Introduction to Rubber Microwave Vulcanization Technology – Huiyan Microwave.doc

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Introduction to Rubber Microwave Vulcanization Technology – Huiyan Microwave Author: Nanjing Huiyan Microwave System Engineering Co., Ltd. I. Principles and Advantages of Microwave Rubber Vulcanization Technology: 1. Principles of rubber vulcanization and advantages of microwave rubber vulcanization Raw rubber becomes soft when heated and hardens and becomes brittle when cooled; it is difficult to shape, prone to wear, soluble in organic solvents such as gasoline, contains double bonds within its molecules, is susceptible to addition reactions, and ages easily. To improve the properties of rubber products, a series of processing steps are carried out on raw rubber during production. Under certain conditions, a chemical reaction occurs between the raw rubber in the compound and vulcanizing agents, causing the linearly structured macromolecules to crosslink into three-dimensionally networked macromolecules, thereby endowing the compound with excellent properties such as high strength, high elasticity, good wear resistance, and corrosion resistance. This process is called rubber vulcanization. The vulcanization process is generally divided into four stages: induction, pre-vulcanization, main vulcanization, and over-vulcanization. To achieve this reaction, external energy must be applied to bring it to a certain vulcanization temperature, after which the rubber is kept at that temperature range to complete the entire vulcanization process. Rubber vulcanization can be carried out using various methods. The traditional method is to use vulcanization processes such as steam or far-infrared heating for the rubber compound. However, since the heating temperature is achieved through slow heat conduction from the outside to the inside of the material, and rubber is a poor heat conductor, the rate of heat transfer within the rubber from its surface to the inner layers is very slow; most of the time is spent bringing the rubber to its vulcanization temperature. Therefore, the heating time is long, the efficiency is low, and the sulfurization uniformity is poor. In particular, the old manufacturing processes used magnesium silicate (talc) to prevent rubber sticking, which resulted in dust spreading throughout the rubber production facilities, with dust levels in the air far exceeding the standards set by environmental protection authorities. Moreover, the overall vulcanization state of the rubber is not ideal, as under normal heat conduction conditions, the surface of the vulcanized rubber heats up at a different rate than the inner layers, resulting in uneven vulcanization. Microwave heating is completely different from traditional heating methods; it involves using microwave energy to penetrate into the material being heated in order to heat it throughout. As a result, heating occurs rapidly, it is efficient and energy-saving, **it reduces the vulcanization time of rubber, improves the uniformity of heating, and leads to higher quality vulcanization. It is possible to advance from the induction stage, during which rubber tends to stick together easily, to the pre-vulcanization stage in a short amount of time. The use of talcum powder in the traditional manufacturing process is eliminated, thereby meeting environmental requirements. This production process allows most of the manufacturing steps to be carried out on a single production line; it features a high degree of automation, low energy consumption, reduced labor needs, stable production, and uniform product quality, **thereby improving the working conditions in production. 2. Current application status of microwave rubber vulcanization technology: Since its introduction in the 1970s, microwave rubber vulcanization technology has seen rapid adoption, particularly the widespread use of microwave continuous vulcanization lines in the production of rubber extruded products; its development pace has been unprecedented. Japan has seen rapid development in microwave continuous vulcanization technology; to date, more than 450 such production lines have been built there, and over 100 of them have been exported to countries around the world. Microwave vulcanization technology has **become a common production method in industrial applications abroad. It is not only widely used for the vulcanization preheating of various extruded rubber strips and hoses, but also for the vulcanization preheating of various types of tires. Our country has **imported dozens of continuous vulcanization production lines for microwave sealing strips from Germany, Japan, Spain, the UK, and other countries.** However, imported microwave vulcanization production lines also have many problems, such as high prices and high maintenance costs, an unreasonable design of the microwave chamber, low microwave efficiency, and insufficient level of automation in control. With the development of microwave energy application technology in China, numerous systems utilizing the microwave rubber vulcanization process have been replicated and modified locally. Some manufacturers of imported equipment have collaborated with companies specializing in microwave energy applications to address the issues associated with those imported rubber vulcanization devices, resulting in significant improvements in product quality and output. Since 2000, the successful development of multi-tube microwave vulcanization equipment has reduced the cost of such equipment as well as the difficulty of its maintenance. Today, microwave vulcanization technology for rubber is becoming increasingly mature, with continuous improvements to the equipment itself, which are aimed at achieving higher levels of automation, reducing energy consumption, and minimizing environmental pollution, in order to meet the ever-rising demands of users. This technology holds great potential and a vast market outlook. II. Microwave rubber vulcanization equipment and production process: The most practical basic process flow for microwave rubber vulcanization at present is as follows: The molded products extruded from the extruder are conveyed via conveyor belts or roller conveyors to the microwave vulcanization unit, where the rubber is rapidly heated to the vulcanization temperature. It then enters a hot air chamber for secondary vulcanization, where it remains at a certain temperature for a specific period of time, thereby completing the foaming and vulcanization processes for that product. If a hot air tank is not used at this time and vulcanization is carried out entirely in a microwave tank, it would be a great waste of energy; however, using it in combination with a hot air tank makes it more economical. The components of a microwave rubber vulcanization production line include an extruder, high-temperature shaping equipment, microwave vulcanization equipment, hot-air vulcanization equipment, a cooling section, a traction machine, a cutting machine, and a punching machine. Extruder: Used to extrude rubber raw materials into the desired shape and structure. The rubber produced through extrusion can be of single-layer type (sponge or solid rubber), two-layer composite type (sponge and solid rubber), three-layer composite type (steel core, sponge, and solid rubber), or four-layer composite type, etc. The structure and performance of the extruders used vary depending on the type and specifications of the rubber. High-temperature setting equipment: It is primarily used to rapidly vulcanize and set the surface of rubber that has just been extruded, thereby preventing deformation or sticking to the conveyor belt, which could damage its surface. Microwave vulcanization equipment: It uses microwave heating to raise the temperature to that required for vulcanization as a whole, and this process takes only a few dozen seconds to one or two minutes. Hot air vulcanization equipment: Keeps the rubber strip within the temperature range required for vulcanization to continue the process. Cooling section: Used to cool the rubber strip to a temperature at which it can be cut and collected. Traction machine: Provides the power for the rubber strip to move forward. The above is only the basic configuration for vulcanized rubber strips in general. When it comes to rubber strips that form the framework of the vulcanization zone, the front section of the extruder is equipped with a steel core feeding device, while in the rear section, equipment such as punching machines and steel core shaping machines may be installed as needed ； A cutting machine is not required when vulcanizing non-strip continuous products. The microwave heating equipment is the core component of the entire microwave vulcanization process. The uniform heating design of microwave heating equipment is particularly important; the design for uniform heating by microwave heaters is a prerequisite for consistent vulcanization of rubber. In addition, the composition ratio of the rubber mixture, its color intensity, and the surface finish all affect its microwave absorption properties, and all these factors need to be taken into consideration in order to make appropriate adjustments during the microwave heating process to meet the requirements of that process. III. Example introduction of microwave rubber vulcanization production lines: Taking the HMXJ10S type microwave rubber vulcanization production line manufactured by Nanjing Huiyan Microwave System Engineering Co., Ltd. as an example, this section introduces such production equipment. The process flow is as follows: This production line utilizes foreign-specific multi-tube feeding technology for microwave magnetrons, ensuring good electromagnetic uniformity ； For microwave power distribution, a top-level touch screen and a programmable controller (PLC) are used for fully automatic control. Adopt various microwave suppression techniques to prevent microwave leakage ； Use air ducts to enhance the effect of hot air ； After being tested by relevant departments, the entire production line meets and even exceeds **the latest standards in terms of performance and technical specifications. This has opened up a new path for the use of microwave technology in rubber vulcanization in our country, bringing it to an advanced level domestically. Special designs can be carried out according to user requirements. Main technical specifications of the equipment: The entire production line is controlled by a console, with a remote computer and an PLC industrial controller used for status control and status display. All devices use variable frequency control for speed regulation, ensuring that the conveyor speeds of each device are consistent; individual control of each device is also possible. The control system consists of an upper-level computer (industrial PC) and a programmable controller (PLC) that are used to manage the entire production process; the human-machine interface is operated via a touch screen. The upper-level computer is used to establish and modify the vulcanization process parameters for rubber products, with the data and parameters being accessible. Programmable controllers are used to control the operating status of various devices. The console includes all the controllers for operating the system and the status indicators. The interlock status panel provides parameters regarding the status of each microwave generator, cooling water flow rate, and service door interlocks. The indicators on the control panel provide information on energy generation, interlock status, and its performance in operational and standby modes. The industrial computer carries out full-process control of the microwave system and hot air system, provides comprehensive data storage and historical curve displays, allows access to processing data and parameters for various rubber products, enables arbitrary setting of microwave power and temperature for dynamic control, and features a user-friendly interface. Adjust the microwave power or the transmission speed based on the material temperature ； The microwaves are automatically cut off when the heater door moves or when the material runs out ； An alarm is triggered when the cooling water flow decreases, and the microwave turns off automatically after a certain period of time. The temperature measurement system is far-infrared and contactless, with a measurement range of 0°C to 500°C; it features intelligent adjustment and automatic temperature display. The infrared temperature controller monitors the sulfides to prevent oversulfidation. The magnetron is equipped with a thermal switch for protection against overheating and burnout, and can undergo 100,000 cycles of startup and shutdown at temperatures between 130°C and 160°C. Emergency stop switches are installed on the control panel, at the inlet and outlet points, and every two meters along the equipment, to shut down the system promptly in case of abnormal conditions. Microwave energy measurement devices are installed at the equipment’s inlet and outlet to detect electromagnetic leakage, issuing an alarm when the leakage exceeds the specified limit. A microwave suppressor is installed outside the cavity to control microwave leakage. The heating chamber is equipped with an insulating layer, while the microwave chamber has a wave-shaped stirrer to ensure uniform heating. 1. The console is equipped with an Advantech industrial computer, operable via keyboard or mouse ； 2. The iFIX configuration software, which offers stable and reliable performance ； Clear image quality and powerful features. 3. The touchscreen serves as the user control interface, utilizing a 10” screen from Mitsubishi Corporation’s A970 series in Japan ； (Set device-related control parameters within the touch screen.) 4. The PLC uses the Mitsubishi FX2n series, along with multiple Mitsubishi AD-DA conversion modules, to enable automatic control functions related to the equipment ； 5. Use RS-485 communication to achieve 1:N communication control with multiple frequency converters ； 6. Use a PID algorithm to control the temperature of the three sections of hot air ； 7. Multi-point communication between the industrial computer and PLC (Mitsubishi) using RS-485 ； 8. The industrial computer stores real-time control information and curves, which can be retrieved at any time ； 9. The PLC has independent operation capabilities as well as control functions via an industrial computer, and it can be switched between these modes ； 10. The control system can control and monitor each component, detect the operating status of equipment in real time, and issue alerts promptly in case of any emergencies ； The status indicators include: a) Door status: The microwave device will stop automatically when the door is opened while it is in operation ； b). Cooling water flow rate: If the flow rate of the cooling water used for cooling decreases or the supply is interrupted, the machine stops automatically ； c). Temperature monitoring: indicates over-vulcanization of rubber products or excessively high temperatures, allowing for automatic shutdown ； d). Material shortage detection: If there is a lack of material in the rubber products, the machine will stop automatically ； e). Speed detection, etc.: Automatically detects the speed of the conveyor belts across the entire production line. f). Microwave leakage measurement: Online microwave leakage measurement devices are installed at the inlet and outlet of the equipment, which emit an alarm when the leakage exceeds the specified limit. 11. Each operator has a dedicated password ； It can be connected to the higher-level DCS. 12. Both the inlet and outlet are designed using advanced microwave suppression technology to control microwave leakage. 13. A completely new hot air duct design **reduces air resistance while improving efficiency ； Main technical parameters of the equipment: Input power supply voltage (AC): 380V±10%, 50Hz, three-phase; Total input apparent power: ≤150kVA; Microwave frequency: 2450±50MHz; Microwave output power: ≤10kW, continuously adjustable; Hot air output power: 30kW×3; Control type: PID control; Operating temperature range: 0～40℃; Cooling water flow rate: 4～6L/min; Microwave leakage level: Complies with **health standards. The operating environment should be free of flammable and explosive gases as well as corrosive gases, with as little dust as possible. Dimensions of the microwave vulcanizing machine: 8.6m×0.57m×1.5m; Dimensions of the hot air vulcanization chamber: 9m×0.57m×1.5m; Dimensions of the cooling section: 6m×0.6m×1.5m; Transmission speed adjustment method: Frequency conversion; Transmission speed: 1.5~15m/min; Adjustable distance between the traction machines: 0～80mm; Power consumption of the traction machines: 2 KW; Transmission mechanism used by the traction machines: Single-sided synchronous toothed belt; Relative humidity: ＜75%