KR19990009039A - Engine tappet with excellent wear resistance and its manufacturing method - Google Patents

Abstract

The present invention relates to an engine tappet having excellent wear resistance and a method for manufacturing the same, in particular, WC 44 to 80wt%, Co 4 to 10wt%, Ni 15 to 50wt%, Cr 5 to 20wt%, B 0.5 to 4wt% Hard coating layer containing alloy powder containing Fe 2 ~ 4wt%, Si 0.5 ~ 4wt%, C 1.0wt% or less and Cu, Mo etc. are inevitably mixed with impurities. It relates to an engine tappet excellent in wear resistance, characterized in that formed on the contact surface.

In addition, the present invention is in contact with the cam in the body of the tappet WC 44 ~ 80wt%, Co 4 ~ 10wt%, Ni 15 ~ 50wt%, Cr 5 ~ 20wt%, B 0.5 ~ 4wt%, Fe 2 ~ 4wt%, Si After the thermal spray coating on the alloy powder material containing 0.5 to 4wt%, C 1.0wt% or less, Cu, Mo and the like inevitably mixed impurity, characterized in that the coating layer is remelted The present invention relates to a method for producing an engine tappet having excellent wear resistance.

Description

Engine tappet with excellent wear resistance and its manufacturing method

The present invention relates to an engine tappet having excellent wear resistance and a method for manufacturing the same. Particularly, in an OHC type oversized diesel engine, a lower end of a push rod in a valve train composed of a rocker arm, a push rod, and a tappet It relates to a high wear resistance engine tappet (Tappet) and a method of manufacturing the same to form a high hardness coating layer of a material having a high melting point and low adhesion to the cam material on the surface of the tappet perturbing along the outer peripheral surface of the cam while being connected to .

In general, as shown in Fig. 1, the mechanism for opening and closing the cylinder valve 1 in the engine is called a valve train system, and the valve train includes a rocker arm 3, a push rod 4, and a tappet 5. have.

At this time, the tappet 5 is coupled to the lower end of the push rod 4 and perturbed to the outer circumferential surface of the cam 6, and reciprocates the push rod while moving in accordance with the displacement of the outer circumferential surface of the cam.

Recently, as the demand for high power, high fuel consumption, and maintenance-free engines has increased due to environmental protection and consumer protection campaigns, the operating environment of the valve train system is becoming more severe and requires a long life.

Therefore, damage to the valve train system causes incomplete combustion, which increases exhaust gas and soot, and excessively decreases the performance of the entire vehicle system as the engine noise and vibration become excessive.

Among them, the failure of the tappet 5, which is a key element, is mainly due to sliding friction at high speed in contact with the cam 6, and thus peeling phenomenon due to scuffing or surface fatigue caused by sliding wear. In-fittings dominate.

At this time, when scuffing and fitting occurs on the surface of the tappet (5), the wear is rapidly developed, so the fuel is incompletely burned due to the increase of engine noise, the inconsistent timing of valve opening and closing, or the instability of the valve tightness. Will give birth to.

Another problem is that if the tappet 5 has an error exceeding the allowable range or excessive abrasion occurs in the perturbation with the cam 6, accurate vertical contact is not made and the load is parallel to the cam shaft 7. May cause active cam walking.

Generally, steel and cast iron are widely used as materials of the cam 6 and the tappet 5, and various techniques such as high frequency induction hardening, carburizing, and nitriding are used as the surface hardening technology of the steel, and all of them improve the hardness of the surface. In addition, compressive stress is retained to impart wear resistance and fatigue resistance.

In addition, in the case of using the chilled cast iron (Chilled Cast Iron) as the material of the cam (6) and tappet (5), the seven cast iron and quenched cast iron system is typical.

And the cast iron system used as the tappet (5) is to precipitate the cementite cementite (Fe₃C) by increasing the cooling rate at the time of casting, and in the metallographic structure, the pearlite base changed from austenite by A1 transformation and Consists of needle cementite.

In addition, quenching cast iron is quenched and tempered (Quenching Tempering) for the cast iron, the base is martensite, or tempered (martensite) martensite, consisting of tempered carbon decomposed from cementite and cementite.

The reason why many of these materials are used is that cementite has high hardness, excellent wear resistance, and excellent scuffing effect and fitting resistance because the matrix structure prevents plastic flow.

However, currently widely used seven cast iron or quenched cast iron is excellent tappet material as described, but because the casting is a material inherent many problems.

For example, quenched cast iron is a material that undergoes complex processes such as melting, quenching, annealing, quenching, and tempering.If the chemical composition, cooling rate, and heat treatment conditions are uneven, the amount of cementite and carbon Alternatively, since the hardness of the matrix is easily decomposed due to frictional heat and high surface pressure, the wear resistance and scuffing resistance are likely to be nonuniform.

In addition, there is a method of manufacturing a hardened tappet by carburizing carbon steel or alloy steel to martensite the surface, and it is known that martensite has lower abrasion resistance than seven cast irons due to its lower thermal stability and hardness than cementite.

In addition, when the cast iron material is used in a high efficiency engine where the contact surface pressure (load) of the cam and tappet continues to increase, not only strict production control, quality control, and process control but also heat resistance must be sufficiently satisfied. Difficult to withstand the high surface pressure required by high horsepower engines

Therefore, as described above, the conditions for using the valve train system, such as increase in valve lift, increase intake / exhaust valve size, and increase in valve spring load to meet the market demand of high output and low fuel consumption, will be severe. In response to the tendency of load to increase at the contact of, there is a need for a tappet material with excellent durability and wear resistance that can solve the problems of the current material.

In order to overcome this, Japanese Patent Application No. 62-182407 and Japanese Patent Application No. 62-185806 present rocker arms and tappets for joining sintered layers of high-melting cemented carbide powders containing carbide, nitride and boride together with nickel powder. have.

However, in these patents, only the concept of bonding cemented carbide layer is introduced, and the manufacturing cost including the material cost is very high without the detailed manufacturing technique or the specific method of achieving the dilution.

The present invention is a high melting point on the surface of the tappet perturbing along the outer circumference of the cam while being connected to the lower end of the push rod of the valve train consisting of a rocker arm, a push rod, and a tappet in an OHC (Over Head Cam) type large diesel engine It is an object of the present invention to provide an engine tappet having excellent abrasion resistance and a method of manufacturing the same, wherein a coating layer having a high hardness is formed of a material having low adhesion to a material.

In order to achieve the above object, the present invention is WC 44 ~ 80wt%, Co 4 ~ 10wt%, Ni 15 ~ 50wt%, Cr 5 ~ 20wt%, B 0.5 ~ 4wt%, Fe 2 ~ 4wt%, Si 0.5 ~ 4wt Wear resistance characterized by forming a hard coating layer made of alloy powder material containing%, C 1.0wt% or less, and Cu, Mo, etc., which are inevitably mixed with impurities, on the contact surface of the body of the tappet with the cam. Provides excellent engine tappets.

In addition, the present invention is in contact with the cam in the body of the tappet WC 44 ~ 80wt%, Co 4 ~ 10wt%, Ni 15 ~ 50wt%, Cr 5 ~ 20wt%, B 0.5 ~ 4wt%, Fe 2 ~ 4wt%, Si After the thermal spray coating on the alloy powder material containing 0.5 to 4wt%, C 1.0wt% or less, Cu, Mo and the like inevitably mixed impurity, characterized in that the coating layer is remelted Provided is a method for producing an engine tappet having excellent wear resistance.

Hereinafter, the present invention will be described in detail.

In general, the cause of scuffing during breakage of the tappets is that if the entire diameter is in linear contact when the tappets and the cams are in line contact, the tappets stop and do not rotate and mainly cause sliding friction. This is because wear is caused by repeated local friction.

In addition, even if the rolling contact is made by the rotation of the counterparts when the tappet and the cam contact, if the hardness is less than HV800, higher hardness is preferable because the effect is not expected in terms of pitting resistance performance due to repeated fatigue.

In addition, the local tappet surface peeling off due to excessive surface pressure and frictional wear causes rapid lateral crack growth, encroaching on adjacent surfaces, and eventually causing the surface to fall off, resulting in deterioration of component life. Needs to be hardened.

On the other hand, because the cam and the tappet make sliding contact, the surface state of the other side affects the relative surface, and if there is a metal chemical affinity, adhesion or sintering occurs between the surfaces.

At this time, the adhesion increases the friction coefficient again, and the increase of the friction coefficient causes the surface of the lower side of the hardness of the frictional heat to be damaged, and the resulting wear particles are in a state of increasing hardness than the original due to the work hardening effect.

Here, the surface where the wear progressed becomes rough surface roughness is to attack the relative surface.

Therefore, as a method for reducing the wear between the contact surface of the cam and the tappet, the friction coefficient is reduced to reduce the frictional heat generated from the contact surface, and the scuffing resistance is improved by using a material of high melting point (high melting point carbide or nitride), Attempt to increase the contact surface matrix structure to increase the fatigue strength and to improve the fitting resistance, and to prevent damage to the cam surface by selecting a material with low adhesion and cam aggression to the cam material.

In the present invention, the coating layer formed by using a material having a high melting point and low adhesion to the cam material ensures a high hardness value, thereby providing a surface property excellent in scuffing resistance and fitting resistance by tappets, thermal spraying and remelting treatment. It relates to a manufacturing method.

And the present invention is achieved by providing a tappet excellent in wear resistance, characterized in that the body made of carbon steel or low alloy steel and the cam contact surface of the body is a flame spraying or high speed salt spray coating of the thermal spraying material.

The thermal spraying material of the thermal spray coating layer uses a tungsten carbide employing Co as a binder in a hard phase and is formed by mixing a nickel-chromium base alloy.

In general, the parts or parts that require abrasion resistance may have a difference in behavior depending on the use environment, but two characteristics must be provided to satisfy the required quality, such as fitting resistance and scuffing characteristics.

Therefore, in the present invention, in order to reinforce adhesion wear, that is, slip resistance in terms of obtaining scuffing resistance, tungsten carbide (WC), a hard compound having a Vickers hardness of 1300 or more, was used. The content of Co and Ni-based self-alloying was adjusted to give excellent toughness in the rolling friction state.

The coating powder is largely divided into tungsten carbide reinforcement phase and base alloy, and in view of the component ratio, tungsten carbide and cobalt, which are reinforcement phases, are usually produced in a weight ratio of 88:12.

Because tungsten carbide is easily exposed to the oxidizing atmosphere during the spray coating process in an appropriate atmosphere environment, particles are lost due to oxidation in flight or become weak and unstable in the stable WC, and become metastable such as W₂C, η and ε. In addition, in order to secure the toughness of the coating structure, Co must be mixed and then agglomerated into lumps of appropriate size by sintering and equivalent processes.

The lump size of the carbide thus prepared is usually several micrometers to several hundred micrometers, but the particle size of the carbide itself before forming into a lump form is a fine grain which does not exceed 5-7 micrometers at maximum, and should be distributed in size within 1-5 micrometers normally.

This is because when the particle size of the carbide alone is too large, the coating surface acts as a factor that may cause abrasion, such as severe scoring, on the contact surface of the counterpart when friction wear with the counterpart.

Through experiments, particles with an average size of 10 μm or more of WC cause scuffing wear on the counter cam, and tappets show that fitting wear of Orobis classification number 6-8 occurs. I learned.

As a result, when using particles with an average particle size of 5μm or less, Orobis classification number 9 or more satisfactory wear results were obtained, and when treated under 2μm on average, 10 times showed no signs of damage such as scuffing at all. The more satisfactory wear state was obtained.

Carbide alone contained 44 wt% as the lower limit by weight (wt%) and contained up to 80 wt% as the highest content.

If the tungsten carbide is 44wt% or less, the sliding resistance of the wear resistance required by the tappet for a high power engine, which is the object of the present invention, is inferior, and it is very disadvantageous to the occurrence of fitting due to the low hardness.

On the contrary, in the case of containing more than 80wt% of carbide, the role of the binding metal is difficult to be expected, and the sprayed layer shows very low density and fragility, so brittle fracture occurs in a high surface pressure use environment.

At this time, Co forms a total solid solution with Ni as 4-10 wt%, and strengthens Ni together with other additive elements in the alloy to improve wear resistance and protect the WC phase. However, the price of Co is expensive and more than 10wt% is ineffective, so it is limited.

The base alloy contains 15 to 50 wt% of Ni, 5 to 20 wt% of Cr, 5 to 4 wt% of B, 5 to 4 wt% of Fe, 0.5 to 4 wt% of Si, 1.0 wt% of C, and Cu and Mo impurities. It may contain 1.0wt%. The alloy thus produced has a much lower melting point than that in the conventional in situ composition, since B, Si, etc., have a process composition with Ni and Cr.

Accordingly, the spray defects such as pores and oxides present in the coating film coated by flame or high speed flame spray can be easily removed by remelting by an external heating source.

That is, since only the coating film is heated up to the melting point without damage or melting on the surface of the reinforcing phase and the coating base material, there is almost no pore and a metal bond is obtained between the base material and the coating film.

Here, Ni and Co, which are physically and chemically similar in the composition of the base alloy, may substitute a role, and thus, cobalt may be used as a mother alloy instead of nickel.

The reason for limiting the base alloy composition range used in the present invention is described below.

Ni is suitable as a coating material for tappets, which has affinity with steel, which is the body material of tappet, hardness and modulus of elasticity equal to steel, and has excellent heat resistance and corrosion resistance. The amount of the mother alloy to be employed is insufficient, and if it is more than 50wt%, there is a high possibility of generating a weak phase during solidification after remelting.

Cr is a solid solution alloy of Ni, which has corrosion resistance and heat resistance. Its original strength is sol, and it is ineffective at below 5wt%, and carbide is formed at 20wt% or more, resulting in non-uniformity and oxidation of tissue during remelting.

B, Si has a process reaction in Ni and Cr, but the effect is less than 0.5wt%, there is no increase in effect due to precipitation at the grain boundary above 4wt%.

C increases the base strength by dispersing the matrix of solid solution at the time of solid solution strengthening and quenching in the multicomponent alloy composition, but it is meaningless because it remains as vulnerable unemployed graphite at 1wt% or more.

The present invention will be described in more detail with reference to the following Examples.

The coating powder used in the embodiment of the present invention was a base alloy of Ni-based alloy using WC-Co alloy as a reinforcing phase and WC 61.6 wt%, Co 8.4wt%, Ni 19.8wt% , Cr 5.4wt%, Fe 2.1wt%, Si 1.2wt% and C 0.3wt% or less and impurities.

When the amount of Ni is reduced and Cu, Mo, etc. are added below 3wt%, the known hardness increases due to precipitation hardening.

Carbide self-particle size ratio is 3-4 micrometers in average particle size, and WC-C-Co particle | grains are distributed in the range of 15 micrometers-45 micrometers on average in the thermal spray powder. The coating layer thickness after coating and magnetic treatment can be 0.2-0.9 mm. However, even if the size of the powder is different from the embodiment of the present invention, it does not depart from the scope of the invention.

The method of apply | coating the alloy powder of this invention to the surface of a to-be-processed material is based on thermal spray coating, such as powder flame spraying, plasma, and high speed flame spraying.

However, if the coating layer is required to have a particularly excellent coating layer such as fitting resistance and scuffing resistance, HVOF (high speed flame spraying) should be applied to obtain the perfect remelting treatment.

Although the defects of the thermal spray coating layer are destroyed in the post-melting step, the experiments of the present inventors have obtained the best quality in the combination of the high-speed flame spraying and the post-melting process.

It is a subsonic velocity of 300M / sec for a normal flame sprayer, but it is usually 1400M / sec for a high speed flame sprayer, and some are internally defective from the beginning because they collide with the surface at a tremendous speed of 2200M / sec to radiate thermal and kinetic energy. Because this is very small.

If the surface of the product is circular and rotation is required during coating, the speed of attachment between the center and the edge is different, so it is a matter of course to consider the control device to avoid this.

As a method for remelting tungsten carbide-dispersed coating film, a special torch having a diagonal length of 10 to 25 mm between flame discharge holes using a heat source such as oxygen-acetylene or oxygen-propane is required. The intensity should also be somewhat weaker than a normal torch.

In this experiment, the gas flow rate ratio was set to 3: 4 with oxygen: acetylene, and during remelting, if the localized zone is heated to high temperature, the coating layer is rapidly thermally expanded and peeling should be avoided.

In other words, preheat the product to 300 ~ 550 ℃ at a distance of 100 ~ 130mm and then move the torch nozzle closer to 30 ~ 40mm and change the fluidity when the surface is red. Stop and cool it by soaking in a suitable medium.

At this time, if it is overheated or delayed, it is completely melted and flows or oxides are generated on the surface.

In particular, the cold forged product shape of the wear-resistant tappet to be applied in the present invention can not obtain a sound quality because the absorption path of the heat input from the heating heat source is asymmetric or non-uniform.

Therefore, the present inventors fix the tappet to a lathe or a rotating turntable to perform remelting, and the edge and the center of the tappet are heated by heating the front body as well as the central body side with a slow heating and cooling rate from the side perpendicular to the rotation axis in the preheating process. Despite the difference in thickness, it achieves a uniform temperature and reaches a remelting temperature.

The optimum remelting temperature in the composition used in the present invention ranges from about 1050 to 1110 ° C. and the holding time is in a few seconds to one minute.

As a result of the experiment, remelting was possible to obtain good quality if only temperature and heat input were properly controlled not only by the torch but also by the heating method by heat treatment furnace or high frequency heating.

The quality of the fabricated product showed very high hardness of HRA82 ~ 87, and microscopic observation by optical microscope showed that pores after spraying were completely removed and WC particles were evenly distributed throughout the film. It was.

The wear test through the fitting test was performed under the conditions of 1000rpm, spring static load 174.5kg, holding temperature 75-85 ℃ in single-acting tappet-cam tester, and after 10 ⁷ cycles of test run time, no fitting or scuffing was observed. It was confirmed that the contact.

In the test under the same conditions, it was confirmed that the fitting and scuffing were partially performed in the seven tappet, the high frequency tappet, and the thermal spray coating tappet by the high-speed flame.

The tappet obtained through the above process has almost no pores and forms a metal bond with the base material interface. Due to the hard particles of the fine particles, the tappet shows high durability due to excellent fatigue resistance, fitting resistance and toughness of the surface layer.

This suppresses wear such as fittings or scuffing that occur at the cam and tappet contact surfaces in the existing engine, and thus increases engine noise, prevents incomplete combustion, or environmental pollution caused by exhaust gas.

Claims (8)

WC 44 ~ 80wt%, Co 4-10wt%, Ni 15-50wt%, Cr 5-20wt%, B 0.5-4wt%, Fe 2-4wt%, Si 0.5-4wt%, C 1.0wt% or less, and consequently An engine tappet having excellent wear resistance, characterized in that a high hardness coating layer using an alloy powder material composed of impurities contained in the contact surface with the cam is formed in the body of the tappet. The method of claim 1, The alloy powder material is WC 44 ~ 80wt%, Co 19 ~ 60wt%, Cr 5 ~ 20wt%, B 0.5 ~ 4wt%, Fe 2 ~ 4wt%, Si 0.5 ~ 4wt%, C 1.0wt% or less, and inevitably An engine tappet having excellent wear resistance, characterized by being composed of impurities contained. The method of claim 1, The alloy powder material is WC 44 ~ 80wt%, Ni 19 ~ 60wt%, Cr 5 ~ 20wt%, B 0.5 ~ 4wt%, Fe 2 ~ 4wt%, Si 0.5 ~ 4wt%, C 1.0wt% or less, and inevitably An engine tappet having excellent wear resistance, characterized by being composed of impurities contained. The method of claim 1, Among the alloy powder material, WC is an engine tappet having excellent wear resistance, characterized in that the particle diameter of 1 ~ 5㎛ managed. WC 44 to 80wt%, Co 4 to 10wt%, Ni 15 to 50wt%, Cr 5 to 20wt%, B 0.5 to 4wt%, Fe 2 to 4wt%, Si 0.5 to 4wt% , C 1.0wt% or less, and after the thermal spray coating of the alloy powder material composed of impurity contained inevitably, after the re-melting treatment to the coating layer, the manufacturing method of the engine tappet excellent in wear resistance. The method of claim 5, The thermal spray coating is a powder flame spray or a plasma or high-speed flame spray coating method characterized in that the engine tappet excellent wear resistance characterized in that the coating. The method of claim 5, The re-melting treatment is a method for producing a wearable engine tappet, characterized in that performed by torch heating or heat treatment furnace heating or high frequency heating using a heat source such as oxygen-acetylene or oxygen-propane. The method of claim 7, wherein Remelting by torch heating is to preheat the coating layer first at 300 to 550 ° C., and then to reheat the torch nozzle closer to the preheated coating layer at about 1050 to 1110 ° C. within a few seconds to one minute. A method for producing an engine tappet having excellent wear resistance.