Vapor degreasing, solvent application

Use Cold cleaning, vapor degreasing, resins application, dry-film photoresist processing, adhesive solvent, in aerosols as solvent and vapor-pressure depressant. 

Caution Vapor degreasing solvents should not be used unless their application and performance are known or are discussed with the cleaning agent manufacturer. The manufacturer s recommendations regarding concentration, temperature, and PPE should be followed for safe handling and use of the cleaning agent. 

Caution Vapor degreasing solvents should not be used unless their application and performance are known or are discussed with... 

Trichloroethane was a major solvent, particularly for cold and vapor degreasing. It was phased out for emissive uses in the United States in 1996 because of its ozone depletion potential. The only application left is as chemical precursor for HCFC-141b and HCFC-142b. However, both are subject to phaseout schedule of the Montreal Protocol,... 

Improperly stabilized methylene chloride, perchloroethylene, 1,1,1-trichloroethane, and trichloroethylene are subject to decomposition under vapor degreasing conditions to form corrosive acid by-products. For this reason, only solvent grades suitably stabilized for vapor degreasing applications should be used. 

The high boiling point, increased solvency and low surface tension of 3M HFE-7100 make it suitable for use in vapor degreasing applications as a neat (pure), azeotropic or co-solvent parts cleaner. In addition, its chemical and thermal stability, non-flammability and low toxicity make it useful for other industrial applications such as specialty solvent and heat transfer applications. 

HFE-7200/ 3MCo. Ethoxy nonafluorobutane Neat, co-solvent or azeotrope in vapor-degreasing applications 10 78 13.6 30 None 109... 

The available solvents for open-top vapor degreasing have been trichloroethylene (Ref. 3, Chapter 20) and n-propyl bromide (Ref. 3, Chapter 21) — both of which raise concerns about their effects on human health. Few credible options have been developed (Ref. 2, Chapter 2.12.3.1) to clean these parts which don t involve emission of these hazardous materials. That is why this application was exempted from further regulation in the updated NESFIAP for Flalogenated Solvents (Chapter 1.28). 

Figure 2.29 shows the simplest equipment arrangement (not to scale) in which these five actions or functions are incorporated into the facilities of a basic externally sealed enclosed vapor degreaser. The parts are washed (APPLICATION of solvent), rinsed (SEPARATION of solvent), and dried (EVAPORATION of solvent) in the work chamber. PURIFICATION of solvent occurs in a distillation column. Similarly located is where REMEDIATION of solvent occurs so that soils can be collected, concentrated, and disposed (reused). 

They are called cosolvent processes because more than one solvent is used to clean parts in the same application (Chapter 3.f). Some of these processes are chameleons in that they appear externally to be conducted in conventional vapor degreasers — having a two-sump immersion cleaning apparatus and an attached distillation column. 

These steps are enumerated and described in Chapter 1.2. Operation of superheat in open-top vapor degreasers is explained in Chapter 1.20 For reference, solvent cleaning operations with trichloroethylene and n-propyl bromide are conducted at their boiling points - 86°C (187"F) and 71"C (160°F), respectively. It is this author s experience that Class II cosolvent processes have found more interest in Europe than in the US. The chief application is removal of flux residues from printed wire boards (PWBs). 

This appears to be an application of Heisenberg s Uncertainty Principle (Ref. 1, Chapter 4.2.3). In the same way that one can t simultaneously measure the position and momentum of a particle, one can t use an air amplifier to collect only the solvent molecules which have escaped beyond the capability of the vapor degreaser to retain them and not pull additional solvent vapor from the throat of the open-top vapor degreaser. Both can t simultaneously be done. 

The straightforward application is purging with clean air the work chamber of a large (21 cubic feet) enclosed vapor degreaser. Conditions in the chamber prior to starting the purge were a vacuum of 750 TorrV (10 mm Hg absolute) with only solvent present. The desired outcome is to have the chamber contents displaced to where the exhaust concentration in ambient air is no more than half of the currently posted exposure limit for the chosen cleaning solvent. These posted exposure limits are toluene (100 ppm), n-propyl bromide (10 ppm), perchloroethylene (25 ppm),... 

The complicated application involves use of lip vents attached to an open-top vapor degreaser in which each of the six solvents noted above is being independently used. The assumed feed and exit concentrations are 20 x and 1 x the exposure limit respectively. Complications arise from the intersection of three factors (1) the fictitious feed and exit concentrations to and from the adsorber are different for each of the six solvents (because they have different posted exposure limits. Footnote 55), (2) each solvent has a different adsorption vs. concentration response (Figure 4.17), and (3) each solvent has a different solubility (Table 4.10) in and with water (condensed steam). For example, the range of solvent concentrations for n-propyl bromide or trichloroethylene is 200 ppm to 10 ppm, and that for CFC-113 is 1000 ppm to 20,000 ppm. Solubility data of many cleaning solvents in water, and of water in cleaning solvents, are available in Appendix 1, Table A1-5. 

One simply can t use those two solvents in this application (open-top vapor degreasers) for reasons of... 

Uses 1,1,1-trichloroethane was used as a solvent in numerous industrial applications such as cold and hot cleaning, vapor degreasing and in textile processing and dry cleaning. Fluorochlorohydrocarbons were made from it. The world capacity in 1984 amounted to 600 000 tonnes per year. 

Such comprehensive data for present consumption are not any longer collected by EPA, which does not mean that there is no improvements. It is known from literature that open systems are analyzed and modelled to reduce emissions and closed systems are popular in industrial applications. Vapor degreasing is an example of enclosed systems which permits control of solvent emissions. n-Propyl bromide is a popular new solvent used in metal cleaning. 

It has a rather low PEL so the vapors must be contained. This is rather difficult since MEC has a boiling point of 39.8°C. This low boiling point makes it applicable as a solvent for vapor degreasing temperature-sensitive materials. It is a very aggressive solvent and can damage plastics and rubbers. 

These materials have a wide range of boiling points, from a low of 39°C for methylene chloride to a high of 121°C for perchloroethylene. Trichloroethylene and perchloroethylene are the solvents most commonly used for vapor degreasing, particularly the former. Considerable detail on the equipment required and the vapor degreasing process is given in Ref. [3]. The discussion of chlorinated solvents is of historical and technical interest because the use of nearly every one of them has been banned. The health, safety, and environmental risks of this class of materials are far too high to justify their use in spite of the excellent results that their application can yield. 

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