Energy-saving technologies in injection molding

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Drawing on processing technologies such as those used for rubber, metals, and ceramics, plastic processing technology has seen rapid development in recent years. The main molding methods include injection molding, extrusion molding, foam molding, blow molding, rotational molding and coating molding, as well as composite molding. China’s plastic industry began to develop after the founding of the country, and it expanded rapidly after the policy of reform and opening up. “During the 11th Five-Year Plan period, China’s output of plastic products increased by 20.1% on an average annually, while its value added grew by 20.06% per year on average. According to the latest data from the **Statistics Bureau, from January to November 2016, the total output of plastic products manufactured by enterprises above a certain scale across the country was 69.895 million tons. From January to December, the main revenue generated from rubber and plastic products amounted to 3,236.02 billion yuan. From January to November, more than 240,000 units of specialized equipment for plastic processing were produced by enterprises above that scale, representing a 7.6% increase compared to the previous year, indicating strong growth in this sector. Injection molding is an important processing method in plastic manufacturing; 80% of engineering plastics are produced using this method. The rapid development of industries such as automobiles, construction, home appliances, food, and pharmaceuticals has driven the advancement and improvement of injection molding technology. At present, about 50% of the plastic machinery produced in our country are injection molding machines. In major producing countries such as the United States and Europe, the output of injection molding machines is increasing year by year; injection molding is one of the molding methods that is developing fastest in terms of technology. Due to process and cost considerations, injection molding machines often operate continuously, making them major consumers of electricity – hence they are commonly referred to as “electric tigers”. According to statistics, the annual electricity demand for plastic processing alone in our country is enough to consume the entire amount of electricity generated by the Three Gorges Dam in one year; reducing energy consumption in injection molding processes has thus become a key focus in energy-saving efforts within the industrial sector. The electrical energy consumption in injection molding processes involves three main systems: power drive, barrel heating, and plastic drying heating. These three components account for over 95% of the total energy consumption in injection molding, and they represent the main areas for the development and application of energy-saving technologies. Taking a 200-ton injection molding machine of a certain brand as an example, the power consumption of its drive system is 18.5 kilowatts, the heating requirement for the barrel is 14.3 kilowatts, and the 100-kilogram hot air dryer requires 6 kilowatts of power; in total, this amounts to 38.8 kilowatts. If the machine operates at full capacity, it will consume around 87,000 kWh of electricity per year, which translates to 650,000 tons of carbon dioxide emissions (0.75 kilograms of carbon dioxide per kWh). The following details the development history of energy-saving technologies in injection molding, as well as predictions regarding the application of new energy-saving technologies, which can also serve as a reference for other molding techniques and methods. The main steps of the injection molding process in a power-driven system are: mold locking – plastic injection – holding pressure – cooling – mold opening – product removal. Each stage requires different pressures and flow rates; consequently, the load varies and so does the power consumption. In the past, injection molding processes mostly used hydraulic systems with positive displacement pumps; the oil pump motor provided a constant flow rate at a constant speed, and any excess hydraulic pressure was returned to the tank through a relief valve, which meant high-pressure throttling and resulted in the oil pump motor consuming more unnecessary energy. During the holding pressure and cooling, as well as the part removal phases, the injection molding machine remains in a stationary state; the demand for flow rate and pressure is virtually zero. However, the motor of the metering pump system continues to discharge oil into the hydraulic circuit. Due to the presence of system back pressure, additional electricity is wasted unnecessarily, resulting in energy losses of 25% to 80%. To reduce unnecessary power consumption, transitional technologies such as variable frequency technology and variable pump technology were subsequently developed. Thanks to 10 years of development in energy-saving technologies, the current mainstream technologies and products are servo energy-saving systems, including hydraulic servos and fully electric servos. Servo systems boast excellent properties such as energy efficiency, precision, stability, and fast response, along with a high cost-performance ratio. Almost all injection molding equipment manufacturers offer servo-driven energy-saving systems as their main products, with these systems accounting for over 90% of market usage. Some brands have even stopped producing injection molding machines that rely on metering pumps and are not energy-efficient. Meanwhile, the injection molding factories at the end of the supply chain have also gradually adopted servo energy-saving technologies through energy-saving upgrades, leading to the widespread adoption and acceptance of such technologies. Barrel heating system: The function of the barrel heating system is to maintain the temperature of the raw material within a set range. During the initial heating phase when the injection molding machine is turned on, as well as when working with plastics that require high temperatures, more heat is needed, resulting in higher power consumption. The technological development path of energy-saving cylinder heating includes: conventional heating coils (mica or ceramic), conventional heating coils + energy-saving insulation sleeves, electromagnetic energy-saving heating coils, infrared heating energy-saving coils, and superconducting far-infrared energy-saving heaters. In the past, ordinary heating coils were used, resulting in high surface temperatures, low heating efficiency, high energy consumption, and high costs associated with secondary cooling. However, the procurement cost was low and the accessories were inexpensive, so they were classified as low-value consumables. It is gradually phased out due to the requirements for high product quality, energy savings, and reduced processing costs. Currently, although conventional heating coils still dominate the market, some forward-thinking users have begun to use energy-saving products such as conventional heating coils combined with energy-saving insulation sleeves, electromagnetic heating coils, infrared nano-heating coils, and dual-effect energy-saving heaters. A comparison of the features of various energy-saving heating products is shown in Table 1. As can be seen from the comparison of the features of energy-saving barrel heating products in the figure above, new energy-saving technologies are continuously developing and improving. Recently, the **National Development and Reform Commission published on its official website the \"Catalogue of Key Energy-Saving and Low-Carbon Technologies\" (2016 edition, energy-saving section), recommending the \"dual-effect energy-saving heater\" as having the most advanced comprehensive performance. According to statistics, the adoption rate of energy-saving heating products is currently very low, accounting for less than 5% of the market. Due to their mature and stable technology, clear development trends, and increasing user acceptance, there is great potential for growth and market opportunities; outdated, energy-intensive barrel heating products will be completely phased out. Plastic drying and heating system: The drying effect on plastics has a significant impact on the quality of injection-molded products. Especially for certain engineering plastic materials with special properties, it can greatly affect the visual quality of the products (such as gloss and cracks), their performance requirements (such as bending strength and tensile strength), as well as their plasticization capacity and molding efficiency. During the injection molding process, drying and dehumidifying most plastics is a necessary requirement of the manufacturing process. Moreover, significant electricity consumption occurs throughout the entire production cycle, and hot air drying equipment is the most commonly used type. In the past, due to low procurement costs, non-energy-efficient hot air drying equipment was widely used. Its disadvantages included high energy consumption, low heating efficiency, high surface temperatures, significant heat loss, easy overheating and caking of the materials, as well as low safety levels. For example, a 100-kilogram hot air dryer could be purchased for less than 5,000 yuan, but the annual electricity cost associated with its use could exceed 20,000 yuan – a difference of several times. Users focused only on the low procurement cost while ignoring the high electricity consumption during operation, which resulted in reduced profits and lower competitiveness for enterprises. At present, the adoption rate of energy-saving plastic hot air drying equipment is very low, accounting for less than 1% of all plastic processing and manufacturing enterprises; therefore, there is great potential for development and numerous market opportunities in the future. Forecast of energy-saving trends in plastic processing over the next five years. Looking at the evolution of energy savings in power drive systems, quantitative pump systems have gradually given way to energy-efficient servo power systems. Users’ attitude toward energy savings has evolved from indifference, experimentation, acceptance, and widespread use; this awareness of energy savings has grown stronger, leading to its adoption, and after about 10 years, the adoption rate has reached nearly 100%. We predict that within the next 5 years, comprehensive energy savings in plastic processing will be achieved in this regard, as shown in Figures 1 and 2. The main reasons are as follows: on the one hand, the return on investment for using energy-saving systems is extremely high (over 50%), generating pure profits for enterprises; on the other hand, there is **government support**, allowing enterprises to receive more **subsidies**