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Only One Products
Wire Rod for Engine Valve Springs |
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Engine valve springs are made of specialty steel wire rod and play a vital role in automobile engines. Installed above the cylinders, valve springs control the movement of the intake and exhaust valves.
In general, automobile engines work by repeating the following process. On the intake stroke, the intake valve opens and a mixture of air and gasoline goes into the cylinder. After the air and fuel mixture explodes in the cylinder, the exhaust exits from the exhaust valve. Valve springs are 2 mm to 5 mm in diameter and weigh 30 g to 50 g. These critical parts expand and contract several thousands of times per minute.
Kobe Steel was the first company in Japan to develop and manufacture steel wire rod for engine valve springs. This product fully shows our competitiveness, along with that of wire manufacturers.
By establishing inclusion removal technology in the 1980s, we have gained edges in quality, productivity, and cost, which enabled us to attain the world's largest market share. Our wire rod for engine valve springs account for 53% of the annual world market of 90,000 tons. This means that roughly one in every two cars on the globe uses engine valve springs made of Kobe Steel's wire rod.
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| History |
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Kobe Steel is a pioneer in manufacturing
wire rod for engine valve springs. The establishment of inclusion
removal technology was the most significant technological development
in our history of wire rod development. The technology was made possible
by an inclusion assessment system, which focuses on fatigue fractures
caused by nonmetallic inclusions, or impurities, in the steel.
As valve spring steel becomes stronger, inclusions increase. By analyzing
inclusion composition and shape and by controlling the composition
in the steel refining process, the inclusions can be made more elastic.
The melting point of inclusions contained in steel produced in the
conventional way is over 1600 C. When the inclusion removal technology
is utilized, the melting point of the inclusions becomes lower, at
1500 C. or less. In the hot-rolling and wire-drawing stages, the inclusions
are drawn, made smaller, and rendered harmless. Through this technological
advancement, Kobe Steel's market share of wire rod for engine valve
springs increased considerably. |
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| Timeline of Wire Rod Development |
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| 1930 |
First Japanese manufacturer to
begin trial production of high carbon steel wire rod. |
| 1934 |
Started full production of high
carbon steel wire rod. |
| 1941 |
Began production of wire rod for
aircraft engine valve springs. |
| 1980s |
Established inclusion removal
technology. |
| Around 1985 |
Developed high strength steel
by increasing carbon to silicon-chrome base and adding vanadium. |
| Early 1990s |
Achieved higher strength by applying
surface improvement technology. |
| Around 1995 |
Developed ultra-high strength
wire rod for engine valve springs. |
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| R&D, Production and Supply |
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The following sections and laboratories closely
cooperate in conducting R&D to fulfill high the quality demands
at Kobe Steel: the Wire Rod & Bar Products Development Section,
Wire Rod & Bar Technological Section, Steelmaking Technology Section,
and Rolling Technology Section at Kobe Works; the Research and Development
Laboratory at Kakogawa Works; and the Material Research Laboratory
at Seishin Area.
Wire rod for engine valve springs are manufactured at Kobe Works,
in an integrated process from the blast furnace to rolling. After
the hot metal comes out from the blast furnace, it goes through pretreatment,
decarburization at the basic oxygen furnace, chemical adjustment,
inclusion composition control, and continuous casting. After these
processes, the blooms are heated, rolled, and cooled to produce wire
rod with diameters of 5.5 mm to 9 mm.
The wire rod is then supplied to wire manufacturers, which scalp the
surface, adjust the composition and draw the wire rod to the diameter
of the finished engine valve springs. The wire is further strengthened
by oil tempering. After this, the wire in coils is supplied to spring
manufacturers. Here, the engine valve springs are finally produced.
Kobe Steel maintains close cooperation with wire and spring manufacturers.
At the same time, as an integrated steelworks, we undertake R&D,
manufacturing, and assessment. Superlative quality control is our
most significant edge. |
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| Looking Ahead |
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Automobile engines are expected to become more powerful
and more fuel-efficient. In Japan, 70% of the engine valve springs
are made of high strength steel. Also over the past few years, Europe
and North America have seen a rapid increase in the use of high strength
steel.
The emergence of hybrid cars is one move in this trend. As hybrid
cars are powered by both engines and motors, the engines need to be
smaller and lighter. With regard to car bodies, there are moves toward
legislation to leave more space between the engine and bonnet to protect
a pedestrian's head in car accidents. Estimates show that by using
engine valve springs that are 1 gram lighter, fuel consumption improves
by 0.2%, and rotating speed by 100 to 200 rpm. Thus, the demand for
even more sophisticated wire rod for engine valve springs may well
increase in the future.
To address these trends, Kobe Steel will improve its inclusion removal
technology in anticipation of smaller springs. At the same time, we
aim to bolster our total competitiveness as a corporate group, by
working earnestly with secondary processors to reduce heat treatment
and further simplify processes. In Europe, some customers are starting
to look for stable suppliers. Not only for customer needs within Japan,
but also for users throughout the world, Kobe Steel continues to develop
new kinds of steels and new processes to further strengthen a number
one product: wire rod for engine valve springs. |
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