Class II A cosolvent machines

For Class II A cosolvent machines (flammable cosolvents), the chosen RA cosolvent from Table 3.4 is dimethyl carbonate whose boiling point is 92°C (194.0°F). 

One with such a need might well elect to use the Class II A cosolvent machine because its commonly selected VOC-exempt (in the US) flammable RA cosolvent, dimethyl carbonate, has a considerably higher boiling point than does a commonly selected non-flammable RA cosolvent, HFC-43-10mee. 

It is the expectation of this author that a user in any US locality must inform their (1) insurance carrier, and (2) AHJ of an intent to use flammable solvents on site in a cleaning machine. Surely, this is one of the advantages of a Class II B cosolvent machine (no flammable solvents) vs. a Class II A cosolvent machine, and a reason for the subclassification. 

Explosion-Proof Facilities for Class II A Cosolvent Machines... 

There is a substantial business in producing Class II A cosolvent deaning machines capable of safely cleaning with isopropanol, and to a lesser extent, ethanol (Ref. 3, Chapter 12). The investment required for such machines is justified by the high value of the cleaned objects. 

Item Single Solvent Substitution Cosolvent Machine (Chapter 3.6.3)... 

Substitution of Two Solvents in a Class II B Cosolvent Machine (Chapter 3.6.3)... 

The simple process diagram of either a Class IIA or Class II B cosolvent machine is shown in Figure 3.12. Part surfaces are dried as they contact hot RA vapor, which is then condensed as shown in Figure 1.14 and described in Chapter 1.8. 

So removal of greases, synthetic oils, and waxes from surfaces may be limited by the degree to which their viscosity can be reduced by being heated in a Class II B cosolvent machine. ... 

The same process steps (Figure 3.12) are involved in operating either a Class II A or a Class II B cosolvent machine — yet not all machines of the same dass are the same. 

Figure 3.12 is a process diagram of either Class II cosolvent machine. It s not a photograph of a Class II B working machine (as is Figure 3.15 ). And even if it were a photograph, the necessary differences between Class II A and Class II B cosolvent machines wouldn t be evident ...

There are two general differences between Class II A and Class II B cosolvent machines. One is significant the other is dominant . The significant difference is about cosolvent physical properties. The dominant difference is about electro-mechanical/safety design issues. 

Apmdent user would choose Class IIB cosolvent machines vs. Class II A in every case where performance and specification allows. 

Second, soils best cleaned by Class II A (flammable) cosolvent machines generally display low levels of polar and H-bonding intermolecular force. And it is the soils best cleaned by Class II B (non-flammable) cosolvent machines which display high to moderate levels of polar and H-bonding intermolecular force. That segregation is an outcome, not a specification. 

There is no inherent reason, other than cost, to locate the SA and RA cosolvent sumps into separate equipment envelopes. This arrangement is perfectly feasible, though not produced commercially. It is shown for Class III (miscible) cosolvent machines in Figure 3.33. The patent claims (described in Endnote GG) refer to a Class II cosolvent machine with separate sumps but don t specify whether they must be located in separate equipment envelopes. 

Class II cosolvent machines can have SA or RA materials which are either easily ignited by a spark in oxygen, or not. That distinction is the basis for an important subclassification of Class II cosolvent processes ... 

In all Class II cosolvent machines, the SA is often a VOC (in the US), and the RA can be VOC exempt. Wben tbe latter is so, tbe volatile VOC-exempt RA can act (because of immisdbility) as a barrier to keep the VOC SA from being emitted . However, where either (or both) an SA or an RA cosolvent which are also VOC exempt (anywhere) can be chosen for optimum performance, that choice is normally made (Chapter 3.6.3). 

A user chooses Class IIA cosolvent machines for one of two reasons (1) the cosolvent (SA) whose HSPs best match the HSPs of the soil mixture has a flash point < 140°F and there is no SA cosolvent with similar HSPs which has a flash point > 140°F, or (2) the user is required by spedfication to use an SA which happens to have a flash point < 140°F. No user rationally chooses to use an SA or an RA which has a flash point <140°F. That choice is made out of necessity because the solvent "works or is "spedfied." Said another way, the fact that users choose to use the Class II Acosofvent process is a aedible endorsement of the design, functionality, and inherent safety of these solvent deaning machines. 

Two points are easily seen. First, a broad spectrum of soils can be cleaned with the SA and RA cosolvents used Class II cosolvent machines. 

With a different solvent in each of two sumps in a Class II cosolvent machine, at what temperature is cleaning/ rinsing/drying done ... 

In a Class II cosolvent machine there is no fluid transfer. 

A third aspect of difference is that multiple heat sources (or sinks) are required with a Class II cosolvent machine, instead of just one with a single-solvent degreaser. 

But a hydrolysis reaction between tramp water and the solvents used in Class II cosolvent machines doesn t occur, because there are no chlorinated or brominated solvents present. In these machines, water is not a reactant, but a diluent. Water simply accumulates unless it is removed. 

Figure 3.29 Comparison of the Energy Requirements for Operating a Class II vs a Class III Cosolvent Machine...

As this book is published, interest in the US in Class II cosolvent machines is apparently located in California. These machines are a practical way of conducting useful solvent cleaning operations while remaining in compliance with highly restrictive regulations about emissions of VOCs. 

V. Water is not involved in commercial cosolvent machines of Class II, III, or IV. The example of the kerosene dryer was noted to provide a simple explanation and a practical example of Class II cosolvent machines. 

Actually a more relevant example of Class II cosolvent machines, and of the kerosene dryer, is the fluorocarbon-based dryer for removal of water from part surfaces. Flere the substrate is to be dried by displacement. Drying in this manner avoids an energy consuming drying step (evaporation of water) and can greatly expedite subsequent processing of the substrate component. No thermal stresses are applied to components on surfaces. 

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