Air Pollution can be added to improve the cleaning per
acceptable alternative to MCF from an en
formance.
vironmental perspective.
bility issue and VOC problem can be solved with proper equipment design.
Aqueous cleaning has several advantages over organic solvent cleaning. The sub stances used are not flammable or explo sive. Aqueous systems can clean particles and films better than solvents, and are par ticularly useful for cleaning inorganic or polar materials. They can also effectively remove organic films, oils and greases. Depending on the specific cleaning ap plications, there may also be disadvantages.
b) Semi-aqueous Cleaning
c)Non-halogenated Organic Solvents
Semi-aqueous cleaning systems involve the use of an organic cleaning formulation, followed by water washing and drying. A surfactant is sometimes added to the organic formulation to improve wetting, emulsification and rinsing properties. It is a liquid cleaning process,either at ambient tempera
These solvents - petroleum distillates, synthetic hydrocarbon formulations, alcohols, ketones, esters, glycol ethers, Nmethyl pyrollidone - have good cleaning ability for a wide variety of soils, especially heavy grease, tar, waxes and hard-to-remove soils. These organic solvents are compat ible with most rubbers, plastics and metals, and they can be used for cleaning watersensitive parts. There is no wastewater stream to manage, and the solvents are re cyclable by distillation. Flammability is a concern but it can be mitigated with proper equipment design. Dry ing times are slower than with chlorinated solvents, and VOC control may be required.
Parts with blind holes and small crevices
may be difficult to clean, and some aque ous cleaner residues can be difficult to rinse.
Drying certain part geometries with crev ices and blind holes may also be a challenge; drying equipment is often required. In some instances, aqueous cleaning equipment re quires more floor space. The presence of metal ions in the aque ous system can cause corrosion or scaling of metal parts. Deionized water may have to be used in the final rinse stages and thor ough drying may be required. In some ap plications, expensive high-purity water is needed. Energy consumption is probably higher than solvent cleaning in applications that require heated rinse and diy stages, and wastewater treatment may be required prior to discharge, but the associated costs may be offset by the savings from not having to buy an organic solvent. Aqueous cleaning is generally the most
ture or heated.
Semi-aqueous systems provide good cleaning ability, especially for heavy grease, tar, waxes and hard-to-remove soils. They are compatible with most metals and plas tics. The non-alkalinity of the process pre vents etching of metals, and a rust inhibitor can be included in the formulation to pro tect parts from rusting. With semi-aqueous systems, rinsability problems may occur and drying equipment may be required. A semi-aqueous system can be a costly process because of recycling or disposing of wastewater. Flammability is a concern with semiaqueous cleaning products that have a low flash point because these products become extremely volatile when sprayed in a con centrated form. Some cleaners are "vola
tile organic compounds"(VOCs),which can contribute to the formation of smog; emis sions of VOCs to the environment may, therefore, be subject to regulatory control in your region. However, both the fiamma-
d) Halogenated Solvents The halogenated solvents - trichloroethylene, perchloroethylene, methylene chloride, perfluorocarbons and HCFCs have good cleaning ability for a wide vari ety of soils and are compatible with most substrates. The capital costs to switch from MCF are low; some halogenated solvents are"drop in"replacements for MCF,requir ing no new equipment. They can clean water-sensitive parts, and there is no waste water. Halogenated solvents can be recy cled by distillation. Trichloroethylene, perchloroethylene and methylene chloride have been declared "toxic" under the Canadian Environmental
Protection Act(CEPA),and controls may be implemented on their use in the future. If you are considering switching to one ofthese substances, ensure that you minimize emis sions through recovery devices. Some halo genated solvents have low Occupational Exposure Limits and will require more de manding standards to be met. Trichloro ethylene and perchloroethylene are currently identified by Environment Canada as VOCs and some type of control may be required. HCFCs have been suggested as possible substitutes for CFCs. They are less ozonedepleting, but they are not acceptable long-
Cut micro-flock
sizing time by 90%... Two high-performance microscopes configured for wastewater analysis are available from OLYMPUS.
Both feature the Olympus
term substitutes and are scheduled for
Wastewater Reticle™, for use
phase-out over the next three decades (by January 2000 in Ontario). The toxicity of
with the 10X phase contrast objective, to facilitate particle counting that can cut micro-flock sizing time by a staggering 90% without sacrificing accuracy. These Olympus microscopes are equipped for image-enhancing phase
some HCFCs is also a concern. HCFCs
Illustrated: OLYMPUS BX-40
contrast microscopy.
should only be considered as alternatives to MCF if no other technically and economi cally feasible options exist because they of fer no advantages over MCF with respect to ozone depletion potential. Environment Canada has published a comprehensive booklet, a pamphlet and two updating newsletters that contain informa tion on regulations, suppliers of alternatives, case studies and sources of assistance and
For details on our in-lab demonstration offer, call Bev Silverman, at 1-800-387-0437, Ext. 3301. CARSEN GROUP INC.,
Precision Instrument Division
151 Telson Road, Markham, Ontario L3R 1E7 FAX: [905] 479-1610
20
For more information, Circle reply card No. 175
advice. To obtain these documents, send
your request to the following, and specify whether you would like the information in English or French: Ms.Kathy Deeg,Energy Pathways Inc., 251 Laurier Avenue West, Suite 500, Ottawa, Ontario, KIP 5J6, Tel; (613) 235-8086, Fax: (613) 235-2190.
Environmental Science & Engineering, July 1995