GB2129342A - Method for making a reinforced cast article - Google Patents

Abstract

To produce a connecting rod (10), a bundle of undirectional inorganic reinforcing fibres (F) is shaped such that its second moment of area about the Y axis of the connecting rod is less than its second moment of area about the X axis of the connecting rod (for example an ellipse as shown in Fig. 4) and is positioned in a mould such that a fixed minimum gap surrounds it. A molten light metal alloy is squeeze cast into the mould forming a matrix of the alloy and the bundle. Also disclosed is a method of preparing a coherent bundle of uni-directional inorganic fibres, at least some of which are metallic or metal coated, wherein the bundle is placed into a shaping container and heated to partially fuse the metallic or metal coated fibres to each other. <IMAGE>

Description

SPECIFICATION Methods for making a reinforced cast article This invention relates to a method of making a reinforced cast article such as a connecting rod for an internal combustion engine.

Many component parts of internal combustion engines have heretofore been made of various types of steel. It has been a recent desire that these parts be replaced by ones of a light metal to reduce the overall weight of the engine. One example of such a replacement and the attendant problems encountered would be a piston connecting rod.

Connecting rods must have at least a certain compressive or buckling strength, particularly in the rod portion thereof, yet still fit within certain tightly restrained dimensions. Conventional steel alloy rods are relatively slim in the direction of rotation in order to rot come into contact with the piston skirt. In attempting to make a connecting rod out of an aluminium alloy, sufficient buckling strength must be retained and the rod must be able to fit within the necessary locus of space defined by the piston, the crankshaft, and the crankcase.

It has been discovered that the necessary buckling strength can be imparted to the connecting rod made of a light metal alloy by providing a reinforcing bundle of uni-directional fibres in the core of the rod portion. The light metal alloy fills in the interstices in the bundle to form a metal fibre matrix.

However, to stay within the necessary locus of space, it has been discovered that it is necessary to reorientate the position of the ribs of the rod portion of the connecting rod to a position at right angles to that of a conventional steel rod.

That is, the rod portion must be designed such that the second moment of area Ix about an axis X which is perpendicular to the longitudinal axis of the rod and parallel to the direction of its rotation is larger than the second moment of area ly about an axis Y which is perpendicular to the X-axis and the longitudinal axis of the rod.

Ix > ly The present applicants have proposed previously two different types of connecting rods which are made of a light alloy each having a rod portion reinforced by a bundle of uni-directional inorganic fibres.

The connecting rod includes a smaller annular shaped end portion and a semi-annular shaped larger end portion at the ends of the rod portion. The smaller annular portion can be considered to have a centre axis perpendicular to the direction of rotation of the rod. The rod portion can be considered to have a longitudinal axis. The Y-axis is defined as parallel to the central axis and perpendicular to the longitudinal axis. The X-axis is defined as perpendicular to both the centre axis and the longitudinal axis.

In these previous designs, the second moment of area of the core about the Y-axis (I(c) y) is generally equal to or greater than the second moment of the core of area about the X-axis (I(c) x). In the embodiment shown in Figure 5 (to be described later) (I(c) y) is larger then (I(c) x). As shown in Figure 6 (to be described later), the second moment of area of the core about the X-axis is equal to the second moment of area of the core about the Y-axis.

When the second moment of area of the core about the Y-axis is greater than the second moment of area of the core about the X-axis, sufficient buckling strength is given to the rod portion of the connecting rod. In this manner, a fibre bundle reinforced light alloy connecting rod gives a comparable performance equal to that of a connecting rod being made entirely of steel or the like.

However, certain difficulties are encountered in casting such a connecting rod. That is, when the second moment of area of the core about the Y-axis is larger than the second moment of area of the core about the X-axis (I(c) y > I(c) x), the fibre bundle is generally shaped as an ellipse having its major axis along the X-axis. As noted above, ly of the rod must be kept less than Ix of the rod. This requires that the bundle divide the rod-shaped portion into two sections forming the side ribs of the connecting rod. When a light molten metal alloy is cast into a mould to form the matrix with the fibre bundle, a chill surface is easily formed at the boundary between the uni-directional-bundle of inorganic fibres and the cavity of the mould. Often, the bundle actually contacts the side wall of the cavity.As a result, a cold shut is apt to occur at the chill surface when the connecting rod is being cast thereby creating a defect in the rod. This "cold shut" type of defect occurs when there is an insufficient gap between the bundle and the side wall of the mould cavity to permit the molten metal to flow and close around the outer surface of the bundle. A ridge or valley is created at the edge where the metal ceases to flow.

In the case of the uni-directional bundle of inorganic fibres having a circular shape as shown in Figure 6, wherein the second moment of area of the core about the Y-axis equals the second moment of area of the core about the X-axis, (I(c) y = (I(c) x), the gap formed between the uni-directional bundle of inorganic fibres F and the cavity within the mould is very small. Thus, the moltel metal may chill in this gap more easily which could cause a cold shut in filling the molten metal into the mould.

To form the uni-directional bundle of inorganic fibres, stainless steel fibres or other metallic fibres or non-metallic fibres such as silicon carbide, carbon, alumina, and the like could be used. It would be of great advantage to use non-metallic inorganic fibres having a lower specific gravity than metallic fibres in order to produce a composite connecting rod which is light in weight. However, certain problems occur in attempting to use solely non-metallic inorganic fibres in that it is difficult to keep the bundle tightly together in the casting process because it is difficult to have the fibres adhere to one another.

Further, in order to produce a reinforced article or connecting rod having a light metal alloy formed into a matrix with a bundle of uni-directional fibres, it would be desirable to pre-heat the bundle of fibres prior to the casting steps and to have the bundle of fibres retain a certain amount of the heat so that no chilling of the molten metals being cast would occur upon contact with the bundle. The usual nonmetallic inorganic fibres having a low thermal conductivity. Therefore, it takes a considerable length of time to heat the bundle properly so that it will retain sufficient heat to provide good filling performance by preventing chilling of the casting metal.Further, since most non-metallic inorganic fibres have very low co-efficients of thermal expansion compared with the metal to be formed into the matrix, a certain amount of residual stress in the matrix will be retained after the connecting rod has been produced because the fibre bundle does not contract as much or as fast as the surrounding metal.

According to one aspect of the present invention, there is provided a method of making a connecting rod for an internal combustion engine, said rod having first semi-annular end portion, a second annular end portion, and a rod portion therebetween, said second annular portion having a centre axis, said rod portion having a longitudinal axis, an X-axis perpendicular to said longitudinal axis and perpendicular to said centre axis, and a Y-axis perpendicular to said longitudinal axis and parallel to said centre axis; the method comprising the steps of shaping a bundle of inorganic reinforcing unidirectional fibres such that a second moment of area of the bundle about the Y-axis (I(c) y) taken across a cross-section perpendicular to the longitudinal axis is less than a second moment of area of the bundle about the X-axis (I(c) x), positioning said bundle in a mould, said mould having cavities to form said semi-annular portion, said annular portion and said rod portion, the cavity to form the rod portion being sized such that Ix of the finished rod is greater than ly of the finished rod, said bundle being positioned to bridge from said cavity for said semi-annular portion and to produce a fixed minimum gap between said bundle and the cavity for said rod portion; and squeeze casting a molten light metal alloy into said mould forming a matrix of said alloy and said bundle.

The step of forming the bundle can include forming a core bundle of a plurality of uni-directional inorganic non-metallic fibres, surrounding the core bundle with a plurality of uni-directional metallic fibres or non-metallic fibres having a metal coating, placing the surrounded core bundle in a heatresistant shaping container, and heating the contained surrounded cored bundle at least partially to fuse the uni-directionai metallic fibres to each other and to the core bundle or at least partially fuse the nonmetallic fibres having a metal coating to each other and to the core bundle.

The bundle can be shaped as an ellipse in cross-section having a major axis on the Y-axis and a minor axis on the X-axis.

According to a second aspect of the present invention, there is provided a method making a reinforced cast article. said article having end portions and a centre portion, comprising the steps of forming a bundle of inorganic reinforcing uni-directional fibres, said bundle including a proportion of metallic fibres, placing said bundle in heat-resistant shaping container heating said contained bundle at least partially to fuse said metallic fibres to each other, positioning said partially fused bundle into a mould having cavities for producing said article leaving a fixed minimum gap surrounding said bundle in a section of said cavities for producing said centre portion, and squeeze casting a molten light metal alloy into said mould forming a matrix of said alloy and said bundle.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a perspective illustration showing the inserting of a uni-directional bundle of fibres into a heat-resistant pipe for pre-heating and preparing the bundle of fibres in accordance with the present invention; Figure 2 is a plan view showing the relation between a metallic mould and a uni-directional bundle of inorganic fibres in accordance with the present invention; Figure 3 is a longitudinal front sectional view of a connecting rod made in accordance with the present invention; Figure 4 is a cross-sectional view taken along lines IV--IV of Figure 3;; Figure 5 is a cross-sectional view of comparative example I taken along lines IV--IV of Figure 3; and Figure 6 is a cross-sectional view of comparative example II also taken along line IV--IV of figure 3.

EXAMPLE I A bundle of 70,000 stainless steel fibres F (SUS 32 in accordance with Japanese Industrial Standards (JIS)) each having an outside diameter of 25 microns was prepared and inserted into a heat resistant tube P. The tube could be made, for example, of silica glass. The shape of the cross-section of the tube is an ellipse as shown in Figure 1. The bundle of stainless steel fibres is heated at 7000C for 10 minutes. In this manner, the stainless steel fibres are partially fused together. That is, at the points where the different fibres touch each other, they are fused or welded together. The temperature of about 7000C is critical because If heated at a higher temperature, the fibres lose strength. The major axis diameter of the ellipse is 12 mm and the minor axis diameter is 9.2 mm. The bundle is 136 mm long.The bulk density is 3.1 grams/cc and the theoretical ratio of cross-sectional area of the individual fibres making up the bundle to that of the actual bundle is 39.7%.

A mould is prepared having a ram-up core 5 for forming an annular shaped body 11 of a small diameter and a ram-up core 6 for forming a semi-annular shaped body 12 of larger diameter. The mould 2 includes cavities 3 and 4 together with a longitudinal cavity section 9 for forming the rod portion of a connecting rod. The cavity 3 forms the small end portion 11 and the cavity 4 forms the large end portion 12 of the connecting rod. The uni-directional bundle of inorganic fibres prepared above is laid within previously prepared concave portions 7, 8 of the ram-up cores 5, 6 as a bridge extending down the longitudinal cavities of section 9.The major axis of the elliptical cross-section of the bundle is placed parallel to the Y-axis thus making the second moment of area about the Y-axis (I(c) y) smaller than the second moment of area about the X-axis (I(c) x).

A fixed minimum gap is present between the unit directional bundle of fibres F and the wall of the longitudinal cavity section 9. The gap is from 1.5 to 2.0 mm. Using an aluminium alloy (AC 4 D in accordance with Japanese Industrial Standards) as the matrix metal M, the alloy is filled into the unidirectional bundle of inorganic fibres and squeeze cast to produce the connecting rods. The connecting rod is further machined. The end portions of the uni-directional fibre bundle extending into the finished annular shaped body of small diameter 11 and the semi-annular shaped body of large diameter 12 are appropriately trimmed. The resulting minimum cross-sectional area A of the rod shaped portion of the connecting rod is 209 mm2. The volume fraction Vf of this bundle in the cross-sectional area was 1 6.4 percent.The second moment of area about the Y-axis of the core of this connecting rod is 1 700 mm4 and the second moment of area about the X-axis of the core is 7630 mm4. Despite the reorientation of the core, the rod is found to have sufficient buckling strength for long, useful service in an engine.

COMPARATIVE EXAMPLE 1 The connecting rod of this Comparative Example 1 was prepared in an identical manner to that of Example 1 of the present invention except that the uni-directional bundle of inorganic fibres was formed having an elliptical cross-section with the major-axis oriented along the X-axis and the minor axis oriented along the Y-axis precisely as shown in Figure 5.

COMPARATIVE EXAMPLE II A connecting rod of this Comparative Example II was prepared identically to the connecting rod of the Example 1 of the present invention except that the uni-directional bundle of inorganic fibres had a circular cross-section precisely as shown in Figure 6. The circular cross-section had a diameter of 10.5 mm. The bulk density and cross-sectional area ratio are the same as Example 1; that is, 3.1 grams per cc and 39.7 percent. The gap between the bundle of fibres and the sidewalls of the cavity 9 of the mould was from 1.0 to 1.5 mm.

The following results were obtained after evaluating the tendency for cold shuts and the filling performance of the metal into the bundle to form the matrix after squeeze casting: TABLE 1

Shape of cross-section Filling of the unidirectional Tendency to performance bundle of form a of metal inorganic fibre cold shut into bundle Present Invention I(c) y < I(c)x none good Comparative Example I I(c) y > I(c)x very high good Comparative Example II I(c) y = I(c)x very high poor As can be readily understood from the comparison of the above Table and Figures 4, 5 and 6, when a sufficient gap g is formed between the uni-directional bundle of inorganic fibres and the sidewall of the cavity of the mould, the performance of casting is simplified.

Therefore, the tendency for cold shuts is reduced.

In Comparative Example II, the diameter of the uni-directional bundle of inorganic fibres would have to be reduced to less than 9.5 mm to form the same fixed minimum gap as is formed with the present invention between the uni-directional bundle of inorganic fibres and the sidewalls of the cavity for forming the rod portion. Additionally, in Comparative Example II, in order to maintain the same volume fraction percentage of fibre bundles to total rod cross-section, the bulk density of the fibre would have to be increased to 3.8 grams/cc. The cross-sectional area ratio would then become 48.5 percent which results in a 23 percent increase when compared with Example 1 of the present invention.

Thus, the filling performance of the matrix would decrease.

Consequently, the particular orientation and shaping of the bundle of the uni-directional fibres in accordance with the present invention permits a sufficient gap to be retained between the bundle and the wall of the mould which ensures that the molten metal flows smoothly, that the tendency for forming a cold shut is decreased, and that the filling performance of the matrix is good, while, in actual practice, retaining sufficient strength.

EXAMPLE II A bundle F 1 of uni-directional fibres made of 306,000 alumina fibres each having a diameter of 10 microns surrounded by 91,000 stainless steel fibres F 2 having a diameter of 12 microns (SUS 32 in accordance with Japanese Industrial Standards). The surrounded bundle F 1, F 2 was inserted into a heat-resistant tube P having an ellipse shape in cross-section. The heat-resistant tube was then heated at 7000C for 10 minutes whereby the stainless steel fibres F 2 were at least partially fused and combined with one another and the alumina fibres which they surrounded. The resulting bundle F of uni-directional fibres had an ellipse shape with a major axis diameter of 12 mm and minor axis diameter of 9.2 mm. The weight of the bundle was 19.1 grams and the bundle had an overall length of 136 mm.

The bundle was placed into a mould and cast in an identical manner to that of Example 1. The smallest minimum area A in cross-section of the rod portion of the connecting rod so formed was 209 mm2 and the volume fraction Vf in this smallest cross-section of the bundle of fibres F was 1 6.4 percent. The volume fraction of alumina fibres was 11.5 percent and the volume fraction of stainless steel fibres was 4.9 percent. The ratio of volume fraction of alumina fibres to volume fraction of stainless steel fibres was 7:3.

The second moment of area of the core with respect to the Y-axis (I(c) y) was 1 700 mm4 and the second moment of area of the core with respect to the X-axis (I(c) x) was 7,630 mm4. The rate of stress reduction at the smallest cross-sectional area portion of the rod portion of the connecting rod was 34.2 percent.

In Example 1, the bundle of unit directional fibres made only of stainless steel having an identical size, had a weight of 36.5 grams and a rate of stress reduction at the smallest sectional areaportion of the rod portion of the connecting rod was 20.7 percent.

Thus it can be readily seen that a two-component uni-directional fibre bundle is lighter in weight than a bundle made only of metallic fibre and permits a rate of stress reduction which is improved over that of a bundle made only of metallic fibre.

It is not absolutely necessary for these improvements that the metallic fibres surround a core of only non-metallic fibres. That is, the metallic fibres may be mixed uniformly into the bundle of nonmetallic inorganic fibres or non-metallic inorganic fibres having a metal coating may be mixed uniformly into the bundle of non-metallic fibres.

It will further be appreciated that the present method provides for a cast article to be produced that is connecting rod for an internal combustion engine, to be made whilst avoiding the possibility of a cold shut defect in the article. Also, the method produces a light-weight connecting rod having a bundle of uni-directional fibres therein which keeps the advantage of low weight by utilizing non-meta!lic inorganic fibres yet is capable of being heated more quickly and being better to retain an appropriate, proper shape.

It will further be appreciated that the present method provides a cast article to be produced that is reinforced by a bundle of uni-directional inorganic fibres in which the residual stress after casting is reduced.

Claims (12)

1. A method of making a connecting rod for an internal combustion engine, said rod having a first semi-annular end portion, a second annular end portion, and a rod portion therebetween, said second annular portion having a centre axis, said rod portion having a longitudinal axis, an X-axis perpendicular to said longitudinal axis and perpendicular to said centre axis, and a Y-axis perpendicular to said longitudinal axis and parallel to said centre axis; the method comprising the steps of shaping a bundle of inorganic reinforcing uni-directional fibres such that a second moment of area of the bundle about the Y-axis (I(c) y) taken across a cross-section perpendicular to the longitudinal axis is less than a second moment of area of the bundle about the X-axis (I(c) x), positioning said bundle in a mould, said mould having cavities to form said semi-annular portion, said annular portion and said rod portion, the cavity to form the rod portion being sized such that Ix of the finished rod is greater than ly of the finished rod, said bundle being positioned to bridge from said cavity for said semi-annular portion and to produce a fixed minumum gap between said bundle and the cavity for said rod portion; and squeeze casting a molten light metal alloy into said mould forming a matrix of said alloy and said bundle.

2. A method as claimed in Claim 1, wherein the step of shaping the bundle includes forming a bundle of a plurality of uni-directional metallic fibres, placing said bundle in a heat-resistant shaping container, and heating said contained bundle at least partially to fuse said uni-directional metallic fibres to each other.

3. A method as claimed in Claim 1, wherein the step of shaping said bundle includes forming a core bundle of a plurality of uni-directional inorganic non-metallic fibres, surrounding said core bundle with a plurality of uni-directional metallic fibres oriented in the same direction as said core bundle, placing said surrounding core bundle in a heat-resistant shaping container, and heating said container surrounded core bundle at least partially to fuse said uni-directional metallic fibres to each other and to said core.

4. A method as claimed in Claim 1, wherein the step of shaping the bundle includes forming a core bundle of a plurality of uni-directional non-metallic fibres, surrounding said core bundle with a plurality of unidirectional non-metallic fibres having a metal coating and being oriented in the same direction as said core bundle, placing said surrounded core bundle in a heat-resistant shaping container, and heating said contained surrounded core bundle at least partially to fuse said uni-directional metal-coated metallic fibres to each other and to said core.

5. A method as claimed in Claim 1, wherein the step of shaping said bundle includes forming a bundle of a uni-directional uniform mixture of metallic fibres and inorganic, non-metallic fibres, placing the mixed bundle in a heat resistant shaping containing, and heating said contained bundle at least partially to fuse said metallic fibres to each other and to said inorganic non-metallic fibres.

6. A method as claimed in Claim 1, wherein the step of shaping said bundle includes forming a bundle of a uni-directional uniform mixture of inorganic non-metallic fibres having a metal coating and inorganic non-metallic fibres, placing the mixed bundle in a heat-resistant shaping container, and heating said contained bundle at least partially to fuse said inorganic non-metallic fibres having a metal coating to each other and to said inorganic, non-metallic fibres.

7. A method as claimed in any one of the preceding claims, wherein said fixed mimimum gap is from about 1.5 to about 2.0 mm.

8. A method as claimed in Claim 2 or any one of Claims 3 to 7 as appendant to Claim 2,wherein said heating step is at a temperature of 7000C.

9. A method as claimed in any one of the preceding claims, wherein said bundle is shaped as an ellipse in cross-section having a major axis on said Y-axis and a minor axis and said X-axis.

1 0. A method of making a reinforced cast article, said article having end portions and a centre portion, comprising the steps of forming a bundle of inorganic reinforcing uni-directional fibres, said bundle including a proportion of metallic fibres, placing said bundle in a heat-resistant shaping container, heating said contained bundle at least partially to fuse said metallic fibres to each other, positioning said partially fused bundle into a mould having cavities for producing said article leaving a fixed minimum gap surrounding said bundle in a section of said cavities for producing said centre portion, and squeeze casting a molten light metal alloy into said mould forming a matrix of said alloy and said bundle.

11. A method of making a reinforced cast article such as a connecting rod for an internal combustion engine, substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.

12. A reinforced cast article such as a connecting rod for an internal combustion engine when produced by the method as claimed in any preceding claim.