What You Need to Know About Rubber Product Manufacturing via Calendering Process

Calendering Process and Principles

In the manufacturing of rubber products, the process of forming a pre-mixed rubber into a thin film of specific thickness, width, or shape, or suspending a thin layer of rubber on textile, is known as calendering. Calendering serves various purposes such as calendaring, laminating, coating, frictioning, laminating, sheeting, and filtering.

Principles of Calendering

During calendering, as rubber material is introduced between the two working rolls of the calendering machine, rotation of the rolls causes the material to be drawn into the gap between them. The rubber material is then stretched into a thin film with a defined thickness and width. Various process phenomena during calendering are related to the flow characteristics and viscoelasticity of the rubber material.

Types of Calendering Machines and Specification Representation

Calendering machines are sophisticated and come in various types, with several classification methods:

  1. Based on the number of working rolls:
    • Double-roll
    • Triple-roll
    • Four-roll
  2. Based on purpose:
    • Sheet Calender: for sheeting or textile coating, typically three or four rolls with equal rotational speeds. Learn more about our Sheet Calender product for detailed information.
    • Friction Calender: for textile frictioning, usually three rolls with specific speed ratios.
    • Universal Calender: combines functionalities of sheet and friction calenders, often three or four rolls with adjustable speed ratios. Explore details about our Universal Calender product specifications.
    • Pattern Calender: for manufacturing rubber sheets with patterns, one of the rolls is engraved.
  3. Based on roll arrangement:
    • I-type, △-type, T-type, L-type, Z-type, S-type, etc.

Specification Representation

Calendering machine specifications are typically represented as the outer diameter of the rolls × the working length of the rolls. For example, a calendering machine with specifications Φ610×1730 can be denoted as XY-4T-1730 in China, where XY indicates a rubber calender, 4T signifies a four-roll arrangement, and 1730 represents the length of the working part of the rolls in millimeters.

Importance of Compensation Measures in Calendering Machine Design

In the calendering process, the horizontal pressure on the rolls is exceptionally high as rubber material passes through the nip. Additionally, the weight of the rolls induces elastic bending (known as deflection) that results in a thicker center and thinner sides in the calendered rubber sheet. To overcome this, compensation measures are crucial in the design of calendering machines to ensure precision in the calendering process. Common compensation methods include concave-convex coefficient method (mid-high method), shaft crossing method, and anti-bending method (load method).

Understanding the Calendering Effect and its Impact on Product Performance

The difference in performance characteristics of the product in the longitudinal and transverse directions after calendering is referred to as the calendering effect. This effect manifests as higher tensile strength, lower elongation, and greater shrinkage along the longitudinal (calendering) direction, and lower tensile strength, higher elongation, and reduced shrinkage along the transverse direction. The primary reason for the calendering effect is the directional alignment of rubber molecules and needle-like or plate-like particles after calendering.

From a processing perspective, efforts should be made to minimize the calendering effect to avoid inconsistencies in semi-finished products, making operations more challenging. This emphasizes the importance of meticulous quality control and precision in the calendering process to achieve desired product properties.

For additional information on calendering or to share your thoughts, feel free to leave a comment or reach out to us via email at contact@mechmill.com. We also welcome suggestions for discussion topics.

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