Coating machine spray guns commonly use a multi-hole structure, with three-hole designs being relatively common. These holes are typically used to control the coating liquid, atomizing air, and auxiliary airflow. By coordinating these channels, the spray gun can atomize the coating liquid into fine droplets and produce a consistent spray pattern, helping distribute the coating more evenly over the tablet surface. The exact number and configuration of holes vary depending on the spray gun design and coating process, so not every spray gun uses exactly the same three-hole arrangement.
Key Difference Between Perforated and Non-Perforated Coating Machines
High-efficiency intelligent coating machines are generally divided into perforated coating machines and non-perforated coating machines. Their main difference lies in the heat-transfer method and heat-transfer efficiency between the heated air and the product.
Perforated coating machines use a drum with perforated sections, allowing filtered hot air to pass through the product bed and exit through the lower part of the drum. This provides higher heat-transfer efficiency and makes them suitable for pharmaceutical tablets, larger pellets, and other products requiring organic film coating, water-soluble film coating, or sustained- and controlled-release coating.
Non-perforated coating machines use a fully enclosed drum without conventional perforations. Heated air circulates through a specially designed air-exchange system, resulting in relatively lower heat-transfer efficiency. These machines are commonly used for micropellets, small pellets, drop pills, granules, and similar products, as well as sugar coating, film coating, and sustained- or controlled-release coating.
How Does a Perforated Coating Machine Work?
In a perforated coating machine, the tablet cores continuously tumble and circulate inside a clean and enclosed rotating drum. Internal guide plates help maintain a stable movement pattern, ensuring sufficient mixing and improving coating uniformity.
After temperature-controlled mixing, the coating solution is delivered to the spray gun through a peristaltic pump and sprayed onto the tablet surface in a fine mist. At the same time, the air-handling system supplies filtered clean hot air to the machine. Under controlled negative pressure, the hot air passes through the moving product bed and exits through the perforated section at the bottom of the drum. This accelerates the drying of the coating solution and gradually forms a continuous, dense, and smooth film.
The entire process can be managed through a PLC control system, which coordinates parameters such as spray rate, airflow, temperature, and drum speed.
Why Is the Spray Gun Structure Important?
The spray gun directly affects the atomization quality, spray coverage, and coating uniformity, making it a critical component of the coating system. For pharmaceutical equipment, spray guns need to be designed according to GMP requirements and the specific coating process while also providing good corrosion resistance, cleanability, and operating stability.
High-quality spray guns are commonly manufactured from stainless steel for easier disassembly and cleaning. Flow rate, spray angle, and spray pattern can be adjusted according to process requirements. A properly designed spray-hole structure can also reduce dripping and clogging, improve spray consistency, and minimize coating-material waste.
Hansheng Automation can manufacture custom spray guns and related precision mechanical components for coating machines according to customer drawings and technical specifications. For non-standard parts requiring controlled hole diameters, connection dimensions, mating tolerances, or surface finishes, we can develop suitable precision machining solutions based on the actual application requirements and support both prototype and small-batch production.
Application Features of Perforated Coating Machines
Perforated coating machines perform spraying, mixing, and drying in an enclosed environment, helping reduce the dispersion of powder and splashing of coating liquid during operation. This can improve the working environment and reduce the risk of cross-contamination between different products.
Because of their relatively high heat-transfer efficiency, perforated coating machines can shorten drying times and improve production efficiency. They are particularly suitable for conventional tablets and larger pellets and offer a broad range of coating applications.
Some machines are also equipped with specialized air-exchange systems that allow hot and cold air to be switched according to process requirements. Certain air paddles can function as either air inlets or outlets, while the opening diameter can be customized according to process needs, such as approximately 0.6–3.0 mm, to accommodate different coating specifications.
Structural Features of Non-Perforated Coating Machines
Non-perforated coating machines use a fully enclosed drum structure, usually equipped with specially designed guide plates to ensure smooth product movement and reduce chipping and edge damage. The drum wall and guide plates can be polished to a smooth finish, which also facilitates cleaning and maintenance.
Compared with perforated models, non-perforated coating machines generally have lower heat-transfer efficiency. However, their enclosed structure and circulating airflow system make them suitable for certain specialized coating processes. The appropriate machine configuration should be selected based on product characteristics, coating formulation, batch size, and drying requirements.
Large-Drum-for-Small-Batch Design
Some high-efficiency coating machines are equipped with a large-drum-for-small-batch mechanism. This system adjusts the effective coating space inside the drum, allowing smaller quantities of product to be processed efficiently in a larger coating pan.
For example, certain 150-type machines can process approximately 20–40 kg of tablet cores through an appropriate internal adjustment mechanism. This expands the usable production range and helps reduce unnecessary coating-material consumption caused by an oversized drum.
Temperature-Controlled Mixing System
Perforated coating machines are commonly equipped with temperature-controlled mixing tanks to maintain the uniformity and stability of the coating medium. Some systems use electric heating combined with pneumatic agitation, with compressed air driving the agitator and stepless speed control providing stable mixing.
Depending on the process requirements, the coating medium can typically be maintained from ambient temperature to approximately 80°C. Components that come into contact with the coating medium are generally manufactured from stainless steel, while internal and external surfaces may be polished to facilitate cleaning.
For pharmaceutical equipment manufacturers, components such as spray guns, mixing tanks, shafts, bushings, supports, connectors, and other non-standard parts also require consistent machining accuracy and dimensional quality. We can provide made-to-drawing precision machining services for high-efficiency coating machine components based on customer 2D engineering drawings or 3D models. We select appropriate machining processes according to the material, dimensions, tolerances, surface roughness, and actual operating environment of each component.
