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.
[Illustration: Fig. 107.--J. LUCAS, LTD., AIROSTYLE PLANTS, SHOWING THE
TWO BAYS OF ONE COMPLETE UNIT.]
[Illustration: Fig. 108.--AIROSTYLE PLANT INSTALLED FOR MESSRS. THE GAS
LIGHT AND COKE CO., LTD. GENERAL VIEW.]
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.
[Illustration: Fig. 109.--AIROSTYLE PLANT INSTALLED FOR THE GAS LIGHT
AND COKE CO., LTD., SHOWING HOOD IN GREATER DETAIL AND A METER WITH
MASKS AFFIXED.]
SAFE BAKING HEATS OF PIGMENT COLOURS.
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.
White 160° 4 hours.
Pale Blue 175° 2-3 "
Pale Gray " " "
Pale Green " " "
Pale Yellow " " "
Gray 200°-225° 4-3 hours
Bright Red " " " "
Green " " " "
Yellow " " " "
Dark Blue " " " "
Olive Green 240°-275° 4-3 hours
Maroon " " " "
Brown " " " "
Black - any heat up to 600°
COMMENTS ON THE ABOVE.
A well-known English firm, commenting on the above says:--
"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."
DIPPING AND SPRAYING PAINTS COMPARED.
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."
[Illustration: Fig. 110.--AIROSTYLE PLANT INSTALLED FOR THE GAS LIGHT
AND COKE CO., LTD. OPERATOR AT WORK ON GAS METERS.]