Adolf Heil.

The manufacture of rubber goods : a practical handbook for the use of manufacturers, chemists, and others online

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The quality of cut sheet (German, Patentplatte ; Italian, foglia
segata; French, feiiille anglaise) has undergone considerable reduc-
tion. Sheet formerly made from pure Para has been gradually
lowered in price, other mixtures of raw rubber being used instead
of Para, and at present sheet containing as much as 30 per cent, of
surrogate is sold. Red cut-sheet is prepared by the addition of
vermilion to the rubber. Green sheet has disappeared again from
the market.

The cost of working a cut-sheet plant is not very high.

It requires altogether six men for a monthly production of
about 2500 kilos, of medium thickness. The consumption of
ammonia or carbonic acid is quite insignihcant, but lubrication
must be reckoned at about 30 kilos, of oil per month. To cut a
block weighing about 75 to 80 kilos, into No. 18 sheet takes about
twenty hours ; but, on the other hand, a similar block can be cut
into No. 9 sheet in about five hours. Once the block is fixed in
position on the machine and trimmed, it pays to keep the machine
running continuously until the whole block is cut out, on account
of the saving of time, on the one hand, and on the other hand, of
the reduction of waste.

15. Manufacture of Rubber Shoes.— The manufacture of rubber
shoes or galoshes forms a separate branch of rubber manufacture.
Special methods are demanded in most of the operations connected
with it, leaving the preparation of the raw rubber out of account.
The reasons for this are as follows : —

1. The use to which galoshes are put differs greatly from that
of other rubber goods, and puts great demands upon the strength
and elasticity in every direction, especially in the seams, Avhile at
the same time elegance, a good finish, comfort and ease of manipu-
lation are necessary qualities.

2. In the manufacture of galoshes, mixings of the most varied
nature, from the finest to the lowest qualities, in all possible thick-
nesses of sheet, as well as in the form of sheet spread on fabrics
of all kinds, the rubber layer varying both in quality and in
thickness, have to be made up together from a comparatively large
number of small separate parte, and this must be done in such
a way that the finished article shall appear as if it came from a



12



178 RUBBER MANUFACTURE.

mould ; indeed the uninitiated often actually look upon the rubber
shoe as a moulded article.

3. The making-up — that is to say, the manufacture proper of
rubber shoes — can only be carried out by hand. The machines
invented by the American, Doughty, have not come into use in
spite of their ingenious design, the cost of working them being
too high.

4. Such large quantities as 4000 to 12,000 pieces, according
to the size of the factory, are vulcanised at a time, so that the
greatest care must be given to mixing, labour, and organisation.

Before passing on to a description of the manufacturing pro-
cesses, a few points of general importance' may be discussed.
Galoshes, like all other kinds of shoes, are made up on lasts ; the
size and shape of the last determines that of the shoe, and since
rubber shoes are made in an extraordinary number of shapes and
sizes, it is necessary in a galosh factory to have a considerable
stock of lasts, in the first place of different sizes and shapes, and
secondly, a sufficient number of pairs of each size and shape. The
lasts are made either of wood, iron, or aluminium. Iron lasts
possess the advantage of heating up rapidly in the vulcanising
chamber, and of not being subject to appreciable wear or to
fracture. On the other hand, their great weight adds considerably
to the labour of making up the shoes, and of carrying them to and
fro in the factory. The expansion of the metal by heat is also a
disadvantage, because it always results in some distortion of the
seams. Wooden lasts, though more subject to wear than, metal
ones, are lighter to handle, and do not undergo any appreciable
expansion on heating, provided they have been well dried before-
hand. To ensure that this is so, the wood, in the form of small
blocks, is stored for a long time in a very warm place — directly
over the boilers, with advantage — before it is shaped out ; from this
stock the oldest blocks are always taken for use first, blocks which
have sometimes been drying for a year and which neither shrink
nor crack, nor otherwise alter in the heat. Maple is the most
suitable material to use.

Another point of general importance is the uniform colour of
the whole shoe, and every mixing used should either be black in
itself, or should become black during vulcanisation. These black
mixings are 2:)re2jared by the addition of carbon-black, as well as by
the addition of pitch prepared on the factory by heating coal-tar.
In this operation the tar is heated and kept continually stirred
until it forms, on cooling, a tough mass ; resin and wax are some-



MANUFACTURE OF SOFT-RUBBER ARTICLES. 179

times added while the heating is going on in order to impart a bright
polish to the mixings in which the pitch is used. The resin-
content should, however, be extremely limited, and if it is put in
at all, should not exceed about 5 per cent., otherwise the mixings will
easily crack. Thickened coal-tar pitch communicates to the mixings
in which it is used a greater degree of tackiness and softness in an
unvulcanised state than one usually meets with, even when the
soft kinds of raw rubber are used. This is certainly an advantage
in the case of certain mixings, but it necessitates the most stringent
adhesion to the proportions of a mixing which has been found
by trial to be satisfactory ; for if the right quantity be exceeded
to the smallest extent, the rubber may become so soft that.it is
impossible to work it, and after vulcanisation it may not possess the
necessary elasticity. In Para mixings and others of approximately
equal quality, such as are used for proofing many of the fabrics,
neither pitch nor carbon-black is employed, but instead of these
litharge is added; such mixings do not, of course, become black
until they are vulcanised. Oil-black and gas-black are the kinds
of carbon-black used ; this pigment is the one for mixings which
need show no particular polish, and which might also show. up
grey. An addition of more than f per cent, of black is rarely
necessary, since all these mixings also contain lead compounds ;
when pitch is present the black is added in still smaller quantities,
and reduces the tackiness of the pitch in some degree.

Coming now to the manufacture itself, we see that the separate
parts of which a rubber shoe is composed can be grouped under
three (fistinct headings, viz. the sole,' the upper, and the inside.

(a) The Sole. — The foundation of the shoe is with rubbers, as
with leather shoes, the sole. This part is subject to the greatest
amount of wear, and must therefore not only be made of tough,
firm rubber, but must also be fairly thick, as much, sometimes, as
7 mm., the actual thickness varying according to whether it is a
child's, a woman's, or a man's shoe. In all other kinds of rubber
goods which are made up from sheet, sheet of such thickness is
always built up from several layers of thinner sheet, because it is too
difficult a matter to calender such thick sheets. The sheet rubber
for the soles of shoes, however, is not only run on the calenders to
the desired thickness, but these also impart to it the usual well-
known pyramidal impression and the manufacturer's brand ; more-
over, the sheet has to be run. of uneven thicknesses, because the
instep and the heel are all in one piece with the sole ; the sheet
has therefore to be thickest at the heel and thinnest at the instep.



i8o



RUBBER MANUFACTURE.



It will be clearly seen from this that the calendering of such
sole-sheet presents certain difficulties. In particular, the calenders
(fig. 84) must be of great strength, and therefore the rolls are com-
paratively narrow — only a little wider than the length of the soles.
On the final roll are engraved the necessary markings, which are
repeated at convenient intervals so as to leave room to enable each
sole to be cut out well. Since a sheet of uneven thickness is to be
calendered, the rolls cannot be run at equal speeds, but only in
such a way that there is always plenty of rubber in front of the
final pair of rolls, from between which the finished sheet, bearing
the requisite makings, emerges. Furthermore, the rubber must be
kept very warm, to ensure the sheet being absolutely homogeneous

and free from air-bubbles.
Nevertheless, if the rubber
has been well-worked
beforehand, and is kept
warm, the sole sheet can
generally be successfully
run from the engraved
rolls. The sheets then pass
on to tenters, the size of
|hv which is regulated by the
^, leno^th of the cuttino'-out
s,a?rf table or the cutting -out
machine. Before the indi-
vidual soles are cut out,
the sheet is submitted to a
certain treatment which is
most advantageous, but in rubber goods is restricted to this instance
and to the manufacture of unvulcanised Para strips for cables.
This consists in dipping the sole -sheet for a short time (five
minutes) into boiling Avater, the result being that during subse-
quent vulcanisation there is practically no perceptible shrinkage,
and the shoe, which is stretched tightly on the last, is thus pre-
vented from cracking and becoming distorted.

The soles are cut out either by hand or by machine, the
advantage of the one method over the other being dependent upon
the kind of trade done ; for the machines, however ingeniously con-
structed, can in any case only cut out one sole at a time, because
the edges must be cut obli(|uely to ensure a perfect join between
the upper and the sole. Hand labour is just as ceiiain as regards
this detail, and when performed by skilled hands is very nearly as




^S^^'



Fig. S4.



MANUFACTURE OF SOFT-RUBBER ARTICLES.



T«I



rapid as machine labour. In both methods zinc templates, of size
and shape corresponding to those of the shoes to be made, are used.
The following are current sole-mixings : —



A.



West Indian .


5,000 gms.


B. Ceara Ift


4,000 gms


Reclaimed


2,500 .,


Substitute (odourless)


3,000 .,


Substitute (odourless)


2,000 ,,


Carbon -black .


800 ,,,


Carbon black .


800 ,,


Litharge (free from




Litharge (free from




peroxide)


2,700 ,


peroxide)


2,500 „


Whiting .


25,000 .,


Barytes .


10,000 ,,


Barytes .


5,000 ,,


Whiting .


30,000 ,,


Sulphur .


150 ,,


Sulphur .


250 ,,







Of course the sole mixing varies with the quality of the shoe.

(b) TJte U23per. — Like the sole, the upper includes several parts
bearing distinctive names ; the front part, the side pieces, and the
back part, surround the whole shoe in a single piece. This does not
get such hard wear as the sole, but, on the other hand, it is subject to
a great deal of stretching, bending, and twisting, and must therefore
be quite pliable, so as not to crack. Consequently the thickness of
the upper need only be small ; it is hardly ever more than 0*4 mm.,
and is generally just the same for all kinds of galoshes turned out
by any one factory. An ordinary set of three-roll calenders is
all that is required to run the sheet,' but these should work
absolutely smoothly and evenly. The slightest amount of vibra-
tion will result in the production of stripes and other inequalities
in the soft rubber ; of course these are to be found on other kinds
of sheet, but are not so detrimental to its usefulness, whereas in
this instance a smooth surface is the chief desideratum. The
rubber should be particularly well mixed, and in this the soft
nature of the mixing due to the pitch which it contains will be of
assistance; otherwise it would need to be worked too long and
heated too much to do it any good. The comparatively soft state
of the mixing also determines the nature of the further handling of
the sheet. The sheet is first of all not rolled up like others, because
it would stick together ; and even if a layer of cloth were run in
between successive layers of sheet, the impression of the cloth and
other roughnesses would be formed on the sheet when it had lain
for a short while. It is therefore cut off as it comes from the
calenders in lengths of 2 to 3 metres, according to circumstances, and
the pieces are spread out on cloth-covered frames, which can then
be packed on top of one another.

Calenders are also made which cut out the uppers direct, but. of
course^ the two rolls which carry the knives have to be changed for
every different size of shoe. One cannot superimpose several layers



152 RUBBER MANUFACTURE.

of sheet for cutting purjDOses, because the rubber is too tack}^, and
the use of chalk, which one would adopt in the ordinary way, is
prohibited by the circumstance that the upper portions of the whole
surface have afterwards to be stuck on. The upper parts must be
carefully treated after being cut out, until they are used, each
separate piece being placed between cloths bound together in book
form.

The mixing for the uppers has the following composition : —



Peruvian Para . . 5,000 gms.
Barytes . . . 5,000 \,
Lithopone . . . 5,000 ,,
Litharge (free from per
oxide)



"Angel red" . . 1,000 gms.

Sulphur . . . 200 ,,

Carbon-black . . 200 ,,

Pitch mixture . . 1,200 ,.



2,000 ,,

The " Pitch mixture " consists of —

Pitch .... 10,000 gms. i American resin la . 250 gms.

Carnauba Avax . . 500 ,, j Trinidad asphalt . 50 ,,

(c) 21ie Inside. — Under this heading are classed all those portions
which are covered by the upper and the sole, and of which only
the lining is visible in the finished shoe. All the parts belonging to
this category consist, in order to give the necessary support to the
galosh, of more or less thickly proofed materials, of the most varied
kinds, such as webbing, canvas, cloth, and even wadding and fur.
These materials are generally proofed on the calenders ; in the case
of webs, which are only very thinly coated, the spreading-machine
may also be used. With regard to the quality of the mixings the
following classification ol the various parts can be made : inner-
soles, half-soles, caps, heel-pieces, instep pieces, and the so-called
German or Russian spurs. The mixings used are of the cheapest ;
they need be possessed of no remarkable properties, either because
the fabrics on which they are spread are very strong, the rubber
on them being only present as a cement to unite them to the other
parts of the shoe, or because they have a double covering, and are
sometimes, also, completely enclosed between other strong parts as
a filling-up material. On the other hand, a certain amount of
toughness is necessary, and this is produced by the admixture of
fibrous material, the waste from unvulcanised proofed cloth being
used for the purpose. The following mixing is about a standard
quality : —



West Indian


10,000 gms.


Carbon-black . . 500 gms


Reclaimed .


15,000 .,


Sulphur . . . 600 ,,


Substitute, brown


10,000 ,,


China-clay . . . 15,000 ,,


Pitch ....


1,500 ,,


Whiting . . . 10,000 ,,


Proofed cloth waste


5,000 ,,


Borneo mixture (from


Litharge (free from per-




Besk) . . . 2,000 „


oxide)


12,000 ,,





- MANUFACTURE OF SOFT-RUBBER ARTICLES. 1 83

For the inner soles, as will be noticed in rubber shoes of quite
different makes, red and light-grey cottons of various shades are in
favour, but other fabrics are also used, in brown and other colours.
The coating of rubber should be about 1 mm. thick. After they
have been taken from the calenders the cloths are rolled up ready
for cutting out. There are no special precautions to be observed
in the latter process, and it is the general practice to punch them
out by machinery, about 10 thicknesses at a time. The inner sole
covers the whole length of the sole inside the shoe, whereas the
half -sole, which comes between this and the outer sole, and corre-
sponds roughly with the welt of a leather shoe, extends only from
the toe to the instep. It has neither insertion nor outer layer of
cloth ; it is cut out by machinery, but also partly b}^ hand, as are
the instep pieces and the heel-pieces. The cap which surrounds
the heel and forms the thickest part of the upper shoe may be as
much as 5 mm. in thickness, and has fabric on both sides. Greater
difficulty attends the cutting-out of this part and its preparation
for use than is experienced with the parts already mentioned. For
it must be sloped off quite gradually down to the two sides of the
shoe which meet it in front, or uncomfortable ridges and sharp
edges would be formed where the two parts join, that is, about
one-third of the length of the shoe from the back. On this
account the two front edges of the cap are cut obliquely, leaving
a cut edge about 10 mm. wide which laps over the canvas of
the side piece. This cutting can be done best by hand, because
the caps for different shoes are of different thicknesses. The
spurs Avhich have been mentioned, and which are attached to
this part, are cut out of sheet which has been run on calenders
with engraved rolls similar to those on which the sole-sheet is
calendered, with the individual spur-moulds at short distances
from one another.

On account of the low quality of the mixing used, and of the
great strain put upon the spurs when the galosh is being taken off,
the spurs are covered bj^ hand with proofed linen. This is inti-
mately united with the rubber of the spurs by tightly pressing the
whole for a few minutes in a heated press, the plates of which are
provided with holes into which the spurs fit. The remainder of
the inside parts are proofed with a different mixing. These parts
include the lining of the upper, the web lining, the web sole, the
toe-cap, the thin cap, and the proofed fabric which is used for
covering over the seams. All these fabrics have a thin coating of
a good mixing, which may be described as a Para quality with



1 84



RUBBER MANUFACTURE.



a little litharge added; the following is the composition of the



Para .

Manaos, negroheads

Kassai, Upi;er Congo



1,500 gms.

500 ,,
5.000 ,.



Rape oil substitute (bi'own) 1,500 gms.
Litharge (free from peroxide) 900 ,, .
Sulphur . . . . 300 ,,



The proofing is in each case on one side only. The lining of the
upper consists, as a rule, of webbing of the same colour as that
used for the sole lining, and is prepared for use in .the same way.
In both instances besides the fabrics mentioned, special linings are
sometimes used, such as wool, wadding, and fur. The web lining is
identical in size with the lining of the upper, and unites the latter
with the upper itself. The same relation holds between the web
sole and the thin cap. The toe-cap forms the toe of the shoe, and
serves both to give strength and as an ornament, its shape being
visible on the outside ; it is generally heart-shaped. The proofed
fabric used for covering over the seams is cut into strips about
6 mm. wide for use. A component part which is only occasionally
used remains to be mentioned, viz. rubber-coated twine. This is
used in the manufacture of rubber galoshes, the method adopted
being to lay short pieces of it under the outer coating of rubber.
It is 25i*epared by dipping twine into rubber solution.

Two parts of the rubber shoe which occupy an exceptional
position, and cannot be brought under either of the above headings,
remain to be mentioned ; they are the cap-lining and the so-called
French spurs. Cap-linings are only used in making up men's
shoes. They form the inside of the heel-piece, and are made from
approximately the same mixings as the soles, the amount of raw
rubber being increased, however, by a good 5 per cent. They are
united on the outer side directly to the upper. The French spurs
are made from a mixing which is very much the same as that from
which the uppers are made, but which contains no tar. The sheet
from which they are cut is run in the same way as that used for
Russian spurs, and the spurs are also pressed in moulds in the same
way, but they are not covered with cloth. They are fastened to
the outside of the shoe by means of rubber solution.

(d) Making-iip. — Just as the various parts of the shoe are
carried to the cutting-out room on endless conveyor bands, they are
taken in the same way, after they have been cut out, to the
making-up room. The making-up of a rubber shoe is not at all a
simple matter. An ordinary shoe consists of eight different parts,
a high-buttoned shoe of seventeen parts, whereas, on the other
hand, a rubber boot is made up of twenty-three parts, and not one



MANUFACTURE OF SOFT-KUBBER ARTICLES.



85



of these is superfluous. The most interesting jDart of the manu-
facture is carried out in the makino^-
up rooms. Making-up is a difficult
process, requiring accurate know-
ledge, and it is carried out almost
entirety by female labour. First of
all the separate parts, with the ex-
ception of the webs, are spread with
solution, and tlie inside portions, in
particular the linings of the uppers,
are laid on the lasts. On top of
these the caps are rolled down by
means of the ordinary hand rollers
as used in other parts of the factory,
and then the inner sole is put on.
The places where these meet, and
in particular all inside seams, are
covered with the proofed strip men-
tioned above, in order to make them
more durable, but the seams must
also be made perfect before this is
put on. The half-sole is now put on,
and then the instep-pieces and heel
pieces, after these the web lining and,
if required, the German or Russian
spurs; the uppers, and finally the
soles, are added, the French spurs be-
ing put on if required. All the parts
must adhere firmly to one another
without air-spaces between them, and
without interspaces. The ornamen-
tation seen on the upper is produced,
so far as it is not due to the outlines
of the toe-cap or to pieces of twine
which have been put under the outer
coat, by means of a small toothed
wheel, which is also used to press
the seams together. An average
woman worker can turn out a maxi-
mum quantity of about forty pairs
of shoes per day.

(e) Varnishing. — This is the final operation before the shoes are






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Online LibraryAdolf HeilThe manufacture of rubber goods : a practical handbook for the use of manufacturers, chemists, and others → online text (page 16 of 21)