21-05-2013, 02:27 PM
Investigation Wear behavior of ZA 27
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Abstract
ZA-27 alloy is an important member of the ZA family of alloys with a high strength is reported to have properties equivalent to those of aluminium alloys. Abundant availability, good bearing and mechanical Properties such as wear resistance, anti-seizure properties, yield and tensile strengths scored in favour of extensive use of these alloys for bearing applications.Dry sliding wear behavior of ZA 27 fabricated by sand casting process was investigated. The wear properties of the ZA 27 alloy were studied by performing dry sliding wear test using a pin-on-disc wear tester. Experiments were conducted based on the plan of experiments generated through Taguchi's technique. A L9 Orthogonal array was selected for analysis of the data. The influence of applied load, sliding speed and sliding distance on wear rate was investigated using Minitab 15.To analyze the dry sliding wear resistance the model was chosen as 'smaller the better' and confirmation tests were carried out to verify the experimental results.
INTRODUCTION
The zinc–aluminium (ZA) family of casting alloys are gaining wide commercial importance for many industrial applications. Zinc-based alloys have been observed to hold potential to effectively substitute a variety of ferrous and non-ferrous alloys in several tribological and other general engineering applications. Superior wear performance of zinc-based alloy tribo components has been reported in heavy mining machineries in comparison to conventionally used bronze and gun metal counterparts in slow-to-medium speed conditions.
However, one of the major limitations of the zinc-based alloys has been observed to be their property deterioration at temperatures above 100oC Reinforcement of the (zinc-based) alloy system through hard and thermally stable ceramic phases has been suggested to be an effective measure to alleviate the problem. Hardness and thermally stable ceramic reinforcements in zinc based alloys led to less strength than the matrix alloy at ambient temperature while examples of trend reversal also exist depending on the nature and type of the dispersoid phase. Further, the composites attained improved elevated temperature strength, increasing reinforcement content bringing about further improvement in the property. The dispersoid phase also caused higher hardness superior elastic modulus greater dynamic modulus, better damping capacity and less coefficient of thermal expansion of the matrix alloy. The reinforcement phase brought about improved wear resistance (inverse of wear rate) of the matrix alloy, but at the cost of higher friction coefficient. Superior wear characteristics of the composite to that of the matrix alloy at higher sliding speeds and pressures could be attributed to suppressed cracking tendency of the reinforcement phase under the conditions of high frictional heating, The latter enabling the reinforcement particles to display their positive effects of providing thermal stability to and load transfer from the softer and ductile matrix. Very limited studies have been carried out as far as the effects of parameters like the silicon particle reinforcement in the matrix and changing environmental conditions such as the influence of oil and solid lubricant particles therein on the sliding wear behaviour of zinc-based alloys are concerned. In view of the above, an attempt has been made in this study to analyze the sliding wear behaviour of a zinc-based alloy under the influence of varying applied loads in dry condition.
In this project the tribological properties of the ZA 27 alloy were tested using a Pin-on-Disc apparatus. Sliding wear tests were performed by using the tribo tester by varying load, speed & sliding distance.
WEAR
Wear is the erosion of material from a solid surface by the action of another surface. It is related to surface interactions and more specifically the removal of material from a surface as a result of mechanical action. The study of the processes of wear is part of the discipline of tribology. The complex nature of wear has delayed its investigations and resulted in isolated studies towards specific wear mechanisms or processes. Some commonly referred to wear mechanisms (or processes) include, adhesive wear, abrasive wear, erosive wear. Adhesive wear can be defined as wear due to localized bonding between contacting solid surfaces leading to material transfer between the two surfaces or the loss from either surface. For adhesive wear to occur it is necessary for the surfaces to be in intimate contact with each other. Surfaces, which are held apart by lubricating films, oxide films etc. reduce the tendency for adhesion to occur. Abrasive wear can be defined as wear that occurs when a hard surface slides against and cuts groove from a softer surface. It can be account for most failures in practice. Hard particles or asperities that cut or groove one of the rubbing surfaces produce abrasive wear. This hard material may be originated from one of the two rubbing surfaces. In sliding mechanisms, abrasion can arise from the existing asperities on one surface (if it is harder than the other), from the generation of wear fragments which are repeatedly deformed and hence get work hardened for oxidized until they became harder than either or both of the sliding surfaces, or from the adventitious entry of hard particles, such as dirt from outside the system. Science and in industrial research. Adhesive wear occurs when two bodies slides over each other, or are pressed into one another, which promote material transfer between the two surfaces Two body abrasive wear occurs when one surface (usually harder than the second) cuts material away from the second, although this mechanism very often changes to three body abrasion as the wear debris then acts as an abrasive between the two surfaces. Abrasives can act as in grinding where the abrasive is fixed relative to one surface or as in lapping where the abrasive tumbles producing a series of indentations as opposed to a scratch. According to the recent tribological survey, abrasive wear is responsible for the largest amount of material loss in industrial practice. Erosive wear can be defined as the process of metal removal due to impingement of solid particles on a surface. Erosion is caused by a gas or a liquid, which may or may not carry, entrained solid particles, impinging on a surface. When the angle of impingement is small, the wear produced is closely analogous to abrasion. When the angle of impingement is normal to the surface, material is displaced by plastic flow or is dislodged by brittle failure.
MATERIAL SELECTION
ZA 27 is superior bearing performance than bronze alloys. The ZA 27 alloy have high strength is reported to have properties equivalent to those of aluminium alloys. Abundant availability, good bearing and mechanical Properties such as wear resistance, anti-seizure properties, yield and tensile strengths scored in favour of extensive use of these alloys for bearing applications. The ZA 27 alloys offer low energy demand and pollution free, melting with low melting losses and requires no special heat treatment to develop optimum performance. Compare with bronze the ZA 27 alloy hold great promise of high strength, excellent bearing, wear resistance and long service life at significant lower cost.
MATERIAL PREPARATION
The material composition for prepare ZA 27 alloy is Aluminum 27%, Magnesium 0.02%,Copper 2.6%, Silicon 2.8%,zinc 70.30. Previously the mould was set up with 25 mm circular shape pattern with 300 mm length. The ZA 27 alloy is taken out from the meting process in the temperature controlled electrical furnace using sand casting method.
METHODOLOGY
ZA 27 alloy is taken as investigation material to investigate the abrasive wear behavior. The conceptual procedure was followed to determine the abrasive wear rate of ZA 27. Experimental work- Sliding wear test were performed using pin on disc friction and wear tester to determine the wear rate of sliding surface under dry condition by varying load, by varying rotating speed and by varying sliding distance. Results and discussions The determined coefficient of friction and wear rate were plotted as a function of applied load, varying distance and sliding velocity to compare the tribological properties under different process parameters. Optimization of wear behavior of ZA-27 using Taguchi optimization technique.
OPTIMIZATION
Optimization is the discipline of adjusting the process in order to optimize the process parameters without violating some constrains. The various optimization processes are as follows: Simulated annealing, Genetic algorithm, Taguchi method, Gradient- based search, Response surface methodology The purpose of this project is to find the optimum parameters to produce low wear rate for ZA-27 alloy using Taguchi method. The Taguchi method involves reducing the variation in a process through robust design of experiments. The overall objective of the method is to produce high quality product at low cost to the manufacturer. The Taguchi method was developed by Dr. Genichi Taguchi of Japan who maintained that variation. Therefore, poor quality in a process affects not only the manufacturer but also society. He developed a method for designing experiments to investigate how different parameters affect the mean and variance of a process performance characteristic that defines how well the process is functioning. The experimental design proposed by Taguchi involves using orthogonal arrays to organize the parameters affecting the process and the levels at which they should be varied; it allows for the collection of the necessary data to determine which factors most affect product quality with a minimum amount of experimentation, thus saving time and resources. Analysis of variance on the collected data from the Taguchi design of experiments can be used to select new parameter values to optimize the performance characteristic
CONCLUSION
Wear rate of the ZA-27 alloy was investigated on the pin on disc tribo meter conforms to the specification of ASTM ,under dry condition by varying specific loads, by varying rotating speed and by varying sliding distance. The experimental results was optimized by Taguchi optimization technique.
The contribution of process parameters for wear rate of ZA-27 are in the order of Sliding distance, Load and Speed.