Where slow drying japans are employed, such saving is of considerable advantage, although it must not thereby be assumed that an extravagant wastage of paint occurs, for it must be borne in mind that with a spraying plant there is no loss through evaporation from open pots and gradual drying up of the paint on the sides of the pots, or absorption of same in the brushes employed. Actually, therefore, although it would appear that considerable wastage occurs, yet in practice it is found to be economical, and even where intricate forms, such as cycle frames, wheels, carriers, etc., or bedstead work are to be dealt with no undue loss is experienced, and such small loss as may be noted is compensated for ten times over in the saving of time effected.
When selecting a ventilator for the plant, the fact must not be overlooked that the fine particles of paint, etc., drawn off by the ventilator gradually coat the blades of the fan, sufficiently to materially increase the friction, and to absolutely prevent the exhausting of the air should multiple bladed fans be adopted.
Experience has shown, therefore, that for such work as compressed air painting multiple bladed fans are to be avoided, even though these are scientifically designed and admirable for many classes of exhaust work.
Not more than 8 to 10 blades should be employed, and there must be no belt-drive taken through the air shaft, this being a source of continual annoyance in addition to creating a loss of efficiency.
Where simple impellor fans are used, long spindles should be employed permitting an outside drive, but a better type of fan is the central draught type, preferably ball bearing, as these run for years with no attention save occasionally filling up with grease and periodical cleaning.
It may be argued that many of the foregoing remarks are not properly within the scope of this book, yet on further consideration it must be conceded that they all have a bearing upon the ultimate efficiency of the installation, and are the outcome of years of experience.
When arranging a compressed air painting plant considerable thought must be given to the most convenient position, and where stoves for artificially drying on the paint, japan, etc., are employed, care must be taken that a sufficient number of these stoves are provided to give the plant full scope, for a very material saving per annum is effected, additional to that accruing through the labour-saving effect of the apparatus, by the fact that the stoves are filled more quickly.
Where bulky work is to be handled, the plant must be so arranged as to give ample room for getting the work to and from the hoods.
The volume of exhaust air will depend on the character of the paint and the size of the cabinet. For large articles a large cabinet is required, and a proportionately larger fan will be needed. From 500 to 1,000 cubic feet of air per minute should be supplied for each worker. A hurricane of air is not required; all that is needed is to keep the air moving away from the worker, and the ordinary type of wall fan may be sufficient for a simple installation, but cannot be used for large plants.
Airostyle Central Draught Steel Plate Fan.