Blog RSS Feed en Copyright 2017 2017-08-15T15:45:00+00:00 <![CDATA[Factors when Choosing Screen – Part 3 Quality]]> By Justin Marriott

Product Manager - Key Filters

In the last two installments of this series, we reviewed the different weave patterns in reverse Dutch twill weave (RDW) screen and the important factors to consider when selecting the correct mesh size for your application. Now the discussion will turn to the importance of quality screen construction and how skimping on higher grade screen can cost you in the long run.

Continuous Belt Screen changer can deliver uniform extrusion pressures, varying as little as ±20 PSI. To accomplish this level of performance the screen changer must be able to reliably advance the screen at regular intervals. To do this, a sufficiently large force must be applied to the screen to overcome the friction between it and the breaker plate that results from the pressure the polymer melt applies to the screen as it passes through the pores in the mesh. Choosing “economy” screen made of lower strength wire can result in a tear when tension is applied during the screen advance sequence. Anyone who has experienced a torn screen will instantly regret not using a higher quality screen when facing lost production time due to a complete line shutdown and the added frustration of cleaning up the resulting mess.

We know the pain of having a screen fail. We’ve tested economy screens on the screen changers in our melt filtration lab and let’s just say they didn’t perform to the high standards we expect from an RDW screen. We also tensile tested each of these lesser screens and the results were shocking. Over half of the economy screen received was not able to pass our strict tensile strength requirement, with their tensile strength averaging 20% below our requirement.

So, is it worth the savings? Absolutely not! In one of our previous articles we analyzed the cost of good quality RDW screen and revealed that the screen can produce 2,194 Ibs. of product for every $1.00 of screen consumed. The cost of screen is inexpensive compared to the cost of a line shut down for 3-5 hours. Downtime can not only ruin your day but also ruin your bottom line.

At Key Filters, our screen is rated at a minimum of 190,000 PSI and each roll of screen is tensile tested in accordance with our quality controls to guarantee this rating. Not only do we test our screens to confirm required tensile strength, but we also enforce high standards for screen cleanliness. Belt screen is expected to filter out impurities but lower quality screen is often coated with residual oils or dirt/dust particles that can contaminate the polymer melt. In most applications this is simply unacceptable.

In the fourth and final installment to the “Factors for Choosing Screen” series we’ll look at some of the value-added features that a good quality screen should offer.

<![CDATA[Auto Knife Positioning Systems Part 2 – Benefits]]> Boost Efficiency with Automation

By Joe Connelly

Product Manager – Winding and Slitting

In our last article we discussed the various types of automatic knife positioning systems available to the converting industry. But who benefits from using these systems in their slitter rewinders?

Just-in-time manufacturing and inventory reduction practices have required converters to change machine setups more frequently. Contract converters are also accustomed to frequent machine changeovers and compressed delivery schedules to satisfy customer requirements. Time spent setting up a converting machine for the next job equates to lost production capacity and reduced operator productivity, which in turn has a negative impact on the productivity and profitability of the entire converting operation. Any steps taken to reduce machine setup time and to free-up machine operators for other duties can have a significant impact on improving overall operating efficiency.

For converters that process a variety of slit widths and rewind diameters off the same mill roll, avoiding long stoppage time between sets to setup the slitting components can impact productivity greatly. Arranging the slitting pattern automatically with the push of a button allows the operator time to prepare the next set of cores and start the next set more quickly. An automatic knife positioning system can reduce setup time greatly, particularly when only one operator is tending to the machine. While the operator is unloading the machine, setting up the rewind shafts, and loading new cores, the positioning system is busy moving knives to their next location in preparation for the next run. For other operations that require not only multiple width changes, but also multiple material changes, having an automatic system working in the background while the operator is busy tending to the unwind and rewind sections eliminates this added setup time. Knife locations can typically be stored as recipes in the control system for recall the next time this setup is required. Another convenient time saver.

Finally, positioning accuracy for an automatic system will provide more consistency from run to run and minimize the chance for operator error in positioning knives. This will result in fewer mistakes, less wasted material, and improved customer satisfaction (fewer returns/claims), all of which will have a positive impact on profitability. 

<![CDATA[Auto Knife Positioning Systems Part 1 – Types]]> Improve Productivity with Automation

By Joe Connelly

Product Manager – Winding and Slitting

If you are seeking ways to improve productivity of your  slitting operation, one way is to consider automating your knife positioning process. There are a variety of ways to accomplish this, and each approach differs in its cost and level of complexity. However, when understanding the added benefits of improved knife placement accuracy, faster changeover times, and improved operator safety, the costs are, in most cases, easily justified.

When we refer to knives being positioned automatically we are generally describing systems that use computer guided actuators to place slitting tooling in designated locations without operator intervention. These typically fall into three main categories: male knife positioning only, female knife positioning only, or systems that place both male and female knives together. Male only systems are most commonly used to position either score knife holders or razor blade holders. Female only systems are typically used to locate a female (or bottom knife) ring in a rotary shear system, leaving the male (or top knife) holder to be positioned by the operator. Male and female systems position both male and female knives using either a common actuator, which requires removal of the web prior to initiating the positioning sequence, or are “web in” systems that use two separate actuators to position the knives while the web remains threaded through the machine. The most sophisticated systems have separate actuators on each knife holder to simultaneously position all holders. In all cases, knives can typically be positioned within five thousandths of an inch (or about 0.1 mm) of their intended location. Positioning is usually completed in a few minutes, while simultaneously actuated systems can do so in mere seconds.

In our next article, find out who can benefit from using automatic knife positioning systems.

<![CDATA[TDO Systems Part 2 - Tenter Clips and Chains]]> By Ken Forziati

Director of Business Development & Product Management

The process of transverse direction orientation (TDO) is used to produce plastic items such as PETG shrink sleeve film, or combined with machine direction orientation (MDO) to produce products such as BOPP film. In a previous article we explained that there are two key components in a TDO tenter that make this possible; the tenter rail hinge and the tenter clip and chain system. In this article we’ll look at tenter clips and chains and explain the two basic types along with their advantages and disadvantages.

A tenter clip is the mechanism that clamps onto the edges of the plastic sheet as it travels through the TDO. A typical TDO would have hundreds or thousands of these clips.The clips are part of (or attached to) chains that ride on rails that can be adjusted inward and outward relative to the centerline of the machine to achieve the desired amount of stretching. One type of clip used mostly in high speed commodities such as BOPP and BOPET is the bearing clip. Each bearing clip is supported by an arrangement of typically up to 9 ball bearings that ride along a steel band called a monorail. This type of clip allows for a smooth travel with little to no vibration and minimal ongoing lubrication requirements. However, bearings have a limited lifespan.The higher the stretching forces and the faster they travel, the quicker they wear out. This type of clip offers high productivity but with it comes a higher overall cost, not just in the initial cost of the machine but also with ongoing maintenance. To minimize downtime, companies who use this type of clip and rail system will purchase a spare necklace - a full length of clips and chain for either side of the tenter - that can be swapped periodically with a worn necklace so that bearings can be replaced off-line before they fail in large numbers. Maintaining these spare necklaces can prove very expensive and time consuming.

The other basic type of tenter clip and chain used in TDO systems is the sliding block style, where the chain to which the clips are attached travels inside a rail channel sliding on wear strips made from special low-friction materials. This type of tenter clip is best used in moderate speed lines such as those used for specialty films like battery separator materials, PTFE membranes, and shrink films, as well as for applications for heavier gauge film such as OPS and BOPLA. Sliding block clips tend to vibrate if the gaps between rail joints are excessively large or uneven, similar to how a train makes the well-known clickety-clack sound when traveling down the track. However, if these joints are engineered properly then the vibration can be greatly minimized. Also, since these blocks are sliding in the rail channels, ongoing automatic lubrication is required to reduce friction and prolong the life of the wear strips. The biggest benefit of a sliding block tenter clip system is cost. A new system is roughly one-half to one-third the cost of a bearing clip system and even less expensive to maintain. The clips themselves are very robust and the wear strips last many times longer and are easier to replace than the bearings on a bearing clip.

As you can see, as with any two comparable technologies, each has pros and cons. When deciding which type to use for your application, you need to weigh the options: smoother operation but high cost and high maintenance of the bearing clip or low cost and low maintenance but sensitive operation of the sliding block. Keep in mind too that sliding block clip systems can run at relatively high speeds when the rail joint spacing is reduced and the correct amount of lubrication is applied. Ultimately, a combination of product requirements and budgetary considerations will influence which system will perform best for your application.

In our experience, for all applications other than high speed commodity film lines, the added cost of bearing clip systems is rarely justified.

<![CDATA[TDO Systems Part 1 - Rail Hinges]]> By Ken Forziati

Director of Business Development & Product Management

Plastics orientation is the straightening and aligning of polymer chains that occurs in a variety of manufacturing processes used to produce many everyday plastic items. It is the intended outcome when stretching plastic sheet in width to produce transverse direction oriented (TDO) products such as shrink sleeve film, or when combined sequentially with machine direction orientation (MDO) to produce products such as BOPP film. This is accomplished by using a tenter frame to convey material through an oven while concurrently stretching it transversely at optimal process conditions to achieve the desired level of polymer orientation. One of the key components of this system that makes this possible is the tenter rail hinge, but not all hinges are created equal.

In a TDO machine, the rails that guide the tenter chain are typically manufactured in rigid straight lengths that are joined by a hinge that allows the rail sections to articulate relative to each other.These hinges are mounted on translating cross members that allow the distance of the rails relative to the centerline of the machine to be adjusted inward and outward to accommodate various widths of products and to achieve the desired rail profile to provide the required stretch ratio and strain rate.

The design of the tenter clips and rail hinges are critical in determining how much a tenter rail section will be able to articulate. Originally, these were constructed from a series of smaller sections of rail with sufficient clearance between segments to allow a small amount of articulation - on the order of 4° each. To achieve large diverging angles, many segments would be added to a multi-joint. This took up valuable space which reduced the access to the web and necessitated longer tenter frames. Because of this, multi-joints had a sizable negative impact on capital cost, and on operating expenses.

Parkinson Technologies’ Marshall and Williams Plastics brand developed SuperFlex™ hinges to overcome the limitations of traditional multi-joint hinges with the goal of providing a large articulation angle in a compact footprint at a competitive cost. SuperFlex hinges provide a smooth arc of travel for the tenter chain, supporting higher line speeds and reduced wear and lubrication requirements, and can articulate up to 20°. By using SuperFlex hinges at all rail joints in a tenter frame (something that would not have been practical using multi-joints) Marshall & Williams Plastics tenter frames have significant flexibility with respect to rail profile, making them more versatile from a process standpoint.

The importance of the rail hinge is critical to the finished product in an orientation system and the SuperFlex hinge adds an even higher level of performance at a more competitive cost. However, there is another component that is just as important. The tenter clip and chain, which was briefly mentioned above, also plays a critical role but again not all clip systems are created equal. In the follow-up article we’ll discuss the advantages and disadvantages of the most commonly used types, the sliding block and the bearing clip.

<![CDATA[Preventive Maintenance Part 2 – Inspection List]]> An Inspection Schedule will go a Long Way

By Joe Connelly

Product Manager – Winding and Slitting

You know the importance of a scheduled maintenance for that machine that’s given you years of hard work. Making sure that you inspect every aspect of your  web handling system or converting machine is critical to your operation. You might be interested to know that one rule of thumb for a machine running 24/7 should be to have a quick visual inspection once a month and a thorough inspection every six months.

In a  previous preventive maintenance article, we discussed back-up batteries and how replacing them will save time and money, and ultimately a lot of headache. However, the battery isn’t the only part of a machine that can be overlooked. Here is a list of other items that should be inspected.

  • Belts – like any engineer can attest, moving parts that are in constant contact with other parts will eventual wear and ultimately fail. This holds especially true for belts since they’re usually made of a rubber material for their flexibility. When conducting a visual inspection be sure to look around and below all belts, if dust particles are visible you may need to replace them sooner than later. If larger pieces are visible then the belts need replacing immediately. This could also indicate misalignment or a tension problem.
  • Bearings – a lot of times you’ll hear a bearing fail before you see it. A clear scraping sound will indicate a worn out or completely failed bearing. To keep a bearing in good working order be sure to top off the grease when doing any type of inspection.
  • Fasteners – during a visual inspection be sure to check all fasteners. Replace any that are loose or broken, you don’t want anything to fall off while the machine is running.
  • Air Cylinders – check for faulty seals in all air cylinders. A clear indication is any escaping air when the cylinder is activated. A cylinder not working at full capacity is a safety risk.
  • Wires –during a quick visual inspection, be sure that all wires look to be intact, especially on the terminal strips. When conducting a thorough inspection give each of those connections a light tug. If they come out too easily then you should fix the connector so that it is held firmly. Over time the machine’s vibration can disconnect any loose wires which could shut it down.
  • Gear Boxes – gears usually need to be checked during a thorough inspection since getting to them usually takes more time. However, some boxes may be out in the open, which can be easier to inspect during a visual inspection. Check the gear teeth for wear and chipping. If you can get into a gear box you should have the ability to move the gears by hand to see if there is any significant play where one gear is moving more freely than the other. You may even hear a clear audible sound of the teeth hitting one another. This is a clear indication of a worn gear box and should be fixed or replaced immediately.
  • Turret Bearings – web handling and converting machinery like a turret winder or slitter use roller bearings to support the turret disc. These roller bearings are engineered to structurally support the weight of the disc, shafts, rolls of material, and all the components. However, these could eventually fail. When doing the visual inspection check to see if there is a groove in the turret disc or if the spacing isn’t concise between the turret disc and the frame. Roller bearings should be replaced immediately if there is any indication of failure.

Shutting down your machine for just a few hours every so often for inspection will go a long way in keeping that workhorse going for decades to come. 

<![CDATA[Preventive Maintenance Part 1 – Back-up Battery]]> This Often-Ignored Warning Can Lead to Unnecessary Costs

By Joe Connelly

Product Manager – Winding and Slitting

Your workhorse machine has given you decades of service due to your diligent maintenance practices and emphasis on safe and careful operation over the years. Overlooking one small and easily missed reminder can stop you dead in your tracks and result in costly downtime and service visits. This inexpensive component (usually less than $20.00) can save your organization a lot of grief if it is an included item in your preventive maintenance regimen.

Web handling systems and converting machines have used Programmable Logic Controllers (PLCs) for decades. Many of these legacy machines also have some form of operator control station that uses a small interface screen or Human Machine Interface (HMI). The programs for the PLCs and HMIs are usually developed by the original equipment manufacturer (OEM) and stored in the device’s memory. Very often a small back-up battery in the PLC and HMI retains this custom software and other critical register values when power is interrupted to the machine. As equipment gets older, these batteries get weaker and incapable of keeping the memory functional. Usually there is some form of reminder or indicator light to alert you once the battery power falls below a safe value. If these reminders are ignored and the battery dies, the program may get erased the next time power is removed from the machine. We have also seen numerous instances where the program remains intact, but critical register values are not accurately retained, and the machine does not operate properly. All it takes to prevent this is to be sure to pay attention to the low battery warnings and replace the back-up batteries when needed. The procedure is typically straight-forward but must be done properly and with power maintained to the device to prevent accidental program loss.

Staying on top of your back-up batteries’ replacement schedule can save you time and money. If you are not confident replacing the battery yourself or if you have any questions, it’s always best to contact the  OEM to request assistance. They have the original programs and tuning parameters to restore the machine to factory settings should anything happen during the replacement or if you’ve already waited too long.

While you’re checking the back-up battery it’s probably a good time to check other items on your preventive maintenance list. In the follow-up article we’ll look at other items that should be high on your list.

<![CDATA[Factors when Choosing Screen - Part 2 Mesh Size]]> By Justin Marriott

Product Manager - Key Filters

In a previous article we discussed the RDW weave patterns and how the screen will behave differently depending on the weave pattern design. This is an important factor to assure consistent flow of the melt polymer through the continuous belt screen changer. However, it’s not the only factor. The mesh size also plays a crucial role in assuring consistency of the melt.

Mesh size is simply the number of openings in one linear inch, for example a 48 x 10 mesh will have 48 openings per inch in the horizontal direction and 10 openings per inch in the vertical direction. As mesh size increases the size of the openings will decrease, and thus the size of particles retained. It is very important to remember mesh size is not a precise measurement of particle retention size. This is because screens can be made with different materials and different thickness of wire. This variable allows two filters of the same mesh size to have completely different particle retention sizes. While it is standard practice to order screen based on mesh sizes it is best to verify the particle retention size normally measured in microns of the screen to ensure it meets your filtration requirements. There are two major aspects to consider when selecting the correct mesh size for your application.

  • Pressure – What is the maximum clean and dirty ΔP (pressure differential) your application can tolerate? Increasing mesh size will result in finer filtration at the expense of higher extrusion pressures. Understanding what pressure your application can tolerate will assist in selecting an appropriate mesh.
  • Particles to be removed - What type of particles are you trying to remove and how much contamination is there? Are the particles hard such as scale, catalysts, additives, pigment agglomerates, foreign material, “black specs,” etc.? Or are the particles soft like gels or crosslinked polymers? Is there only minor contamination in the parts-per-million range or much more significant levels of contamination?

The type(s) and amount of contamination you are trying to remove will help determine the mesh size needed to best accomplish this. For hard particles, the micron size of the screen has to be smaller than the size of the contamination you are looking to remove. If the contamination level is high, then the micron size should be only slightly smaller to avoid quickly fouling the screen and needing to advance it excessively. If the contamination level is low, then an even smaller micron size can be used, if desired to remove finer particles as well.

The most common hard particles often can be removed with filtration levels in-line with the capabilities of a continuous belt screen changer (400 down to 55 micron). Softer particles, on the other hand, generally require finer filtration as they tend to deform or divide when filtered. For example, if trying to remove gels from the process, 20-micron or finer filtration may be required, which would push ΔP beyond the capability of a continuous belt screen changer to make reliable screen advancements. In this case we would recommend placing a 20-micron or finer candle filter (sintered metal is the most common filter media for this type of filter) downstream of the continuous belt screen changer. Using a coarser mesh continuous screen belt in the upstream screen changer provides the ability to filter out larger contaminates before they overwhelm the candle filter. This provides a wider range of filtration and extends the time between cleanings of the candle filter.

There are a few more factors that will be discussed in a follow-up article, including the quality of screen construction, how screens are tested, and some additional features that make a screen more functional. 

<![CDATA[Factors when Choosing Screen - Part 1 Weave Pattern]]> By Justin Marriott

Product Manager - Key Filters

In one of Parkinson Technologies’ previous articles, we discussed the use of reverse Dutch twill weave (RDW) filter belts used in ribbon-style continuous belt screen changers. We discussed the four basic types, how they differ, and how they evolved into the RDW style which offers the combination of strength and durability required for continuous belt screen changers. However, there are other factors to consider when choosing screen. The RDW weave pattern is one of them.

RDW is most commonly produced in three types of patterns: Straight Twill, Broken Twill, and Chevron Twill. Each of these patterns generally will have the same porosity for a given mesh size, but will have variations in the resulting torque that is applied to the screen. During the weaving process, pressure is applied to the wires increasing the torque in the screen, this additional torque will pull the screen to one direction or the other, introducing some skew. Skew in a screen ribbon could potentially cause problems in a continuous belt screen changer by binding and not allowing the screen to pass through freely. The difference between the weave patterns is as follows:

  • Straight Twill: The least expensive to produce it alternates the over-under (2 or 3 wires) in a regular or repeated manner, this gives the appearance of a straight diagonal weave. Torque will be the highest in this weave resulting in more skew compared to broken or chevron patterns.
  • Broken Twill: Reverses the over-under pattern within a defined distance (example a 50mm broken twill reverses the pattern every 50mm); this reduces material torque when weaving over straight twill. Torque will be neutralized each time the pattern is reversed which will tend to track the ribbon one way then back to the other reducing the overall skew in a single direction. This is the most commonly stocked pattern for Key Filters continuous screen applications because it effectively balances performance and economy.
  • Chevron Twill: Uses a repeated reversal in the pattern (every 5 or 10 wires) which gives the very noticeable “herringbone” pattern. The pull on the wires when weaving is constantly neutralized by the reversal essentially leaving neutral torque throughout the weave. This will not have any pull to one side and will result in a straight ribbon. This type of pattern will be the most expensive to produce, and while the mesh size is guaranteed, there is a possibility that when the herringbone pattern intersects you can have a larger micron size at that intersection point then you would in the rest of screen.

As you can see, the screen will behave differently depending on the weave pattern design. Choosing the right pattern is important for any melt filtration application. However, a high percentage of applications will often use the Broken Twill pattern which Parkinson Technologies readily stocks.

The weave pattern is not the only factor when choosing screen. In our next article, we’ll discuss mesh size and how pressure and the particles to be removed need to also be considered when selecting the correct size.

<![CDATA[Value of Independent Pilot Lab Trials Part 2]]> 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.