Top Nip Rolls
& Idler Rollers

Idler Rollers

Idler rollers have to attain precision characteristics to avoid incontinuity in web tension. In the case of wide web widths, and/or substantial tension tolerances, idler rollers must be rigid to provide uniform tension across the web. Rollers that lack adequate hardness become evident when the center of the web tends to have less tension than the web edges. Sometimes a long roller can have undesirable deflection under its own weight. This parameter is termed "self-loaded deflection."

If web speed is constant, the difference in upstream and downstream web speed must be minimized with low drag bearings. Low drag bearings can be applied with steel, aluminum, and carbon fiber rollers.

Another important aspect of idler roller performance is rotational inertia. During web acceleration or deceleration, low rotational inertia is required to minimize the web tension upstream and downstream of a roller. Rotational inertia results in "dynamic drag" which resists acceleration. In addition to web tension variation, excessive rotational inertia can cause the accelerating web to slip on the roller, often causing damage to the web material.

In some applications, the parameters of web speed, roller diameter, and roller length are such that roller vibration is a problem. To reduce roller vibration, and the associated web tension fluctuation, the roller's natural frequency of vibration (critical speed) must be increased above that of the operational web speed.

Composition:

Aluminum & Steel Idler Rollers

Aluminum Idler Rollers generally have good precision and low drag bearings. Compared with steel rollers with similar dimensions, aluminum rollers have improved rotational inertia, bearing life and installation difficulty. However, neither self-loaded deflection nor critical speed is improved, and stiffness is substantially reduced.

Steel Idler Rollers generally satisfy requirements for precision, stiffness, and low drag bearings. However, the high density of steel can lead to problems with rotational inertia, self-loaded deflection, critical speed, and possibly with bearing life and installation difficulty.


Carbon fiber idler rollers

Carbon Fiber Composite Idler Rollers are designed for reduced weight and high critical speed. Lightweight, low-inertia rollers allow faster web speeds, reduce vibration, decrease waste, and improve product quality.

To simultaneously achieve high rigidity and low inertia, a material with a high stiffness to density ratio is required. This ratio, also known as specific modulus, must be maximized to achieve minimum self-loaded deflection and maximum critical speed. This important material property is also advantageous in bearing life and roller installation. The commercial roller composition with the highest stiffness to density ratio is carbon fiber (graphite) composite, whose specific modulus is nearly triple that of steel or aluminum. Carbon fiber idler rollers are extremely valuable to many demanding web handling applications. These high performance rollers permit higher web speeds, more precise web tension, higher product quality, and less down time than is possible with metal rollers of any design.


Feature Advantage Benefit
Low Rotational Inertia
(Reduced mass moment of inertia by up to 80%)
  • Rollers spin at line speed
  • Far less web scratching
  • Reduced roller wear
  • Dissipates static electricity
  • Quicker response to changes in line speed
  • Fewer web breaks
  • Far less start-up waste
  • Less web stretch
  • Less web wrap-up in the event of a web break
  • Extended roller life and reduced coating thickness
  • Less horsepower and/or fewer motors required
  • Lower energy consumption
High Stiffness
(High Modulus)
  • Less deflection
  • Less web wrinkling
  • Longer bearing life
High Specific Modulus
(High Stiffness to Density Ratio)
  • Faster line speeds with less vibration. (Higher critical speed)
  • More throughput and better product quality
  • Less self-loaded deflection
  • Less web wrinkling across wider spans
Low Mass
  • Super lightweight
  • Easier and safer handling
  • Less bearing wear
  • Longer bearing life
Low Momentum
  • More accurate transducer measurements
  • More precise tension control
  • Less lay-on roller bounce
  • Higher quality wound rolls with less air entrapment
  • Quicker dancer and accumulator roller response
  • Better dancer and festoon performance with consistent tension control and less web stretch

Courtesy of


Top

Please contact Future Design if you have any questions,
or if you would like a quotation for Top Nip Rolls and/or Idler Rollers.




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