Open-top machines

The workload should be retained in the vapor zone for its final vapor condensate rinse until condensation ceases to facilitate drying. Work withdrawn earlier may emerge wet with solvent condensate. Insufficient contact time is encountered most frequently in hand-operated, open-top machines. 

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. 

One can see from this discussion, and the associated images of Figures 1.44 to 1.46, and Table 1.11, that low temperature refrigeration is critical to successful vapor degreasing in open-top machines. Operating cost spent on electricity to provide refrigeration is well-justified (usually). Low temperature refrigeration keeps the solvent in the tank to save cost, protect employees, and the environment ... 

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. 

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. 

Note in Figure 3 26 that both sumps are open to the ambient atmosphere as cosolvent processes are implemented in relatively inexpensive open-top machines... 

It is likely that the rinsing chamber for this application is an enclosed machine because of the exceptionally low boiling point of the RA cosolvent. It would be impractical to conduct this operation in an open-top machine. 

When the Class III cosolvent process is considered for use with some soils, the RA best matched to the SA is HFC-365mfc. To use a cosolvent whose boiling point is 89°F (32°C) in an open-top machine is ridiculous. But a dual-chamber machine with one chamber enclosed might be an entirely practical choice for certain parts. 

In contrast to urethane casting systems, open-topped molds cannot be used for all parts. Inhibitation of polymerization at the exposed surface of the nylon reaction mix by moisture in the air will produce a tacky surface. If this is to be machined off to produce a finished part, open topped molds may be used. 

Molds with open-topped risers and vents, like those used for casting of metals, may be used for certain thick parts. Makeup for polymerization shrinkage comes from the volume of material in the vents and risers which are eventually machined off. 

S. Open-top vapor degreasers constructed in the past used drinking water from city utilities for the purpose of cooling. Some of those machines survive, consuming water and discarding it after one use. 

All five, and essentially no others, are the necessary functions which must be incorporated into any successfully operated cleaning apparatus -whether an open-top solvent vapor degreaser, enctosed solvent vapor degreaser or a multistage machine practicing aqueous technology. 

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. 

Commonly used in atmospheric open-top vapor degreasers, and enclosed vapor degreaser which operate at atmospheric pressure, ultrasonic transducers are seldom found in machines which create a vacuum environ-ment " ". The reason is perceived cost — of the needed... 

The replacement proposed in Table 3.5 includes both a change in cleaning chemicals and a change in cleaning processes. The single solvents are normally used in an open-top vapor degreaser (Chapter 1) or an enclosed machine (Chapter 2). 

For open-top vapor degreasers with their cover dosed, the lip vents can only release solvent vapor which is not condensed by the upper cooling coil and has then risen to the top of the machine. That volumetric emission rate should be very low because there is little Inward leakage of air to provide fluid to entrain the uncondensed solvent vapor Into the lip vents. 

The concentration of solvent in vapor emitted from airless enclosed machines is much higher than the same in vapor emitted from the lip vents of open-top vapor degreasers. The reason for this has to do with the nature of the two vapor degreasers. 

Box Feeder. A device for feeding clay to preparation machines. It consists of a large metal box, open topped, with the bottom usually formed by a steel-band conveyor or by a conveyor of overlapping steel slats for plastic clay the feeding mechanism may be a number of revolving screw shafts. 

However, it is not always possible to run a pilot-plant test in order to determine the depth of cut. A well-accepted alternative approach makes use of the more sophisticated test leaf illustrated in Fig. 18-97. This test leaf is designed so that the cake and precoat are extruded axially out the open end of the leaf. The top of the retaining wall on this end of the leaf is a machined surface which serves as a support for a... 

Variable-speed basket centrifuges rotate on a vertical axis. The cyhndrical perforated basket, connected at one end to a bowl head or hub, is driven from below or suspended from above by a driveshaft. It is capped at the other end with a weir ring. The hub may be a solid piece or with an annular opening. If the hub is a sohd piece, the shiny is introduced into the basket at low speed despite the fact that the earths gravity may influence the annular pool. The settled sohds can be removed from the top only when the machine is at rest. Otherwise,... 

A semi-guarded machine is an open machine in which part of the ventilating openings in the machine, usually in the top half, are guarded as in the case of a guarded machine but the others are left open. 

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