What is a Rubber Calender?
Calendering is the use of strong shearing force between rollers and the corresponding processing temperature, so that the viscous-flowing material is extruded and extended many times, and finally becomes a sheet product with width and thickness. Both plastics and rubbers have a calendering process, and polyvinyl chloride resin is the raw material in plastics.
Calendering is the use of strong shearing force between rollers and the corresponding processing temperature, so that the viscous-flowing material is extruded and extended many times, and finally becomes a sheet product with width and thickness. a processing method.
In the process of calendering, with the help of the shear force produced between the rollers, the material is extruded and sheared many times to increase plasticity, and it is extended into a thin product based on further plasticization. The extrusion and shearing action of the roller on the plastic changes the macrostructure and molecular shape of the material, and plasticizes and extends the plastic under the coordination of temperature. As a result of the rollers, the layer becomes thinner, while stretching increases both the width and the length of the layer. During the calendering process, while the roller is extruding and shearing the material, the roller is also subjected to the reaction force from the material. The force that tries to separate the two rollers is called the separation force. The rollers can be designed and processed into a slightly waisted drum shape, or the shafts of the two rollers can be adjusted to cross a certain angle or prestressed, which can overcome or reduce the harmful effect of the separation force to a certain extent and improve the calendered products. uniformity of thickness. During the calendering process, the thermoplastic is subjected to large shear stress, so the macromolecules will be oriented along the advancing direction of the film so that the resulting film has anisotropy in physical and mechanical properties. This phenomenon is calendaring effect. The size of the calendering effect is affected by the calendering temperature, rotation speed, feed thickness, physical properties, etc., heating up or increasing the calendering time can reduce the calendering effect.
What is the Calendering Effect?
Due to the large shear stress and tensile stress caused by the speed ratio in the longitudinal direction of the calender on the calender, the calender also produces molecular orientation along its longitudinal direction, so the film has anisotropy in physical properties. This phenomenon is called calendering effect or orientation effect in calendering. The size of the calendering effect is affected by factors such as the calendering temperature, the rotational speed and speed ratio of the rollers, the amount of material in the roll gap, the thickness of the product, and the properties of the material. The calendering effect makes the calendered product anisotropic. The tensile strength and elongation at break increased parallel to the calendering direction, while the tensile strength and elongation at break perpendicular to the calendering direction decreased. When heated in the free state, the film shrinks in the longitudinal direction and expands in the transverse direction and thickness due to the effect of desorption. Therefore, the thinner the calendered product, the more difficult it is to guarantee its quality. This is why the calendering method is rarely used when the film thickness is less than 0.05mm, and the extrusion blown film is used for production.
What Calendering Equipment is There?
Mixing machinery:
Plastic refining machinery:
Calendering machinery:
The basic structure of the calender is mainly composed of a machine base, a frame, a roller, a roller distance adjustment device, a stopper device, a roller bearing, a lubricating device, a transmission device, and heating and cooling devices.
Calendering is the use of strong shearing force between rollers and the corresponding processing temperature, so that the viscous-flowing material is extruded and extended many times, and finally becomes a sheet product with width and thickness. a processing method.
In the process of calendering, with the help of the shear force produced between the rollers, the material is extruded and sheared many times to increase plasticity, and it is extended into a thin product based on further plasticization. The extrusion and shearing action of the roller on the plastic changes the macrostructure and molecular shape of the material, and plasticizes and extends the plastic under the coordination of temperature. As a result of the rollers, the layer becomes thinner, while stretching increases both the width and the length of the layer. During the calendering process, while the roller is extruding and shearing the material, the roller is also subjected to the reaction force from the material. The force that tries to separate the two rollers is called the separation force. The rollers can be designed and processed into a slightly waisted drum shape, or the shafts of the two rollers can be adjusted to cross a certain angle or prestressed, which can overcome or reduce the harmful effect of the separation force to a certain extent and improve the calendered products. uniformity of thickness. During the calendering process, the thermoplastic is subjected to large shear stress, so the macromolecules will be oriented along the advancing direction of the film so that the resulting film has anisotropy in physical and mechanical properties. This phenomenon is calendaring effect. The size of the calendering effect is affected by the calendering temperature, rotation speed, feed thickness, physical properties, etc., heating up or increasing the calendering time can reduce the calendering effect.
What is the Calendering Effect?
Due to the large shear stress and tensile stress caused by the speed ratio in the longitudinal direction of the calender on the calender, the calender also produces molecular orientation along its longitudinal direction, so the film has anisotropy in physical properties. This phenomenon is called calendering effect or orientation effect in calendering. The size of the calendering effect is affected by factors such as the calendering temperature, the rotational speed and speed ratio of the rollers, the amount of material in the roll gap, the thickness of the product, and the properties of the material. The calendering effect makes the calendered product anisotropic. The tensile strength and elongation at break increased parallel to the calendering direction, while the tensile strength and elongation at break perpendicular to the calendering direction decreased. When heated in the free state, the film shrinks in the longitudinal direction and expands in the transverse direction and thickness due to the effect of desorption. Therefore, the thinner the calendered product, the more difficult it is to guarantee its quality. This is why the calendering method is rarely used when the film thickness is less than 0.05mm, and the extrusion blown film is used for production.
What Calendering Equipment is There?
Mixing machinery:
- Mixer
- The mixer is a raw material compounding equipment on the production line of calender molding products. Common ones are ribbon mixers, Z-type mixers, and high-speed mixers.
- Ribbon mixer: A ribbon mixer is also called a kneader. It was used earlier in the mixer. It consists of a frame, an upper cover, a stirring paddle, a mixing chamber, and a discharge device.
- Z type mixer: The Z-type mixer is a kneader, so named because the shape of the stirring paddle is approximately Z-shaped. The structure of the Z-type mixer is more complicated than that of the ribbon mixer. It also consists of a mixing chamber, a stirring paddle, and a transmission. The mixing chamber of the Z-type mixer is composed of two semi-cylindrical shapes to form a W shape. The discharge method can be at the bottom of the mixing chamber, or the mixing chamber can be turned over to form an inclined angle, and the material can be discharged from the upper part of the mixing chamber.
- High-speed mixer: The high-speed mixer is the result of improving the changing structure based on the previous mixers. Because of the high working speed of the stirring paddle, people are used to calling it a high-speed mixer. The high-speed mixer also consists of a mixing chamber, a stirring paddle, and a transmission. Due to its relatively high working speed, the shape of the stirring paddle is different from that of ordinary mixers. The stirring of raw materials is completed by cooperation with the baffle plate.
Plastic refining machinery:
- Internal mixer: The internal mixer evolved from the open mill. The internal mixer is to replace the two rollers of the open mixer with rotors processed into special shapes and seal them up. Through the movement of the two rotors, the material is subjected to continuous shearing and kneading in the closed chamber. The internal mixer is mainly composed of a mixing chamber, rotor, pressing device, unloading device, heating, and cooling device, transmission device, and other parts.
- Open mill, refiner: Replace the two rotors of the internal mixer with two rollers, and uncover the mixing chamber. It became a mill. The open mill is simple in structure, easy to manufacture, and easy to operate, and is widely used in the plastic products industry. The disadvantage is that the workers consume a lot of physical strength, and the plastic sheets need to be mixed by hand at higher temperatures.
- Extruder: The extruder is the feeder. To improve the utilization rate of the equipment, and improve the quality and output of plastic refining, the extruder was developed. The extruder consists of an extrusion system, feeding system, transmission system, heating system, and electrical control system.
Calendering machinery:
The basic structure of the calender is mainly composed of a machine base, a frame, a roller, a roller distance adjustment device, a stopper device, a roller bearing, a lubricating device, a transmission device, and heating and cooling devices.
- Sort by the number of rollers: The roller is the main part of the calendering equipment. The number of calender rolls can be divided into the two-roll calender, three-roll calender, four-roll calender, and five-roll calender.
- Sort by roller arrangement: According to the standard GB/T13578-92, it can be divided into I-shaped, L-shaped, inverted L-shaped, and S-shaped. In addition to the standard provisions, there are Z-shaped and S-shaped and L-shaped composed of five rollers.
- I-shaped calender "I"-shaped calender is a relatively early structural form, mainly used for calenders consisting of two rolls and three rolls. It is now mainly used for the production of thicker films and sheets. The calender with this structure has the advantages of simple structure, easy manufacture, and low manufacturing cost. However, the application is inconvenient, manual feeding is required, the feeding amount is not uniform, and the uniformity of the thickness of the formed film product is poor.
- L-shaped calender Add a roller to the lower roller side of the I-shaped three-roll calender to become the L-shaped four-roll calender. The L-shaped calender is more suitable for the production of plasticizer-free products. If plasticizer-containing products are produced, the apparent quality of the products will be affected by the action of volatile gases such as plasticizers. This kind of structure has a low feeding position. During production, foreign objects such as tools are easy to fall between the two rollers, causing damage to the roller surface. Special attention should be paid to frequent inspections during production.
- Inverted L-shaped calender The calender with the inverted L structure is to add a roller to the upper roller side of the I-shaped three-roll calender. Calenders with this structure are currently widely used in China. The quality of PVC film products produced by the inverted L-shaped calender is relatively stable, the thickness of the products is uniform, and the error value is small. The feeding position is relatively high, and the production is relatively safe. Products will not be affected by volatile gases such as plasticizers.
- S-shaped or Z-shaped calender The structure and composition of S-shaped and Z-shaped calenders are the same. If the horizontally arranged Z-shaped four-rollers are rotated at an angle, they become S-shaped four-rollers. Both arrangements are suitable for the production of shaped soft and rigid films and sheets. It is also ideal for the production of double-sided lamination of artificial leather. The force between the rollers of the S-shaped or Z-shaped calender is relatively uniform, the size of the force tends to be the same, and there is no floating phenomenon of the rollers. The thickness of the products produced is uniform, the error variance is small, and the product quality is stable. The running distance of the molten material on the four rollers is nearly equal, and the temperature change of the molten material when running on the roller surface is small, which is beneficial to the stability of the product quality during the high-speed production of soft films. The feeding of the melt is easy and the operation is relatively convenient.
Reference: ppfocus
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