Thin Tungsten Sheet of X-ray Shielding Material for CT Machine

The thin tungsten sheet used for X-ray shielding material of CT machine is a high precision material with thickness of 0.1-0.2 mm and dimension tolerance of <0.01 mm. At present, the thickness tolerance of ultra-thin and high-precision tungsten sheet used for the collimator shade plate, the core component of CT machine, must reach (+5%) in order to ensure the stability of X-ray signals detected and obtain high-resolution images. How to make the tungsten sheet deform uniformly in hot working, and the surface is easy to handle, without causing surface indentation is the core issue to ensure tolerance. The choice of lubricating materials and methods is very important.

In the rolling process of thin tungsten sheet, the slab of tungsten sheet must be heated at 180-220 ℃, then the atomized graphite emulsion powder is sprayed uniformly on the tungsten sheet, and the graphite powder layer with thickness of 10-20 micron is formed after 20-30 minutes of heat preservation and drying, and then the rolling temperature is heated, and the processing rate is 60%. The specific process is as follows:

Graphite emulsion was prepared with S-1B superfine graphite powder according to the formula of graphite:water=1:4 (volume ratio). Tungsten sheet with thickness of 0.9mm was heated to 180 ℃. Graphite emulsion was sprayed on tungsten sheet with spray gun and dried to form graphite powder layer with thickness of 10um. The sprayed tungsten sheet was rolled at 600 ℃ with a 60% processing rate. The thickness of tungsten wafer is 0.2 + 0.01 mm, and the surface quality meets the requirements of medical high-precision tungsten wafer.

The concentration of graphite emulsion is adjusted according to the same thickness of tungsten wafer. Generally, the thickness of tungsten wafer is large and the proportion of water in graphite emulsion is small. The thickness of tungsten wafer is small and the proportion of water in graphite emulsion is large. The drying temperature of Sprayed Tungsten sheet should not be too high. It is advisable to use 200 +20. Otherwise, the graphite emulsion will not bond tightly with the surface of tungsten sheet, resulting in bubbling, which can not achieve the purpose of lubrication processing. Usually when the processing rate of tungsten sheet reaches about 60%, the processing should be stopped, the surface of tungsten sheet should be washed by acid and alkali, the residual graphite should be removed, and then sprayed again. By repeating the above process repeatedly, the dimension tolerance and surface quality control of tungsten wafers can reach the required level. All spraying and processing processes are hot-processed, the temperatures are spraying/baking 200 20 and hot-working 600 900 respectively. With the deformation of tungsten sheet, the processing rate of the coating is always controlled at about 60%.

The above process can solve the disadvantageous effect of lubrication coating on tungsten tolerance control and surface quality improvement. As a result, the processing rate of graphite emulsion falling off from the surface of tungsten wafer increases from about 40% to about 60%, and the surface roughness can reach 1-2 micron. The dimension tolerance is (+0.01 mm), which effectively improves the bonding strength between graphite and tungsten sheet surface, and can be used to mass produce ultra-high precision tungsten sheet for CT machine.

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