Rubber calendering process

Rolling refers to the mix on the calender frame made of film or tape semi-finished material process, which includes tablet, close quote, profiling and textiles hanging plastic and other operations.

A: calender

Calender generally consists of work rolls, frame, frame, gear, speed and pitch devices, roller heating and cooling system, lubrication system and emergency stop devices and other components.
Calender many different types, to meet different process requirements, a total set of rollers there are two, three and four dollars.

Two rollers are arranged in the form of vertical and horizontal.
Three-roll arrangement in the form of an upright, L-type, triangular type.
Four-roll arrangement in the form of L, Z type and S-type and other.
The number and arrangement in the form of rolls of various process operating ease, semi-finished rolling the level of quality has a significant impact.

Process according to purpose to points, there are tablet calender, calender eraser, general calender, pressure-type rolling machine, laminating calender, steel rolling machines.

Tableting calender: calendered film for textile or gum paste. Mostly three-roll or four-roll, each roll speed equal.
Eraser calender: textiles for the eraser. Usually three-roll, between the rollers have a certain ratio, the roll speed is greater than the upper and lower roll speed. With rubber, the lower ratio between the rollers rub-woven fabric.
General calender: also it is known as the universal calendar, both the role of the two calender. Usually three or four roll roller speed ratio between each roll can be changed.

II: calendering process

1: Prepare before the rolling process
Before rolling, the need for plastic materials and textiles pre-processing technology is ready.

1.1 hot glue for plastic materials and refining

Before entering the rubber calender, need to first turn on the hot mill refining, the refining process called hot or warm up. Soak aims to improve the rubber mixing uniformity, to further increase the plasticity of rubber to improve the rubber compound to increase the thermal plasticity. Soak two-step process in general, are open on the miscellaneous mill, the first step is called smelting, pass through the low-temperature thin, soft rubber make uniform; the second step is called fine refining, roll away from the larger roll temperature higher, in order to raise the temperature of rubber, thermoplastic larger. While promoting rubber and textile adhesion. Crude refining roll temperature is generally 40 ℃ -45 ℃; roll from 2-5mm; thin through 7-8 times. Thin refining roll temperature is usually 60 ℃ -70 ℃; roll from 7-10mm; refining turned 6-7 times.
Soak for glue and processes: smelting - refining fine - Glue - calender rolling.

1.2 textile drying

In order to improve the adhesion properties of rubber and textiles, rolling to ensure quality, the need for textile drying, reducing the water content of textiles, general control of moisture content within 1% -2%, the moisture content is too general to reduce rubber adhesion and textiles, but too dry will harden textiles, injured in the rolling process, reduce the strength. Also in the drying process, so that the textile material is also conducive to a rubber temperature by thermal motion of molecules to permeate the cracks in the textile, enhance the adhesion of the rubber and textiles.
Drying textile generally in vertical or horizontal drying machine, dryer is composed of a series of drying rollers. After drying the textile directly into the calender rolling, you can not park, so as to avoid a resurgence of moisture, so in practice dryer calender is composed of the linkage.

2: rolling process

1) tablet
Tablet is already preheated plastic material used in the case of calender roll speed equal to prepare a certain thickness and width of the film, can be used two rolls, three-roll or four-roll calender machine.

A: Effect of tabletting speeds as follows

 roll temperature roll temperature depends on the nature of the compound, usually with plastic or high elasticity of rubber roller temperature should be higher (increased thermoplastic); gum containing low or small elastic rubber roller temperature should lower. In addition, in order to make a smooth film between the rolling roller, between the rollers should have a certain temperature difference. For example, natural rubber package hot roll, the film is moved from one roll to another roll, the latter roll temperature should be higher; and general synthetic rubber, by contrast, is easy to pack cold roll, roll temperature at this time so the order should be natural rubber instead.
 rubber plasticity plasticity large, good fluidity, film smoothness, shrinkage is small, but easy to produce sticky roller phenomenon plasticity is too large; low plasticity, poor mobility, the film is not smooth, large shrinkage.
 roll speed roll fast, large capacity, but the shrinkage, the surface is not smooth. Calender roll speed should be based on the compound of plasticity, temperature.

B: tabletting often appears quality problems and reasons

Quality tablet are: smooth surface, uniform thickness, no crepe, internal rubber dense, no air bubbles. Causes of quality problems often appear as follows:
Internal bubbles: due to high moisture content of complexing agents, softeners large volatility, high temperature rolling, the plot too much glue, put the film properly, return water and more plastic, rolling thick film and the like.

Surface shrinkage: Because rubber low plasticity, shrinkage, rubber and plastic return ratio is uneven, soak inequality.

The film surface is not smooth: due to low plasticity of rubber, roll temperature low, rolling speed, rubber and other self-sulfur colloid.

Uneven film thickness: Due to the uneven plasticity rubber, plastic temperature fluctuations lead to uneven shrinkage, both sides of the roll gap is inconsistent, winding tension is not the same and so on.

2) fit
By calender bonding two thin layers of film bonded together process. Generally used to make a thick, high quality requirements of the film and two different compounds composed of film, cloth layer film and the like.
The method of bonding two roll calender bonding method, a three-roll calender bonding and four-roll calender bonding method. Four-roll calender fit together high efficiency, good quality, high precision, but the big rolling effect.

3) Pressure type
Pressure-type plastic material is a cross-sectional shape of certain semi-finished or patterned surface of the process of manufacturing shoes outsole, cycle tire tread and the like. Available two roll-pressure, three-roll, four-roll rolling machine, which must have a roll or several rolls engraved patterns.
For profiling requirements are: exact specifications, a clear pattern, dense rubber.
On the rubber formulation and process operation should pay attention to the following points:
Formula should be added the right amount of fillers to reduce gum content, so that rolling size, shape accurately, a clear pattern;
Formulated with appropriate softening agent, increase the plasticity of rubber, reduced elasticity;
If necessary, adding an appropriate amount of reclaimed rubber, reclaimed rubber to reduce rolling, extrusion expansion ratio improved semi-stiff, thereby making accurate specifications, a clear pattern;
To ensure that there is a constant rubber plasticity, for the plasticity of the mix, soak degree, return glue mixed with the proportion must be strictly controlled;
Pressure type used in the process to improve the roll temperature, reduce speed and other methods to improve the quality of rolling;
Rolling out of the semi-finished products to be rapidly cooled, so that the pattern shape, flow pattern to prevent deformation.

4) textile hanging plastic

A: hanging plastic method

The method can be divided into hanging plastic glue stick, glue stick pressure and eraser three.

Gum paste: is the use of two of the same speed on the calender rolls will stick to a certain thickness of the film on the textile process. Gum paste commonly used three-roll calender or four-roll calender, a three-roll can only stick side, four-roll time can be attached to both sides. When gum paste, the rotational speed of bonding two rollers should be the same, but the speed for two rubber rollers to the same, but also different, there is a certain ratio, helping to eliminate air bubbles, tight fit better.

Pressure gum paste: This method is identical in form with gum paste, the difference is two stickers have also accumulated a certain amount of glue between the rubber roller, use a pressure of stacking gel rubber cloth pressed into the cracks. This method is rubber, good adhesion, but the cord vulnerable.

Eraser: Eraser is extrusion pressure and shear roll calender roll utilizing different speed ratios produced the rubber squeeze rub textile gap to process. It is usually on a three or four-roll calender roll performed.
When the eraser work roll speed ratio of 1: 1.3-1: 1.5 range, the greater the ratio, the stronger the rub, rubber penetration, the better, but stretch a textile by the more big eraser usually used only for hanging plastic canvas.

B: hanging plastic process of the main factors

Plasticity: plasticity big rubber good liquidity, strong penetration, good adhesion plastic and cloth, tape smooth surface, small shrinkage, but low strength vulcanized rubber. Natural rubber gum paste plasticity 0.4-0.5, 0.5-0.6 degrees plastic eraser is more appropriate.

Roll temperature: high temperature roller, raise the thermoplastic rubber, but easy to produce when the temperature is too high scorch.

Roll speed: big roll speed, rolling speed, large capacity, but the compound force a short time, and shrinkage, the tape surface is not smooth. And because the force a short time, the penetration of rubber into the cloth cracks of a reduced ability to decrease the adhesion of glue and cloth. Slow roll speeds the opposite effect. Usually roll speed depends on plasticity of rubber may be, plasticity large, roll speed fast; small plasticity, slow roll speed.

Roll distance: When rolling on, roll plays for the glue effect, the roll gap according to the size of hanging plastic thickness to be. In cooperation with the lower roll from the paste, which directly affects the size of the roll from the hanging plastic quality. As the next roll distance is too small, and not through the textile or easily crushed; if the roll gap is too large, the loss of pressure rollers, glue is not well attached to the textile, poor adhesion.

C: hanging plastic common quality problems and reasons

Out of gum: the layer peeled off. Cause: The textile drying is not good, high moisture content; cloth with oil, dust and other debris; rubber soak uneven small plasticity; rolling temperature is low, fast, roller pitch too big.
Cord jumper bend: rubber plasticity uneven; cloth roll too loose; the rubber roller plot too, local excessive force; ply weft tightness.

Out of pocket: This is the central cord loose and tight on both sides of the phenomenon. Reason: textiles uneven force, the force is greater than the central edge; textile itself uneven density, elongation inconsistent.

Partial pressure, crushed discounts: partial pressure is due to roll away from the side of the large side of small, cloth delivery errors, inconsistencies caused tension roller bearings;

Crushed generally due to improper operation, resulting in such as roller pitch, speed, volume control is not good glue and other reasons. The discount is due to take-up mattress is too loose, hanging with a cooling roll tape speed inconsistencies caused.
Ma face or surface appear small pimple: The reason is usually insufficient rubber soak, small plasticity; soak uneven; high temperature rubber compound produced from sulfur or sulfur-containing particles from the like.

Third, several common characteristics of rolling rubber

1) Natural Rubber
Thermoplastic large and small shrinkage, easy rolling. Natural rubber easy to adhere to hot rollers, rolling should be proper control of the temperature difference between the rollers, so that the film can be smoothly transferred between rollers.

2) SBR
Thermoplastic small, large shrinkage, so for calendered rubber must be sufficiently masticated. Because of hot rolled SBR, sensitivity is significant, and its operation differ from natural rubber, natural rubber calendering temperature should be below (generally lower 5 ℃ -15 ℃), from high to low temperature difference between the rollers.

3) butadiene rubber
Rolling temperature should be lower than those of natural rubber, styrene-butadiene rubber rolled semi-finished material than the smooth, tight and supple.

4) Neoprene
Universal neoprene at 75 ℃ -95 ℃ when easy to stick rollers, rolling difficult. Rolling should be cryogenically (65 ℃ or less) or high-temperature method (95 ℃ above). After rolling to quickly cooled. If the rubber compound by adding a little wax, stearic acid or mixed with a small amount of butadiene rubber can be reduced sticky roller phenomenon.

5) EPDM
Good rolling performance, over a wide temperature range (80 ℃ -120 ℃) ​​continuous operation, when the temperature is too low rubber shrinkage, easy to produce bubbles. In addition, the rolling rubber should select the appropriate Mooney viscosity.

6) butyl rubber
In the absence of the filler is not rolled, long filler is easier rolling. Butyl rubber stick cold roll off the hot rollers, each roller should maintain a certain temperature range when rolling.

7) nitrile rubber
Thermoplastic small, large shrinkage in the rubber compound added fillers or softeners to reduce shrinkage. When the filler weight accounting for more than 50% of the raw rubber is important in order to obtain a smooth surface of the film rolling. Nitrile rubber compound viscosity is small, easy to stick chill roll.

Fourth, rubber calender precautions

Calendering process comprises the rubber compound into a certain film thickness and width; the pressure on the film some kind of pattern, as well as articles on the skeleton structure, covered by a thin layer of fabric glue (such as rubber insert, gum paste), etc. . Depending on the type of product and the appearance of specific calendering process have tabletting, compression type, ply rubberized canvas and eraser. Rubber calendered to produce the finished product (rubber balloon, balloon plugging, etc.) so that the characteristics of the rubber itself strengthened.

Rolling plastic material used should be required to have a good package rolls, mobility, scorch and contractility. During the formulation, should note the following:

1, the rolling characteristics of the various raw rubber: natural life and high strength plastic, roll package, good fluidity, easy rolled, followed by butadiene rubber, neoprene bag roll good, but sensitive to heat large, easy to produce sticky roller, SBR and NBR illiquid, difficult to compare rolling, rolling film shrinkage big, no matter what the choice of raw rubber, are required to have a sufficiently low viscosity in order to obtain good flowability;

2, the choice of filler: rolling in general, the amount to be blended with fillers, in favor of the rolling operation, carbon black, silica, calcium carbonate, are applicable. Clay should not be used, recycled plastic in favor of rolling;

3. Add softener can achieve good rolling effect, but should be selected according to specific requirements of the rolling operations, tableting requires film has some very nature, not easily deformed, the use of plasticizing effect is not too great softener: If the ointment . Guma solid resin, asphalt, rosin;

4, the curing system: calender normally produced at a higher temperature (90-110 ℃) ,, performed for the cure system of choice should be considered first scorch easily. Typically rolling rubber Mooney scorch time should be controlled in 20-25 minutes.