://www.parkinsontechnologies.com/blog/a-good-winder-wont-necessarily-fix-a-bad-web#When:14:44:00Z Eliminate unpredictable results by revealing all process challenges

While it’s natural for processors to blame the  winder when defects appear in roll goods, more often than not the root cause of the problem can be traced to the process upstream. A poorly designed winder or a good winder applied to the wrong application can certainly exacerbate typical roll defects like starring, edge profile variation, and telescoping. However, there are many web problems created by upstream processes or equipment issues that can’t be rectified by a well-designed winder. Non-uniform thickness profiles can lead to severe gauge banding, wavy edges, and baggy lanes; formulation deficiencies combined with overly tight winding create blocking issues; deformed web due to misaligned process rollers, process inconsistencies, and/or inadequate tension control can result in wrinkles that are impossible to eliminate from the finished roll.

When these flaws can’t be overcome through upstream process optimization, it can lead to plenty of frustration, production waste, and delays. That’s why—if you’re in the market for a winder replacement or upgrade—it’s important to convey any quality issues you’re currently having to the winder manufacturer before purchasing a new machine. Additionally, a winder manufacturer that’s paying attention to the requirements will ask to review and observe current performance, if possible. That way, all parties understand the process challenges and together can accurately establish appropriate expectations regarding winding results from the new machine. For example, unresolved problems in upstream sections of the production line may require tradeoffs such as winding looser packages or smaller diameter finished rolls to reduce the likelihood that winding defects will occur.

If you don’t let the winder manufacturer know about current problems you’re having with finished roll quality, your results with a new machine could be unpredictable and disappointing. It’s like visiting the doctor and not divulging all of your symptoms and then expecting him or her to provide the correct treatment!

Evaluating your entire production process is critical in determining what areas must be addressed before specifying a new or rebuilt winder. In many cases, changes to upstream equipment or process parameters are also required to ensure that you achieve the highest levels of quality that you desire in your finished products. 

For more information on roll and web defects read Roll and Web Defect Terminology by Duane Smith

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2017-01-04T14:44:00+00:00
<![CDATA[Differential vs. Locked-Core Rewinding]]> https://www.parkinsontechnologies.com/blog/differential-vs.-locked-core-rewinding https://www.parkinsontechnologies.com/blog/differential-vs.-locked-core-rewinding#When:12:08:00Z There is often some confusion as to what type of rewinding method is appropriate for certain slitter rewinder applications. To shed some light on the topic, we’ve put together a quick overview on the differential versus locked-core method below.

Differential rewinding: In slitter rewinders, the most common type of center winding is the duplex type slitter rewinder. This is an application of center winding that very often utilizes a differential rewinding technique. A large majority of the materials that are converted have minute variations in thickness (gauge) across the web width and, when the material is slit and the individual strips are wound onto the rewind shafts, subtle differences in each roll’s diameter begin to develop as more and more layers of material are wound. These diametrical differences require slightly different rotational speeds in order to maintain the same surface speed, and thus the same web tension, of each wound package. When differential rewinding, the individual rewinding rolls are not positively locked onto the winding shaft and are allowed to slip relative to one another, hence the term “differential” winding. Each wound roll is driven from its center at a slightly different speed to maintain a consistent outer surface speed. This method enables high-quality rewinding of materials that have non-uniform gauge by winding each roll with uniform tension.

What would happen without differential action? The thicker, or heavy-gauge areas of the material would wind tightly, which could cause the material to stretch or the core to collapse. At the same time, thinner, or lighter-gauge areas would wind loosely, potentially causing the roll to telescope and/or fall apart during handling.

Locked-core rewinding: Locked-core rewinding describes a technique in which the cores are fixed to the rewind shaft. They are usually held in place by air expanding lugs to keep them from slipping. One reason why the locked-core method might be used is if you need to rewind a full width roll without slitting. It is also commonly used on surface type slitter rewinders where the winding shaft is not driven from its center. Some materials that are extensible and not easily damaged when stretched can be slit and center wound successfully in a locked-core manner, however these applications are not very common and must be carefully analyzed before ruling out the need for differential winding shafts.

For more information on the slitting and rewinding process and its various methods, please see our Dusenbery® Slitting Techniques Guide

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2016-09-20T12:08:00+00:00