Spray pre-treatment

The advantage of spraying is that the process combines mechanical action with chemical reaction.  Typically each process will take less than half of the time required by a dipping system.

The usual arrangement of a spray pre-treatment plant is to have a tunnel that contains the sprays, mounted above a series of tanks that contain the process and rinse liquids.  The process may be carried out on a continuously moving line of product, or may index through the spraying tunnel.

Either way the same process schedule applies, but whereas an indexing system will allow product to drain above the holding tank, in a spraying system a drain zone is required between each process.  Thus an indexing system can offer a shorter process tunnel length, but with limited throughput of about twelve component loads per hour.  Whereas a system using a continuously moving conveyor is only really limited by the factory space available.

The system requires regular planned maintenance to ensure that each of the spray nozzles are clean and that the intended spray pattern is being achieved. Access is provided into the tunnel for maintenance and adequate safety procedures should be in place whenever internal access is required.

The system requires regular planned maintenance to ensure that each of the spray nozzles are clean and that the intended spray pattern is being achieved.

Access is provided into the tunnel for maintenance and adequate safety procedures should be in place whenever internal access is required.

The design of a continuous spray system is based on the track speed and the size of the component loads.  The tunnel requires an entry and exit zone equal to the length of the longest component, and drain zones again equal to the longest component, to avoid the loss of spray either through the tunnel ends or between zones.  Drainage is important as cross-contamination will reduce the effectiveness of the processes.  The actual process zone lengths are determined by the process time and track speed.

Pre-treatment produces waste by-products; depending on the condition of the components there may be a need to collect and remove oil or grease on a regular basis. 

Some of the processes also generate waste, zinc phosphate, for example - which is probably the most commonly used corrosion inhibitor for ferrous metals produces a sludge that needs to be removed from the holding tank.

Many of the process require heat; cleaning, pickling, phosphate conversion etc. operate at up to 50ºC.  Lower temperature materials are being introduced to save energy, and alternative systems are being developed that are more environmentally friendly.

Pengrave Engineering Ltd, off Delta Way, Bridgtown, Cannock, Staffordshire WS11 0DJ
Tel: 01543 577142 Fax: 01543 577930 Email: sales@pengrave-engineering.co.uk