DESC:Field of the invention:

The present invention relates generally to engine cylinder liners and more particularly, to an engine cylinder liner composition.

Background of the invention:

A cylinder liner is a cylindrical component that is placed in an engine block. The cylinder liners in internal combustion engines are made up of gray cast iron due to their excellent castability, high damping capacity, high thermal conductivity, good wear resistance and good machinability.

The flake graphite microstructure in gray cast irons is preferred as a solid lubricant to offer low friction and oil consumption characteristics. The general composition for such cylinder liners includes carbon: 3.00 to 3.80, silicon: 2.00 to 3.00, manganese: 0.50 to 1.00, chromium: 0.40 to 0.60, phosphorus: 0.40 to 0.80 and sulphur: 0.20 max.

However, the gray iron cylinder liner lacks tensile strength that makes it to be re-considered while designing high durability cylinder liners. Further, high strength cylinder liners generally prefer ductile iron (DI) or compacted graphite iron (CGI). However, DI and CGI fail to offer all the advantages offered by gray iron grades. Hence, the best way is to retain all the benefits of gray cast iron and still improve its strength which can be achieved by careful addition of alloying elements.

Generally, high strength gray iron cylinder liners are alloyed with nickel, chromium, molybdenum, copper and tin. However, addition of these elements considerably increases the cost of the cylinder liner, especially addition of nickel. Further, use of these elements fails to provide required honing surface. Though addition of only chromium and molybdenum increases strength levels up to the range of 275 MPa, high additions result in formation of excessive carbides which is harmful to the part function and machinability.
Accordingly, there exists is a need of an engine cylinder liner composition that overcomes the above mentioned drawbacks of the prior art.

Summary of the Invention

In one embodiment, the present invention discloses an engine cylinder liner composition and process of preparation thereof. The engine cylinder liner composition comprises a predefined amount of carbon, silicon, manganese, chromium, phosphorus, sulphur, molybdenum and copper that is added in a predefined proportion to form a resultant alloy that has a tensile strength in the range of 300 to 350 MPa. In one preferred embodiment, the engine cylinder liner composition is in a range from about 3.2% to about 3.5%, silicon in a range from about 1.7% to about 2.2%, manganese in a range from about 0.6% to about 1.0%, chromium in a range from about 0.25% to about 0.40%, phosphorus of about 0.2% maximum and sulphur of about 0.10% maximum, molybdenum in a range from about 0.30% to about 0.40% and copper in a range from about 0.85% to about 1.05%.
In another embodiment, the present invention discloses a process for preparation of engine cylinder liner composition that includes an initial step of inspection of a raw material that is followed by charging of the raw material. In next step, the raw material is weighed based on purity thereof and subsequently added to a furnace in a predefined sequence and melted at various temperature conditions. In further step, the molten material is transferred to a tapping ladle and subjected to inoculation. In next step, the inoculated molten material is transferred to a pouring ladle wherein the inoculated ladle is poured in a plurality of centrifugal dies by a spout inoculation method in order to form a plurality of casting. In final step, the plurality of castings is removed after a predefined time and subjected to shot blasting followed by a final inspection thereof.
Brief description of the drawings:
FIG. 1 shows a graphical presentation of % copper Vs tensile strength;
FIG. 2 shows a microstructure of a resultant grey cast iron; and
FIG. 3 shows a graphical presentation of compositions prepared in accordance with the present invention Vs tensile strength.
Detailed description of the invention:
The invention described herein is explained using specific exemplary details for better understanding. However, the invention disclosed can be worked on by a person skilled in the art without the use of these specific details.
References in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
References in the specification to “preferred embodiment” means that a particular feature, structure, characteristic, or function described in detail thereby omitting known constructions and functions for clear description of the present invention.
In general aspect, the present invention describes a new gray cast iron alloy with a specific chemical composition and an inoculation method adapted to be used in centrifugally cast cylinder liners of internal combustion engines.
In one aspect, the present invention provides an engine cylinder liner composition (hereinafter, "the composition"). The composition includes a predefined amount of carbon, silicon, manganese, chromium, phosphorus, sulphur and molybdenum added in a predefined proportion with respect to weight of gray cast iron. In the context of the present invention, the engine cylinder liner composition comprises carbon in a range from about 3.2 % to about 3.5 % based on the total weight of gray cast iron. Further, the composition comprises silicon in a range of from about 1.7 % to about 2.2 % based on the total weight of gray cast iron. Furthermore, the composition comprises manganese in a range of from about 0.6 % to about 1.0 % based on the total weight of gray cast iron. Moreover, the composition comprises chromium in a range of from about 0.25 % to about 0.40 % based on the total weight of gray cast iron. Further, the composition comprises phosphorus of about 0.2 % maximum based on the total weight of gray cast iron and sulphur of about 0.10 % maximum based on the total weight of gray cast iron. Furthermore, the composition comprises molybdenum in a range of from about 0.30 % to about 0.40 % based on the total weight of gray cast iron. Moreover, the composition comprises copper in a range of from about 0.85 % to about 1.05 % based on the total weight of gray cast iron.
In the context of the present invention, the copper element increases ductility by way of increasing the pearlite phase percentage. The pearlite percentage is directly proportional to strength. Accordingly, the copper element increases strength. Further, the copper element decreases wear resistance properties of the material due to natural ductility thereof. In the context of the present invention, the molybdenum retains wear resistance. It is understood here that the molybdenum is air hardenable element that helps in increasing the wear resistance by way of increasing hardness.
Hence, in preferred composition of the present invention, copper and molybdenum are added to grey cast iron grade with various ranges. The composition of the present invention does not include nickel thereby providing cost effective solution to the present costlier alloyed grades used for the cylinder liners. The composition and the process of the present invention are useful in preparing durable and wear resistant liners.
In another aspect, the present invention provides a process of preparation of the engine cylinder liner from the disclosed composition as described hereinafter-
The process of the present invention includes an initial step of raw material inspection. Specifically, all the raw materials required for cast iron manufacturing such as pig iron, pure copper, steel scraps, silicon and molybdenum are examined to check properties such as purity, dimension and the like.
In next step, a predefined amount of each raw material is calculated and weighed based on purity. All the weighed raw materials are added in an induction melting furnace in a predefined proportion with respect to gray cast iron. The raw materials are added in the furnace in a predefined sequence. Preferably, Pig Iron ingots are added in the induction melting furnace followed by heating. Subsequently, Steel and Cast Iron scrap parts are added to the furnace when the temperature of the furnace reaches to 800 0C. Further, boring wastages are added for being melted in the furnace. Subsequently, the molten metal is allowed to heat at a temperature of 1400 0C followed by chilling in a coin die and tested for chemical composition thereof. If any of the elements in defined chemical composition are not falling in the range then accordingly Ferro silicon, Molybdenum, Copper and Chromium are added to enhance the chemistry to a specific range. Every major elements addition or change chemistry will be checked by spectrometer and recorded.
In this one embodiment, the predefined temperature of the furnace is in range from about 14000 C to about 14500 C. However, it is understood here that the predefined temperature may vary in other alternative embodiments of the present invention. In further step, molten composition is transferred to a tapping ladle. In the next step, tapping ladle is inoculated and molten metal is transferred to a pouring ladle.
In the next step, the pouring ladle is inoculated. In a further step, the spout inoculation is achieved by adding inoculants in dies wherein Graphite is nucleated to a specific form by adding Barium or predetermined other mixtures therein. In this one embodiment, inoculation is carried out in three different points namely at the tapping ladle, at the pouring ladle and at the spout. The spout inoculation involves the inoculation carried out at the time of pouring the molten metal in the centrifugal dies. However, it is understood here that the inoculation may be carried out at any or all the three points in an alternative embodiments of the present invention. In this one embodiment, barium based inoculants having a predefined size, preferably from about 0.2 to about 0.6 mm, are added in the centrifugal dies in a predefined proportion of about 0.1% of the total molten metal weight in order to achieve better graphite nucleation and predominate Type-A structure in the cylinder liner castings (As shown in Fig. 2). It is understood here that Type-A structure is a type of graphite form having random flake graphite in a uniform distribution.
In the context of the present invention, the inoculants preferably have a size in a range of 0.2 to 0.6 mm in order to be completely dissolved in a short amount of time. It is understood here that inoculation is advantageous in a way of the late addition time thereby avoiding fading of the inoculation effect. Further it is understood here that such type of inoculation may be used in automatic moulding systems. It is further understood here that the inoculants are not placed on the bottom of the ladle but added as steadily as possible to the molten metal stream.
In the next step, the inoculated molten composition is poured to a plurality of centrifugal dies. The castings are removed after a predefined time. In the next step, a shot blasting is performed for cleaning, stripping, strengthening and polishing the grey cast iron. In the last step, final inspection is carried out.
The cast iron produced by this process achieves good castability, machinability, durability, noise damping capacity and wear resistance. The process includes a spout inoculation that provides better honed surface for low co-efficient of friction and excellent lubrication effect during functioning.
Examples:
Hereinafter, the present invention will be described in more detail based on examples. The examples are not intended to limit the scope of the present invention. It is believed the invention will be better understood from the following detailed examples:
Example 1: Tensile strength study for engine cylinder liner composition
With reference to the process for preparation of an engine cylinder liner composition. Initially the raw materials were added to a furnace in a predefined amount and in a predefined sequence. Initially, Pig Iron ingots were added in the induction melting furnace thereby initiating heating thereof. As the temperature reaches at 8000 C, Steel and Cast Iron scrap were added. In next step, boring wastages were added so as to initiate melting of the previously added raw materials. As the temperature reached 14000 C, the molten metal was allowed to cool in a coin die and tested for chemical composition. If any of the raw materials in defined chemical composition were not falling within the range, then Ferro silicon, Molybdenum, Copper and Chromium were added accordingly to enhance the chemistry to a predefined range. The observations of changing material properties were taken on addition of each raw material by spectrometer. The observations recorded during the process are stated in Table 1.
A comparative study for various proportions of the engine cylinder liner compositions was performed in order to study tensile strength of the engine liner composition prepared using aforementioned process for preparation. The results obtained during said study were tabulated as below-
Table 1: Comparison of existing alloy materials Vs engine cylinder liner composition of the present inventions
Elements Existing
Material Trial 1 Trial 2 Trial 3 Trial 4

Carbon % 3.2 - 3.5 3.2 - 3.5 3.2 - 3.5 3.2 - 3.5 3.2 - 3.5
Silicon % 1.7 - 2.0 1.7 - 2.2 1.7 - 2.2 1.7 - 2.2 1.7 - 2.2
Manganese % 0.6 - 0.8 0.6 - 0.8 0.6 - 0.8 0.8 - 1.0 0.6 – 1.0
Chromium % 0.25 - 0.40 0.25 - 0.40 0.25 - 0.40 0.25 - 0.40 0.25 - 0.40
Phosphorus % 0.6 - 0.8 0.4 - 0.6 0.2 - 0.4 0.2 max 0.2 max
Sulfur % 0.1 max 0.1 max 0.08 max 0.1 max 0.1 max
Molybdenum % 0.30 - 0.40 0.30 - 0.40 0.30 - 0.40 0.30 - 0.40 0.30 - 0.40
Copper % 0 0.2 - 0.4 0.4 - 0.6 0.6 - 0.8 0.9 – 1.0
Tensile Strength
(MPa) 260 262 262 275 310

As evident from FIG. 2, FIG. 3 and Table 1, the engine cylinder liner composition of the present invention was observed to include alloying elements like copper, chromium and molybdenum. The engine cylinder liner composition was observed to have minimum 30% superior tensile strength compared to regular grades and wear resistance thereof. It was observed that tensile strength of the grey cast iron increases with increase in amount of copper. However, it was also observed that the amount of phosphorus should not exceed above 0.2%. High tensile strength of about 300-350 MPa was achieved by increasing the amount of copper and maintaining amounts of other raw materials in predefined ranges.
The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.
It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present invention.

,CLAIMS:
1. An engine cylinder liner composition comprising:
a gray cast iron substrate alloyed with a plurality of alloying elements, the plurality of alloying elements having percentage content essentially by weight of carbon in a range from about 3.2% to about 3.5%, silicon in a range from about 1.7% to about 2.2%, manganese in a range from about 0.6% to about 1.0%, chromium in a range from about 0.25% to about 0.40%, phosphorus of about 0.2%, sulphur of about 0.10%, molybdenum in a range from about 0.30% to about 0.40%, and copper in a range from about 0.85% to about 1.05%, based on the total weight of the gray cast iron.
2. The engine cylinder liner composition as claimed in claim 1, wherein the gray cast iron substrate alloyed with a plurality of alloying elements has a tensile strength in a range from about 300 MPa to about 350 MPa.
3. A process for preparation of an engine cylinder liner composition comprising the steps of:
inspecting a predefined amount raw material followed by charging and weighing based on purity,
adding the raw material in a predefined sequence based on total weight of gray cast iron substrate to a furnace,
melting the raw material in the induction melting furnace at a predefined temperature conditions between the range of about 800 0C to about 1450 0C,
transferring a molten material to a tapping ladle,
inoculating the molten material in the tapping ladle followed by transferring the molten material to a pouring ladle,
inoculating the pouring ladle by way of a spout inoculation by adding a plurality of inoculants in dies,
pouring the inoculated molten material to a plurality of centrifugal dies to form castings followed by removal thereof after a predefined time, and
performing a shot blasting of the castings to form the engine cylinder liner composition.
4. The process of preparation of the engine cylinder liner as claimed in claim 3, wherein the raw material includes percentage content essentially by weight of carbon, silicon, manganese, chromium, phosphorus, molybdenum and copper based on the total weight of the gray cast iron.

5. The process of preparation of the engine cylinder liner as claimed in claim 3, wherein the inoculants are barium based inoculants having size from about 0.2 mm to about 0.6 mm.

6. The process of preparation of the engine cylinder liner as claimed in claim 3, wherein the inoculants are added in a proportion of about 0.1% of the total molten metal weight.