Although precision engineering methods make fitting a simple matter, some activities still require that parts be assembled using hand fitting. Scrapers are acknowledged as tools suitable for removing material from parts that need to fit together.
What is Bearing scraper?
A bearing scraper is a precision tool with multiple sharp-edged blades. It is operated by hands to level out high spots on soft metal engine bearings.
The scraping process is aimed at achieving the correct geometrical alignments by evenly spreading the points of bearing contact.
Need of scraping for marine bearing
Scraping is the key to maintenance when it comes to marine bearings and scrapping of marine bearings is essential for the following reasons:
- To increase accuracy levels
- To remove very minimal amounts of metal from a precision surface and eliminate high spots caused by the rapid fluctuation of cyclic load on bearings during high speeds
- To ensure easy mounting of machinery components by providing a flat and accurate bearing surface
- To increase joint rigidity
- To remove scoring marks making the surface smooth
- To increase lubrication efficiency
Construction of scraper tools
Hanger– A small hole in the upper body of the scraper that is meant for placing the tool upright in the kit room or the designated area.
Handle– The handle starts from the top and follows till the edge of the shaft is generally made up of wood usually circular in shape to provide grip and facilitate handy and easy operation.
Shaft/Shank– This is the longitudinal cylindrical metallic part generally made of hardened or tempered steel which starts at the periphery of the handle and leads to the blade.
Blade– The lowermost operating part of the scraper is the blade whose shape may be triangular, curved as per the desired type of scraping and the scraper.
Types of scrapers
Flat or chisel type scraper- This type of scraper is also called the end scraper and looks like a chisel. It comes with sharp and slightly rounded ends aimed at the corner’s operation.
Triangular Scraper- A triangular scraper, generally made up of bronze or a white metal has a triangular blade with three corners running to a common point. Their typical use is to deburr holes or the internal surfaces of bush-type bearings.
Curved scraper– A curved scraper is incorporated with relief on its bottom and an integral shank fitted with the handle made of wood to provide grip. While it facilitates light scratch even in thin areas of an engine bearing, crankshaft main journal bearings or rod bearings.
Preparations done before scraping
- We should not attempt to scrape off three or four-thousandths of an inch of metal on a large surface.
- High spots should be identified before scraping through test fitting and once the camshaft bearings have been changes, test fitting could be done by rotating the camshaft once.
- The surfaces that are to be made flat should be checked against the surface plate and in case of bearing; as it is a curved surface, it must be checked against its mating surface.
- The surfaces that are to be scraped and the reverence surface should be perfectly cleaned.
- A thin film of Prussian blue should be applied on the reverence surface and the high spots could be determined by lightly rubbing the work against the blued reference surface which would determine the areas to be scrapped.
- Visible burrs should be removed before scraping with the aid of files.
Methodology of scraping
- To use the bearing scraper, we should rest the left wrist on the work or the vice if the workpiece is mounted on it.
- We should use a movement from the wrist or pulling with the left hand and et the blade slide over the workpiece while scraping it.
- When it is not possible to use two hands in close support, one must switch to the scraping tools with a negative contact angle to prevent digging in and chatter.
- After determining the areas to be scraped and the job done by curved bearing; we should then rematch the work to the reference surface until the work surface is covered uniformly with the coating of blue.
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Source- marineinsight
