In a high‑efficiency coating machine, hot air is not simply blown into the coating pan; it enters through a coordinated combination of negative pressure suction and directed channelling, forming a continuous, controllable hot‑air circulation loop. The typical path is as follows:
Inside the sealed rotating drum, an exhaust fan creates a sustained negative pressure at the outlet side, keeping the drum's internal pressure below atmospheric level. Clean hot air from the heating source (electric or steam heat exchanger) is drawn into the inlet of the air‑distribution pipe-usually located at the upper right side or at one end of the drum centre-and then guided along internal flow channels into the working zone. The hot air traverses the tumbling core bed (tablets, pellets, etc.), where it contacts the coating medium and removes solvent, before being collected through duck‑bill shaped air‑blades that are embedded in the material bed and feature numerous fine orifices. Finally, the air is exhausted from the other side of the distribution pipe, forming a complete "intake‑penetration‑exhaust" cycle.
In this process, the cross‑sectional shape of the distribution pipe, the diameter and spacing of the air‑blade orifices, and the sealing clearance at the drum‑to‑exhaust interface jointly determine the airflow rate, velocity, and distribution uniformity. For instance, if the orifices are too large, hot air may "short‑circuit" through thin zones of the bed, causing local over‑drying; if too small, resistance increases, raising the negative‑pressure requirement and energy consumption. Consequently, for different materials (e.g., traditional Chinese medicine pills, chemical tablets, sustained‑release pellets), the dimensions of these critical structures often need adjustment-a flexible need that standard parts cannot fulfill.
Hansheng Automation can custom‑manufacture flow‑divider plates inside the distribution pipe, air‑blade orifice plates, and drum‑end sealing rings according to your material properties and process targets. We use 316L stainless steel or heat‑resistant engineering plastics, with aperture tolerances precisely controlled to ±0.02 mm via laser cutting or EDM, and offer various surface roughness finishes (Ra 0.4–1.6 μm) to suit different coating‑liquid adhesion requirements. Moreover, we can optimise the transition elbow design at the exhaust interface based on on‑site negative‑pressure measurements, reducing vortex losses and improving hot‑air penetration efficiency by 15%–20% while lowering fan energy consumption. Whether for new machine component selection or retrofit plate replacement on older units, we respond quickly to your drawings, ensuring that the airflow path precisely matches your process needs.
In summary, the entry of hot air into the coating pan is not a simple "blowing" action but a pneumatic process that relies on the precise interplay between negative‑pressure field and flow‑directing components. Our custom‑made flow guides and sealing assemblies provide the essential physical foundation for stable, efficient operation, helping you achieve the optimal balance between coating uniformity and drying efficiency.
