Valve Seat Inserts Research Articles

Approach to enhance the heat transfer of valve seats through thermal analysis

The valve seat insert is a component of the engine cylinder head, whose primary function is to seal the combustion chamber and absorb the valve's heat, releasing it to the engine cylinder head. The valves experience high temperatures owing to high thermal loading and low heat absorption in the valve seat, which can potentially damage the engine. Therefore, the thermal characteristics of the valve seat must be optimised to increase the heat transmission between the valve and its seat. Here, three copper alloy valve seats, brass, beryllium copper, and bronze copper, were tested against the existing sintered iron valve seat, and their temperature maps were determined using actual engine operation conditions. The instantaneous heat transfer coefficients of the valves, seats, and engine cylinder head during the four-stroke cycle were evaluated using a one-dimensional thermal simulation analysis. The values obtained were used to assess the finite-element model using a three-dimensional thermal simulation in the Ansys software. The results show that the brass, beryllium-, and bronze-copper valve seats increased the overall heat flux by 4.46%, 4.16%, and 2.06%, respectively, compared to those for sintered iron. Thus, the results are essential to improve the thermal characteristics of the copper alloy valve seat imposed on the cylinder head. For validation, an experimental engine thermal survey and uncertainty magnification factors were used to validate the model. The results indicate that the maximum difference between the simulation and experimental values is 8.42%. Therefore, this approach offers a direct and comprehensible application for evaluating the temperature distribution, heat gradient, and heat flux of the cylinder head of air-cooled spark-ignition moped motorcycle engines using copper alloy valve seat materials at intermediate engine speeds. Furthermore, this method is applicable as a platform for the automotive industry to improve the heat transfer of the structural parts of internal combustion engines.

Investigating the thermal characteristic of copper alloys valve seat towards engine performance enhancement of MODENAS CT115 through steady-state analysis

MODENAS CT115 engine is a single overhead camshaft (SOHC) engine, with a rated power of 8.8 horsepower at 9000 rpm. One of the main concerns of engine research is the overheating of engines. Overheating can affects the performance of an engine by leading to a loss of strength and thermal strain. To prevent failure, thermal analysis is used to determine the flow of heat with precision to optimise temperature distribution. The investigation is done using ANSYS Thermal simulation on the CAD model of the engine cylinder head, intake and exhaust valve, and intake and exhaust valve seat insert. The comparison to the existing valve seat insert is made using three different valve seat insert materials: Beryllium-copper C17200, Bronze-copper C61300, and Brass C36000. The research results proved that Brass C36000 provides the best thermal reduction and heat transfer increment compared to the existing valve seat insert material.

Computational Analysis of Dissimilar Materials Engine Valve: Technical Note

Engine exhaust valve are exposed to severe thermal loads and chemical corrosion. Exhaust valve opens and closes 2000 times per mile for passenger cars. Generally the material for manufacturing exhaust valve and exhaust valve seat insert have properties for working at high temperature continuously and resistance to corrosion due to their surrounding environment. Usually engine valve is made up of austenitic steels. This valve is to be replaced by a light weight dissimilar materials preferably by an Al6061 and FE 430 steel. In this paper, computational fluid dynamic analysis of such valve is presented. The flow characteristics and strength of the valve are assessed.

Copper infiltrated high speed steel skeletons

Purpose: This article is a monographic summary of the most important research results from the last 10 years regarding HSS based materials. This materias were produced with powder metallurgy technology using spontaneous infiltration. The presented results answer the question of how iron, tungsten carbide and copper additives influence the final properties of these materials and present additional microstructural phenomena revealed during their manufacture. Design/methodology/approach: Materials were produced by spontaneous infiltration. Porous skeletons for infiltration were produced by pressing and pressing and sintering of mixed powders. Copper was used as the infiltrant. Findings: The molten copper was drawn into the porous skeletons, through a capillary action, and filled virtually the entire pore volume to get the final densities exceeding 97% of the theoretical value. Research limitations/implications: As part of further research, microstructures of M30WC composites obtained by direct infiltration of copper into as-sintered porous skeletons using TEM are planned. Practical implications: Efficiant mechanical strength, high hardness, adequate heat resistance and good wear resistance of M3 type 2 HSS powder produced by woter atomisation make it an attractive material for manufacture of valve train components, for example valve seat inserts. Originality/value: The novelty in the article are the results of research on the microstructure made using TEM, the results of testing materials after heat treatment, untypical for high- speed steels. The article attempts to explain the influence of iron addition on properties - such a slight loss of mass as a result of its addition. The second aim of this work is to analyse the microstructural changes during sintering porous skeletons made from HSS with WC additions.

High temperature corrosion behaviour of aluminised FC 25 cast iron using pack cementation

Purpose This study aims to apply the pack cementation to develop the Fe-Al layers on the surface of FC 25 cast iron in order to increase the high-temperature corrosion resistance of the alloy. Design/methodology/approach Pack cementation was applied on the surface of FC 25 cast iron at 1,050°C. The bare and aluminised alloys were subjected to the oxidation test in 20 per cent O2-N2 at 850 °C. Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD) were used for characterisation. Findings The layers of pack cementation consisted of Fe2Al5, FeAl2 and FeAl, and solid solution alloyed with Al. The oxidation kinetics of the bare cast iron was parabolic. Mass gain of the aluminised cast iron was significantly decreased compared with that of the bare cast iron. This was because of the protective alumina formation on the aluminised alloy surface. Al in the Fe–Al layer also tended to be homogenised during oxidation. Originality/value Even though the aluminising of alloys was extensively studied, the application of that process to the FC 25 cast iron grade was originally developed in this work. The significantly reduced mass gain of the aluminised FC 25 cast iron makes the studied alloy be promising for the use as a valve seat insert in an agricultural single-cylinder four-stroke engine, which might be run by using a relatively cheaper fuel, i.e. LPG, but as a consequence requires the higher oxidation resistance of the engine parts.

High thermal conductivity valve seat inserts and guides

High thermal conductivity valve seat inserts and guides

Heat Treatment of Sintered Valve Seat Inserts

The characterization of sintered valve seat inserts (VSIs) after being subjected to different heat treatment operations has been carried out. The VSIs were obtained from three different alloys by mixing iron powder with AISI M3:2, AISI M2 high-speed steels, and AISI D2 tool steel. After sintering, the VSI were quenched in air followed by double tempering at seven different temperatures. The cooling rate during air quenching was measured by means of a thermocouple type k attached to a data acquisition system. The characterization of the mechanical and physical properties of the VSIs was achieved by measuring relative density, apparent hardness and crush radial strength. The resulting microstructures for the sintered parts were interpreted using the isothermal and continuous cooling transformation diagrams for similar alloys. The VSI obtained with AISI M3:2 and AISI M2 high-speed steels after air quenching and double tempering at 600 oC showed the best results in terms of apparent hardness and crush radial strength.

Failure analysis of worn valve train components of a four-cylinder diesel engine

Abstract This work investigates the causes of excessive wear occurring at the rocker arm/pushrod and rocker arm/valve interfaces of a diesel engine for industrial cleaning machines, after only 1000 h of engine operation. In this engine, the recent replacement of tappets by hydraulic valve lifters not only reduced the running time but also required supplementary maintenance. The chemical composition of the worn components was verified by optical emission spectroscopy. The microstructures, mechanical properties and surface textures were determined by optical microscopy, Vickers hardness and non-contact 3D profilometry. To evaluate the wear mechanisms, the worn surfaces were analyzed by scanning electron microscopy with energy dispersive spectroscopy. The results indicated non-uniform wear damage at the rocker arm/valve interface, probably due to a misalignment of valves with respect to valve seat inserts. For rocker arms and pushrods, improper austenitization parameters and/or unsuitable design of the inductor left some free ferrite, responsible for non-compliance with required specifications for the induction hardening treatment. All worn surfaces were characterized by material removal by scuffing; initiation of fatigue cracks was also observed at the rocker arm/valve interface, and probably erosive cutting occurred at the rocker arm/pushrod interface.

Surface texturing to promote formation of protective tribofilms on combustion engine valves

In a combustion engine, the valve system controls the flow of gases in to and out of the combustion chamber. The contacting surfaces experience a harsh tribological situation with high temperatures, high speed impacts, corrosive environment and high closing forces causing micro sliding in the interface. The components have to endure in the range of hundreds of millions to a billion operational cycles, resulting in extreme demands on low wear rate. Such low wear rates can be accomplished by the protective action from tribofilms forming from oil residues, avoiding a pure metal-to-metal contact. Such tribofilms are found on well-functioning engine valves from a variety of engines, but some stationary gas engines experience problems with wear occurring seemingly randomly at normal running conditions. For some reason, the tribofilm has not protected the surfaces sufficiently, causing wear. One way to combat the random behaviour could be to promote robust function of the protective tribofilms by texturing the valve sealing surfaces to improve the capture and storage of oil residues. By stabilising the supply in this way, the damage from periods with low access to tribofilm forming material could be reduced. The present work demonstrates that turning of the valve seat inserts, creating valleys perpendicular to the sliding motion, can be developed into a useful solution. The amount and localisation of tribofilms became more predictable and stable than without the texture, leading to reduced component wear. The valleys should not be too wide, since this increased the amount of exposed metal if the tribofilm flaked off. When having the same width, the deeper valleys showed less flaking off of the tribofilm.

Wear protective capacity of tribofilms formed on combustion engine valves with different surface textures

The valve system controls the flow of gases into and out of the cylinders of combustion engines. As the combustion chamber is repeatedly filled with air and emptied from combustion residues, the contacting surfaces of the valve and valve seat insert (VSI) are exposed to high temperatures, high speed impacts, corrosive environment and high closing forces. Since the expected wear life of the components is hundreds of millions of operational cycles, the wear rate has to be extremely low. Previous studies have shown that this is accomplished by the continual formation of protective tribofilms on the surfaces, formed from oil additive residues.For some stationary gas engines, seemingly random occurrence of severe wear, i.e. without correlation to special running conditions, calls for an improved understanding of the wear protective abilities of these tribofilms. Further, the potential of making the protection more robust by using simple textures on sealing surfaces is investigated.Real valves and VSI's were therefore run in a dedicated test rig, previously shown capable of forming tribofilms similar to those found in real engine valves. Two surface textures, turned or ground, were tested. After a running in phase where fully covering tribofilms were formed, the tests were continued without adding the oil residues needed for replenishing the tribofilm. The flow of oil residues was either completely stopped or only intermittently open. The resulting wear was monitored during testing and after finishing the tests remaining tribofilms were analysed with SEM and EDS. The severity of the wear was graded and the presence of tribofilm and localization of wear was correlated.The endurance of the tribofilms was surprisingly high for both textures. Typically the tribofilms exhibited better wear resistance than the underlying metals. Once fully formed, the tribofilms can therefore endure for a long time without addition of new tribofilm forming material. Both textures showed the first sign of wear after roughly the same time and then followed the same progression, when the flow of oil residues was cut. With the intermittent oil residue supply, both textures performed even better. Especially the turned texture showed only slow, mild wear.

Sliding Wear Study on the Valve-Seat Insert Contact

The aim of this work was to investigate the sliding wear coefficient k, using an experimental sliding wear study on the valve-seat insert contact. Commercial inlet valve and seat inserts were used as test specimens. The tests were performed at room temperature and at 200℃, using test duration of 72,000 cycles and 18,000 cycles, respectively, and both in dry sliding conditions. A load of 5 N, an average speed of 22 mm/s and sliding distance of 2.2 mm were used for all tests. The sliding wear coefficients were calculated using experimental and analytical methods. The wear volume was higher in the tests at 200℃ both in valve and seat insert specimens. The principal wear mechanisms observed in valve specimen were oxidation and abrasion.

Higher quality, better mechanical properties of PM valve seat inserts: By identifying key parameters in copper infiltration process

Since usage of aluminum cylinder heads, valve seat inserts (VSIs) have significantly gained in importance. The VSI in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. One point everyone does seem to agree upon is that VSI plays a critical role in the longevity of the valves. Together with the valves they seal off the combustion chamber of the cylinder head. The VSI prevents the impact/burning of the valve into the cylinder head. It draws heat away from the valves and conducts it into the cylinder head. This provides most of the cooling that the valves receive and is absolutely critical with exhaust valves.

Numerical and experimental analysis of dynamic oblique impact: Effect of impact angle

Surface failures under dynamic oblique impact occur in many mechanical systems. In automobile engine, valve seat insert works under complex vibrating conditions. This leads persistently to the evolution of contact pressure, stress and strain as a function of time. By simplifying the system to a ball-on-flat configuration, the contact dynamic behavior was investigated as a function of impact angle. In order to better understand experiments on the experimental bench test, a finite element model was developed. Experimental and numerical results show an evolution from permanent reciprocating sliding at low angles to an intermittent motion called multi-impacts at higher angles. Experimental electrical contact resistance measurements confirm the observed evolutions. As a consequence, shearing stress is reduced when plastic deformation is increased with multi-impacts.

Dry Sliding Wear Behaviours of Valve Seat Inserts Produced from High Chromium White Iron

Abstract In this present study, wear behaviours of high chromium white iron valve seat inserts and tappets used in the automotive sector were investigated. Wear behaviours of three different rates of high chromium white cast irons (containing 10, 12 and 14% chromium) were examined under heavy service conditions. For that purpose, the produced valve seat inserts were characterized through Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD) and hardness measurements. They were tested at a sliding speed of 1 ms−1, under 120 N load and for six different sliding distances (500, 1000, 1500, 2000, 2500, 3000 m) by using a standard wear apparatus (pin-on-disk type). The result showed that as the amount of Cr increased in the alloys, their hardness decreased. The decrease in the hardness were considered to be as the result of transformation of M7C3 carbides into M23C6 carbides in the structure. This decrease in hardness with increasing chromium content also increased the weight loss. Thus, it was determined that the white iron with 14% Cr (which had a greater amount of M23C6 carbides) was subjected to the highest wear.

Research on Wear Surface Morphology of PCBN Tools in High-Speed Machining Valve Seat Insert

A series of experiments was conducted in high speed dry turning of valve seat insert with PCBN cutters. The main tool wear surface morphology was observed by utilizing scanning electron microscopy and digital microscope. The experimental results indicate that the tool wear surface morphology is rake face wear, flank wear, chipping, flaking and breakage.

On the physical nature of tribolayers and wear debris after sliding wear in a superalloy/steel tribosystem at 25 and 300 °C

Dry sliding wear of metals is strongly affected by the formation of oxide particles and their incorporation into compacted oxide layers, so-called glaze layers. A high-temperature reciprocating pin-on-disc tribometer was used to study the tribological response of a Ni-based Alloy 80A pin on a cast iron disc at ambient temperature and at 300°C. Alloy 80A is used for valves and specific cast irons are used for valve seat-inserts in automotive diesel engines, where wear limits the service life of the valve/seat-insert tribosystems. Measurements of the friction coefficient, the total linear wear and the electrical contact resistance were used to monitor the formation of oxide layers during the experiments. Electron dispersive X-ray (EDX) element mappings from the surface regions with wear scars provide clear evidence for the formation of glaze layers and material transfer between pin and disc. Focused ion beam (FIB) micromachining was used to cut out thin lamellae from specific surface regions of glaze layers and from metallic wear particles. These lamellae were investigated in a transmission electron microscope (TEM). It was shown that the glaze layers generated at 25 and 300°C exhibit distinct differences, which led to a reduction in wear rate by a factor of five at the higher temperature. We also report on the mechanical mixing of oxide particles and metal matrix that results in a metal/oxide nanocomposite directly below the sliding surfaces. Such composite structures were also observed inside of metallic wear debris.

Wear mechanism study of exhaust valve system in modern heavy duty combustion engines

The increasing demands from environmental legislations are changing the conditions that the valve system is exposed to in heavy duty engines. Increased pressures, higher temperatures and lower amounts of soot which can build up a protective film are some of the increasing challenges which the system has to endure. Three pairs of valves and valve seat inserts with the same material and design properties but with different service condition have been analyzed with a variety of analytical instruments to gain information of how the wear occurs. The wear mechanisms found were a combination of oxidation, where many different oxides were found, adhesive wear, which was seen both in form of material transfer and flow lines. On top of Sample Mild and Hard there were tribo films of thickness varying from 1 to 5 μm consisting of Ca, O, P, S and Zn. The film has in all cases protected the underlying surface from wear but in some cases seems to have a corrosive impact instead.

The influence of laser hardening on wear in the valve and valve seat contact

In internal combustion engines it is important to manage the wear in the valve and valve seat contact in order to minimise emissions and maximise economy. Traditionally wear in this contact has been controlled by the use of a valve seat insert and the careful selection of materials for both the valve and the insert. More recently, due to the increasing demands for both performance and cost, alternative methods of controlling the wear, and the resulting valve recession, have been sought. Using the heating effect of a laser to induce localised phase transformations, to increase hardness and wear resistance, in materials has been used since the 1970s, however it is only in recent years that it has been able to compete with more established surface treatment techniques, particularly in terms of cost, as new laser hardware has been developed. In this work, a laser has been used to treat the valve seat area of a cast iron cylinder head. In order to optimise the laser parameters for use on the head, preliminary tests were carried out to investigate the fundamental wear characteristics of untreated cast iron and also cast iron with a range of laser treatments. Previous work has identified the predominant wear mechanism in the valve and valve seat contact as impact on valve closure. Two bespoke test machines, one for testing basic specimens and one for testing components, were used to identify the laser parameters most likely to yield acceptable results when applied to a cylinder head to be used in a fired dynamometer test.

Fabrication and impact wear testing of Al-SiC<SUB align=right>p composite valve seat inserts for automobiles

Composite materials are replacing the materials used in various fields and are the candidate materials for future growth. Aluminium matrix composites are the class of composite materials finding widespread applications in automotive, aircraft, defence and appliance industries. In the present work, Al-SiCp composite valve seat inserts with 10, 15, 20 and 25 wt% of SiCp were fabricated through powder metallurgy as well as die casting process. An impact wear-testing machine was fabricated to study the impact wear behaviour of steel and Al-SiCp composite valve seat inserts. The inserts were made to impact under 19.6 N load, against a stationary or rotating austenitic stainless steel disc at 500 rpm. The wear volume and reduction in height were measured for Al-SiCp composite valve seat inserts with different weight percent of SiCp and the steel valve seat inserts currently used in engines. The Al-SiCp composite valve seat inserts with 15, 20 and 25 wt% SiCp showed better wear resistance than the steel valve seat inserts against both stationary and rotating austenitic stainless steel disc under 19.6 N load. The mechanism of wear during impact wear tests without sliding is adhesion and plastic deformation due to sudden high compressive force developed during the impact of the valve seat insert on the plate.

Development of powder metallurgy T42 high speed steel for structural applications

Abstract Water atomized T42 high speed steel powders have been processed by a powder metallurgy (PM) route in order to obtain a fully dense material suitable for valve seat inserts (VSI) in diesel engines. Two different heat treatments (isothermal annealing and multitempering) were designed leading to the targeted hardness value (50 HRC). Microstructural characterisation of the heat-treated material was carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fracture strength and fracture toughness have also been investigated. The wear behaviour was evaluated through pin-on-disc tests at service temperature (360 °C). The obtained results demonstrated the excellent wear resistance of the VSI material without severe wear of the countermaterial (valve).