Supply of Compressed Air—Paint Supply—Exhaust.

The forms of spraying apparatus having been selected, consideration must next be given to the following details, viz.:—(1) The supply and degree of pressure of the compressed air. (2) The form and location of the paint supply. (3) The arrangement of an exhaust installation to carry away the fumes and waste paint. These will be dealt with in their order.

It is clear that attention has to be paid to a convenient arrangement of reducing valves controlling the pressure of air to the sprayer, and also providing, what is in many cases indispensable, a pressure feed of colour to the sprayer, either from a large pot mounted over the hood, or a special type of bowl screwed on to the sprayer.

Some makers still advocate a simple type with small bowl screwed on to the sprayer, and no means of controlling the pressure save by adjusting the safety valve on the main tank, thus necessitating that each operator shall work at the same pressure, arguing that reducing valves, pressure feeds, etc., etc., are unnecessary refinements, but it may be safely claimed that such opinions are made without due consideration of the advantages of the more complete system, and that the consensus of opinion is in favour of such refinements, giving, as they undoubtedly do, a further increase in speed, and, in many cases, making practicable what would otherwise be impossible, as well as ensuring that whatever work is to be done, the most suitable pressure is instantly available.

In the equipment of an efficient compressed air plant for painting, the type of compressor employed, and the arrangement of the air main, should first be decided upon.

The compressors must be designed to give an absolutely pure supply of air free from oil or grit, and the air-main must be so arranged as to avoid any trouble due to condensation. This is overcome, first, by using, at least for high-class work, a horizontal air compressor, water cooled, with a sensitive sight-feed needle valve lubricator to the cylinder, capable of delicate adjustment, so as to avoid excess of lubrication. Needless to say, the machining of the cylinder, piston, etc., of the compressor must be of the highest class to ensure satisfactory running under such conditions. Then a suitable air filter must be fitted to the intake of the compressor. This filter should be of large diameter, and have a gauze screen and wad of cotton wool.

The air valves should be so arranged that they may be removed without breaking the water joint, and be so arranged that they may be taken out and replaced in a few seconds.

The main tank must be provided with safety valve drain cock and pressure gauge, and the air main, of not less than ¾ in. diameter barrel, preferably steam barrel, must be arranged to travel in a downward direction from the main tank towards an end station tank, which is a duplicate in miniature of the main tank or receiver. All branches must be taken upwards off the main. Such an arrangement, if care is taken that the end station tank has its relief valve set to blow off before the main tank safety valve acts, ensures that all moisture is collected in the end station tank.

The Airostyle and Lithos, Ltd., claim to be the originators of such a system, and it is here explained in print for the first time.

All experiments with a view to scrubbing or purifying the compressed air of moisture, oils, etc., on the air main side of the main tank, other than the above simple expedient, have proved more or less failures, either from want of appreciation of the increased capillary attraction set up in the tanks and air main, or from the difficulty of satisfactorily and frequently cleaning out such scrubber as may be inserted, and the incidental difficulty created in the prevention of dust being carried out of the scrubber throughout the system.

It need hardly be said that ample air must be provided in order to have sufficient pressure always available for the full number of operators employed, and this point is one which cannot be too strongly emphasized, for in too many cases firms have installed small compressors and have been misled as to their maximum capacity, mainly through over anxiety on the part of the salesman to secure his order for apparatus, he apparently having been afraid to ask a high figure for a really efficient compressor.

One of the Aerograph types of power pump and tank is shown below. It is strongly built, easy working, and is fitted with metal extending rings and metal valves, which will supply enough air for three spraying painters.[Pg 119]
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[Pg 121] In the illustration is shown the pump fitted with an automatic regulator, but this may be dispensed with if desired. The regulator, therefore, will be found of great value, not only in saving power, but also in the wear and tear of the pump. The tank is fitted with an air gauge and a speed valve, and the dimensions of the air receiver are 18 inches diameter by 30 inches high, and the pump has a bore of 3 in. while the stroke is 7 in. The power required is 1 h.p.

The Supply of Paint.

For lacquering or coating small articles a spray may be used which is constructed with a cup to contain the paint, but for any heavy painting where large surfaces are to be covered quickly a cup on the handpiece is not of much utility, and it is necessary to provide a means to keep the supply of paint to the handpiece continuous. This is done in two ways: By an overhead paint pot, allowing gravity to carry the paint to the handpiece, or by an enclosed paint pot with a regulating valve and pressure applied to the surface of the paint by compressed air. In some situations all that is required is an overhead paint pot, the weight of the liquid feeding it to the handpiece. An enclosed paint pot has the very great advantage that (with a proper valve) the feed of the paint can be regulated to a nice degree. The paint pot shown in Fig. 77 has a damped cover which is capable of being quickly removed, and a low-pressure feed to the paint is obtained from a reducing valve. This can be set so that the paint can be forced to the handpiece to secure a uniform flow whether the paint be thick or thin.

The Exhaust Installation.

We next reach the question of arranging a satisfactory form of exhaust installation, which has been found to be absolutely essential in order to insure the health of the operator.

This exhaust question obviously opened up special problems in the direction of convenient forms of hoods or work benches, so arranged as to carry away the fumes created by the paint distributor without unduly inconveniencing the operator by reason of the draught set up.

By some firms use is made of the exhaust to collect the residue or surplus paint drawn off by employing a ventilator, which sets up a medium pressure, and interposing between the outlets of the hood and the air shaft some form of perforated screen or screens which are readily removable, or in some cases revolvable and self-cleaning.

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.

This fan is designed and made by the Airostyle and Lithos, Ltd., and is invariably specified in all their medium and large installations for compressed air painting. It is very carefully designed and built specially for the work, and is fitted with ball-bearings.

As will be seen from the illustration, Fig. 79, it is worth serious attention on the part of intending users.

It is made in many sizes, from 2,000 to 23,000 cubic feet capacity, and is very largely used, not only for Airostyle plants, but also for general ventilation work.

In the above figure is shown a motor-driven propeller fan manufactured by the Paasche Air Brush Co. It is made in various sizes, varying in air delivery from 1,200 to 10,000 cubic feet per minute.

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Location of the Work Cabinets.

As to the position of the spraying benches, it is a little curious to note that in not a few cases these cabinets are placed facing the window, the idea being to obtain as much light as possible for the process. A moment's consideration, however, will show that this is not the correct position, because the workman faces the light, which is thrown on the back of the article he is spraying, in exactly the wrong position for his purpose. The cabinets should be lighted from the back of the workman and be, as far as possible, directed from the roof or the top of the room, so that it comes directly on the article to be sprayed. Clearly it is necessary to provide as good a light as possible in order that no part of the work shall be missed.

Artificial light will, as a rule, be provided for working on dark days and after the sun sets, and here again the same provision must be made. Plenty of light arranged in such a manner that it is directed on the front of the object to be painted is essential in every case.

After due provision has been made for a suitable exhaust, which question should be left in the hands of the specialist in compressed air painting if satisfaction is to be guaranteed, other questions need attention, such as provision of means for handling the work, special turn-tables, which should be ball-bearing, if possible, to ensure light running and enable even heavy articles to be turned about when spraying, and when examining the work.

The Fumexer.

In connection with the Aeron, the makers supply a special form of cabinet or booth, made of steel, which is called by them the "Fumexer," and is illustrated in Figs 83 to 89.

These are made in various sizes, from 3 feet to 16 feet wide, and 4 feet to 18 feet deep. They are each fitted with turn-table and specially constructed fans for drawing out the air, and with it the superfluous paint, enamel, etc.

Fig. 84 shows a side view of an 8-ft. Fumexer indicating the style of construction and funnel-shaped back clear to the floor.

The steel Fumexer with the Autocool electric exhaust fan installed is claimed to insure a maximum exhaust efficiency, and to completely remove all fumes arising from the work in the finishing room—at a minimum of power consumption.

The Fumexer is a fire-proof steel booth specially designed and built for the height of service. It is constructed of heavy sheet steel on an angle iron frame, with wire glass windows in sides and top. Provision is made for electric lights—reflector and sockets being built in.

The back of the Fumexer is funnel-shaped clear to the floor, which arrangement, together with the large fan opening, gives maximum exhausting results, especially on large work. The short exhaust pipe running from the back opening is easy to clean and permits of the placing of the Fumexer near outside wall.

To take care of all classes and styles of work, the Fumexer is regularly made in a variety of sizes as above mentioned with the proper number of fans installed. Other sizes to meet any special requirements are made to order.

A turn-table, which is adjustable, tilting and revolving—either floor or suspended type—is supplied with the Fumexer. This device facilitates the handling of a large percentage of work. The floor type turn-table is not fastened to the floor nor Fumexer and can be removed when not required.

The Autocool electric exhaust fan installed in all Fumexers is an exclusive Aeron system product, and is particularly adapted to the work required of it.

In Fig. 85 is illustrated the side and front views of a 4-foot single exhaust fan installation Fumexer with suspended type turn-table.

The fan motor, completely enclosed and protected from fumes, is automatically cooled by a stream of pure air which is continuously drawn through the motor. This means a fan of increased efficiency. The motor is only one-twelfth H.P. and will do the required work at one-tenth or less the power consumption of other styles of exhausting methods.

Autocool fans are made in one size only, the number of fan units being increased for Fumexers above five feet in width. In this way the right number can easily be adapted to any kind of work. The makers claim that by this arrangement a better distribution of exhaust is obtained, and the vapour is moved quickly at low pressure through the large fan openings—this accounting for the small amount of power used.

The next illustration shows the Autocool electric exhaust fan both closed for use and with motor and blades swung inward for cleaning.

In Fig. 86 is shown a special Fumexer with three exhaust fan installation and automobile body.

This equipment, together with type D Aeron with V spray head or type M Aeron with V-A spray head and the air transformer set, is used for priming and surfacing automobile bodies.

Two very interesting illustrations are Fig. 88, the one on the left being a Fumexer with automatic elevating and revolving turn-table, while that on the right is a Fumexer with wheel-jack.

The turn-table is revolved by a 1/8 H.P. electric motor, furnished in either direct or alternating current. The speed of rotation is adjustable through a wide range by means of a friction wheel and disc. The table is started and stopped by either hand lever or foot pedal entirely independent of motor.

A ten-inch elevation of the table is accomplished by compressed air acting on a piston which supports the revolving parts. A hand lever controls this feature, and the speed of elevation and lowering is adjustable for different classes of work.

This turn-table is especially designed for handling box-like work, finished inside and outside in the same or different materials. The elevation feature makes possible the painting of an article one colour inside and another outside in one operation without interference. It is also well adapted for use on other classes of small work.

The Fumexer in operation is shown in Fig. 89.

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Accessories.

It is difficult to classify accessories as readily as the sprayers themselves; we must content ourselves with a description of some of these as supplied by the firms mentioned in the previous chapter.

One of the most complete plant supplied is that installed by the Airostyle & Lithos, Ltd.

They have, in addition to the sprayers, a system of carrying a specially designed colour pot on a bracket over the hood clearly seen in Fig. 77. Such a colour pot has a clamped cover, making an airtight joint, and so arranged as to be readily taken off for cleaning or re-charging, and with a spun copper container, offering no obstruction to the flow of the paint and reducing loss to a minimum. Connections are provided on the top for the pressure feed, for filling up by means of a funnel, and for permitting the use of the compressed air as a means of driving out the paint from the flexible tube before leaving the instrument after work is finished each night.

Another accessory is a smaller pressure bowl made to screw directly on the pistol sprayer and designed to make possible the use of many coloured enamels, while still retaining the advantage of the pressure feed. Pressure is conveyed into the bowl through a flexible tube from a special type of reducing valve, shown in Fig. 77.

This illustration shows the connections as universally employed on Airostyle plants.

The reducing valves are so designed as to give in case of the top valve a pressure up to 15 lbs. for the pressure feed, and in the lower one any pressure instantly from atmospheric pressure up to the maximum.

It is the practice to take the air pressure from the air main through the reducing valve into the low pressure tank, as shown, as this further ensures that absolutely pure air shall be delivered to the sprayer and a steady supply of air at any pressure is always available.

The low pressure tank is, as shown, a very simple type, albeit soundly made, and a drain tap is provided at the base of same.

Last, but not least, comes the type of flexible tubing employed, and this is the outcome of much experimenting, in that the same is unaffected by the action of turpentine, white spirit, or even naphtha.

Before leaving this question the reader is referred to the numerous illustrations (see pages 155 to 185), as these give a far better idea of the completeness of the Airostyle plants than is possible in this chapter.

Turn-tables.

To facilitate handling of goods to be sprayed, a turn-table is usually found of considerable service. These turn-tables vary according to the class of work that is being dealt with. In Fig. 87 is shown one made by the Aerograph Co., Ltd., which is 20 inches in diameter by 12 inches high. It is made entirely of cast iron, excepting the cone seated bearing, which is of hardened steel, which rotates freely and is nicely finished. The weight is 98 lbs. Sometimes turn-tables are provided with projecting points to prevent the article being sprayed from moving, while in other cases the top of the table is provided with ridges for the same purpose.

In all small turn-tables a conical bearing of hardened steel, properly lubricated, is sufficient for the purpose, but in the larger work it is desirable to employ ball-bearings. Whichever method is used, it is essential that the table turns very freely so that it can be moved almost with a touch.

Fig. 90 shows the Paasche turn-table, which can be raised or lowered into suitable positions as well as tilted[Pg 135]
[Pg 136]
[Pg 137] at any angle. It revolves freely with a gentle touch. Larger sizes are supplied. The necessity of providing for carrying off the fumes which arise in paint spraying has already been dealt with.

The Auto-Electric Air Heater.

This invention is the property of the DeVilbiss Manufacturing Company, and is intended to overcome the tendency of the air to cool as it leaves the nozzle in spraying, while it tends to keep it heated till it reaches the work. It also raises the temperature of the varnish or enamel, producing a smooth, even finish.

In addition to heating the air, the auto-heater warms the nozzle, thereby raising the temperature of the varnish. Because of the heated air and warmed material there is a complete elimination of the pitted, pebbled or mottled effect so noticeable when "short oil," quick setting or heavy bodied varnishes or enamels are sprayed on flat surfaces. The auto-heater enables Aeron users to improve the quality of many classes of work—in many instances it opens up an entirely new field of usefulness. The auto-heater and the air transformer set together insure clean, dry and warm air at the proper pressure, which is an important factor in the production of the best Aeron results.

The auto-heater applies the heat at the last possible point before the air enters the Aeron; as a consequence there is absolutely no loss or waste of heat, as would be the case if the air were heated at some other point and then passed through the hose to the machine. It is very easy to understand that if air heated before entering the hose retained sufficient heat to be of service when reaching the nozzle, it would be so hot that it would destroy the hose. In the only practical way, the auto-heater maintains the heat in the air at the proper degree till the spray reaches the work.

The auto-heater is light, yet rugged in construction. It has no exposed contacts. The conductor wires run through the air hose. It can be attached to any style of Aeron without difficulty. There is an automatic cut-off furnished with every auto-heater. Placing the Aeron in the cup holder, or hanging it on the hook, automatically cuts off the current—picking up the Aeron automatically turns on the current. This automatic control effects a great saving in current. As a protection against overheating the auto-heater is equipped with a fusible safety disc, which melts, allowing the air to escape, if current is left turned on by accident when the Aeron is not in use. This safety device operates within four minutes. Several extra discs are furnished with every outfit. The auto-heater can be connected to any electric light socket, and consumes only 250 watts current when in operation.

The construction of the auto-heater will be understood on reference to Fig. 91.

Another interesting heater is supplied by the Airostyle & Lithos, Ltd., a number of which are in use in this country Its general form can be seen on reference to Fig. 102, page. 165, which shows a gas-heated type. The same heater is also supplied either electrically or steam heated.

In all types it has the same general features, namely, a water-jacketed colour pot, a special coil for heating the air supply, which is afterwards passed through the water jacket for the dual purpose of raising the temperature of the jacket and damping down the air temperature at the same time. To a convenient standpipe the hot air is carried and distributed to the pistol, and also to a special jacket round the colour tube.

The Airostyle pistol is provided with an adjustment which admits of the hot air by-passing the whole time so, maintaining the pistol at the same temperature as the colour pot and ensuring a steady flow of the japan.

The heaters are mounted on a stand at the side of the hood and are complete with pressure gauges, regulating valves, special burner for gas, or an electrically heated pot giving three heats, or for steam giving a wide range of temperatures controlled by the steam pressure through a reducing valve. It must be explained that the same result is obtained no matter which form of heater is employed, and that in no case can the japan be burnt. The heaters are used for thick black tar varnish, or cycle japans, also for certain gum or glue mixtures and special varnishes.

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