Self-cleaning

Cerium is a component of misch metal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. The oxide is an important constituent of incandescent gas mantles and is emerging as a hydrocarbon catalyst in self cleaning ovens. In this application it can be incorporated into oven walls to prevent the collection of cooking residues. 

Electromagnetic flow meters ate avadable with various liner and electrode materials. Liner and electrode selection is governed by the corrosion characteristics of the Hquid. Eor corrosive chemicals, fluoropolymer or ceramic liners and noble metal electrodes are commonly used polyurethane or mbber and stainless steel electrodes are often used for abrasive slurries. Some fluids tend to form an insulating coating on the electrodes introducing errors or loss of signal. To overcome this problem, specially shaped electrodes are avadable that extend into the flow stream and tend to self-clean. In another approach, the electrodes are periodically vibrated at ultrasonic frequencies. 

Air cleaning systems are often used to remove dust or vapors from plant or process exhaust streams. Dust collecting systems such as filters or electrostatic precipitators that handle heavy loads of dust are usually designed to be self-cleaning, but it is stiU. necessary to enter the air cleaner periodically for inspection or repair. Dust deposits inside the equipment are likely to be stirred up and inhaled by unprotected workers. Baghouses are particularly likely to cause exposure because large amounts of dust may be retained in the cloth and released when the bags are handled. 

Fig. 2. Self-cleaning suspended magnetic separator over conveyor mn (cross-belt), where A = conveyor belt width B = distance to magnetic belt.

Fig. 3. Suspended magnets, where A = conveyor belt width B = suspension height C = overall height D = distance to magnet centerline and E = location of lift point, (a) Manually cleaned over conveyor mn system, (b) manually cleaned over head pulley, and (c) self-cleaning separator over head...

Selection. Suspended magnet selection requires deterrnination of the burden depth using one of the following formulas. For installation flat over the belt or transverse self-cleaned mounting, the burden design is calculated as... 

The advantages claimed for organotin polymer-based antifouling paints include constant toxicant deHvery vs time, erosion rate and toxicant deHvery are controUable, no depleted paint residue to remove and dispose, 100% utilization of toxicant, polishing at high erosion rates, surface is self-cleaning, and function is continuously reactivated. 

Since there are no dead spaces in a SHE, the helical flow pattern combines to entrain any solids and create high turbulence creating a self-cleaning flow passage. 

Another type of trough-and-screw mixer with a large volume available for mixing is the AP Conti (List AG) machine shown in Fig. 18-53. These self-cleaning-type mixers are particularly appropriate when... 

Electrostatic-Separation Machines The first electrostatic machines to be used commercially employed the principle of contact elec trification. These were free-fall devices incorporating large vertical plates between which an electrostatic field was maintained. Tribo-elec tric separation (contact charging) has experienced an increase in apphcations due to advances in mechanical self-cleaning and electrical design as well as the development of efficient precharging techniques. 

Self-cleaning effect Slight Medium/High High Low... 

Self-cleaning A filter similar to the rotary viscous in which the filter plates are passed through an oil bath to remove the collected dust. 

Self-cleaning An air-cleaning device that has the ability to be mechanically or chemically cleaned. 

Reverse air cleaning filters Filters that become self-cleaning by dislodging the impacted dust when the gas flow is reversed. 

SELF CLEANING design prevents corrosive buildup. There are no boffles or blades to wear within colleciion oreo. Entire orco it octi ve—no deod oreos for Qccumulotion of dust. 

Not self cleaning, fouls and plugs relatively easily. 

Reliable enclosed filters of ample effective filtering area should be used for both stages. The filter design should not allow the pressure drop to exceed 7kN/m (1 Ibf/in ) across second-stage fine filters in clean conditions. Filters should preferably be of the duplex or self-cleaning type, and installed so that oil spillage will not occur during operation. 

For installations in areas of heavy contamination, such as quarries or cement works, additional filtration or automatic self-cleaning is required otherwise, the air filter will clog up rapidly. Filter condition indicators are available and are recommended. 

Oil strainers may be of metal mesh and within the sump, in which case the sump must be opened for cleaning. Self-cleaning disc strainers are also used, the dirt falling into a drain pot or into the sump itself. There is an increasing tendency to provide replaceable fabric oil filters external to the compressor body, following automobile practice. 

Quite recently (2001) titanium dioxide has been used to coat "self-cleaning" windows with a very thin film about 5 x 10-6 cm thick. The titanium dioxide acts as a catalyst for the decomposition of dust and grime by solar ultraviolet light. Probably more important, it lowers surface tension so that rain water "sheets down" the window, washing away dirt. 

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