Unlocking the Secrets of Calender Equipment in Paper Making

Although the calendering process is vital in the paper industry, it is frequently overlooked. The calendaring process of the paper-making collection equipment focuses primarily on the enhancement of certain paper properties like surface smoothness and gloss, and evenness of the paper sheet’s thickness. It is clear that the equipment performs a very particular function; however, what is its function? Which parameters are most critical to its operation? In this article, we will look into the mechanics of calendar equipment, their influence on the characteristics of the paper after production, and how the manufacturers seek to improve performance. This examination of calendering technology will benefit industry employees as well as those interested in the processes of paper making.

What is a Calender in Paper Production?

A calender in paper production also refers to a finishing machine that smoothens the surface of the paper and controls the thickness using rollers. It enhances the paper’s finishing, gloss, and printability, increasing its value for several uses, including printing and packaging. Consistency is critical in paper production, and the calendering step is fundamental to achieving uniform quality in the calendered paper.

Understanding the Role of Calendering

Calendering is a crucial step in the strip production of paper in which the quality and the appearance of the paper are refined and improved in the final steps of production. Information retrieval does show a growing interest from both professional and industrial users concerning calendering and its effects on process optimization and production outcomes. In paper manufacturing, precision calendering allows uniform thickness, which is particularly beneficial for demanding applications such as packaging and high-quality printing. In addition, calendering sharpens and slickens the surface of a paper, which boosts clarity of prints and the aesthetics of the paper. This increases precision in industries such as publishing and advertising, but also caters to a higher demand from customers for products manufactured from sophisticated grade papers.

Components of a Calender Machine

The principal parts of a calendar machine comprise a set of heavy rollers or bowls constructed from steel, cast iron, or polymer composites, along with a sturdy frame that supports the rollers, heating or cooling systems of the rollers, and controls for pressure, speed, and temperature.

How Calendering Affects Paper Properties

Calendering improves the smoothness, gloss, and printability of paper and reduces its thickness and bulk; however, it can weaken its strength and dimensional stability.

How Does a Calendering Machine Work?

The Process of Calendering in Detail

The calendering process starts with a sheet or web of a material, such as paper, being fed into a series of rollers. These rollers apply specific pressure and heat, such as temperature and force, altering the material’s surface and thickness properties. Generally, rollers are organized in parallel stack pairs that can be finely adjusted to achieve the desired results.

• Feeding the Material: There are bending components and devices in the machine that guide the paper into it with a certain linear speed. These systems control tension so that an even and controlled feed of the web is achieved.
• For Calendering Operations: Application of Pressure: The rollers, which are often made of steel or covered in synthetic polymer or a composite material, apply substantial pressure to the paper. Depending on the product requirements and the calender type, the pressure can vary anywhere between 20 to 1000 N/mm².
• Control of Temperature: In order to remove moisture and enhance the surface characteristics of paper, heat can be applied using heated rollers. Depending on the material and expected results, the temperature can yield anywhere between 80°F to over 500°F.
• Roller Speed Optimization: The critical zone of concern is the balancing of temperature, pressure, and quality while fine-tuning the temperature to a high of around 2000m/min for production value.
• Moisture Control: The threshold for moisture percentage is 4%-7%. Skewing either way causes a brittle web and uneven finish due to dryness or excess moisture, respectively.
• Smoothing and Finishing: Heat and pressure exuberant the tension within the material, lowering its thickness and simultaneously raising smoothness while giving a matte or gloss finish when required.
• Output Inspection: Results after calendering yield the need for post inspection for uniformity within thickness, surface detail, and dimensional stability. Caliper measurement of gloss (measured in gloss units, GU) and smoothness (measured via PPS or Sheffield units) also provides a gauge to regulatory standards.

Injectability of Reduced porosity, printability, exquisite precision, and surface characteristics enhances calendering. The process makes calendering both pivotal and in demand within the domains of quality high-end paper, textiles, and packaging, where refined technical films are manufactured.

Types of Calender Machines

Key Features of a Paper Calendering Machine

• High Pressure Rollers: Consists of several rollers which exert consistent pressure to achieve the target smoothness and gloss levels of the surface.
• Temperature Control System: Applies heat to the rollers in a controlled manner, ensuring optimal surface finishing for the material processed.
• Adjustable Nip Settings: Adjusts the gap between the rollers to be more precise for particulate materials.
• Automation and Control Systems: Implements Automated systems like Programmable Logic Controllers (PLC) for more accurate control and measurements of set operational parameters.
• High Speed Operation: Allows accuracy and consistency when working on materials at high speeds.
• Material Handling Capabilities: Includes material feed, alignment, and tension control during the processing step for smoother operation.
• Durable Build and Wear Resistance: Made from high-grade materials, so that the machine can operate continuously and requires less upkeep and servicing.
• Compatibility with Coatings: Can handle surfaces that underwent pre-coating while ensuring no requisite finish is lost.

Why is Calendering Technology Important?

Enhancing Paper Quality and Surface Smoothness

Improving the quality and smoothness of the paper’s surface results from kaolin clay application, as well as polishing calendering rollers to improve uniformity and printability.

Impact on Different Paper Grades

Calendering processes are essential for satisfying smoothness, gloss, bulk, stiffness, and grade-specific stiffness parameters for diverse types of papers.

Role in Producing Coated Paper and Tissue Paper

The calendering process is of primary importance in the production of coated and tissue paper as it improves the evenness and shine of surfaces, their smoothness and gloss, while increasing their printability. Additionally, it optimizes coating coverage and controls thickness to improve overall quality and functionality.

What are the Different Types of Calendering Solutions?

Exploring Soft Calender and Hard Calender

Soft calendering employs rolls with a soft, elastic cover that improves paper uniformity, density, and printability, while hard calendering uses hard rolls to achieve a smooth surface finish, bulk control, consistent thickness, and uniformity.

Understanding Super Calender and Belt Calender

Super calenders utilize alternating rolls of hard steel and soft fiber covers to enhance a paper’s density, smoothness, and gloss, while belt calenders use a belt and roll apparatus that is heated to provide extended dwell time, preserving bulk and achieving high-quality finishes.

Choosing the Right Calendering Solution for Your Needs

As with every piece of equipment, application requirements guide my decision on the calendaring solution best suited for a given application. In some cases, achieving high gloss and smoothness of quality printing paper requires the use of a super calender. In contrast, if retaining bulk while achieving a high-quality finish is important, a belt calender is preferable due to its long dwell time, which helps retain bulk while achieving premium results. My choice is always driven by outcome requirements and the tradeoff between the competing performance parameters.

Who are the Leading Calendering Machine Manufacturers?

Top Companies in the Paper Machinery Industry

The worldwide paper machinery market is strongly competitive due to the advanced innovation of the calendering technology by several major companies. The latest findings include:

• Valmet Oyj – The global leader in the production and paper pulp machinery, Valmet is one of the best in the industry with its technologies concerning the paper production processes, including calendering systems. Valmet is recognized for its reliable sustainability and operational efficiency, and continuously updates its product portfolio to meet the changing requirements of the industry.
• Andritz AG – Andritz is mainly known for its all-inclusive offerings in the paper industry. Their advanced calendaring machines for finishing premium papers also focus on product value addition. Andritz is also one of the major suppliers for manufacturers, owing to its innovation focus along with energy efficiency.
• Voith Group – As one of the old-time players in the paper machinery business, Voith offers modern production compliant with high precision calender machines. Their portfolio is broad and caters to both standard as well as specialty papers.
• BMB S.p.A. – Operating in Europe, BMB focuses on the advanced calendering systems with longer lifespans and better quality. They have a strong focus on flexibility, which permits clients to make papers with desired attributes. Jagenberg Group – Known for efficient calendaring and coating technologies, Jagenberg offers sturdy machinery tailored to high-performance industrial requisites. Their focus on engineering reputation is one of the core drivers of their brand image in the industry.

These companies foster innovation and provide confidence in the paper machinery industry, addressing varying customer needs for value while focusing on environmental impact and operational effectiveness.

Innovations in Calendering Technology

Developments in the calendering technology include Electrode calendering, automated high-temperature cleaning systems, new roller designs focusing on uniform pressure and precision, and bolstering operations through machine learning models, which increase efficiency, sustainability, and product quality.

Future Trends in Calendering Solutions

Breyer GmbH, TRANSMATIC, Coatema Coating Machinery, and Reliable Rubber & Plastic Machinery are amongst the leading manufacturers of calendering machines. Foremost futuristic trends are directed towards automation as well as sustainability, and advanced cleaning technologies, such as BW Converting’s EPIC System.

Frequently Asked Questions (FAQs)

Q: What is the purpose of a paper calender machine in the context of a paper manufacturing process?

A: To enhance the surface properties of the paper web, a paper calender machine is utilized during the paper manufacturing process. It polishes the rough surfaces of the board or paper and provides adequate smoothness and gloss so that it can be used for different grades of paper and board.

Q: What is the difference between a hard nip calender and a soft nip calender?

A: In a hard nip calender, the application of pressure through the use of hard rollers results in increased gloss and smoothness of the finish. A soft nip calender, on the other hand, employs softer rollers which offer more flexibility in the calendering process and is used for softer finished board grades.

Q: What can be the focus of the calender section of a paper machine?

A: The focus of the calender section of a paper machine is to control the thickness, gloss, and smoothness of the paper, thus regulating the finish. This part contains multiple rollers through which the paper web passes to obtain the desired quality of paper surface finish.

Q: Why is calendaring important for coated paper and board?

A: Coated paper and board benefit from calendering because it improves surface roughness and glossiness together. Paper appearance can be a critical requirement for printing. Thus, the calendering process offers a favorable roughened surface than required for a given grade of paper or board.

Q: How does hard nip calendering affect the paper and board properties?

A: Hard nip calendering improves gloss and smoothness by compressing the paper web between hard rollers. This is a critical process in achieving desired paper and board properties for premium printing and packaging.

Q: What are the benefits of using a machine calender in a paper mill?

A: Application of machine calender in a paper mill aids in refinement in the finishing operations, resulting in uniform thickness and improved surface finish of the paper. Improved print quality and appearance are important for kraft paper as well as coated paper and board products.

Q: In what ways do board machines integrate with the calendering process in the papermaking?

A: Board machines operate alongside the calendering process so that surface characteristics for the board and paper produced are achieved. Calendering also assists in determining the prescribed thickness, smooth level, and polish required for the properties of the board and the quality of the product.

Q: What is the impact of deflection on paper calender machine workings?

A: In a paper calender machine, deflection can be described as the bending of rollers under load, which may disrupt the uniformity of the paper web. Calendered surface accuracy and paper or board consistency are strongly bound by deflection control.

Q: Are there any other imperfections that calendering cannot fix?

A: The challenges of surface finish, smoothness, and gloss are surmountable through calendering. However, not all flaws in paper or board are correctable this way. Calendering is often a part of a well-defined paper-making strategy and not the only remedy, using other methodologies and quality assurance procedures.

Q: What factors influence the choice of calendering equipment in paper making?

A: Selection of calendering equipment is based on the finish and smoothness of the paper and board. Surface finishing requirements and the smoothness of paper or board produced also determine the equipment to be used in calendering. Moreover, the type of paper or board to be produced, for instance, kraft or coated paper, production rate, and stringent quality standards are critical in choosing the calendering machine.

Reference Sources

1. Examination of the calendar roll machines in situ grinding process using innovative tools  

• Authors: S. Ayyappan, R. Subramaniam
• Journal: Materials and Manufacturing Processes
• Date of Publication: 11th June 2019
• Citation Token: (Ayyappan & Subramaniam, 2019, pp. 1136–1142)

Abstract:  

• This paper considers the grinding of calendar rolls used in the production of rubber products such as tires and papers. Special attention is given to the errors encountered in calendar roll machines, like web wrinkling and misregistration of cuts.
• Methodology: The study was based on designing and constructing sharpening devices for grinding rolls, which had to be cambered in situ. The findings showed it is possible to achieve better results with in-situ grinding of rolls due to less machine idle time, which is now three times lower relative to conventional methods of roll grinding, and predominant systematic errors associated with inordinate end play of the rolls are effectively eliminated.
• Conclusions: The new devices facilitated the production of coated fabrics from rubbers of reinforced fibers with deviation from nominal thickness of 1-2 microns, which markedly increased efficiency and quality of production.

2. Optimal Volume Scheduling and Planning of Paper Production with Smooth Grade Changes between Product Grades

• Authors: R. Voronov et al.
• Source: Electronics
• Publication Date: July 25, 2023
• Citation Token: (Voronov et al., 2023)

Summary:

• This article focuses on the problem of order scheduling of paper production on several paper machines, with special attention given to the enhancement of the volume calendar plan with regard to trim losses and smooth transitions between various product grades.
• Methodology: A mathematical model, which includes parameters such as grammage, roll diameter, and type of product, was developed by the authors. Optimal schedules were obtained using a combination of simplex, column generation, and local search algorithms.
• Key findings: The new scheduling strategy was validated with actual production data, and it was proven that, compared to manually generated schedules, paper production operations were better aligned with customer order deadlines.

3. Research and Evaluation Technique on Echelon Utilization of Double Life Equipment concerning Calendar Life

• Authors: Pisheng Qin et al.
• Journal: Applied Sciences
• Date of Publication: 28 January 2023
• Citing Token: (Qin et al., 2023)

Abstract:

• This research addresses the assessment of a double-life equipment, its usage, and calendar life, which is important from the equipment utilization optimization standpoint in manufacturing environments.
• Research Approach: The authors used a recursive approach to compute controllable life span in echelon usage and worked out a method of life time value distribution evaluation that includes calendar life.
• Major Insights: The developed approach enhances the accuracy of life evaluation of the equipment and demonstrate that the management of double-life equipment greatly benefits from calendar life considerations, which improves efficiency.

4. Calender

5. Paper