By R. Duane Smith, product manager - specialty winding, Davis-Standard Converting Systems
All web processes require conveying a web straight through a process without distortion or defects such as wrinkles. A converting process or film-producing line requires the use of idler rolls to provide control of a web as it is conveyed. The selection of idler rolls seems simple at first glance; however, today’s web producing and converting lines often must handle a wide variety of substrates resulting in wide tension ranges at ever increasing maximum speeds. The design considerations for web-handling idler rolls include selecting the right roller material, diameter, bearings and roll surface. Then, the proper roller spacing and alignment need to be determined to successful convey a paper, film, foil and/or nonwoven web material. This paper addresses these considerations to help ensure the ability to consistently produce a quality web product, which will dead-shaft roll and live-shaft roll (see Figure 1). Both designs have their place on converting machinery with the selection
ultimately improve productivity and profitability from the production line.
The most common roll material for film, aluminum foil, lightweight paper and extensible nonwoven substrates is aluminum, which is sometimes anodized to give it a harder surface. The aluminum roll is lightweight, easy to machine and does not rust.
Paper and paperboard usually require a steel roll that is chromeplated. The higher modulus of elasticity of steel produces less roller deflection for running higher web tensions and higher nip loadings. Steel, being much harder than aluminum, is more durable and less prone to be damaged during normal use and cleaning. However, a steel roll is heavier than the aluminum roll with a greater inertia (WK2) resulting in more tension being or mild steel and require stainless steel in the area of the coater. Due to material and manufacturing costs the stainless roll is more expensive than aluminum or mild-steel rolls.
Carbon-fiber composite rolls are used in high-speed and lighttension applications where lightweight, low-inertia rolls are required. The primary advantage of this material is that it weighs less than half that of aluminum and it is stiffer, resulting in a roll that turns easier and has a greater critical speed. Carbonfiber material is less durable than aluminum or steel and is often covered with a metal, plastic or fiberglass sleeve. The roll itself is more expensive than conventional metal rolls due to material and manufacturing costs, which require diamond or carbide tooling. However, due to lower inertia, if a mechanical or electrical drive can be eliminated, the overall cost may be less.
Two designs cover the idler rolls used in converting lines: The required to accelerate and keep the roll turning.
often determined by customer or machinery-builder preference. Following is a comparison of these two types of roll construction.
Roll cost – The dead-shaft design, especially in lengths under 100 in. and roll diameters up to 6 in., is considerably less expensive.
Bearing size – The dead-shaft design can use smaller bore bearings because the shaft does not rotate, thus reversal of journal stress does not exist. Smaller bearings mean less bearing friction, but also less bearing life.
The cost of aluminum is greater than steel, but the machineability of it is also better, so the overall cost of these rolls is about equal.
Stainless-steel idler rolls often are required where the substrate is used, such as in the photographic industry or other cleanroom applications. Some coatings, PVDC for instance, attack aluminum
FIGURE 2. Idler-roll diameter Bearing lubrication and access – Many dead-shaft rolls today use bearings sealed for life (they cannot be lubricated). In the dead-shaft design, the bearing rotates with the roll, making it impossible to inspect or lubricate the bearing when the machine is running. Replacing the bearings in the dead-shaft roll requires dismantling of the roll. The bearings, being in the roll head, can be subject to coating splash, heat from dryers, etc. Conversely, the live-shaft roll can have the bearings outside of this environment, so these negative features of the deadshaft roll are positive features of the liveshaft roll. Roll inertia – The dead-shaft roll has less inertia due to the non-rotating journals and smaller heads. Using a 6-in. diameter, 1⁄2-in. wall and 66-in. face steel roll as an example, the dead-shaft roll has a WK2 of 9.1 lbs/ft2. The liveshaft roll has a WK2 of 9.5. This is a 5-percent difference and, in most cases, is insignificant. Also, the live-shaft roll can be supplied with non-contact seal bearings lubricated with a few drops of oil. This provides an extremely freeturning roll.
Idler-roll diameter
The leading factors in determining roll diameter are substrates, roll width, tension (which causes deflection) and web speed. As modal or whip balancing of slender rotating elements is recommended at aspect ratios greater than 16:1, typical rolls should be designed below this level. This also will reduce the potential for machining problems due to deflection caused by tool force (see Figure 2). How much deflection across the roll face is permissible? I am sure you can ask people from various converters and machinery builders and get different answers. For general converting (handling paper, film and laminates), a Rule of Thumb for most materials is a maximum loaded deflection of 0.0015 in. per each 10 in. (0.15 mm/meter) of roll-face length. This rule is application-dependent and may vary ±50 percent depending on the substrate and web tension vs. web thickness. The experience of the machine builder and the converter must determine the
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acceptable limits. The natural (unloaded and/or unwarped)
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t continued from page 45 deflection determines the natural critical speed of the idler roll. Normally, the roll’s diameter is selected so the maximum running speed (rpm) is kept below 70 percent of the roll’s first critical speed. For very stiff webs or materials that tend to crack or delaminate if curled, the roll diameter is determined by the maximum bend radius that these materials can tolerate without causing permanent damage to the substrate.
Again, it is difficult to give an exact figure, only guidelines based on substrates, web width and experience. A good Rule of Thumb for an
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FIGURE 3. Roll spacing
FIGURE 4. Air greasing extrusion-coating or similar converting line handling paper and films is that the roll spacing should be twothirds of the maximum web width (see Figure 3). If the machine is primarily used with lightweight papers and thin non-extensible films and foils, roll spacing should be half the maximum web width. For heavier paper and paperboard, spacing greater than two-thirds may be permissible. Generally, vertical web leads can tolerate longer spans than horizontal leads, and for web widths over 100 in. (2.5 m), this rule is no longer valid.
However, prior to a pull roll, treater or slitter, etc., the idler roll should be located closer to ensure a good layflat web. In some cases, it may be desirable to have a longer span between rolls. Longer web spans can be tolerated if a spreader roll is used at the outgoing position.
As the web travels through a process line, it tends to pull a layer of air with it (see Figure 4). The air traveling with the web can get trapped between the idler roll and the web, causing loss of traction commonly referred to as “air greasing.” This is a function of speed, web width, amount of wrap and web tension. When handling thin extensible films, the tension is low and “air greasing” can occur at speeds around 500 fpm (150 mpm). For porous materials, such as many nonwovens, “air greasing” is generally not a concern.
Positive traction between the web and roller is very important to ensure that the idler roll turns at web speed, so the web does not weave through the process and to ensure that the slower-turning roll does not scratch the web surface.
The solution to “air greasing” is to provide a surface on the roll for the air between the web and the roll to compress into and/or escape. This can be done by roughening the roll’s surface, so that the web is supported by the peaks and the air can be compressed into the valleys, or by machining grooves into the roll surface to let the air escape. Two types of grooves are used (see Figure 5). First, the spiral and circumferential type (Vent-Air) grooves are cut into the roll with a lathe. This grooving can be done in a short amount of time and it is the least expensive method. The second type of grooving, Herringbone, is a longitudinal type done by milling and takes more time, making it more costly. Although both are effective at reducing air entrainment, traction improves the most with the herringbone or longitudinal designs. The experience of the machine builder will aid in determining applications requiring this added expense.
The roller conveyor is suitable for conveying various kinds of goods in boxes, bags and pallets. Bulk materials, small items, and irregular items need to be transferred to pallets or swing boxes, which can carry a single piece of heavy material or withstand large impact loads. Easy to connect and filter between roller systems. It can be used to form multiple roller lines and other conveyors or special logistics units to meet complex process needs. Stacking drum can be used to achieve the stacking and conveying of materials. High reliability, easy to use and maintain.
Equipment characteristics of roller conveyor
It is easy to connect and filter between roller conveyors, and can be used to form complex logistics transportation systems with multiple roller lines and other conveyor equipment or special units to meet various process needs. The roller conveyor has the advantages of simple structure, high reliability and convenient use and maintenance.
The roller conveyor is suitable for flat bottom conveying goods. It is mainly composed of a driving roller, a frame, a bracket and a driving part. It has the characteristics of large volume, fast speed and stable operation, and can realize a variety of co-linear shunting transmission.
Structural form: It is divided into power type, non-power type and electric drum type from the driving form, and it is divided into horizontal conveying, inclined conveying and steering conveying according to the layout form.
Dimensions: The internal width of the roller conveyor is specified by the customer and can be produced according to customer requirements. The standard inner diameter of the turning roller line is 300, 600, 900, 1200mm, etc., and other special specifications can be adopted according to customer requirements. S is designed according to the weight, size and linear speed of the conveyed object.
Frame material: carbon steel spray, stainless steel, aluminum profile.
Power mode: reducer motor drive, electric drum drive, etc.
Transmission mode: single sprocket, double sprocket, O-belt, flat friction transmission belt, timing belt, etc.
Speed regulation mode: variable frequency speed regulation, continuously variable transmission, etc.
Features: The roller conveyor is easy to connect and filter. Complex logistics and distribution systems can be composed of multiple roller lines and other conveying equipment or special units to meet various process requirements. Stacking rollers can be used for stacking and conveying materials. Roller conveyors have advantages. Simple structure, high reliability and easy maintenance. The power roller line considers the tensile strength of the chain, and the longest single line length generally does not exceed 10 meters.
Custom roller conveyor, please call or confirm the following technical parameters:
1. The length, width and height of the conveyed object;
2. The weight of each conveying unit.
3. The bottom of the conveyor;
4. Are there special working environment requirements (such as humidity, high temperature, chemical effects, etc.)
5. The conveyor is non-powered or motor driven.
In order to ensure the smooth transportation of goods, at least three rollers must be in contact with the conveyor belt at any time. If necessary, the tray should be added to a soft bag.
1. Selection of drum length: For goods with different widths, the width of the drum should be selected. Generally, the conveyor + 50mm is used.
2. Selection of roller wall thickness and shaft diameter: According to the weight of the conveyor, it is evenly distributed on the contact rollers, calculate the load required for each roller, and determine the wall thickness and shaft diameter of the roller.
3. Roller material and surface treatment: Determine the material and surface treatment (carbon steel galvanized, stainless steel, blackened or coated) according to different conveying environments.
4. Selection of the installation method of the roller: According to the specific requirements of the entire conveyor, the installation method of the roller is selected: spring-loaded, internal gear shaft type, flat tenon type, and pin shaft type.
For the cone drum of a bending machine, the width and taper of the roller surface depend on the size of the cargo and the turning radius.
Contact us to discuss your requirements of Idler Roller Manufacturer. Our experienced sales team can help you identify the options that best suit your needs.