Construction and Equipment of a Soap Plant.
No fixed plan for the construction and equipment of a soap plant can be
given. The specifications for a soap factory to be erected or remodeled
must suit the particular cases. Very often a building which was
constructed for a purpose other than soap manufacture must be adapted
for the production of soap. In either case it is a question of
engineering and architecture, together with the knowledge obtained in
practice and the final decision as to the arrangement is best solved by
a conference with those skilled in each of these branches.
An ideal soap plant is one in which the process of soap making, from the
melting out of the stock to the packing and shipping of the finished
product, moves downward from floor to floor, since by this method it is
possible to utilize gravitation rather than pumping liquid fats and
fluid soaps. Convenience and economy are obtained by such an
arrangement.
The various machinery and other equipment for soap manufacture are well
known to those connected with this industry. It varies, of course,
depending upon the kind of soap to be manufactured, and full
descriptions of the necessary machinery are best given in the catalogs
issued by the manufacturers of such equipment, who in this country are
most reliable.
To know just what equipment is necessary can very easily be described by
a brief outline of the process various soaps undergo to produce the
finished article. After the saponification has taken place in the _soap
kettle_ the molten soap is run directly into the soap _frames_, which
consist of an oblong compartment, holding anywhere from 400 to 1,200
pounds, with removable steel sides and mounted upon trucks, in which it
solidifies. In most cases it is advisable to first run the soap into a
_crutcher_ or mixer which produces a more homogeneous mass than if this
operation is omitted. Color and perfume may also be added at this point,
although when a better grade of perfume is added it must be remembered
that there is considerable loss due to volatilization of same. When a
_drying machine_ is employed the molten soap is run directly upon the
rollers of this machine, later adding about 1.0% zinc oxide to the soap
from which it passes continuously through the drying chamber and is
emitted in chip form ready for milling. After the soap has been framed,
it is allowed to cool and solidify, which takes several days, and then
the sides of the frame are stripped off. The large solid cake is cut
with wires by hand or by a _slabber_ into slabs of any desired size.
These slabs are further divided into smaller divisions by the _cutting
table_. In non-milled soaps (laundry soaps, floating soaps, etc.), these
are pressed at this stage, usually by automatic presses, after a thin
hard film has been formed over the cake by allowing it to dry slightly.
In making these soaps they are not touched by hand at any time during
the operation, the pressing, wrapping and packing all being done by
machinery. For a milled soap the large slabs are cut into narrow oblong
shapes by means of the cutting table to readily pass into the feeder of
the _chipper_, the chips being spread upon _trays_ and dried in a _dry
house_ until the moisture content is approximately 15%.
The process of milling is accomplished by passing the dried soap chips
through a _soap mill_, which is a machine consisting of usually three or
four contiguous, smooth, granite rollers operated by a system of gears
and set far enough apart to allow the soap to pass from a hopper to the
first roller, from which it is constantly conveyed to each succeeding
roller as a thin film, and finally scraped from the last roller to fall
into the _milling box_ in thin ribbon form. These mills are often
operated in tandem, which necessitates less handling of soap by the
operator. The object of milling is to give the soap a glossy, smooth
finish and to blend it into a homogeneous mass. The perfume, color,
medication or any other material desired are added to the dried soap
chips prior to milling. Some manufacturers use an _amalgamator_ to
distribute these uniformly through the soap, which eliminates at least
one milling. When a white soap is being put through the mill, it is
advisable to add from 0.5% to 1% of a good, fine quality of zinc oxide
to the soap, if this substance has not been previously added. This
serves to remove the yellowish cast and any translucency occasioned by
plodding. Too great a quantity of this compound added, later exhibits
itself by imparting to the soap a dead white appearance. Inasmuch as the
milling process is one upon which the appearance of a finished cake of
toilet soap largely depends, it should be carefully done. The number of
times a soap should be milled depends upon the character of a soap being
worked. It should of course be the object to mill with as high a
percentage of moisture as possible. Should the soap become too dry it is
advisable to add water directly, rather than wet soap, since water can
more easily be distributed through the mass. As a general statement it
may be said it is better policy to overmill a soap, rather than not mill
it often enough.
After the soap has been thoroughly milled it is ready for plodding. A
_plodder_ is so constructed as to take the soap ribbons fed into the
hopper by means of a worm screw and continuously force it under great
pressure through a jacketed cylinder through which cold water circulates
in the rear to compensate the heat produced by friction and hot water at
the front, to soften and polish the soap which passes out in solid form
in bars of any shape and size depending upon the form of the _shaping
plate_ through which it is emitted. The bars run upon a _roller board_,
are cut into the required length by a special _cake cutting table_,
allowed to dry slightly and pressed either automatically or by a foot
power _press_ in any suitable soap _die_. The finished cake is then
ready for wrapping and after due time in stock reaches the consumer.
Besides the various apparatus mentioned above there are many other parts
for the full equipment of a modern soap plant, such as remelters, pumps,
mixers, special tanks, power equipment, etc. As has been stated,
however, practical experience will aid in judging the practicability as
to installation of these. The various methods of powdering soap are,
however, not generally known. Where a coarse powder is to be produced,
such as is used for common washing powders, no great difficulty is
experienced with the well known Blanchard mill. In grinding soap to an
impalpable powder the difficulties increase. The methods adapted in
pulverizing soaps are by means of disintegrators, pebble mills and
chaser mills. The disintegrator grinds by the principle of attrition,
that is, the material is reduced by the particles being caused to beat
against each other at great velocity; a pebble mill crushes the
substance by rubbing it between hard pebbles in a slowly revolving
cylinder; the chaser mill first grinds the material and then floats it
as a very fine powder above a curb of fixed height. The last method is
particularly adapted for the finest of powder (140 mesh and over).