Tech-articleSpray coating applications

The use of nozzles for the applications of coatings is common in many industries. Broadly speaking coating systems can be broken down into four main groups

 

Spray bar on conveyor1 Continuous conveyor

Typical coating applications will involve a spray bar deployed over a product conveyor. A line of spray is produced and the motion along the conveyor ensures the entire product is coated as it passes under the spray bar. Normally such setups deploy flat fan nozzles.

Whilst the conveyor will be moving continuously the product may be spaced at intervals. This means that spraying may only be required when a product passes under the spray bar. If they process is fast moving then such systems will require precise control and this will often mean air actuated spray nozzles are required.

Dosing can be controlled by the flow through the nozzle as well as by the speed of the conveyor.

For simple continuous spraying systems hydraulic flat fan nozzles may be suitable. For systems that requires stop start spraying or other more precisely controlled on/ off cycles air actuated nozzles will be required. Air atomisation of the spray itself may also be desirable in many coating applications as this can create a very fine spray with small droplet sizes at low flaw rates meaning better cohesion of the coating. (please click on the nozzle icons below to access data sheets)

hydroPulse Flat fan nozzle box (NF) XAer air atomising , full cone, external mix, narrow spray angle nozzle Flat Fan, Air atomising, Internal mix nozzle (XApf)


2 Stop start conveyor

In this system product is moved under a spray bar and stopped whilst the coating is applied. The conveyor then moves the product on. This may involve several spray coating points i.e. multiple applications of spray.

Typically full cone nozzles will be deployed so that an even coating of fluid is delivered to the stationary target. In most cases air actuation of the nozzle will be required to ensure a responsive on / off cycle. Air atomisation of the spray itself may also be suitable to reduce the droplet size to improve cohesion. (please click on the nozzle icons below to access data sheets) 


Low flow maxipass full cone nozzle XAer full cone external mix air atomising nozzle

3 Drum coating

Drum coating spray barThe coating of pelleted or tablet products needs as different type of system. Running tablet along a conveyor would clearly only coat one side and the sheer number of product would mean turning each one would be impractical. As such these types of product are typically coated in drum coating machines. The uncoated product is moved around in a cylindrical drum whilst spray of coating fluid is applied. The random motion of the products ensures that an even coating is applied to each product. This type of coating is very common in the pharmaceutical industry for tablet coating.

Typically high precision air atomising nozzles will be used in these applications. As the spray is being directed at a moving mass of many tablets it is desirable to spray very fine droplets. Finely atomised sprays means a greater randomisation of fluid and thus a more even coating. (please click on the nozzle icons below to access data sheets)

SAM Air Atomising Nozzle XAer air atomising , full cone, external mix, narrow spray angle nozzle Flat Fan, Air atomising, internal mix deflected

Fluid-bed-coating-top4 Fluidised bed coating

Similar to the drum coating process this variation sets the uncoated tablets moving upwards in a chamber in an air current. The solid product thus becomes “fluidised” i.e. it behaves much like a fluid with randomised movement of individual particles. A spray is injected into the air current so that it hits the moving tablets thus applying the coating. As the tablets are temporarily suspended in an air stream when they come into contact with the coating spray the contact is potentially from all angles and so an even 3d coating can be applied. This process relies on the randomised movements of the target pellets / granules so they behave in a fluid like way when they meet the similarly randomised droplets. As such the process mimics the mixing of two fluids. 

The nozzles required for this type of application need to have very well controlled patterns, droplet sizes and flow rates. Slight areas of over spraying with increased fluid   density can, for example, result in product sticking together. As such, SAM nozzles, with their independent air inlets for actuation, atomisation and spray angle are the logical choice. (please click on the nozzle icons below to access data sheets)

fluid bed coating bottom spray wurster

SAM Air Atomising Nozzle

Engineering considerations

For more details on selecting nozzle and spray set up please click on the items in the blue menu to the right hand side of the page. There are many factors to consider when selecting nozzles for spray coating applications we consider three of the most important: achieving accurate dosing, achieving accurate coverage and adjustments needed when spraying viscous fluids.

Coating engineering considerations

Coating nozzles