By the next operation of _shearing_ or _cropping_, the long hairs are
cut off arid a uniform surface is thus obtained. Shearing was in former
times done by hand, by means of shears, but is to-day universally
effected by means of a cutting device which works on the same principle
as an ordinary lawn-mower, in which a number of spiral blades set on the
surface of a rapidly revolving roller pass continuously over a straight
fixed blade underneath, the roller being set so that the spiral blades
just touch the fixed blade. Before the piece comes to the shearing
device the nap is raised by means of a rotary brush. Shearing may be
effected either transversely, in which case the fixed blade is parallel
to the warp, or longitudinally with the fixed blade parallel to the
weft. In the first case, the piece being stretched on a table, over
which the cutter, carried on rails, travels from selvedge to selvedge.
The length of the piece that can be shorn in one operation will
naturally depend upon the length of the blade, but in any case the
process is necessarily intermittent, many operations being required
before the whole piece is shorn. In the longitudinal shearing machines
the process is continuous, the pieces passing from the beam in the
stretched condition over the rotary brush, under the fixed blade, and
then being again brushed before being beamed on the other side of the
machine. Shearing once is generally insufficient, and for this reason
many of the modern machines are constructed with duplicate arrangements
so as to effect the shearing twice in the same operation. In the
finishing of certain woollen goods the pieces, after having been milled,
raised and sheared, go through these operations again in the same
sequence.
After these operations the goods are pressed either in the hydraulic
press or in the continuous press, and according to the character of the
material and the finish desired may or may not be steamed under
pressure, all of which operations are described below.
New cloth, as it comes into the hands of the tailor, frequently shows an
undesirable gloss or sheen, which is removed before making up by a
process known as shrinking, in which the material is simply damped or
steamed.
_Worsteds and Unions._--The pieces are first singed by gas or hot plate
(see BLEACHING), and are then usually subjected to a process known as
"crabbing," the object of which is to "set" the wool fibres. If this
operation is omitted, especially in the case of unions, the fabric will
"cockle," or assume an uneven surface on being wetted. In crabbing the
pieces are drawn at full breadth and under as much tension as they will
stand through boiling water, and are wound or beamed on to a roller
under the pressure of a superposed heavy iron roller, the operation
being conducted two or three times as required. From the crabbing
machine the pieces are wound on to a perforated shell or steel cylinder
which is closed at one end. The open end is then attached to a steam
pipe, and steam, at a pressure of 30 to 45 lb., is allowed to enter
until it makes its way through all the layers of cloth to the outside,
when the steam is turned off and the whole allowed to cool. Since those
layers of the cloth which are nearest the shell are acted upon for a
longer period than those at the outside, it is necessary to re-wind and
repeat the operation, the outside portions coming this time nearest to
the shell. The principle of the process depends upon the fact that at
elevated temperatures moist wool becomes plastic, and then easily
assumes the shape imparted to it by the great tension under which the
pieces are wound. On cooling the shape is retained, and since the
temperature at which the pieces were steamed under tension exceeds any
to which they are submitted in the subsequent processes, the "setting"
of the fibres is permanent. After crabbing, the pieces are washed or
"scoured" in soap either on the winch or at full width. In some cases
the crabbing precedes the scouring. The goods are then dyed and
finished.
The nature of the finishing process will vary considerably according to
the special character of the goods under treatment. Thus, for certain
classes of goods cold pressing is sufficient, while in other cases the
pieces are steamed under pressure in a manner analogous to the treatment
after crabbing ("decatizing"). The treatment in most common use for
worsteds and unions is hot pressing, which may be effected either in the
hydraulic press or in the continuous press, but in most cases in the
former.
In pressing in the hydraulic press the pieces are folded down by hand on
a table, a piece of press paper (thin hand-made cardboard with a glossed
and extremely hard surface) being inserted between each lap. After a
certain number of laps, a steel or iron press plate is inserted, and the
folding proceeds in this way until the pile is sufficiently high, when
it is placed in the press. The press being filled, the hydraulic ram is
set in motion until the reading on the gauge shows that the desired
amount of pressure has been obtained. The heating of the press plates
was formerly done in ovens, previous to their insertion in the piece,
but although this practice is still in vogue in rare instances, the
heating is now effected either by means of steam which is caused to
circulate through the hollow steel plates, or in the more modern forms
of presses by means of an electric current. After the pieces have thus
been subjected to the combined effects of heat and pressure for the
desired length of time, they are allowed to cool in the press. It is
evident that portions of the pieces, viz. the folds, thus escape the
finishing process, and for this reason it is necessary to repeat the
process, the folds now being made to lie in the middle of the press
papers.
[Illustration: From Ganswindt,' _Technologie der Appretur_.