After installing a precision automatic spray gun to apply a chemical coating to insulated glass (IG) units, Norwich-based double glazing manufacturer Zenith Windows began to make material savings in excess of £10,000 a year. Installed during the Christmas shutdown to replace a previous auto spray device, the new electrically controlled automatic gun from Spraying Systems virtually eliminated wastage of an expensive chemical. “It paid for itself in the first week," reported production engineer Kevin Thurlow.

The spray application at the final stage of manufacture is critical. The purpose of the chemical is to finish the outer surface of the window, leaving it ultra smooth, inhibiting dirt retention and making it easy to clean.

However, the chemical itself is very expensive and the spray control system is designed to prevent wastage. A neutraliser is applied by hand to the IG units, which then pass under a traversing spray gun. Sensors at the gun detect the edges of the units on the moving conveyor, switching the gun on or off, so that it only sprays when over glass. Speeds are synchronised to avoid missed patches or doubled coverage.

But control is only effective if the spray gun responds by shutting off instantly on command, without further discharge of chemical. In practice, each time the solenoid cut off pressure, the gun previously in use continued to drip chemical. There were also problems of blockage caused by crystallisation of accumulated chemical at the orifice. This made it difficult to reduce consumption by using spray tips in smaller orifice sizes. All this changed when the new gun was installed.

Records kept by Zenith over a 2-year period showed that the average number of units covered per litre of chemical, which had declined from 137/litre to 132/litre from one year to the next, rose to 158 units per litre. This represents a chemical and cost saving of 13.3% since switching to the Spraying Systems gun.

Other points noted by production staff were that the spray operation was generally cleaner, with no dripping, no blockage problems, no fouling up of sensors and no liquid blobbing on belt or glass surfaces. Spray coverage is even and consistent and a tip with fine orifice can be used without difficulty.

The Model 26 automatic spray gun recommended by Spraying Systems on this application is designed for electric control and fast response, being capable of up to 1000 on/off cycles per minute. A version rated at 1500 cycles/minute is also available.