CN1297797A - Cam shaft of iron-base surface composite material and its manufacture - Google Patents

Abstract

In the camshaft with an iron-based surface composite material layer provided by the present invention, the cam matrix is high-strength gray cast iron or ductile iron, and the iron-based composite material layer on the working surface of the tip is composed of carbides or carbides uniformly distributed on the iron matrix. Oxide ceramic reinforced phase is combined, and there is a diffusion transition layer formed during casting and sintering between the two. Its manufacturing method is to make the corresponding powder into a compact, fix it after pre-sintering treatment or directly coat the powder on the surface of the mold, pour high-temperature molten iron, sinter and cool. The camshaft has high wear resistance, good comprehensive performance, less manufacturing process, short cycle time and low cost.

Description

Iron-based surface composite material camshaft and manufacturing method thereof

The invention belongs to the technical field of metal matrix composite products and its manufacture, and relates to a camshaft with iron-based surface composite materials reinforced by ceramic particles as a working surface and a manufacturing method thereof.

The camshaft is a key part of the intake and exhaust mechanism of the engine. With the increase of the speed and pressure of the high-speed engine, it is required to have the characteristics of being able to work normally under the conditions of high pressure, high speed and severe wear, but the existing hardenable type Neither the camshaft nor the chilled cast iron camshaft was adequate. Their cams either lack a hard reinforcement phase, or have a hard reinforcement phase with low hardness (only HV800), and their shape is poor, prone to peeling and pitting, so the cams of these two camshafts are prone to excessive wear, The incomplete combustion of the engine results in a decrease in power, an increase in fuel consumption and aggravation of environmental pollution.

One of the objectives of the present invention is to overcome the defects of existing camshafts and provide a camshaft with a sintered layer structure of iron-based surface composite material on the working surface.

At present, there is only the "casting and sintering method for preparing iron-based composite material" disclosed by the inventor in the application number 99114851.7 for the method of manufacturing the camshaft with the iron-based surface composite material sintered layer structure on the cam face. The process steps of the method include: manufacturing casting moulds, manufacturing compacts, fixing compacts, smelting molten iron, pouring and sintering. It is feasible to produce an iron-based surface composite material camshaft with more fusible components in the compact according to the process steps and conditions of the method, but because the cam part of the camshaft has a thin wall, generally less than 22mm, Therefore, when casting and pouring, the heat provided by the molten iron is not much. When the coating layer or compact contains more refractory components, it is difficult to complete the sintering and densification of the cam tip during the casting process, and black spots will appear. Skin, gray spots, slag and other defects. If the supplementary sintering measures disclosed in 99114851.7 are adopted, the energy consumption will be large and the completion period will be long. In addition, the binder used in the production of compacts in this method is a water-based binder, and the water contained therein evaporates slowly. Even after a long time of baking, it is not easy to be completely removed, and holes will be formed in the compacts. cause defects.

Therefore, the second object of the present invention is to solve the problems existing in the prior art, and provide a method that can ensure the sintering and densification of the green compact during the casting process, and has low energy consumption and short cycle time.

The third object of the present invention is to provide a method that can solve the problems caused by the use of water-based adhesives.

One of the objects of the present invention is achieved by such a technical solution: the camshaft shown in this technical solution is composed of a shaft bottom, a journal and a cam, and the working surface of the cam tip is an iron-based surface composite material layer , so that the working surface of the cam tip should have high wear resistance and good heat resistance and corrosion resistance; the cam body is ductile iron or gray cast iron to provide the strength, plasticity and toughness that the cam body should have; due to the iron base The surface composite material layer is formed by casting and sintering, so there is a diffusion transition layer between the cam matrix and the iron-based surface composite material layer to provide a strong metallurgical bond.

Among them, the iron-based surface composite material layer is composed of WC, VC, TiC, (Cr, Fe) ₇ C ₃ , (Cr, Fe ) ₂₃ C ₆ and other carbide ceramics or Al ₂ O ₃ , ZrO ₂ and other oxide ceramics or a combination of two or more ceramic reinforcement phases, and the thickness is controlled at 1-4mm. The material layer is formed by sintering and densifying the coating layer or compact on the surface of the casting mold at the cam tip of the camshaft using the heat of molten iron during the manufacturing process, and is finally formed at the cam tip.

The diffusion transition layer is composed of a carbide combination of uniformly distributed reticular chromium on the iron martensite or martensite+austenite or pearlite matrix, with a thickness of 0.5-1.5mm.

The second object of the present invention is achieved by adding a technical solution of a pre-sintering process on the basis of the process steps of the existing method, that is, after the green compact is manufactured, it is firstly pre-sintered and then fixed on the mold On the surface. The pre-sintering temperature is 500-1400°C, and the temperature is kept at this temperature for 10-120 minutes.

The third object of the present invention is achieved by adopting such a technical scheme of the binder with higher solvent volatility. Specifically, the binder used in the manufacture of the compact is an alcohol-based organic binder, and its addition is 2-7%. Since the alcohol solvent contained therein is volatile and can be burned off when ignited, the disadvantages of using water-based adhesives are completely eliminated. Not only that, for the organic binder, if the compact is pre-sintered, it can be completely decomposed and carbonized, which is very beneficial to avoid pores.

In order to improve the fluidity and lubricity of the powder, prevent the compact from collapsing, cracks, delamination and other defects, and improve the strength of the compact, 0.1-1.5% of molding agent can also be added when manufacturing the compact. The molding agent can be selected from one or both of zinc stearate, polyethylene glycol, buna rubber and paraffin.

In addition, because the present invention adopts the pre-sintering process, it is easy to complete the sintering and densification of the green compact during the casting process, so the pouring temperature of molten iron can be selected in a temperature range lower than that of the prior art, that is, 1400-1550°C. It is beneficial to reduce the consumption, reduce the oxidation and burning loss of molten iron, and improve the service life of the furnace lining.

Compared with the prior art, the present invention has the following advantages:

1. The camshaft with iron-based surface composite material layer provided by the present invention, because the cam working surface contains a large amount of high-hardness ceramic reinforcement phase (hardness HV1800-3000), and its shape is also very good, so the cam has both ceramic material It has high wear resistance and heat resistance, and maintains the high strength and high toughness of steel materials. It can be hard on the outside and tough on the inside. It has excellent comprehensive performance and can withstand higher loads and harsher working environments. Especially Suitable for modern high speed engines.

2. Since the manufacturing method provided by the present invention adds a pre-sintering process, it can not only ensure that the green compact containing more refractory components is sintered and densified during the casting process, and completely eliminate defects such as black skin, gray spots, and slag, but also The method of the present invention can also rapidly remove the alcohol solvent in the alcohol-based organic binder used in the manufacture of compacts, completely decompose and carbonize the organic binder, and avoid the generation of pores.

3. Because the present invention replaces the original water-based binder with an alcohol-based organic binder, the solvent in the binder is easy to remove, the removal time is short, there is no energy consumption, and holes in the sintered layer will not be caused.

4. Since the present invention also proposes that a molding agent can be added, the fluidity and lubricity of the powder can be improved, and defects such as collapse, cracks or delamination of the compact can be prevented, and the quality of the sintered layer of the iron-based composite material can be guaranteed.

5. Since the pouring temperature of the invention can be greatly reduced, not only the energy consumption is reduced, the oxidative burning loss of molten iron is reduced, but also the service life of the furnace lining is improved.

Description of drawings:

Fig. 1 is a schematic diagram of the front view of a camshaft of a four-cylinder engine;

Fig. 2 is an enlarged view of the A-A sectional structure of the cam in Fig. 1 .

The embodiments of the camshaft and the method for manufacturing the camshaft of the present invention are given below in conjunction with the accompanying drawings, and will be described in detail.

Example 1:

As shown in Figures 1 and 2, the camshaft of this embodiment is composed of a shaft bottom 1, a journal 2 and a cam 3, and the working surface of the tip of the cam 3 is located on the outer surface of the cam body 4, which is an iron-based surface composite material layer 5. It is carbonized by uniform distribution of WC, VC, TiC, (Cr, Fe) ₇ C ₃ , (Cr, Fe) ₂₃ C ₆ on the iron martensite or martensite + austenite or pearlite matrix It is composed of one or two or more ceramic reinforcing phases in material ceramics or oxide ceramics such as Al ₂ O ₃ , ZrO _{2 ,} etc., and the thickness is 1-4mm. Cam matrix 4 is made of ductile iron or gray cast iron. Since the iron-based surface composite material layer 5 is formed by casting and sintering, a diffusion transition layer 6 is also formed between the cam matrix 4 and the iron-based surface composite material 5 . The diffusion transition layer 6 is composed of carbides of iron martensite or martensite + austenite or pearlite matrix uniformly distributed reticular chromium, with a thickness of 0.5-1.5 mm.

Embodiment 2～7:

(1) Manufacture of casting molds Use coated sand, no-hardening resin sand or green mold sand to make casting molds of camshafts according to conventional methods.

(2) Manufacture the compact according to the combination ratio of Examples 2 to 7 listed in Table 1, place various powders with a particle size≤50 μm together in a ball mill, and add 8 to 20% of the total weight of the powder in absolute ethanol ; Wet mixing for 8 to 48 hours, the speed is 60 to 200 rpm.

The proportions of the components of the fusible alloy powder added in each embodiment are shown in Table 2.

Take out the mixed powder and dry it, add alcohol-based organic binder with 2-7% of the total weight of the powder, mix it evenly, put it into a metal mold on a hydraulic press, and press it with a unit pressure of 100-1000MPa to a thickness of 1 ~ 4mm compact. In addition, 0.1-1.5% of molding agent can be added to the powder. The molding agent can be one or both of zinc stearate, polyethylene glycol, buna rubber and paraffin.

(3) Pre-sintering treatment The compact is carried out pre-sintering treatment in a vacuum sintering furnace, and the temperature and holding time of each embodiment pre-sintering treatment are respectively:

Example 2 1300°C for 20-60 minutes

Example 3 1400°C for 10 to 60 minutes

Example 4 600°C for 40-80 minutes

Example 5 800°C for 30-70 minutes

Example 6 700°C for 40-80 minutes

Example 7 500°C for 50 to 120 minutes

(4) Fixing the green compact Fix the cooled green compact on the surface of the mold with a binder or steel wire. If it is fixed with an adhesive, the adhesive can be any one of 502 glue, PVA aqueous solution, water glass, etc.

(5) Smelting molten iron The corresponding charge is smelted in the induction furnace according to the conventional method, and the corresponding treatment is carried out.

(6) Pouring and sintering The high-temperature molten iron is poured into the mold at a pouring temperature of 1400-1550°C, and the heat of molten iron is used to complete the sintering and densification of the compact to form an iron-based surface composite material layer on the cam tip.

Embodiment 8～9:

In this embodiment, the composition of the green compact is made according to the composition ratio of Examples 8 to 9 listed in Tables 1 and 2, and the manufacturing process is the same as before except for the pre-sintering process, and is omitted. The difference is that none of the compacts in this embodiment have undergone pre-sintering treatment, but they all need to be ignited to burn off the alcohol-based solvent in the compacts.

Example 10:

The manufacturing process of this embodiment is the same as before, except that there is no compaction manufacturing, pre-sintering treatment or no treatment, and compaction fixing process. The powder formula for making compacts in this embodiment is the same as that in Example 8, and an alcohol-based organic binder accounting for 6-8% of the total powder weight is added to the powder to make a paste, which is directly coated on the molded cam. corresponding surface, and then ignite to burn off the alcohol-based solvent in the coating layer.

The present invention is not limited to the above embodiments.

Table 1

Table 2

Claims (9)

1. cam shaft of iron-base surface composite material, constitute by (1), axle journal (2) and cam (3) at the bottom of the axle, it is characterized in that cam parent (4) is spheroidal graphite cast iron or gray cast iron, the working surface of cam (3) is Fe-base surface compound material layer (5), and also has diffusion transition layer (6) between cam parent (4) and Fe-base surface compound material layer (5).

2. cam shaft of iron-base surface composite material according to claim 1, the thickness that it is characterized in that cam Fe-base surface compound material layer (5) is 1～4mm, the thickness of diffusion transition layer (6) is 0.5～1.5mm.

3. cam shaft of iron-base surface composite material according to claim 1 and 2, it is characterized in that cam Fe-base surface compound material layer (5) serve as reasons on the martensite of iron or martensite+austenite or pearlite matrix evenly distribution WC, VC, TiC, (Cr, Fe) ₇C ₃, (Cr, Fe) ₂₃C ₆Deng carbide ceramics or Al ₂O ₃, ZrO ₂Constitute Deng one or both or two or more ceramic enhancement phase in the oxide ceramics.

4. cam shaft of iron-base surface composite material according to claim 1 and 2 is characterized in that serve as reasons evenly the distribute carbide of netted chromium of diffusion transition layer (6) in the cam (3) constitutes on the martensite of iron or martensite+austenite or pearlite matrix.

5. method of making cam shaft of iron-base surface composite material, its process step has: make casting mold, make pressed compact, pressed compact is fixed, melting molten iron, cast and sintering, after it is characterized in that pressed compact is made, need to handle through presintering earlier to be fixed on the casting mold again, pre-sintering temperature is 500～1400 ℃, and is incubated 10～120 minutes under this temperature.

6. the method for manufacturing cam shaft of iron-base surface composite material according to claim 5 is characterized in that used Bond is the alcohol radical organic binder when making pressed compact, and its addition is 2～7%.

7. according to the method for claim 5 or 6 described manufacturing cam shaft of iron-base surface composite material, also added 0.1～1.5% forming agent when it is characterized in that making pressed compact.

8. the method for manufacturing cam shaft of iron-base surface composite material according to claim 7 is characterized in that used forming agent is one or both in zine stearate, polyethyleneglycol, buna, the paraffin.

9. according to the method for claim 5 or 6 or 8 described manufacturing cam shaft of iron-base surface composite material, it is characterized in that pouring temperature is 1400～1550 ℃.

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