Blog RSS Feed en Copyright 2017 2017-08-15T15:45:00+00:00 <![CDATA[Development of Safety Standards for Film and Sheet Winding Machinery]]> By Joe Connelly

Product Manager – Winding and Slitting

As a manufacturer of machinery for the plastics industry, one of our main concerns when designing, engineering, and building these machines is to always keep safety in mind. Operating machinery can always carry the risk of injury. Workers can be struck by moving parts, trapped between rollers, belts, and pulleys, and cut or punctured by sharp edges. That’s why safety standardization efforts are developed to define, for example, the type of guarding, fencing, or torque limitation. Safety standards will often include requirements for both the manufacturer and user of the machinery.

Currently, the Plastics Industry Association (PLASTICS) who is accredited by ANSI to develop, approve, reaffirm, revise, or withdraw American National Standards and Technical Reports, is seeking additional participants for efforts related to machinery safety. They are particularly in need of voting members that are not primary equipment manufacturers.

Current projects of interest include development of standards for safety of film and sheet winding machinery, granulators, strand pelletizers and dicers as well as review of the robot integration safety standard. The Machinery Safety Technical Committee serves as the consensus body for all B151 standards activities and any other technical standards work related to machinery safety. Voting on PLASTICS standards will be done on a company basis.

Each company that is interested in becoming a voting member on the technical committee must complete a membership application. There is no fee for participation in PLASTICS standards development efforts. Most of the work will be done via teleconference, web conference or email, although an occasional in-person meeting is possible. As an active member of the Machinery Safety Technical Committee, Parkinson Technologies feels that a diverse collection of viewpoints and experiences allows for the development of comprehensive, yet practical safety standards.

If interested, please contact Megan Hayes ( or fill out the application available on the PLASTICS Machinery Safety Standards Website.

<![CDATA[Importance of Tension in an Unwind Stand - Part 2 Control System]]> By Joe Connelly

Product Manager – Winding and Slitting

Maintaining the proper web tension at the unwind is critical to the success of a web process. In most situations, two components work together to achieve and maintain the desired tension. In the previous article we discussed one of these components, the braking system, which plays the vital role of applying torque in proportion to the desired web tension. We will now focus our attention on the control system, which provides the required signals to the braking system to regulate the web tension. Control systems are open loop or closed loop and various configurations of each of these exist.

What are the differences between open and closed-loop tension control systems for unwind applications?

In the most basic form of open-loop systems, the operator manually sets the tension by continuously adjusting the braking torque as the unwinding roll’s diameter changes. This is accomplished by manually adjusting the supply pressure to the pneumatic brake, or in the case of a motor driven unwind, adjusting the torque setpoint to the drive. A more refined open-loop method is computer based and requires some upfront calibration during commissioning to determine how much braking torque is generated at the unwind spindle when a known supply pressure or motor torque is set. The control system uses this information to adjust the braking torque as the unwinding roll’s diameter changes. Without a direct measurement of this instantaneous diameter, an estimated diameter can be calculated by knowing how big the roll diameter was at the start, how thick the material is, and the length of material that has been unwound since the start. 

Although the cost of this method is higher as the machine needs a computer-based control system and a device to measure the length of material that has been unwound, it’s not always perfect.Since the roll’s diameter is calculated in the program and not actually measured, improper entry of material thickness or starting diameter can lead to instability in web tension, which can cause variations in finished roll formation. An open-loop tension control system can be an economical alternative for less demanding applications, but to ensure finished roll quality, requires accurate operator entry of processing parameters plus the skills and experience needed to make real-time adjustments to the process.

A closed-loop system, also known as a feedback control system, uses some form of continuous tension measurement to automatically adjust commands to the braking system to maintain the desired web tension.It uses the concept of an open loop system as a forward path but uses tension feedback to compare to the tension setpoint value and makes automatic adjustments to maintain web tension without operator involvement. Feedback is most accurately accomplished with a force measuring roller installed in the web path to measure the actual force, or tension, that’s been applied to the web. This device, also called a loadcell roller, provides a signal to the control system that is compared to the desired setpoint and the process is adjusted to minimize the difference, or error between these two values. 

Another feedback method is to use a translating dancer roller (more commonly pivoting but linear designs exist) that has been calibrated to exert a force to achieve a desired tension in the web, and uses a device to measure its position along its translating path. Because the force exerted is constant, any change in position is a result of either an increase or decrease in web tension. This position signal is then used in a similar manner as the loadcell signal to adjust the process to keep the dancer roller in a fixed position, oftentimes in the mid-stroke of its total travel. Although not a direct measure of how much tension is being applied to the web, if properly calibrated a dancer system can be used quite effectively in combination with a closed-loop tension control system to deliver web at a desired tension to the downstream process. The translating feature of a dancer can be an advantage in certain applications, such as automatic splicing unwind systems, to absorb minor tension disturbances that occur during the splicing sequence, and not create web handling defects.

The act of unwinding material into a downstream web process may seem simple on the surface, but to achieve the required tension control accuracy there are often more complex requirements that aren’t immediately apparent.If your process is being impacted by unstable unwinding tension, please contact us for assistance.

<![CDATA[Importance of Tension in an Unwind Stand - Part 1 Braking System]]> By Joe Connelly

Product Manager – Winding and Slitting

Many web processing applications need a way to unwind web material into a subsequent operation. Whether used inline in an extrusion laminating process or offline in a slitting and rewinding operation, an unwind stand must deliver the material into the process while maintaining the proper web tension to ensure reliable web transport. It’s the tension control requirements that can complicate the simple act of unwinding the material.

Why does an unwind need to maintain tension in a web processing operation?

Maintaining tension in the web results in process stability. If the tension goes slack, web traction is compromised resulting in web wander, improper lamination, or wrinkling. Too much tension can also cause wrinkling or can permanently distort or even tear the material. Maintaining the proper web tension at the unwind can be a critical component to the success of a web process.

To control the correct amount of tension, there are two components at play: a braking system that does the physical job of regulating the tension and a tension control system which acts as the command center to signal how much braking to apply. These two systems need to work together, one as the brain and the other as the brawn.

Braking systems commonly used on unwinds come in two variations, mechanical braking and motor generated braking. Each one has advantages and disadvantages but they both provide the vital role of applying torque in proportion to the desired web tension to the shaft or chuck that supports the parent roll.

Mechanical Braking – this type of braking can either be achieved through pneumatic pressure or electrical power, but the concept is similar. They use either air operated brake calipers or electro-magnetic force to generate the correct amount of braking force (or drag). Mechanical brakes are typically the most cost effective to purchase, install, and operate. However, there are wear items, like the brake pads, that need to be replaced from time-to-time. One disadvantage is that sometimes the torque required to accelerate the parent roll exceeds the minimum controllable torque of the mechanical brake. In this case a motor is required to provide assistance.

Motor Driven –when a parent roll must be quickly accelerated to operating speed, the material is very elastic, or the roll is severely out of round, then a motorized unwind should be considered. Since the motor is driving the unwind shaft, it’s able to feed the material into the web processes while maintaining the correct amount of tension. This is especially beneficial when bringing material up to speed in an automatic splicing system or if the material is too delicate to be pulled. When the unwind spindle is being overhauled by the downstream process, the motor regulating torque to the unwind spindle needs to hold the web back and in doing so, regenerates power that must be dissipated somewhere. One big advantage when using today’s more sophisticated AC motor control systems with a driven unwind is the ability to harness this power and feed it back onto the supply buss, which can then redirect this power to pull rolls or winding spindle drives, thus saving on overall power consumption.

Every unwind system is material dependent. The type of material, thickness, speed, width, size of the mill rolls, and how the roll will be used in the web process all need to be considered when engineering an unwind.

In Part 2 of this series, we’ll discuss the types of control systems used to regulate the tension in the braking system. 

<![CDATA[The Key Aspects of a Machine Direction Orienter - Part 2 Process Conditions]]> By Ken Forziati

Director of Business Development & Product Management

Machine Direction Orienters (MDOs) are relatively straight forward devices. Their primary function is to induce orientation in the polymer structure of plastic film or sheet in the machine direction by stretching it longitudinally at an optimal process temperature. This results in down-gauging a film’s thickness while retaining or improving its physical properties. The process may also be used to modify performance characteristics such as tensile strength, modulus, elongation, clarity, haze, shrinkage, oxygen barrier, water vapor barrier, porosity and so on. However, just how these characteristics will be affected by orientation will depend on the polymer and overall formulation of the precursor sheet in addition to the conditions at which the material is processed.

As mentioned previously in Part 1, to orient material we need to heat and apply a longitudinal stretching force using a series of rollers running at increasing surface speeds. Depending on the application, the MDO will be designed using a single or multi-stage stretching section. These configurations simply refer to the number of draw rollers used in the stretching process. A single-stage machine employing one pair of draw rollers generally would be less-expensive than a multi-stage machine employing additional draw rollers, but a multi-stage machine may enable the product to run faster and provide more output. However, it’s never that straight forward.

So, which configuration would work best? Does your application require an MDO that utilizes a single-stage or multi-stage configuration?

Before we dive into these questions, we need to first understand the critical process conditions: mainly how the stretch rate, stretch ratio, and the line speed influence one another and ultimately affect the results of the material being oriented.

  • Stretch Ratio – The stretch ratio (also referred to as the draw ratio) is one of the primary process conditions that will be adjusted in an MDO. It’s a measure of the overall elongation of the film or sheet. In the simplest terms, it is the ratio of the finished length to the initial length of the material being stretched, and nominally is the ratio of the output speed to the input speed of the draw section of the MDO. If the input line speed is set at 100 fpm and the stretch ratio is set at 2:1, then the output speed would be 200 fpm and we would be doubling the length of the film in the process.
  • Stretch Rate – the stretch rate or related strain rate is a measure of how quickly the length of the material is increasing in the stretching process. In the example of a universal tensile testing machine, it would simply be a factor of the speed at which the moving gripper is pulling on the fixed sample or the change in length per unit of time relative to the original length of the sample before stretching. In an MDO it is a little more complicated as the “sample” is not fixed, but continually moving through the machine and the stretching is occurring over a set distance. So, in this case the stretch rate is a factor of the stretch ratio, the line speed, and the distance over which the stretching is occurring; not necessarily easy to define as it is will depend on configuration of the draw rollers, gap between the draw rollers, location of any nip rollers, and frictional forces acting on the web.For a given stretch ratio, the stretch rate will increase roughly proportionally to line speed.
  • Line Speed – the speed at which the web is fed through the process is a critical design parameter and will greatly affect the configuration of the MDO. Increasing the line speed at a given stretch ratio for any machine will increase the stretch rate and decrease the residence time on all the heat transfer rollers.

The stretch ratio needed for any given application is typically fixed over a narrow range and dependent primarily on the general family of polymer being used. The strain rate is often a limiting factor as many materials will have an upper limit after which it will tend to break rather than stretch. So, the overall process line speed will be limited by the combination of stretch ratio and strain rate due to the interdependence of these process conditions.

It’s impossible to explain how all materials will perform in a single or multi-stage process in just one article. However, a good rule of thumb is that for applications were the stretch ratio and/or line speed are relatively low, single-stage machines are often adequate. Also, for unique applications where a high strain rate is desirable (for example, PTFE), single-stage machines are preferred. However, for applications running at high speeds and/or where the strain rate needs to be limited (such as the MDO for a BOPP line), multi-stage stretching will be needed.

Another benefit of a multi-stage stretching configuration is that it makes any given MDO more versatile giving you flexibility to run a wider range of materials and process conditions. This can be useful in situations where there is uncertainty in either the process conditions or the range of products you will run on the MDO during its useful life.

We haven’t even touched upon how all material can be affected by the temperature, not to mention the unforeseen primary and secondary effects that can occur. This will be discussed in the next article.

<![CDATA[The Key Aspects of a Machine Direction Orienter - Part 1 Heating Methods]]> By Ken Forziati

Director of Business Development & Product Management

When we’re discussing Machine Direction Orientation (MDO), we are describing machinery that heat and uniaxially stretch materials such as plastic film and sheet in the longitudinal (i.e. “machine”) direction over a series of rollers. The basic concept is relatively straight forward yet designing the right machine for the application is anything but simple. Over the next few articles I’m going to explain the key aspects of an MDO and how they relate to different applications. There are a lot of considerations that go into designing and building an MDO. I hope that you find these articles helpful in understanding the inner workings of these machines.

Let’s start at the molecular level. Orientation is defined as the straightening and alignment of polymer chains in plastic products like fiber, film, and sheet.The process of orienting plastics involves heating and stretching materials in a solid phase using specialized machinery to produce a less-random, more uniform arrangement of the polymer chains. The goal may be to increase material yield by down-gauging a film’s thickness while retaining or improving its physical properties. But, the process may also be used to attain a wide range of performance characteristics (mechanical, optical, shrink, barrier, porosity, etc.)that would not otherwise be possible.

So how exactly is this achieved? How do you down-gauge the film’s thickness while retaining or improving its properties?

An MDO can be used in line with a melt extrusion-casting process or offline as an independent roll-to-roll operation. In an MDO process, film is heated to the optimal stretching temperature via thermal conduction by direct contact with the surfaces of a series of heated rollers commonly referred to as pre-heat rollers. The optimal stretching temperature is typically just above the glass transition temperature or Vicat softening point of the material. Once the sheet has reached the proper temperature, it is subjected to a longitudinal stretching force imparted by a series of draw rollers running at increasing surface speeds. After the film is stretched, it may be annealed (stress relieved, heat set, etc.) in some fashion by maintaining or increasing the process temperature for some period of time, before its temperature is reduced via surface contact with a series of cooling rollers. An MDO is typically comprised of these three or four primary sections: preheating, stretching, annealing (optional), and cooling.

The first key aspect that you need to consider when thinking about an MDO is the heating medium you’re going to use in your application. There are four common types and I’ll quickly explain each one to give you a better idea of when it’s used.

  • Water: Using water or a water-glycol mixture as the circulating fluid in the heating system is relatively inexpensive since water is abundant and water heating systems are common and relatively simple. The primary downside, is that the maximum process temperature of a water system will be limited to just 275°F. This limits the range of polymers that can be processed and is not suitable in applications where higher temperature annealing is required. To achieve temperatures above 212°F the water system needs to be pressurized, which can create a safety concern if components fail. Water quality issues also must be considered and addressed to ensure that the service life of components is not compromised due to corrosion or scale.
  • Oil (or Synthetic Heat Transfer Fluids): Using petroleum-based or synthetic heat transfer fluids in the heating system enables much higher process temperatures – typically to 500+°F. However, these systems are more complex and the cost of the fluids themselves is not insignificant.Safety precautions also need to be considered when working with these systems as the fluids are flammable.
  • Electric: To achieve even higher process temperatures, rollers that are directly heated electrically – either through induction or resistance heating elements – can be used.These rollers are often jacketed with a self-contained fluid to ensure uniform heating across the roller surface.Due to the complexity of construction, the high operating temperatures and resulting electrical loads, this method of heating is relatively expensive.Installation is often simpler, however, as the MDO will not require any plumbing for the heated rollers.
  • IR: The three heating methods listed above are used to heat the rollers from the interior. An infrared radiation element is external and in an MDO application is used in two ways; to heat the web over an extended gap between rollers or combined with one of the above methods to increase heating capacity. Since heating by conduction with the roller surface is inherently unbalanced, in some applications adding heat on the exposed side can be beneficial.

Of course, the choice of heating method will be limited primarily by the process temperature requirements of the polymer(s) being oriented. Some may require high heat while others may require less to stretch the material to the right specifications, and in many applications, you may need a combination of heating elements to achieve the proper results.

In the next article I’ll discuss the different process conditions to consider in MDOs such as stretch ratios, stretch rates, line speed, and single-stage vs multistage stretching. 

<![CDATA[Factors when Choosing Screen – Part 4 Value-Added Features]]> By Justin Marriott

Product Manager - Key Filters

In last three articles of the “Factors When Choosing Screen” series we described the three types of weave pattern, an explanation on the importance of mesh size, and how the quality of the screen plays a critical role. In this last installment we’ll look at a value-added feature that any good quality screen should offer.

As we already discussed, weave pattern, mesh size, and the screen quality are important considerations when choosing screen for continuous belt screen changers. However, are there any added features that could be beneficial when choosing screen? Well, what if there were a way to reduce operational downtime when the RDW (Reverse Dutch Weave) screen is depleted? 

At some point a spent roll of screen will need to be replaced to continue the melt filtration operation. During this time the extruder must be shut down so every minute wasted during this process results in loss of revenue. Traditionally this process can take 30 minutes or more to remove the remaining spent screen by hand. To do this an operator would need to manually pull the spent screen from the outlet of the screen changer. To install the fresh screen roll it is good practice to have a second operator on the inlet side feeding the fresh screen while the spent screen is being removed. This is to reduce the opportunity of the inlet and outlet chambers freezing the cavity created from the removal of the spent screen which would result in additional downtime. This practice absorbs two or more operators, introduces safety concerns, and is time consuming.

Listening to our customer base, Parkinson Technologies’ Key Filters brand introduced ScreenLync™, a first-of-its kind feature that adds safety and efficiency to continuous belt screen changer operation. This innovation enables the operator to clip a new full RDW roll to the end of the spent RDW roll allowing a roll change to be accomplished in under 5 minutes, thereby reducing operational downtime. By clipping each end of the RDW rolls together, a single operator can pull the fresh roll into the screen changer without the need of another operator. 

Using this technology in conjunction with the model KCH’s unique screen puller system, which is attached to the outlet of the melt chamber to draw fresh screen into the melt stream, eliminates the need to manually pull the screen.This technology not only eliminates the need for two operators but allows for a screen change without the safety concerns of manually pulling on the screen. Available on all roll sizes this value-added feature has been embraced by many melt filtration operations.

We hope this four-part series was helpful to you in understand the importance of RDW screen weave pattern, mesh size, quality, and the ScreenLync value-added feature for use in continuous belt screen changers. We are confident that with the knowledge of understanding which screen is best for your application, your operation should run safely and efficiently.

<![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.