The difference between rubber calender and mixing mill.

I. Core Functions and Uses

• Open Mills
  Mainly used for mastication and mixing of rubber:
  • Mastication: Breaking the molecular chains of rubber through mechanical shearing force to reduce its elasticity and improve plasticity (facilitating subsequent processing).
  • Mixing: Uniformly blending rubber with various compounding agents (such as carbon black, sulfur, accelerators, etc.) to form rubber compounds with stable performance.
    In short, the core of an open mill is to "process the internal composition and state of rubber" to prepare for subsequent molding.
• Calenders
  Mainly used for the molding processing of rubber:
  Through rotating rollers, rubber compounds are pressed into semi-finished products with specific shapes, sizes, and precision (such as rubber sheets, rubber plates, rubber-cloth composite layers, etc.), or to realize the bonding of rubber with fabrics, metal frameworks, and other materials (such as tire treads, conveyor belt surfaces).
  In short, the core of a calendar is to "endow rubber with specific shapes and structures".

II. Structure and Roller Design

• Open Mills
  Usually equipped with 2 parallel rollers, both of which are working rollers, generating shearing force through a speed difference. The surface precision of the rollers is relatively low, mainly to meet the needs of shearing. The auxiliary system is mainly a heating/cooling system, which controls the temperature of the rubber compound.
• Calenders
  Commonly have 3 or 4 rollers (such as three-roll or four-roll calenders), which can be arranged in different configurations (such as L-type, Z-type, S-type). Multiple rollers have different functions, such as feeding rollers, calendering rollers, and laminating rollers, which work together to complete processes like calendering and laminating. The surface precision of the rollers is extremely high (to ensure the uniformity and smoothness of the thickness of calendered products), and some rollers can adjust the gap precisely. In addition to temperature control, the auxiliary system is also equipped with precision gap adjustment devices, tension control systems (for substrates such as fabrics), thickness detection devices, etc.

III. Differences in Working Principles

• Open Mills
  The core is "shearing and mixing". The two rollers rotate in opposite directions with a speed difference (speed ratio 1:1.2~1:1.5). When the rubber compound is brought into the roller gap, a strong shear deformation occurs inside the rubber due to the speed difference. This effect breaks the entanglement between rubber molecular chains, causing them to break or disperse, thereby achieving mastication or mixing. During operation, manual repeated turning of the rubber is required to ensure uniform force on the rubber compound.
• Calenders
  The core is "extrusion and molding". Multiple rollers, through precise speed matching and gap adjustment, continuously thin, stretch the rubber compound, or composite it with other materials. The rubber compound is subjected to uniform pressure between the rollers, forming a flat thickness or complex structure, and the processing process is highly continuous.

IV. Processing Process and Characteristics

• Open Mills
  The processing is intermittent, requiring batch feeding and manual assistance in turning the rubber, resulting in low efficiency. The rubber compound forms a "rubber package" on the rollers, which is manually cut, folded, and then re-fed into the roller gap. The uniformity depends on the operator's experience. In addition, it has high requirements for the plasticity of the rubber compound, which needs to be masticated to a suitable state in advance.
• Calenders
  The processing is continuous, with rubber compounds fed continuously and directly output as molded products, which is efficient and suitable for large-scale production. The quality of the products depends on the precise control of the equipment, such as roller gap precision, temperature, and speed synchronization, with little manual intervention. At the same time, it can handle rubber compounds in various forms (such as sheets, blocks) and can be compounded with other materials (such as rubber-fabric lamination).

V. Application Scenarios

• Open Mills
  Mostly used in small and medium-sized production or laboratories, suitable for the initial processing of rubber compounds, such as: mastication of natural rubber and synthetic rubber; mixing to prepare basic rubber compounds (such as raw rubber for tires and seals); adjustment of small amounts of rubber compounds or processing of reclaimed rubber.
• Calenders
  Mostly used in large-scale industrial production, suitable for molding processes, such as: production of thin rubber sheets and rubber plates (such as waterproof rolls, industrial rubber plates); calendering of tire treads and sidewalls; compounding of rubber with fabrics (such as canvas, nylon cloth) (such as conveyor belts, rubber belts); calendering of inner/outer layers of rubber hoses and rubber belts.

Summary: Core Differences