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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
1. Celluloid 1 lb.
Amyl Acetate 2 lbs.
Acetone 2 lbs.
Ether (Syph. Meth.) 2 lbs.
2. Same as before with the addition of 1/5th part of
camphor.
3. Celluloid 1 lb.
Amyl Acetate 5 lbs.
Acetone 5 lbs.
Picture frames are also finished in black having a semi-gloss
finish, which gives an excellent effect and is most durable.
It is very important in this class of work that ample ventilation be
given to the apartment in which the work is done in such a way as to
avoid draught. Heated air, of course, takes up moisture much more
readily than cold air, and unless means are provided for adequate
ventilation the air will become moisture charged, and the work will
thereby be adversely affected. This is a point which is frequently
overlooked.
SPRAYING SHIPS' HULLS.
It is the opinion of the author that the painting of ships' hulls may
be done by means of spraying with a great saving of time. Although
there are no available statistics, it is probable that many thousands
of acres of surface on ships' bottoms are re-painted every year. A
careful enquiry has shown that some experiments have been made in this
direction, but that they have always been of a somewhat perfunctory
character. The very large surface gives an opportunity for the use of
the spray which is almost unequalled in its possibilities. There are,
however, certain difficulties in connection with this work, which have
doubtless had much to do with the fact that it has not, thus far, been
adopted to any considerable extent.
The first of these is that the composition applied is not ordinary
paint, but one which is mixed with arsenic, mercury and other poisonous
compounds, which are added in order to destroy animal and vegetable
life and prevent the adhesion of barnacles and other marine growth. So
necessary is this that compositions are made suitable for different
waters through which the vessel must pass, and it is well known that
those vessels which sail by regular routes need much less frequent
painting than a tramp steamer which may sail in any direction and
through any sea. The reason is, that in the first case the composition
is specially made to withstand the growth of life in well-defined
waters, while in the case of tramp steamers it must be more or less of
a general nature.
The point, however, which has now to be dealt with, is that the
addition of arsenic, etc., added to the paint, causes it sometimes to
settle out, but it is suggested that this could be easily overcome
by an agitating apparatus in the paint pot. As explained elsewhere,
such an apparatus is frequently used in ordinary painting, when the
composition of the paint demands it.
The second and more serious objection to spraying ships' hulls is that
the work must be done in the open, and that the wind will carry away
a portion of the paint and prevent it reaching the surface required.
It is suggested, however, this might perhaps be overcome by adopting
a form of enclosed cabinet, which would screen the operator from the
wind. This could be rendered portable by being mounted on a platform
with wheels, and a system of elevators, and be adopted with a little
ingenuity to reach the higher parts of the vessel. In any case, the
subject is one which is well worth the attention of those interested in
spraying, owing to the immense field it opens up.
In this connection attention may be directed to the illustrations which
appear on pages 252 to 254 of the apparatus used for spraying by the
Pennsylvania Railroad for painting their freight cars. This apparatus
may be adapted, with suitable modifications, for ship painting also.
SLATE ENAMELLING.
The usual procedure followed in connection with enamelling on slate for
mantel-pieces, stall-board, signs and other work of the kind, is to
get the slate slabs quite smooth and level by means of a slate planing
machine. A coat of "black varnish" or enamel is then sprayed on, and
is stoved at 160° to 170° F. Careful rubbing down with powdered pumice
and water is next done, when the work receives a second coat of enamel.
It is again stoved and then rubbed down by hand to a finish with
rottenstone and oil. Sometimes, the slate receives three coats, the
finish being left with a high gloss, but more frequently the semi-gloss
obtained by rubbing with rottenstone is preferred. It is unsafe to
stove slate at higher than 260° F., as it is likely to break when
cooling.
Formerly, a great deal of this class of work was done in imitation of
various marbles, mostly worked on a black ground, but "marbling" is
now done but rarely. The method is to employ a shallow tank of water
upon which are placed colours in imitation of the veins of the marble
to be imitated. This colour is of a special kind, made to float, and is
manipulated on the surface. The slab of slate, which has received one
coat, is then dipped gently in the water, when the colour adheres to
it. A coat of stoving varnish completes the operation.
Many slate enamellers still employ the old method of applying the
enamel by means of brushes, but it is only a question of time before
compressed air will be used almost exclusively, for the reason so
frequently urged in this work, viz., that the spray eliminates brush
marks and, therefore, greatly reduces the work of rubbing down.
SPRAYING COLOUR SPECIMENS.
Specimens of various colours in distemper, oil, varnish and enamel are
sent out in very large quantities by the various manufacturers of those
goods, and the preparation of these specimens may be very considerably
facilitated by using a suitable spraying machine. When distemper is
used fairly large sheets of paper are usually employed, and these are
cut up by means of a guillotine machine when dry. Ordinary oil paint
and varnish paints may in like manner be sprayed, but when an enamel
finish is desired it is usual to apply the paint on the back of a sheet
of thin white celluloid, which gives the appearance which would be
obtained by the application of varnish. In spraying celluloid sheets
it will be found that after a little practice the paint may be laid
on much more uniformly than is possible by means of a brush. This can
easily be demonstrated by holding up the painted sheet to the light,
when it will be found that the paint applied by a brush shows more
inequalities or streaks than that when sprayed.
Stencilling may be done very well on either paper or celluloid sheets;
in the case of these specimens, for example, supposing it was desired
that each specimen of colour when cut up should bear a number, it
would not be difficult to cut a stencil in zinc or leadfoil, repeating
the number as many times as there are specimens to be cut out of each
sheet. The tinfoil would then be fixed in position and the spraying
done over it, which would mark each piece with a number. Then the coat
of colour can be sprayed all over the surface. The plan above would be
followed in the case of celluloid, but when ordinary paper is used the
process would, of course, have to be reversed and the number put on
last.
In some cases where a very great brilliancy of colour is required,
this is done by the process of glazing, which is described elsewhere
in this book; for example, a comparatively dull red could be very much
brightened by spraying a coat of madder or crimson lake. Here, again,
if celluloid is used the glazing colour will go on first and the ground
colour afterwards, but in ordinary circumstances the ground work would,
of course, be first applied.
Probably the most complete plant for preparing colour specimens is
in use by Mander Brothers, the well-known paint, varnish and colour
manufacturers, of Wolverhampton. The spraying of colours is mostly done
on celluloid sheets, and four cabinets of the Airostyle type are in
more or less constant use. These cabinets have glass sides and top hung
on hinges so that they may be opened when desired. The pressure of air
is usually from 30 to 35 lbs., with an additional 5 lbs. on the paint
pot. One coat is sufficient, because, of course, it can be made as
thick as may be necessary according to the particular specimens being
prepared. The saving of time is estimated at, at least, 33 per cent.
In dealing with celluloid sheets it is obviously of importance to adopt
some safe means of storing them while drying. Formerly Messrs. Mander
Brothers had a long series of double clips by which the sheets were
suspended while drying, but this method has been abandoned owing to the
danger involved of fire. Now suitable tin-lined cabinets are provided
having from top to bottom a series of cleats which support open wire
trays. Each sheet of celluloid as it is painted is placed on a wire
tray which is slipped in the cabinet, where it dries in 12 hours.
TRAMCARS.
[Illustration: Fig. 95.--GENERAL VIEW OF AIROSTYLE PLANT FOR 16
OPERATORS ON SMALL WORK.]
[Illustration: Fig. 96--VIEW OF AIROSTYLE PLANT FOR 16 OPERATORS,
SHOWING VENTILATOR.]
As far as the author can gather information, the processes described
in this book are not used in Great Britain to any extent in the finish
of tramcars, but are gradually making headway in America, particularly
for the final coats. There appears to be no reason, however, why
"flowing-on," as described in Chapter XIII., should not be used to a
much greater extent than is at present the case. The earlier coats,
being very stiff, might be applied by means of brushes, and these
coats could be followed by spraying, and finally the finishing coats
could be flowed on.
Formerly, this work was done almost in the same way as that by which
the fine finish of a carriage body is produced, viz., the building up
of a perfectly smooth surface by a large number of coats, rubbing each
one down carefully and finishing with two or more coats of varnish,
these being also rubbed down excepting the last.
In modern practice these methods are greatly simplified, and at least
several coats, which were formerly thought to be necessary, are
dispensed with. The finish is often obtained by applying a coat of a
suitable enamel, rubbing this down, and then giving a final finish of a
good flowing varnish.
It is suggested that spraying, or flowing-on, could be used for some of
this work with very great advantage in the saving of time.
In dealing with many paints which are to be stoved, a well-thought-out
system should be in use of conveying the articles from the finishing
rooms to the painting apparatus and thence to the ovens. If more than
one coat is given it will be necessary to arrange also for conveyance
after the parts are baked back to the painting plant for the next coat.
As a rule, a system of overhead runways, such as is described for use
in paint dipping, will be found the most economical method to adopt.
It will be observed that in the list of trades and articles which
may be successfully painted by mechanical means, given on pages 3 to
6, there are many which are omitted from the detailed descriptions.
The reason for this is that the main principles are in all cases
practically the same and the details must necessarily vary, not only
with the goods being dealt with, but according to the extent of the
operations and the accommodation of the factory available.
Thornley & Knight, Ltd., of Birmingham, specialise in this business,
and have sold, during the last few years, many thousands of gallons of
their air-drying coloured japans, for use on car bodies. Many of the
largest motor car manufacturers have adopted the process.