Paints, Lacquers, Varnishes, Etc. used in Spraying.
Under the head of "Paints used for Dipping" some information has been given in respect to the paints suitable for that purpose. Some, but not all, paints are suitable for both dipping and spraying, the exceptions being the heavier or more viscous compounds, which are not suitable for painting by immersion because they are too thick. Tar, enamel, and the heavier varnishes may be given as examples, although they may be successfully applied by the spraying process.
Sometimes in dealing with the heavier compounds the application of heat is an advantage. This may be applied to either the paint or the compressed air or to both in order to increase the fluidity of the compound. It is important when heat is thus applied that the temperature of the room in which the spraying is done should be raised correspondingly, so that the heavier paints, enamel, etc., do not congeal by being directed against a cold surface. Under most circumstances it is unnecessary to apply heat, provided that the spraying room is kept at a temperature of not less than 60° F. both in summer and winter.
As already intimated, the preparation of paints, lacquers and varnishes for both dipping and spraying necessitates a close study of the special requirements. In the case of paint the particles of pigment must be very finely divided as coarse material would tend to choke up the spraying apparatus, or if even they did not actually have that result they would require a greater pressure of air and thus add to the cost of working. Zinc oxide, the various grades of black and most bright reds, are examples of finely ground pigments which are well suited for spraying.
In buying materials for this purpose it is well to purchase of those firms who have made a special study of the subject. The following is a list of a few such firms, all well known to the writer, and although it by no means exhausts the list yet anyone desiring to buy materials may very safely leave themselves in their hands.
Messrs. Docker, Bros., Ltd., Birmingham; Gittings, Hills and Boothby, Ltd., Tower Varnish Works, Long Acre, Birmingham; Goodlass, Wall and Co., Ltd., Seal Street, Liverpool; A. Holden and Sons, Ltd., Bradford Street, Birmingham; Indestructible Paint Co., Ltd., King's House, King Street, London, E.C.; Lewis Berger and Sons, Ltd., Homerton, London, N.; Llewellyn Rylands, Ltd., Balsall Heath Works, Birmingham; Mander Bros., Wolverhampton; Postans and Morley Brothers, Ltd, 19, Lionel Street, Birmingham; The Frederick Crane Chemical Co., Birmingham; Thornley and Knight, Birmingham; Wilkinson, Heywood and Clark, Ltd., Caledonian Works, Poplar. E.; Pinchin, Johnson and Co., Ltd., Bevis Marks, London.
The following are American firms:—
The Moller and Schumann Co., Chicago, Ill.; John Lucas and Co., Inc, Gibbsboro', N.J.; The Chicago White Lead and Oil Co., Chicago, Ill.; John W. Masury and Son, New York, N.Y.; The Glidden Varnish Company, Cleveland, O.; The Sherwin-Williams Co., Cleveland, O.;
STOVING ENAMELS.
We now reach these important enamels, and extract the following from the foreword of the little book above mentioned. Messrs. Wilkinson, Heywood and Clark claim to be the first successful makers of stoving blacks, which was in the days before the introduction of bicycles. Though originally introduced for cycle work, stoving enamel produces a most successful finish for all kinds of materials. In the United States of America such enamels are used in great quantities for finishing standardised motor bodies. These black enamels have gained a very high name for themselves, as properly baked they are extraordinarily hard, brilliant and tough, and when applied over such material as tin sheets are flexible enough to withstand being bent double without showing signs of cracking. An important feature are the coloured enamels made by the same firm, which run through a whole series of yellows, reds, browns, greens and blues, and are hard, durable and tough, and can be stoved without changing colour. We extract the following notes on the "Application of Stoving Enamels," and fully endorse the recommendations offered:—
1. All work should be perfectly free from dirt, grease or oil, before application of enamel.
2. Every trace of moisture should be removed before enamelling. This can be effected by stoving the work, previous to enamelling, at a light heat. Moisture on work will cause enamel to blister and burn.
3. Always when using brushing or dipping enamels, allow the enamel to set slightly (i.e., after the surplus paint has dried off) before putting in the baking oven. This will prevent uneven stoving and eliminate "fat edges," as far as possible.
4. Oven heat should be increased gradually. Never place enamelled work into a hot oven at once, but raise the heat by degrees, until the full temperature is obtained.
5. Most of our enamels are sent out slightly thick; should an easier working material be desired, in the case of colours or blacks, add kerosene gradually until the required consistency is obtained. Coloured enamel should always be stirred before use, to prevent the pigment settling and the light medium rising. If this is not done, the appearance of the work will lack body and appear dull and lifeless. This applies especially to dipping enamels. To render white stoving enamel thinner, add pure turpentine only, stirring well, until a uniform consistency is obtained.
6. It is quite possible to over-bake enamels and spoil the colours, and likewise under-baked enamels will not be tough enough to withstand hard wear. Particular attention should be paid to the directions on the package labels, as the various pigments require different temperatures.
7. Stoving enamels, if left in an opened can, tend to thicken considerably. For this reason, keep the can closed when not actually using the enamel.
For thinning purposes we recommend kerosene. Sp. gr. 810 at 60° F.
8. Ovens should be properly ventilated to allow the proper oxidation necessary in baking.
Enamels.
It has already been pointed out in these pages that the success of painting by dipping, spraying, "flowing on," in fact, all other mechanical means, depends upon the exact properties of the materials used. The same is true with enamels, which are made from a large variety of formulÆ so as to dry slowly or quickly in the air, or when subjected to heat in a stove. The author feels he cannot do better than take as a guide to the properties of enamels in general the extremely useful handbook published by Wilkinson, Heywood and Clark, under the head of "Enamels for every Purpose." This book gives practically all the information concerning enamels likely to be required by the average user. The products are divided up under different heads, for example, one page is headed "Heat Resisting and Slow Drying Enamels." These dry fit to handle in 16 hours, and dry bone hard in 24 hours. They are made to withstand heat up to 212° F., and for this reason are suitable for enamelling iron baths, radiators, etc., particularly so as to effectively resist hot water without softening or peeling. They are made in a number of beautiful colours. A somewhat similar series of enamels is made which dry quicker, viz., in 8 hours fit to handle and quite hard in 12 hours. They are useful for touching up radiators, stoves, steam pipes, etc., and are made in white and a dozen or more colours. The next series which demands our attention are "Dipping Air Drying Enamels." They dry in 8 hours and are quite hard in 12 hours. They are claimed to produce a finish equal to that obtained by a quick air drying brushing enamel with the labour of brushing eliminated. For a finish done by immersing the article to be painted these are capital enamels, but they require to be used with a stirrer of some sort in the tank.
Hints on Stoving or Baking.
The degree of heat to which an article is subjected after being painted or japanned will obviously depend upon the kind of coating used. It is safe to assert as a general rule that the heat applied must not be higher than the particular paint or enamel is made to withstand, for, if this be exceeded, it will inevitably result in a loss of elasticity, of the protecting film and, hence, its durability.
The following hints are taken from a very useful little pamphlet issued by the Moller & Schumann Co., of Chicago, Ill. The degrees of temperature given refer to their products, and would doubtless have to be modified in some cases, according to the nature of the paint being dealt with. They will, however, form a very useful guide.
Fig. 107.—J. Lucas, Ltd., Airostyle Plants, showing the Two Bays of One Complete Unit.
Fig. 108.—Airostyle Plant Installed for Messrs. The Gas Light and Coke Co., Ltd. General View.
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Black Japan Finishes.
One or more coats rubbing finish japan, reduced as thin as possible and still cover well.
Bake each coat at 250° to 350° for 3 to 4 hours. Sandpaper each coat lightly.
One or more coats finishing black japan reduced to brushing consistency (not too thin).
Bake each coat at 300° to 350° for 3 to 4 hours. Sandpaper each coat lightly. Rub the last coat with pumice. Apply transfer and striping to last coat of japan.
Bake these at 150° for 1 to 2 hours.
One or more coats finishing copal brushed as it comes from the can. This protects the transfer and striping and increases the depth of the finish.
Bake each coat at 175° for 2 to 3 hours. Rub each coat and polish the last coat.
If finishing copal is omitted, leave the last coat of japan in gloss, or rub and polish as preferred.
Steel Furniture Enamels.
One or more coats of first coat enamel, reduced as thin as possible and still cover well. When brushed on, use steel preservative for back and underside of metal, one coat only, baked at same time as first coat of first coat enamel.
Bake each coat at 250° for 3 hours. Sandpaper each coat lightly. One or more coats of finishing enamel.
Bake each coat at 250° for 3 hours. Sandpaper all but the last coat. Rub the last coat with pumice.
Enamels when rubbed have a different colour than the surface colour; this must be taken into account in finishing.
Transfer and striping, if any, should be put over last coat of finishing enamel. Bake at 150° for 1 to 2 hours. One or more coats of finishing copal.
Bake each coat at 175° for 2 to 3 hours. Rub each coat, and polish the last coat.
If finishing copal is omitted, leave the last coat of enamel in gloss, or rub and polish as preferred.
The same enamel will bake to different shades at different heats and varied lengths of time, so care must be observed to get uniform results.
Imitation Wood Effects.
One or more coats of ground colour; back of metal one coat steel preservative, both reduced as thin as possible, and still cover well. If the steel preservative is used by dipping, only one coat of ground colour is generally used.
Bake each coat at 250° for 3 hours. Sandpaper each coat of ground colour. One coat of graining colour, reduced with turpentine brushed on, and grained by hand, or with tools as in general graining. This may be done by machine or as transfer work.
Bake the graining colour at 200° for 2 to 3 hours. Sandpaper lightly.
Put on transfer and striping, if any, over last coat of finishing enamel.
Bake at 150° for 1 to 2 hours. One or more coats of finishing copal.
Bake each coat at 175° for 2 to 3 hours. Rub each coat. Rub and polish the last coat.
In this work, at least one coat of finishing copal is necessary to protect the graining colour.
White Work—Bedsteads, Etc.
White work cannot be finished with one coat, because no white pigment has sufficient covering power.
Two or more coats of first coat white enamel.
Bake each coat at 120° to 150° for 3 to 4 hours. Sandpaper each coat lightly.
Two or more coats of finishing white enamel.
Bake each coat at 120° to 150° for 3 to 4 hours. Sandpaper each coat lightly except the last coat.
For gloss finish, leave last coat as it is; for eggshell finish, rub the last coat.
Finishing copal is rarely used over whites because of colour.
Transparent Colour Varnishes.
These varnishes are used over smooth, clean, bright metal. As the metal shows through the varnish, no primer or filler can be used.
One coat only is applied, usually by brushing or by a coating machine; however, it may be dipped or sprayed.
Bake at 225° for 3 hours.
The more these varnishes are reduced, the lighter the colour becomes.
Fig. 109.—Airostyle Plant Installed for the Gas Light and Coke Co., Ltd., showing Hood in Greater Detail and a Meter with Masks Affixed.
All colours are more or less affected by heat. They lose their brilliancy, become very much darker and sometimes turn black when baked at too high a heat.
Prolonged heat (not too high) kills the elasticity of the enamel. It does not affect the colour.
To assure brilliancy of the colour, the following highest heats can be used with safety.
"Generally speaking, the information given therein is quite correct, though it should be remembered that instruction as to stoving temperatures which might be quite correct with one maker's materials, might be quite wrong with another's.
"We notice they recommend that all black japan finishes should be stoved at from 250 to 350 degrees. This is the general practice in England, but it also happens that some firms cannot use these high temperatures or some goods will not stand it, and black japans have to be supplied which can be stoved at temperatures of about 180 or 200 degrees Fahr. Such qualities cost rather more to produce.
We also notice it is recommended that finishing varnish should be stoved at 175 degrees Fahr. Personally, we cannot make any clear finishing varnishes which will stand this temperature without discoloration, and even if used over black japan, they would discolour the lining or the striping thereon.
"The temperatures recommended for coloured enamels are also higher than we find satisfactory, and the statement made that the same enamel will bake to different shades at different heats, and that therefore a uniform temperature is necessary to obtain uniform results, seems to confirm our view. In practice we think that uniform results can only be obtained by using a lower temperature. If a workman has to watch the thermometer in a stove to make sure that his enamels will always discolour to the same degree, you can rely upon it that in practice accidents would soon happen."
From the above it can readily be seen that it is necessary to exercise considerable care in the selection of paints for both of these processes. The following opinions on this important subject are given by the firms named.
Messrs. John Lucas and Co., Inc., Gibbsboro', N.J., U.S.A., say:—
"It is our experience that a paint which is suitable for dipping purposes can also be manipulated for spraying. A paint to be suitable for spraying depends largely on two factors, namely:—Gravity, or weight per gallon, and consistency, or fluidity. A paint made from pigments which are heavy gravity will not produce good results for spraying, just as it will not prove satisfactory for dipping, because of the tendency for the pigment to settle out. In the case of spraying such paints produce an uneven finish. A paint such as is ordinarily used for dipping contains sufficient light gravity pigments to make possible reduction with the proper vehicles (depending on the desired finish) so that by spraying a satisfactory coating can be produced so far as finish is concerned. We are not certain whether a coating produced by spraying will wear as long as a coating which is applied either by dipping or by brushing."
The Chicago White Lead and Oil Co., Chicago, Ill., say:—"There is no very intricate or specific formula for this class of material. The following rule we think will prove a safe one to follow:—
"Always select a pigment which will stay in suspension, and also hold with it the extenders such as very fine silica. The addition of a very fine silica to all dipping or spraying paints will add materially to the flowing off and levelling of the finish. The pigments should be ground very fine in varnish, the grade of varnish depending upon the quality of the material to be produced, and reduced to working consistency with varnish and turpentine, or naphtha.
"Linseed oil should be avoided in the preparation of dipping paints, as the tendency of linseed oil to wrinkle is very objectionable. Chemically pure colours, such as green, yellow, para toners, etc., are best adapted as colour bases.
"The above constitute the principles upon which we have produced extremely satisfactory paints for the purpose named. These, coupled with expert workmen, will produce excellent results. The average formula for paints can only be considered as a general guide; the successful blending, tinting, etc., must be perfected by careful and sometimes extended experiments.
"The difference between a dipping paint and spray paint is in the consistency. A spray paint must naturally be made thinner, and consequently only the most dense of colours should be used and a smaller amount of inert pigment as an extender, or leveller. A few experiments with a spraying apparatus (of which some inexpensive hand sprayers can be obtained) will quickly guide the paint man as to proper consistencies to produce best results."
Messrs. John W. Masury and Son, of New York:—"It is practically impossible to give full particulars regarding varnishes and enamels for spraying and dipping, for the reason there are so many different kinds and they vary so much owing to the different character of work that a description of them is out of the question. In a general way it may be said that dipping coatings must be quick setting, so as to avoid runs and sags; it must flow out to a smooth, even surface. The drying quality must depend upon the kind of work being done, character of surface, subsequent exposure, and whether the coating is to be baked or air dried. Dipping varnish and enamels are made for many classes of work, such as all kinds of small iron castings and sheet metal work, as well as wood work, vehicle wheels, parts of automobiles, and in some cases wagon bodies and automobile bodies, these last only in one or two shops. These goods include cheap black baking japans, coloured enamels of various kinds and clear varnishes.
"In regard to spraying enamels, the 'spray brush' is gradually coming into use. These goods must be made to suit the character of the work; the body or viscosity of the material, the pressure used in the spray and character of the surface to be coated, must all be taken into consideration and properly graduated to insure suitable finish.
"In both dipping and spraying work one, two and three coats are frequently used, sometimes the under coats are only dipped or sprayed, while the finishing coat is applied with brush.
"The equipment for dipping will vary also with the article to be dipped; it includes dipping tanks of suitable size and shape, racks for hanging articles dipped, with troughs or trays to collect surplus material. In dipping it is necessary to wipe off with brush the surplus which gathers on lower edge of the article.
"Equipment for spraying requires besides the spraying machine a pressure tank with suitable cocks to regulate pressure, which will vary from thirty to fifty pounds, a suitable hood provided with fan to draw off any fine spray away from the workman, proper racks for taking care of the finished work. Work done with spray does not require any wiping up."
