Kevin Healy, Metallisation Ltd., Dudley West Midlands

Originally Published in "Coatings" July 2000

Stringent requirements in the Aerospace industry result in demands for high quality production, combining accuracy, quality repeatability and above all safety. Metallisation have created an Aerospace Production Cell to delver these requirements. The combination of precision manipulation and tried and tested thermal spraying equipment meets the exacting requirements expected in this field. A full range of  coatings can be applied in the cell including metallic bond coats, repair materials, ceramics and abradables. The thermal spraying cell primarily incorporates the Metallisation P550M mass flow controlled plasma system and the Metallisation Arcspray 140E/s250 automatic system, if required HVOF and flamespray processes can also be incorporated dependant upon the particular application being undertaken. A tilt and turn turntable provides an additional two axes to the six-axis robotic manipulator, ensuring that all areas of the component are accessible for coating.

Due to the possible presence in the cell of the operator for loading/unloading of components, it is important that all safety aspects of the operation are considered and a risk assessment carried out. Based upon these findings the cell incorporates:

1. Emergency stop and booth interlock system to ensure the operators safety when programming and operating the system and has the following features:
   • Access to the both inhibited when in automatic mode.
   • During loading/unloading of the components power to robot motors is removed.
   • For programming purposes the robot can be operated from the remote robot panel. This will allow the robot to operate at reduced parameters and only with the 'enable' switch closed.
   • The booth door can be opened from the inside even when locked.
   • The booth door can only be opened once the turntable faceplate has stopped rotating.
   • E/Stop push button and wall mounted cord pull inside the booth.
   • E/Stop push button on main robot console and operator panel.
   • Interconnection of booth, extraction, robot, Plasma and Arcspray E/Stop push buttons.
   • Additional footswitch located outside the reach of the robot that must be depressed when enabling the robot via the 'enable' switch.
   • Extraction flow switch.
   • Coloured floor area to define working reach of the robot.
2. Gas detection. This again is connected to the E/Stop loop to disconnect power to all electric inside the booth should an alarm situation occur.

3. Continuous extraction through a bifurcated fan in the location of flammable gases.
4. Extraction purge timer on initial switch-on of the system before enabling lights and equipment.
5. Unlike any other plasma spray equipment the PS550M uses a main gas unit incorporating flammable gas segregation, mass flow control and a single electrical cable connection between the gas unit and the operator control panel. This ensures the operator is only able to operate the system externally to the room, with the gas cabinet localised to the gas detection system.

Since thermal spraying processes produce, as by products, noise dust and radiation it is necessary to contain the  equipment in an extracted, soundproof area. The 'Cyclovent' extraction system employed uses a wet collection system capable of achieving the existing limits for emission of dust particulate at 50 mg/m3 as well as being able to achieve much higher levels if required in the future. The extraction system employs a four-stage cleaning process in a single unit.

Stage 1 pre-cleaning is provided by an irrigated cyclone, large particles impact with large water droplets and are removed by the cyclonic action.

Stage 2 is a multi-venturi scrubbing station where the fine water droplets are atomised by the  velocity of air passing  through the  multi-venturi cage.

Stage 3 is a vortex cloud of fine water droplets through which any uncollected particulate is forced to pass, ensuring capture of the particles by the spinning water mist.

Stage 4 sees the clean air, upon its exit, cyclonically propelled into a liquid disengagement zone, which radially separates the particulate contaminated fine droplets from the gas stream without moving parts or conventional mist cleaners.

Apart from its collection efficiency this system also gives the benefits of non internal moving parts, nozzles, packing, eliminators or consumables such as bags or cartridges. The 'Cyclovent' itself is virtually maintenance free with only items such as the fanset and pump requiring a maintenance regime.

With increasing environmental and safety pressures upon industrial processes this form of thermal spraying cell provides an opportunity to produce high-quality coatings in a manner which is simple, clean and safe for the staff operating the system and is also environmentally friendly.

For further information about this article please contact:

Kevin Healy, Metallisation Limited, Dudley, West Midlands DY2 0XH
Phone +44 (0) 1384 252464
Fax +44 (0) 1384 237196
E-mail: rd@metallisation.u-net.com

For other articles presented at the TSSEA conferences or printed in "Coatings" see the publications page or contact TSSEA for further information.

© Copyright 2001 TSSEA