2.3 Rolling Process

Calendering is the process by which the mixing glue is made into film on the calendering machine or made into a semi-finished cloth with a skeleton material, which includes the operation of laminating, bonding, pressing type and textile hanging glue. The main equipment of the calendering process is calendering machine, calendering machine generally consists of a working roller, a rack, a chassis, a transmission device, a speed regulation and pitch device, a roller heating and cooling device, a lubrication system and an emergency parking device. There are many kinds of calendering machine, the working roller has two, three, four, the arrangement form two rollers have vertical and horizontal; The three rollers have upright, Gamma and triangular; The four rollers have Gamma type, L type, Z type and S type, etc. According to the process use of the main pressure sheet calendering machine (used for calendering film or textile adhesive, most three-roll or four-roller, each roll shape is different), glue calendering machine (used for textile glue, three rollers, each roller has a certain speed ratio, medium roller speed is large.
With the help of speed ratio into the textile), Universal calendering Machine (also known as Universal calendering Machine, both press and glue function, three-roll or four-roll, adjustable speed ratio), pressure type calendering machine, bonding calendering machine and steel wire calendering machine.
The calendering process generally includes the following processes: Preheating and dispensing of the mixing glue; guide and drying of the textile (and sometimes dipping glue)
Adhesive on the four-roll or three-roller calendering machine on the press or on the textile adhesive on the machine calendering semi-finished products cooling, coiling, truncation, placement and so on. Before the calendering, it is necessary to pre-process the rubber and textile, the glue into the calendering machine, it is necessary to first in the heat refinery, this process for heat or preheating, the purpose is to improve the mixing uniformity of the adhesive, further increase plasticity, improve the temperature, increase plasticity.
In order to improve the bonding performance of rubber and textile, to ensure the quality of calendering, it is necessary to dry the fabric, water content control in the 1-2%, low moisture content, fabric hardening, easy to damage in the calendering, high water content, poor adhesion. Several common rubber calendering properties of natural rubber thermoplastic shape, small shrinkage, easy to press, easy to adhere to the hot roller, should control the temperature difference of each roller, so that the film smooth transfer; butyl rubber thermoplastic small, shrinkage, so used for calendering of the adhesive to fully plastic. Because the thermal sensitivity of butadiene rubber to calendering is very significant, the calendering temperature should be lower than the natural rubber, the temperature difference of each roller is high to low; neoprene rubber in 75-95 ℃ easy to stick roller, difficult to delay, should use low temperature method or high temperature method, calendering to quickly cool, mixed with paraffin, hard ester acid can reduce the phenomenon of sticky roller;
Can be operated continuously in a wide temperature range, when the temperature is too low, the glue shrinkage is large, easy to produce bubbles, nitrile rubber thermoplastic small, shrinkage, in the glue type to add filler or softener can reduce shrinkage, when the weight of the filler is more than 50% of the weight of raw rubber, can get smooth surface film, nitrile rubber viscous small sticky cold roller.

2.4 Pressing out process
The pressure-out process is by pressing out the cylinder wall and screw parts of the role, so that the adhesive to achieve the purpose of extrusion and preliminary modeling, the pressure out process has also become extrusion process.
The main equipment for pressing out the process is the pressure out machine. The pressure-out characteristics of several kinds of rubber: natural rubber Press speed is fast, semi-finished product shrinkage is small. Body temperature 50-60 ℃, nose 70-80 ℃, mouth 80-90 ℃; butadiene rubber pressure slow, compression deformation, surface roughness, body temperature 50-70 ℃, head temperature 70-80 ℃, mouth temperature 100-105 ℃; Neoprene press out before the use of full heat, fuselage temperature 50 ℃, nose ℃ , Mouth 70 ℃; ethylene Propylene rubber press speed, shrinkage is small, body temperature 60-70 ℃, nose temperature 80-130 ℃, mouth 90-140 ℃. Nitrile rubber pressure out poor performance, pressure should be fully hot.
The fuselage temperature is 50-60 ℃ and the nose temperature is 70-80 ℃.

2.5 vulcanization Process

Earlier, the main use of natural rubber was simply to do a eraser; it was later used to make small rubber tubes. Until 1823, British chemist Mchintosh invented the dissolution of rubber in coal tar and applied it to a cloth to make tarpaulins that could be used in the manufacture of raincoats and rain boots. However, the raincoat and rain boots melt in the summer and become hard and crisp in the winter. In order to overcome this shortcoming, many people were trying to figure it out at the time. American inventor Charlie Goudeil, who is also experimenting with rubber modification, heats natural rubber and sulfur together in the hope of obtaining a substance that remains dry and elastic at all temperatures throughout the year. He was not successful until February 1839. One day he mixed rubber, sulfur and turpentine into a pot (sulfur was only used for dyeing) and accidentally splashed a mixture of pots onto a scorching stove. To his surprise, the mixture did not melt after falling into the fire, but remained charred as it was, and the remaining incomplete charred mixture in the furnace was elastic. He peeled what had been splashed off the stove, only to find that he had prepared the elastic rubber he wanted.
After continuous improvement, he finally invented the rubber vulcanization technology in 1844. In the production process of rubber products, vulcanization is the last processing process. Vulcanization is the crosslinking process in which rubber macromolecules change from linear structure to mesh structure under certain conditions. The Vulcanization method has three kinds of cold vulcanization, room temperature vulcanization and thermal vulcanization. Most rubber products use thermal vulcanization. Thermal vulcanization equipment has sulfide cans, plate vulcanizer and so on.

1 overview
The main raw materials of rubber products are raw rubber, various complexes, as well as fiber and metal materials as skeleton materials, the basic production process of rubber products includes plastic refining, mixing, calendering, pressing, molding, vulcanization 6 basic processes.
Rubber processing process is mainly to solve the plastic and elastic contradictions of the process, through a variety of processing means, so that elastic rubber into plastic plastic rubber, in the addition of a variety of complexes to make semi-finished products, and then through vulcanization is plastic semi-finished products and become high elasticity, physical and mechanical properties of rubber products.

2 Rubber processing Technology
2.1 Plastic Refining Process

Raw rubber molding is the process of transforming raw rubber from a strong elastic state to a soft, easy-to-process plastic state by means of mechanical stress, heat, oxygen, or the addition of certain chemical reagents.
The purpose of raw rubber molding is to reduce its elasticity, increase plasticity, and obtain appropriate fluidity to meet the requirements of various processing processes such as mixing, sub-perfunctory, calendering, molding, vulcanization and sizing, sponge gum manufacturing, etc. Mastering the appropriate plastic plasticizing degree is very important to the processing of rubber products and the quality of finished products. The plasticizing degree should be reduced as much as possible under the premise of meeting the processing process requirements.
With the appearance of constant viscosity rubber and low viscosity rubber, some rubber no longer need to be molded and directly mixed. In the rubber industry, the most commonly used plastic refining methods are mechanical plastic refining and chemical plastic refining method. The main equipment used in mechanical plastic refining is open rubber refining machine, closed-type rubber refining machine and screw plastic refining machine.
Chemical plastic refining is a method of adding chemicals to the process of mechanical plastic refining to improve the effect of plastic refining. The temperature of the opening machine is generally less than 80 ℃, belonging to the low temperature mechanical mixing method.
The dispensing temperature of the mixer and the screw mixer is more than 120 ℃, or even up to 160-180 ℃, which belongs to the high temperature mechanical mixing.
Raw rubber before mixing needs to be pre-baked glue, cutting glue, glue selection and breaking glue and other treatment in order to plastic.
The plastic refining characteristics of several kinds of glue:
When the natural rubber is molded by the opener, the roller temperature is 30-40 ℃, the time is about 15-20min, and when the temperature reaches more than 120 ℃, the time is about 3-5min.
The door and viscosity of butadiene rubber is more than 35-60, therefore, butadiene rubber can not be molded, but after plastic can improve the dispersion of the mating machine Butadiene rubber has cold flow and lacks the effect of plastic refining.
The door and viscosity of maleic gum is low, but it can not be molded.
Neoprene rubber has a large plasticity, before the plastic can be thin through 3-5 times, thin pass temperature in 30-40 ℃.
The molecular main chain of ethylene propylene rubber is saturated structure, plastic smelting is difficult to cause molecular cracking, so to choose the low viscosity of the varieties rather than plastic. Nitrile rubber has small plasticity, high toughness and high heat during plastic refining.

When opening, the use of low temperature 40 ℃ below, small roller distance, low capacity and sectional molding, so that you can receive a better effect.

2.2 Mixing

 Mixing process Mixing refers to the process of mixing all kinds of complexes evenly into raw rubber on the rubber refining machine. The quality of mixing is a decisive impact on the further processing of the adhesive and the quality of the finished product, even if the formula is good glue, if the mixing is not good, there will be uneven dispersion of the mixture, glue can be molded high or too low, easy to scorch, spray, etc., so that calendering, pressing, glue and vulcanization processes can not be carried out
It can also lead to a decrease in the performance of the product. The mixing method is usually divided into two kinds, such as the mixing of the opener and the mixing of the mixer.
Both methods are intermittent mixing, which is by far the most extensive method.
The mixing process of the opener is divided into three stages, that is, the roller (the softening stage of adding raw rubber), the eating powder (adding powder to the mixing stage) and the inversion (after eating the powder so that the raw rubber and the mating agent have reached the stage of uniform dispersion). The mixer mixture is different according to the type, use and performance requirements of the adhesive, and the technological conditions are different. Mixing should pay attention to the amount of glue, feeding order, roll distance, roll temperature, mixing time, roller speed and speed ratio and other factors.
Can not mix insufficient, and can not be too refined. Mixer mixing is divided into three stages, that is, moist, dispersed and nirvana, mixer mixing stone under high temperature pressure.
The operation method is generally divided into a section of mixing method and two-segment mixing method. A mixing method refers to the method of mixing glue by mixing the mixer once, and then pressing the film. He is suitable for all natural rubber or mixed with synthetic rubber not more than 50% of the glue, in a mixing operation, often the use of batch gradual feeding method, in order to make the adhesive does not rise violently, generally the use of slow mixer, can also use a two-speed mixer, add sulfur temperature must be less than 100 ℃.
Its feeding order makes a living glue-small material-reinforcing agent-filler-oil softener-discharge-cooling-plus sulfur and super propellant. The two-stage mixing method refers to the method of mixing glue made two times by mixing the pressure plate of the mixer. This method is suitable for the shortcoming that the content of synthetic rubber is more than 50%, and it can avoid the disadvantages of long mixing time and high glue temperature in the process of mixing method. The first stage of mixing, like a mixing method, is only a non-vulcanized and active propellant, after a mixing of the next piece of cooling, parking a certain amount of time, and then a second phase of mixing. Mix evenly in the back of the rear to expect to add vulcanizing agent on the tablet, after the inversion of the next film. The sectional mixing method has a short time, the mixing temperature is lower, the coordination agent is more evenly dispersed, and the quality of the adhesive is higher.

Feeding ingredients and collecting compound
The principal dangers and safeguards on a Banbury type internal mixer are:

1. The rotors, via the feed opening (contact with rotors or falling in on larger machines) These risks can be guarded against by feed tables or conveyors placed in front of the feed opening, with additional fixed side guards, where necessary.
2. Safe reach distances should meet the requirements of Table 4 of BS EN ISO 13857: Safety of machinery. Safety distances to prevent hazard zones being reached by upper and lower limbs.
   The floating weight trap with the fixed bridge casting from either the feed opening or the rear inspection door. There should be sufficient clearance between the bridge and the fixed bridge casting to prevent a finger-trapping hazard. Prevent access by using the same safeguards as for the rotors.
3. The floating weight and the lower edge of the front hopper door at the feed opening. The trap at the bottom of the weight is more dangerous. Operators are at risk when sweeping down or when adding lubricant or other small ingredients. Where access to the trap is possible, interlock movement of the floating weight with the hopper door.
4. The front hopper door and frame as the door closes and the stops as it opens under power Where powered movement of the door creates a trapping hazard, it's operation should be via a hold-to-run control, located out of reach of the door or a two-hand control on the hopper itself. A front feed table preventing access will also improve safety. Where bin-tipping units feed mixers, enclosing interlocking guards are required to prevent access to shear traps created by the tipping mechanism.

Mixing
Once the compound ingredients have been weighed out they are mixed together using specialised machines capable of dealing with the high stresses involved in shearing rubber.
Mixing can be either by internal mixing or external/open mill mixing which have very different safety problems.

Internal mixing (eg. Banbury or Intermix mixers)
The compound ingredients are fed into an enclosed mixing chamber via a feed hopper and mixed by the shearing action of two winged rotors and the walls of the mixing chamber. There is therefore a continuous nip.
A powered ram or floating weight in the feed throat forces ingredients into the mixing chamber, which is usually water-cooled. The mixed compound is discharged via a sliding or hinged door below the mixing chamber, usually onto a two- roll mill, roller die, twin-screw extruder, conveyor, skip hoist, or wheeled truck.

Many of the rubber compounding additives are fire sensitive, particularly:

1. Sulphurs and organic peroxides (used as curing agents);
2. azodicarbonamide (used as a blowing agent in some open celled rubber/lattices).

Particular care is required in storage areas to make sure incompatible materials, such as carbon black and sulphur, are adequately segregated. There have been incidences of dust explosions in powder handling areas. Many rubber compounding additives such as azodicarbonamide, calcium and zinc stearates, are known to be highly explosive when in a finely divided state. Design dust extraction and collection systems for use with potentially explosive dusts. Good
housekeeping will minimise the risk of secondary dust explosions .

Most of the rubber industry use mechanical handling such as the vacuum bale lifter. These are a reliable and low cost option for handling the standard 33.3kg bales.

Vacuum bale lifter

For larger machines, during maintenance or cleaning the blades should be supported, as shown below:

Some older machines have a fixed knife and an up stroking moving table. These should have interlocking guards to
prevent access to the cutting area. Also, the trap between the lower part of the moving table and the edge of the floor
should be eliminated by safety fairings.

Bale cutting

Before being added to the mixer the rubber may need to be cut into small pieces on a bale cutter or guillotine. These are usually down stroking machines, which should be securely fenced with interlocking access gates. Feed openings/tunnels should also meet safety reach distances.
The standard bale cutter is designed for 33.3kg bales. These are by far the most common machine but some of the larger old type shown below may still be in use. The standard 33.3kg bale can be fed directly into most larger rubber mixers but this small bale cutter is required to get the correct weight for the compound recipe.

Compounding - powder handling, mixing and milling

Introduction
Compounding involves the measuring and mixing together of raw rubber, process oils, carbon black, bulk fillers, and rubber chemicals in pre-determined proportions, termed formulations.
A rubber compounder can typically use between 100 and 200 different ingredients to mix a range of formulations. The finished mixture is known as compound and is the material that is processed into rubber articles by moulding, extrusion, calendering etc.

Carbon black storage handling area, bulk bag emptying. Note specialist HEPA vacuum for clean-up.

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