Conveyorised pre-treatment

Components are handled in a production process.  The dimensions and production volume will determine the process; flow of goods through the system may be continuous or intermittent. 

Continuously moving overhead conveyors are the more common with the various spray processes contained in an enclosed tunnel.  The track speed relates to the volume and product size, and the process will be set by the coating performance required.   The total length of system results from the length of each process stage together with adequate draining between each of the stages. 

For example; consider parts that are 1.5 metres long and spaced 0.5M apart, and the track speed has been set at 2.0M per minute.  The maximum output from this system will be 2 (M/min) x  60 (to give track speed per hour) divided by 2 (M load pitch) or 60 loads per hour.  Assume that this is a three-part system (cleaner and two rinses) - each process will have a time requirement, for example 3 minutes for cleaning and 0.5 minutes for each rinse.  Drainage between each process must, in length be at least equal to the product length to avoid cross-contamination of the process liquids, and a zone of equal length is required at the start and end of the process to prevent the migration of sprayed liquid from the pre-treatment tunnel.

In this example the tunnel length will be made up of entry and exit zones plus two drain zones: 4 x 1.5M = 6.0M and cleaner (3 minutes x 2M/min) 6.0M, and two rinses each (0.5 minutes x 2.0M/min) 1.0M. (6.0 + 6.0 + 2.0) = 14.0M total tunnel length. The spray tunnel is usually mounted above the tanks that hold the process solutions, in this method spent solutions from each stage freely drains back into the appropriate tank. The spray zones envelope the product with stand pipes and high pressure spray nozzles usually forming a grid pattern of 300mm x 300mm.

Some of the processes will require heating, this may be through immersion tubes inside the tank using gas or oil-fired burners.  Alternative methods include external calorifiers where, for example, steam or HPHW may be used to raise the temperature.

Rinses may be sprayed cold, however it is recommended that the final rinse is heated to assist with drying the product.

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