Enclosed machines

A totally enclosed machine is one so enclosed as to prevent the free exchange of air between the inside and outside of the case but not sufficiently enclosed to be termed air-tight and dust does not enter in sufficient quantity to interfere with satisfactory operation of the machine. 1.26.1a Totally Enclosed Nonventilated Machine (IP54, IC410)... 

A totally enclosed nonventilated machine is a frame-surface cooled totally enclosed machine which is only equipped for cooling by free convection. 

A totally-enclosed water-cooled machine is a totally enclosed machine which is cooled by circulating water, the water or water conductors coming in direct contact with the machine parts. 

A water-proof machine is a totally enclosed machine so constructed that it will exclude water applied in the form of a stream of water from a hose, except that leakage may occur around the shaft provided it is prevented from entering the oil reservoir and provision is made for automatically draining the machine. The means for automatic draining may be a check valve or a tapped hole at the lowest part of the frame which will serve for application of a drain pipe. 

A totally enclosed air-to-water-cooled machine is a totally enclosed machine which is cooled by circulating air which, in turn, is cooled by circulating water. It is provided with a water-cooled heat exchanger, integral (IC7 W) or machine mounted (IC8 W), for cooling the internal air and a fan or fans, integral with the rotor shaft (IC 1W) or separate (IC 5W) for circulating the internal air. 

An explosion-proof machine is a totally enclosed machine whose enclosure is designed and constructed to withstand an explosion of a specified gas or vapor which may occur within it and to prevent the ignition of the specified gas or vapor surrounding the machine by sparks, flashes or explosions of the specified gas or vapor which may occur within the machine casing. 

A dust-ignition-proof machine is a totally enclosed machine whose enclosure is designed and constructed in a manner which will exclude ignitable amounts of dust or amounts which might affect performance or rating, and which will not permit arcs, sparks, or heat otherwise generated or liberated inside of the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specific dust on or in the vicinity of the enclosure. 

If the process demands a gradual shift from about pH 9 to a slightly acidic pH, ammonium sulphate together with ammonia can be used. This gives a safer, more uniform development of acidity than can be achieved by making additions of acid to an alkaline bath, although the degree of acidity developed will clearly depend on the ease with which ammonia can escape from the system. In enclosed or partially enclosed machines this system does not function so efficiently [10-12]. 

Examples of areas or equipment that may be successfully protected by total flooding CO2 systems are rooms, vaults, and enclosed machines spaces. An example of a total flooding carbon dioxide system is shown in Figure 7-35. 

Enclosed machines are more fully protected from dust and dampness, but are poorly ventilated, must be larger to avoid excessive heating and cost more. 

Enclosures can be used to partially or completely enclose machines (machine enclosures) or to enclose operators of machines (personnel enclosures). The first approach may be regarded as path control and the second as receiver control. 

Totally enclosed machine cooling is not done by open, direct exchange with... 

Vapor contact. This process step, which can be practiced in enclosed machines, and to an extent in OTVDs, is... 

Until the level of solvent exposure limits in working areas must be reduced below 5 to 15 ppm, the OTVD will have an economically useful life. When area exposure limits for n-propyl bromide, for example, become 1 ppm (as is contemplated in California), only enclosed machines will exist for use with most halogenated solvents. 

The three process steps (Chapter 1.2) incorporated in vapor degreasing are/will be done, not in so-called open-top machines, but in what are known as enclosed machines known as airless and vacuum respectively. They will be covered in Chapter 2. 

This emission of solvent can t be avoided unless the freeboard zone is flushed with nitrogen (as is done with enclosed machines). However, solvent emissions can be minimized by reducing the temperature of the air at the top of the freeboard zone so that more of the solvent is condensed, and retained within the degreaser. Liquid solvent can be removed from the entrained air because it is heavier than air, but vaporized solvent cannot be removed and escapes with air from the degreaser into the work area. 

This simple, basic idea is tme — whatever cleaning process can be conducted in an open-top machine can be condurted in an enclosed vapor degreaser with the benefit of reduced solvent emissions. That s the usual reason enclosed machines are built — to house some cleaning process and limit the emissions of solvent from it. 

A second reason enclosed machines are built is to conduct unique processes which could not otherwise be practiced under ambient atmospheric conditions. Not all cleaning processes are vapor degreasing with solvents at their normal boiling points, or immersion cold cleaning. 

In an airtight enclosed machine one could use methylene chloride " to clean at a much higher temperature than the temperature at which... 

In the mid-1990s these externally sealed machines were exhibited at various trade shows. They drew some interest, but few sales. The reason was that other technologies, such as airless enclosed machines, provided better value. Externally sealed enclosed machines do constrain emissions at the price of increased initial investment and somewhat lengthened cycle time. Airless and airtight enclosed machines do also constrain emissions with similar drawbacks but they enable cleaning processes not possible (pressurized and vacuum operation) with externally sealed enclosed machines, which are basically open-top machines with an airlock as a cover. 

An eductor would be an excellent choice for the vacuum pump in an enclosed machine where the parts are badly soiled with large or abrasive particulate matter, or mobile gelatinous or viscous material. This is because there are no clearances to be fouled in an eduaor and the liquid... 

Vessels for vacuum service in enclosed machines are normally made from an austenitic stainless steel, to achieve excellent corrosion resistance and unusually fine mechanical properties. The most common austenitic alloys are iron-chromium-nickel steels and are widely known as the 300 series — chiefly 304 and 316 stainless steels. While carbon steel is certainly less costly than either grade of stainless steel, there is not enough savings to warrant its use in purchase of an enclosed vacuum machine. 

One might think that the popularity of enclosed machines is ever-expanding. After all, their use circumvents the hazardous potential of chemicals from being realized to either human users or the environment. This is an outcome everyone would favor. 

But not so. Widespread adoption of the enclosed machine awaits. It s the reduction of selling price which limits commercial acceptance. And that isn t... 

Solvent Management in Externally Sealed Enclosed Machines... 

In still other words, the problem of separation of water dissolved in solvent from solvent never has to be faced because they are never combined This approach is the correct one for all three types of enclosed machines externally sealed, airless, and airtight. 

The spectmm of available cleaning processes in an externally sealed enclosed machine is that of any open-top vapor degreaser. For details of a representative process, see Table 1.5 and Figure 1.29. 

There are exactly 760 Torr in one atmosphere. The Torr is a more convenient unit to use in high-vacuum physics and engineering work. Capabilities and limits of enclosed machines are usually specified in the pressure unit of Torr. A benchmark level of pressure (vacuum actually) is 1 Torr. 

---