Adolf Heil.

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

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carbonate, zinc oxide, barytes, and lithopone. The colouring
matters used are Frankfort black, nigrosin, carbon-black, the last-
named only in small quantity, since it is a good conductor, and iron
oxide or caput raortuum. The various materials are weighed off"
and put into a large Pfleiderer machine ; the latter is set in motion
and the resin solution slowly added, the extra spirit necessary being
added later. When the mass has been worked up for about an
hour, and the ingredients are intimately mixed together, the
asbestos and jute fibre, which must be thoroughly disintegrated, are
scattered in gradually in the form of a very light fluff'. It may
here be noted that the asbestos fibre should be teased out as
thoroughly as possible on the fur carder ; the finer the flufi* the
better the properties of the finished mass. The mixing-machine
must be kept going for one and a half to two hours longer, until
the dough is ready for use. The latter is then spread out on sheet-
iron racks to a depth of 2 cm. and put into the vacuum drier. The
alcohol is distilled ofi" and recovered for further use. The drying is
completed at 140° C. with a vacuum of 65 cm. in about 2| hours.

in order to work up the mass still further, it is crushed on the
" Kaiser " mill (fig. 92), and finally ground in the E3:celsior mill.
The powder thus obtained is compressed in moulds and made into
articles of various shapes.

The following mixings may be reconunended as suitable for
difierent purposes: —



Kesin solution 30,000


Alcoliol ....



Ambroin waste (powdered) .



China-clay ....



Magnesia . ...



Talite or atniuid ,



I'lankfort black .

. 4,500

1,750 Iron oxide or

or Nigrosin ....


250 fuchsin

Asbestos fibre


4,000 .

J, ',, waste



Jute fibre ...



Linseed oil .



Ozokerite ....



Burgundy pitch



Colophony ....

2 000



For glossy imitation ebonite : —

Resin solution
Magnesia .
China clay .

2,000 gms.

Zinc white .

, ,

2,000 gms.

3,000 „

Carbon black

750 „

1,200 „

Asbestos fibre,


2,500 ,,


5,000 „

10. Moulding and Pressing Imitation Ebonite Goods. — Every
article is made by compression in steel moulds, made up in three
portions: —

1. The outer casing.

2. The matrix or mould proper.

3. The plunger.

The outer casing encloses the matrix, and must be designed with
very thick walls. It is also designed, as far as practicable, to take
as many different moulds as possible, so that the one casing will
serve for all moulds of a similar type. The plunger serves to
compress the mass, and should be an exact fit to the matrix.

The method of procedure is as follows : —

The powdered mass already described is accurately weighed
out, filled into the mould, and compressed by means of the plunger
under small hydraulic presses at a pressure varying from 75 to 300
atmospheres. The moulds are put into hot-air ovens for about ten
minutes, then slightly cooled, and the matrix and plunger forced
out of the jacket in the same way as they were put in, when the
finished article drops out of the matrix. The manufacture can be
carried through very rapidly, and an experienced hand can mould
as many as 400 pieces of simple construction — e.g., handles —
per day.

The final process consists in buffing on emery-wheels and

Imitation ebonite which is to have a good polish after coming
from the press must, on the other hand, remain for about ten
minutes under the press at 75 atmospheres pressure.

Naturally the material cannot be worked, drilled, or turned
very well, since it breaks very easily, but where moulding is
possible it constitutes a cheap e.. v. trie insulating material, w^ith a
high resistance amounting to as much as 80,000 megohms, and can
easily be applied to the insulation of metal parts of the most varied



Nearly all waste rubber is used over ao^ain in some form or other.
The factories which have been established for the express purpose
of reclaiming waste rubber have latterly advanced beyond the
stage when old rubber shoes constituted the chief form of rubber
waste worked up by them, although such old shoes are the basis
of a very considerable proportion of the reclaimed rubber used in
rubber factories. But, except in a few instances, the reclaiming of
old rubber shoes is not, as a rule, carried out in the rubber factory,
but in special factories. This statement holds good, also, for old
bicycle tyres. The tj^pical reclaimed rubber factories of Theilgaard
in Copenhagen have been already so clearly described in the
Gum'ini-ZeiUing'^ that it is only necessary here to refer the reader
acquainted with German to the articles in question.

The following short account is therefore concerned only with
the reclaiming process as carried out in the rubber factory itself.

The fact that by no one of the reclaiming processes at present
in use is it possible from vulcanised waste to reproduce uiivulcan-
ised ((ievulcanised) rubber, must be assumed to be well known.
The sole result of reclaiming processes as now applied is to render
the rubber plastic again. If in any given instance the vulcanisa-
tion coefficient is reduced as a result of the reclaiming process, the
reduction is . only slight, and indicates that the rubber substance
has undergone some decomposition. The only case in which this
is not absolutely true is that of cut-sheet (or other cold-cured)
waste, but the reduction is in this case due to the removal from
combination with the rubber, not of sulphur, but of chlorine, a
result which is achieved with comparative ease ,by heating the
waste with solutions of the alkalis or alkaline earths.
1 1904, xix. pp. 87-93.

225 I?


Practically the only rfeally important operation in the whole
process of working up rubber waste is the sorting of the waste.
By carrying this out in a rational way the subsequent processes
can be very much simplified.

Cut-sheet waste may be first of all referred to. This kind
of waste is generally reclaimed by heating with alkali; the
alkaline solution attacks the chlorine of the rubber, and to a still
greater extent the white substitute. It is not possible to prevent
the waste in question from becoming more or less dark in colour as
the result of the heating and subsequent plasticising process (during
which process the caustic liquor is, of course, washed out of the
rubber), and as a rule, therefore, the ' uncoloured waste is not
treated separately from the black; indeed in many factories the
red waste is also included with these. As a result of such treat-
ment with caustic soda, and subsequent heating in steam at a
pressure of about 5 to 8 atmospheres in order to render it plastic,
cut-sheet waste yields a product which can be more or less used in
the place of raw rubber in a number of mixings. The vulcanisa-
tion coefficient of such a product is very low, and there is, therefore,
room for a considerable degree of after- vulcanisation. This pro-
duct, however, often smells very unpleasantly of the decomposition
products of the white substitute. Its use in red goods which
contain golden sulphide is not to be recommended.

Floating waste is either uncoloured (grey), red, or black, for a
good white which floats cannot be produced on account of the high
specific gravity of the white pigments [or, rather, on account of the
large proportions of such pigments required to mask the natural
colour of the vulcanised rubber]. Floating waste is, therefore,
sorted into " grey," " red," and " black." The sorted waste is gener-
ally heated with oil after being finely ground on roller mills with
three rolls (fig. 100), which are also in part fluted. By this means a
highly plastic mass of great stickiness is produced, which imparts
to mixings in which it is employed a very great power of absorbing
mineral compounds. Red floating waste should be specially ex-
amined to see that it contains no cold-cured waste, so that the
golden sulphide may not change colour on reclaiming. To reclaim
red floating bottle-washers it is only necessary to heat them under
suitable conditions. Heating with oil is generally conducted in
jacketed heaters, and the waste is kept well agitated during the
process. Bottle-washers, on the other hand, are heated in the
ordinar^^ vulcanising heaters in steam at a pressure of 11 to 12
atmospheres. The heated bottle-washer waste must, of course, be



afterwards dried in the vacuum drier before being run out into
sheet. That floating . bottle-washers can be plasticised witliout the
addition of any oil is due to the fact that the so-called " Para-
factis," . which is used in considerable proportions in bottle-ring
mixings, usually contains about 45 per cent, of acetone-soluble oily
and waxy constituents. With between 30 and 45 per cent, of this
substitute in the mixing theie is, therefore, present in the Avaste
between 14 and 20 per cent, of oils and wax, which is ample to
plasticise it, for the amount of rubber present is only between
48 and 63 per cent.

In non-floating waste a distinction is made between that which

Fig. 100.

contains fabric and that which does not. Both kinds of waste,
again, are sorted according to colour. Drab waste, and frequently
also red, generally contains considerable quantities of free sulphur.
For this reason this kind of waste is often desulphurised before it
is heated with oil, by grinding it into fine crumb and then boiling
it up with a solution of caustic soda or of sodium sulphite. The
waste is then thorouglily washed and heated with about 20 per
cent, of its weight of rosin oil, castor oil, or palm oil, occasionally
also with paraffin wax. In a few factories this heating process is
carried out under vulcanising presses, but most works probably
employ for the purpose the jacketed heater with agitator.

The treatment of waste containing fabric insertions formerly
gave rise to all kinds of difficulties in removing the insertion. Only


in the case of dark waste could acids be used to destroy the fibrous
material. The acid treatment, too, was accompanied by a number
of drawbacks, such as evolution of sulphuretted hydrogen, de-
composition of whiting and other fillers, with formation of gypsum,
etc., so that an important step forward was taken when other
methods of destroying the fabric were introduced. One is now
enabled by the use of these methods to reclaim both white and red
waste containing insertion.

It is usual to free the plasticised waste, either on the refining
roller mill or on a tube machine provided with a fine sieve, from
all coarse particles that may still be present.

The possibility of reclaiming certain kinds of black waste, either
without any addition, or by adding very small quantities of oil, etc.,
depends upon the presence in such waste of quite considerable
quantities of pitch. In rubber shoes the resinous and oily sub-
stances of the varnish are present in addition to the pitch. Proofed,
uncured canvas waste is sometimes ground up into fibre and then
added to the mixing direct, or else the unvulcanised rubber is
recovered in an extraction apparatus, with the object of using it
again for solution.

It must, of course, be admitted that the regeneration of rubber
on the works itself is always less satisfactory as regards the product
turned out than the recovered rubber produced by factories which
make reclaiming a special business. For one thing, the price of old
rubber is very much inflated by an extensive demand on the part
of a large number of works, much more so than if the whole were
being purchased by just a few large reclaiming works ; and it is
further obvious that the sorting and blending of the waste can be
done to a much greater nicety when dealing with the large quantities
used in a reclaiming works, than when, as in the case of a rubber
factory reclaiming waste for its own use, one has to deal only with
comparatively small quantities of material. Moreover, the cost of
reclaiming is naturally higher in a rubber works than it is in a
special factory. For these reasons the practice of reclaiming in
rubber factories is gradually being given up.

[A process which seems likely to prove of considerable value in
a number of cases, is that described under Gare's English patent
No. 12,454, 1906. In this process the two following well-known
facts find practical application, viz. (1) that when heated in contact
with air, vulcanised waste is decomposed ; (2) that when heated out
of contact with air such waste is softened. According to the process
the waste rubber is finely ground, and is then highly compressed


in moulds in order to drive out all air from between the fragments
of waste. The mould, still under pressure, is then heated at about
205'^ C. for a length of time depending on the size of the mould, and
is then allowed to cool before being opened. Under this treatment
the waste amalgamates and forms an extremely dense mass,
possessing good properties, and taking the shape of the mould
accurately. Such articles as buffers, cab tyres, etc., are those to
which the process is best adapted.]



Specific gravity plays a considerable part in the rubber trade,
not so much in estimating the quality of a given sample of
rubber, as in ascertaining whether, for example, two samples
of rubber from different sources will yield the same length
per lb. of gas tubing, etc., of a given size, or, in the case of such
goods as are bought by weight and sold again by size -or by the
article, the same number of articles. The dealer in rubber goods
knows far too much nowadays to regard specific gravity as a
criterion of quality.

Specific gravity is a relative number; it shows how many
times heavier or lighter a given article is than the volume of water
at 4° C. which it- displaces. Hence the article in question should,
strictly speaking,, be weighed at a temperature of 15° C. and the
result calculated, by the aid of factors, to water at 4° C. It is
not usual to employ so accurate a method of specific gravity deter-
mination in the rubber trade. The article in question is simply
weighed in distilled water at 15° C, and the value found is
subtracted from the weight of the article in air. The latter value
is then divided by the difference between the two weights, and
it is customary to call this quotient the specific gravity; it
serves generally as a basis for the calculations of seller and buyer.
Articles which float in water must either be weighed in some
liquid which is lighter than water, or be attached to a glass sinker
and then weighed in water. If the unknown quotient be called
X, the weight of rubber y, the loss in weight of rubber + glass when
immersed in water z, and the loss in weight of the glass alone in
water u, the specific gravity can be readily calculated from the
following formula •



For practical methods of carrying out the determination, reference
may be had to the very useful little book by Marzoll, Anleitung
zur Geividdberechnung teclinischer Gummiwaren, sowie zur
Ermittelung der specifischen Zahlen, Dresden, 1904.

The method of determining the specific gravity of rubber goods
by weighing in air and in water is so simple, and capable of being
carried out so quickly, that there would appear no object in
attempting to simj)lify it still further, whether by having a number
of standard solutions ready made up to definite specific gravities, so
that the pieces of rubber may be dropped into each in turn until
in one of them it is found to just float (a method which is not so
simple in practice, on account of the great difiiculty of keeping the
standard solutions accurate, and the necessity for cleansing and
drying the sample after immersion in one solution before it is put
into the next), or by adopting Minikes' modification of the floating
method. This consists in dropping the sample of rubber into a
test-tube graduated on two opposite sides and containing a solution
of zinc chloride (of sp. gr. 2-000), diluting the solution until the
rubber just floats in it, and then reading ofi* the specific gravity
from the graduations. The particular rubber article being examined
is often too large to be put into the Minikes test-tube, and must
not be cut.

Since, therefore, all determinations of specific gravity can be
carried out on a good Mohr-Westphal balance, a Reimann's sinker
is provided with the balance, so that where necessary thfe weighings
can be carried out in media other than water, and the specific
gravity determined by means of the sinker-thermometer which has
5 c.c. displacement. A good method of dealing with floating
rubber goods is to weigh them in alcohol or in similar liquids of
specific gravity less than I'OOO.


Absorptive power of reclaimed rubber

Accumulators, hydraulic, 75.
Accumulator cases, 216.
Acid-resisting rubber, 104.
African rubb^T, 14, 15, 17, 18, 19.
Air, compressed, 129, 139.
Air-cushions, 155.
Air, hot, 85.
Air-markings, 136, 152.
Albuminoids of rubbi-r, 17.
Alkali nitrites, 137.

solution, cau.stic, 225.
Aluminium bronzes, 90.
Ambroin, 221.
American rubber, 6-19.
Ammonium carbonate, 136.

nitrite, 137.
Analysis of rubber, 17.
Analytical values, 19.
Arrangement of a rubber factory, 1.
Asbestos fibre, 191, 223.

sheet, 192.
Asiatic rubber, 16.
Asphaltum in mixings, 116.
Asphalt varnish, 217.

Balls, 136.

mixings for, 137.

painting, 139.

vulcanising press for, 138.
Ball valve, 135.
Band saws, 144.
Bands, elastic, 158.
Beaded edge of tyre, 152.
Beaming machine, 130.
Behaviour of rubbers on mixing rolls, 41.
Belting, 145.

calenders, 146.

vulcanisation of, 14.
Belt-folding machine, 145.
Bent-lever press, 218.
Benzine, 162, 164.
Benzole, 82, 162.
Besk, 19, 115.
Bicycle tyres, 150.
Billiard-strip, 135.
Blisters in hose, 131.
Blocks for "cut-sheet," 174.

Blooming, 63.
Boilers, 3.
Bolivian Para, 7.
Bottle-washer waste, 226.
Braided hose, 125.
Braiding machine, 126.
Brake rubbers, 150, 154.
Brass mandrels, 129,
Bronze-colour printing, S9.

CABLE-co:iting machine, 188.
Cable, insulated, 188.

insulation, 190.
Cables, electric, 188.
Cab-tyres, 135.
Calabashes, 8.
Calendered sheet, 197.
Calendering sheet-rubber, 47, 54, 155.

Calenders, 46, 197.
Calotropis gigantea, 16.
Cameta, 10.
Canvas hose, 129.

lining, 130, 141.
Caps of galoshes, 182.
Carbon bisulphide, 82.

black, 178.

dioxide, 137.

tetrachloride, 82.
Carding machine, 223.
Castilloa elastica, 13.
Casting tin, 213.
Caucho, 12.

Caustic soda solution, 227.
Ceara rubber, 11.
Centrifugal machine, 34, 38, 206.

covering with ebonite, 220.
Celluloid spreading-knife, 126.
Ceylon Para, 11, 17.
Chalking apparatus, 121, 140.

machine, 170.
Chemical properties of rubber, 19.

valuation of rubber, 17.
Chloride of sulphur, 59.
action of, 80.

of zinc, 229.
Chlorine content of reclaimed rubber, 225.
Coal-tar addition, 116.

colours, 88.




Coating cable, 188.

machine, 188.
Cold vulcanisation, 80.
Collection of '« Para," 7.
Collodion solution, 218.
Coloration of rul)bcr, 20, 103.
Coloured effects on waterproof, 88
Combs, manufacture of, 218.
Compresser, 175.
Condenser, 175.
Cone drive, 175.

Contraction of rubber, 101, 145, 152.
Control, analytical, 104,
Conveying bands, 184.
Cooling capacity, 175.
Copal, 222.

Copper, action on rubber, 90.
Cord, 139, 145.
Couplings, 31.

Cryptostegia grandiflora, 16.
Cut-sheet, 173.

manufacture, 173.

thicknesses of, 177.

waste, 225. .
Cutting-out machine for galoshes, 180.
"Cyclone," 206.

Dead Borneo, 19, 115.
Deckle straps, 135.
Decomposition products, 82, 226.
Depolynierisation, 20, 39, 41.
Designs in relief on waterproof, 168.
Dew-formation on cold-cured goods, 82,

Diathermancy (of ebonite), 202.
Dies of tube machine, 139.
Dipping bench, 98.
Discharging electricity from proofed

" sheet, 93.
Distillation (destructive) of rubber, 21.
Dolls, rubber, 137.
Doubled waterproof fabrics, 84.
Doubling calenders, 84, 87.

rollers, 55.
Draw-plate, 76.
Drum-moulds for tyres, 152.
Drying-plant, 36.
Drying washed rubber, 34.
" Dryness " of mixings, 116.
Dyestuffs, 88.

Ebolite, 221.

Ebonite, covering articles with, 220.

dust, air-separation of, 206.
centrifugalising, 206.

expansion of, 202.

imitation, 221.

manufacture, 201.

mixings, 206.

moulded goods, 217.

rods and tubes, 214.

sheet, 208.

waste, 203.
Elasticity, 196.
Embossing calenders, 171.
Enamelling, 156.

Engine-room, 3.
English hose, 125.
Engraved roller, 171. .
Eraser rubber, 195.
Estrada, 8.
Evaporation pipes, 175.

Felted asbestos, 191.
Feuille anglaise, 177.
Ficus ehistica, 16.

plantations, 16.
Figure-eight cut, 135.
Fillers, 104.
Filter flannel, 206.

press, 156.
Flower-tubing, 141.
Foglia segata, 177.
Forcing apparatus for removing hose from

mandrels, 129.
Freezing-chamber, 174.

plant, 174.
Frictioning, 57.
Frictions, 101.
Funtumia, 14.

Galoshes, 177.
Gas-bags, 155.
Golden sulphide, 109.
Grease rubber, 196.
Grinding rolls, 205, 206.

waste rubber, 226.
Grooved rolls, 145.

wheels, 189.
Guayule, 14, 62.
Gutta Jelutong, 19, 115.

Hancounia speciosa, 12.
Heating tank, 23, 27.
Heel-pieces, 182, 183.
Herb-rubber, 14.
Hevea brazilensis, 6, 12, 41. '

latex, 7.
High-pressure hose, 125.
High-tension cable, 190.
Hollander, 26, 29.
Hollow articles, 134.

needle, 139.
Hose, 120.

outer coat, 123.

inner coat, 128.

lining, 130.

shop, 5.
Hot-air chambers, 85, 187.
heater, 85.
vulcanisation, 85.
bench, 210, 211.
water bottles, 155.
Hydraulic autoclave press, 135, 153.

pressure, 147, 174.
Hydrocellulose, 193.

Hydrochloric acid formation in cold cure,

Imitation leather cloth, 171.
Ingredients of mixings, 104.
Inner coating of hose, 128.



Inner soles, 182.

tubes, 150.
Insertions, 122.
Insides of galoshes, 182.
Instantaneous release,. 45.
Instep pieces, 179, 182.
Insulating power, 191.
Insulation (electrical), 104, 188.

resistance, 191, 224.

tubes, 215.
** Ite" compositions, 192.

"Kaiser" mill, 204, 223.

Kickxia, 14,

Knife for "cut-sheet" work, 175.

Lake pigments, 88.
Landolphia, 14.
Lasts for galoshes, 178,
Latex, yield of, 8.
Leuconotis eugenifolius, 16.
Linseed oil, 206, 211.

varnisli, 186.
Litharge, 63, 101.
Lithopono, 104.
Loom, 130.

Madagascar rubber, 15.
Magnesia usta, 63, 102, 214.

addition to mixings, 103, 141, 208.
Making-up galoshes, 184.
Mandrels, 121.
Mangabeira, 12.
Manhole washers, 144.
Manihot glaziovii, 11, 41.
Manometer, 67.
Maple wood, 178.
Masticators, 174.
Mattogrosso Para, 10.
Melting-point of rubber-sulphur mixture,

Melting tin, 203.
Metallic sulphides, 60.
Micranda siphonoides, 7, 41.
Microporosity, 137.
Mixing, 40, 41.
ebonite, 208.
rolls, 40, 44.

with cylindrical sieve, 45.
room, 42.
Mixings, various, 105-109.
for accumulator cases, 216.

balls, 137.

belting, 147.

cushions, 155.

dolls, 139.

ebonite, 206.

insulation tubes, 216.

enamels, 156.

elastic bands, 158,

imitation ebonite, 223.

inner tubes, 150. '

rollers, 150.

rubber stamps, 161.

shoes, 181, 182, 184.

Mixings for shoe-linings, 184.
vulcanised asbestos, ] 91.
Moisiure in insertions, 131.
Mono-rubber, 19.
Motor tyres, 152.
Moulding, 134.

ebonite goods, 217.
Moulds for imitation ebonite work, 224.
Murupita, 7.

Negroheads, 9,
Nitrites, alkali, 137.
Nitrogen, 137.

Odour of cold-cured goods, 91.
Oil, addition to mixings, 103, 117.
Oil-resisting qualities, 105.
Ornamentation of waterproof, 86.
Outer-covers (of tyres), 152.
Oxidation of crude rubber, 23, 35.

vulcanised rubber, 22.
Ozokerite, 137.

Packing sheet, 141.
Paper rollers, 147.
Para, 6, 100, 203.

entretine, 8.

hard and soft cure, 9.

plantation, 11.

slieet, 196.
Paraffin wax, addition of, 103, 117, 140.
Pedal-rubber punch, 155.
Perambulator tyres, 155.
Peripheral speed, 189.
Peruvian ball, 12.
Petroleum, 118.

Physical properties of rubber, 19.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20

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