Nitrogen Vulcanization System in Tire Vulcanization Link

Author and source: Global Marketing Center KIZZA.LONE from ICONVEY Tire Manufacturing Industry Chief Engineer Discussion Group
Title:Tire Manufacturing Link
Nature of the article: Summary and arrangement of public information

1. The origin and characteristics of nitrogen vulcanization system

In order to improve product quality, reduce equipment investment and reduce energy consumption, people have made many improvements to the vulcanization process. In addition to directly improving the design of the vulcanizing machine itself, in recent years, the vulcanization heating medium has been improved and developed rapidly. The superheated water is developed to steam/inert gas, and then to the steam/nitrogen vulcanization medium mode, that is, the nitrogen-filled vulcanization process. At present, the nitrogen-filled vulcanization process of tires is an advanced vulcanization process technology abroad. The application of this process will greatly reduce the energy consumption of tire production, and play a very positive role in protecting the environment, saving energy, and improving product quality. Both at home and abroad are competing for development. tire manufacturing link

At present, the domestic radial tire vulcanization process generally uses two traditional vulcanization processes, namely, the vulcanization process of superheated water medium and direct steam medium.

The superheated water medium vulcanization process was once used in domestic and foreign production. The temperature of superheated water is generally controlled at 170-180°C, the internal pressure is maintained at 2.2-2.6Mpa, and the curing time is controlled at 20-30min. The properties are relatively stable, the quality of the tires is good, and the appearance qualification rate is high. The problem is that the inner temperature of the superheated water vulcanization is too low, and the time is too long. It takes 20-30 minutes to vulcanize a tire, and as many as 40-50 minutes, and the production efficiency It is very low. In order to expand the production scale, it is necessary to increase the vulcanizing machine, expand the workshop, increase the power consumption and personnel allocation, and the investment scale is large, which has become a bottleneck hindering the expansion of the radial tire production scale. tire manufacturing process

The direct steam medium vulcanization process is to directly charge high-pressure saturated steam into the capsule, the internal pressure is generally 1.6-1.9Mpa, the temperature reaches 190-210°C, and the vulcanization time is 10-15min. The advantage of this method is high production efficiency, but there are strict requirements on the process and equipment of the entire tire production process, and even on the storage conditions and time of semi-finished products. Because it is saturated steam, the corresponding relationship between internal pressure and temperature determines that the internal pressure cannot be too high. Therefore, during the vulcanization process, the internal pressure is low, especially at the shoulder of the tire, and the finished tire is prone to bubbles, delamination, and steel wires. The end points of the belt layer are loose and the compactness of the rubber is deteriorated, which affects the high speed and durability of the tire, and its application effect is greatly restricted.

From the above, the superheated water vulcanization process of high pressure and low temperature and the direct steam vulcanization process of low pressure and high temperature have obvious advantages and obvious disadvantages. The two vulcanization processes produce two situations in which the product quality is good but the production efficiency is low, or the production efficiency is high and the product quality is not easy to guarantee. How to unify the above two methods, both high pressure and high temperature can be ensured, so that the quality of the tire after vulcanization is more stable, and it can also achieve high production efficiency, this is the way people have been looking for for many years.

The first method that people found was the vulcanization method of steam/inert gas, but the gas produced by the inert gas generator is considered to be non-flammable, and it is toxic, and it is easy to cause carbon monoxide poisoning in a closed workshop without good ventilation conditions. Danger. Later, it was found that the use of high-pressure nitrogen vulcanization with abundant resources can completely solve the above problems. The basic process is to first fill the capsule with high-pressure saturated steam, and after the embryo is heated up for a certain period of time, then fill with high-pressure pure nitrogen to maintain the pressure to achieve high temperature and high pressure vulcanization conditions, thereby achieving the unity of quality and efficiency. Compared with the traditional steam or superheated water vulcanization method, this process has the following advantages:

⑴ Reduce production cost

Water heating and pumping are eliminated, thereby reducing vulcanization energy costs by 60-80%. Using low-pressure nitrogen to set the shape eliminates the use of low-pressure steam for shaping, saving water treatment and discharge costs.

(2) Improve tire quality

The integrity of the tire stack is improved due to the increased cure pressure. It can monitor the leakage of the bladder and adjust the curing time during the curing process, thereby reducing the probability of defective products.

(3) Increased production efficiency

Compared with superheated water, the vulcanization cycle is shortened by nearly 30%, which reduces the demand for the number of vulcanizers per unit of output and reduces equipment investment.

(4) Save energy

Since the high-temperature steam only passes for a certain period of time, and the stereotyped steam is cancelled, the steam consumption is reduced by about 80% in the whole vulcanization process, which can save a lot of energy and reduce the production cost of the vulcanization part by about 50%.

(5)Erosion phenomenon, saving equipment operation and maintenance costs, reducing downtime costs.

Since the high-pressure nitrogen is high-purity nitrogen, the oxygen content is very small, which greatly reduces the aging effect of oxygen on the capsule, which can increase the life of the capsule by 25-100%, save the cost of the capsule by nearly 1 million yuan per year, and eliminate the pipeline. Erosion phenomenon, saving equipment operation and maintenance costs, reducing downtime costs.

(6)Stable and adjustable pressure

The nitrogen vulcanization system is adopted, the pressure is stable, can be adjusted arbitrarily within a certain range, and the pressure boost is convenient, which plays a great role in the uniformity and balance of the tire, especially the improvement of the wear resistance of the tire.

(7)Harmless

The nitrogen vulcanization system is adopted, which is beneficial to environmental protection. Nitrogen resources are abundant, and there is about 78% nitrogen in the air. The nitrogen preparation system is easy to operate and clean. Nitrogen can be directly discharged into the atmosphere, and there are no harmful chemicals or three wastes to be treated.

According to the data, this vulcanization method is currently used in major tire production companies such as the United States and Japan.

The nitrogen-filled vulcanization process of radial tires is an international advanced tire vulcanization process. The tires vulcanized by this process have high uniformity and balance, which is very beneficial to the high speed and durability of the tires. driven distance.

2. Determination of nitrogen vulcanization process conditions

Vulcanization is the last process in the production and processing of radial tires. In this process, the rubber undergoes a series of chemical reactions, turning the linear rubber into a three-dimensional network rubber, thereby obtaining valuable physical and mechanical properties and becoming a valuable engineering material.

The vulcanization process is a process in which the rubber macromolecular chains undergo chemical changes and form crosslinks. In the process of production and processing, this cross-linking reaction can be completed after a period of time under a certain temperature and pressure. Therefore, pressure, temperature and time are the main factors that constitute the vulcanization process conditions, and they have a decisive influence on the vulcanization quality, which is usually called the three elements of vulcanization. Therefore, it is very important to select and determine the vulcanization process conditions reasonably and correctly.

Rubber is a poor conductor of heat, and the temperature difference between its surface layer and inner layer increases with the thickness of the section. Since the tire is a thick product, the vulcanization process must consider the influence of heat conduction, heat capacity, cross-sectional shape of the model, heat exchange system and the vulcanization characteristics of the rubber compound and the thickness of the product on the vulcanization.

Superheated water vulcanization and high temperature steam vulcanization are basically inconvenient to maintain the internal pressure, internal temperature and external temperature during the entire tire vulcanization process. During the entire vulcanization process, the heat conduction form is relatively simple, and the process conditions are relatively easy to determine. Nitrogen-filled vulcanization is in the tire vulcanization process. First, high-temperature saturated steam is introduced into the bladder for a certain period of time to provide the temperature conditions required for vulcanization, and then high-pressure nitrogen is added to provide the high-pressure conditions required for tire vulcanization. After a certain period of time, make each part of the tire meet the vulcanization characteristics of the rubber compound, and then release the mold to complete the entire vulcanization process.

In this process, there are three differences. One is the determination of the time for introducing high-temperature saturated steam into the bladder. If the time is short, the vulcanized tire may be under-vulcanized and undercooked. If the time is long, the tire may have satisfied the rubber compound. The vulcanization characteristics of high-pressure nitrogen are added, and the pressure has no effect at this time, and the meaning of nitrogen-filled vulcanization is lost. Therefore, it is very important to master the time of nitrogen injection. The second is that the high-temperature steam is turned off after a certain period of time, and the steam will not be supplemented after the high-pressure nitrogen is introduced. Therefore, during the tire curing process, the internal temperature is gradually reduced, unlike the superheated water. The internal temperature of the vulcanization is constant. The temperature field changes are complex, which requires that the vulcanization characteristics of each part of the tire should meet certain requirements. Third, due to the high temperature and low pressure of high-temperature steam, and the high pressure and low temperature of high-pressure nitrogen, the two media are mixed in the capsule, and the temperature and pressure will change accordingly. The pressure will drop during vulcanization. In order to meet the high pressure requirements of vulcanization, nitrogen should be added to maintain pressure in time; due to the drop in temperature during the vulcanization process, condensed water will be generated in the pipeline and the bladder, and the condensed water should be removed in time to keep warm. Therefore, in the process of nitrogen-filling vulcanization, the determination of the three elements of temperature, pressure and time is much more complicated than that of superheated water and high-temperature steam vulcanization. There must be scientific methods to determine more reasonable vulcanization conditions.

3. Nitrogen-filled vulcanization equipment

The key to the implementation of nitrogen filling and vulcanization of tires is to obtain high-purity nitrogen, with a nitrogen content of 99.9995%. Three options are available: commercial channel supply (eg liquid nitrogen), large on-site nitrogen generators, and small on-site nitrogen generators. More practical is a small on-site nitrogen plant.

The composition principle of nitrogen vulcanization station

The function of the nitrogen station is to provide a certain pressure of high-purity nitrogen as the internal pressure medium for tire vulcanization. The nitrogen vulcanization station is mainly composed of four parts: nitrogen production system, nitrogen purification system, nitrogen pressurization system and pressure control system, as shown in the attached figure. The task of the nitrogen production system is to pass the air through the nitrogen production equipment, and use the molecular membrane principle to produce nitrogen of a certain purity; the task of the nitrogen purification system is to use the principle of hydrogen to reduce oxygen to purify this nitrogen with high purity, so that the nitrogen content is as high as More than 99.99%; the task of the nitrogen pressurization system and the pressure control system is to pressurize this high-purity nitrogen with a compressor and control it to meet the requirements of the vulcanization process.

The composition of nitrogen vulcanization station

The diagram of the composition of nitrogen vulcanization station

The working principle of the system and its control

Nitrogen production system

Nitrogen production system consists of filter, heater, flow regulation and purity assurance system. After the compressed air from the air compressor is filtered, heated and sent to the membrane separator (semi-permeable polymer membrane), the oxygen and water vapor are removed, and the dry nitrogen is produced. The system controls the purity of nitrogen by regulating the flow of nitrogen gas through the flow regulating valve located downstream of the separator, and maintains the stability of the operating pressure of the system through the pressure regulating valve.

In addition, the control equipment includes temperature sensors, temperature controllers, pressure switches, oxygen detectors, PLCs, etc. The temperature sensor and controller control the temperature of the heater, thereby preventing the condensate from entering the separator. When the pressure switch at the outlet detects that the nitrogen consumption is low (high pressure), the system stops entering air and maintains a standby state to save energy. When the pipeline pressure drops, the system is restarted. The oxygen detector is used to detect nitrogen content to prevent unqualified nitrogen from being output into the pipeline (unqualified nitrogen is exhausted). PLC is used for input, display, setting, alarm and control output of each process parameter.

At present, the commonly used nitrogen production systems include membrane separation and pressure swing adsorption.

Membrane separation nitrogen production technology

The membrane separation nitrogen production technology is made by using the principle of different permeability when oxygen (O2) and nitrogen (N2) in the air pass through a special hollow fiber membrane. Oxygen water and other impurities in the air are quickly discharged as waste gas due to the fast permeation speed, while N2 is enriched to the other end of the membrane tube due to poor permeability, and is used as a product gas for users.

Membrane separation nitrogen production principle

Membrane is an integrated component of polyester micro hollow fiber bundles. Each micro hollow fiber is similar to human hair. These fiber bundles separate 78% of the air through different permeation rates of air components. N2 and 21% O2. Among them, oxygen and water vapor in the air are a kind of fast gas. And quickly permeate through the membrane fibers to be desorbed, while nitrogen passes through its hollow fiber pores to get bundled finished nitrogen. The entire separation process does not have any moving parts, and only relies on compressed air to complete the above process.

Has the following characteristics:

1. Fewer moving parts and low failure rate.

2. The N2 purity and yield are easy to adjust.

3. The high-efficiency air source treatment system greatly prolongs the life of the membrane module.

4. Compact structure, beautiful appearance, easy to move.

5. High oxygen and nitrogen separation efficiency, energy saving and consumption reduction.

Pressure swing adsorption (PSA) nitrogen production technology

Pressure swing adsorption (PSA) is a new gas separation technology, which has been rapidly developed abroad since the late 1960s and early 1970s. The gas mixture separates. It uses air as raw material, and uses a high-efficiency, high-selectivity solid adsorbent to selectively adsorb nitrogen and oxygen to separate nitrogen and oxygen in the air. At present, carbon molecular sieves are widely used in the field of nitrogen production. The separation effect of carbon molecular sieve on nitrogen and oxygen is mainly based on the different diffusion rates of these two gases on the surface of carbon molecular sieve. The gas (oxygen) with smaller diameter diffuses faster and enters the solid phase of molecular sieve more. In this way, a nitrogen-enriched component can be obtained in the gas phase. After a period of time, the adsorption of oxygen by molecular sieves reaches equilibrium. According to the different characteristics of carbon molecular sieves for adsorbed gases under different pressures, reducing the pressure makes carbon molecular sieves desorb oxygen. This process is called regeneration. The pressure swing adsorption method usually uses two towers in parallel, alternating pressurized adsorption and decompression regeneration, so as to obtain a continuous nitrogen flow.

Process principle

Technical characteristics of pressure swing adsorption

The raw air is taken from nature, and nitrogen can be produced only by supplying compressed air and power supply. The equipment has low energy consumption and low operating costs.

The nitrogen purity is easy to adjust. The nitrogen purity is only affected by the nitrogen exhaust volume. The ordinary nitrogen purity can be adjusted arbitrarily between 95% and 99.99%; the high-purity nitrogen generator can be arbitrarily adjusted between 99% and 99.999%.

The equipment has a high degree of automation, fast gas production, and can be operated by unmanned personnel. Start and shutdown only need to press a button, and nitrogen can be produced within 10-15 minutes of startup. The process flow of the equipment is simple, the structure of the equipment is small, and the floor space is small. The equipment is highly adaptable.

Process flow diagram

Purification system

This system consists of chemical reactor, automatic hydrogenation device, adsorption device, etc. The purity of nitrogen generated by the nitrogen production system does not meet the technical requirements, so it is input into the chemical reactor, and the oxygen in it is chemically reacted with the additional hydrogen to remove excess oxygen. The automatic hydrogenation system controls the amount of hydrogen added according to the oxygen content in the nitrogen after the reaction, so as to avoid the reduction of nitrogen purity caused by the addition of excess hydrogen. The adsorption device adsorbs other excess components in the nitrogen after chemical reaction, so that the purity of nitrogen at the outlet is as high as 99.99% or more.

Pressurized system

The pressurization system is the compressor to pressurize high-purity nitrogen, and its control is ordinary electrical control and interlocking of tire manufacturing link

Pressure control system

It consists of a single-loop control system. The nitrogen pressure is controlled within the process requirements through pressure detection, regulator and control valve. tire manufacturing link

The tire manufacturing industry chief engineer discussion group

At present, ICONVEY and its brother brand HONG’S BELT are deeply rooted in the field of tire manufacturing, and have jointly designed manufacturing processes and developed corresponding solutions for a large number of well-known tire manufacturing brands. Welcome international colleagues to join our tire industry discussion group, immediately send an email to info@iconveytech.com or info@hongsbelt.com to apply for permission to enter the tire manufacturing industry chief engineer discussion group, and become friends with international bigwigs. Tire Vulcanization Link Vulcanization System

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