The Bearings Bench Lateral by Changing the Spacer Stack Length - Research Paper Example

Introduction Bearings are regarded as type of support element of the rotating shaft. Bearings are used for the loading purpose, and the type and sizeof the bearing is based upon the rotating speed of the shaft and its diameter. The bearings dampen the vibration impact of the shaft, and provides cushion to the rotating shaft, and the impeller or rotor mounted of the shaft. The bearings are of two different types' i.e. anti-friction bearings and friction bearings. The anti-friction bearings are commonly known as ball bearings, whereas friction bearings include ball bearings, roller bearings, and angular tapered ball bearings. The difference between these two types of bearings is based upon their design and manufacturing process, the application of these two different types of bearings is based upon the load and speed of the shaft. The ball-type bearings are commonly used where the speed of the shaft is high; however sleeve bearings are preferred for high load machines. This specific case is relevant to wind turbine, generally the load of the wind turbine is low, and however it has high speed therefore based upon generic technical evaluation the anti-friction bearings i.e. ball-type bearings are preferred. The ball-type bearings are lubricated through greasing or oil, the limited amount of oil or grease is required after specific period, which is actually positive aspect of using ball-type bearings. The sleeve bearings generally require forced supply of lubrication oil to prevent any damage to the bearing material; this requires entire circuit for the lubrication inclusive of pumps, heat exchangers and filters. The space economy is vital for wind turbine; therefore the ball-type bearings are preferred for such machinery design. Material Compatibility The raw material generally preferred for the manufacturing of the ball-type bearing is steel alloy. As per the standard practices, high alloy steel bar is used for the fabrication of the outer races, inner races, wear rings and automotive rings; the recommended materials are BMS-931 and 8720H. The automotive rings and wear rings are fabricated from steel alloy 1040, 52100 or 8720; the BMS 931 material is used for the fabrication of bearing races. The raw material used for the manufacturing of the bearings is provided in rolls; the same form is used for manufacturing of bearing parts including cages and seal cases. The cages and seal cases are fabricated from "usually low alloy or plain carbon steels such as 1008 or 1015 steel" (Bruce, 1997). The bearing manufacturing begins with the forging of the steel bar into cups, cones, wear rings, and automotive rings; the forging process is hot forging and shall be helpful in the release of t he thermal and residual stresses from the material. The forging process is descriptive process; it includes the exposure of the steel bar in the induction heater system, the heating process shall be immediately stopped once the temperature reaches the melting point of the material; this temperature provided "maximum formability for hot forging". After the exposure towards high temperature, the hot bar is "sheared into slugs once it reaches the forging press; then the slug is upset, partially formed, and pierced" (Schmid, 2000). Manufacturing of Inner and Outer Race The manufacturing of the inner and outer race of the ball-type bearings has been summarised. The raw material i.e. forged rings of SAE-52100 Steel are introduced into turning operation, from where centre-less grinding is applied, the object is then heat treated, and hardness testing is verified. The process of rough grinding them commences, and ends with finish grinding. The object undergoes the honing and super finishing, followed by washing. The object is then coated with anti-rush agent before shipment (Bruce, 1997). Forging Process Normally more than seven parts are produced after every minute through this forging press. As per the recommended procedure, "the smaller forgings are rolled into larger rings in open die ring rolling where the part is worked between a king wheel and mandrel" (Bruce, 1997). The directionality to the grain structure is possible through ring rolling; the exercise is responsible for the achievement of the desired shape and size of the part. Such procedure is responsible for the "increase in the application strength and fatigue life of the part". Once the ring rolling is completed, the object is "further sized on diameter to bring it closer to near net shape; the forging then is placed on the draw line which offers several options for cooling: air, controlled temperature etc" (Schmid, 2000). The object then undergoes the process of cold forming, where seal cases and sages are produced through multi-station transfer presses, the process is applied directly upon the object which is sheet steel. The process is significant, and can handle several objects at a time, "the press produces over 600 parts per minute for seal cages and over 850 parts per hour for seal cases" (Bruce, 1997). The seal cases are "phosphated and chemlocked" before these undergo moulding, the cages on the other hand are "wheelabrated and then phosphated". The deburring process is then initiated to remove the sharp edges and loose materials; the removal of such materials will "relieve surface tension" (Schmid, 2000). The process wheelabrator can be explained as the bombardment of the surface component with peas-sized shot. Once the deburring process is completed, the cages are than phosphated. These parts are then "closed as part of a unitized assembly with the cone and rollers". Cold header is used for the stamping of roller pre-forms through steel coil, "a draw line straightens and reduces the coil before it is fed into the header". As per recommended practice, "the header shears a length of the bar and forces it into a tapered die forming the head and body". After series of experiments, it was estimated that cold header can produce 3,000 rollers in hourly basis. The seal is produced through rubber compounds; this rubber is "compression moulded onto the seal cases using vacuum presses" (Bruce, 1997). The mixing of the rubber compound continues until its dispersion is witnessed, after its dispersion occurs then the compound is rolled into "pig and loaded into hydraulic extruder" (Schmid, 2000). During this process the extrusion of the rubber compound occurs in the form of specific size and weight through "vulcanizing or moulding operation". During vulcanization process, the seal casing and pre-form compound are fused in the mould cavitities. The seal curing is controlled through hydraulic pressure, platen position, and platen pressure; all these are function of vacuum presses. The press cavities are evacuated through a vacuum storage reservoir during the vulcanizing process. The vacuum procedure is recommended; it is regarded as "consistent and defect free operation". In the next stage, an adhesive gasket material is coated upon the outside diameter of the seal casing. The application of the adhesive gasket shall maintain perfect seal between the seal casing and the cup counter bore; "the seal is pre-lubricated with grease between the dust lip and fluid lip" (Schmid, 2000). Machining Soon after this process machining is started. All the constituent parts of the bearings; "forged components i.e. cups, cones, wear rings, tubing components i.e. spacer, wear rings, and castings components i.e. backing rings, end caps" are all machined. The machining of all these parts can be conducted on multi-spindle chucker and single spindle CNC lathes etc. Heat Treatment Once the machining process is completed, the heat treatment process is started. All the important components of the ball-type bearings are heated. The intent of heating exercise is to "proper wear and fatigue resistance" to the material (Groover, 1996). The components of the bearings are initially carburized, and then soaked in a carbon gas solution. The exposure to the carbon gas condition is possible through "regulation of gas flow, furnace temperature, and process time", this shall "assure accuracy, consistency and maximum efficiency of the operation". Once the exposure of the high temperature through case carburizing is achieved, the parts are "cooled to room temperature, heated in a rotary furnace, oil quenched and drawn to provide a case-hardened part with controlled dimensions" (Thyer, 1991). After the completion of the manufacturing process, the "heat treat case depth, hardness, carbon content, grain structure and retained austenite are verified". In later stages the heat treated components are exposed with rotary try furnaces. The pusher tray furnaces are successful assembly, and it offers "consistent environments for carburization, cool down, reheat, quench, and tempering of a continual product flow" (Groover, 1996). This fabrication process has therefore emerged as "more capable, more consistent, and cost less than the pit furnaces" (Thyer, 1991). Soon after this process, the bearing undergoes the process of grinding. The intent of grinding the object is to achieve required geometry, dimensions and surface finishes of the desired parts of the object. Grinding Grinding process can be summarised as "face grinding, outside diameter grinding and inside diameter grinding are operations performed on all cups, cones and wear rings" (Thyer, 1991). The grinding process is considered to be critical, the process handles and verifies the roundness, concentricity, profile and bore sizes. The verification of the dimensional characteristics is critical, and it is essential to ensure the compliance of the recommended design against the actual design by ten thousandth of the inch. After the process of grinding is completed, the rollers or balls are inspected, the intent of the inspection is to verify the non-existence of imperfections on the surface of the rotating elements; this exercise is conducted through computerized automatic camera inspection systems in special cases. In the case of ball-type bearings installed on the wind turbine, the inner race is rotary, whereas the outer race is stationary. The inspection of the ball-type bearings is conducted through eddy-current testing, which verifies the hardness of the roller; the ultrasonic inspection system has been proposed to detect "external and internal defects such as seams and pipe defects" (Thyer, 1991). The rollers are then assembled with the cage and cone, the assembly is possible through fully automated machine. From here onwards the object is shifted to closing press; the closing press consists of an arrangement such that "bars of the cage are closed in around the rollers in order to maintain spacing" (Groover, 1996). The recommended diameter variation of the rollers is 0.0005". Once the manufacturing is completed, the entire object is inspected. The calcium-rich zinc phosphate is coated on the cups, cones, and wears rings. The significance of this process is that it assists in the identification of the "grinding burns on raceways", and through coating the raceways are protected during the assembly process (Thyer, 1991). Assembly The part is then assembled; the advanced techniques have been established to ensure desired assembly of the objects. In most of the industries, the automatic, power lateral machines have been installed which estimates the lateral movement of the cones, and "optimizes the bearing's bench lateral by changing the spacer stack length" (Groover, 1996). Fig.1 Grinding of inner and outer races. Fig. 2 Manufacturing process under-progress. Fig. 3 Manufacturing of bearing balls. Fig. 4 Manufacturing process under progress. Fig 5. Manufacturing of cages for ball-type bearings. Fig 6. Assembling of ball-type bearings under progress. References 1. Kalpakjian & Schmid. Manufacturing Engineering and Technology. Addison-Wesley Publication. 2000. 2. Bruce Gregg et al. Modern Materials and Manufacturing Processes. US Imports & Phipes Publication. 1997. 3. Kalpakjian. Manufacturing Processes for Engineering Materials. Addison-Wesley Publication. 1997. 4. Mikell P Groover. Fundamentals of Modern Manufacturing. Wiley Publication. 1996. 5. GE Thyer. Computer Numerical Control of Machines. Butterworth-Heinemann. 1991. Read More