Coil Spring Failure - Assignment Example

Coil spring failure According to Bartolozzi (2011), a coil spring is a mechanical device that is tied in a spiral shape or pattern and found in suspension systems. Coil springs are used in the front and rear suspension springs to hold up weight of a vehicle when a load is added. Coil spring absorb the shock when the wheel is compressed. Coil springs are made up of flexible material which assumes the shape of a helix when compressed and later returns to the initial length whenever a load is removed. The coil spring is manufactured using spring steel which is a low carbon steel with high yield strength. There are two types of coil springs which include, constant coil springs that restore the vehicle to the original ride height and handling the performance, and the variable coil springs which change in resistance as the pressure gets stronger and stiffer when the load increases (Wulpi, 1984). The type of a failure that happens to a coil is breakage (Collins, 2003). This occurs when ripped seals in struts of vehicles cause fluid leakage that can cause strain on the coil spring damaging them to breakage point. The breakage also occurs due to decrease in hydraulic pressure which may cause the springs to come in to contact with other suspension components, or exhaust components break lines leading to breakage of the coil spring. The fracture can be caused by riding on a blown out tire that exposes the vehicle springs and other suspension components in to direct contact with road way making the suspension component to be stressed beyond normal limits leading to fracture. Environmental factors Environmental factors cannot be isolated from the functioning of the coil suspensions and other suspension components. One of the factors that have negative influence in the operations of the coil spring is temperature. An increase in temperature alters the elastic modules and the elastic limits of spring materials. This reduces the strength of the module leading to eventual breakage if it is exposed to rough road or excessive load. The other environmental factor that causes coil spring breakage is the corrosion. This starts with the emergence of winter. Winter usually accompanied by snow, ice, cold temperatures, and salt in roads. Due to the poor design of coil springs, they allow road debris to collect around the bottom of the coil spring. This causes water and salt to mix with the road debris where they form a grinding paste. This paste accelerates the corrosion of the coil spring at the bottom of the coil. Thus, in case of a sudden impact on the coil spring caused by driving over a speed bump or rough road with huge deep holes the spring breaks (Wulpi, 1984). Confirming the material and process The confirmation of the material and the process used in manufacturing the coil spring is best evaluated using the Edu park software. This software is designed for the teachers and students to assist them to search for materials and data that they require on coil spring. It also assists in graphing of features and to support systematic material, as well as, process selection. Before using the Edu park software, it is important to determine, the expected functions of coil spring. Functions of coil spring The coil spring helps to maintain the stability of the vehicle and enables the driver to control the vehicle easily by absorbing the shock and maintaining the weight that could have caused the instability of the vehicle. A malfunctioned suspension system accelerates the wear and tear of the vehicle because the stress exerted on the car is not controlled hence destabilizing the system. In addition, it may lead to accident because the vehicle is unable to balance the weight. List of attributes The coil spring possess very significant attributes which include ability to control spring and suspension movement, ability to prevent premature tire wear, and provide consistent handling of the vehicle and braking. They should also keep the tires in contact with the road in order to facilitate smooth running of the road and maintain dynamic wheel alignment which is crucial to the stability of the car. These suspension systems are also in a capacity to control vehicle bounce, dives, rolls sway and acceleration squat which if not properly controlled can lead to accidents (Collins, 2003). They are also capable of maintaining even and balanced tire and brake wear and obviously reduce the driver fatigue. These attributes are reflected in the values listed below and tested using Edu park software. Values of springs These are the various factors that affect the strength of the spring. These factors are analyzed below to help determine the efficiency of the spring using Edu park software. The first factor is the stability or buckling of spring. The stability of the spring is crucial to its operation. The coil springs lose stability once the free length of the spring becomes longer and the supporting devices are not stable to distribute the load evenly throughout the circumference of the circle. Buckling in a coil spring can be controlled by preventing excessive deflection of the spring. According to Gilles (2012), absolute stability can be guaranteed if the critical length set below a given limit. The strength of the material has been illustrated by the figure below. Edu park software was used to show all the essential features, as well as, deformation that can be caused to the spring. The second factor that can be considered is fatigue loading. According to Gilles (2012), the coil spring is designed to last infinitely. This is based on the consideration that it has to sustain millions of cycles in operation daily without failure. The helical springs are not used for both compression and extension springs rather they are built with a preload such that the working load is additional. This gives the spring ability to sustain huge weights throughout the lifespan of the vehicle. Edu park software clearly shows this ability in the figure below. The third factor is spring relaxation. The springs are usually subjected to different capacities of loads. The springs are expected to operate for a long period of time without changes in spring rates or dimension. It is important to avoid subjecting the springs to full loads and stress that exceed the maximum strength of the material. This is because excessive load may cause permanent deformation that prevents the spring from providing the required force or releasing the stored energy for subsequent operations. However, springs are subjected to some amount of relaxation which is defined as the function of the spring material and the amount of time the spring is exposed to higher temperatures or stress. There are also static springs that are efficient with constant load applications where a spring with constant deflection spring is cycled in a specified range (Gilles, 2012). Using the Edu park software the selection of the materials is done with great caution to ensure that they possess the right attributes for proper relaxation. Edu park illustrated the following characteristics for proper relaxation. This figure from Edu Park showed that the material to be selected should be as light as possible while at the same time it should be stiff enough. Having identified these specific functions of the spring system, it is important to demonstrate the design of the springs. Coil springs allow the frame and the body of the vehicle to ride with minimal disturbance while the tires and the suspension navigate the bumps on the road. These springs are designed such that when a vehicle meets a bump on the road or additional load is placed on the car, the springs at the rear and front tires absorbs the load by compressing (Gilles, 2012). The functions of coil springs are enhanced by the shocks and struts assist to scheme how fast the springs and the suspensions move. This scheming enables the tires to maintain a firm contact with the road. When springs are deflected, they accumulate energy. The spring’s inertia then causes it to bounce and overextend before re-compressing. This process repeats itself until all the energy stored into the springs is used. It is however, important to note that operations of the springs rely greatly on the efficiency of the shocks and struts. This is because they allow the tires to oscillate between two or more continuous diminishing circles hence limiting excessive movement and maintain the vertical road placed upon the tires (Wulpi, 1984). If the shocks are worn out, the vehicle loses contact with the road because the vehicle uses up all the energy exerted by the pump bouncing back and forth. The experiment below using Edu park was used to show the structure of the material. It is fundamental to note that the design of the springs in terms of diameter and length help to determine their efficiency and strength. The coil spring is made up of round spring steel rod that is tied into a coil. The principle behind its function is that by increasing the diameter, the coil becomes stronger while increasing the length makes it more flexible. The strength of the spring is measured using the deflection rate which is expressed as a function of the amount of time taken to compress the spring by 1 inch (Wulpi, 1984). Environmental effects on components The study also found out that temperature plays a very crucial role in altering the elastic module of the spring. It was found that the elastic module of spring alloys decreases with increase in temperatures. Hence, increase temperature causes an irreversible decrease in strength of the spring materials (Collins, 2003). This irreversible change may occur either by reducing the spiral load at a fixed length when the vehicle is loaded or reducing the spring load at a fixed rate. The decrease in strength occurs rapidly at first, and then progresses in a decreasing rate over a given period until it is unable to hold the load of the vehicle any longer. This makes the car uncomfortable to ride on and difficult for the driver to control it hence compromising the safety. It is therefore clear that temperature levels affect the operations of machines. These effects are extended to other uses such as construction, automobiles, shipping industry among other diverse users of steel. The other environmental effect identified was the corrosion of metals. Though a plastic coating is applied to coil springs when they are being manufactured in order to reduce the risk of corrosion, the contact between coils as the spring is repeatedly compressed cause damage to the coating. This damage exposes the surface where the formation of a grinding paste occurs (Collins, 2003). Corrosion also exposes the micro structure of the coil material to the atmosphere which makes it susceptible to hydrogen embrittlement process. This is a process of electrolytic action between the salty solution and the iron in the coil spring which causes generation of free hydrogen atoms which penetrate inside the steel and cause microscopic cracking. These cracks continue to spread and combine over time which ultimately leads to the spring breakage Conclusion The research has found out that the corrosion of steel due to environmental effects such as increased temperatures and the process of embrittlement weakens many metals. This discussion has focused on the coil spring system which helps the car to hold its weight. The malfunction of this system compromises the comfort and safety of the persons. This research also looked at the controlled electronic suspension system that has integrated the whole suspension system giving the cars a new stability in which shock absorbers, struts and springs work together. There are also desirable attributes of the coil springs and best way of strengthening their material. References Bartolozzi, R., & Frendo, F. (January 01, 2011). Stiffness and strength aspects in the design of automotive coil springs for McPherson front suspensions: a case study. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 225, 10, 1377-1391. Collins, J. A. (2003). Mechanical design of machine elements and machines: A failure prevention perspective. New York, NY: Wiley. Gilles, T. (2012). Automotive service: Inspection, maintenance, repair. Clifton Park, NY: Delmar, Cengage Learning. Wulpi, D. J., & American Society for Metals. (1984). Failure analysis. Metals Park, Ohio: American Society for Metals. Read More