However, they need careful handling and are prone to absorbing moisture from the atmosphere with the result that they can go lumpy.

Make sure that you use a powder with the correct grain size for the stock you are printing. The grains must be at least as large as the biggest recesses in the stock's surface, otherwise they will not hold the sheets apart.

Spray powder can be used with stock of any weight or type and presses down to A4 size can now be fitted with a spraying device. However, beware of trying to swap spray powder equipment between presses because most systems are

designed to work with one make and size of press only.

STORAGE

If spray powders are kept in ideal conditions their is almost indefinite. However, powders are sensitive to wide changes in temperature, and this can have an adverse affect should it fall outside what is considered normal room temperature. Avoid storing powder containers on concrete floors or in a situation where the surrounding temperature could drop greatly overnight. This could result in moisture precipitation from the atmosphere, captured inside the containers, and spoil the powder.

COMMON PROBLEMS

A problem with spray powders is poor flow out of the spray nozzles and this is usually due to the powder being damp. Check the spray applicator container where the powder appears to have ceased flowing. Do not leave powder in the applicator for long periods when it is not being used, such as during a weekend. Powders which are hygroscopic will take up moisture from the atmosphere, especially in areas of high humidity.

If the air supply to the applicator is damp, which it may be if it is direct from the factory airline as opposed to a separate dry air supply, then this might be the source of the problem.

Kinks in the powder flow tubes can lead to blockages and poor flow, so check regularly that this is not acause of obstruction.