Rubber calendering machine common problems and solutions

1、Calendering process and calendering principle?
In the manufacture of rubber products, the process of making a certain thickness, width or shape of film from the blended rubber in advance, or hanging a thin rubber layer on the textile, is called calendering. Calendering can be used to complete the operation of pressing, pressing, gluing, rubbing, laminating, thin pass and filtering rubber.
Calendering principle: When the rubber is added to the calender between the two working rollers, the rubber is brought into the roller gap due to the rotation of the rollers, and the rubber is rolled into a film with a thickness and width. During the calendering process, the adhesive material flows viscously on the one hand and deforms elastically on the other. Therefore, the various process phenomena in calendering are related to the fluidity of the rubber and the viscoelasticity of the rubber.

2、What kinds of calendering machines are there? What are the specifications and models?
Calender is a relatively sophisticated and complex machinery and equipment, and there are many types. There are several classification methods as follows:
According to the number of working rollers: double-roller, three-roller, four-roller.
According to the use of the classification are:
Sheet calender: used for pressing sheet or textile paste, usually three rollers or four rollers, each roll speed is the same.
Calender: used for textile rubbing, usually three rollers, with certain speed ratio between rollers.
General-purpose (universal) calender: This calender has the functions of the above two types of calenders, usually three or four rollers, and the speed ratio of each roll can be adjusted by the auxiliary gear.
Press calender: Used for manufacturing films with patterns or certain shapes on the surface, one of the rollers is engraved with a pattern.
Steel wire calender: It is used for gluing steel cord fabric and consists of four rollers.
According to the arrangement of the rollers, there are: I type, △ type, T type, L type, Z type, S type, etc.
The specification of calender can be expressed by the outer diameter of the roller × the length of the working part of the roller, such as calender specification Φ610×1730. The model of our calender can be expressed as XY-4T-1730, where XY means rubber calender, 4T means four-roller arrangement. 1730 means the length of the working part of the roller (mm). .
3、Why do you need to use compensation measures when designing calender
In the process of calendering machine, when the rubber material passes through the roll pitch, the transverse pressure given to the roller is very high, and the weight of the roller itself causes the roller to produce a certain elastic bending (the bending degree is called deflection), which results in the phenomenon that the calendered film is thick in the middle and thin on the sides. In order to overcome this drawback, usually in the design of the calender, some compensation measures are taken to ensure the precision of calendering, commonly used compensation methods are; concave and convex coefficient method (in high method); axis cross method and anti-bending method (to load method), etc.
4、What is the calendering effect, and how does it affect the performance of the product?
   The difference in performance of calendered products in the longitudinal and transverse directions is called the calendering effect, i.e., the tearing strength along the longitudinal direction of the film (calendering direction) is large, the elongation is small, and the shrinkage is large; while the tearing strength along the transverse direction of the film is small, the elongation is large, and the shrinkage is small. The main reason for the calendering effect is that the rubber molecules and needle-like or flaky particles
The calendering effect is mainly due to the orientation arrangement of rubber molecules and needle-like or flaky particles after calendering.  For the calendering effect, from the processing point of view, should be eliminated as far as possible, otherwise it will cause the deformation of semi-finished products (longitudinal and transverse direction shrinkage inconsistency), to bring operational difficulties. However, from the perspective of the product, some products require high longitudinal strength (such as rubber wire) to be used; in some products require uniform strength distribution (such as ball guts), it should be eliminated. When conducting physical and mechanical properties tests, pay attention to the cutting direction should be consistent with the calendering method.
   Eliminate the approach: try not to use or not to use needle, flake filler (such as calcium carbonate, clay, talc); improve the calendering temperature, increase the molecular activity energy.

 5, calendering preparation process in which? What are the requirements for each purpose?
(1) Hot refining: before the rubber is added to the calender, it should be refining in the open refiner first, in order to improve the uniformity of filler dispersion and thermal plasticity in the rubber, so that the rubber is soft and easy to calender. This process is called hot refining or preheating. It is divided into two steps: the first step is called coarse refining, using low temperature thin pass to make the rubber soft and uniform; the second step is called fine refining, with larger roll distance and higher roll temperature to increase the rubber temperature and obtain uniform and larger thermal plasticity, in order to make the rubber warm up and soften quickly, the roll speed ratio of the refiner is large. It can take the range of 1:1.7~1.28. The amount of rubber piled up on the hot refiner should be kept at a certain level during operation.
The conditions of coarse and fine refining are controlled as follows:
Coarse refining Roll 2-5mm Roll temperature 40-45℃ Thin pass 7-8 times
Fine refining Roll distance 7-10mm Roll temperature 60-70℃ 6-7 times through
2) Feeding and conveying: The feeding method has a very important relationship to prevent air from mixing into the rubber. Generally, continuous feeding is used, then the amount of feeding is equal to the amount of consumption. The number of additions should be more, and the amount of each addition should be less, so as to prevent air entrapment.
(3) calender operation preparation: check the equipment before driving, the focus is: roller surface condition, including whether the position is normal, whether the temperature is uniform and consistent, there is no foreign body or trace; check whether the bearing rotation is normal, and observe the refueling condition, surface thermometer, thickness gauge, splint, winding shaft bar is ready, the motor adjustment is normal, the rotation sound has no abnormal.
(4) temperature control: control the calender roll temperature is an important part of ensuring the quality of calendering, generally synthetic rubber calendering roll temperature is lower than the natural rubber, the upper roll temperature is higher than the middle and lower roll temperature. Roll temperature also depends on the formula, plasticity, process method, speed and other calendering methods.
(5) Textile drying, textile in the calendering before all must be dried to reduce the water content of the textile to improve the temperature of the textile. After drying, the textile should not be parked, so as not to absorb moisture back to moisture. Textile moisture content should generally be controlled at 1-2%, moisture content will reduce the adhesion of rubber and textile, but too dry will also damage the textile or make the textile hard, reducing the strength.
6、What are the operation methods of pressing process?   
Pressing is to press the preheated rubber material into a film of certain thickness and width with the calender at the same roll speed. There are two types of operation methods: middle and lower rolls without glue accumulation and glue accumulation. The middle and lower rolls are close to or slightly lower than the middle rolls, and a proper amount of accumulation of glue can make the film smooth and reduce bubbles, and the denseness of the film is good.
Good, but it will increase the calendering effect. This method is applicable to styrene-butadiene rubber. However, it should not be operated too much, otherwise it will bring in air. No accumulation of rubber method is the opposite, applicable to natural rubber.
7、What factors should be controlled when pressing the sheet?
1) Roll temperature: The roll temperature should be determined according to the nature of the rubber material. Usually, the mixing temperature should be higher for the rubber with high rubber content or elasticity. In order to make the film move smoothly in the roller, the temperature of each roller should be a certain temperature difference. For example, natural rubber is easy to stick to the hot rollers, so when the film moves from one roll to another, the temperature of the latter roll should be higher. Butyl rubber, on the contrary, its adhesion to the roller is increased with the decrease of the roller temperature.
2）Plasticity of rubber material: large plasticity, good fluidity, easy to get smooth film, but too large plasticity, and easy to produce sticky roller phenomenon, small plasticity, the surface of the pressed film is not smooth, shrinkage rate is large.
(3) Roll speed: fast roll speed, large production capacity, but the roll speed should be decided according to the plasticity of the rubber, plasticity of the rubber, roll speed can be faster; plasticity is small, the roll speed should be slower.
8、What are the requirements for the quality of the press sheet? What are the common quality problems? What are the main reasons?
The quality requirements of the pressed sheet are: smooth surface, hundred degree uniformity, no wrinkles, no self-sulfur particles, dense internal rubber and no bubbles.
Quality faults and causes that often occur during the process:
1) Internal bubbles, mainly due to high water content of compounding agent in the rubber; volatile softening agent; high calendering temperature; too much rubber accumulation; improper way to put in the rubber roll; more water in the return rubber and too thick calendering film.
2）Surface crinkling; the main reason is that the plasticity of rubber is low, so that the shrinkage rate is large; the ratio of rubber and return rubber is uneven, and the heat refining is uneven, so that the rubber itself is soft and hard, and the shrinkage is inconsistent, etc.
(3) Surface roughness; the main reason is that the plasticity of rubber is small, the roll temperature is low, the calendering speed is large, and the rubber has self-sulfur particles, etc.
(4) Uneven film thickness, the main reason; uneven plasticity of rubber; large fluctuations in rubber temperature, resulting in uneven shrinkage, in addition to the operation of both sides of the roll distance is not consistent or winding tension is not equal, will also affect the film thickness.

9、What is laminating and what are the process methods and requirements for laminating?
Lamination is the operation of laminating two thin layers of film into one by calender. It is usually used to manufacture thicker films with higher quality requirements, as well as films composed of two different adhesive materials, sandwich layer films, etc.
The laminating process methods are:
(1) Two-roller calender lamination, which is carried out by ordinary two-roller refining machine with equal speed. The advantage is that the lamination thickness is larger (up to 5 mm) and the operation is simple, but the precision is poor.
2）Three-roller calender lamination, using a three-roller calender to laminate the previewed film or tape with the newly calendered film.
(3) Four-roller calender laminating, this method can calender two pieces of film at the same time and laminating, high efficiency, good quality and accurate specification, but the calendering effect is larger. When laminating films, it is required that each film has the same plasticity, otherwise it will produce delamination and drumming. When laminating two layers of film with different formulas and thicknesses, it is best to use the "simultaneous lamination method", in which two fresh films from the calender are laminated, so that they can be completely sealed and free of bubbles.
The film will not wrinkle, but the calendering effect is larger.
10、What are the key points to note when calendering?
Calendering is the process of pressing the rubber into semi-finished products with certain cross-sectional shape or pattern on the surface, such as shoe outsoles and force tires.
Pressing requires accurate specification, clear pattern and dense rubber. Therefore, there are strict requirements for the rubber formula and process conditions.
The rubber formula should mainly control the rate of rubber content. When the rate of glue is high, the pattern will disappear easily after pressing. Therefore, in the formula of pressed rubber, appropriate amount of filler and softener should be added. The addition of recycled rubber and vulcanized grease in the compound is an effective measure to prevent the pattern from collapsing.
The main purpose of compression molding is to use the fluidity of the rubber to shape. Therefore, the plasticity of the rubber material is required, and the plasticity of the compounding rubber, the degree of heat refining, and the proportion of return rubber should be strictly controlled.
Film from the calender out, should take the rapid cooling method, so that the pattern set, to prevent flat collapse deformation.
11、What is the purpose of textile and glue and hanging glue?
Textile hanging glue is to make a thin layer of glue on the surface of the textile through the gap of the calender roller to make a hanging glue curtain or a hanging glue canvas as the skeleton layer of rubber products.
The purpose of hanging glue of curtain or canvas is to make the textile and line, layer and layer closely synthesize each other as a whole, together with the role of external forces, and after hanging glue, can also improve the elasticity of the textile, water resistance, to ensure that the products have good performance. 
 12、What are the methods of hanging glue and how do they differ?
Textile hanging glue can be divided into three kinds of glue, pressure glue and glue rubbing.
Glueing is to use the pressure of two rollers with the same speed on the calender to glue a certain thickness of film on the textile. The difference between pressure gluing and gluing is that when gluing is carried out, there is an accumulation of glue between the two rollers of pressure gluing, so that the pressure of the accumulation of glue can be used to squeeze the glue into the seam of the cloth, thus improving the adhesion of the cloth to the glue.
Rubber rubbing is to use the shear force and roller pressure generated by the different speed of the calender rollers to squeeze and rub the rubber into the gap of the textile to improve the adhesion of the rubber to the textile.
The rubber rubbing method can be divided into two kinds: one is the middle roller rubber method (also called thin rubbing or package rubbing), when the textile passes through the middle and lower roller seam part of the rubber is rubbed into the textile, the remaining rubber is still wrapped in the middle roller. The adhesion obtained by this method is higher, but the amount of hanging glue is small, and the flex resistance of the finished product is poor, the other is the middle roller does not wrap method (also known as thick rub or light rub method), when the textile through the middle and lower roller seam, the glue material is all rubbed into the textile, the middle roller no longer wrapped glue, the glue layer obtained by this method is thicker, which can improve the flex resistance of the finished product, but the adhesion is lower, and easy to fluctuate, and the amount of glue is also more.
13、What are the effects of roll temperature, roll speed and plasticity of rubber on textile hanging?
Appropriate increase of roll temperature can increase the fluidity of rubber, smooth the surface of calendering tape, and the penetration of rubber is large, which is good for improving the adhesion. However, if the roll temperature is too high, the glue material is easy to scorch.
If the plasticity of the rubber is large, the fluidity is good, the penetration is large, and the adhesion between the rubber and the cloth is high; the surface of the cloth is smooth, and the shrinkage is small;
The roll speed is fast and the calender speed is fast, because the rubber is under pressure for a short period of time, it shows greater elasticity, the pressure is small and the adhesion between rubber and cloth is poor.
The speed of calendering should depend on the plasticity of the rubber material, the plasticity is large, the speed can be faster, at present the factory usually adopts the calendering speed as follows:
35-40m/min.
Thin cloth rubbing 5-25m/min
Thick sail rubbing glue 30-40m/min
14、The common quality problems and their causes in the operation of hanging glue?
1）Falling glue (falling skin) is the phenomenon of bad adhesion of glue and textile. The reasons are: the textile is not well dried, high water content; there is oil, dust, etc. on the surface of the cloth; the rubber is not hot enough, the plasticity is small, the calendering temperature is low, the speed is too fast, the roll distance is too large.
2）Curtain fabric jumping and bending, the reasons are: uneven plasticity of rubber material, fabric roll is too loose; too much rubber accumulation in the middle roller, local force is too large, the weft line of curtain fabric is not uniform.
(3) out of the pocket, the phenomenon that the middle of the curtain fabric is loose and the two sides are tight. The reasons are: the textile is unevenly stressed, the middle is bigger than the side, the temperature of the lower roller is too high, the adhesive surface sticks to the lower roller's stress; the textile itself has uneven density and the elongation is not consistent.
4）Pressing deviation, pressing bad, folding, pressing deviation is caused by the roll distance is large on one side and small on the other; incorrect cloth delivery; inconsistent roller bearing tightness and so on. Pressing bad is generally caused by improper operation, such as roll distance, speed and the amount of accumulated glue is not well controlled, etc. Folding is due to the padding rolled too loose, hanging glue cloth and cooling roller speed inconsistent
caused by.
5) The surface is pockmarked or has small bumps due to: insufficient heat refining of rubber; small plasticity, uneven heat refining; high heat refining or calendering temperature, self-sulfur rubber or self-sulfur rubber particles in the rubber mix.