How a rotary bell atomizer works

ProBell is a rotary atomizer used in automated finishing processes. The automatic, electrostatic sprayer can be mounted on robots, reciprocators or fixed mounts

This review of the ProBell starts with component identification, and then covers the three areas of rotary bell atomizer operation:

• Air and fluid flow through the applicator
• Spraying, cup washing and purging
• Electrostatics

The first component is the bell cup. The bell cup atomizes paint by rotating at speeds up to 60,000 rpm. ProBell cups come in three sizes: 15 millimeter, 30 mm, and 50 mm.

The splash plate distributes the paint evenly across the inside surface of the bell cup prior to atomization

The air cap and cover direct the shaping air to the correct diameter for the bell cup. The three sizes of ProBell air caps match the three bell cup sizes: 15 mm, 30 mm, and 50 mm.

The fluid tube and nozzle deliver paint or solvent to the bell cup assembly. ProBell has six nozzle sizes: 0.75 mm, 1.0 mm, 1.25 mm, 1.5 mm, 1.8 mm, and 2.0 mm. 

The air turbine assembly is driven by compressed air and provides rotating speeds of up to 60,000 RPM.

The ProBell rotary atomizer has three fluid valves: the paint valve, the solvent valve and the dump valve. 

All incoming fluid lines enter the ProBell through the fluid bracket. This is also the connection point for grounding.

There are three coiled fluid tubes in solvent borne models and one for waterborne models. The coiled fluid tubes provide a more resistive path between the high voltage and the ground.

There are also nine air lines and connections for various functions, such as triggering valves, bearing air, and shaping air. 

There’s also a low voltage cable that brings low voltage to the power supply. 

The magnetic pickup monitors the rotational speed of the turbine. 

First, set the air bearing supply between 70 and 100 psi. The bearing air should be on all the time to keep the bearing in a floating condition.

The turbine is a matched fit to the air bearing, so there’s a dimensional tolerance that requires a clean, dry air supply. 

The bearing air has a return line that provides a pneumatic signal back to the controller pressure switch, so the controller has verification that the air supply to the air bearing is active and ready for operation.

The next air supply is for the inner shaping air. This flow captures and propels the paint towards the part being painted.

The outer shaping air helps bring in the pattern to define the pattern shape and improve transfer efficiency.

Dual shaping air provides a higher degree of pattern control and pattern adjustability. It also makes it easier to paint into small spaces and corners.

Turbine air is used to drive the turbine at a rotational speed of 10,000 to 60,000 rpm. A valve-to-piston (V-to-P) ratio is used to adjust this air flow to the turbine to maintain the programed speed.

Brake air is used to reduce the speed of the turbine for fast speed changes. 

The magnetic pickup sensor we mentioned earlier is monitoring the rotation of the turbine, providing feedback to the controller by fiber optics.

The spraying process begins when an air signal goes to the paint valve, and the paint valve becomes active. The paint travels through the top side of the dump valve, through the paint valve, and continues out to the bell cup. The rotation of the bell cup, with the assistance of the inner and outer shaping air, then creates atomization.

For a cup wash, the paint valve is shut off, and an air signal goes to the solvent valve. Once the solvent valve is triggered we’re going to send solvent to both the inside and the outside of the bell cup. The bell cup is still rotating to assist the wash.

For the paint line purge, the paint and solvent valves will be shut off and an air signal will trigger the dump valve to go active. Solvent from a feed source, such as a color change valve or a proportioner’s purge sequence, flushes the ProBell’s fluid line.

Once the fluid line is clean, the paint valve can be triggered to flush the bell cup. Air from an outside source, such as a color change valve, can be introduced to remove the solvent from the gun in preparation for service. If service is not required, solvent can be left in the system.

Electrostatic operation of the ProBell rotary atomizer includes these steps:

1. When loading the ProBell with paint, the electrostatic must be off.
2. Once paint is loaded out to the bell cup, the electrostatics can be turned on. 
3. The controller is going to send a signal to the ProBell’s internal power supply through a low voltage cable.  The power supply then amplifies the signal up to 100 kV or 100 kilovolts. 
4. The high voltage is sent to the turbine, the air cap, and the bell cup. 

When the electrostatics are turned off, the high voltage power is bled back through the power supply’s internal resistor.