[b]1 Introduction[/b] my country has experienced a power shortage for nearly two years, and the situation became even more severe in 2004, with 24 provinces and municipalities experiencing power outages in the first half of the year. In the first half of this year, electricity demand continued to grow rapidly, driven by a 9.7% GDP increase, characterized by "rapid growth in industrial electricity consumption and persistently high growth in electricity consumption by high-energy-consuming industries." However, the increase in power supply capacity was limited, resulting in a persistent power shortage and exacerbating the power supply-demand imbalance, further expanding the scope and areas of power shortages. my country is a major global shoe manufacturing country, with over 20,000 shoe manufacturing enterprises. Fujian Province is a major plastic shoe manufacturing base, ranking among the top in annual shoe production and exports. Quanzhou City has introduced over 1,000 shoe production lines, and Jinjiang City is a famous "Shoe Capital of China," with specialized manufacturers in leather, shoe materials, chemical raw materials, and digital mold making. It currently has over 3,000 shoe production and operation enterprises, with an annual output of over 700 million pairs of shoes… Power outages have severely impacted the normal production of these enterprises. From January to July this year, the increase in plastic costs has made the competition in China's plastic manufacturing industry increasingly fierce. Energy saving, as an important means for enterprises to increase efficiency, reduce consumption, reduce operating costs, and improve competitiveness, has become particularly meaningful and has been gradually recognized and accepted by people. [b]2 Working principle of fully automatic disc-type plastic injection molding machine[/b] As we all know, there are a large number of successful cases of frequency conversion energy saving transformation of horizontal injection molding machines in China. The fully automatic disc-type plastic injection molding machine of shoe manufacturing enterprises is a common type of electrical equipment in shoe manufacturing enterprises, known as the "electricity tiger". my country is a major shoe manufacturing country with a large number of shoe manufacturing equipment, but there are relatively few units involved in energy saving transformation at present. The main reason is that people are not familiar with the working principle of the fully automatic disc-type plastic injection molding machine. 2.1 Mechanical characteristics of fully automatic disc-type plastic injection molding machine Fully automatic disc-type plastic injection molding machine (hereinafter referred to as: disc machine) (1) This machine is specially used to produce various high-grade single-color, double-color and triple-color sports shoes, casual shoes soles, men's and women's children's shoes soles, etc. (2) The raw materials are suitable for producing various thermoplastic materials such as foam, such as PVC, TPR, etc. (3) The machine is controlled by computer program (single-chip microcomputer, PLC), the main and auxiliary machines are precisely controlled, the operation is simple, and the maintenance is easy. 2.2 Comparison between disc machine and traditional horizontal injection molding machine (1) Hydraulic motor The oil pumps of both horizontal injection molding machine and disc machine are quantitative pumps. During the injection process, the oil pump pressure changes frequently. The traditional way to maintain low pressure is to release pressure through proportional valve, while the motor runs at full speed at the power frequency. The energy waste is very serious. (2) Classification of disc machine According to the model of disc machine, it is divided into single-color machine, two-color machine, three-color machine, etc. Among them, the single-color machine has only one main machine, similar to the horizontal injection molding machine. The two-color machine consists of one main machine and one auxiliary machine. The auxiliary machine is responsible for the actions of injection, melting, upper mold, lower mold, etc. The main machine includes the actions of the auxiliary machine and has an additional action of disc rotation to realize the movement and positioning of the mold. [b]A three-color injection molding machine consists of one main machine and two auxiliary machines.[/b] (3) Number of molds A horizontal injection molding machine generally only has one set of molds in operation. When the production process changes, the molds need to be replaced. The number of molds for a rotary injection molding machine varies depending on the model. Generally, there are 18, 20, 24, or 30 sets of molds. According to the production process, the effective use of the mold position can be set through the control panel. For example, the TY-322 model has 24 mold positions (24 molds can be installed). During production, all or some molds can be flexibly selected as effective mold positions as needed. When the rotary injection molding machine is working, the large turntable performs a high-speed clockwise rotation. The PLC or microcontroller performs the program calculation. When only an effective mold position is detected, the turntable starts to decelerate when the PLC or microcontroller scans a deceleration signal. When the positioning signal is reached, the turntable performs precise positioning. Otherwise, if no effective mold position is detected, the large turntable continues to rotate to the next effective mold position. As long as there is a mold locking or mold opening signal, the horizontal injection molding machine will perform the relevant actions. (4) Pressure Adjustment Method: Both horizontal injection molding machines and rotary injection molding machines use pressure proportional control. However, the injection pressure of each mold on a rotary injection molding machine (which has more molds) can be independently set via the control panel, making it suitable for manufacturing products with different injection volumes. The parameters of a horizontal injection molding machine are consistent for each product. (5) Mold Working Method: When a horizontal injection molding machine is working, the fixed mold is stationary. Only the movable mold performs left and right locking or opening actions when instructed, moving in a straight line. When a rotary injection molding machine is working, the fixed mold and the movable mold are moved and positioned by the large turntable. When there are locking and opening instructions, the hydraulic cylinder performs rising or falling actions. When taking out the product, the operator manually opens the movable mold and takes out the product. (6) Rotary Disc: The fully automatic rotary plastic injection molding machine is named for its circular turntable and is often abbreviated as rotary machine (shoe sole machine). The disc is divided into several equal parts. For example, the TY-322 is divided into 24 mold positions. If neither the main machine nor the auxiliary machine detects a valid mold position, and both the main machine and the auxiliary machine are in the mold-opening state, the PLC or microcontroller issues a command, and the disc is pressured by the main machine to rotate at high speed. The system automatically detects the valid mold position, and the disc decelerates and is precisely positioned. (7) Cooling method Traditional horizontal injection molding machines have the concept of "cooling time". Cooling water circulation is installed on the mold to protect the mold and product cooling. The disc machine is different. It does not have a cooling water circulation system because after the product is formed, the disc machine itself is in a rotating state or standby state for a period of time. In addition, several cooling fans are installed on the machine to cool the mold and product. 2.3 Working principle of disc machine The various actions in the injection process of the disc machine, such as mold clamping, injection, melting, mold opening, and disc speed, have different requirements for speed and pressure. They are set by the proportional values ​​on the control panel, such as P1 setting the mold closing pressure, P2 setting the first injection pressure, P3 setting the second injection pressure, and P4 setting the feeding pressure. When the flow and pressure requirements of the rotary disc machine change, a proportional valve (overflow valve) located at the oil pump outlet regulates the load pressure and flow, allowing excess high-pressure oil to overflow back to the oil tank. A single-color rotary disc machine has only one main unit, primarily providing pressure to the system to complete the injection, melting, and mold-locking/opening actions. It also controls a turntable system to move and position the mold. Two-color machines have a main unit and auxiliary units. They mainly consist of heating, injection, melting, and mold-locking systems. A three-color machine is similar to a two-color machine, consisting of one main unit and two auxiliary units. The main unit is responsible for the rotation and positioning of the disc. The rotary disc machine operates in both manual and automatic modes. In manual mode, the operator must provide corresponding commands for the machine to complete the actions, such as injection, melting, upper and lower mold operation, and disc rotation. When running automatically, after each mold position is selected, the feed rate, pressure, and time are set, and the material pipe temperature has reached the set value, start the main oil pump, switch the manual/automatic unlocking to the automatic position, and press the automatic start button once to start automatic operation and complete all steps. (1) If the mold position is currently in use, after pressing the automatic start button, the feed rate is the set amount of this mold. If the feed rate does not reach the set amount, there is a mold locking action. Only the fast mold locking action is allowed. The slow mold locking action will only occur after the feed rate reaches the set amount. After the mold locking stops, the injection and mold opening actions are performed. (2) If the mold position is not currently in use, after pressing the automatic start button, the disc will move to the next mold position that is in use. When the feed rate reaches the set amount, the feed action will also be performed with the set amount of the next mold position that is in use. After the disc is positioned, the mold locking action will be performed quickly (with time setting). When the timer stops and the feed rate reaches the set amount, the slow mold locking action will be performed. After the mold locking stops, the injection and mold opening actions will be performed. (3) When the main and auxiliary machines are used simultaneously, the disc will only run and rotate to the next mold position after both the main and auxiliary machines have completed their automatic actions up to the mold opening. (4) When the disc pauses before the "slow point," the disc will detect the movement at the "slow point" and slow down to the positioning stop. If the mold position is in use, after positioning, the mold will perform actions such as mold locking until the mold opens. The disc will not move, but the feeding action will execute the feeding of the next mold position, and the disc pause will be released (rotated clockwise). The disc will then move to the next mold position. If the mold position is not in use, the disc will perform positioning in the nearest mold until the disc pause is released, and then move to the next mold position. (5) During automatic operation, switching from automatic to manual mode will stop all actions except for the disc performing slow positioning (the disc switches during operation). Manual operation can be used to reset. 2.4 The main manifestations of the power consumption of the disc machine The power consumption of the disc machine is mainly manifested in the following parts: (1) Power consumption of the hydraulic system oil pump; (2) Power consumption of the heater; (3) Cooling fan. For shoe manufacturing enterprises, power consumption is the main part of their production cost. Among the above power consumption, the power consumption of the hydraulic oil pump accounts for about 80% of the total power consumption of the disc machine. Therefore, reducing its power consumption is the key to energy saving of the disc machine. 3 Power saving principle of the disc machine The disc machine has a very violent sudden change process in its operation, which has a great impact on the machine and affects the life of the entire injection molding system. At present, there are a lot of old equipment in domestic shoe manufacturing enterprises with low automation and high energy consumption. The machine is generally designed according to the maximum production capacity, but in fact, it often does not need that much power during production. The speed of the oil pump motor remains unchanged, so the output power is almost unchanged, and there is a phenomenon of a large horse pulling a small cart in production. Therefore, a lot of energy is wasted. Due to the unique characteristics of the main and auxiliary machines and rotary molds in disc-type machines, the number of effective mold positions used during production is often limited. For example, the TY-322 model has 24 sets of molds, but sometimes only a dozen or so are used. During trial runs and sampling, even fewer molds are used. This means that the main and auxiliary machines are frequently in a standby state for extended periods. The auxiliary machine only performs actions when it detects an effective mold position. While the disc is rotating, the auxiliary machine does nothing, but normally the motor continues to operate at its rated speed. During this time, the high-pressure overflow section not only does no useful work but also generates heat, causing the hydraulic oil to overheat—a wasteful and harmful process. We adopted sensorless vector control frequency converter technology for disc-type machines (as shown in Figure 2). The frequency converter detects the pressure and flow signals from the disc-type machine's computer board in real time. The pressure or flow signal of the disc-type machine is 0-1A. After internal processing, it outputs different frequencies to adjust the motor speed. That is, the output power is automatically tracked and controlled synchronously with the pressure and flow. It is equivalent to turning a fixed-displacement pump into an energy-saving variable pump. The original hydraulic system matches the power required for the whole machine operation, eliminating the loss of high-pressure overflow energy in the original system. This can greatly reduce the vibration of mold closing and opening, stabilize the production process, improve product quality, reduce mechanical failures, extend the service life of the machine, and save a lot of electricity. [b]4 Case Study of Energy-Saving Retrofit of Disc-Type Machines[/b] The energy-saving retrofit of a disc-type machine of a shoe material company in Jinjiang City, Quanzhou, Fujian Province is taken as an example. (1) Purpose of energy-saving renovation of disc machine: In the highly competitive shoe manufacturing industry, the main operating costs of enterprises are employee wages and electricity costs; due to competition among enterprises, the processing cost of plastic parts is decreasing, and the proportion of electricity costs in costs is increasing; saving electricity costs, reducing costs, extending equipment service life, and improving enterprise competitiveness are issues of concern to many operators in the industry. (2) Model of disc machine to be renovated: Dongguan Taiyu fully automatic disc plastic injection molding machine. (3) Power of disc machine motor: one main machine 22kW; two auxiliary machines 22kW×2. On July 22, 2004, in the first floor sole molding workshop, two KV2000-Z0220-4T sensorless vector frequency converters from Shenzhen Comron were used to carry out energy-saving renovation of the main machine and auxiliary machine of the disc machine. During the renovation, two-color sports shoe soles were produced, and the molding cycle was 30s. A three-phase four-wire electricity meter was installed on the energy-saving device for energy-saving rate testing. The energy-saving rates for the main unit and the auxiliary unit were 38% and 43%, respectively. The average local electricity price in Quanzhou, Fujian is 0.80 yuan/kWh. This plastic products factory operates continuously 24 hours a day. If we calculate based on 30 working days per month: When operating on mains power, the electricity cost per month is 7.2 × 24 × 30 × 0.80 = 4147 yuan; when operating with frequency conversion energy saving, the electricity cost per month is 4 × 24 × 30 × 0.80 = 2304 yuan. The monthly electricity savings per unit are approximately 1843 yuan; the customer can recover the cost in about six months. [b]5 Precautions for Frequency Conversion Energy Saving[/b] 5.1 Characteristics of Frequency Conversion Energy Saving (1) Simple operation, running synchronously with the disc machine, no adjustment is required; (2) High reliability: retain the original control mode and oil circuit of the disc machine unchanged; adopt the mains power/energy saving operation control mode so as not to affect production in case of failure; (3) Soft start: reduce machine vibration, extend the service life of equipment and mold; effectively reduce noise and improve the working environment; significantly reduce system heat generation and stabilize oil temperature; extend the service life of sealing components, reduce downtime maintenance rate, save a lot of maintenance costs, and increase the installed capacity of transformers; (4) High return on investment: depending on the process, all investments can be recovered in about 6 to 12 months through electricity cost savings. 5.2 Precautions for Frequency Conversion Retrofit of Fully Automatic Disc Plastic Injection Molding Machine (1) Selection of frequency converter and characteristics of KV2000 frequency converter After using frequency conversion energy saving, the production cycle will be extended. While saving electricity, production efficiency is reduced to varying degrees. This is because general-purpose frequency converters, using traditional V/F control technology, suffer from long start-up times, slow response speeds, and insufficient torque, leading to reduced torque and insufficient pressure. Some even increase the capacity of the frequency converter to compensate for the slow response, causing long-term overload of the oil pump motor, increased temperature rise, or burnout. Using a sensorless vector frequency converter can solve these problems. Shenzhen Comron Electric Technology Co., Ltd. has recently launched the KV2000 series high-performance sensorless vector control frequency converter, as shown in Figure 3. The KV2000 series frequency converter is a new generation of widely applicable multi-functional standard frequency converter, providing greater torque for the motor at low speeds and automatically compensating for motor speed fluctuations under high loads. It boasts excellent dynamic characteristics and superior overload capacity to meet a wide range of application needs. The KV2000 frequency converter features automatic motor parameter tuning, speed accuracy up to 5‰, and low-frequency torque up to 150%. It offers three control modes: sensorless vector control, output power (torque) control, and standard V/F control. Modern communication functions, high output frequency of 0-650Hz far exceeding that of traditional general-purpose frequency converters, rich built-in PID functions, unique cooling fan, nearly 200 control functions designed for industrial machinery, speed tracking function, unique automatic variable carrier frequency of 2-16.9kHz. It is suitable for constant torque and constant speed control of various plastic machinery, chemical textiles, water pumps, fans, printing machines, conveyor belts, food packaging machinery, metal processing machinery and other general machinery. By using KV2000 frequency converter for energy-saving renovation, it can achieve high power saving rate and ensure that the original production efficiency and quality remain unchanged. (2) The influence of frequency converter on the temperature of disc machine and the solution. Frequency converter is a power semiconductor device, which has the problem of high frequency interference and low frequency harmonics. However, due to the lack of professional technology of some application units, it causes interference to the control system of machine equipment, especially the temperature system. In severe cases, the system will not work properly. This frequency converter has the function of automatically adjusting the carrier frequency during operation, which minimizes the interference of frequency converter on the temperature system. When the temperature system is disturbed, a series of measures can be taken to solve the problem, such as connecting a dedicated grounding wire; adjusting the carrier frequency; adding a magnetic ring, filter, and AC output reactor to the output side; and adding a 1:1 isolation transformer of equal power to the original heating system circuit. (3) Electrical protection The KV2000 sensorless vector inverter has full-range protection functions: undervoltage, overvoltage, and overcurrent protection, preventing motor stall, overload, and overheating protection, ensuring that the inverter and motor are not damaged. When designing the system, the protection of the motor in the mains power state should be considered. If the switch is directly from the power saving state to the mains power state, it is equivalent to the motor starting directly, and the starting current is 4 to 7 times the rated current. The impact on the equipment and the power grid is very large, and it is easy to cause premature damage to the contactor, or even the motor to burn out. It is recommended that when switching, the motor (the original Y-Δ device) must be stopped first, then the power saving device should be switched, and finally the motor should be started. [b]6 Conclusion[/b] For most enterprises, electricity costs are the last cost beyond their control. It's commonly believed that electricity expenses are difficult to control, and paying for electricity is a matter of course, because the amount of electricity consumed by electrical equipment is determined by its electromechanical characteristics, and subjective control is powerless. Clearly, this view is wrong. Given the severe electricity situation nationwide, our enterprises should focus on energy conservation and the application of advanced technologies to minimize energy consumption, protecting the environment while creating economic benefits for the enterprise. Practice has proven that by applying high-performance, high-quality KV2000 sensorless vector control frequency converter technology and a series of technical management measures, enterprises can reduce operating costs by at least 20-60%. [b]References[/b] [1] User Manual for KV2000 Sensorless Vector Inverter [Z]. Shenzhen Comron Electrical Technology Co., Ltd. [2] User Manual for Fully Automatic Disc-Type Plastic Injection Molding Machine [Z]. Dongguan Taiyu Plastic Machinery Co., Ltd. About the Author: Nie Huinan graduated from the Mechatronics major of Fujian National Defense Industry Technical School and has long worked in the field of frequency converters and drives.