21/8/2011
Ngành sản xuất các sản phẩm phụ tùng cao su nhựa kỹ thuật đòi hỏi nhiều thông tin, từ các nguyên liệu hóa chất, các ứng dụng cho đến các nhà cung cấp. Từ đó khi cần thiết, để nghiên cứu một bánh xe cao su, cao su chịu dầu các kỹ sư nhanh chóng có được nguồn để sử dụng. Blog Cao su Việt xin trích một đoạn trong trang web hữu ích, mời các bạn đọc.
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These rubbers include grades suitable for service at
temperatures to 250°C and having maximum resistance to oils and greases. Some
are considered specialty materials and are quite expensive.
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| Đệm cao su bằng cao su tổng hợp Neoprene |
Neoprene (CR; BC, BE): Except for polybutadiene and polyisoprene, neoprene is
perhaps the most rubberlike of all, particularly with regard to dynamic
response. Neoprenes are a large family of rubbers that have a property profile
approaching that of natural rubber, and with better resistance to oils, ozone,
oxidation, and flame. They age better and do not soften on heat exposure,
although high-temperature tensile strength may be lower than that of NR.
These materials, like NR, can be used to make soft,
high-strength compounds. A significant difference is that, in addition to
neoprene being more costly than NR by the pound, its density is about 25%
greater than that of natural rubber. Neoprenes do not have the low-temperature
flexibility of natural rubber, which detracts from their use in low-temperature
shock or impact applications.
General-purpose neoprenes are used in hose, belting,
wire and cable, footwear, coated fabrics, tires, mountings, bearing pads, pump
impellers, adhesives, seals for windows and curtain-wall panels, and flashing
and roofing. Neoprene latex is used for adhesives, dip-coated goods, and
cellular cushioning jackets.
Chlorinated polyethylene (CM; DE): This family of elastomers is produced by
the random chlorination of high-density polyethylene. Because of the high
degree of chemical saturation of the polymer chain, the most desirable
properties are obtained by crosslinking with the use of peroxides or by
radiation. Sulfur donor cure systems are available that produce vulcanizates
with only minor performance losses compared to that of peroxide cures. However,
the free radical crosslinking by means of peroxides is most commonly used and
permits easy and safe processing, with outstanding shelf stability and optimum
cured properties.
Chlorinated polyethylene elastomers, sold by the Dow
Chemical Co. under the trade name Tyrin, are used in automotive hose
applications, premium hydraulic hose, chemical hose, tubing, belting, sheet
packing, foams, wire and cable, and in a variety of molded products. Properties
include excellent ozone and weather resistance, heat resistance to 300°F (to
350°F in many types of oil), dynamic flexing resistance and good abrasion
resistance.
Chlorosulfonated polyethylene (CSM; DE): This material, more commonly known as
Hypalon (Du Pont), can be compounded to have an excellent combination of
properties including virtually total resistance to ozone and excellent
resistance to abrasion, weather, heat, flame, oxidizing chemicals, and crack
growth. In addition, CSM has low moisture absorption, good dielectric
properties, and can be made in a wide range of colors because it does not
require carbon black for reinforcement. Resistance to oil is similar to that of
neoprene. Low-temperature flexibility is fair at -40°F.
Hypalon is a special-purpose rubber, not particularly
recommended for dynamic applications. It is used generally where its
outstanding environmental resistance is needed. Typical applications include
coated fabrics, maintenance coatings, tank liners, protective boots for spark
plugs and electrical connectors, cable jacketing, and sheeting for pond liners
and roofing.
Nitrile (NBR; BF, BG, BK, CH): The nitriles are copolymers of butadiene and
acrylonitrile, used primarily for applications requiring resistance to
petroleum oils and gasoline. Resistance to aromatic hydrocarbons is better than
that of neoprene but not as good as that of polysulfide. NBR has excellent
resistance to mineral and vegetable oils, but relatively poor resistance to the
swelling action of oxygenated solvents such as acetone, methyl ethyl ketone,
and other ketones. It has good resistance to acids and bases except those
having strong oxidizing effects. Resistance to heat aging is good, often a key
advantage over NR.
With higher acrylonitrile content, the solvent
resistance of an NBR compound is increased but low-temperature flexibility is
decreased. Low-temperature resistance is inferior to that of natural rubber,
and although NBR can be compounded to give improved performance in this area,
the gain is usually at the expense of oil and solvent resistance. As with SBR,
this material does not crystallize on stretching, and reinforcing materials are
required to obtain high strength. With compounding, nitrile rubbers can provide
a good balance of low creep, good resilience, low permanent set, and good
abrasion resistance.
Tear resistance is inferior to that of natural rubber,
and electrical insulation is lower. NBR is used instead of natural rubber where
increased resistance to petroleum oils, gasoline, or aromatic hydrocarbons is
required. Uses of NBR include carburetor and fuel-pump diaphragms and aircraft
hoses and gaskets. In many of these applications, the nitriles compete with
polysulfides and neoprenes.
Epichlorohydrin (CO, ECO; CH): Epichlorohydrin rubber is available as a homopolymer (CO)
and a copolymer (ECO) of epichlorohydrin. Reinforced, these rubbers have
moderate tensile strength and elongation properties, plus an unusual
combination of other characteristics. One of these is low heat buildup, which
makes them suitable for applications involving cyclic shock or vibration.
The homopolymer has outstanding resistance to ozone,
good resistance to swelling by oils, intermediate heat resistance, extremely
low permeability to gases, and excellent weathering properties. This rubber
also has low resilience characteristics and low-temperature flexibility only to
5°F -- characteristics that may be unsuitable for some applications.
The copolymer is more resilient and has low-temperature
flexibility to -40°F, but it is more permeable to gases. Oil resistance of both
compounds is about the same. Typical applications include bladders, diaphragms,
vibration-control equipment, mounts, vibration dampers, seals, gaskets, fuel
hose, rollers, and belting.
Ethylene/acrylic: This family of rubbers is sold by Du Pont, under the trade name of Vamac.
Introduced in 1975 in masterbatch form, the family was expanded in 1983 by the
addition of a gum polymer. Vamac materials provide, at a moderate price, heat
and fluid resistance surpassed by only the more expensive, specialty polymers
such as fluorocarbons and fluorosilicones. The material has very good
resistance to hot oils, hydrocarbon-based or glycol-based proprietary
lubricants, transmission and power-steering fluids. It is not recommended for
use with esters, ketones, highly aromatic fluids or high-pressure steam. A
special feature of Vamac is its nearly constant damping characteristic over
broad ranges of temperature, frequency, and amplitude.
The polymer is recommended for applications requiring
a durable, set-resistant rubber with good low-temperature properties and
resistance to the combined deteriorating influences of heat, oil, and weather.
It is used in various automotive components such as mounts, gaskets, seals,
boots, and ignition-wire jackets. Electrical applications include oil-well
platform cable jackets, plenum cable, transit-wire jackets, and marine cable.
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| Phớt cao su nhân tạo FKM |
Perfluoroelastomer (FFKM): Chemical resistance of perfluoroelastomer parts is similar to that
of PTFE, and mechanical properties are similar to those of the fluorocarbon
rubbers. This high-performance, high-priced rubber, produced by Du Pont as
Kalrez, and by Greene, Tweed & Co. as Chemraz, is essentially unaffected by
all fluids, including aliphatic and aromatic hydrocarbons, esters, ethers,
ketones, oils, lubricants, and most acids. However, some fully halogenated
fluids and strong oxidizing acids may cause swelling. The parts are suitable
for continuous service to 290°C and intermittent service to 316°C. Resistance
to ozone, weather, and flame is exceptional. Radiation resistance is good and
high-vacuum performance excellent.
Perfluoroelastomer parts are used primarily in
demanding fluid-sealing applications in the chemical-processing,
oil-production, aerospace, and aircraft industries.
Acrylate (ACM, ANM; DF, DH): These are specialty rubbers based on polymers of
methyl, ethyl, or other alkyl acrylates. They are highly resistant to oxygen
and ozone, and their heat resistance is superior to that of all other
commercial rubbers except the silicones and the fluorine-containing rubbers.
Water resistance is poor, however, so the acrylates are not recommended for use
with steam or water-soluble materials such as methanol or ethylene glycol.
However, flex life is excellent as is permeability resistance. Resistance to
oil swell and deterioration is also excellent at high temperatures.
Low-temperature flexibility is not good, and these
rubbers decompose in alkaline solutions and are swelled by acids.
Low-temperature flexibility and water resistance can be improved, but only with
a marked decrease in heat and oil resistance. These materials are used
extensively for bearing seals in transmissions, and for O-rings and gaskets.
Polysulfide (PTR; AK, BK): These polymers have outstanding resistance to oils,
greases, and solvents, but they have an unpleasant odor, resilience is poor,
and heat resistance is only fair. Abrasion resistance is half that of natural
rubber, and tensile strength ranges from 1,200 to 1,400 psi. However, these
values are retained after extended immersion in oil.
Basic properties of polysulfide polymers are
determined by the type of chain structure and the number of sulfur atoms in the
polysulfide groups. Increased sulfur concentration improves solvent and oil
resistance, and also reduces permeability to gases. These materials are used in
gasoline hose, printing rolls, caulking, adhesives, and binders.
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| Sản phẩm cao su silicone |
Silicone (VMPQ, PVMQ; MQ, PMQ, FC, FE, GE): Silicone rubber comprises a versatile
family of semiorganic synthetics that look and feel like organic rubber, yet
have a completely different type of structure from other rubbers. The backbone
of the rubber is not a chain of carbon atoms but an arrangement of silicone and
oxygen atoms. This structure gives a very flexible chain with weak interchain
forces, which provides a remarkably small change in dynamic characteristics
over a wide temperature range.
Silicone rubbers have no molecular orientation or
crystallization or stretching and must be strengthened by reinforcing
materials. The cost of silicone rubbers is not as dependent on petroleum cost
as are costs of the synthetic organic rubbers. Although silicones are at the
high end of the cost range for rubbers, they can be made to withstand
temperatures as high as 600°F without deterioration. At the other end of the
scale, silicones retain useful flexibility at -150°F.
While the strength of silicone rubbers is lower than
that of other rubbers, these materials have outstanding fatigue and flex
resistance. They do not require high tensile strength to serve in dynamic
applications. Fall-off in tensile properties with extended exposure to high
temperature is much less than for other rubbers. Resistance to chemical
deterioration, oils, oxygen, and ozone is also retained under these conditions.
Chemical inertness makes these materials well suited for surgical and
food-processing equipment. One and two-part silicone sealants are used as
structural adhesives and weatherseals in commercial buildings.
Fluorosilicone (FVMQ; FK): This type of silicone provides most of the useful qualities of
the regular silicones plus improved resistance to many hydrocarbon fluids such
as fuels. Exceptions are ketones and phosphate esters; however, FVMQ rubbers
can be blended with conventional dimethyl silicones, which have good resistance
to these fluids at temperatures to 300°F. The FVMQ rubbers are most useful
where the best in low-temperature flexibility is required in addition to fluid
resistance, although resistance to fluids (especially those containing
aromatics) is poorer than that of the FKM-type fluorocarbon rubbers.
Fluorosilicone rubbers have moderate dielectric
properties, low compression set, and excellent resistance to ozone and
weathering. They are expensive and definitely special purpose. Typical
applications include seals, tank linings, diaphragms, O-rings, and protective
boots in electrical equipment.
Fluorocarbon (FKM; HK): Generally produced as a copolymer of vinylidene fluoride and
hexafluoropropylene, the fluorocarbons are high-performance, high-cost rubbers
known generally as Viton (Du Pont) and Fluorel (3M). These rubbers have
outstanding resistance to heat and to many chemicals, oils, and solvents
compared to any other commercial rubber. In air, fluorocarbon rubber parts
retain at least half of their original properties after 16-hr exposure at
600°F. These same compounds offer low-temperature stability to -40°F.
In the reinforced state, these rubbers offer moderate
tensile strength but relatively low elongation properties. They resist
oxidation and ozone, and they do not support combustion. Several versions are
available, and conventional compounding produces formulations within a hardness
range of 65 to 95 Shore A. Fluorocarbon rubbers are severely attacked by highly
polar fluids such as ketones, hydrazine, anhydrous ammonia, and Skydrol
(phosphate ester) hydraulic fluids. Postcuring is required to develop optimum
properties. Typical applications are seals, gaskets, diaphragms, pump
impellers, tubing, and vacuum and radiation equipment.
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| Nhựa PU thích hợp cho nhiều sản phẩm cao su |
Urethane (AU, EU; BG): These rubbers, combinations of polyesters or polyethers and
diisocyanates, are unusual in that physical properties do not depend on
compounding materials. Urethanes crosslink and undergo chain extension to
produce a wide variety of compounds. They are available as castable or liquid
materials and as solids or millable gums.
Urethane polymers have outstanding abrasion
resistance, excellent tensile strength and load-bearing capacity, and
elongation potential, accompanied by high hardness. Other properties include
low-temperature resistance, high tear strength, either high or low coefficient
of friction, good radiation resistance, and good elasticity and resilience,
even in very hard stocks.
Typical applications include seals, bumpers,
metal-forming dies, valve seats, liners, coupling elements, rollers, wheels,
and conveyor belts, especially where abrasive conditions are present.
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