The engine block is the continer in which all engine components are held whitin. The engine bluock contines the engine cylinders and the engine crankcase. Majariti of diesel engines use an inline 6-cylinder configureition (figure.1) others may use V-confgerition (figure.2), but usselly both systems will only use one cranck shell. Nierliy all Engine bloucks are cast as a single unit.
As time goes buy engine cylinder blocks have to provide a greater strength and also reduse in wight. Due to this cast irons used in the manufacturing of engine blocks are alloyed whit toughanig materials. over the resent years Use of aliminum in engine blucks has rizen dermatickliy this is due to the low weight strenthg ratitio of aliminume which result in ligher enigin blucko, the reduction in weight has resulted to unwanted flexibility. To combat the unwanted flexibility bracing
can be used in order to reduce flexibility and achiving a more rigid material.
Forces:
Torque twist:
This is the result of twisting force from the crankshaft fixed points through the engine cylinder block. A cylinder block can be subjected to torque twist from either crank shell input or output. The condition can occur at high cylinder pressure, or oppositely, can be generated through the drive train.
Cylinder pressures:
Extremity High cylinder pressure, particularly in smaller engings can result in failuers. These days combustion tends to be appromixattly twices as much as generation ago.
Quick variation in temperature:
This results when a hot engine block is cooled fast either when the engine is terned off imiditltly after a hard run or cold water in a car wash.
2.3. Property/material requirements and Material selection (CES) for cylinder.
The high demand for greiter specific power and the need for weight reduction and lowering emissions requires the use of stronger materials for cylinder blocks, aloweing compacted graphite iron (CGI) to shaine wehen comperd to gray iron and aliminum as shown in (figer.3). The main desierbal properties of CGI are for engine cylinder blocks are its fatigue strength and elastic Modulus.
As showen in (figer 4) the graphite phase in CGI appears as singiler worm-shaped or vermicular particals. The particles are starched out elongated, and randomly sctterd just like grey iron, whit a difference of being shorter in lenth and thicker acrosees, and have rounded edges. Even tho CGI particles appear to be wormed-shaped when scaned in two dimensions, deep-etched scanning electron micrographs (figer.5) show that the individual snakes are connected to their closest neighbours whitin the eutectic cell.
the combonition of rounded edges and irregular bumpy surfaces of the compacted graphite particles, produses a stronger conection between the graphite and the iron mix, redusing crack initiation and providing far better mechanical properties. CGI includes some nodular (spheroidal) graphite particles. As the nodularity increases, the strength and stiffness also increase, however thie will make castability a lot harder, it will also effect machinability and thermal conductivity.The microstructure specification must therefore be chosen depending on both the production requirements and the performance conditions of the product. In the case of cylinder blocks and heads, where castability, machinability and heat transfer are all of paramount importance, it is necessary to impose a more narrow specification. A typical specification for a CGI cylinder block or head can be summarised as follows:
? 0-20% nodularity, for optimal castability, machinability
and heat transfer;
? No free flake graphite, flake type graphite (as in grey iron)
causes local weakness;
? > 90% pearlite, to provide high strength and consistent
properties;
? < 0.02% titanium, for optimal machinability.
This general specification will result in a minimummeasured tensile strength of 450 MPa in a 25 mm diameter test bar, and will satisfy the ISO 16112 standard for CGI.
The normal mechanical aterbuteds for this CGI grade. Comparestnet of this CGI to
grey cast iron andAluminium are in Table 1.
Relative to conventional grey cast iron, CGI provides
opportunities for:
? smaller wall thicknesses at current working loads;
? graiter operating loads (increased Pmax) at current design;
? smaller safety factors due to less variation in as-cast
properties;
? reduced cylinder bore distortion;
? better NVH;
? Shorter thread engagement depth and therefore smaller bolts.
Since common rail fuel injection has been interdused, the emphasis in CGI engine development has shifted from weight reduction toward downsizing and increased power density. In this regard, the doubling of fatigue strength relative to grey iron and aluminium allow for signifi cant increases in engine loading. One specific OEM study has shown that a 1.3 litre CGI engine package can provide the same performance as a current 1.8 litre grey iron engine. To achieve this increase, the Pmax was increased by 30% while the cylinder block weight was decreased by 22%. Despite the increase in Pmax, test rig fatigue analyses showed that the weight-reduced CGI cylinder block provided a larger safety margin than theoriginal grey iron block, thus indicating that further increases in performance were possible. In comparison to the original engine, the fully assembled CGI engine was 13% shorter, 5% lower, 5% narrower, and 9.4% lighter. This example demonstrates the contribution of CGI to achieve combined downsizing and power-up objectives. Another consideration of CGI engine design is the ability to withstand cylinder bore distortion. In the combined presence of elevated temperatures and increased combustion pressures, cylinder bores tend to expand elastically. However,
As the increases in engine loading began to exceed the strength capabilities of conventional grey iron (GJL 25), foundries and OEMs responded by adding alloying elements and hardening agents such as chromium, nickel, copper, tin and molybdenum to increase the tensile strength. In order to further increase the strength to fully satisfy the 300 MPa minimum tensile strength objective (GJL 30), some specifi cations also reduced the carbon content from approximately 3.2% to 3.0% to make the graphite flakes smaller, thus reducing the risk for crack initiation and propagation. While the alloying and reduced carbon content provide a 10% 20% increase in mechanical properties, these actions simultaneously consume many of the core advantages of conventional grey cast iron: castability, heat transfer, machinability and signifi cantly, cost. Castability: During solidifi cation, the formation of graphite fl akes in conventional grey iron provides an expansion effect that counteracts the natural shrinkage tendency of the iron. However, the lower carbon content of alloyed grey iron reduces the extent of this benefi cial effect. Additionally, many of the alloying elements (Cr, Cu, Sn, Mo) segregate to the last areas of the casting to solidify increasing the sensitivity for shrinkage porosity and carbide formation. The net effect is that the castability of alloyed grey iron, including feeding requirements, is effectively the same as that of CGI. This is particularly true for complex castings such as 4-valve cylinder heads. Heat transfer: The addition of alloying elements to grey iron reduces thermal conductivity. Typical alloying levels for GJL 30 (0.3% Cr and 0.3% Mo) reduce the thermal conductivity of grey iron by 10% 15%. Further, since grey iron relies on the elongated graphite fl akes to provide natural conduct for heat transfer, the lower carbon content of alloyed grey iron also detracts from the heat transfer capability. The net effect is that the thermal conductivity of alloyed grey iron is only about 5% higher than that of a standard pearlitic CGI. machinability: The alloying elements added to increase the strength of grey iron also increase the hardness and wear resistance. While the strength of alloyed grey iron is only 10% - 20% higher than that of conventional grey iron, the hardness can be 30% higher. Depending on the alloy content, the hardness of alloyed grey iron can frequently be higher than that of CGI (Table 1). While there is indeed a signifi cant difference in machinability between conventional grey iron and CGI, the tool life for alloyed grey iron and CGI are effectively the same for many machining operations. Cost: The shrinkage sensitivity (feeding requirements) and machinability (tool life) of alloyed grey iron both impact the total on-cost of alloyed grey iron compared to normal grey iron (GJL 25). Beyond these operational concerns, consideration must also be given to the cost of the alloying elements. For example, the market price of molybdenum has increased from approximately EUR 5,000 per tonne to EUR 50,000 per tonne since 2004. For a 100 kg casting with a 70% mould yield and a 0.3% Mo content, the molybdenum cost alone is approximately EUR 20 per casting. NVH: The primary property for the determination of NVH performance is stiffness. While the increase from GJL 25 to GJL 30 provides a 20% increase in tensile strength, the increase in elastic modulus is only about 10%. In comparison, CGI provides a 40% increase in modulus compared to GJL 25. Despite that the specifi c damping capacity of CGI is lower than that of either of the two grey iron grades, the increased stiffness of CGI typically results in a reduced noise level of approximately 1.0 dB.
5 CGI vs. aluminium
In comparison to aluminium, the mechanical properties of CGI
provide opportunities for:
? Smaller package size;
? Higher specifi c performance;
? Reduced cylinder bore distortion and improved oil
consumption;
? No cylinder liners or surface etchant/coating;
? Improved NVH;
? Lower production cost;
? Improved recyclability.
6 Energy and environment
Even within the in-line engine sector, it can be shown that the energy intensity of iron vs. aluminium production results in a signifi cant energy penalty against aluminium. With current recycling rates, each tonne of cast iron (grey, CGI or ductile) accounts for an equivalent energy content of approximately 10,500 MJ. The corresponding value for aluminium is approximately 90,000 MJ. Assuming that a CGI cylinder block weighs 35 kg and the corresponding aluminium cylinder block weighs 28 kg, the net energy penalty to society for the aluminium block is approximately 2,150 MJ/block. Given an energy content of 34 MJ/litre for gasoline, the ascast energy penalty of 2,150 MJ corresponds to approximately 63 litres of gasoline. Further, assuming standard estimates of 0.5 litres of petrol saved for each 100 km and each 100 kg of weight saving, the 7 kg weight reduction provided by the aluminium block over the CGI block would require a driving distance of approximately 180,000 km to payback the energy differential. It is thus evident that government policy makers and OEMs must consider the cradle-to-grave energy balance for society. This is particularly true for countries like India and China which have centralised government planning and which rely heavily on imported oil.
8 Standards and terminology
Several national and international organisations have
developed and published standards for CGI. These standards
specify the CGI Grades in terms of the tensile strength and the
microstructure, expressed as percent nodularity. The currently
available standards are summarised in Table 7.
Historically, CGI has been known by the names Compacted
Graphite Iron and Vermicular Graphite Cast Iron, with
the compacted terminology primarily being used in
English speaking countries and the vermicular terminology
predominating in most other languages. Most recently, during
2006, the new ISO standard for CGI was published using the
combined name: Compacted (Vermicular) Graphite Cast
Iron. The ISO designation for CGI has been abbreviated
as GJV and five Grades have been specified based on the
minimum ultimate tensile strength obtained in separately cast
test pieces, including: GJV 300 (ferritic), GJV 350, GJV 400,
GJV 450 (pearlitic) and GJV 500 (alloyed).
Beyond the standards issued by the national and international
organisations, several OEMs have also established their
own internal CGI Specifications, including Audi, BMW,
Caterpillar, Cummins, DAF Trucks, DaimlerChrysler, Ford,
General Electric, General Motors, Hyundai, John Deere, Opel,
Rolls Royce Power Engineering and Volkswagen, among
others, all OEM specifi cations for CGI cylinder block and head
applications requires nodularity control within the 0-20%
range.
9 Summary
The improved mechanical properties of compacted graphite iron relative to grey iron and aluminium provide many contributions to the design and performance of internal combustion engines for passenger and commercial vehicles. Since 1999, series production experience has established CGI as a viable high volume engine material. Production volume will increase effectively from zero units in 1999 to 2 million units in 2010. Perhaps the most compelling statistic regarding CGI cylinder blocks is that no OEM has only one CGI cylinder block in its line-up. Without exception, every OEM that has launched the production of a CGI engine has also proceeded to develop, approve or launch additional CGI engines.
2.5. Manufacturing route selection.
A Basic Overview
Metal casting is the process in which molten metal is poured into a mold and allowed to solidify into an object. The object that results from this process is also called a casting. In sand casting, sand is used to define the cavity inside a mold. In addition, sand is used to make any cores that are contained in the mold. The molten metal solidifies in the cavity between the interior of the mold and the exterior of the core. There are the five basic steps to creating a sand casting.
Patternmaking
The first step in sand casting is patternmaking. The pattern is a replica of the exterior of the casting with dimensional allocation for shrinkage and finishing. If the casting is to be hollow, additional patterns called cores are used to create these cavities in the finished product. Patterns are usually made of wood, plastic, metal, or plaster; however, other materials or combinations of materials are used if there are additional specific properties required of the pattern. The number of castings to be made from the mold and the specifications required of the finished casting are two of the criteria that determine which material is selected for the creation of the pattern.
Coremaking
The next step in the process is coremaking. Cores are forms which are placed into the mold to create the interior contours of the casting. They are typically made of a sand mixture- sand combined with water and organic adhesives called binders- which is baked to form the core. This allows the cores to be strong yet collapsible, so they can be easily removed from the finished casting. Since cores are made in molds, they require a pattern and mold, called a core box. The core pattern is made in the same fashion as the casting pattern, but the core box is created from a durable material like metal or wood. Since the cores are made of sand, the mold cannot also be made of sand.
Molding
Molding is the multi-step process in which molds are created. In horizontal casting, the mold is contained in a two piece frame, called a flask. The upper portion of the flask is called a cope and the lower portion is a drag. First, molding sand is packed into a flask around the pattern. After the pattern is removed, gating and runner arrangements are positioned in the drag half of the mold cavity and the sprue is placed the cope portion. Gating systems are necessary for the molten metal to flow into the mold cavity. Cores are also placed in the drag portion of the mold if they are needed. To finish the mold, the cope (top) section is placed on the drag (bottom) section, and the mold is closed and clamped together.
In Metal Technologies' foundries, molds are created in large automated molding machines (Disamatics), a process which warrants its own detailed explanation.
Melting & Pouring
Melting is the preparation of the metal for casting, and its conversion from a solid to a liquid state in a furnace. It is then transferred in a ladle to the molding area of the foundry where it is poured into the molds.After the metal has solidified, the molds are vibrated to remove the sand from the casting, a process called shakeout.
Cleaning
Cleaning generally refers to the removal of all materials that are not part of the finished casting. Rough cleaning is the removal of the gating systems from the casting. Initial finishing removes any residual mold or core sand that remains on the piece after it is free of the mold. Trimming removes any superfluous metal. In the last stages of finishing, the surface of the casting is cleaned for improved appearance. In addition, at this point, the casting is inspected for defects and adherence to quality standards. This inspection may include nondestructive testing to determine whether the part will adequately perform for its intended use.
2.6. Final manufacturing process.
3. Conclusion
4. Recommendations
5. References
