What is a Back Scratcher?

Scraper is the main tool for scraping. Generally, T12A high carbon tool steel is used to make the scraper. According to the different scraping surfaces of the workpiece, the scraper can be divided into three categories: flat scraper, triangular scraper and crescent scraper. The flat scraper is mainly used to scrape flat surfaces, such as flat plates, flat tracks, tables, etc., and it can also be used to scrape outer curved surfaces. The triangular scraper is one of the commonly used tools for scraping bearing pads. Bearing bores, etc.

The scraper is the main tool for scraping. The quality of the scraper is an important factor that determines the efficiency and quality of the secondary cutting. Therefore, pay attention to the correct selection and sharpening of the auxiliary knife when scraping.

The material of the auxiliary knife is T12A high carbon tool steel, which has a better effect. The hardness after quenching is RC60 ~ 65. For the purpose of saving, you can use medium carbon steel as the blade body, and weld a section of high carbon steel blade in front. ^[1]

The treatment of the blade edge part mainly includes rough grinding, heat treatment and fine grinding.

Scraper rough grinding

Before quenching the scraper, the upper and lower planes should be smoothed on the coarse grinding wheel, and then the edge of the scraper and the arc shape of the blade should be ground into different arcs according to different scrapers.

Scraper heat treatment

When processing high carbon tool steel, immerse the cutter head 25 mm long in a salt bath furnace, heat it to 760 ° ~ 780 ° C, then take it out and cool it in water. The quenching length should not be too long, as it will affect the elasticity of the scraper. Because the scraper requires high hardness, it should be immersed in water for quenching during quenching without tempering. If you do not have a salt bath furnace, you can also heat it in the stove. When heating, pay attention to observation. The heating should be uniform. When the temperature reaches 760 ~ 780 , the blade head becomes dark pink. At this time, it should be quenched quickly. Do not overheat when heating. If the temperature is too high, even if it is cooled to a suitable temperature and then quenched, it will expand the lattice of the scraper tissue, causing the scraper to be polished.

Scraper grinding

After the blade is quenched, the large surface and the blade can be ground on a fine grinding wheel first, and it should always be cooled in water during grinding to prevent annealing. If it is ground well during rough grinding, it can be sharpened directly on the oil stone after quenching. The whetstone of the grinding blade should use white corundum (GB) whetstone with high hardness, and the particle size is better in the range of M7 ~ M5 (800 ~ 1000). When sharpening the scraper, work hard to sharpen the two large surfaces of the scraper. When grinding, use the edges and corners of the stone as much as possible. Because it is more convenient to use the middle of the oil stone, the result is that the stone is quickly ground into a saddle shape. When sharpening the large surface of the scraper, be careful not to grind the large surface into an edge composed of several planes, smooth the large surface, and observe whether this plane passes all the way to the edge of the cutting edge. The smoothness of the surface should be polished to 12 or more.

If it is a scraper for rough scraping, lightly grind the end edge on a fine grinding wheel and use it. After using blunt, the same treatment. If it is a fine knife, the end should also be sharpened on the oil stone. The angle of the forward tilt of the scraper during grinding should be determined according to the difference between the coarse and fine scraper.