During the operation of a feed coating machine, the uniformity of coating thickness directly impacts the quality and stability of the feed product. As a core process parameter, the roller speed differential plays a decisive role in controlling coating thickness. The roller speed differential refers to the relative difference between the speeds of the coating roller and the substrate. Its adjustment essentially alters the shear field and the flow state of the coating liquid to achieve precise control of coating thickness. When the coating roller speed exceeds the substrate speed, the resulting speed differential generates directional shear forces, encouraging the coating liquid to form a uniform fluid layer on the substrate surface. Conversely, if the speed differential is too small or negative, the coating liquid tends to accumulate on the substrate surface, resulting in localized excess thickness.
In the feed coating process, the coating roller speed determines the amount of coating liquid supplied per unit time, while the substrate speed influences the time the coating liquid spreads on the substrate surface. When the coating roller speed is fixed, increasing the substrate speed shortens the contact time between the coating liquid and the substrate, resulting in a reduced coating thickness. Conversely, decreasing the substrate speed prolongs the contact time, resulting in a thicker coating. However, simply adjusting a single parameter can easily lead to coating edge effects or center thickness fluctuations. Adjusting the roller speed differential can create a dynamically balanced shear force field. For example, when coating high-viscosity feed slurry, appropriately increasing the roller speed differential can enhance the shear effect, allowing the slurry to quickly level on the substrate surface and avoiding uneven coating caused by excessive viscosity.
Optimizing the roller speed differential requires consideration of the coating roller's textured structure. Coatings in feed machinery often use micro-concave rollers or comma-shaped scraper rollers. The depth, shape, and density of the surface texture directly impact the coating liquid transfer efficiency. When the roller speed differential matches the texture parameters, the coating liquid can evenly fill the cells and release stably under shear forces. If the roller speed differential is too large, the coating liquid in the cells may be ejected due to centrifugal force, resulting in streaky coating defects. If the roller speed differential is too small, the coating liquid is not fully released, and granular protrusions may form in the cells. Therefore, the optimal roller speed differential range for different texture structures must be determined through experiments to ensure that the coating liquid transfer volume is synchronized with the substrate's movement speed. Ambient temperature and humidity significantly influence the effectiveness of roller speed differential adjustment. In high temperatures, the viscosity of feed slurry decreases and its fluidity increases. In this case, the roller speed differential can be appropriately reduced to prevent excessively thin coatings. In low temperatures, the slurry viscosity increases, requiring an increased roller speed differential to enhance shear and promote leveling of the coating liquid. Furthermore, humidity fluctuations affect the surface tension of the substrate. If the ambient humidity is too high, the surface tension decreases after the substrate absorbs moisture, making it easier for the coating liquid to spread. Therefore, the roller speed differential needs to be reduced to control coating thickness. If the humidity is too low, static electricity on the substrate surface increases, enhancing the adhesion of the coating liquid to the coater. In this case, the roller speed differential can be appropriately increased to prevent coating buildup.
Online monitoring and closed-loop control are key to improving the accuracy of roller speed differential adjustment. Modern feed machinery coaters are typically equipped with laser thickness gauges or ultrasonic sensors that collect real-time coating thickness data and dynamically adjust the roller speed differential via a PLC system. If the coating thickness deviates from the set value, the system automatically adjusts the coating roller speed or substrate speed, creating a closed-loop feedback loop. For example, if the coating is too thick in a certain area, the system can reduce the coater roller speed or increase the substrate speed to quickly eliminate the thickness deviation. If the coating is too thin, the system adjusts the parameters in the opposite direction to replenish the coating liquid.
From a long-term operational perspective, the stability of the roller speed difference depends on the mechanical precision of the equipment. The radial runout and axial parallelism of the coating roller, as well as the synchronization of the drive system, all affect the actual effect of the roller speed difference. Therefore, regular equipment calibration is necessary to ensure that the movement paths of the coating roller and substrate are strictly parallel to avoid local roller speed difference variations caused by mechanical deviation. Furthermore, the use of high-precision servo motors and reducers can improve the response speed and accuracy of speed control, providing hardware support for roller speed difference adjustment.
Roller speed difference adjustment is the core method for achieving coating thickness uniformity in feed machinery coaters. By scientifically matching the speed relationship between the coating roller and substrate, combined with the characteristics of the anilox structure, environmental parameters, and online monitoring technology, a dynamically optimized shear force field can be established to ensure high spatial and temporal consistency of coating thickness. This process not only requires precise control of process parameters, but also relies on the deep coordination of equipment performance and material properties, ultimately providing reliable guarantee for the quality stability of feed products.
