I. Introduction
Rubber is a specific type of polymer called elastomer: a large
molecule that can be stretched to at least twice its original
length and returned to its original shape. Early forms of rubber
had many glue-like properties, especially in hotweather. In cold
temperatures, rubber became hard and brittle. Polymers have
distinct additives which classified into four: the filler, added
primarily to provide reinforcement and secondly to reduce cost;
plasticizer, reduce hardness with a given level of filler, and can
help with filler incorporation and dispersion; colorants, is
similar as to a dyes but this colorant is dissolves in the polymer
and the last is the flame retardant, To improve their flame
resistance a number of products may be added to the compound,
either inorganic or organic.
Every machine plays a major role in occupying each processes of
a given product which makes the product precisely in the exact
length, width, or any other specification that required by the
costumers and lessen the productivity errors because machine are
run by its program according to its command.
Rubber has become an important natural polymer in society. We
make rubber from rubber trees (natural latex) and from oil
(synthetic rubber). We use both types of rubber in many products.
Like the Mesoamericans (Aztecs and Mayans) before them, athletes
and children today play with rubber balls. Of course, the most
common use for rubber is in automotive tires. But pencil erasers,
shoes, gloves, dental dams and condoms contain the ubiquitous
substance, too. In many products, rubber is added as a protective
coating for either weatherproofing or shockproofing.
II. Definition of Terms
Accelerator
A chemical which speeds up the vulcanization reaction. This
allows the rubber to cure in a shorter timeframe, at a lower
temperature or both.
Autoclave A vessel that vulcanizes rubber products in a
pressurized steam environment.
Backrinding
Tearing or distortion of a moulded rubber product at the line of
separation of the mould pieces. Factors which can have an influence
on backrinding are blank weight, blank shape, temperature, moulding
pressure and breathe cycles.
Carbon black
A black pigment and reinforcement filler used in rubbers. Carbon
black is a form of amorphous carbon that has a high
surface-area-to-volume ratio. The degree of reinforcement increases
with decreasing particle size.
Compound A term applied to a mixture of polymers,
reinforcements, curatives and other ingredients to produce a rubber
material. The compound is prepared according to a prescribed
formula and mixing process.
Copolymer
A polymer composed from two different monomers, for example an
NBR composed of polybutadiene and acrylonitrile.
Cure time
The required amount of time needed to complete the curing
process to a pre-determined level. The time taken to cure is
dependent on the temperature, material type and section of the
rubber profile.
Curing temperature
The temperature at which vulcanization takes place.
Elastomer (also known as rubber)
A general term used to describeboth natural and synthetic
polymers possessing the ability to return to their original shape
after the deforming force is removed.Microwave curing
Vulcanization of rubbers by heat produced by high frequency
radiation.
Mill
A machine with two counter-rotating rolls used for rubber
mastication, mixing or sheeting.
Mould shrinkage
Dimensional loss in a moulded rubber product that occurs during
cooling after it has been removed from the mould.
Plasticizer
A substance, usually a heavy liquid or oil, which is added to an
elastomer to decrease stiffness, improve low temperature
properties, reduce cost and/or improve processing.
Polymer
Literally means many units and is a large molecule constructed
from many smaller monomers.
Shrinkage
The reduction in size upon cooling of a moulded rubber part.
III. Polymers
The polymer, or blend of polymers, is the fundamental component
in determining the properties of the compound. It is selected to
optimize service performance and processing requirements while also
taking cost into account. Very high molecular weight polymers can
for example produce extremely tough materials. They can however
lead to problems with poor flow, poor joins and particularly
backrinding.
Polymers made up of two types of monomer are known as copolymers
or dipolymers, while those made from three are called
terpolymers.
Figure 1: Single Monomer units polymerized to form a polymer
Figure 2: Two different monomers from a copolymer( or
dipolymer)
Figure 3: Three different monomers form a terpolymer.
IV. Polymers AdditivesPolymer additives are similar and
controlled by the molecular structure. The entired type of polymers
additives are the fillers, plasticizers, stabilizers, colorants,
and flame retardant. Each of the type of polymers additives have
their own purposes to enhance and modify many properties.
FillersFillers are added primarily to provide reinforcement and
secondly to reduce cost. They fall into two basic categories:
reinforcing or semi-reinforcing, and diluent.
The most popular reinforcing and semi reinforcing fillers are
carbon blacks, which are categorized primarily by means of particle
size. Carbon blacks and nonblack fillers become more reinforcing as
particle size decreases. Highly reinforcing fillers can make a
compound tough, which can result in poor flow. Carbon blacks are
alkaline in nature and tend to accelerate cure.
Diluent, or non-reinforcing, fillers have a large particle size
and do not 'bond' to the polymer in the same way as reinforcing
fillers. They are mainly added to reduce cost. Examples include
soft clay, calcium carbonate, and talc.
PlasticizersPlasticizers need to be compatible with the polymer.
They reduce hardness with a given level of filler, and can help
with filler incorporation and dispersion. Special types of
plasticizer can improve the low temperature flexibility of some
rubber types like, nitrile and neoprene. Process aids can also
assist with filler dispersion, although they are normally added to
improve processability downstream. High levels of
plasticizer/process aid can bloom to the surface of make-up and
give knitting problems (flow marks and poor joins) in the
manufactured product. They can also create difficulties when
bonding to metal. Excessive softening of the compound can lead to
air trapping in the mould.
Plasticizers can also cause problems when a product is subjected
to thermal cycling or certain solvents, as they can leach out at
high temperatures and adversely affect the low temperature
properties.
Colorants
Colorants may play a major role is a coloring agent for polymer.
This colorant is similar as to a dyes but this colorant is
dissolves in the polymer. Pigments are filler materials that do not
dissolve, but remain as a separate phrase, normally they have a
small particles size and a refractive index near to that parent
polymer.
Flame Retardants
Most elastomers support combustion, and the resulting
by-products can be extremely hazardous. To improve their flame
resistance a number of products may be added to the compound,
either inorganic or organic. They include antimony trioxide, zinc
borate, aluminium hydroxide and chlorinated paraffins.
Flame retardants are added to different materials or applied as
a treatment to materials to prevent fires from starting, limit the
spread of fire and minimize fire damage. Some flame retardants work
effectively on their own; others act as synergists to increase the
fire protective benefits of other flame retardants. A variety of
flame retardants is necessary because materials that need to be
made fire-resistant are very different in their physical nature and
chemical composition, so they behave differently during combustion.
The elements in flame retardants also react differently with fire.
As a result, flame retardants have to be matched appropriately to
each type of material. Flame retardants work to stop or delay fire,
but, depending on their chemical makeup, they interact at different
stages of the fire cycle. To better understand how flame retardants
work, its helpful tounderstand the fire cycle:
Initial ignition source can be any energy source (e.g., heat,
incandescent material, a small flame). Ignition source causes the
material to burn and decompose (pyrolysis), releasing flammable
gases. If solid materials do not break down into gases, they remain
in a condensed phase. During this phase, they will slowly smolder
and, often, self-extinguish, especially if they char, meaning the
material creates a carbonated barrier between the flame and the
underlying material. In the gas phase, flammable gases released
from the material are mixed with oxygen from the air.In the
combustion zone, or the burning phase, fuel, oxygen and free
radicals combine to create chemical reactions that cause visible
flames to appear. The fire then becomes self-sustaining because, as
it continues to burn the material, more flammable gases are
released, feeding the combustion process.
When flame retardants are present in the material, they can act
in three key ways to stop the burning process. They may work to:
Disrupt the combustion stage of afire cycle, including avoiding or
delaying flashover, or the burst of flames that engulfs a room and
makes it much more difficult to escape. Limit the process of
decomposition by physically insulating the available fuel sources
from the material source with a fire-resisting char layer.
Dilute the flammable gases and oxygen concentrations in the
flame formation zone by emitting water, nitrogen or other inert
gases.
V. Machine used in the Manufacturing Rubber Products:
Roll MillRubber is a material that shares some of the properties
of both solid and liquid. Tough raw natural rubber will be loaded
into a mill, where counter-rotating steel rollers grind it into a
softened, semi-fluid mass. This action, in the presence of oxygen
in the air, tears the long, chain-like rubber molecules into
shorter lengths. The rubber becomes softer and easier to process,
and it readily accepts any other ingredients that may be needed to
create a "compound". A compound is the total combination of the
rubber polymer and modifiers, such as reinforcing fillers, oils,
pigments, antioxidants, vulcanization chemicals, and any other
polymer additives.
Strip Cutting MachineThis invention relates to a machine for
cutting sheets of material into any desired predetermined lengths,
and is particularly to a rubber strip cutting machine. Objects of
this invention are to provide a machine which will cut rubber
strips into any desired length at a point in the process
immediately following the operation of the calender or tubing
machine, so that the continuous strip or sheet of rubber is fed
directly from the calender or tubing machine to the cutting
machine, and means are provided for carrying the severed strips
from the cutting machine at a higher rate of speed than the travel
of the sheet of stock material so that such cut strips may be
delivered in an orderly manner into the press room or other
suitable part of the factory.When it is considered that the
material which this machine is adapted to handle and cut is of an
easily deformed type, it is to be appreciated that the usual modes
of controlling sheet material by means of stops against which the
material strikes, or by passing the material between contact
actuating members, is unserviceable and inoperative where the
material as described above.This invention, however, is designed to
overcome the defects noted above which result from the distortion
of the strip and its failure to operate the devices, and objects of
such invention are to provide a novel form of strip cutting machine
which is adapted to operate upon easily deformed flexible and
yielding stock, and which is so constructed that the exact width or
length of the strips may be maintained throughout the operation of
the machine.
Mandrel MachineAn object used to shape machine works, tool
components that grips or clamps materials to be machined and a tool
component that can be used to grip other moving tool components.
Also used in industrial composite fabrication such as infilament
winding. During the manufacturing process, resin-impregnated
filaments are wound around a mandrel to create acomposite
materialstructure or part. The structure is cured and the mandrel
is removed. One problem with this type of process is that the
mandrel can be very difficult to remove once the part has been
cured. As a result, engineers have created a new type of mandrel
that has the ability to change shape and be easily extracted. When
heated above a certain temperature, the mandrel becomes elastic and
can be manipulated into the desired shape and then cooled to become
rigid again in the new shape. It can then be used in the filament
winding process.
AutoclaveAnautoclaveis a device used forsterilizationthat
supplies by subjecting them to high pressure saturated steam at
121C for around 1520 minutes depending on the size of the load and
the contents.Most buffers and other solutions used in any lab are
sterilized before use to prevent bacterial and fungal growth during
storage. There are two basic techniques for sterilizing solutions:
autoclaving and sterile filtration. Most buffers and other salt
solutions are autoclaved, because filtration of large volumes is
time-consuming and disposable sterile filters are expensive.
However, before autoclaving any solution you should always check
whether it contains any heat labile ingredients. If it does, the
heat-labile substance will usually have to be prepared separately,
filter-sterilized, and added to the remainder of the solution after
autoclaving.
VI. What is Vulcanization?The word vulcanization may we connect
about rubber but what means is just putting air to expand and can
be used as a finished product but totally this word has a broad
section of terms and meaning. Vulcanization is an irreversible
process during which a rubber compound, through a change in its
chemical structure cross-linking, becomes less plastic and more
resistant to swelling by organic liquids. The result is that
elastic properties are conferred, improved, or extended over a wide
range of temperature. The term vulcanization was originally
employed to denote the process of heating rubber with sulfur, but
has been extended to include any process with any combination of
materials which produces this effect. Vulcanization can be carried
out under numerous conditions.
VII. Rubber Hose Manufacturing Flow Chart
RubberMilling ProcessCutting Process
Final Layering ProcessVerificationInitial Layering Process
Trimming ProcessVulcanization ProcessMicrowave Curing
Process
ShipmentPackaging
VIII. Rubber Hoses Manufacturing Process
Factory makes a low pressure and medium pressure rubber hoses.
The intended use is what determines the rubber composition.
Function also determines the color because the industrial hoses are
now often color coded.
The rubber arrives with a factory from the supplier in roll
strip. The first step is to run a through a mill. The roller heat
the rubber softening and smoothening it to an even texture.
The next machine cuts the rubber in strips to the precise width
and thickness required for the size of hose they're going to
construct.
Workers lubricate a steel mandrel that see exact size of the
hoses bore. As the mandrel spins, they wrap a rubber strip around
it, measuring and layering if necessary to build the thickness
thereafter.
Next, they add one or more reinforcement layers. This strip is
made of high strength synthetic fabric that's been coated in
rubber. It design to withstand the pressure to which the holes to
be subjected.
The last layer of rubber forms the hoses outside covering. After
verifying that the final diameter is correct, they wrap the entire
hose construction tightly in wet nylon tape. The tape would later
shrink and compress all the materials together.
This factory also makes hoses with a bilt in attachment on the
end. They position on the mandrel, glue the first layer of rubber
through it then they reinforced the bond with special textile
strips and tightly round high strength carbon steel wire. They
continue the wire more loosely down the body of the hose as the
specific angle design to withstand vacuum pressure.
Carbon steel wire
Bilt in Attachment
Then they wrap the hose in soft stretchy rubber strips that
fills the gaps between the wires.
Next comes the layer of high strength rubber coated fabric then
finally the exterior covering. Light blue rubber for the model.
They pressure wrap again with wet nylon tape then to make the
hose more flexible, they create corrugations by wrapping it tightly
in rope. Whats under the ropes compact creating a dip.
They add another layer of nylon tape to hold the rope in place.
When construction is finished, the hoses on their respective
mandrills go in to an "auto clave" a cylindrical chamber into which
they feed hot steam at high pressure.
This vulcanization process has it called, triggered a chemical
reaction that cures the rubber to make it elastic. As the hoses
come out and cool, the worker remove the shrunk tape. The layers
are solidly compress. They wash the nylon tape and then rewind and
reuse it.
Now workers begin the process of removing the hose from the
mandrels. They tight one end with a rope to create a pressure
then gently pump water between the mandrill and rubber. The
lubricant they applied earlier has prevented the rubber from
sticking to the steel so the hoses separate easily.
They simply slide it off from the mandrel. Workers will now trim
the ends, cut the hose to length for customer ordered then coiled
and package the hose.
IX. References:
http://www.wisegeek.com/what-is-synthetic-rubber.htm
http://www.google.com/patents/US1684158
http://www.most.gov.mm/techuni/media/PR_02034_13.pdf
Elastomer Engineering Guide 7; James Walker
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