A PORTABLE PAINT SPRAYER FOR RAILWAY AND OTHER WORK.
Mr. M. E. McDonnell, Engineer of the Pennsylvania Railroad Company,
Altoona, Pa., U.S.A., very kindly furnishes the author with the
drawings which will be found on the following pages. He says:--The
Company does very little painting by dipping. The spray process is,
however, used very extensively, a large percentage of our freight
cars having been painted by this method for years. The method is very
satisfactory and also economical. The saving in the cost of labour in
the spraying method is approximately 60 per cent. In some cases the
saving is greater than this. In one of our largest shops the cost of
application per unit for a given number of square feet is thirty-eight
and nine-tenth cents with the spray as compared with one dollar with
brush. It might be said that more paint is applied per coating when the
brush method is used. A given surface which would require 10 gallons of
paint for one coat by the brush method would require approximately 7
gallons by the spray method.
When painting a freight car a more uniform coating is obtained when
the brush is used, due to the fact that the paint can be brushed out
behind ladders and other things which would obstruct spraying, while in
the application of the paint with a sprayer it is necessary to apply
a thicker coating at certain points in order to reach other points
which are obstructed, and which must, therefore, be approached from a
side angle. The spray however, reaches certain crevices which cannot
be reached with the brush, which is in some cases advantageous with
the painting of freight equipment cars. Our Company would not consider
returning to the brush method of painting.
The machines which we use for spraying the paint are made in the
Company shops.
The following is a description of the apparatus referred to:--
It consists of a stout steel cylindrical receptacle 11½in. internal
dia. by 24in. in depth, and having a capacity of about 12 gallons. It
is supported on a special wheelbarrow of wood with trundling wheel of
cast iron. The bottom of the receptacle is so low down that it rests
on the ground when in use, by lowering the handles of the barrow. The
paint is placed in this cylinder and is forced out by air pressure,
introduced through the lid of the receptacle, at from 80 to 90 lbs.
pressure per square inch. This air is provided from the shop compressor
range or by a separate compressor. The paint pipe penetrates the
cover and is extended nearly to the bottom of the receptacle. The air
pressure on the surface of the paint forces it through this pipe to the
atomizer.
A branch from the air supply is also taken to the atomizer and a third
air branch taken to the bottom of the receptacle and carried through
a 1in. iron pipe stopped at the end with a screw plug, but perforated
with a number of 1/8in. holes. This latter is for agitating the paint
and prevents settlement. The atomizer is shown clearly in the drawing.
It consists of an air jet impinging on a vena contracta nozzle and
surrounded by the paint forced through from the receptacle. The air
blast carries the paint through the orifice immediately opposite to the
nozzle and there reduces it to a fine spray. A hose is attached to the
exit of the atomizer and the atomized paint is carried by the blast to
the spray pipe, which is slightly fan-shaped and flat.
The cover is fastened by four hook-clamps, and is, therefore, readily
removable. An air pressure gauge reading to 120 lbs. is also provided,
and the valves are so arranged that the regulation of both the paint
and the air supply are easily adjustable.
It will be noticed that, in the atomizer, a vena contracta is
arranged so that it may be adjusted in its position in relation to
the air orifice. The use of this is to provide for paint of various
consistencies. Very great care has been taken in designing the details;
as, for example, the provision of a scraper to clear off accumulations
from the periphery of the trundling wheel.
[Illustration: Fig. 139.--PLAN OF PAINT SPRAYING APPARATUS USED BY THE
PENNSYLVANIA RAILROAD, PRINCIPALLY FOR FREIGHT CARS.]
[Illustration: Fig. 140.--ELEVATION OF APPARATUS SHOWN IN FIG. 139.]
[Illustration: Fig. 141.--DETAILS OF APPARATUS SHOWN IN FIGS. 139 AND
140.]