It is important that all of your idler rollers function properly in your machine. If your idler rollers are designed poorly or require maintenance, web wrinkles, poor tension control and web defects will occur. Some things to consider regarding idler rollers when your web behaves poorly in your process are:
- Remember the web handling principle: A web will seek to align itself perpendicular to a roller in its entry span to that roller. What that means to you is your web will actually move to stay at a 90 degree angle to each idler roller in your machine. Idler rollers which are skewed to each other throughout a machine will affect the web because the web will bend to stay perpendicular to each idler roller. If your rollers are not level and parallel to each other web wrinkles and web guiding problems will occur. Check that all of your idler rollers are level and parallel in your machine. Laser alignment of rollers may be required to achieve optimum positioning.
- Idler rollers should be balanced. Each time an idler roller revolves, unbalance will cause tension fluctuations in the web. In extreme cases machine vibration may occur. Dynamically balance all of your idler rollers, especially in high speed applications.
- Bearing maintenance is critical. The web handling principle (stated in number 1 above) only applies when webs are in traction with rollers. Improper bearing operation can cause idler rollers to slow or stop spinning. When your web loses traction with idler rollers, web handling, tension control and web guiding problems will result. Check that all of your idler rollers spin freely.
- Low inertia rollers, either thin wall or engineered shape, can help with traction, balancing and tension issues. Lighter weight rollers will start faster, spin freer and stop easier.
- Idler roller mounting blocks should be designed to allow for level and parallel adjustment while also providing rigid mounting. Idler rollers can move to become skewed to each other over time. If there is no provision for this occurrence, idler roller alignment can become difficult, time consuming and expensive.
- Idler roller surface should be flat. Any imperfections, such as diameter fluctuations across the rollers face, or taper can affect your web. Web wrinkles and other web defects can occur. Idler rollers can be designed with a concave profile to assist with wrinkle removal, albeit a passive effect.
- Idler roller surface should be smooth. A smoothness finish should be specified. Idler rollers can be designed with grooves to allow air to exhaust from between the web and rollers face. This is extremely beneficial to assist with keeping smooth, non-porous webs in traction with idler rollers, especially in high speed applications. However, be careful when considering the groove design, it may cause defects in your web if it is too extreme or aggressive for your web.
- Idler rollers can be covered with a variety of coatings. Plasma coatings can assist where traction is required and where adhesives must be handled. Rubber coverings can provide very high coefficient of friction between the web and roller face to assist with traction. Chrome and nickel plating can offer extremely smooth finish. Be aware of your options when it comes to idler roller coverings and coatings and consider how they can assist your web handling and operation.
- Consider idler roller placement in your machine. Consider the number of idler rollers, as well. Idler rollers have two functions: to route your web through your process and to support the web. Oftentimes, long unsupported web lengths can cause issues with web handling and wrinkles will occur, due to insufficient web support.
Written By: Jeffrey Damour, Sales Manager, Converter Accessory Corporation, Wind Gap, PA, Phone - 800-433-2413
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