Valve recession: From experiment to predictive model

Increasing demands on engine performance and cost reductions have meant that advances made in materials and production technology are often outpaced This frequently results in wear problems occurring with engine components. Few models exist for predicting wear, and consequently each wear problem has to be investigated, the cause isolated and remedial action taken. The objective of this work was to carry out experimental studies to investigate valve and seat insert wear mechanisms and use the test results to develop a recession prediction tool to assess the potential for valve recession and solve problems that occur more quickly. Experimental apparatus has been developed that is capable of providing a valid simulation of the wear of diesel automotive inlet valves and seats. Test methodologies developed have isolated the effects of impact and sliding. A semi-empirical wear model for predicting valve recession has been developed based on data gathered during the bench testing. A software program, RECESS, was developed to run the model. Model predictions are compared with engine dynamometer tests and bench tests. The model can be used to give a quantitative prediction of the valve recession to be expected with a particular material pair or a qualitative assessment of how parameters need to be altered in order to reduce recession. The valve recession model can be integrated into an industrial environment in order to help reduce costs and timescales involved in solving valve/seat wear problems

Using spindle noise to monitor tool wear in a turning process

A tool condition monitoring system can increase the competitiveness of a machining process by increasing the utilised tool life and decreasing instances of part damage from excessive tool wear or tool breakage. This article describes an inexpensive and non-intrusive method of inferring tool condition by measuring the audible sound emitted during machining. The audio signature recorded can be used to develop an effective in-process tool wear monitoring system where digital filters retain the signal associated with the cutting process but remove audio characteristics associated with the operation of the machine spindle. This study used a microphone to record the machining sound of EN24 steel being face turned by a CNC lathe in a wet cutting condition using constant surface speed control. The audio signal is compared to the flank wear development on the cutting inserts for several different surface speed and cutting feed combinations. The results show that there is no relationship between the frequency of spindle noise and tool wear, but varying cutting speed and feed rate have an influence on the magnitude of spindle noise and this could be used to indicate the tool wear state during the process

A straightforward and low-cost pre-inspection measurement method for small gears

On-line or rapid inspection of parts is essential in streamlining manufacturing processes. A novel pre-inspection method for measuring small gears is proposed. This method requires little specialist equipment outside that normally found in a laboratory or on a shop floor. Gears are measured using a standard optical microscope. These are then processed using an image processing algorithm to give a percentage error in tooth profile. This allows only gears of sufficiently high quality to be “passed on” to more sophisticated inspection techniques. The technique is used to analyse sub-centimetre diameter gears produced using WEDM. It is found that the technique provides a simple but effective method of determining how close a gear is to the required geometry. While the result is basic, it is extremely quick and inexpensive to perform alongside the manufacturing process. This method provides a capability to small companies and production lines for pre-inspection of gears before detailed analysis without purchasing specialist equipment

Friction and wear response of vegetable oils and their blends with mineral engine oil in a reciprocating sliding contact at severe contact conditions

Although many studies investigating the tribological performance of pure vegetable oils have been conducted, a better understanding of vegetable oil tribological performance at extreme conditions is still needed. Similarly, little work has been carried out to study the influence of the vegetable oils on the performance of a lubricant formed from a blend of vegetable oil and conventional mineral engine oil. This work presents the tribological performance of vegetable oils, and their blends with mineral oil, in a high temperature and contact pressure reciprocating contact. Palm and soybean based vegetable oils were mixed with a commercial mineral engine oil at a 1:1 ratio by volume. The conventional mineral oil was also tested to provide a benchmark. The pure palm oil exhibited lower friction than soybean oil, but for wear performance, this was reversed. The friction performance of the palm oil was competitive to that of the mineral engine oil. The mineral engine oil was far superior in wear resistance over both vegetable oils. When blended with mineral engine oil both vegetable oils demonstrated a reduction in coefficient of friction when compared to their pure oil states. An improvement in wear performance was observed for both a blend of palm oil and mineral engine oil (25% improvement) and that of soybean and mineral engine oil (27% improvement). This work shows that for palm oil and soybean oil, the performance of a blended oil is influenced by its vegetable oil component and that tribological characteristics of vegetable oils are dominant. That said, the significant limitation of these vegetable oils is their ability to provide a satisfactory level of wear resistance. It is suggested that any future work in this area should have a greater emphasis on the enhancement of wear resistance

Friction and wear response of vegetable oils and their blends with mineral engine oil in a reciprocating sliding contact at severe contact conditions

Although many studies investigating the tribological performance of pure vegetable oils have been conducted, a better understanding of vegetable oil tribological performance at extreme conditions is still needed. Similarly, little work has been carried out to study the influence of the vegetable oils on the performance of a lubricant formed from a blend of vegetable oil and conventional mineral engine oil. This work presents the tribological performance of vegetable oils, and their blends with mineral oil, in a high temperature and contact pressure reciprocating contact. Palm and soybean based vegetable oils were mixed with a commercial mineral engine oil at a 1:1 ratio by volume. The conventional mineral oil was also tested to provide a benchmark. The pure palm oil exhibited lower friction than soybean oil, but for wear performance, this was reversed. The friction performance of the palm oil was competitive to that of the mineral engine oil. The mineral engine oil was far superior in wear resistance over both vegetable oils. When blended with mineral engine oil both vegetable oils demonstrated a reduction in coefficient of friction when compared to their pure oil states. An improvement in wear performance was observed for both a blend of palm oil and mineral engine oil (25% improvement) and that of soybean and mineral engine oil (27% improvement). This work shows that for palm oil and soybean oil, the performance of a blended oil is influenced by its vegetable oil component and that tribological characteristics of vegetable oils are dominant. That said, the significant limitation of these vegetable oils is their ability to provide a satisfactory level of wear resistance. It is suggested that any future work in this area should have a greater emphasis on the enhancement of wear resistance

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. © 2009 Elsevier B.V. All rights reserved

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

Formation of white etching cracks at manganese sulfide (MnS) inclusions in bearing steel due to hammering impact loading

Wind turbine gearbox bearings (WTGBs) are failing prematurely, leading to increased operational costs of wind energy. Bearing failure by white structure flaking (WSF) and axial cracking may both be caused by the propagation of white etching cracks (WECs) and have been observed to cause premature failures; however, their damage mechanism is currently not well understood. Crack initiation has been found to occur at subsurface material defects in bearing steel, which may develop into WECs. One hypothesis for WEC formation at these defects, such as non-metallic inclusions, is that repetitive impact loading of a rolling element on a bearing raceway, due to torque reversals and transient loading during operation, leads to high numbers of stress-concentrating load cycles at defects that exceed the material yield strength. In this study, a number of tests were carried out using a reciprocating hammer-type impact rig. Tests were designed to induce subsurface yielding at stress concentrating manganese sulfide (MnS) inclusions. The effects of increasing surface contact stress and number of impact cycles, with and without surface traction, were investigated. Damage adjacent to MnS inclusions, similar to that observed in a failed WTGB raceway, was recreated on bearing steel test specimens. It has been found that increasing the subsurface equivalent stresses and the number of impact cycles both led to increased damage levels. Damage was observed at subsurface equivalent stresses of above 2.48 GPa after at least 50,000 impact cycles. WECs were recreated during tests that applied surface traction for 1,000,000 impacts

Sensitivity study of a valve recession model

The aim of this work was to carry out a sensitivity analysis of a valve recession model. For the sensitivity study, the effects of the param eters on the valve recession mode l were investigated, for both, light duty and heavy duty engines. It was seen that for light duty engines, the impact component parameters had the gr eatest effect on valve recession and for heavy duty engines the sliding wear component p arameters have an increasing con- tribution to the overall valve recession

Combining DLC, Shot blasting, chemical dip and nano fullerene surface treatments to reduce wear and friction when used with bio-lubricants in automotive contacts

The interaction of three bio-lubricant base oil candidates with seventeen combinations of surface treatment was studied, comparing wear scar volumes and coefficient of friction results. Substrates were initially ground, then a combination of superfinished, Dymon-iC™ DLC, an impact technique of ultra-fine shot blasting method doped with Tin and Molybdenum Disulfide, a calcium based chemical dip containing calcium sulfate and nano fullerene, were used.DLC is well reported to reduce friction. Some reports suggest wear in coated contacts is independent of the type of lubricant used, whilst others report that bio-lubricants offer reduced friction and wear in combination with DLC. Shot blasting can also reduce wear and friction, due to the surface dimples acting as lubricant reservoirs, making hydrodynamic lubrication more likely. Previous work has also explored the performance of surface texturing in combination with coatings, some reporting higher friction when surface texturing and DLC is used. As a surface coating, fullerene has been shown to have significantly lower wear and friction than DLC coatings. The calcium based chemical treatment used has no published data.A ball on flat reciprocating wear tester was used with bio-lubricant base oil candidates, jojoba and soybean oil, with a mineral base oil used for comparison. Wear scars were analysed using a scanning electron microscope.Coefficient of friction results from testing with bio-lubricant base oil candidates’ soybean and jojoba oil were lower than tests with mineral base oil. A hybridized coating combination of superfinish, diamond like carbon and chemical dip gave the highest wear protection for tests with the mineral base oil and bio-lubricant base oil candidate soybean oil. A hybridized coating combination of superfinish, impact technique and chemical dip gave highest wear protection when tested with bio-lubricant base oil candidate jojoba oil. Results showed no overall improvement in wear protection when substrates were processed with the impact technique. Superfinishing substrates improved the performance of both the chemical dip and DLC