Need of Lapping Machine for Valve Component: A Case Study – Mechanical projects
Lapping process is characterized by its low speed, low pressure, and low material removal rate. This process is used in achieving finer surfaces and closer fits, correction of minor imperfections, and maintaining close tolerances. During the process of lapping, the mechanisms of surface formation and removal rate are decisively influenced by the movement type of the individual grains within the lapping abrasive. A gate valve is used to start and stop the flow of fluid. So the wedge and seat ring of a valve are in continuous pressure of fluid flow and due to opening and closing of valve these component get wear and they need lapping during reconditioning. This paper will share the need, requirement and application of lapping during the reconditioning of valve. This paper will explore the current working condition of lapping machine in valve industry. It will elaborate the effect of abrasive particals, working speed, surface roughness and other related parameters. What are the difficulties they are facing during the valve reconditioning related to lapping, will be disscussed. Current set up and the changes required in this model are suggested with the proposed model.
Lapping is a micro finishing operation which is required to require getting a mirror like surface finish on the meting component. It provides a good strength to joint formed. Lapping has been used extensively in the manufacture of optical mirrors and lenses, ceramics, hard disk drive, semi-conductor wafers, valve seats, ball bearings, and, and many more parts. Several factors need to be considered during the process of lapping. This includes factors such as type of machine, condition of the lap plate surface, speed of the lap plate, type of abrasive, type of carrier fluid, slurry concentration, slurry flow rate, size and shape of abrasive, material of the lap plate, rigidity of the lap plate, applied force on the work piece, time of operation and duration between the two consecutive instances of application of fresh abrasive slurry.
NEED OF LAPPING FOR VALVE COMPONENT
Valve lapping is a essential part of maintenance work that often interrupt production work. Repairing leaking valve in industry is a laborious operation involving extended downtime, production losses and substantial unwanted cost. The given figure shows different parts of a gate valve.
COMPONENT THAT REQUIRE LAPPING
Wedge of a valve :
This is a wedge of a valve which is under continuous pressure of fluid flow. The sizes of the wedge varies as per the size of valve for example 2”,4” ,6” etc. valves . To close the valve these wedge are mesh with the seat ring. These wedge requires lapping after 60-70 openings of valve. To get a leak proof component these portion requires lapping.
Seat Ring :
Wedge or disc meshes with the seat ring of valve. It is actually a ring made up of stainless steel , bronze etc. material. The shape of seat ring goes on changing with continuous use. It becomes tapered and get leaked so it requires lapping. Size of seat ring also varies as per the size of valve. Small size seat rings are either press fitted or they may be welded to sustain fluid pressure.
DEVELOPMENT OF LAPPING MACHINE
A visit to an industry it is being observed that they were performing lapping operation on a set up which was developed by them. They fixed the lapping tool to the conventional lapping machine which is fixed. They fixed the valve on a vice and perform lapping on the valves. Observing the operation we are trying to propose on model which will be portable, can be handled y one person and it will reduce the set up time also.
PROPOSED MODEL OF LAPPING MACHINE
A high torque drilling machine is used which will be generating a shaft speed of around 240 rpm. Through this shaft rpm is transferred to reduction gear box which will reduce it to 80-100 rpm. This speed is best for performing low speed lapping operation . This gear box is mounted on holding plate which has holes on it. This plate will help us to hold the set up on frame for lapping wedge or hold the set up on body of valve. Shaft through that gear box is connected with the lapping plate which is made up of cast iron . A guide is provided at the centre to keep lap steady. The distance between seat ring and body of valve will vary according the size of valve. So length of shaft will be according to the size of valve.
ABRASIVE MATERIAL USED FOR LAPPING
The most commonly used abrasive materials for lapping of valves seats are alumina and silicon carbide. It is the objective of this research to obtain sufficient data by lapping. Three types of abrasives: (1) garnet, (2) alun-dum (aluminum oxide), and (3) crystolon (silicon carbide) (4) CARBURANDM (silicon carbide) were used to lap the work pieces. Generally, the high peaks are abraded by coarse grains of average diameter about 80 mm (F80: coarse lapping), the average height s peak s by grain size between 40 and 20 mm (F40 and F20: average lapping ) and the low height s peaks by fine grain size of 7 mm (F7: fine lapping ) are available for lapping. We will perform coarse lapping and fine lapping on valve component.
The above research work and the proposed model can provide benefit in the lapping of valve component. Model will provide portability and reduce the set up time for lapping to some extent. The paper shows the importance of lapping operation in a valve industry. It show the size and type of abrasive used for valve lapping. As compared to the available machine for lapping, this proposed model will be the cheaper model. It will prove to be an economical model. The number of labors require to operate this machine is only one and less skilled labor can operate this model.
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