Rubber calendering process:
Calendering refers to the process of making the rubber into a film or a semi-finished product with a frame material on a calender, which includes operations such as pressing, pressing, pressing and spinning.
The calender is usually composed of working rollers, racks, stands, transmissions, speed control and distance adjusting devices, roller heating and cooling devices, lubrication systems and emergency stop devices.
There are many types of calendering machine, in order to meet the different process requirements, a total of two sets of rollers, three and four.
Second: calendering process
1: Preparation process before calendering
Before the rolling, the need for rubber and textile pre-processing, that is, preparation process.
1.1 compound of the heat and glue
Before the compound enters the calender, it is necessary to first reflow it on a hot melt mill. This process is called heat or preheating. The purpose of refining is to improve the uniformity of the mixing of the compound, to further increase the plasticity of the compound, to improve the temperature of the compound and to increase the thermoplasticity. The heat process is generally divided into two steps, are carried out on the miscellaneous, the first step is called rough refining, through the low temperature thin pass, so that the rubber becomes soft and uniform; the second step is called refining, roll distance, Higher, in order to improve the temperature of the compound, to obtain a greater thermal plasticity. While enhancing the adhesion of the compound to the fabric. Roughing roll temperature is generally 40 ℃ -45 ℃; roll distance 2-5mm; thin pass 7-8 times. And fine refining roll temperature is generally 60 ℃ -70 ℃; roll distance 7-10mm; refining 6-7 times.
Hot and glue process: rough refining - fine refining - for the plastic - calender rolling.
2: calendering process
The sheet is prepared by using a two-roll, three-roll or four-roll calender in the case of a pre-heated compound, which is made to have a certain thickness and width by means of a calender at a roller speed equal to each other.
The bonding process is a process in which two layers of thin film are bonded together by a calender. Usually used in the manufacture of thicker, higher quality requirements of the film and two different compounds composed of film, cloth film and so on.
There are two roll calendering method, three roller calendering machine paste method, four roller calendering machine paste method. Four-roll calendering machine with high efficiency, good quality, high precision, but the calendering effect.
3) pressure type
Pressure is made of plastic materials made of a certain shape of the semi-finished or surface pattern of the process, such as the manufacture of rubber shoes at the end of the tires, such as tires. The press can be carried out with two rolls, three rolls, four rolls calender, which must have a roller or a number of rollers engraved with patterns.
The requirements of the pressure type are: accurate specifications, clear patterns, rubber density.
Third, the rolling characteristics of several commonly used rubber
1) natural rubber
Thermoplastic, shrinkage is small, easy rolling. Natural rubber easy to adhere to the hot roller, rolling should be appropriate to control the temperature difference between the rollers, so that the film can be successfully transferred between the rollers.
2) styrene butadiene rubber
Thermoplastic small, high shrinkage, so for the rolling of the compound must be fully plastic. As the styrene butadiene rubber on the calendering heat, the sensitivity is very significant, its operation and natural rubber is different, the rolling temperature should be lower than the natural rubber (generally low 5 ℃ -15 ℃), the roller temperature difference from high to low.
3) Butadiene rubber
The calendering temperature should be lower than that of the natural rubber, and the rolled semi-finished product is smoother, tight and soft than the styrene-butadiene rubber compound.
General-purpose neoprene at 75 ℃ -95 ℃ easy to roll, difficult to roll. Calendering should be low temperature method (65 ℃ below) or high temperature method (95 ℃ above). After the rolling to quickly cool. If you add a little paraffin in the compound, stearic acid or mixed with a small amount of butadiene rubber can reduce the phenomenon of sticky roller.
5) Ethylene-propylene rubber
Rolling performance is good, can be in a wide temperature range (80 ℃ -120 ℃) continuous operation, the temperature is too low when the plastic shrinkage, easy to produce bubbles. In addition, the calendering compound should select the appropriate Mooney viscosity.
6) butyl rubber
In the absence of filler can not be calendering, packing for a long time easier to roll. Butyl rubber viscous roll, desorption roller, rolling each roller should maintain a certain temperature range.
7) nitrile rubber
Thermoplastic small, shrinkage, in the compound by adding filler or softener can reduce the shrinkage. When the weight of the filler accounted for more than 50% of raw rubber, in order to get the surface smooth film. Nitrile rubber rubber adhesive is small, easy to stick cold roll.
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