Blinding of screens

Although many commercial crystallizers operate with some form of selective crystal removal, such devices can be difficult to operate because of fouling of heat exchanger surfaces or blinding of screens. In addition, several investigations identify interactions between classified fines and course product removal as causes of cycling of a crystal size distribution (7). Often such behavior can be rninirnized or even eliminated by increasing the fines removal rate (63,64). 

Blinding of Screens and Methods of Prevention.— Blinding is of two kinds (1) agglutinative, as with flour mill products, which is relieved by brushing or rubbing on yielding screens and (2) of the sort where the particles are not de-... 

The screen is typically constructed of a vv edge-bar with an aperture betvv een adjacent bars, which opens up to a larger radius. This prevents solids from blinding the screen as vv ell as reduces conveyance torque. For abrasive materials such as coal, the screens are made of vv ear-resistant materials such as tungsten carbide,... 

Vibration Amplitude and Frequency Speed and amplitude of vibration should be designed to convey the material properly and to prevent blinding of the cloth. They are somewhat dependent upon the size and weight of the material being handled and are related to the angle of installation and the type of screen surface. The object, of course, is to see that the feed is properly stratified for the most efficient separation. 

Fluid flow through fixed bed reactors usually is downward. Instead of screens for supporting catalyst in the vessel, a support of graduated sizes of inert material is used, as illustrated in Figure 17.27. Screens become blinded by the small particles of catalyst. A similar arrangement is used at the top to prevent disturbance of the catalyst level by the high velocity fluids. 

Temazepam (15 mg) was compared with triazolam (0.125 mg), zolpidem (5 mg), and placebo. After a single-blind placebo screening weak 335 elderly insomniacs were randomized to 28 days of double-blind treatment with the... 

Screening (Fig. 1C) is a type of surface filtration to separate solids and liquid by screens with openings smaller than particle size. It is usually employed among the first few steps of a SLS process. Vibrations and other mechanism are often applied to avoid blinding of the screens. 

Two techniques are used — screening and classification. Dry screening is routinely practised at sizes down to about 3 mm and can be extended to as low as 300 pm with dry products. Screening at smaller apertures causes blinding of the screen. Wet screening is widely used for sizes as low as about 0.5 mm. Classification of suspensions in water or air is used to divide at smaller particle sizes. 

---