Improvement of wear resistance of cast iron blocks

Four-stroke engines splash oil on the bore wall for lubrication and cooling. To scrape off the excess oil, the contact pressure of the oil control ring is set
high. This decreases oil consumption. Hence, the bore wall should have higher wear resistance. To raise durability, a hard gray cast iron containing phosphorus (P) is often used (high-P cast iron in Table 2.2). Figure 2.16 shows the microstructure of high-P cast iron. The increased P crystallizes from the melt as hard steadite. It has a chemical composition of Fe3P. The curious shape of steadite stems from its low freezing point. The iron crystal solidifies first. Then, the residual liquid solidifies to form steadite in the space between the iron crystals. This alloy composition has good wear resistance because of high hardness, but low machinability. Hence, instead of using this composition for an entire block, it is typical to enclose it as a wet or dry liner in a normal cast iron block (2 in Table 2.1) or aluminum block (3 and 5 in Table 2.1, described later).
The mileage required for commercial diesel engines is very high, being as much as 1,000,000 km. These engines have high combustion temperatures. Engines requiring very long durability use additional heat treatment on the bore surface. A nitrided liner4 is often enclosed to increase hardness. A phosphate conversion coating on the liner also prevents corrosion. Instead of  enclosing a hard liner, interrupted quench hardening by laser or induction heating can also be applied to the bore wall of the monolithic cast iron block.


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  • The science and technology of materials in automotive engines
    Hiroshi Yamagata
    Woodhead Publishing and Maney Publishing
    on behalf of
    The Institute of Materials, Minerals & Mining
    CRC Press
    Boca Raton Boston New York Washington, DC
    WOODHEAD PUBLISHING LIMITED
    Cambridge England


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  • Honing, lubrication and oil consumption

    Cast iron has been successfully used for monolithic blocks. This is because the casting process can mass-produce large complex shapes. The cylinder bore must have high dimensional accuracy. Honing is the finishing process used to give accurate roundness and straightness. It is performed after the fine boring process. Figure 2.10 shows a micrograph of a honed bore surface.
    The honing whetstone carved the crosshatch pattern. During engine operation, the groove of the crosshatch holds lubricating oil. The resulting oil film generates hydrodynamic lubrication Figure 2.11 is a picture of a honing machine. The tool shaft installs a honing head with a segmented whetstone at its end (Fig. 2.12). The whetstone grinds the bore by exerting an expanding pressure. The vertical motion of the head together with revolution generates the crosshatch pattern. The sharpness of the whetstone determines the profile of the crosshatch. A dull honing
    stone with an excess pressure gives an unwanted over-smeared surface. Ideally the finished surface exposes graphite without burr. The quality of the honing is measured by surface roughness value.

    The graphite in the cast iron block works as a solid lubricant during machining as well as in engine operation. A solid lubricant gives a low frictional force without hydrodynamic lubrication. Graphite, MoS2, WS2,
    Sn, and Pb are all well known as solid lubricants. The low frictional force of graphite comes from the fact that the crystal structure has a very low frictional coefficient during slip at the basal plane. Figure 2.13 shows a schematic representation of the mechanism. The crystal slides easily along its basal plane even with a low shear force. The graphite decreases friction for tools during machining. The brittle nature of graphite makes chips discontinuous.The resultant high machinability gives high dimensional accuracy to cast iron parts. The graphite also works as a solid lubricant to prevent seizure of the piston or piston ring even under less oily conditions.

    The micro-burr of the crosshatch disrupts the oil film to obstruct hydrodynamic lubrication. Additional Mn-phosphate conversion coating (refer to Appendix H) chemically removes the micro-burr to increase oil retention.This prevents seizure during the running-in stage. As well as dimensional accuracy, the surface profile also determines oil retention which, in turn, greatly influences wear resistance. An appropriate profile should be established. One pass finish with the whetstone usually shapes the surface profile to the normal type shown in Fig. 2.14(a)2. An additional finish, scraping off the peak, generates the trapezoid pattern shown in Fig. 2.14(b). This finishing is called plateau honing.

    A customer does not want to change engine oil frequently. Less oil consumption is therefore required. Figure 2.152 compares the oil consumption of a 1.9L car engine, measured by the final oil consumption value (FOC). For a normal type profile, the low Ra = 0.12 μm, middle Ra = 0.4 μm and high Ra = 0.62 μm. For the plateau type, the low Ra = 0.14 μm, middle Ra = 0.32 μm and high Ra = 0.88 μm. The oil consumption is least in the normal type of low Ra. However, it is worth mentioning that the scuffing resistance of the low Ra surface is poor. When the bore wall temperature is high, the plateau surface shows excellent resistance to scuffing although oil consumption is high. This feature comes from the fact that the plateau shape can maintain
    more lubricating oil without disrupting the oil film.


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  • The science and technology of materials in automotive engines
    Hiroshi Yamagata
    Woodhead Publishing and Maney Publishing
    on behalf of
    The Institute of Materials, Minerals & Mining
    CRC Press
    Boca Raton Boston New York Washington, DC
    WOODHEAD PUBLISHING LIMITED
    Cambridge England



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  • Valve Failure

    Three types of valve failure have been observed:
    -valve recession;
    -guttering;
    -torching.
    Valve recession, the most common form of wear in diesel engine inlet valves, is caused by loss of material from the seat insert and/or the valve. Guttering is a hightemperature, corrosive process usually caused by deposit flaking. Torching or melting of a valve is triggered by a rapid rise in the temperature of the valve head, which may be caused by preignition or abnormal combustion.
    Inlet valve wear is a particular problem in diesel engines because the fuel is introduced directly into the cylinder. The inlet valve, therefore, receives no liquid on its seating face and seats under rather dry conditions.
    Exhaust valve wear is less prominent than inlet valve wear as combustion products deposited on the seating faces provide lubrication. Exhaust valves are more likely to fail due to guttering or torching. Such failures are rarely seen in inlet valves.


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  • E N G I N E E R I N G R E S E A R C H S E R I E S
    Automotive Engine Valve Recession
    R Lewis and R S Dwyer-Joyce
    Series Editor
    Duncan Dowson
    Professional Engineering Publishing Limited,
    London and Bury St Edmunds, UK



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  • The cast iron monolithic block

    The use of cast iron blocks in Table 2.1 has been widespread due to low cost as well as formability. Figure 2.2 shows a V6 block used for a car engine.
    The block is normally the integral type where the cylinders and upper crankcase are all one part. The cylinders are large holes that are machined into the
    block. The iron for the block is usually gray cast iron having a pearlitemicrostructure, typically being JIS-FC200 (Table 2.2). The microstructure is shown in Fig. 2.7. Gray cast iron is so called because its fracture has a gray appearance. Ferrite in the  microstructure of the bore wall should be avoided because too much soft ferrite tends to cause scratching, thus increasing blow-by.

    Cast iron blocks are produced by sand casting. For cast iron, the die casting process using a steel die is fairly rare. The lifetime of the steel die is not adequate for repeated heat cycles caused by melting iron. As its name
    suggests, sand casting uses a mold that consists of sand. The preparation of sand and the bonding are a critical and very often rate-controlling step.
    Permanent patterns are used to make sand molds. Generally, an automated molding machine installs the patterns and prepares many molds in the same shape. Molten metal is poured immediately into the mold, giving this process very high productivity. After solidification, the mold is destroyed and the inner sand is shaken out of the block. The sand is then reusable. Two main methods are used for bonding sand. A green sand mold consists of mixtures of sand, clay and moisture. A dry sand mold consists of sand and synthetic
    binders cured thermally or chemically.
    Figure 2.8 shows a schematic view of a sand mold used to shape a tube. This mold includes a sand core to make the tube hollow. The casting obtained from using this mold is shown in Fig. 2.9. Normally, molten iron in a ladle is gently poured into the cavity under the force of gravity using a filling system. The sand core forming an inside hollow shape is made from a dry sand component. The bore as well as the coolant passages in the cylinder block are shaped as cored holes.













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  • The science and technology of materials in automotive engines
    Hiroshi Yamagata
    Woodhead Publishing and Maney Publishing
    on behalf of
    The Institute of Materials, Minerals & Mining
    CRC Press
    Boca Raton Boston New York Washington, DC
    WOODHEAD PUBLISHING LIMITED
    Cambridge England


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  • The cylinder

    The cylinder must maintain an accurate roundness and straightness of the
    order of μm during operation. The cylinder bore wall typically  experiences local wear at the top-dead-center point, where the oil film is most likely to fail, and scratching along the direction of travel of the piston. Figure 2.5 shows vertical scratching caused by scuffing. The grooves caused by scratching increase oil consumption and blow-by. In extreme cases, the piston seizes to the bore wall. The demand for higher output with improved exhaust gas emission has recently increased heat load to the cylinder even more. A much lighter weight design is also required.An engine generating high power output requires more cooling, since it generates more heat. Automotive engines have two types of cooling systems, air-cooled and water-cooled. Figure 2.1 shows the air-cooled type and Fig.2.2 the water-cooled type. Whilst an air-cooled engine may use a much simpler structure because it does not use the water-cooled system, the heat management of the cylinder block is not as easy. As a result, most automotive engines nowadays use water-cooled systems. It would be no exaggeration to say that the required cooling level for an individual engine determines its cylinder structure.
    Figure 2.6 shows cutaway views of four different types of cylinder block structure. The monolithic or quasi-monolithic block (on the right) is made of
    only one material. It is also called a linerless block because it does not contain liners (described later). The bore wall consists of either the same material as the block or a modified surface such as plating to improve wear resistance. It is normally difficult for one material to fulfill the various needs listed in Fig. 2.4. However a liner-less design in multi-bore engines can make the engine more compact by decreasing inter-bore spacing.
    The other designs in Fig. 2.6 (on the left) incorporate separate liners. A liner is also called a sleeve. A wet liner is directly exposed to coolant at the outer surface so that heat directly dissipates into the coolant. To withstand combustion pressure and heat without the added support of the cylinder block, it must be made thicker than a dry liner. A wet liner normally has a flange at the top. When the cylinder head is installed, the clamping action pushes the liner into position. The cylinder head gasket keeps the top of the liner from leaking. A rubber or copper O-ring is used at the bottom, and sometimes at the top, of a wet liner to prevent coolant from leaking into the crankcase. A dry liner presses or shrinks into a cylinder that has already been bored. Compared to the wet liner, this liner is relatively thin and is not exposed to the coolant. The cast-in liner design encloses the liner during the casting process of an entire cylinder block.
    Table 2.1 lists various types of cylinder structures, their processing and characteristics. Cylinder blocks are normally made of cast iron or aluminum alloy. The aluminum block is much lighter. Various types of materials are combined to increase strength. In the following sections, we will look at the blocks of four-stroke engines. Those for two-stroke engines are discussed in the final section.



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  • The science and technology of materials in automotive engines
    Hiroshi Yamagata
    Woodhead Publishing and Maney Publishing
    on behalf of
    The Institute of Materials, Minerals & Mining
    CRC Press
    Boca Raton Boston New York Washington, DC
    WOODHEAD PUBLISHING LIMITED
    Cambridge England



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  • Nonbattery Energy Storage: Ultracapacitors and Flywheels

    Ultracapacitors
    Ultracapacitors are devices that can directly store electrical charges—unlike batteries, which store electricity as chemical energy. A variety of ultracapacitor materials and designs are being investigated, but all share some basic characteristics-very high specific power, greater than 1 kW/kg, coupled with low specific energy. The U.S.
    Department of Energy mid-term goal is only 10 Wh/kg (compared to the U.S. Advanced Battery Consortium midterm battery goal of 100 Wh/kg). Other likely ultracapacitor characteristics are high storage efficiency and long life. Ultracapacitors’ energy and power characteristics define their role. In electric vehicles, their high specific power can be used to absorb the strong power surges of regenerative braking, to provide high power for brief spurts of acceleration, and to smooth out any rapid changes in power demand from the battery in order to prolong its life. In hybrids, they theoretically could be used as the energy storage mechanism; however, their low specific energy limits their ability to provide a prolonged or repeatable power boost. Increasing ultracapacitors’ specific energy is a critical research goal.

    Flywheels
    A flywheel stores energy as the mechanical energy of a rapidly spinning mass, which rotates on virtually
    frictionless bearings in a near-vacuum environment to minimize losses. The flywheel itself can serve as the rotor of an electrical motor/generator, so it can turn its mechanical energy into electricity or vice versa, as needed. Like ultracapacitors, flywheels have very high specific power ratings and relatively low specific energy, though their energy storage capacity is likely to be higher than ultracapacitors. Consequently, they may be more practical than ultracapacitors for service as the energy storage mechanism in a hybrid. In fact, the manufacturer of the flywheel designed for Chrysler’s Patriot race car, admittedly a very expensive design, claims a specific energy of 73 Wh/kg, which would make the flywheel a very attractive hybrid storage device. Mass-market applications for flywheels depend on solving critical rotor manufacturing issues, and, even if these issues were successfully addressed, it is unclear whether mass-produced flywheels could approach the Patriot flywheel’s specific energy level.


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  • Advanced Automotive Technology: Visions
    of a Super-Efficient Family Car
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