In the production of tires, the rubber compound in different parts of the tire has different formulas due to different performance requirements. In addition to various rubbers, the main components of the rubber compound should be added with different properties of carbon black, zinc oxide, stearic acid, anti-aging agent, accelerator and sulfur, etc., in order to be processed into various tire parts by various rubber mixing equipment. The compound.
The process mainly consists of: carbon black storage, weighing and feeding system; oil storage, metering and feeding system; chemical small material weighing system; large powder (such as zinc oxide) weighing system and mixer mixing system. The mixing machine rubber mixing system is composed of natural rubber heating, rubber block chopping and mixing system, weighing and feeding system and internal mixer.

4.1 Mastication of natural rubber
4.1.1 Preparation of natural rubber before mastication
(1) baking glue
The weight of the natural rubber plastic bag (block), the domestic tobacco sheet glue is 50kg for each plastic bag, and the international tobacco sheet glue is 101.5~113.4kg for each. Due to the characteristics of natural rubber, before the mastication, it must be heated and baked to eliminate the crystallization state of the natural rubber raw rubber and reduce the hardness, otherwise it will increase energy consumption and even damage the machine during mastication. The baking operation is usually carried out in a baking room. The baking room is a closed building with steam heating pipes around and below. The natural rubber plastic bag should be placed in the baking room and should not be in contact with the radiator.

The natural rubber bag has a baking temperature of usually 50 to 70 °C. Too high a baking temperature will reduce the physical and mechanical properties of the rubber. Baking time: 36~72h in winter and spring~24~36h in summer and autumn.

(2) Cutting, selecting glue, compounding
The large rubber plastic bag is not easy to process. The domestic natural rubber plastic bag has a size of 600mm×400mm×250mm and weighs 50kg. The international standard tobacco sheet rubber is about 700mm × 700mm × 600mm and weighs about 100kg. Due to the large size of the raw rubber plastic bag, it is not convenient to put into the mastic processing of the internal mixer (or open mill). Therefore, before the mastication, it is necessary to use the 80kN and 160kN single-knife vertical hydraulic cutting machine, 800kN six-knife hydraulic cutting machine. Machine, 1000kN 10-knife horizontal hydraulic cutting machine cut into small pieces of 10~15kg.

Always remove any dirt from the outside of the bag before cutting.

After the plastic bag is cut, it is necessary to select the rubber to remove the mildew, debris or hard block, and store it for storage.

The production of raw rubber, especially natural rubber, due to its production characteristics, the quality of the plastic bags will be inconsistent. In order to improve the consistency of the quality of the rubber compound, a new process has been developed in recent years, and the plastic bag is pulverized and premixed. The newly developed natural rubber crushing premixing production line can break the large rubber block into 40~90mm small rubber blocks, so as to realize the premixing, automatic weighing and conveying of the raw rubber to the rubber mixing equipment platform, in order to make the process Continuous and automated. In addition, when this process is used, natural rubber production can be directly crushed by a newly developed high-power crusher without heating and decrystallization.

4.1.2 Mastication
(1) Purpose and Mechanism The chopped raw rubber block is mechanically or chemically processed into a rubber having a certain Mooney viscosity to facilitate the mixing process of the lower process and carbon black and related chemicals.

The basic mechanism of mastication is that the large molecular weight raw rubber acts on the main chain and side chain of the rubber to reduce the average molecular weight of the rubber by the action of mechanical force and oxygen, and the addition of a peptizing agent, thereby improving the rubber. Plasticity. This is the "chain-breaking theory" of plastics. After the raw rubber that has been "broken", it can enter the mixing operation of the next process.

(2) Open mill mastication
Masticating rubber with an open mill is the most traditional method of mastication. Before the rubber is plasticized by the open mill, the rubber that has been cut into small pieces is broken by a two-roller. The distance of the broken rubber roller is usually 2~3mm, and the roller temperature is about 45°C. The film that has been broken into a certain weight by the broken green film is used for the next process for mastication.

The open mill for raw rubber breakage is a type of open mill, the roll is short and thick, the back roll surface is grooved, and the front roll is a light roll. The speed ratio of the roller can reach 1:1.3, and the specification of the commonly used broken glue machine is Ф560×Ф510×800.

In order to make the plasticized plastic reach the plasticity of 0.50 or more, the method of segmental mastication is required. The time of each mastication is about 15~20min, and then the next piece is cooled and parked for 4~8h before the next stage of mastication. The plasticity of the mastication of the open mill is about 0.30 for one segment, about 0.40 for the second segment, and about 0.50 for the third segment.

When masticating with a chemical degumming agent, the roll temperature can be increased to 70-75 ° C, and the mastication time can be reduced by about half.

The speed ratio of the roll mill for mastication is usually 1:1.25 to 1:1.27. The mastication process conditions of the open mill are easy to control and the equipment investment is small, but the labor intensity is large and the operation is troublesome.

(3) Screw Molding Machine Mastication
The raw rubber is plasticized by mechanical mechanical agitation and thermal oxidative cracking of the rubber in the barrel. Screw mastication can make the plasticizing operation continuous, but the plasticizing rubber can discharge the glue temperature up to 150~180 °C, the rubber thermoplastic is large, the plasticizing quality is unstable and it is easy to produce "pseudo-mastication".

When the raw rubber is usually plasticized by a screw plasticizer, it is necessary to configure a plurality of open mills for refining and masticating, and at the same time, the plasticating rubber is cooled and cooled, and then compressed, and then parked for use.

High temperature plasticizing is prone to pseudoplastication of elastic recovery.

Commonly used screw plastic machines are available in three sizes: Ф250, Ф300 and Ф380.

(4) Mastic mixer
Mastic mixer mastication is a mastication process commonly used in the production of contemporary tires. In the internal mixer of the internal mixer, the raw rubber is subjected to intense friction, tearing, shearing, tumbling and oxidative cracking between the ribs of the two rotors and the wall of the mixing chamber to achieve a plasticizing action for improving the plasticity. The mastication of the mixer is high temperature mastication because the mastication temperature can be as high as 140~160 °C.

Mastication of the mixer is affected by factors such as plasticizing temperature, plasticizing time, rotor speed, compression pressure, amount of glue, and addition of chemical degumming agent.

When using F270 internal mixer to plasticize raw rubber, the rotor speed is generally 20/40r/min, the compression pressure is 0.5~0.6MPa, and the raw rubber block temperature is 40~50°C.

Mastication of raw rubber with a mixer also has a section of mastication and segmentation. During a period of mastication, the raw rubber is put into the mixer and masticated according to the conditions specified in the process to the required plasticity, that is, the discharge material is suitable for rubber for tread rubber, such as rubber for tread rubber, which is not very high in plasticity. The degree can be 0.25~0.35.

For plasticizers requiring a Vickers plasticity of 0.35 to 0.50, two-stage mastication is generally required. After the first stage of mastication, the rubber is cooled by tableting, and the second stage of mastication is carried out for more than 4 hours to achieve the desired plasticity. In the tire production, the rubber with higher plasticity requirements such as curtain rubber is mainly made of two-stage plastic. In the actual production, the second stage of mastication can be carried out in succession with the mixing process.

When the plasticity of the plastic compound is required to be above 0.50, it can be achieved by three-stage mastication. When using a chemical peptizer in the mastic rubber of the mixer, the mastication efficiency can be improved. When adding 0.3%~0.5% raw rubber by weight of peptizer, the plasticizing time can be shortened by 30%~50%.

(5) Molding example
The rubber used in tire production includes natural rubber, styrene butadiene rubber, butadiene rubber, chlorinated butyl rubber and the like. With the improvement of rubber production process, the reinforcement of rubber mixing equipment, some tires have no need for plastics, such as all-steel radial tire rubber. For the bias tire No. 3 tobacco sheet glue and the standard No. 1 glue need to be masticated, the other will not be masticated.

When masticating with a Ф560 mill, the temperature of the rolls is (55±5) °C for pure rubber, (70±5) °C for DM, and 70 kg for capacity. The thin pass roller is 1~1.2mm.

When masticating with a 140L internal mixer, the pure plastic molding capacity is below 140kg, and the discharge temperature is controlled below 175°C.

When using a screw plastic mixer to masticate, control the temperature of each part: the head temperature is 90~100°C, the tail temperature is below 60°C, the body temperature is 80~100°C, and the tail temperature is below 180°C. The plasticity can reach 0.40.

4.2 Rubber mixing
Rubber mixing process is an extremely important process in tire production. Rubber and carbon black, small powder (zinc oxide, stearic acid, antioxidant, accelerator, sulfur, pine tar and accelerator) must be mixed evenly. To ensure the quality of the tires.

Rubber mixing has two processes: open mill mixing and mixer mixing. The mixing and mixing machine has poor sanitary conditions, high labor intensity and low efficiency. At present, it is generally not used except in some cases.

See Figure 16 for the modern mixing process with mixer mixing. It is equipped with automatic carbon black conveying, automatic weighing and feeding system, small material automatic weighing system, rubber weighing and conveying system and computer automatic control system. It has a high level of mechanized automation, high efficiency, good quality and clean environment. The application of the AGV trolley in the rubber mixing plant further increases the level of automation.

The quality of rubber mixing has an important influence on the extrusion and calendering of the next process. If the rubber is not uniformly mixed, the plasticity is too high or too low, which may cause scorch and frosting of the rubber compound, causing calendering and extrusion. It is difficult to carry out the work normally. Therefore, the mixing operation must produce a good quality rubber compound.

4.2.1 Mixing and discharging control

When the rubber compound is mixed to a certain level in the internal mixer, it is necessary to discharge the cooling from the machine, so that the rubber compound meets the temperature requirements specified by the process, and the quality is ensured, and energy consumption is saved.

Modern mixer mixing operations typically use three methods for debinding control: mixing time, compound temperature, and mixing energy.

In tire production, it is possible to determine the optimum mixing time, optimum mixing temperature and optimum mixing energy consumption to achieve good dispersibility.

A comprehensive control method can usually be used, and when any of the three control methods reaches the glue discharge requirement, the glue is discharged.

4.2.2 Number of mixing sections

The mixing of rubber in the internal mixer and the compounding agent can satisfy the process requirements without a single mixing process, and it is necessary to carry out multiple (ie, multi-stage) mixing processing to meet the tire production requirements. The segment and the segment should be separated by a certain period of time, that is, the mixed rubber in the previous section needs to be parked for a certain period of time before the next section can be processed.

In actual production, the rubber used for bias tires generally uses two-stage mixing, while the radial rubber compound uses 2~5 sections of mixing. For example, the rubber compound is mixed with 2~3 sections, and the load is meridian. The rubber compound is mixed in 3~4 stages, and the steel wire and curtain rubber are mixed in 4~5 stages. This is because the radial tire rubber is different from the bias tire rubber compound. The radial tire rubber has high hardness, high viscosity and difficult mixing. Therefore, multi-stage mixing is required to make the ingredients evenly dispersed, especially the distribution and dispersibility of carbon black and sulfur in the rubber compound, which has a great influence on the quality of the rubber compound.

The high-speed, high-pressure, high-shear-rate internal mixer is more suitable for mixing hard rubber with high viscosity. It is most suitable for the masterbatch of rubber compound, that is, the compound with no sulfur added.

According to the data of Shandong Huanghai Tire Company, the company uses GK400N internal mixer to process the masterbatch at 45~55r/min. After the rubber compound is kneaded in the internal mixer for 2~3min, it reaches the extreme temperature of 160~170°C and must be discharged. After cooling for more than 8h, it will be put into the mixer again. For the tread rubber, three-stage rubber mixing is required, and for the belt rubber, five-stage rubber mixing is required. The flow for the 3-stage rubber mixing process is shown in Figures 17, 18 and 19. The masterbatch of the all-steel radial truck tire tread rubber is parked for at least 8 hours, and the final rubber is parked for at least 4 hours.

4.2.3 Mixing example

When producing radial tires, the mixing conditions of the rubber compounds used in the components of the radial tire structure are shown in Table 3. The parking time between the segment and the segment is at least 3h. The masterbatch can be produced at a high speed of 60 r/min in a F270 or F370 internal mixer, and the final refining can be produced at a low speed of 20 m/min by a F (or GK) 270/F370 internal mixer driven by a DC motor.

The final refining and vulcanization is carried out in an internal mixer. When the radial tire steel wire curtain rubber is finally refined, the debinding temperature is ≤100 °C.

For the all-steel radial tire tread rubber, when the three-stage mixing is used, the discharge temperature of one section is about 150 °C, the second section is about 140 °C, and the temperature of the three-stage sulphur finishing rubber is (105±5) °C.

4.2.4 Modern one-time mixing process

The multi-stage mixing process of the rubber compound, because the rubber material is parked and cooled between the segments and the segments, the multi-stage mixing energy consumption is time-consuming and labor-intensive. To this end, since 2010, two kinds of one-time rubber mixing process equipment have been developed and promoted and applied in tire enterprises.

(1) Low temperature one-time mixing process
The low-temperature one-time mixing process uses natural rubber and synthetic rubber particles which are only broken by the crusher without passing through the baking, and have a particle size of 40 to 80 mm. The equipment for implementing the low-temperature one-time mixing process consists of one internal mixer, six to seven 55m/min high-speed Φ660 and Φ710 automatic openers, and one set of direct film cooling devices, as shown in Figure 20. The system can complete the mastering and vulcanization final mixer to complete the mixing of the masterbatch at one time. The refined masterbatch is discharged on the first open mill to complete the vulcanization operation, and the lower temperature is ≤110°C. . Then, through the split conveying system, the liquid is transferred to the relevant mill to continue to replenish the mixing and cooling. Finally, the film is weighed and then fed into the tablet opener, and the film is passed through the film cooling device to ≤40 °C. Store for future use.

The one-time low-temperature mixing system is more suitable for the mixing of white carbon black rubber. By controlling the discharge temperature, the degree of silanization reaction of the white carbon black can be improved, and the dispersion degree of the white carbon black can be improved.

The one-time low-temperature rubber mixing system can save energy by 15%~20%, increase production capacity by 150%~200%, reduce equipment area by 50%, reduce operating personnel, and through production test, compared with traditional rubber mixing, tires Wear resistance can be increased by 10% and rolling resistance by 2% to 5%.

(2) Superimposed internal mixer low temperature one-time mixing process
The mixing process of the superimposed mixer (or tandem mixer) plus the open mill was introduced into the domestic tire enterprise from abroad in 2000, and then developed, produced and promoted in domestic rubber machinery enterprises. The superimposed mixer is composed of the upper machine and the lower machine. The specification of the lower machine is larger than that of the upper machine, which is convenient for the cooling and replenishing of the rubber under the upper machine. The upper machine is a complete internal mixer. The lower machine has no feeding and pressing device, and the discharge port of the upper machine is directly connected with the feeding port of the lower machine.