The calender is composed of two or more rollers, arranged according to the heating method, and can be divided into cold pressing and hot pressing. Cold pressing is suitable for materials that do not require heating, such as graphite film, graphite sheet, absorbent Wave materials, shielding materials, magnetic materials, non-ferrous metal materials, etc. Hot pressing is divided into water heating, electric heating, oil heating and electromagnetic heating. They are all machines that press and stretch rubber, silica gel, silicone rubber, phase change materials, PTFE or plastics and other materials into films of a certain thickness and surface shape at a certain temperature, and can glue fiber curtain canvas or steel wire curtains.. Calenders can be divided into two-roller, three-roller, four-roller and five-roller calenders according to the number of rollers; according to the arrangement of the rollers, they can be divided into “L” type, “T” type, “F” type, “F” type, etc. Z” type and “S” type etc.

Ordinary calenders are mainly composed of rollers, frames, roller distance adjustment devices, roller temperature adjustment devices, transmission devices, lubrication systems, control systems and roll removal devices. In addition to the main parts and devices of ordinary calenders, precision calenders also have added devices to ensure calendering accuracy, such as pressure maintaining systems, bearing gap adjustment systems, etc.

Product classification

Pressing calender is used to press rubber, graphite sheets, absorbing materials, shielding materials, magnetic materials, and non-ferrous metal materials into a certain thickness and cross-sectional shape.

The universal calender can perform various tasks such as gluing, gluing and tableting.

Experimental calender for testing purposes.

Characteristic parameters

There are many parameters that characterize a calender, including the number of rollers and their arrangement, the diameter and length of the rollers, the speed range, speed ratio and production capacity of the rollers, the minimum thickness and thickness tolerance of the rolled products, the thickness of the rollers. lateral pressure and driving power, etc.

Aspect ratio

The length and diameter of the roller refer to the length and diameter of the working part of the roller. This is a characteristic parameter that characterizes the size of the calender.

1. Roller length

The roller length characterizes the maximum width of the product that can be rolled. Since space for baffle plates needs to be left at both ends, the effective length of the roller is the length of the roller minus the length of the non-working surface (approximately 15% of the roller length).

2. Roller aspect ratio

The ratio of the length and diameter of the working part of the roller is called the aspect ratio. The aspect ratio of the roller (or roller diameter) mainly affects the thickness and dimensional accuracy of the rolled products (except for the reducing roller). In addition to being related to the performance of the rolled material, the material of the roller and the length of the working part, it mainly depends on the quality requirements of the rolled products.

3. The relationship between roller diameter, transverse pressure and power, aspect ratio and stiffness

The relationship between roller diameter and transverse force and power is shown in the figure. The larger the diameter of the roller, the greater the lateral force, and the greater the required driving power, almost in a linear relationship.

The aspect ratio of the roller mainly affects the stiffness of the roller. The figure shows the rigidity ratio of a roller with a diameter of φ610mm under different aspect ratios. It can be seen from the figure that the greater the aspect ratio, the worse the rigidity.

4. Determination of roller length, diameter and aspect ratio

The length, diameter and aspect ratio of the roller are mainly determined according to the production process requirements of the product, that is, based on the type of raw materials to be processed, the thickness range and width range of the rolled product, the rolling speed of the roller (ie, output requirements) and other requirements.

In order to ensure the thickness and dimensional accuracy of rolled products, according to practical production experience, the roller aspect ratio should be limited to the following range (except for reducing diameter rollers):

When processing soft materials (such as rubber), the general aspect ratio is 2.5 to 2.7. Maximum does not exceed 3;

For processing hard materials, the aspect ratio should be about 2.0 to 2.2.

Standard series of roller length and diameter: φ360 × 1120; φ450 × 1200; φ550 × 1600; φ610 × 1730; φ710 × 1800

Roller speed and speed ratio

The linear speed of the calender roller refers to the circumferential speed of the roller, expressed in “m/min”. The linear speed of the roller is a parameter that characterizes the production capacity of the calender, and is also one of the parameters that characterizes the advanced level of the calender.

1. Roller speed

The roller speed is mainly determined based on the process use of the calender and the automation level of the production. The roller speed should be able to meet the requirements of the calendering process operation, that is, the roller speed should be adjustable.

Internationally, the rolling speed generally reaches 50-90 m/min, and some have reached 115 m/min. The average rolling speed of steel wire can reach 50 m/min. When cold rolling is used (the rolled two-layer film is directly pressed onto the weftless steel wire cord), the average rolling speed can reach 30 m/min.

2. Speed ​​adjustment range

The range in which the roller can be infinitely variable is called the speed regulating range. Due to the wide variety of processed materials and large performance differences, in order to meet both the production capacity and the requirements for slow start-up and operation, the speed adjustment range of the calender is generally required to be about 10 times.

The maximum speed is mainly determined based on the requirements of production capacity, and the minimum speed is mainly determined based on equipment startup, operational safety and convenience.

3. Speed ​​ratio

Due to the different process requirements for gluing, gluing or sheeting during calendering, the speed ratio requirements of the rollers are also different. The speed ratios of different positions on the same calender are also different.

The roller speed ratio is related to the calendering process and material properties.

• In order to eliminate air bubbles in the rubber material, the feeding roller generally has a speed ratio, usually 1:1.1~1:1.5, and the national standard mostly uses 1:1.1~1:1.4. For soft rubber materials, take the smallest value.
• (For glue wiping operations, in order to allow the glue material to penetrate into the fabric, the wiping rubber roller requires a speed ratio. The larger the speed ratio, the greater the shearing force and the better the glue wiping effect. However, if the speed ratio is too high, it will damage the strength of the textile and easily cause the rubber material to burn. If the speed ratio is too small, the penetration of the rubber material will be poor. Generally, 1:1.2~1:1.5 is used, and the national standard mostly uses 1:1.4~1:1.5.
• For operations such as tableting, laminating, and gluing, since the main requirement is to obtain extrusion force, constant speed calendering is generally used with a speed ratio of 1:1.

4. Factors to consider when selecting roller speed

Roller speed directly affects the power consumption and production capacity of the calender. The higher the roller speed, the higher the power and output, and the higher the requirements for the mechanization and automation level of the calender. Therefore, when choosing roll speed consider:

• Calendering process requirements;
• The manufacturing level of the calender;
• The automation level of the calendering unit.
• The roller speed should be able to be adjusted smoothly and widely;
• The roller speed should be as high as possible during calendering, which is conducive to exerting the equipment’s capabilities.

It can be seen that the roller speed indicates the advanced level of the calendering unit.

Since an electric motor is used to drive each roller individually, the speed ratio between the rollers can be adjusted arbitrarily within a certain range (from 1:1 to as high as 1:1.3), so that a variety of operations can be completed on one calender. This makes the adaptability of the machine wider and helps increase the roller speed.

Lateral pressure

Characteristics of lateral pressure

1. The concept of lateral pressure: When the rubber material passes through the gap between the rollers, it produces radial force and tangential force on the roller. The radial force is perpendicular to the roller surface, trying to separate the rollers. This force is called lateral pressure., also called separation force.

2. Characteristics of roller lateral pressure.

When the rubber material passes through the roller gap of the calender, the thickness of the rubber material gradually decreases from large to small, and the pressure gradually increases, as shown in the figure.

(1) In areas a and b, the passage speed of the rubber material is slower in the center of the roll gap and fastest on both sides. But as the rubber material advances, this speed difference gradually decreases.

(2) When reaching point b, the speed of all parts is the same and the pressure reaches the maximum value.

(3) When reaching the roller distance, that is, point c, the speed of the rubber material in the center of the roller gap is greater than that on both sides of the roller gap, the pressure gradually decreases, and the film thickness increases.

(4) Until point d, the thickness of the film no longer increases and the pressure of the rubber on the roller drops to zero.

It can be seen that the lateral pressure of the rubber material in the roll gap is uneven, and the maximum value will be slightly ahead of the roll distance.

Factors affecting lateral pressure

There are many factors that affect the transverse pressure during the calendering process. The main aspects are:

1. Types and properties of processed rubber materials;

Different types of rubber result in different transverse pressures. Different types of rubber have different hardness and viscosity, resulting in different transverse pressures. The greater the hardness and viscosity, the greater the lateral pressure.

2. Thickness of rolled products;

The thinner the product thickness, the smaller the roll gap and the greater the separation force. When the roll gap is extremely narrowed, a huge separation force will be generated between the rollers. This is because the smaller the roll gap, the thinner the thickness of the product, rigid extrusion is formed between the rollers, and the separation force increases sharply. From the perspective of roller maintenance, this is absolutely not allowed for general calendering machines.

3. Roller diameter and calendering width.

The larger the roller diameter and calendering width, the greater the lateral force generated.

4. The size of the wrapping angle when adding glue (i.e. the amount of material stored at the feed port);

The larger the rubber wrapping angle is, the larger the working surface of the roller will be and the greater the lateral pressure will be.

5. The speed of the roller;

The relationship between roller speed and lateral pressure is complicated.

(1) When the roller speed increases, the amount of molten material rolled per unit time increases, causing the lateral pressure to increase;

(2) As the roller speed increases, the frictional heat of the melt increases. The temperature rise causes the viscosity of the melt to decrease, which reduces the lateral pressure;

(3) The roller speed increases, which increases the pressure and thus the lateral pressure, etc.

Therefore, the relationship between roller speed and separation force is the comprehensive result of several aspects. According to actual measurements, as the roller speed increases, the lateral pressure increases slowly.

6. Roller temperature

The higher the processing temperature of the roller, the lower the viscosity and better fluidity of the material, and the smaller the lateral pressure generated. On the contrary, it is bigger.

7. Glue adding method (continuous or intermittent);

When the sheet or strip materials are fed left and right, the feeding is relatively continuous and uniform, so the impact on the roller is smaller and the fluctuation of the lateral pressure is smaller. When the block feeding is used, the feeding is intermittent and not Uniform, the impact on the roller is large, and the fluctuation of the lateral pressure is also large.

Power consumption

1. Transmission power:

Calender transmission power refers to the power required to drive the calender rollers. Its characteristics are as follows:

(1) Large transmission power. Since the calender is a heavy machine and the rollers rotate at a high speed, the transmission power is very large.

(2) Power consumption is relatively stable. In addition, because the rubber material processed on the calender has been preheated and softened, the lateral pressure is small, and the rubber material passes through the roller gap at one time, and the deformation of the rubber material before and after calendering is not large, so the operation is relatively stable. Therefore, the electric is relatively stable and does not have peak loads like the open mill.

2. Power calculation:

Power consumption is also an important parameter in calender design, which is difficult to accurately obtain using theoretical formulas. Here we briefly introduce several empirical formulas for approximate calculation:

(1) Power calculation for single motor transmission

A. Calculated based on roller linear speed

N =a·L·v

where a——calculation coefficient

L——The length of the working part of the roller

v——Calendering linear speed

B. Calculated by number of rollers

N=K·L·n

In the formula, K——calculation coefficient

L——The length of the working part of the roller

n——number of rollers.

The common shortcoming of the above two formulas is that they do not consider the properties and processing methods of the rubber being processed, as well as the impact of the diameter of the roller on power, and their impact on power consumption is very large. It can be seen that the above two formulas are one-sided.

C. Analogy calculation

With the help of several known machine characteristics and power consumption, the calculation coefficients a and K are calculated, and then the power of the designed (unknown) calender is calculated using the above formula.

(2) Power calculation when multiple motors are driven

In a calender, due to the different positions of each roller, different process uses, and different rotational linear speeds, each roller consumes different power during the calendering process. Under normal conditions, the feed roller consumes more power than the laminating roller.

A. The power consumption of the two rollers during calendering is proportional to the linear speed of the rollers.

If the linear speeds of the two rollers are V1 and V2 respectively, and the powers are N1 and N2 respectively, then:

N1/N2==V1/V2

B. The power consumed when applying glue is only 6% of the total power.

Npaste=0.06N total η

In the formula, N is the power of the rubber roller,

N total——effective total power,

η—-Total transmission efficiency.

Based on the above two points, the power occupied by each roller can be calculated.

Applications

In plastic machinery, the calender is usually combined with pilot devices such as material conveying, screening, metering, kneading and mastication, follow-up devices such as extraction, traction, embossing, cooling, thickness measurement, coiling and cutting, as well as transmission, monitoring and heating. Devices and other equipment form a complete calendering production line to produce soft and hard films, sheets, artificial leather, wallpaper, flooring rolls and other products.

Product classification

There are many classification methods for calenders in plastic machinery. The number of pressing rollers is divided into two-roller, three-roller, four-roller and five-roller types. The pressing roller arrangement can be divided into F, Z, S and L types.

Internal composition

Different from other plastic machinery, the calender is composed of a frame, a pressure roller and its adjustment device, a transmission system and a heating system. The frame is usually made of cast iron and is directly installed on both sides of the cast iron or cast steel machine base. Support roller bearings, shaft cross or roller pre-bending device, roller adjustment device, lubrication device and other auxiliary devices. The pressure roller is made of chilled cast iron or cast steel. Its aspect ratio is selected according to the bending strength of the pressure roller material, which is about 2.6 to 3.5. In order to compensate for the uneven thickness of the product caused by the bending deformation of the pressure roller, the pressure roller is often made into a waist-drum shape. The roller cross device and the roller pre-bending device can also be used to eliminate the uneven thickness of the product. Each pressure roller is driven by an independent motor. The pressure roller is generally heated by water vapor or superheated water, and the temperature difference between the two ends is required not to exceed 1°C. Each pressure roller has an independent automatic heating system. Modern calenders use roller bearings instead of traditional sliding bearings to save energy, improve bearing life and product thickness accuracy.

Production thickness

Depending on the specifications of the calender, the thickness of the soft PVC film produced is also different, ranging from 50 to 1000 micrometers, the minimum thickness of rigid PVC film is 60μm.

Mechanical bottleneck

For the calendering process, product dimensions and surface quality are the most important control parameters. The overall dimensions of the coil generally require thickness tolerances of ±0.015mm and ±0.05mm along the length and width directions respectively; the surface must be flat and smooth. If these requirements are not met, it will be difficult to ensure uniform bonding pressure between the PVC film and the magnetic plate during subsequent lamination, which will affect the bonding strength.

Technical background

The chinese bonded ferrite magnet manufacturers all use calenders with a bearing structure. The bearing material is generally copper or nylon and is lubricated with butter. The bearing bush is easy to wear, causing radial runout during the rotation of the roller, making it difficult to ensure product dimensional tolerances. Therefore, the calender must use high-precision double-row radial roller bearings and use thin oil lubrication to reduce bearing wear and ensure the thickness tolerance of the magnetic plate along the length direction.

Due to the poor fluidity of the granular material, especially due to the influence of intermolecular forces and roller deflection along the width direction, the rolled magnetic plates often appear thick in the middle and thin on both sides along the width direction. Out of tolerance dimensions will cause the roll to be tight in the middle and loose on both sides during rewinding. To solve the problem of excessive thickness, an inverted “L”-shaped four-roll calender with a complex structure can be used. The calender has shaft crossing and shaft pre-bending functions. However, the calender has a complex structure, is expensive, occupies a large area, is inconvenient to maintain, and has high factory building costs and equipment operating costs. Therefore, there is a need to design a two-roller open calender with superior performance.

Design and production

The key to the design of a two-roller open calender is the roll structure, material selection, roll surface treatment and determination of technical parameters, followed by the configuration of functions. In terms of roller structure, we have adopted a medium-height design of extra-large roller diameter that is different from the rubber and plastic products industry. Medium-height = (D-d)/2, as shown in Figure 7. The purpose is to compensate for the deflection deformation of the roll caused by rolling stress, and to increase the rolling force in the middle of the roll, forcing the magnetic particles to flow to both sides. At the same time, we have designed suitable steam heating methods for different roll heating methods that may be used during rolling. Hollow rollers and peripheral drilled rollers suitable for oil heating and water heating. Through production practice, the heating methods of both pass types can meet the process requirements for temperature fluctuation errors of the roller surface. In terms of material selection, we use alloy chilled cast iron material with good wear resistance and strong rigidity. The hardness of the roller working surface reaches HS72~75. However, alloy chilled cast iron rolls often cause “ice flower-like cloud spots” to appear on the roll surface after a short period of use due to casting defects and additives in the granular materials that may corrode the roll surface, making it impossible to roll out smooth magnetic plates. Special treatment of the roller surface is necessary. Special treatment mainly includes surface spraying with wear-resistant materials and hard chromium plating. We use the latter. In order to enhance the bonding strength between hard chromium and alloy chilled cast iron, nickel plating is required before chromium plating. The thickness of the chromium plating layer after grinding is generally 0.05~0.08mm. It should be particularly pointed out that when producing a PVC film- coated magnetic plate, the horizontal two-roller calender is best configured with one chrome-plated roller and the other with an alloy chilled cast iron roller. Since the surface of the magnetic plate rolled by alloy chilled cast iron rollers is relatively rough, it is beneficial to enhance the bonding strength between the PVC film and the magnetic plate.

Parameter formulation

The principle of setting the design parameters of the calender is to produce qualified magnetic plates in one calendering process as much as possible. The internal residual stress of the magnetic plate after repeated multi-pass rolling is very large. After bonding with the PVC film, due to the difference in shrinkage between the two, the PVC film and the magnetic plate will be debonded, the PVC film will be exposed at the edge of the magnetic plate, and the magnetic plate will be uneven. and other phenomena. Through calculation and experimental correction, we determined that the optimal technical parameters of the magnetic plate calender for producing widths less than 1000mm are: the roll aspect ratio is 2.5 to 3, the middle height is 0.1 to 0.3‰ of the roll diameter, and the roll linear speed is ≤ 3.5 m/min, the roll surface temperature is 60~80℃, the speed ratio is 1:1, and it is equipped with an edge scraping device, roll surface temperature and roll gap display device. There have been different opinions on the selection of roll speed ratio. Some people believe that the shear force of a roll with a smaller speed ratio (such as 1:1.03) can promote further plasticization of the pellets during the calendering process. In fact, this plasticizing effect is extremely small, but it will cause scratches on the surface of the magnetic plate and amplify small defects due to the shearing effect of the differential speed of the rollers.