CN111644599B - Three-dimensional continuous network structure graphite/cast steel composite material and preparation method thereof - Google Patents

Abstract

The invention provides a graphite/cast steel composite material with good antifriction property, shock absorption property, heat conductivity, electric conductivity, strength and toughness and lower density and thermal expansibility and a normal-pressure preparation method with low cost. The composite material is composed of interconnected network structure graphite and cast steel which are communicated with each other in three-dimensional space, and respective advantages of the graphite and the cast steel are combined, wherein the volume percentage of the graphite is 10% -50%. The preparation method comprises the following steps: (1) preparing a three-dimensional network graphite preform by adopting a polyurethane foam precursor slurry coating process and a chemical bonding heating curing method; (2) carrying out metallization treatment on the surface of the graphite preform; (3) and pouring molten steel into the graphite preform by adopting a normal-pressure casting infiltration method, and cooling and solidifying to obtain the graphite/cast steel composite material with the three-dimensional continuous network structure. The invention can be used as materials for self-lubricating antifriction, vibration reduction/sound insulation, heat conduction, electric conduction, electronic packaging and the like and applied to the fields of machinery, metallurgy, environmental protection, aerospace, electronics and the like.

Description

A kind of three-dimensional continuous network structure graphite/cast steel composite material and preparation method thereof

technical field

The invention relates to the field of metal matrix composite materials, in particular to a three-dimensional continuous network structure graphite/cast steel composite material and a normal pressure preparation method thereof.

Background technique

Three-dimensional Co-continuous Network Metal Matrix Composite (or Interpenetrating Network Metal Matrix Composite, INMMC for short) is a new field of composite material research that has been paid more and more attention by domestic and foreign material researchers in recent years. This composite material has a completely different form of spatial topology from traditional composite materials, that is, the metal matrix phase and the composite phase (or modified phase) are continuous (connected) in three-dimensional space, showing an interwoven network structure. This topological structure in which the two phases are intertwined and coiled, penetrated and penetrated each other in three-dimensional space is a brand-new composite modification structure in the field of synthetic materials. This structural form makes this type of material have more unique strength properties, anti-friction/anti-wear properties, vibration/sound insulation properties, thermodynamic properties, electromagnetic properties and chemical properties, etc., and has isotropic properties. Mechanical equipment, environmental protection, aerospace, electronic communications and other industries are used as anti-friction/anti-wear materials, high-damping vibration-absorbing/sound insulation materials, high-efficiency heat-conducting/conducting materials, high-temperature-resistant structural materials, and electronic packaging materials with good technology Feasibility, has a very broad development prospects.

In the field of mechanical equipment, gray cast iron is generally used as the material used to manufacture various fuselage, guide rails and other important parts, because it has good wear resistance, vibration damping, casting performance and low notch sensitivity, and It has good machinability, simple melting ingredients and low cost. However, the dynamic loads that various important and heavy machinery and equipment bear are becoming larger and more complex, and the related components are generating more and more serious vibration, fatigue and wear. To further reduce these hazards, materials with high strength, high damping, and high wear resistance are required at the same time.

In response to the above problems, we have taken the lead in developing a three-dimensional network structure silicon carbide/gray cast iron composite material at home and abroad. It is used to replace gray cast iron to manufacture important castings such as bed and guide rails. We use the polyurethane foam precursor hanging molding method and high-temperature sintering process to first prepare a silicon carbide foam preform with a uniform and inter-penetrating pore structure, and then perform surface metallization treatment on it, and then use the atmospheric pressure casting and infiltration molding process to prepare Three-dimensional network structure of silicon carbide/gray cast iron composites. The relative wear resistance of the composite material is as high as 4.7 times to 7.9 times that of gray cast iron, the average friction coefficient is 46% to 89% of that of gray cast iron, and the amplitude attenuation is faster than that of gray cast iron. Not as good as gray cast iron, it is difficult to meet the performance requirements of increasingly advanced and heavy machinery and equipment.

Ductile cast steel recently developed at home and abroad is also a new material with good anti-friction/wear resistance and shock absorption. Its strength is higher than that of gray cast iron, but its anti-friction/wear resistance and shock absorption are lower than those of cast iron . Its anti-wear properties are attributed to the supporting skeleton of carbides, and its anti-friction properties benefit from the self-lubricating ability of the graphite phase. If graphite is added, its anti-friction/wear resistance will be improved, but there will be too many carbides, and the graphite in molten steel will also float unevenly during the smelting and pouring process, resulting in uneven distribution of graphite, which will significantly reduce toughness and strength. Therefore, the graphite content of ductile cast steel generally cannot exceed 1.8%, and its performance improvement space is limited.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, and to provide a product with good friction reduction, shock absorption/sound insulation, strength, toughness, electrical/thermal conductivity, low density and thermal expansion at the same time. The three-dimensional continuous network structure graphite/cast steel composite material and the normal pressure preparation method thereof are simple in process and low in cost.

The technical solution of the three-dimensional continuous network structure graphite/cast steel composite material of the present invention is that the composite material is composed of interconnected network structure graphite and cast steel that are all connected in three-dimensional space, wherein the volume of graphite accounts for 10%～ 50%.

It can be seen from the above solutions that the composite material of the present invention combines the respective advantages of graphite and cast steel, and has unique strength properties, friction reduction properties, vibration reduction/sound insulation properties, electrical conductivity/thermal conductivity properties, and the like.

Further, the interconnected network structure graphite is obtained by impregnating a polyurethane foam precursor in a water-based graphite slurry, then extruding the excess slurry, and then drying and heating to solidify.

The technical solution adopted in the above-mentioned preparation method of the three-dimensional continuous network structure graphite/cast steel composite material is that the method comprises the following steps:

(1) The three-dimensional network graphite preform was prepared by the polyurethane foam precursor hanging molding process and the chemical bonding and heating curing method;

(2) Metallizing the surface of the three-dimensional network graphite preform to improve the wettability between graphite and steel;

(3) Using the normal pressure casting and infiltration method, pour molten steel into the three-dimensional network graphite preform with interconnected pores, and then cool and solidify to form a three-dimensional continuous network structure graphite/cast steel composite material.

In the present invention, cast steel is used as the metal matrix phase, graphite (flake graphite powder is used in the present invention) as the composite phase (modified phase), and the atmospheric pressure casting process is used to prepare the three-dimensional continuous network structure graphite/cast steel composite material; Graphite with excellent lubricating properties, and the graphite content can be changed in a wide range by changing the pore size and skeleton thickness of the graphite preform, and at the same time, the graphite distribution is networked and the distribution density is controllable, thereby significantly changing the anti-friction effect. The novel composite material obtained by the invention can simultaneously have good anti-friction/wear resistance, shock absorption/sound insulation, strength, toughness, electrical/thermal conductivity, low density and thermal expansion, and the production process is simple and the production cost is low. Low, can replace gray cast iron, ductile cast steel, three-dimensional network structure silicon carbide/gray cast iron composite materials for the manufacture of various fuselage, guide rails and other important parts.

Further, the specific steps of the step (1) are as follows:

a. Cut 5-25ppi (that is, the number of pores per inch) of the polyurethane foam material according to the shape and size requirements, and perform surface modification treatment on the obtained polyurethane foam material block to obtain a polyurethane foam precursor;

b. Prepare water-based graphite slurry;

c. Fully immerse the polyurethane foam precursor obtained in step a in the water-based graphite slurry prepared in step b, and extrude the excess slurry in the polyurethane foam precursor. After removing the extrusion force, the polyurethane foam precursor By virtue of its own elasticity, it returns to its original shape. At this time, a graphite slurry layer is evenly wrapped on the skeleton of the polyurethane foam precursor;

d. The polyurethane foam precursor wrapped with graphite slurry is naturally dried at room temperature, and then heated at an appropriate temperature to cause chemical bonding and curing, that is, a three-dimensional network structure graphite preform with required strength is obtained.

Still further, in the step a, the specific steps of performing the surface modification treatment on the polyurethane foam block are as follows: dipping with an aqueous solution of a polymer flocculant, and then naturally drying for use. By performing surface modification treatment on the polyurethane foam material block, the subsequent sizing molding process of the polyurethane foam precursor can be carried out more smoothly, and the sizing quality can be easily ensured.

Still further, the specific steps of preparing the water-based graphite slurry in the step b are: weighing the graphite powder, the binder, the rheological agent, the defoaming agent and the wetting agent respectively according to the mass percentage ratio; Wet the rheological agent with 3 to 10 times of tap water, stir and activate it, and store it for 24 hours for later use; then add graphite powder to the prepared rheological agent slurry, and add an appropriate amount of tap water to stir; then add the binder, Wetting agent and defoaming agent and appropriate amount of tap water, fully stirred for 30 to 60 minutes; finally processed with a colloid mill for more than 3 minutes; the processed slurry was allowed to stand for more than 24 hours for later use.

Further, calculated by mass fraction, the water-based graphite slurry includes the following components: 100% graphite powder, 5-14% binder, 1.7-3.8% rheology agent, 0.01-0.05% defoamer, moisturizing agent 0.01-0.05%, Wetting agent 0.2-0.5% and tap water, wherein, the addition amount of tap water is added according to the viscosity requirements of graphite slurry; the binder is silica sol and water-soluble phenolic resin, and the rheological agent includes sodium-based rector Stone powder and sodium carboxymethyl cellulose, calculated by mass fraction, sodium-based rectorite powder 1.5-3%, sodium carboxymethyl cellulose 0.2-0.8%, silica sol 3-8%, water-soluble phenolic resin 2-6% ; Described defoamer is n-butanol; Described wetting agent is fatty alcohol polyvinyl chloride ether. In the above scheme, the role of the binder is to obtain high strength; the role of the rheological agent is to make the slurry have better fluidity and thixotropy, so that the slurry is in a solidified state when it is at rest, and then resumes flow when it is stressed. The addition of wetting agent can improve the wetting properties of the polyurethane foam precursor and the slurry, so that the amount of the slurry on the foam increases. With the increase of the amount of the slurry on the polyurethane foam precursor , the bulk density of the polyurethane foam precursor increases, thereby increasing the strength of the prepared three-dimensional network structure graphite preform.

In addition, in the step d, the polyurethane foam precursor wrapped with the water-based graphite slurry is naturally dried at room temperature, and heated at an appropriate temperature to cause chemical bonding and curing. The specific steps are: soaking the polyurethane foam precursor. After the slurry is formed, it is naturally dried for more than 1 day, and then placed in a heating furnace to be heated to 350°C to 450°C for 2h to 3h.

In the above scheme, when the polyurethane foam precursor is heated and solidified, it is necessary to heat up slowly, so that the organic matter is fully volatilized and eliminated, otherwise the organic matter and structural water in it volatilize too fast, and it is easy to cause the foamed graphite body to generate greater stress. And cause damage; the heating temperature should not be too high, otherwise the polyurethane foam precursor will be ablated and the strength and plasticity of the preform will be reduced.

Further, in the step (2), the specific steps of metallizing the surface of the three-dimensional network graphite preform are as follows: using anhydrous ethanol to clean the three-dimensional network graphite preform, drying and saving it for later use, and then using polyethylene containing polyethylene The ethanol solution of butyral and phenolic resin is used to prepare the alloy powder into metal slurry, and the slurry is dip-coated on the surface of the cleaned three-dimensional network graphite preform, and then placed in a constant temperature and humidity drying oven at 100°C for drying. And save it for future use, wherein, the alloy powder is a mixture of Cu-Cr-Ti, Ti and Cr are added in an amount of 6 to 16%, the balance is Cu, and the addition of polyvinyl butyral and phenolic resin is alloy. 1 to 3% of the powder mixture, the viscosity of the metal paste was adjusted to (3 to 7) × 10 ^-3 Pa.s with ethanol.

By the above method, a layer of Cu-Cr-Ti metal film is coated on the surface of network graphite, which can replace the direct contact between metal and graphite, thereby improving the wettability of the graphite/metal interface, so that the subsequent recombination between graphite and metal can be carried out smoothly. , while avoiding the surface oxidation of graphite when it is in contact with high-temperature molten metal, and improving the mechanical properties of the composite material.

Further, the specific steps of the step (3) are: fixing the three-dimensional network graphite preform in the prepared resin sand mold cavity, under atmospheric pressure conditions, using the static pressure and dynamic pressure of molten steel under the action of natural gravity, The molten steel is poured into the three-dimensional network graphite preform, and cooled and solidified to form, that is, the three-dimensional continuous network structure graphite/cast steel composite material is obtained. When preparing the resin sand mold, the inner surface of the resin sand mold cavity is coated with a layer of alcohol Based on zircon powder coating or corundum powder coating, and immediately ignite and burn to dry the coating and prevent casting defects on the surface of the composite material.

It can be seen from the above scheme that the atmospheric pressure casting and infiltration molding process of the three-dimensional continuous network structure graphite/cast steel composite material is simple and the preparation cost is low; and the inner surface of the resin sand cavity is coated with a layer of alcohol-based zircon powder coating or corundum powder coating. It can prevent the surface of the composite material from being rough, and avoid casting defects such as sand washing, sand inclusion, and sand sticking.

Description of drawings

Fig. 1 is the macroscopic topography of described three-dimensional network graphite preform;

Figure 2 is a physical comparison diagram of the three-dimensional continuous network structure graphite/cast steel composite material and gray cast iron material prepared by the present invention.

Detailed ways

Hereinafter, the present invention will be described in detail with specific examples.

The composite material of the invention is composed of interconnected network structure graphite and cast steel that are all connected in three-dimensional space, wherein the volume ratio of graphite is 10% to 50%. In this embodiment, the volume ratio of graphite is specifically 18%, and flake graphite with excellent lubricating properties is used. The interconnected network structure graphite is obtained by impregnating a polyurethane foam precursor in a water-based graphite slurry, extruding excess slurry, and then drying and heating to solidify.

The preparation method of the above-mentioned composite material adopts the following steps:

(1) The three-dimensional network graphite preform was prepared by the polyurethane foam precursor hanging molding process and the chemical bonding and heating curing method;

(2) Metallizing the surface of the three-dimensional network graphite preform to improve the wettability between graphite and steel;

(3) Using the normal pressure casting and infiltration method, pour molten steel into the three-dimensional network graphite preform with interconnected pores, and then cool and solidify to form a three-dimensional continuous network structure graphite/cast steel composite material.

Specifically, the steps a, b, c, and d of preparing the three-dimensional network graphite preform by adopting the polyurethane foam precursor hanging molding process and the chemical bonding and heating curing method are shown in the following.

a. According to the shape and size requirements, the polyurethane foam material with the required pore size is cut into pieces, and the obtained polyurethane foam material block is subjected to surface modification treatment to obtain a polyurethane foam precursor.

In this step, the pore size of the polyurethane foam precursor basically determines the pore size of the final product foam, and the polyurethane foam precursor must have a certain degree of hydrophilicity and sufficient resilience to easily absorb the water-based graphite slurry. And to ensure that the shape can be quickly restored after the excess slurry is extruded. Based on this, the flexible polyurethane foam with a three-dimensional network skeleton structure is suitable for the production of the polyurethane foam precursor in the present invention. The material has strong hydrophilicity, good pore uniformity, high resilience, strong adsorption, and tensile strength. Large, high through porosity, less inter-network film, will not be torn when dipping slurry, can rebound after dipping slurry, avoid collapse and cause plugging. Specifically, in this embodiment, a polyurethane foam precursor with a pore size of 8 ppi is selected. In order to facilitate the subsequent slurry forming process of the polyurethane foam precursor, the polyurethane foam precursor needs to be subjected to surface modification treatment in advance before impregnating the graphite slurry. The specific steps of the surface modification treatment of the polyurethane foam block are as follows: the polyurethane foam block is impregnated with an aqueous solution of a polymer flocculant with a certain mass concentration, and then naturally dried for use to obtain a polyurethane foam precursor. In this embodiment, the aqueous polymer flocculant solution may be an aqueous solution of polyethyleneimine (PEI, polyethyleneimine) with a concentration of 15-20%; or may be an aqueous solution of polyacrylamide (PAA, polyacrylamide) with a concentration of 15-20% 25%.

b. Prepare water-based graphite slurry.

This step is specifically as follows: Weigh the flake graphite powder, the binder, the rheological agent, the defoaming agent and the wetting agent respectively according to the mass percentage ratio; firstly, wetting the rheological agent with 3 to 10 times of tap water and stirring Activated and stored for 24 hours for later use; then add graphite powder to the prepared rheology agent slurry, and at the same time add an appropriate amount of tap water to stir; then add binder, wetting agent, defoaming agent and appropriate amount of tap water one by one, and fully stir for 30 ~60min; finally, use a colloid mill to process for more than 3 min, and then leave the processed slurry to stand and age for more than 24h for use to obtain a water-based graphite slurry. Here, the flake graphite powder of 325 mesh is selected (fine 325 mesh, carbon content ≥ 97%, spherical particles are preferred), and tap water is used as the solvent. Specifically, calculated by mass fraction, the water-based graphite slurry includes the following components: 100% of flake graphite powder, 5-14% of binder, 1.7-3.8% of rheology agent, 0.01-0.05% of defoamer, Wetting agent 0.2 to 0.5% and tap water, wherein the amount of tap water is added according to the viscosity requirements of the graphite slurry. In the present invention, the viscosity of the water-based graphite slurry is controlled at 0.01-0.05 Pa s. More specifically, the binder is silica sol and water-soluble phenolic resin, and the rheological agent includes sodium-based rectorite powder (sodium-based LT powder) and sodium carboxymethylcellulose (CMC), calculated by mass fraction , sodium-based rectorite powder 1.5-3%, sodium carboxymethyl cellulose 0.2-0.8%, silica sol 3-8%, water-soluble phenolic resin 2-6%, the defoamer is n-butanol, the The wetting agent is fatty alcohol polyvinyl chloride ether. The function of the rheological agent is to make the slurry have better fluidity and thixotropy, so that the slurry is in a solidified state when it is still, and restores its fluidity when it is stressed; the addition of a wetting agent can improve the polyurethane foam precursor. The wettability with the slurry increases the amount of the slurry on the foam. With the increase in the amount of the slurry on the polyurethane foam precursor, the bulk density of the polyurethane foam precursor increases, so that the The strength of the obtained three-dimensional network structure graphite preform is increased. After completing the configuration of the graphite slurry, before the precursor hanging process, use a rotational viscometer to measure the viscosity of the slurry, and control the viscosity of the slurry to 0.01-0.05 Pa s, so as to facilitate the coating and hanging, and it will not be blocked due to hole blocking. affects the porosity.

c. Fully immerse the polyurethane foam precursor obtained in step a in the water-based graphite slurry prepared in step b, and extrude the excess slurry in the polyurethane foam precursor. After removing the extrusion force, the polyurethane foam precursor By virtue of its own elasticity, it returns to its original shape. At this time, a graphite slurry layer is evenly wrapped on the skeleton of the polyurethane foam precursor. In this embodiment, the thickness of the graphite slurry layer depends on the pore size specification of the polyurethane foam precursor. The larger the pore size of the precursor, the larger the thickness of the graphite slurry layer. For the 8ppi polyurethane foam precursor, the graphite slurry layer thickness is 0.2 to 0.4 mm. The graphite slurry layer is used to wrap the skeleton of the precursor to a certain thickness, thereby enhancing the strength of the precursor and ensuring that the through porosity and adsorption tensile strength of the precursor are good. To ensure that the entire precursor will not be torn, and can quickly rebound after immersion in the slurry to avoid collapse and cause hole plugging.

In step c, it should be noted that the pretreated polyurethane foam precursor needs to be repeatedly squeezed to remove air before dipping into the slurry. When the slurry is impregnated, it needs to be uniform and consistent to avoid local insufficient infiltration. After dipping, it is necessary to knead repeatedly to make the slurry evenly adhere to the pores of the polyurethane foam precursor with a three-dimensional network structure, and at the same time extrude the excess slurry to ensure that the material has a high porosity. Observed under the light, the product should be evenly transparent. The pore size of the obtained polyurethane foam precursor should be basically the same.

The specific impregnation molding process is as follows:

1) Put the tools (enamel plate, hand-push drum, balance scale, etc.) required for the hanging operation on the designated position of the workbench;

2) Wear medical rubber gloves on the left hand;

3) Pour the slurry into the porcelain basin;

4) Immerse the polyurethane foam precursor into the slurry, and gently pinch the polyurethane foam material by hand;

5) Put the polyurethane foam precursor with graphite slurry into the enamel basin, roll it back and forth with a manual roller and beat it several times;

6) Observed under the light, the product should be uniformly light-transmitting, and those that are not light-transmitting should be tapped or rolled with a roller;

7) Weigh the product with a balance and adjust its weight according to technical requirements;

8) After shaping, place the product neatly on the aluminum plate covered with thin paper.

d. The polyurethane foam precursor wrapped with graphite slurry is naturally dried at room temperature, and then heated at an appropriate temperature to cause chemical bonding and curing, that is, a three-dimensional network structure graphite preform with required strength is obtained.

This step is carried out after the dip molding process. After the polyurethane foam precursor is dipped and formed, it is naturally dried for more than 1 day, and then placed in a heating furnace and heated to 350°C to 450°C, kept for 2h to 3h, and cooled to room temperature after 3h to obtain a three-dimensional network structure graphite preform. .

The key to heating and curing is to control the heating temperature and speed. It is necessary to heat up slowly, so that the organic matter can be fully volatilized and eliminated, otherwise the organic matter and structural water in it will volatilize too fast, and it is easy to cause the foamed graphite body to generate large stress and cause damage; the heating temperature should not be too high, otherwise it will cause damage. The ablation of the polyurethane foam precursor reduces the strength and plasticity of the preform.

The physical properties of the prepared three-dimensional network graphite preform are shown in the following table.

After the preparation of the three-dimensional network structure graphite preform, it is necessary to modify the surface of the graphite preform to improve the wettability between graphite and steel, and enhance the wetting and casting infiltration ability of metal to graphite, thereby improving the Mechanical properties of composite materials. The invention adopts the metallization treatment process to modify the surface of the graphite material, and coats a layer of Cu-Cr-Ti metal film on the surface of the network graphite, which can replace the direct contact between the metal and the graphite, thereby improving the wettability of the graphite/metal interface , so that the subsequent composite between graphite and metal can be smoothly carried out, and at the same time, the surface oxidation of graphite when it is in contact with the high-temperature metal liquid can be avoided, and the mechanical properties of the composite material can be improved.

The specific steps of metallizing the surface of the three-dimensional network graphite preform in the present invention are as follows: using anhydrous ethanol to clean the three-dimensional network graphite preform, drying and saving it for later use, and then using a polyvinyl butyral and phenolic resin containing The alloy powder is prepared into a metal slurry by ethanol solution, the slurry is dip-coated on the surface of the cleaned three-dimensional network graphite preform, and then placed in a constant temperature and humidity drying oven at 100 ° C for drying and storage for future use. It is a mixture of Cu-Cr-Ti, the addition amount of Ti and Cr is 6-16% respectively, the balance is Cu, and the addition amount of polyvinyl butyral and phenolic resin is 1-3% of the alloy powder mixture, respectively. The viscosity of the metal paste was adjusted to (3 to 7)×10 ^-3 Pa.s with ethanol.

Here, when copper is bonded with materials with different expansion coefficients at high temperature, it can alleviate the stress generated at the bonding interface, and after copper is melted, it can well wet graphite or penetrate into the graphite body, thereby enhancing the relationship between graphite and copper. bonding force between. Adding an appropriate amount (12%-16%) of Ti and Cr to Cu can reduce the wetting angle of Cu and C at 1100 °C from 140° to a wetting angle ≤ 23° to promote interfacial bonding.

After completing the preparation of the three-dimensional network graphite preform in step (1), and performing metallization on the surface of the three-dimensional network graphite preform in step (2), enter the three-dimensional continuous network structure graphite/cast steel composite in step (3). Material preparation: Using the normal pressure casting and infiltration method, under atmospheric pressure conditions, pour molten steel into the prefabricated three-dimensional network graphite preform with interconnected pores to obtain a three-dimensional continuous network structure graphite/cast steel composite material.

The specific process is as follows: the three-dimensional continuous network structure graphite preform is pre-fixed in the resin sand cavity, and under atmospheric pressure conditions, only the static pressure and dynamic pressure of the molten steel under the action of natural gravity are used to pour the molten steel into the three-dimensional network graphite. The prefabricated body is cooled and solidified to form a graphite/cast steel composite material with a three-dimensional continuous network structure.

In this process, the materials used include metallized three-dimensional network graphite preform, silica sand, furan resin, organic sulfonic acid solution curing agent, sample model, alcohol-based zircon powder or corundum powder coating, sand box, Metal charge, etc. The specific process is as follows.

(1) Modeling method

The sand mold is made of furan resin no-bake sand.

The ratio (mass ratio) of silica sand, furan resin and organic sulfonic acid solution curing agent is shown in the following table.

Mixing process: using a batch sand mixer, first mix the silica sand and the organic sulfonic acid solution curing agent for 2 minutes, then add the resin binder and continue mixing for 1 minute, and then the sand will be produced immediately.

Molding process: Fill the sand box with resin self-hardening sand mixed evenly, and demould after curing and molding.

(2) Casting process

In order to increase the static pressure and dynamic pressure of molten iron and make the pouring position favorable for molten steel filling and casting feeding, top casting is used. Put the sprue and the entire sample cavity completely in the lower box, the sprue is located on the upper mold, and try to increase the height of the upper mold and the sprue cup, so that the gating system can fully exert the feeding effect during the liquid shrinkage. Select a larger cross-sectional area of the inner runner, pour as quickly as possible, and use a closed pouring system, that is, ΣF straight > ΣF horizontal > ΣF inner. The height of the indenter shall not be less than 240mm.

(3) Paint

In order to obtain castings with smooth surface and avoid casting defects such as sand flushing, sand inclusion, and sticking sand, a layer of alcohol-based zircon powder coating or corundum powder coating is applied to the inner surface of the cavity, and the coating is immediately ignited and burned to dry the coating. .

(4) molten steel smelting

Use cast carbon steel of ZG200-400 and above grades.

(5) Pouring temperature

In order to improve the filling ability of molten steel and the wettability with the surface of the three-dimensional network graphite preform, the pouring temperature should be as high as possible, around 1480 °C. Within a certain temperature, the surface energy of liquid metal will decrease linearly with the increase of temperature, and the wetting angle of metal and graphite will decrease with the increase of temperature.

(6) Unpacking time

In order to reduce the thermal stress caused by uneven wall thickness during the cooling process, it is required to pour for 5 hours before opening the box. At this point, a three-dimensional continuous network structure graphite/cast steel composite material is obtained, as shown in the upper part of Figure 2 (the lower part of Figure 2). for gray cast iron).

The obtained three-dimensional continuous network structure graphite/cast steel composite material was wire-cut and the cross-sectional morphology was observed. It was found that the graphite skeleton was relatively uniformly distributed in the metal matrix, the graphite/cast steel interface was clear, and there was no obvious reaction layer. There are obvious casting defects such as holes and pores, and the casting infiltration effect is ideal. After testing, the main properties of the three-dimensional network structure graphite/cast steel composite material prepared by the present invention are as follows:

Bulk density ≤6.8g/cm ³ , which is more than 6% lower than that of gray cast iron;

Tensile strength ≥230MPa, more than 50% higher than gray cast iron;

The relative wear resistance is more than 6.5 times that of gray cast iron;

The average friction coefficient is below 74% of gray cast iron;

The damping ratio is more than 2.1 times that of gray cast iron.

It can be seen that the antifriction/wear resistance and shock absorption/sound insulation properties of the new composite material prepared by the method of the present invention are significantly improved than those of gray cast iron, the density is lower, and the strength basically reaches the level of gray cast iron, and the production process of atmospheric pressure casting is compared. Simple and low production cost, it can replace gray cast iron and ductile cast steel to manufacture important parts such as fuselage and guide rails of various important and heavy machinery and equipment, and obtain better use effects.

The present invention can be used as anti-friction/anti-friction material, high-damping vibration-absorbing/sound insulation material, high-efficiency electrical/thermal conductivity material, high-temperature resistant structural material, electronic packaging material, etc. in mechanical equipment, environmental protection, aerospace, electronic communication, etc. industry.

Claims (6)

1. A preparation method of a three-dimensional continuous network structure graphite/cast steel composite material is characterized in that the composite material is composed of network structure graphite and cast steel which are communicated in a three-dimensional space, wherein the volume ratio of the graphite is 10-50%; the network structure graphite is prepared by dipping a polyurethane foam precursor into water-based graphite slurry, extruding redundant slurry, drying and heating for curing, and the method comprises the following steps:

(1) preparing a three-dimensional network graphite preform by adopting a polyurethane foam precursor slurry coating forming process and a chemical bonding heating curing method;

(2) carrying out metallization treatment on the surface of the three-dimensional network graphite preform to improve the wettability between graphite and steel;

(3) pouring molten steel into the three-dimensional network graphite preform communicated with the pores by adopting a normal-pressure casting infiltration method, and cooling, solidifying and forming to prepare a graphite/cast steel composite material with a three-dimensional continuous network structure; the cast steel is cast carbon steel with ZG200-400 and above;

the specific steps of the step (1) are as follows:

a. cutting 5-25 ppi of soft polyurethane foam material with a three-dimensional network skeleton structure into blocks according to shape and size requirements, and carrying out surface modification treatment on the obtained polyurethane foam material blocks to obtain a polyurethane foam precursor, wherein ppi is the number of holes per inch of length;

b. preparing water-based graphite slurry;

c. fully soaking the polyurethane foam precursor obtained in the step a in the water-based graphite slurry prepared in the step b, extruding redundant slurry in the polyurethane foam precursor, recovering the polyurethane foam precursor to the original shape by virtue of the elasticity of the polyurethane foam precursor after the extrusion force is removed, and uniformly wrapping a layer of graphite slurry layer on the framework of the polyurethane foam precursor;

d. naturally drying the polyurethane foam precursor wrapped with the graphite slurry at normal temperature, and heating at 350-450 ℃ to perform chemical bonding and curing to obtain a three-dimensional network structure graphite preform with required strength;

the step (2) of carrying out metallization treatment on the surface of the three-dimensional network graphite preform comprises the following specific steps: cleaning a three-dimensional network graphite preform by using absolute ethyl alcohol, drying and storing for later use, preparing alloy powder into metal slurry by using an ethanol solution containing polyvinyl butyral and phenolic resin, dip-coating the slurry on the surface of the cleaned three-dimensional network graphite preform, then placing the three-dimensional network graphite preform into a constant-temperature constant-humidity drying oven at 100 ℃ for drying and storing for later use, wherein the alloy powder is a Cu-Cr-Ti mixture, the addition amounts of Ti and Cr are respectively 6-16%, the balance is Cu, the addition amounts of polyvinyl butyral and phenolic resin are respectively 1-3% of the alloy powder mixture, and the viscosity of the metal slurry is adjusted to (3-7) x 10-3 Pa.s by using ethanol.

2. The method for preparing the three-dimensional continuous network structure graphite/cast steel composite material as claimed in claim 1, wherein the step a of performing surface modification treatment on the polyurethane foam material block comprises the following specific steps: and (2) carrying out dipping treatment by adopting a polymeric flocculant aqueous solution, and then naturally drying for later use, wherein the polymeric flocculant is a polyethyleneimine aqueous solution with the concentration of 15-20% or a polyacrylamide aqueous solution with the concentration of 15-25%.

3. The method for preparing the three-dimensional continuous network structure graphite/cast steel composite material as claimed in claim 1, wherein the step b of preparing the water-based graphite slurry comprises the following specific steps: respectively weighing graphite powder, a binder, a rheological agent, a defoaming agent and a wetting agent according to the mass percentage for later use; wetting a rheological agent by using tap water of which the volume is 3-10 times that of the rheological agent, stirring and activating the rheological agent, and storing the rheological agent for later use after 24 hours; adding graphite powder into the prepared rheological agent slurry, and simultaneously adding a proper amount of tap water for stirring; then, sequentially adding a binder, a wetting agent, a defoaming agent and a proper amount of tap water, and fully stirring for 30-60 min; finally processing for more than 3 min by using a colloid mill; and standing and aging the processed slurry for more than 24 hours for later use.

4. The method for preparing a three-dimensional continuous network structure graphite/cast steel composite material as claimed in claim 3, wherein the water-based graphite slurry comprises the following components by mass fraction: 100% of graphite powder, 5-14% of binder, 1.7-3.8% of rheological agent, 0.01-0.05% of defoaming agent, 0.2-0.5% of wetting agent and tap water, wherein the addition amount of the tap water is added according to the viscosity requirement of the graphite slurry; the binder is silica sol and water-soluble phenolic resin; the rheological agent comprises sodium-based rectorite powder and sodium carboxymethylcellulose, and the mass fractions of the rheological agent include 1.5-3% of the sodium-based rectorite powder, 0.2-0.8% of the sodium carboxymethylcellulose, 3-8% of silica sol and 2-6% of water-soluble phenolic resin; the defoaming agent is n-butyl alcohol, and the wetting agent is fatty alcohol polyvinyl chloride ether.

5. The method for preparing the graphite/cast steel composite material with the three-dimensional continuous network structure as claimed in claim 1, wherein the step d of naturally drying the polyurethane foam precursor wrapped with the water-based graphite slurry at normal temperature and heating at a proper temperature to cause chemical bonding and solidification comprises the following specific steps: after the polyurethane foam precursor is subjected to slurry dipping and molding, the polyurethane foam precursor is naturally dried for more than 1 day, then the polyurethane foam precursor is put into a heating furnace to be heated to 350-450 ℃, the temperature is kept for 2-3 h, and after 3h, the polyurethane foam precursor is taken out of the furnace to be naturally cooled to normal temperature, so that the graphite preform with the three-dimensional network structure can be obtained.

6. The method for preparing the three-dimensional continuous network structure graphite/cast steel composite material as claimed in claim 1, wherein the step (3) comprises the following specific steps: fixing the three-dimensional network graphite preform in a prepared resin sand cavity, pouring molten steel into the three-dimensional network graphite preform by utilizing static pressure and dynamic pressure of the molten steel under the action of natural gravity under the condition of atmospheric pressure, and cooling, solidifying and forming to obtain the graphite/cast steel composite material with the three-dimensional continuous network structure; when the resin sand mold is prepared, a layer of alcohol-based zircon powder coating or corundum powder coating is coated on the inner surface of a resin sand mold cavity, and ignition and combustion are immediately carried out, so that the coating is dried, and casting defects on the surface of the composite material are prevented.

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