Cosolvent machine

It s just that there are a variety of types of cosolvent machines which use a variety of similar solvents to clean parts. Fortunately, there is a simple classification system which makes it easy to choose which type is most useful for a given application. 

It s still simple. Cosolvent machines and processes exist because a single solvent isn t the best choice for both deaning/rinsing, and rinsing/drying of parts. 

Broadly tme, it s the legitimate and urgent concerns about SHE issues of these (and like) solvents which are the reasons why cosolvent machines have been created, devdoped, and used. If TCA were not an ozone depleting compotmd, if TCE presented no concerns about toxidty or cardnogenidty, or if n-propyl bromide didn t raise the same concerns, the reason for the existence of cosolvent machines would be difficult to identify. 

In Class II cosolvent machines, the SA and the RA are immiscible with one another. 

Essentially, this is how the rinsing (Chapter 2.21) and diying sections of any Class II cosolvent machine work, except that kerosene and water are not involved. 

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. 

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

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. 

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. 

Removai of wax from optic surfaces and removai of fiux/residues from PWBs are two broad-based appiications in which both Ciass i and Ciass II cosolvent machines have been used. 

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. 

Item Single Solvent Substitution [Pg.135]

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. 

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

So, If the temperature in either type of Class II cosolvent machine can t exceed the temperature of the most volatile solvent, it also can t ever reach the boiling temperature of the least volatile solvent In other words, while Class II cosolvent machines are capable of vapor degreasing and rapid drying of surfaces, they aren t capable of cleaning in boiling solvent (the SA). 

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). 

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. ... 

Since the RA cosolvent is boiled and condensed, vapor degreasing (rinsing of surfaces with pristine RA cosolvent) can be done in either class of cosolvent machines. Furthermore, surfaces can be rapidly dried because a high difference in temperature can be maintained between the primary cooling coils and the vapor zone above the coils. 

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. 

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. 

An aspect of design, common to both IIA and IIB dasses of cosolvent machines, is the selection of refrigeration type and capability ... 

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. 

Despite this concern, some users of Ciass II cosolvent machines do not use chilled brine. Obviously, these users will experience reduced energy costs and required investment, and also experience increased costs of solvent loss. Certainly, chilled brine is not required for effective cleaning. In Table 1.5 is tabulated a comparison of cooling tower performance vs. that of mechanical refrigeration of "brine." The choice between chilled brine and cooling tower water is simply one of optimization. 

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. 

Fortunately, it is easy to remove water from Class II cosolvent machines, because water is highly immisdble with the RA cosolvent . The displacement-based water separator shown in Figure 3.15 is that which must... 

Fluorinated chemicals used as RA solvents are too inert to react with water and create corrosive acids under the conditions found in Class II cosolvent machines (Ref. 3, Table 22.2). Actually, fluorinated solvents are quite immiscible with water and are used to displace it from surfaces. 

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