LEATHER WORKING MACHINERY
When it is considered that the construction of machinery for the
leather trade had barely started thirty years ago, the wonderful
variety and utility of modern machines are remarkable, and it is a
moot point whether engineering science has not played as great a part
as, or even greater than, applied chemistry.
Excepting the bark mill, various kinds of tumblers, the fulling
stocks, glazing and rolling machines, there were practically no
efficient mechanical aids to lighten the exceedingly laborious
operations incidental to leather manufacture two decades ago; but
so many improvements have lately been made in the construction of
machinery for practically every operation in the trade that most
of the machines require very little skill to work them, and can be
operated by intelligent youths after a few weeks' experience.
The change has been of great benefit to the health of the workers,
for the continual stooping over beams and sloping tables, combined
with the arduous nature of the work, was very injurious. The
reputation that tanning had as a healthy occupation was due more
to the work of the labourers than that of the skin workers. (The
old-fashioned lime-yards and tan-yards were generally in the open,
whereas modern tanneries are roofed.)
Leather trades machinery was not a success at first, probably because
it was very difficult to get the necessary information from leather
manufacturers. However, as the engineers gained more experience of
the methods of leather-making, the defects were gradually remedied
until it may be truly said that the machines now reach a high state
of perfection. It was no uncommon thing for workmen to lose a finger
or two in a machine, but such accidents are now rare, owing to
improvements in the construction of the machines.
Most of the machines used in the leather trade are of the cylinder
type, the raw skins or leather passing between two rollers, of which
the upper one performs the operation while the lower one helps to
draw the material through the machine. To prevent accidents and
control the working of machines, a third roller is often used, which
serves to "feed" the leather or skins to the working cylinders. Of
this type of safety roller, the Seymour-Jones attachment to the
shaving and buffing machine is of great importance.
[Illustration: FIG. 5
SHAVING CYLINDER]
The operations of the tannery, which are performed by cylindrical
machines, are dehairing, fleshing, scudding, samming, shaving,
scouring, striking-out, setting, boarding, buffing, graining,
printing, embossing, and blacking or colouring. The working cylinders
usually vary according to the character of the operation, although
one or two types may be used for at least three different operations.
Where cutting or paring is done, the working cylinder is fitted with
brass blades, or steel blades backed with iron. The blades are spiral
in some machines, and are so arranged that half of them converge to
the left, and half to the right (Fig. 5). When in work, this type of
cylinder not only performs the operation for which it is specially
intended, but also stretches the leather outward, by reason of the
arrangement of the blades or knives. The blades overlap one another
to obviate marking, for if the blades met exactly at the centre they
would make a line on the leather. Figure 6 shows another arrangement
of knives for the process of buffing.
[Illustration: FIG. 6
BLADED CYLINDER FOR "BUFFING" LEATHER]
[Illustration: FIG. 7
BAND-KNIFE SPLITTING MACHINE]
The most important machines outside the working cylinder type are
the splitter, and the glazer. There are several kinds of splitting
machines, but the band-knife machine (Fig. 7) is the most largely
used. This is a veritable triumph of the engineer's art, for it
is possible to make five or six layers, all about the same size,
out of one hide, although leather is only split once or twice as a
rule. Of course, sole, belting, and other thick leathers are not
usually split. The invention of the belt-knife splitting machine
revolutionised the leather trade, and there would undoubtedly have
been a great shortage of leather without it. Formerly, all the
levelling and reducing of substance was done by paring off quite
small pieces with the shaving knife (Fig. 8), a difficult and
laborious work. These parings were only suitable for pulping and
compressing into leather board; but now the flesh splits removed
by the machine can be curried, enamelled, printed, or rolled to
make serviceable leathers, although, of course, not nearly so good
in quality as the top or grain split. The main working part of the
splitting machine is an endless steel knife which passes round two
wheels placed at opposite ends of the machine. The leather is drawn
to the knife through two rollers, of which the lower one is in
sections to allow very thick parts of the hide to pass through the
machine. It would need a large volume to describe in detail all the
different machines used in the leather trade; the constructional
details of only one machine can be given, and, in view of its
importance, the shaver is selected. Reproductions of other machines
will appear in succeeding chapters.
[Illustration: FIG. 8
SHAVING KNIFE]
Nearly every leather trades' engineer constructs shaving machines,
but the Howard-Smith is described here, not because it is the most
popular (unfortunately there is a decided preference for low-priced
machines), but because it is one of the best from an engineering
point of view, and because several improvements are embodied in its
construction.
[Illustration: FIG. 9
SHAVING LEATHER
(Old method)]
This machine consists of nearly one hundred parts and each is made
of the best material available. The advantage of this is obvious when
the question of repairs is fully considered. The first Howard-Smith
machine made has been running more than four years, and has not
cost the owner a penny for repairs, beyond, of course, the expense
of replacing the blades of the working cylinders; whereas it is no
uncommon occurrence for a cheap machine to be thrown on the scrap
heap after a few years' wear. It is always advisable, therefore, to
buy machinery of the best grade.
[Illustration: FIG. 10
DRAWING OF SHAVING MACHINE]
Figure 10 represents a drawing of the shaving machine, _A_ being the
side view, and _B_ the front. The work of the draughtsman generally
appears to the uninitiated to border on the miraculous; he is often
the designer and architect of the machine, and his work is certainly
interesting and skilful.
Many of the heavy parts, such as main castings, pedestals, etc.,
are made in the foundry, which may be part of the leather trades'
engineer's works if he is in a large way of business. The finer
parts, those which might be termed the fittings, are made in the
turnery department; while the machine is assembled in the fitters'
shop.
Figure 10 _A_ shows the side, and 10 _B_ the front construction of
the shaving machine. The figures indicate, by following the arrows,
the principal parts of the machine, which are shown in detail in
sectional tracings. For example, _T._ 65, of which no working parts
are shown in the diagram of the complete machine, is reproduced in
detail in a separate drawing shown in Figure 11. Each part of the
machine is numbered and entered in a stock-book.
In describing the principal parts indicated in Figure 10, it will
give an idea of the assembling of the machine if a beginning be made
with the main iron castings. These comprise the main bed (64), two
side frames (62), and the front frame (58). The side frames are
strengthened by the ribs which form the edge, and which are about
three times as thick as the body of the casting. The object of the
front frame is to support the foot lever (59), the rocking frame (57)
carrying the rubber roll (79), and the wooden roof (75) over which
the leather is passed. The spring (76) pulls back the rocking frame
(57) when relieved by the operator removing his foot from the lever
(59). The long spring (77) lifts up the foot lever (59) when the
latter is released.
The pullies (73) are connected with the knife cylinder which shaves
the leather. The cylinder is obscured by the wheel-guard (65) and is,
therefore, shown separately. This cylinder is comprised of a shaped
piece of steel (turned out of solid metal bars of 4-3/4 in. diameter)
into which spiral steel blades are caulked with copper or brass.
When turned, the body of the cylinder is 4-5/8 in. in diameter, but
the parts forming the bearings are reduced to 1-1/2 in. The number
of blades is twelve, fourteen, or sixteen, according to the kind of
leather shaved, and to the choice of the operator.
It is interesting to note that these blades are now being made in
Sheffield, although, before the war, they had to be imported. The
knife guard (65), shown in detail in Figure 11, is an ingenious
contrivance which prevents the operator's hands being drawn into the
machine. It consists of an automatic shutter worked by a steel chain
from the foot lever. Figure 11 _a_ represents the shutter closed down
on the knife with the rubber roll, on which the leather is carried to
the knife, at a safe distance from the shutters. Fig. 11 _b_ shows
the position when the machine is shaving the leather, the guard being
clear and the rubber roll engaged with the knife.
[Illustration: FIG. 11 _a_.]
[Illustration: FIG. 11 _b_.]
In order to sharpen the blades of the cylinder, a carborundum wheel
is fixed in close proximity, its position being indicated in the
drawing by the wheel cover (67). A bracket for feeding the wheel
to the blades when grinding them is shown at 66. When grinding the
blades, the saddle (68) carries the wheel backwards and forwards
across them. A special feature of the saddle in this particular
machine is the double-thread screw, one a right hand, and the other
a left hand. The saddle (68) is actuated by a "swimmer," as the
makers term it, which engages, say, first the right-hand thread; when
the saddle has travelled to the end of its movement the "swimmer"
automatically enters the left-hand thread, and the saddle is
rotated in the opposite direction. The "swimmer" can be disengaged
instantaneously. A brush (55) is fixed near the cylinder to remove
any leather shavings adhering to the blades. It also acts to some
extent as a fan, and, by creating a current of air, carries the
leather dust away from the operator. A trough is filled with water
to catch the dust from the carborundum wheel, while the knives are
being ground. The trough should be cleared out and refilled with
clean water from time to time. It is essential that no dust from
the grinding wheel comes into contact with vegetable tanned leather
required in a natural or colour finish, otherwise it will cause iron
stains, which are difficult to remove without damaging the leather.
For this reason, the knives should not be ground while this class of
leather is being shaved.
An important detail of the machine under description is a trueing
device. Knives are often roughened owing to the carborundum wheel
wearing irregularly. The trueing device keeps the wheel perfectly
true by means of a diamond held in the end of a screw (78). Another
ingenious arrangement (patented) is a spring (79_a_) placed at the
back of the rubber roll (79), which enables the roll to spring back
when the leather, or any part of it, is too thick for the cutting
cylinder.
A unique advantage of the Howard-Smith machine is that it is
ball-bearing throughout. The main driving shaft revolves on four
massive ball-bearings in case (71). The pullies are firmly fixed
to the driving shaft with keys or feathers. Afterwards the pullies
are machined, so that the whole shaft with its pullies is perfectly
balanced, and the machine runs smoothly without vibration.
The bladed cylinder is likewise mounted on four ball-bearings.
The intermediate driving shaft (70), which is mounted on two
ball-bearings, is connected with a large drum shaft (70_a_) which, in
its turn, sets the carborundum wheel in motion.
[Illustration: FIG. 12
SHAVING-MACHINE
(Haley)]
Fig. 12 represents another make of shaving machine.