WO2010125248A1

WO2010125248A1 - Method for casting a multimaterial object, use of a multimaterial object prepared by the method, mold arrangement, and use of a mold arrangement

Info

Publication number: WO2010125248A1
Application number: PCT/FI2010/050355
Authority: WO
Inventors: Jussi Hellman; Tuomas Himanka
Original assignee: Metso Minerals, Inc.
Priority date: 2009-04-30
Filing date: 2010-04-30
Publication date: 2010-11-04
Also published as: FI20095495A0

Abstract

The invention relates to a method for casting a wear resistant multimaterial object in a casting mold. According to the method, the casting volume defined by the mold inner surfaces is divided into at least two partitions by fitting at least one partition wall into the mold; at least one iron based metallic melt is introduced into each partition; and the metallic melts are allowed to solidify, producing a multimaterial object comprising the metallic melts and the partition wall(s). Further the invention relates to a mold arrangement for casting a wear resistant multimaterial object, the mold arrangement comprising a casting mold, the inner surfaces of which defining a casting volume into which iron based metallic melt can be introduced through a casting channel. The mold arrangement further comprises at least one partition wall adapted to divide said casting volume into at least two partitions; to said partitions are connected separate casting channels, respectively; and said at least one partition wall is adapted to remain as part of the cast multimaterial object.

Description

Method for casting a multimaterial object, use of a multimaterial object prepared by the method, mold arrangement, and use of a mold arrangement

Field of the invention

The invention relates to casting multimaterial objects.

Background of the invention

In the context of the present disclosure, the term 'metal material' refers to an alloy or to a pure metal. In the context of the present disclosure, the term 'metal melt' refers to a metal material which is in a molten state, hi the context of the present disclosure, the term 'multimaterial object' refers to an object consisting of a number of interconnected metal regions.

Traditional methods for preparing multimaterial objects or components by casting from two or more metal materials are based on keeping the metal melts separated, i.e. non-mixed, by means of gravity, centrifugal force, or a density difference, or on casting in several stages, whereby a subsequent metal material is cast on top of or on the surface of a previously cast, solid or at least partly solidified metal material.

In static casting methods (the mold does not move) based on gravity or a density difference the location of the interface of the materials in the cast object can only be influenced by changing the casting position of the object, and in any case the interface of the materials has to be horizontal. Casting in several stages may easily lead to connectivity problems at the interface of the materials e.g. because of an undesirable temperature difference of the melts or the oxidation of a previously formed surface. Also the decreased durability of a sand mold that has been deteriorated by the heat load of the first melt may create problems when the subsequent melt flows into the mold.

By means of the centrifugal force generated by the rotation of the mold it is possible to cast rotationally symmetrical objects in which the boundary line of two materials can be at a constant distance (constant radius) from the center line of the object. With regard to manufacturability, the most significant restriction of the centrifugal casting method is the requirement for rotational symmetry in the object, and with regard to the design of the multimaterial object, the obligatory positioning of the interface of the materials at a constant radius from the geometrical central axis of the object.

From the publication US 7,407,713 it is known to use an aluminum partition wall for casting a multilayer aluminum billet by continuous casting to a water-cooled chill. The publication discloses dividing the mold to two or more separate partitions by means of an aluminum partition wall. The aluminum melts are poured at both sides of the partition wall in the mold, the melts are allowed to solidify, and finally the solidified billet is rolled. As a result, a layer-structured aluminum billet is obtained, in which billet the partition wall is an integral part and connects the cast parts. The chill casting method disclosed in the publication US 7,407,713 is rather unsuitable for casting iron-based mixtures that require high temperatures.

According to the invention it has been observed that significant advantages are achieved in the manufacturing of multimaterial objects by using the sand mold casting technique and one or more metallic partition walls in the mold, hi sand mold casting, metallic partition walls or elements, the purpose of which is to enable the introduction of two or more melts into the mold and keeping them non-mixed, have not been used before. The invention enables casting structurally complex multimaterial objects from a wide variety of metal materials, which may have essentially different toughness and wear-resistance properties with regard to each other. By using known casting and mold techniques, it has not been possible to prepare structurally intact and uniform multimaterial objects by casting, and often not by any other technically and economically advantageous method, from all alloy pairs intended in the present invention. The method according to the invention is cost-effective, because the entire multimaterial object or component with all of its volume fractions made of different materials is formed in a single process. The new mold arrangement according to the invention further makes it possible to extend the scope of the traditional centrifugal casting method e.g. to conical objects and also to object geometries canted in two opposite directions. Simultaneously, by means of the invention, the adhesion between the melts can be improved and the stresses in the interface area can be released during the manufacturing of multimaterial objects. The largest contribution of the new mold arrangement according to the invention is, however, the extension of the scope of centrifugal casting techniques to objects in which there are material boundary lines at variable distances from the geometrical central axis of the rotation movement, which boundary lines can form any angle (coning angle) with the geometrical central axis of the rotation movement.

Disclosure of the invention

The invention relates to a method for the static casting of objects. In particular, the invention relates to a method for casting a wear-resistant multimaterial object in a casting mold.

Particularly, the method is suitable for the static casting of geometrically irregular objects in which the ratio of the sectional areas with respect to any axis is at least 1.1. Geometrically symmetric objects, the sectional area of which with respect to some axis is of the same size and shape along the whole length of the axis may be cast e.g. by continuous casting, which is outside of the scope of the present invention.

The method according to the invention is thus well-suited for both static sand mold casting and for centrifugal casting to a metal mold which in some instances, but not always, may also be wholly or partly sand-lined.

The method is characterized in that it comprises dividing the casting volume defined by the inner surfaces of a casting mold into two or more partitions by placing one or more metallic partition walls in the casting mold; introducing one or more iron-based metal melts into each partition; and allowing the metal melts to solidify, whereby a multimaterial object comprising the solidified metal melts and the metallic partition wall(s) is obtained.

According to an embodiment of the invention, the temperature of said iron-based metal melts is in the range of about 1300 °C to about 1700 °C. According to another embodiment of the invention, each metallic partition wall is prepared from steel.

According to an embodiment of the invention, each metallic partition wall is prepared from a nickel-based material.

According to an embodiment of the invention, said casting mold is a sand mold.

According to an embodiment of the invention, the casting volume, the metallic partition wall(s) and the partitions are symmetrical with respect to their common geometrical central axis, and the method comprises rotating the casting mold and the metallic partition wall(s) around said central axis during the introduction of the metal melts into the partitions.

According to an embodiment of the invention, the method further comprises introducing reinforcement particles into at least one partition before the introduction of the metal melt into said at least one partition to provide a composite structure in said at least one partition.

According to an embodiment of the invention, the material of said reinforcement particles comprises a ceramic, which is selected from the group consisting of oxides, nitrides, carbides and borides, and a metallic binding agent mixed with the ceramics, which metallic binding agent is an iron-, nickel-, chromium- or cobalt-based mixture containing the mentioned other elements or other elements as alloying substances or as impurities.

According to an embodiment of the invention, the method comprises dividing a casting volume defined by the inner surfaces of a casting mold into at least one wear- resistance partition and at least one body partition by fitting at least one compartmenting partition wall in the mold; introducing a melt of a wear-resistant iron- based metal material into said wear-resistance partitions and a melt of a metal material suitable for bearing mechanical loads and as a structural material into said body partitions; and allowing the metal melts to solidify.

According to an embodiment of the invention, the melt to be introduced into said wear-resistance partition comprises one or more iron-based alloys, the hardness of which is greater than about 50 HRC immediately after casting or after heat treatment, working and/or in-service deformation, which alloy is cast iron, chrome iron, nihard, tool steel, heat refined steel or manganese steel rich in chromium and/or other carbide formers, or chromium and nickel.

According to an embodiment of the invention, the melt to be introduced into said body partition comprises one or more of the following: carbon steel, manganese steel, heat refined steel.

The invention further relates to a mold arrangement for casting a wear-resistant multimaterial object. The mold arrangement comprises a casting mold, the inner surfaces of which define a casting volume into which an iron-based metal melt can be introduced via one or more casting channels. The mold arrangement is characterized in that it further comprises one or more metallic partition walls which have been adapted to divide said casting volume into two or more partitions; separate casting channels have been connected to said partitions, respectively; and said one or more metallic partition walls have been adapted to remain as part of the multimaterial object to be cast.

According to an embodiment of the invention, said one or more metallic partition walls are prepared from steel, and the thickness of each metallic partition wall is about 1 mm to about 10 mm.

According to an embodiment of the invention, said one or more metallic partition walls are prepared from carbon steel or stainless steel, and the thickness of each metallic partition wall is about 2 mm to about 5 mm. According to an embodiment of the invention, said casting mold consists of an inner half and an outer half, whereby the inner half is adapted to be inserted within the outer half, and the halves are adapted to be pressed against each other at their edges, whereby a casting volume remains between the halves, to which casting volume an iron-based metal melt can be introduced via a casting channel, and the mold arrangement further comprises a metallic partition wall, which is adapted to be pressed between said edges of the halves and to divide said casting volume to two partitions; separate casting channels are connected to said partitions, respectively; and said metallic partition wall is adapted to remain as a part of the multimaterial object to be cast.

According to an embodiment of the invention, said casting mold is a sand mold.

According to an embodiment of the invention, the casting volume, the metallic partition wall(s) and the partitions have a symmetrical structure with respect to the geometrical central axis of the mold arrangement.

According to an embodiment of the invention, the casting volume, the metallic partition wall(s) and the partitions have a rotationally symmetrical structure with respect to the geometrical central axis of the mold arrangement.

According to an embodiment of the invention, the mold arrangement further comprises means for rotating the casting mold and the metallic partition wall(s) around the geometrical central axis of the mold arrangement during the introduction of the metal melts into the partitions.

According to an embodiment of the invention, said casting mold is a sand mold.

The invention further relates to the use of a multimaterial object prepared by the method in wear parts of crushers for mineral material, such as in wear parts of cone, jaw, impact and spindle crushers. The invention further relates to the use of a multimaterial object prepared by the method in the manufacturing of rolls, rollers, mill rolls and guide rolls used in paper or metal industry.

The invention further relates to the use of the mold arrangement for casting a wear- resistant multimaterial object from one or more iron-based metal melts.

Brief description of the drawings

Figures IA- 1C show cross-sectional images of a casting method according to an embodiment of the invention, in which method is used a partition wall which completely melts into the cast metal melt and is vertical in the casting position.

Figures 2A-2B show cross-sectional images of a casting method according to another embodiment of the invention, in which method is used a corneal partition wall partly melting through the action of the heat of the metal melt and is inclined with respect to the vertical direction.

Figures 3A-3E show cross-sectional images of casting a multimaterial object from two different metal melts by centrifugal casting according to an embodiment of the invention.

Figure 4 shows a two-dimensional cross-sectional image of the casting of a wear part of a cone crusher according to an embodiment of the invention.

Figure 5 shows a three-dimensional cross-sectional image of the wear part of a cone crusher, obtained in the casting of Figure 4.

Figure 6 shows a wear part of an impact crusher as a three-dimensional view, during the casting of which wear part a method and a mold arrangement according to an embodiment of the invention have been used. Detailed description of embodiments

In the following, the invention is described in detail by referring to the appended drawings, in which corresponding reference characters have been used throughout.

In an embodiment of the method according to the invention, the casting of a multimaterial object is performed in a sand mold, in which is provided one or more metallic partition walls, the positioning of which corresponds to the desired material interfaces in the cast object or component. The purpose of the partition walls is to guide and restrict the metal melts to the partitions intended for them in the mold and in the solidifying object, respectively.

When using the method according to the invention, the geometry, the size, and the positioning of the materials of the object to be casted may vary greatly. The object may be, for example, horizontally or vertically unsymmetrical. In a multimaterial object to be cast from two or more melts there may be material boundary lines formed by partition walls at varying distances from the geometrical central axis, which boundary lines may form any angle with the geometrical central axis of the object. When materials differing with respect to their composition and properties are used, for example a carbon steel body material and a wear-resistant high-alloy cast iron, the ratio of their volume fractions may vary in the object and the interface of the materials may be positioned very freely within the object by means of the partition wall(s) dividing the mold. The size, shape and positioning of the mold partitions limited by the partition wall(s) are in practice only limited by the fact that the melt must be introduced from the casting system to each mold partition limited by a partition wall via its own inlet. If the melt volume of the mold is divided into too many partitions separated by partition walls, the casting system will become too complicated, difficult to manufacture and expensive. The smallest possible cross- sectional area and aspect ratio of the separate mold partitions are governed by the constraints imposed on the flow of the melt by the filling, gas removal and charging of the mold during casting and solidification. The suitability of the above mentioned dimensioning of the mold partitions must be checked in accordance with the melt composition, the casting temperature, and the desired mold filling rate to be used during casting.

Inside the walls of the sand mold, outside the object to be formed upon casting, empty space is reserved for the partition wall that expands thermally during the filling of the mold. The common intersection of the sand, the melt and the partition wall is preferably positioned outside the final dimensions of the object to be formed upon casting so that the potential connection defects in this area remain outside the finished object.

Figures IA- 1C show an embodiment of the invention in which a vertical, planar partition wall 12 is used, which partition wall together with the inner walls 10 and 11 of the sand mold divides the mold into two separate partitions 13 and 14 of different sizes, hi the stage of Figure IA, two different metal melts 15 and 16 are introduced into the partitions 13 and 14, respectively, from below, hi Figure IB the partitions have been filled and the melts are allowed to cool. In the stage shown in Figure IB, the partition wall 12 has partly dissolved in the melts, hi the stage of Figure 1C, the melts have solidified and the partition wall has dissolved completely. In the ready multimaterial object the interface of the materials is in a plane. The filling of the mold by the melt preferably starts from the bottom of the mold within the region having the largest diameter.

Figures 2A-2B show another embodiment of the invention in which a conical partition wall 21 and a cone-shaped sand mold are used. The partition wall 21 and the inner wall 20 of the mold divide the mold into two separate partitions, i.e. an outer partition 24 and an inner partition 25. hi the stage of Figure 2 A, a metal melt 22 is introduced into the outer partition 24, and a metal melt 23 is introduced into the inner partition 25. In the stage of Figure 2B, the partitions have been filled by the melts, the melts have solidified, and the partition wall 21 has partly dissolved, hi the ready two-layer- walled multimaterial object the interface of the materials has a shape of a truncated cone surface. Figures 3A-3E show an embodiment of the invention in which centrifugal casting technique is used for the filling of the mold. The mold arrangement used in this embodiment comprises a permanent metal mold consisting of two halves and a conical partition wall remaining in the cast object. The permanent mold comprises a first, outer half 31 and a second, inner half 32, which have been adapted to fit within each other so that a casting volume remains between the halves for the metal melt. The mold arrangement further includes a conical metallic partition wall 33 prepared from sheet metal, which comprises edges that have been adapted to remain pressed between the mold halves when the inner half 32 of the mold is inserted into the outer half 31 of the mold and the halves are pressed and interlocked. The partition wall 33 has been adapted to divide the casting volume of the mold into two parts, i.e. an outer partition 36 and an inner partition 37.

Figure 3 A shows the mold halves separately. To close the mold, the inner half 32 is inserted into the outer half 31, whereby the edges of the halves are pressed against each other and at the same time the partition wall 33 is pressed between the halves. Inclined casting channels 34 and 35, which do not touch the mold halves, lead into the mold and to opposite sides of the sheet metal partition wall, respectively, through openings located along the central axis of the mold halves.

hi the stage of Figure 3B, the mold is closed and metal melt is introduced into both casting volumes. A metal melt 38 is introduced into the outer partition 36 of the casting volume via the casting channel 34 through the outer half of the mold, and correspondingly a metal melt 39 is introduced into the inner partition 37 via the casting channel 35 through the inner half of the mold. The partition wall prevents the mixing of the melts and, in accordance with its shape, forms a boundary line inside the filling casting volume. The distance of the boundary line of the melts from the central line of the mold and the object to be cast may vary significantly, and the layer thicknesses of the melts on the opposite sides of the partition wall may vary freely. During the introduction of the melts, the closed mold, i.e. the mold halves and the partition wall, are rotated around their common geometrical central axis at a rotational speed typical for the casting method, which together with the melt densities determines the centrifugal force exerted on the melts and governing their flow. The casting channels are not rotated. The centrifugal force promotes complete filling of the mold partitions defined by the mold and the partition wall. Rotating the mold facilitates the filling of the mold and the attainment of a dense cast structure without feeds, which has a significantly reducing effect on the consumption of material and energy. The use of a mold arrangement according to the invention does not change the method of determining the rotation speed of the mold as compared to conventional centrifugal casting.

In the stage of Figure 3 C the casting volume of the mold has been filled with the melts, and the melts are allowed to cool. Rotating is terminated after the object has solidified and cooled to some extent.

In the stage of Figure 3D, the mold halves are separated, whereby the cast object is released from the mold. The partition wall has remained as part of the formed object.

In the stage of Figure 3E, the object is finished by cutting the protruding edges and the centre of the partition wall from the cast object by means of water-jet cutting. In Figure 3 E, the lines along which the cutting is performed are indicated by parallel lines.

In the embodiment shown in Figures 3A-3E, which utilizes a centrifugal casting technique, the metallic mold and the object to be casted must be balanced with respect to their geometrical central axis.

According to a particular embodiment, the object to be cast is rotationally completely symmetrical. Alternatively the object to be cast may comprise indentations and protrusions deviating from the rotationally symmetrical shape, such as lugs, but because of the balancing they have to be located symmetrically with respect to the central axis and, in view of opening the mold, they must be slightly canted. The division plane of the metallic mold need not be planar or only canted to one direction, but the division plane may simultaneously contain both surfaces that are canted to the opening direction of the mold and surfaces that are canted to the closing direction of the mold, and correspondingly the objects to be cast may have a geometry that is canted to two opposite directions.

Figure 4 shows the casting of a wear part of a cone crusher by a method according to an embodiment of the invention as static sand mold casting. Figure 4 shows the following parts of a sand mold: a core 40a, an upper part of the sand mold (cope) 40b, and a lower part of the sand mold (drag) 40c. Functionally the mold consists of an outer half and an inner half, which are adapted to fit within each other. A conical partition wall 43 has been provided in the mold, which partition wall comprises, as securely attached, guide parts 44a and 44b that ensure that the partition wall is correctly positioned and remains in place. The partition wall and the guide parts are made of steel, the thickness of which is typically about 1 mm to about 5 mm, often preferably about 2 mm to about 3 mm. The partition wall divides the casting volume remaining between the mold halves into two partitions, i.e. an outer partition 41 and an inner partition 42. Two casting channels 45 and 46 have been provided in the mold, through which casting channels two metal melts 47 and 48 can be brought separately into the inner partition 42 and the outer partition 41, respectively, hi this embodiment the mold is not rotated but the casting is performed conventionally in an ordinary sand mold.

Figure 5 shows a three-dimensional cross-sectional image of the wear part of a cone crusher which was obtained in the casting of Figure 4. Figure 5 shows the casting of a crusher cone of Figure 4 in a situation in which the mold has been filled. The outer periphery 51 of the crusher cone is preferably made of wear-resistant iron. The inner periphery 52 of the crusher cone is preferably made of carbon steel. The partition wall 53 is made of metal. The core 55 is a hardened object prepared from a special sand mixture which is placed in the mold to form holes and cavities in the cast object.

Figure 6 shows an impact crusher wear part, which has been cast in a sand mold. The curved metal sheets 61a and 61b are secured to the long edges of the object and, during casting, to the upper and lower parts of the mold. The metal sheets define curved partitions 62a and 62b in the object. The melts have been introduced from the lower part of the mold through their dedicated channels both to the body partition 63 and to the curved partitions 62a, 62b defined by the metal sheets 61a, 61b. In this embodiment a steel melt was introduced into the body partition 63 and a wear- resistant iron melt was introduced into the curved partitions 62a, 62b.

According to the invention the material of the partition wall is chosen so that the melting temperature and the high-temperature strength according to its composition are in a correct relationship to the casting temperature of the melts and to the surface pressure caused by the melts either so that the partition wall partly or wholly connects to the melts to be used, whereby in both cases the partition wall is intended to form a solid, dense barrier to the intermixing of the melts until the flow of the melts has ceased. On the other hand, the partition wall must melt from its surface so that it connects metallurgically to the other parts of the object to be cast. Preferably, either a partial or a complete melting of the wall takes place at the interface between the partition wall and the melt so that a metallurgical bond is formed between the different material regions of the multimaterial object.

The material of the partition wall may be functional, hi some cases it is possible, by means of a partition wall, to form a bond between materials that cannot be joined to each other directly. By means of a partition wall it is also possible to release stresses caused by the different thermal properties of the melts, such as thermal expansion or phase transitions. The manufacturing material of the partition wall is preferably for example iron-carbon-alloyed steel, carbon steel, or stainless steel. In the case of certain multimaterial structures and metal melts also a nickel-based (> 50% nickel) material may be a preferable partition wall material that exhibits good wetting and bonding with the melt(s).

hi certain cases it is desired that the partition wall(s) remain at least partly as a separate phase region in the final multimaterial structure. In certain other cases it is desired that the partition wall(s) melt completely into the melts to be cast. The melting can be influenced by the material thickness, composition and positioning of the partition wall with respect to the mold and to the temperature zones present in the melt. The partition wall melts and mixes partly or wholly with the other melts. Partial dissolution may also take place if the materials differ chemically significantly. In the case that the partition wall remains wholly or partly undissolved during casting, the properties of the interface region formed by the melts can be influenced by the composition of the partition wall material for example so that thermal stresses during the solidification, cooling, heat treatments and use of the multimaterial structure can be accommodated by means of an intermediate layer (the partition wall). The material of the partition wall can be chosen within the limits imposed by its principal function

(separation of the melts) for example so that the thermal expansion coefficient of the layer falls between the thermal expansion coefficients of the materials formed from the melts.

A partition wall that remains undissolved in the object may also be used to divide the parts of the multimaterial object that are made of a brittle material further into smaller parts, whereby the risk of breaking can be better controlled than in a large uniform material region, and the scope of application of the relevant material as well as the desired product form are extended.

The thickness of the partition wall is determined by the thermal and mechanical stresses imposed upon it. The greater the amounts of melt separated by the partition wall, the greater are the thermal loads and forces it will have to withstand. The partition wall may comprise thicker local segments or support structures abutting the inner mold walls and strengthening the partition wall in areas having a particularly high thermal load, melt erosion or mechanical load. Typically, the thickness of the partition wall and guide and support bodies attached thereto is about 1 mm - about 10 mm, usually preferably about 2 mm - about 3 mm, and in local reinforcements about 5 mm.

As a partition wall is mounted in a mold, care must be taken to make it fit sufficiently tightly against all those inner walls at which an interface of the molten materials is formed. This requires appropriate dimensioning and sufficient measurement accuracy during manufacturing. When anticipating the dimensions and the behavior during casting, the dimensional changes in the metallic partition wall as it is heated during filling of the mold must be taken into account, and sufficient space must be provided for the partition wall to expand within the mold without unduly choking the melt streams. Metallic materials expand when heated according to their thermal expansion coefficient. The expansion tolerance is thus dependent on the size of the partition wall, on the material and on the temperatures used, hi practice, the partition wall can be located within the sand mold in a groove having empty space for the metal to expand. The partition wall may also be provided with a telescoping structure in which metal plates are allowed to slide relative to each other. In practice, for example, a ring attached to the roof of the mold is provided above the upper part of a circular partition wall. As the circular partition wall expands, it slides within a collar.

The cast temperatures used depend on the relevant metallic materials. Through temperatures it is possible to influence the shrinking effects associated with solidification and cooling, and thus to balance various dimensional changes which may cause internal stress in multimaterial objects.

The volume of the multimaterial components to be manufactured is, in a particular embodiment, divided into a wear protected partition or wear protected partitions, which depending on the shape and purpose of the component may be located on the inner or outer surface; and a body partition consisting of a load-bearing structural material connecting the separate wear protected partitions into a unitary multimaterial component. Usually, the structural material of the wear protected partition comprises one or several iron-based metal alloys, the hardness of which is above 50 HRC, preferably above 54 HRC following annealing and/or hot working or working effects occurring during operation. Materials properly fulfilling these criteria are cast iron, tool steel, heat refined steel and manganese steel. The typical basic composition of a preferable chromium iron for this purpose includes about 2 % to about 3.5 % carbon and about 10 to about 30 % chromium. The typical basic composition of a preferable nickel-alloyed cast iron (e.g. Nihard grades) for this purpose includes about 2 % to about 3.5 % carbon, about 3 % to about 7 % nickel and about 1 to about 11 % chromium. The composition of suitable tool steels include an abundance of carbide- forming alloying elements like chromium, vanadium, niobium and tungsten, which form hard metal carbides with the carbon included in the composition. If particularly good wear protection is required in the wear-protected volume, reinforcement particles can be added to the above-mentioned base materials whereby a metal matrix composite material is formed in the relevant area from melt and reinforcement particles. The reinforcement particles are preferably ceramics, like oxide, nitride, carbide or boride, and intermixed metallic binder which may be an iron, nickel, chromium or cobalt based alloy including the above mentioned or other elements. The casting of a composite material containing reinforcement particles has been disclosed in further detail in Finnish patent application No. 20086088.

By placing and dimensioning the cast channels and entrances for each melt, the filling rate for the partitions reserved for the relevant melts can be controlled. The filling rate on each side of the partition wall may be essentially equal, or alternatively it may be different. Often it is preferable to use the same filling rate on different sides of the partition wall.

Example 1

In this example is described the casting of a crusher cone from two metals, i.e. wear resistant cast iron and carbon steel, using the method according to the invention. The weight of such a crusher cone is typically about 1000 kg.

The cast is carried out in a sand mold comprising two separate casting systems. A corneal separation wall prepared from carbon steel or stainless steel is fitted in the mold. The wall separates the materials to be cast at the outer and the inner periphery. The thickness of the separating wall is about 2 to 5 mm. The mold is closed, and subsequently the casting is carried out using two ladles simultaneously, supplying highly alloyed cast iron melt to the outer periphery and carbon steel melt to the inner periphery. The temperature of the cast iron melt is about 1400 ⁰C and the temperature of the carbon steel melt is about 1600 ⁰C. The melts are allowed to solidify in the mold.

The result is a crusher cone, the outer surface of which is prepared from wear resistant cast iron and the inner part of which is prepared from carbon steel which is capable of carrying the forces relating to mounting and operation and is additionally more economic and easily machineable. In comparison to a method according to the state of the art, in which the whole of the crusher cone is cast from wear resistant manganese steel, it has been possible to prolong the service life of the crusher cone by the method according to the invention, since a wear resistant material could be selected for the surface portion without compromising the mechanical properties of the object as a whole.

Example 2

In this example is described the use of the method and mold arrangement according to the invention for casting a conical bimetallic part from chromium iron and structural steel. Here, the centrifugal casting mold is either a water cooled iron or steel mold, or a sand lined and coated iron chill mold. The sheet metal partition wall is fitted between the mold halves and the mold is tightly closed and locked. The mold is rotated during the melt inflow using a rotational speed causing a centrifugal force of several tens relative to gravity. As set forth above, the required rotational speed is determined by the diameter of the cast object, and when a crusher cone is cast it is typically 200 to 400 rpm, however without being limited to this range. The mold rotation is ceased as the object has solidified and cooled to some extent. Subsequently, the object can be removed from the mold and the next corresponding cast cycle can begin.

The present invention is not limited to the embodiments and examples described above. The method according to the invention can be used for manufacturing wear parts related to the crushing of mineral material, for example crusher jaws, side wedges and other plate-shaped wear parts like grinder segment plates; wear parts of impact crushing equipment like distributor plates, anvils, ejector shoes, side plates, crusher plates and impact hammers; rolls, rollers, mill rolls and guide rolls used in the metal and paper industry; and for manufacturing straight, conical and tubular objects like crusher cones and screens.

Claims

1. A method for the manufacture of a wear resistant multimaterial object by static casting, characterized by the following steps:

- dividing the casting volume defined by the inner surfaces of the casting mold into at least two partitions by fitting at least one metal partition walls into the mold;

- introducing at least one iron-based metal melt in each of the partitions; and

- allowing the melts to solidify resulting in a multimaterial object comprising the solidified melts and the metal partition wall(s).

2. The method according to claim 1, characterized in that the temperatures of the iron-based metal melts is in the range about 1300 ⁰C - about 1700 ⁰C.

3. The method of claim 1 or 2, characterized in that each metal partition wall is made from steel.

4. The method of claim 1 or 2, characterized in that each metal partition wall is made from a nickel based material.

5. The method of any claim 1 to 4, characterized in that said casting mold is a sand mold.

6. The method of any claim 1 to 4, characterized in that the casing volume, the metal partition wall(s) and the partitions are symmetrical with respect to their common geometrical central axis and that in the method, the casting mold and the metal partition wall(s) are rotated around said central axis during the introduction of metal melt into the partitions.

7. The method of any claim 1 to 6, characterized in that additionally reinforcement particles are provided in at least one partition before metal melt is introduced in said at least one partition, so as to provide a composite structure in said partition.

8. The method of claim 7, characterized in that said reinforcement particles comprise a ceramic selected from the group oxides, nitrides, carbides and borides, and admixed with the ceramic a metal binder which is an iron, nickel, chromium or cobalt based mixture comprising the aforementioned or other elements as alloying agents or impurities.

9. The method of any claim 1 to 8, characterized in the following steps:

- the casting volume defined by the inner walls of the mold is divided into at least one wear protection partition and at least one body partition by fitting at least one partition wall in the mold;

- a melt of a wear resistant iron based metal material is introduced in said wear protection partition and a melt of an iron based metal material suitable for carrying a mechanical load and as a structural material is introduced in said body partition; and

- the metal melts are allowed to solidify.

10. The method of claim 7, characterized in that the melt introduced in said wear protection partition comprises at least one iron based metal alloy, the hardness of which immediately following the casting, annealing, working and/or working effects during operation is greater than about 50 HRC, said metal alloy being cast iron rich in chromium and/or other carbide formers, or chromium and nickel; chromium iron, nihard, tool steel, heat refined steel or manganese steel.

11. The method of claim 9 or 10, characterized in that the melt introduced in said body partition comprises at least one of the following: carbon steel, manganese steel, heat refined steel.

12. A mold arrangement for casting a wear resistant multimaterial object using static casting, said mold system comprising a casting mold the inner surfaces of which define a casting volume which is adapted for the introduction into it of iron based metal melt through at least one casting channel, characterized in that the mold arrangement further comprises at least one partition wall adapted to divide said casting volume into at least two partitions; separate casting channels being connected to said partitions, respectively; and said at least one metal partition wall being adapted to remain as part of the multimaterial object.

13. The mold arrangement according to claim 12, characterized in that said at least one metal partition wall is made from steel and the thickness of each metal partition wall is about 1 mm - about 10 mm.

14. The mold system according to claim 12 or 13, characterized in that said at least one partition wall is made from carbon steel or stainless steel and the thickness of each partition wall is about 2 mm - about 5 mm.

15. The mold arrangement according to any claim 12 to 14, characterized in that said casting mold consists of an inner half and an outer half, the inner half being adapted to be inserted within the outer half and the halves are adapted to be pressed against each other at their edges, forming a casting volume between the halves, to which casting volume an iron-based metal melt can be introduced via a casting channel, characterized in the mold arrangement further comprising a metallic partition wall adapted to be pressed between said edges of the halves, separate casting channels being connected to said partitions, respectively; and said metallic partition wall being adapted to remain as part of the multimaterial object to be cast.

16. The mold arrangement according to any claim 12 to 15, characterized in that said casting mold is a sand mold.

17. The mold arrangement according to any claim 12 to 15, characterized in that the casting volume, the metallic partition wall(s) and the partitions have a symmetrical structure with respect to the geometrical central axis of the mold arrangement.

18. The mold arrangement according to any claim 12 to 15, characterized in that the casting volume, the metallic partition wall(s) and the partitions have a rotationally symmetrical structure with respect to the geometrical central axis of the mold arrangement.

19. The mold arrangement according to claim 17 or 18, characterized in that the mold arrangement further comprises means for rotating the casting mold and the metallic partition wall(s) around the geometrical central axis of the mold arrangement during the introduction of the metal melts into the partitions.

20. The mold arrangement according to any claim 17 to 19, characterized in that said casting mold is a metal mold.

21. The use of a multimaterial object manufactured according to claim 1 in wear parts of mineral material crushers, such as cone, jaw, impact, and spindle crushers.

22. The use of a multimaterial object manufactured according to claim 1 in rolls, rollers, mill rolls and guide rolls used in the paper or metal industry.

23. The use of a mold arrangement according to claim 12 for casting a wear resistant multimaterial object from at least one iron based metal melt.