Calenders

In the plastics and rubber processing industry, a commonly used machine called a calender is a specialized piece of equipment designed for continuously rolling and shaping plastic or rubber materials. This machine typically consists of two or more temperature-controlled rolls that rotate in opposite directions. The raw plastic or rubber material is fed into the gap between these rolls, where it is flattened, smoothed, and formed into a continuous sheet or film of uniform thickness. Calenders are essential for producing a wide range of products, from thin films for packaging to thick sheets for automotive and industrial applications. The ability to precisely control the thickness and surface finish is crucial for ensuring the quality and consistency of the final product. Moreover, modern calenders often incorporate advanced control systems for greater accuracy and efficiency, adapting to the diverse requirements of the plastics and rubber industries.

・Roll Arrangements

Calenders are designated by the size (diameter × working face length) and number of rolls used, as well as the type (arrangement of rolls). The rolls can be driven by various methods, such as universal drives and gear drives, but currently, most rolls are driven by universal drives.
For power, the individual drive system, which uses dedicated motors for each roll allowing the roll speed ratio to be freely set, has become common. We can modify your calender to an individual drive system, so please feel free to inquire about the feasibility.
We can also design other arrangements according to your needs.

・Overview of Calender Structure

Rolls

Calender rolls are manufactured using the highest quality chilled cast iron. The surface of the rolls is finished to a mirror polish, with roundness precision maintained to within a few microns at room temperature. The surface hardness is above 70º Shore (JIS). Internally, the rolls are machined to ensure uniform wall thickness and even temperature distribution.

About Special Steel Forged Drilled Rolls

Our company also supplies forged steel drilled rolls and recommends them for certain applications. Forged steel drilled rolls have a higher surface hardness compared to chilled cast iron rolls. Additionally, due to their superior rigidity, they can be longer relative to their diameter (L/D ratio of 3 to 4 times), which allows for smaller machinery even for wide-width products.

Roll Crown

When rolling between two rolls, a separating force acts between the rolls, causing them to bend and creating thickness variations in the product. To minimize this error, the roll surface is pre-polished into a curved shape. This process is called crowning, and the difference in diameter between the center and the ends of the roll is called the crown amount. This crown amount is determined for each roll based on its position in the arrangement and the rolling material conditions.

Friction Between Rolls

When adopting an individual drive system, where each roll is driven separately, the rotational ratio between each roll can be freely set. This addresses operational purposes (such as frictioning) and alleviates periodic error variations due to roll eccentricity. There is also a method to give rolls a rotational ratio using gears, which are housed within a pinion stand. This system can also be modified to an individual drive system.

Roll Bearings and Lubrication

Roll Cross Device

Roll Gap Adjustment

For one fixed roll, the other rolls have roll gap adjustment devices attached. The adjustment is made by rotating a push screw via a motor through a reduction gear, moving the roll bearing box, and correcting the product thickness. The movement is read by position sensors and displayed on the control panel.

Roll Bending Device

Pull-Back Device (Zero Clearance Device)

Universal Drive

Large calenders are typically driven via universal spindles that connect the rolls to the pinion stand. This universal drive system absorbs the core fluctuations arising from the required product thickness, ensuring smooth power transmission even at high speeds. The spindles use cross joints, ball joints, and flex-type gear couplings.

Emergency Braking Device

In an emergency, the rotation of the rolls can be stopped instantly by activating push buttons or contact bars on the machine side or control panel. Braking systems such as band brakes, electromagnetic brakes, dynamic brakes, and regenerative braking are employed.

Auxiliary Devices

Calenders also come with auxiliary devices like stock guides, edge cutters, press rolls, take-off devices, and guide rolls. These auxiliary devices are selected based on the application or working conditions.

Mixing Mills

Mixing mills have been used for rubber and plastic processing for a long time. They are mechanically simple, have few failures, and the work in progress can be inspected visually at any point.
Our mixing mills are designed and manufactured to withstand severe use, and we have delivered thousands of units to rubber and plastic-related companies, all of which have received high praise. Depending on the intended use, this machine is also called a sheeting mill or warming mill.

・Description of Main Parts

Rolls

The rolls are made of high-quality chilled cast iron. The surface of the rolls is polished, and the hardness is around 70º Shore (JIS). The interior is hollowed out for heating and cooling. Additionally, drilled rolls may be used to enhance kneading and mixing efficiency.

Roll Bearings and Lubrication

The bearings use either roller bearings or high-lead bronze plain bearings and are housed in specially cast iron bearing boxes. Lubrication systems are designed and manufactured to meet customer requirements, including forced circulation, forced lubrication, or grease lubrication.

Roll Gap Adjustment

Roll Protection

To protect the rolls, frame, and other important parts from damage due to overload, a safety plate is installed between the gap adjustment push screw and the bearing box. If an overload occurs, this safety plate breaks, opening the roll gap and preventing damage to the rolls and frame. Hydraulic protection devices can also be provided depending on the application.

Reduction Gearbox

The reducer houses helical-type gears in a high-grade cast iron or welded steel casing, enabling quiet power transmission. All bearings are roller bearings, and lubrication for the gears and bearings is provided by an oil bath or forced lubrication system.

Bed

Nippon Roll’s mixing mills use common beds made of welded shaped steel, on which the main unit, reducer, and motor are all assembled. The common bed is supported and adjusted by leveling blocks. Depending on the application, a foundation type fixed with foundation bolts may also be used.

Emergency Braking Device

In an emergency, various switches installed around the machine can be activated to stop the rolls instantly. The types of braking devices and switch formats are designed, manufactured, and installed according to consultations.

Auxiliary Devices

Mixing mills come with auxiliary devices such as stock guides, blending devices, dividers, stock pans, and cutters. Stock guides can be fixed, hydraulically movable, or electrically movable, selected based on working conditions. Other attachments can be custom-designed to meet the needs of the client.

Intensive Mixers

Our intensive mixers are closed-type internal mixers of the Banbury type. Intensive mixers are designed to efficiently and economically pressurize and mix materials such as natural rubber, synthetic rubber, various resins, asphalt, cellulose, paint, and enamel. This machine is designed and manufactured with durability and wear resistance in mind to withstand all harsh operating conditions.
The mixing chamber is designed to circulate cooling water for rubber applications to suppress heat generation. For plastics and other materials, steam can be supplied for heating. The mixers are named according to the volume of the chamber, and the types are broadly classified into drop door types and slide door types based on the discharge method.

・Uses of Intensive Mixers

• 1.Mastication of natural rubber
• 2.Mixing various rubbers with carbon black (master batch)
• 3.Incorporating vulcanizing agents into rubber (final mixing)
• 4.Mixing various types of rubber
• 5.Mixing PVC (soft and rigid)
• 6.Mixing various types of plastics
• 7.Mixing flooring tiles (rubber, plastic, asbestos, asphalt, etc.)
• 8.Mixing various adhesives
• 9.Mixing various chemicals

・Features of Intensive Mixers

• 1.Can accommodate any shape as long as it fits in the input size. Suitable for a wide range of materials.
• 2.Superior mixing effects and high efficiency
• 3.Effective cooling and heating with temperature control
• 4.Maintains performance under harsh operating conditions
• 5.Long lifespan
• 6.Easy operation and safe to work with

Mixing in Intensive Mixers

・Overview of Intensive Mixer Structure

Drive System

The two rotors are each connected to the output shaft of the reducer via gear couplings. They are driven by the main motor through the reducer. Consequently, the gears that provide the rotational ratio to the two rotors are also incorporated within the reducer.

Rotors

The two rotors rotate at a fixed ratio to perform mixing. They are made of cast steel, and the blade sections have specially designed curves. The blade tips are hardened and improved for wear resistance through stellite welding. The rotor surface is finished with hard-chrome plating. The interior is hollow to allow for the circulation of cooling water, heating steam, or heat transfer oil.

Rotor Bearings and Lubrication

The Intensive Mixer uses roller bearings and they are housed in metal bodies. Lubrication is performed via forced circulation lubrication from a separate oil tank.

Mixing Chamber

The mixing chamber is composed of four walls made up of metal bodies and mixer bodies. The mixer bodies are hollow to allow the circulation of cooling water or steam. Specifically, for cooling, there are methods such as jet site, drilled site, and jacket types.

Powder Seal Device

Special devices are installed between the mixing chamber and rotor shafts to prevent leakage of the mixed material from the chamber. These devices include MS, DS, and RS types, which are chosen based on the mixed material and conditions.

Raw Material Feeding and Pressurization

Raw materials are fed into the hopper via conveyors, chutes, or manually. The hoppers are designed and manufactured in various types, including single-opening, double-opening, and those with side chutes for chemical addition. Once the raw materials are fed, the floating weight descends by the air cylinder from above, performing pressurization and mixing.

Discharge Device

After mixing is completed, the mixed material is discharged through the discharge door. Discharge devices are broadly classified into two types: slide door and drop door. The slide door type opens and closes by sliding the door using an air or hydraulic cylinder from below. The drop door type opens and closes by rotating the door using a rack and pinion mechanism or a rotary actuator driven by a hydraulic unit and hydraulic cylinder. The advantages of the drop door type are short opening and closing times, no material retention around the discharge, and complete prevention of leakage from the door.

Reducer

The reducer is a sealed casing that incorporates reduction gears and friction gears to provide the rotational ratio to the rotors. The gears use a single helical tooth design. All bearings are roller bearings, and lubrication is forced circulation lubrication along with the gears.

Control Panel

The control panel is usually mounted on the side of the feed opening. It includes air control valves, steam and water control valves, timers, pressure gauges, temperature indicators, ammeters, and other instruments. Depending on the requirements, standalone control panels with various operation buttons, recorders, and circuits can also be designed and manufactured. Recording items can include motor power, motor current, rotor speed, drop door temperature, inner chamber wall temperature, bearing temperature, powder seal part temperature, and heat medium supply temperature, among others, tailored to various requirements.