Powder Coatings Recovery

The function of a powder recovery system is to collect the overspray material and render it suitable for recycling and at the same time to remove the powder particles from the exhaust air stream before discharge into the atmosphere.

There are two main types of collectors:

Cyclone collectors
Cartridge collectors
(there are more designs of collection systems which use these two principles).

Cyclone collectors: The input to the cyclone is connected to the booth while the output is connected to a suitable exhaust fan. The overspray powder arrives at the cyclone inlet at a velocity of about 20 metres per second.

On entering the cyclone chamber tangentially the air/powder mixture is given a rotary motion which creates a centrifugal force on the particles. The larger and heavier particles tend to be ejected to the outside walls of the chamber and fall to the bottom where they are collected. The lighter fractions will stay suspended in the air stream which on reaching the bottom is deflected by a conical tail air/powder mix into a rising spiral which is then carried through the central stack to a filter collector.

For a standard powder the recovery efficiency can be as high as 95%. For lines that have a high % of particles <10m in the recovered powder the recovery efficiency will be reduced (as low as 85%). Inevitably therefore a cartridge filter is used in conjunction with a cyclone solely to prevent discharge of the fine powder to the atmosphere.

The recovered powder is removed from the cyclone by means of a rotary valve and is then passed through a sieve to remove any agglomerates and foreign matter. The recovered powder is then blended with the virgin material in predetermined proportions. Virgin: Reclaim mix ratio should always favour virgin.

Cartridge collectors: In this technique the overspray powder from the application booth arrives at an enclosure containing a number of cartridge filters.

Typical filter materials:

Paper cartridges
Scinter lamellar (plastic)
Polyester cloth
The cartridge filters separate the powder from air by causing the powder/air mix to pass from the outside of the cartridge to the inside through a layer of filter material which retains the powder and allows the air to permeate through and on to the atmosphere.