Another point of importance is that unloading devices, cutting in and out automatically should be avoided at all cost where compressed air is to be used for painting. The reasons are that it is much better to use the surplus air for the purpose of getting rid of the condensation in the way already indicated, and that in addition most unloading devices are in the nature of compromises, and while saving only a small amount of power materially increase the wear and tear by throwing the load in the reverse direction on the gudgeon pin, large and small end of connecting rod and main bearings, and by causing a hammering action to be set up.
This applies in particular to air compressors with automatic valves where the device works by means of a valve closing the air intake entirely, and so setting up a vacuum in the cylinder.
A much better plan is to arrange the compressor to run at a speed sufficient to give a slight reserve of air above what is needed and to have it running constantly during the whole working period.
This may seem at first sight an arbitrary attitude to take up, but it is the result of considerable experience, and need not be considered as extravagant when it is borne in mind that air compressors of more than 40 to 50 cubic feet per minute capacity are seldom employed for such work, and so the maximum power absorbed is light.
The compressor illustrated in Fig. 71 is designed and made by the Airostyle and Lithos, Ltd., and has a number of well thought out refinements, both as to accessibility and form of valve bodies and valves, and also with regard to the filtration of the air and the lubrication of the cylinder. Ring oiler bearings are employed for the crankshaft, and the compressor throughout is as carefully built as a gas engine. The makers claim that an absolutely pure supply of air is delivered by this compressor at all speeds up to 350 r.p.m.
Water cooling is employed and very ample cooling surface is provided, not only for the cylinder but also the cylinder cover is cooled, and has the valves located in pockets in same.
An air compressor is shown in Fig. 72, and another one, which is water cooled, in Fig. 73. These are made by the DeVilbiss Co.
In Fig. 74 are illustrated various forms of air compressors; a pressure gauge, safety valve and drain cock are furnished with each receiver. These tanks have welded seams and are tested to 200 lbs. pressure.
Fig. 75.—Aerograph Air Pump and Tank Combined.
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. 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.
Fig. 77.—The Airostyle Plant—General Arrangement of Accessories.
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.
Fig. 78.—The Paasche Motor Driven Fan.
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.
Fig. 79.—The Airostyle Centre Draught Steel Plate Fan.
Fig. 80.—The DeVilbiss Auto Cool Electric Exhaust Fan, Closed, and Open for Cleaning.
Location of the Work Cabinets.
Fig. 81.—Sketch of Spraying Cabinets, Showing side Lighting.
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.
Fig. 82.—"Aerograph" Spraying Cabinets.
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.
The DeVilbiss "Fumexer" or Spraying Cabinet.
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. 87.—Aerograph Turn-table.
Fig. 90 shows the Paasche turn-table, which can be raised or lowered into suitable positions as well as tilted 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.
Fig. 91.—The Auto Electric Air Heater.
CHAPTER VIII.
Stencils and Masks—The Requirements of Different Trades in Spraying.
Just as in applying paint by immersion some parts which are not required to be painted can be protected, as already explained, so in spraying.
Certain parts are to be left unpainted, such as the plated fronts and glass lenses of cycle lamps. This is effected by the adoption of some system of masking. Such masks are, however, very simple and are sprung on with a simple wire spring or clip, and so held in place while spraying.
A mask has been designed and patented purposely for use when spraying. This is described on page 143. This mask has embodied in it a plunger on the end of which is mounted a rubber sucker, and as the plunger is controlled by a spring, all that is necessary to do is to depress the plunger down on to the lamp, box, or whatever article is to be painted; and as the sucker of the plunger comes into contact with the article first, it grips the surface and the spring behind the plunger forces the mask, which may be any shape, but is preferably of box form, down upon the article. This mask is very practical, but its use is limited, to some extent, to forms of lamps which do not need any stencil or mask. Such a step, needless to say, has only been taken because the system of compressed air japanning is the one ideal method—and one has only to refer to manufacturers who have used it for confirmation of this.
In addition to simple masks, there are many more complicated forms, such as those in use in gas meter manufactories, where there are no fewer than half a dozen points to be masked, and in hardly any case do more than two points remain the same over numbers of meters to be dealt with.
However, this has been overcome by arranging the masks on a spring foundation, and making them capable of sliding adjustment in two or more directions, and the time taken to fix these masks is in no case more than 30 seconds. Seeing that the time taken to brush a meter (even a small one) is not more than seven minutes and the time taken to spray one, with a superior result, is not more than one minute, there is a very considerable saving even after allowing time for fixing the mask.
Fig. 92.—Masks for Gas Meters.
Other stencils are employed for lettering on plates, despatch boxes, and for ornamental work on cash boxes, etc., and need no further description here other than stating that these must be of something stronger than tinfoil, and not too strong to prevent them being pressed firmly down on to the article to be dealt with.
In other cases, stencils are spun or pressed out to exactly fit the article, as in the case of brass lacquered goods, rubber balls, enamelled ironware, etc., and in some cases, where a number of stencils are employed, for one pattern, these are arranged round a common centre, and hinged so that, once the article is in position, stencil after stencil may be readily and accurately brought into position over the work.
For decorative work, very elaborate stencils are employed, with many plates for each design; but such stencils hardly come within the scope of the present work, although they are employed for wallpaper work, and in the textile industries for high-class effects.
The Hart Patent Mask.
Fig. 93.—The Hart Patent Mask.
A very ingeniously constructed, although simple, mask which is suitable for many purposes, but particularly for motor and carriage lamps, has been patented by Mr. Walter William Hart, of the firm of Matthew J. Hart & Sons, Great Barr Street, Birmingham, and others. By this invention means are provided for applying the mask to a plain surface so that it may be immovably held without causing injury to the surface. The mask, too, has the advantage that it can be placed in position with extreme rapidity. By this invention the mask is fastened in position by a suction pad, preferably made of indiarubber, which, when pressed on to the surface to be covered, adheres thereto by the pressure of the atmosphere. In Fig. 93 is shown an inner face view and a sectional elevation of the device. The mask (a) is adapted to have an axial movement in relation to the suction pad (b) so that when such pad has been fixed in position the mask may be pressed close upon the surface it is required to protect. This suction pad (b) is of a conical formation, and is secured to the end of the plunger (c) which passes rearwardly through a hole (d) in the back of the mask, and through a tubular extension (e) passing rearwardly from the back of the mask. The rear end of the plunger has a hole therein, which hole is screw threaded, and to such end a cap (f) is secured. A stud (f) on the interior of the flat end of the cap screwing into the said tapped hole, and the cylindrical portion (f2) of the cap slidingly fitting over the tubular extension (e) on the mask. A spiral spring (g) surrounds the plunger, one end bearing on a shoulder (h) at the rear of the mask and the other end bearing against the cap (f). To fasten the mask, the same is placed in position over the part to be covered and the cap (f) is pressed down, thus pressing the suction pad (b) upon the surface of the article, to which it adheres. A mask constructed according to this invention is capable of a great variety of applications, one of which is in connection with lamps. That shown in the illustration is intended for this purpose.
It will be clear that the shape, however, can be varied according to the article to be painted by spraying; for example, it may be used with advantage for decorative purposes.
MAKING STENCILS.
When it is decided to spray through stencils, it is usual to employ thin copper plates for the purpose, although in wallpaper decoration very heavy copper stencils are used, because, these being held horizontally, the weight increases the stiffness of them, while it prevents them shifting while in use. In ordinary work, however, where a stencil must be used vertically, the lighter stencil will be most useful. If paper is used, the best material is Japanese vellum, which is manufactured from a special fibre and possesses the advantage of being easy to cut and makes remarkably durable stencils. It is imported from Japan by Jas. Spicer & Sons, Ltd., 15, Upper Thames Street, London, E.C. Manilla paper may be had from the same firm, and answers also very well. For some styles of work, lead foil gives good results. Messrs. Locke, Lancaster, and W. W. and R. Johnstone & Co., Ltd., 94, Gracechurch Street, E.C., supply a material which they call "Four-ounce stencil metal," which weighs 4 ounces to the square foot, is made in sheets 6ft. by 2ft. 6in., and in smaller sizes, and costs 2s. per lb. It can be easily cut with a stencil knife, and is most suitable for work on horizontal surfaces. Another paper which may be used is ordinary Whatman's paper. The usual method of cutting is to use a very sharp knife, such as a shoemaker uses, and to cut on a sheet of glass. If any variety of paper is employed, it will be necessary to apply two coats of shellac varnish, ordinarily called "Patent Knotting." This protects the surface of the paper from being worn away by the action of the brush. Some stencil cutters prefer boiled oil for the purpose.
Zinc stencils are sometimes employed. These may be made as follows: The thinnest sheets of zinc are employed for the purpose, and upon this is painted the letters or design to form the stencil. The whole of the zinc which is not to be cut out, or rather, by this process, eaten out by acid, must be protected by means of a varnish made as follows: Take one pint of best asphaltum varnish, two ounces of beeswax and half-an-ounce of rosin and four ounces of Venice turpentine. Melt the beeswax and rosin in the Venice turpentine, and while warm add the asphaltum varnish, mixing thoroughly together. Paint this on the back of the zinc plate and on all parts that are to be protected. Form a dam or little wall made of 6 parts of beeswax and one part of tallow melted together and allow to cool. This is intended to confine the acid to the parts required to be eaten out. Nitric acid is used for the purpose mixed with three parts of water. This is poured on the space inside the dam and allowed to remain on for from 24 to 48 hours, when it will be found to have eaten away the zinc on the parts unprotected. Further information concerning stencils will be found in the book entitled "Stencils and Stencilling," by A. L. Duthie, published by the Trade Papers Publishing Co., Ltd., 365, Birkbeck Bank Chambers, High Holborn, London, W.C., price 3s. 3d.
REQUIREMENTS OF SPECIAL TRADES.
The following hints are given of the requirements of a few special trades:—
Piece Work.
In very many cases where articles are painted by means of compressed air it will be found quite practicable to have the work done by piece work. The exact time taken to spray any particular article can, after a very little practice, be determined quite accurately. In fixing the price to be paid for the work an allowance must, of course, be made for the time taken in bringing the piece to the spraying cabinet and placing it ready to be taken away by the boys or labourers. It is in this detail that speed may be increased so materially. The actual time of spraying to a great extent regulates itself, but if care is not taken considerable waste of time will be occasioned in getting articles ready and taking them away, and a satisfactory arrangement of piece work to both employer and employee will remove this waste of time and will prove more beneficial than day work.
Bookbinding.
The principal use of spraying in this work is to put on the speckled edges of books after they are sewed and before binding. This is usually done by splashing colour from a stiff-haired brush over a comb, but the method is a crude one at best. In using a spray for the purpose one of the simpler forms will do all that is required. The pressure must be lowered and paint removed some distance from the books until the requisite size of the spots or dots of colour is obtained. With a little practice this can be regulated to a nicety.
Carriages.
The remarks which will be found elsewhere, under the head of "Tramcars," apply to some extent to carriages also, and although the superfine finish required for a high-class carriage could hardly be produced excepting by the old-fashioned means, yet the processes of flowing-on and spraying could, without doubt, often be employed for the cheap and moderately cheap style of vehicles of various kinds which are now produced on so extensive a scale.
Cycle Parts.
Many parts of cycles are now painted by means of spraying, although some firms prefer dipping. Whichever process is used it is necessary, as a rule, to give at least two or sometimes three or even more coats, and to get a fine finish to rub down between these coats with powdered pumice and water, and, for the last coat underneath the finish, rottenstone and oil. The parts must always be stoved, as air drying enamels are not, as a rule, sufficiently hard to permit of their resisting the hard wear to which cycles are subjected. It need hardly be said that the method of handling various parts will to a great extent determine the economy effected.
The wearing parts of cycles are sometimes finished in the following manner, which is the method used by the Birmingham Small Arms Co. Although somewhat expensive it is certainly worthy of all praise, because it gives so durable a finish. The iron or steel parts are first thoroughly washed in American turpentine and are then stoved, the result being a perfectly clean surface. A coat of Calcutta linseed oil is then given by means of brushes and the parts are then stoved at 250° F., after which they receive a coat of what is called "Black Rubber Solution," an elastic enamel which dries with a semi-gloss. Then two separate coats of khaki colour japan are given and each are stoved at 280° to 300° F. A little rubbing down between the coats is sometimes necessary, and this is done with glass paper. The parts thus finished are very suitable for work which is to be subjected to very hard wear. At this writing the cycles are all intended for Government, hence the care taken in the finish.
Electrical Work.
Painting by compressed air is done in the case of many parts of electrical apparatus, the process being similar to that previously described. Thus the metal work of fuse boxes may be finished in this way with black japan, and one coat stoved at 250° F. or thereabouts will usually be found to suffice.
Among the large number of electric works where the process is employed may be mentioned those of W. T. Henley's Telegraph Works, Ltd., at Gravesend. The Airostyle is used in this case, and the work is done approximately from twice to three times as rapidly as it was formerly done with the brush.
Fancy Baskets.
Fancy baskets which are made of cane, willow, special straw and other materials can be sprayed with admirable effect in many cases where brushing would be impossible. Indeed, the application of a spray in this work may be considered to have created almost a new industry in a wide range of fancy goods, which may be sprayed with gold paint, or a great variety of coloured enamels may also be employed. In this case celluloid varnishes are also employed with the addition of coal tar dyes for the production of colours such as mauve, blue, moss green, rose pink, amber, orange, fire red, navy blue, etc. The work of spraying in this case is usually done over a bin such as is shown below, a simple wire device being used at the top to support the basket while it is being sprayed, although even this is often dispensed with as the article may be held by the handle, and being very light this is not found to be irksome.
Fig. 94.—Bin for Spraying Light Articles.
Gas Meters.
At the present time less than half a dozen gas meter manufacturers or repairers have a paint spraying plant in use, and these are described elsewhere. The saving, however, by spraying the paint is in this class of work very considerable, amounting to about 1 to 5; that is to say, five times as much work can be turned out with a spraying machine as by hand. It is generally recognised that the quality of the painting is much improved, it being harder and better in appearance and generally more satisfactory. Turn-tables of a simple character are employed, and 24 hours are allowed for the drying of the work. For protecting the indicators, the name of owner or manufacturer and brass plates of similar character, various types of shields or masks are employed, consisting of a plate of requisite shape soldered on to a piece of stiff wire, with turned ends, which embrace the meter and hold it in position. There appears to be no reason why the larger size gas meters should not be painted by spraying, provided that a suitable plant, which would be of a simple character, were provided. There is but little doubt that in a little time every manufacturer of gas meters will find it necessary to employ a spraying plant.
Gas Stoves and Ranges.
In this class of work spraying is used almost exclusively; as only one side of the iron is to be painted the dipping process is obviously unsuitable. The work is done at a pressure of about 45 lbs., but sometimes a little less is sufficient. The usual exhaust is provided and turn-tables are employed having bearing wheels on the outer edge of a circular plate. Those used for the larger ranges are usually level with the floor. In addition to black, all kinds of colours may be used. This work is mostly done piece work. The smaller parts, such as rings, cookers, etc., are also sprayed. The stoving is done at 350° F., but when two coats are given the first is subjected to 450° F.
The interior of the ovens are coated for a finish of oxide of tin, which when stoved at a high temperature assures a great increase of "body" or opacity. Sometimes the finish is left solid, but in most cases the coat is stippled.
The usual overhead runways consisting of hanger on four wheels on V-shaped girder are employed.
Picture Frames, Picture Moulding, Etc.
One of the industries in which paint spraying is strikingly successful is that of preparing picture frames with a "gold" finish. If properly done the result is even better than if gold leaf is used, as the spray covers completely the most elaborate and intricate ornament. Picture frames or mouldings of various shapes and sizes are obtained ready for receiving the various coats necessary to give a gold finish. Formerly the whole of the operations were done by means of brushes, but this method has been wholly superseded by spraying, which approximately does the work five times as quickly and gives a far better result.
Three separate processes are employed; the first is the application of a coat of enamel, the second a coat of bronze or "gold paint," and the third the application of a transparent lacquer. The last protects the bronze from discoloration, and the manufacturers guarantee that such mouldings will last at least 5 years without tarnishing.
The whole of the work is air dried, but to facilitate the operation the workroom is kept at a temperature of about 75°F and the drying ovens up to, say, 80° or even 85°F. The first coat of enamel is sprayed on, and in about two hours is felted down with a pad similar to that used by french polishers. This is dipped in a solvent which removes all inequalities. The actual spraying is done on a long open trough shaped bin some 3 ft. 6 in. from the floor having exhausts at the bottom and thin laths placed across it at intervals of about 18 inches. The long stretches of moulding are placed on these laths lengthwise, the laths holding them in position. The spraying is done directly on them and they are turned from side to side, and when the spraying is completed each length is lifted bodily by two boys, one at each end, on to racks in the drying room which is close by and which has a large number of open iron shelves running from end to end. These shelves are quite close together, so that a large number of lengths of moulding may be dealt with at one time. Heat at about 85°F is admitted at the bottom, and the drying apartment is open from end to end in front so that the mouldings may be readily introduced. This heat also serves to warm the room.
The enamel being dry the length is removed and gone over with a pad as described and the gold paint is then sprayed on over the whole of the work, giving a beautifully fine and compact gold finish. The application of the transparent lacquer completes the operation. The materials used in this work are special spirit varnishes made on a base of celluloid. The exact composition varies with different manufacturers, but the following recipes are based on "The Manufacture of Spirit Varnishes," by Livache and McIntosh (Scott, Greenwood and Son), and will be useful for reference. The great advantage of using celluloid is that a coloured transparent varnish is obtained.
Recipe for Celluloid Varnish.