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I. Introduction to Calender Rolls

Calender rolls are essential equipment in industries such as papermaking, plastic film production, and textile processing, utilized to enhance the surface smoothness and gloss of products. This technology involves passing materials through a heated set of rolls to achieve the desired thickness and surface quality.

In the paper industry, for instance, calender rolls, typically composed of a series of heated rollers, press and dry the paper, thereby improving its smoothness and printability. This process is crucial for producing high-quality printed and packaged products.

In plastic film manufacturing, calender rolls play a similar role. After extrusion molding, the plastic material is passed through heated calender rolls to achieve a smoother and more uniform surface, which is vital for applications requiring high transparency and durability.

In the textile industry, calender rolls apply pressure and heat to fabrics, creating specific texture effects like water repellency or enhanced shine. This not only improves the fabric’s appearance and feel but also imparts additional functionality.

II. Classification by Application

1. Paper Calender Rolls

Paper calender rolls come in two main types: super calenders for fine paper and soft roll calenders for regular paper.

Super calenders use multiple metal and paper pulp rollers arranged vertically to enhance the paper’s surface gloss and smoothness, making it suitable for high-quality printing and packaging.

Soft roll calenders, on the other hand, can run at the same speed as the paper machine or coating machine. They adapt to different paper types, ensuring high moisture content and stable stiffness in the finished product.

2. Film Calender Rolls

In plastic film production, calender rolls improve the surface flatness and gloss of the film, making it more suitable for subsequent processing and use. For example, in producing high-transparency and smoothness packaging films, calender rolls significantly enhance the film’s quality.

3. Non-Woven Fabric Calender Rolls

For non-woven fabrics, calender rolls make the surface flatter and smoother, reducing fiber fluffiness and increasing density and uniformity. This improves the tactile and aesthetic qualities of non-woven fabrics, making them ideal for medical and hygiene products that require high surface quality.

4. Textile Calender Rolls

In textile processing, calender rolls make fabric surfaces smoother and flatter, enhancing both quality and appearance. The treated fabric shows improved shine and handfeel, making it competitive in markets for garments and home textiles.

III. Material Classification

1. Chilled Cast Iron

Chilled cast iron is known for its high hardness, wear resistance, and compressive strength. It withstands significant pressure and friction during the calendering process, effectively flattening and compacting material surfaces. Its surface can be further treated with processes like chromium plating to enhance hardness and corrosion resistance, thereby extending service life. Chilled cast iron is commonly used in materials that require high surface flatness and gloss, such as paper and plastic films.

2. Forged Steel

Forged steel is produced by compressing metal under red-hot conditions using hammers or presses. This process ensures continuity in the metal’s grain structure, resulting in high mechanical performance and durability. Forged steel is suitable for applications demanding high strength, toughness, and wear resistance, including aerospace components, marine parts, diesel engines, heavy machinery, and high-quality cutting tools.

IV. Surface Treatment Methods

1. Polishing

Polishing involves physically abrading the surface of the calender roll with grinding materials to remove roughness, high spots, or uneven areas, resulting in a smoother and more uniform surface. While effective in improving surface quality and repairing minor defects, polishing requires precise control to avoid excessive material removal, which could affect part mating. It is suitable for calender rolls with slight defects or those needing improved surface smoothness under normal operating conditions.

2. Chromium Plating

Chromium plating deposits a layer of chromium onto the calender roll surface using an electroplating process. Chromium provides excellent hardness, wear resistance, corrosion resistance, and luster, significantly enhancing the roll’s performance and appearance. However, chromium plating requires strict process control to ensure even thickness and avoid cracking during heating. Despite higher costs, it is widely used in precision calender rolls in papermaking and plastic film production.

3. Ceramic Coating

Ceramic coating sprays a ceramic layer onto the calender roll surface using a thermal spraying technique. Ceramic materials offer superior hardness, wear resistance, high-temperature stability, and chemical corrosion resistance. This coating can be customized in thickness according to actual needs. Although the coating process is complex and costly, it is suitable for calender rolls operating under harsh conditions, such as high temperatures, pressures, and speeds, or those requiring extremely high-precision surface treatment.

V. Working Principles

1. Fixed Gauge Calender Rolls

Fixed gauge calender rolls have a consistent middle-high position and are usually made of metal materials capable of withstanding high pressure. During operation, these rolls create a pressure zone with another roll or a flat surface, applying uniform pressure to the material and making its surface flatter and smoother. Heating the roll body simultaneously during the pressing process further improves the material’s surface properties.

2. Floating Calender Rolls (Swimming Rolls)

Floating calender rolls, also known as swimming rolls, feature a special hydraulic system that adjusts the roll’s middle-high position through oil pressure changes. When pressure is applied between two rolls, the floating roll compensates for any uneven pressure distribution caused by roll deflection, ensuring uniform line pressure and high-quality calendering.

3. Zoned Control Calender Rolls

Zoned control calender rolls use hydraulic boots or sliding blocks to apply pressure to the roll shell in real-time. The pressure distribution can be adjusted according to actual needs, achieving uniform pressure across the entire width. Combined with a closed-loop transverse control system, these rolls ensure optimal pressure distribution and high-quality output.

In summary, calender rolls are multifunctional equipment that improve material surface characteristics through precise temperature and pressure control. Their applications span various industries, including papermaking, plastic film production, and textile processing, ensuring products meet high-quality standards. Technological advancements continue to drive innovation and development in calender roll technology, promising broader applications and enhanced capabilities in the future.

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