High-strength and high-thermal conductivity new material composite brake drum and preparation method thereof

Abstract

The present disclosure discloses a high-strength and high-thermal conductivity new material composite brake drum and a preparation method thereof. The composite brake drum is composed of an outer layer of high-strength ductile iron and an inner layer of high-thermal conductivity gray cast iron, which are integrated by centrifugal compound casting. The outer layer of the composite brake drum is firstly poured on the production line of iron particle-filled coated sand shells. Due to the fast solidification and cooling of the iron particle-filled coated sand shells, the castings have the characteristics of fine and dense organization structures to ensure the high strength and high toughness of the ductile iron of the outer layer. On this basis, the inner gray cast iron is poured under centrifugal casting conditions, in which a good metallurgical bond between the inner and outer layers is achieved by controlling the centrifugal casting process.

Claims

1. A method for preparing a high-strength and high-thermal conductivity new material composite brake drum, wherein, the high-strength and high-thermal conductivity new material composite brake drum comprises an outer layer and an inner layer, the outer layer is made of high-strength ductile iron, the inner layer is made of low-alloy gray cast iron, and the outer layer and the inner layer are fused together by means of solid-liquid bonding, the preparation method is as below: 1) Smelting molten iron, and after the molten iron is melted, adding 1-1.5% by weight of rare-earth ferrosilicon magnesium spheroidizing agent and 0.8-1.3% by weight of ferrosilicon inoculant at a bottom of a ductile iron ladle for spheroidization while keeping the spheroidization temperature at 1560-1650° C.; pouring the spheroidized molten iron into cavities from a pouring cup at a pouring rate of 15-25 seconds for each cavity while controlling the pouring temperature at 1420-1480° C. for a total pouring period of ≤15 minutes; after the molten iron is completely solidified and when the temperature drops to 950-1000° C., taking it out of the cavities and cooling in air to a temperature of 280-360° C., degating, grinding and cleaning sand to obtain a high-strength ductile iron outer casting of the composite brake drum; 2) Placing the outer casting on a centrifuge, adding a compounding agent to a part of an inner surface that needs to be compounded with gray iron, heating the inner surface rapidly to 770-820° C.; then pouring the inner layer at a pouring rate of 5-12 seconds for each brake drum at a pouring temperature of 1410-1445° C. while keeping the rotating speed of the centrifuge at 550-600 rpm; during the pouring of molten iron in the inner layer, adding SiC of 250-300 meshes along with the molten iron stream at an amount accounting for 3.8-4.3% by mass fraction of the molten iron entering the outer casting; and during the centrifugal pouring of the molten iron, adding an electromagnetic field with a magnetic field strength of 0.15-0.25 T; turning off the electromagnetic field 1 minute after all the molten iron enters the outer casting; then raising the rotating speed of the centrifuge to 1050-1100 rpm, and cooling a shell of the outer casting by spraying; after the molten iron is completely solidified, reducing the rotating speed of the centrifuge to 100-120 rpm, and bringing the temperature down to 500-580° C., stopping spray cooling and shutting down to take out the outer casting and the solidified inner layer, which is finished to obtain the high-strength and high-thermal conductivity new material composite brake drum; wherein, in step 2), the inner layer is made of low-alloy gray cast iron, and the chemical composition of the molten iron as well as mass fractions thereof are controlled at: 3.21-3.75% C, 1.30-2.14% Si, 0.52-1.09% Mn, 0.21-0.48% Cr, ≤0.10% S, ≤0.06% P, the balance Fe.

2. The method according to claim 1, wherein, in step 1), a thickness of a sand shell used for casting the outer layer is 8.0-12.0 mm, the sand shell is composed of, by mass fraction, 40-50% of 150-180-mesh quartz sand, 25-30% of 200-250-mesh quartz sand and 25-30% of 280-330-mesh quartz sand; the combined sand shell is laid at a bottom of a sand box; a liquid inlet of the sand outer shell is inserted into a pouring cup after placing a filter screen on the liquid inlet, and a cover plate is placed above the pouring cup to prevent iron particles from falling into the pouring cup when they are added; all voids except the cavities are filled with iron particles of φ3 mm-φ6 mm and vibrated and compacted, and a covering height of iron particles is not lower than 100-500 mm above upper plane of the sand shell.

3. The method according to claim 1, wherein, the outer layer is made of high-strength ductile iron which is grade QT450-10 or above.

4. The method according to claim 1, wherein, in step 1), grade QT500-7 or QT600-3 is used for smelting molten iron.

5. The method according to claim 1, wherein, in step 1), when molten iron is smelted, the chemical composition of the molten iron in a furnace is controlled at, in percentage by weight: C 3.5-3.9%; Si 1.0-1.5%; Mn≤0.8%; S≤0.03%.

6. The method according to claim 3, wherein, in step 1), grade QT500-7 or QT600-3 is used for smelting molten iron.

7. A method for preparing a composite brake drum, wherein the composite brake drum comprises an outer layer and an inner layer, the outer layer is made of high-strength ductile iron, the inner layer is made of low-alloy gray cast iron, and the outer layer and the inner layer are fused together by solid-liquid bonding, the method comprising: 1) Melting high-strength ductile iron; after the molten iron is melted, adding 1-1.5% by weight of rare-earth ferrosilicon magnesium spheroidizing agent and 0.8-1.3% by weight of ferrosilicon inoculant at a bottom of a ladle for spheroidization while keeping A spheroidization temperature at 1560-1650° C. to obtain spheroidized molten iron; pouring the spheroidized molten iron into cavities from a pouring cup at a pouring rate of 15-25 seconds for each cavity while controlling the pouring temperature at 1420-1480° C. for a total pouring period of ≤15 minutes; after the spheroidized molten iron is completely solidified and the temperature drops to 950-1000° C., taking the solidified iron out of the cavities and cooling in air to a temperature of 280-360° C. to obtain the high-strength ductile iron outer layer of the composite brake drum; 2) Placing the outer layer on a centrifuge, adding a compounding agent to a part of an inner surface of the outer layer, heating the inner surface to 770-820° C., then pouring low-alloy molten gray iron along the inner surface at a pouring rate of 5-12 seconds at a pouring temperature of 1410-1445° C. while keeping a rotating speed of the centrifuge at 550-600 rpm; during the pouring of the molten gray iron, adding SiC of 250-300 mesh along with the molten iron stream at an amount accounting for 3.8-4.3% by mass fraction of the molten gray iron; during the pouring of the molten gray iron, adding an electromagnetic field with a magnetic field strength of 0.15-0.25 T; turning off the electromagnetic field 1 minute after all the molten gray iron is poured; then raising the rotating speed of the centrifuge to 1050-1100 rpm, and cooling the outer casting by spraying; after the molten gray iron is completely solidified, reducing the rotating speed of the centrifuge to 100-120 rpm, bringing the temperature down to 500-580° C., stopping spray cooling, and taking the outer layer and the solidified inner layer off the centrifuge to obtain the composite brake drum; wherein the chemical composition of the low-alloy molten gray iron as well as mass fractions thereof are controlled at: 3.21-3.75% C, 1.30-2.14% Si, 0.52-1.09% Mn, 0.21-0.48% Cr, ≤0.10% S, ≤0.06% P, the balance Fe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to illustrate the technical solutions in the embodiments of the present disclosure more clearly, the following is a brief description of the accompanying drawings that need to be used in the embodiments. It is apparent that the following drawings are only some embodiments of the present disclosure, and other drawings can be obtained without creative effort by any person with ordinary skills in the art based on these drawings.

(2) FIG. 1 is a structural schematic diagram of the high-strength and high-thermal conductivity new material composite brake drum of the present disclosure;

(3) FIG. 2 is a structural diagram of the high-strength ductile iron outer shell of the high-strength and high-thermal conductivity new material composite brake drum of the present disclosure;

(4) FIG. 3 is a schematic diagram showing the assembling process of the sand shell of the high-strength and high-thermal conductivity new material composite brake drum of the present disclosure;

(5) FIG. 4 is a schematic diagram showing the cavity formed by the outer shell of the high-strength and high-thermal conductivity new material composite brake drum of the present disclosure.

(6) Illustrative features are assigned the following reference numerals: 1, outer layer; 2, inner layer; 3, outer shell; 4, inner shell; 5, bottom; 6, flange hole.

DETAILED DESCRIPTION

(7) The embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings in embodiments of the present disclosure. Obviously, the described embodiments are only a part of embodiments of the present disclosure, not all of them. Based on embodiments of the present disclosure, all other embodiments obtained by a person with ordinary skills in the art without creative labor fall within the protection scope of the present disclosure.

Embodiment 1

(8) As shown in FIGS. 1 to 4, this embodiment provides a high-strength and high-thermal conductivity new material composite brake drum and a preparation method thereof. The high-strength and high-thermal conductivity new material composite brake drum include an outer layer 1 and an inner layer 2, the outer layer 1 is made of high-strength ductile iron, the inner layer 2 is made of low-alloy gray cast iron, and the outer layer 1 and the inner layer 2 are fused together by means of solid-liquid bonding; the specific preparation method is as below:

(9) 1) Production of the high-strength ductile iron outer layer 1

(10) The structure of the high-strength ductile iron outer layer 1 is shown in FIG. 2.

(11) The thickness of the sand shell is 8.0-12.0 mm, and the sand shell is composed of, by mass fraction, 40-50% of 150-180-mesh quartz sand, 25-30% of 200-250-mesh quartz sand and 25-30% of 280-330-mesh quartz sand. The combined sand shell is laid at the bottom 5 of a sand box. A liquid inlet of the sand outer shell 3 is inserted into a pouring cup after placing a filter screen on the liquid inlet, and a cover plate is placed above the pouring cup to prevent iron particles from falling into the pouring cup when they are added. All voids except the cavities are filled with iron particles of φ3 mm-φ6 mm and vibrated and compacted, and the covering height of iron particles is not lower than 100-500 mm above the upper plane of the sand shell.

(12) Molten iron is smelted, during which the chemical composition of the molten iron in the furnace is controlled at, in percentage by weight: C 3.5-3.9%; Si 1.0-1.5%; Mn≤0.8%; S≤0.03%. After the molten iron is melted, 1-1.5% by weight of rare-earth ferrosilicon magnesium spheroidizing agent and 0.8-1.3% by weight of ferrosilicon inoculant are added at the bottom of a ductile iron ladle for spheroidization while keeping the spheroidization temperature at 1560-1650° C.

(13) The spheroidized molten iron is poured into cavities from a pouring cup at a pouring rate of 15-25 seconds for each cavity while controlling the pouring temperature at 1420-1480° C. for a total pouring period of <15 minutes. After the molten iron is completely solidified and when the temperature drops to 950-1000° C., it is taken out of the cavities and cooled in air to a temperature of 280-360° C., degated, and ground to clean the sand to obtain a high-strength ductile iron outer casting of the composite brake drum.

(14) 2) Solid-liquid organic fusion between the inner wall of the ductile iron shell of the outer layer 1 and gray cast iron

(15) The flange hole 6 in FIG. 2 is machined to the specified size for the positioning of centrifugal casting.

(16) The ductile iron outer layer 1 is placed on a centrifuge, and a compounding agent is added to the part of the inner surface that needs to be compounded with gray iron. The compounding agent is composed of sodium carbonate, potassium carbonate, sodium fluoride, sodium chloride, cryolite and calcium chloride. The inner surface is heated rapidly to 770-820° C. Then the inner layer is poured with gray cast iron. The chemical composition of the molten iron of gray cast iron of the inner layer 2 as well as mass fractions thereof are controlled at 3.21-3.75% C, 1.30-2.14% Si, 0.52-1.09% Mn, 0.21-0.48% Cr, ≤0.10% S, ≤0.06% P, the balance Fe, 3.9%≤carbon equivalent (C+1/3Si)≤4.3%. The pouring rate is 5-12 seconds for each brake drum, the pouring temperature is 1410-1445° C., and the rotating speed of the centrifuge is 550-600 rpm. During the pouring of the molten iron of gray cast iron of the inner layer 2, SiC of 250-300 meshes is added along with the stream of molten iron at an amount accounting for 3.8-4.3% by mass fraction of the molten iron entering the casting mould. In addition, during the centrifugal pouring of the molten iron of gray cast iron, an electromagnetic field with a magnetic field strength of 0.15-0.25 T is added. The electromagnetic field is turned off 1 minute after all the molten iron of gray cast iron enters the casting mould. The rotating speed of the centrifuge is then raised to 1050-1100 rpm, and the ductile iron shell of the outer layer 1 is cooled by spraying. After the molten iron is completely solidified, the rotating speed of the centrifuge is dropped to 100-120 rpm. When the temperature drops to 500-580° C., the spray cooling is stopped and the centrifuge is shut down to take out the casting, which is finished to obtain the high-strength and high-thermal conductivity new material composite brake drum.

(17) With respect to the high-strength and high-thermal conductivity new material composite brake drum of the present disclosure, the outer layer 1 is made of high-strength ductile iron, the inner layer 2 is made of gray iron with high-thermal conductivity and resistant to thermal fatigue. During the pouring of the molten iron of gray cast iron of the inner layer 2, SiC of 250-300 meshes is added along with the stream of molten iron at an amount accounting for 3.8-4.3% by mass fraction of the molten iron entering the casting mould. Silicon carbide is formed by high temperature smelting of quartz sand, petroleum coke (or coal coke), wood shavings and other raw materials in resistance furnaces. Silicon carbide has a melting point of 2700° C., a specific gravity of 3.2 g/cm.sup.3, and a microhardness of 2840-3320 kg/mm.sup.2, that is, having characteristics of high hardness, low density, and high melting point, etc.

(18) Therefore, it will not be dissolved when added into the molten iron of gray cast iron. Its high hardness may significantly improve the wear resistance of the cast iron. In particular, the density of silicon carbide is obviously lower than the density of Fe (7.8 g/cm3), so under the action of centrifugal force, silicon carbide will be enriched on the inner surface of the composite brake drum, that is the working face of the composite brake drum, thereby significantly improving the hardness and wear resistance of the inner surface.

(19) The outer layer 1 of the composite brake drum is produced by filling a coated sand shell with iron particles, and pouring spheroidized molten iron into a casting mould of the sand shell. Due to the fast solidification and cooling of the iron particle-filled coated sand shell, the obtained casting has the characteristics of fine and dense organization structures, thus ensuring the high strength and high toughness of the ductile iron of the outer layer 1. The coated sand shell of the high-strength ductile iron outer layer 1 consists of three parts: an outer shell 3, an inner shell 4 and a bottom 5, as in FIG. 3. Three sand shells are combined into one to form the cavity of the high-strength ductile iron outer shell 3. A gate is located at the top, which can maximally improve the process yield and the feeding effect, as in FIG. 4.

(20) During the centrifugal pouring of the molten iron of gray cast iron, an electromagnetic field with a magnetic field strength of 0.15-0.25 T is added. The electromagnetic field added during the centrifugal pouring of the molten iron of gray cast iron will generate an electromagnetic force, which may cause the tip of the flake graphite precipitated during solidification to become rounded and blunt, thus preventing the working face from cracking during the use of the brake drum, and at the same time having a significant effect on improving the thermal fatigue resistance performance. The electromagnetic field is turned off 1 minute after all the molten iron of gray cast iron enters the casting mould, and the rotating speed of the centrifuge is then raised to 1050-1100 rpm, which is mainly aimed to promote the low-density silicon carbide to be enriched on the inner surface of the composite brake drum, thereby improving the wear resistance of the brake drum. At the same time, the ductile iron shell of the outer layer 1 is cooled by spraying so as to prevent the strength of the ductile iron shell of the outer layer 1 from decreasing. After the molten iron is completely solidified, the rotating speed of the centrifuge is dropped to 100-120 rpm, the temperature is dropped to 500-580° C., the spray cooling is stopped and the centrifuge is shut down to take out the casting, which is finished to obtain the composite brake drum having excellent comprehensive performance.

Embodiment 2

(21) The outer layer 1 is made of high-strength ductile iron which is a grade of QT450-10 or above, preferably QT500-7 or QT600-3.

Embodiment 3

(22) The outer layer 1 is made of vermicular iron of grade RuT450 or RuT500.

(23) It should be noted that, it is apparent to those skilled in the art that the present disclosure is not limited to the details of the exemplary embodiments described above and that it can be realized in other specific forms without departing from the spirit or essential features of the present disclosure. Therefore, from every point of view, the embodiments should be regarded as exemplary rather than restrictive. The scope of the present disclosure is defined by the attached claims but not limited by the above description. Therefore, it is intended to encompass all variations falling within the meaning and scope of the equivalent elements of the claims within the present disclosure, and any reference numerals in the claims should not be considered to limit the claim involved.

(24) The principle and implementation of the present disclosure are illustrated by specific embodiments in the specification. The above description of embodiments is only for the purpose of assisting in understanding the method and core ideas of the present disclosure. At the same time, for persons with ordinary skills in the art, there will be variations in the specific implementation and application scope based on the ideas of the present disclosure. In summary, the contents of this specification should not be considered as the limitation of the present disclosure.