Since the localization of extrusion coating technology, the development of domestic extrusion coating machine technology has been rapid, showing a strong momentum to catch up with Japanese and South Korean equipment manufacturers.
With the development of extrusion coating technology, the market penetration rate of extrusion coating machines in China has been steadily increasing. Looking at the types of coating machines purchased in the first half of 2015, extrusion coating machines accounted for 70% of the market share. In particular, large and medium-sized lithium battery companies and newly established power battery manufacturers almost entirely adopted extrusion coating machines.
One of the core components of an extrusion coating machine is the intermittent control valve. The intermittent coating function of the extrusion coating machine is entirely achieved by the control of the intermittent valve, and the dimensional accuracy and longitudinal consistency of the coating thickness during intermittent coating are also guaranteed by the control and adjustment accuracy of the intermittent valve.
Currently, pneumatic control valves are used both domestically and internationally due to their low cost and ease of maintenance and control. However, due to the low speed accuracy of the cylinder, they are easily affected by external factors, such as changes in air pressure and friction of the sealing ring, which can affect the opening and closing speed of the intermittent valve, resulting in dimensional drift during intermittent coating (as shown in Figure 1) and unstable thickness deviation at the beginning and end of the coating.
Figure 1 shows the potential dimensional drift phenomenon when using pneumatic valves.
Furthermore, in intermittent coating processes, deviations between the head and tail thicknesses and the standard process values are common (with the head often being thicker). When using pneumatic valves, the opening of the cylinder's flow restrictor is often manually adjusted to regulate the cylinder's operating speed for correction. Since there are no quantified scales or numerical values, this relies entirely on the experience and visual inspection of the on-site operators.
This places high demands on the operational skills and experience of the equipment operators and maintenance personnel. When the cylinder speed fluctuates due to external factors, readjustment is necessary.
In summary, due to their poor resistance to external interference, pneumatic intermittent valves suffer from poor stability and low automation, requiring constant operator intervention to achieve the required process precision. To address these issues, a series of domestically produced servo intermittent valves have been developed and launched. A servo intermittent valve is essentially a valve whose pneumatic drive has been replaced with a servo drive. Currently, successfully validated products include linear servo intermittent valves, servo cam intermittent valves, and servo rack and pinion intermittent valves, with the linear servo intermittent valve demonstrating particularly outstanding performance.
Servo motors are characterized by high speed accuracy, good stability, and insensitivity to external environmental influences; they also offer strong controllability, enabling parameterized control. These characteristics overcome the shortcomings of cylinders, giving servo intermittent valves the following advantages:
1. High speed accuracy and stable operation greatly improve the dimensional accuracy of intermittent coating and prevent dimensional drift due to unstable operating speed of the intermittent valve (as shown in Figure 2).
Figure 2 shows the size distribution of coating on a servo intermittent valve.
2. It enables human-machine interface control and parameter adjustment, improving the automation level of intermittent valves. For the intermittent coating head and tail thickness adjustment method, the running speed and action sequence of the servo motor can be directly modified on the touch screen. The parameters are quantifiable, so a work reference document can be formed, which has strong repeatability and operability, reducing the dependence on human experience.
3. Servo motors have a longer service life compared to cylinders. Even in harsh coating environments, servo motors can last at least 5 years, while cylinders, under frequent, high-pressure conditions, have a service life of less than 1 year.
Because servo intermittent valves have significant advantages over pneumatic intermittent valves and provide a qualitative improvement in the precision of coated products, they will definitely be widely used in extrusion coating equipment in the future. This innovation represents a core technology breakthrough for extrusion coating machines and will bring a milestone improvement to the coating precision of lithium-ion batteries and the automation and intelligence of coating equipment.
Currently, the concept of servo intermittent valves is not yet available in leading lithium battery equipment countries such as Japan and South Korea. The introduction of domestically produced servo intermittent valves is an important manifestation of the independent research and development of domestic lithium battery coating equipment and one of the technological highlights that surpasses Japanese and South Korean lithium battery coating equipment.
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