In the World of Industrial Cleaning, there are numerous methods both mechanical and chemical. Blasting with shells, glass beads, sand, water —even dry ice and the application of chemical solvents , degreasers and other surface cleaners is commonplace and a billion dollar industry. Think about it. For everything you want to re and re, build, paint, plate, coat or in some way finish, a cleaner is used.
Cleaners With A Purpose
Each cleaner type has a specific purpose for which they are intended and work by one of two methods.
Solvent based cleaners remove contaminant by dissolving or thinning the deposit out, spreading it over a larger area or volume but not completely cleaning the surface. The only way to get it completely clean is to rinse with a solvent or use a vapour degreaser.
Water based cleaners emulsify or break-up the contaminant into extremely small particles which are carried off by the cleaner. A detergent action helps keep the particles in suspension. A rinse with fresh water makes a surface completely clean. Oils can sometimes separate and float to the top where they can be skimmed and the cleaner reused to reduce hazardous waste.
Specific additives are sometimes added to enhance characteristics or to make the cleaner more suitable for its intended use. These additives include:
• Chelating Agents
• Sequestering Agents
Methods Of Industrial Cleaning
There are two main types of cleaning processes. One uses chemicals, the other does not. These can be referred to as chemical and mechanical methods.
It doesn’t really do much good to simply spray something on the grime you want to remove. You at least need to wipe it off. This is mechanical action. As a rule of thumb, the more mechanical action applied, the better the end result.
Mechanical methods are those means and machines used to either complete the cleaning process or used in conjunction with a chemical method. These include the basics like hand or power tool scrubbing, brushing, rubbing, or abrading; They also include other specialized processes like high pressure blasting using water, shells, glass beads, sand, and other medium some of which are better than others. There is also hot air stripping, dry ice blasting, laser ablation and ultra and megasonics —even plasma and xenon flash lamps, all of which will be discussed in detail in a future issue. Steam, supercritical fluids and low pressure sprays are also methods of mechanical cleaning.
Cleaning with chemicals is probably the most common methods used in the widest range of industries. This involves the application of a chemical agent either at full concentration or mixed and formulated for a specific type of cleaning. Chemical methods often incorporate mechanical actions in their application, either at the time of application, or the time of removal, or both. There are also other factors which contribute to a chemical methods efficiency.
Chemical cleaning methods require the use of consumables; And they cost money. Often inexpensive in the big picture, using one or more of the following application factors, a cleaner can be used more efficiently and for better cleaning.
Mechanical Action - As described above, using a brush, pressure cleaner or agitation, increases a cleaners effectiveness. Generally speaking, the more violent the mechanical action, the better and deeper the net cleaning will be.
Contact Time - One of the most important factors. The time the cleaning agent is allowed to react with the contaminants. All to often a cleaner is applied them removed without giving it any real chance to do its job. Longer times increase effectiveness. It should be noted that the area should be kept wet with solution. This can be accomplished by wrapping the parts in food wrap or shrink wrap to limit exposure to the air.
Temperature - Adjusting the Temperature of the solution can also have a dramatic effect. Heating up to 90°C will greatly increase some cleaners cleaning power. When mixing concentrates, always use hot or warm water.
Concentration - Adjusting the strength of a cleaning solution will also increase its effectiveness. More and more, industrial cleaners are being sold in concentrated form to be cut by the user to the strengths required. Using a concentrate that you dilute for various purposes goes a long way in the savings department and doesn’t compromise your cleaning needs.
Types Of Cleaners
Chemical cleaning agents are divided into three major types: Aqueous (water-based), solvent based or petroleum based.
Grease, oil, crud, animal and vegetable fats, smoke, soot, dust, oxidation, rust, scale, mineral deposits paint, ink, adhesives, wax and rubber are a few of the various materials which require industrial cleaners for their removal. Each presents a specific challenge and requires a specific cleaner type.
Solvents - Solvent are derivatives of volatile organic compounds or hydrocarbons (petroleum products) and can be used n two ways: to remove a substance, or to put a substance on. They accomplish both by thinning other materials.
Volatile Organic Compounds (VOC’s) are those liquids which evaporate or volatize in air. Since they dissolve many other substances, VOC’s are widely used as cleaning and liquifying agents in fuels, degreasers, solvents, polishes, etc. VOC’s are grouped in five categories:
• Ketones ~ from acetone to diisobutyl ketones
• Alcohols ~ from Isopropyl to hexylene glycol
• Ethers ~ isopropyl ether and MTBE
• Glycol Ethers
• Esters of Glycol Ether.
Petroleum distillates is a term commonly used term to refer to aliphatic hydrocarbons which can be divided into two groups: petroleum distillates and synthetic paraffinic hydrocarbons. Petroleum distillates include:
• mineral spirits,
• white spirits
• aromatics – i.e. toluene & xylene
• Stoddard solvent.
These products may contain traces of benzene and other aromatics. They are flammable at room temperature.
Paraffinic hydrocarbons have lower flammability, lower aromatic content and a narrower boiling range than petroleum distillates. They are also more expensive.
Petroleum distillates have a low surface tension which allows them to penetrate and clean small spaces. They work well on hard to clean organic contaminants like heavy oil, tar, grease and wax and typically can handle high soil loads.
Usually used in immersion systems, when the cleaning power of the both is exhausted, the entire bath must be replaces. Disposal is by approved incineration.
Petroleum distillates are compatible with most materials, including elastomers. Mineral spirits however may not be compatible with EPDM, SBR and silicone.
Water based or aqueous cleaners are grouped according to their pH value. With pH7 being neutral, solutions with a pH higher than seven (pH8~14) are said to be alkaline while those below pH7 are said to be acidic. Pure water has a pH of 7.
The two most common aqueous solutions used are neutral and alkaline.
Aqueous Acidic. Acidic cleaners are effective in cleaning oxidation, rust, lime scale, mineral deposits, protein and blood from metals, glass, chrome, ceramics, plastics, rubber, wood, and concrete products. They can also be used clean aluminum without etching and to remove scale from welding and heat treating.
Common acids found in acidic cleaners include sulphuric, nitric and hydrochloric. Organic acids include acetic, oxalic and cresylic acid. Nitric and hydroflouric acids are also used for brightening stainless steels which become pitted from prolonged exposure to acids which contain chlorides. Some types of stainless steel will rust or dissolve under acidic conditions. Contact between stainless steels and hydrochloric or heated sulphuric acid should be minimized.
If parts are to be painted, cleaning in a phosphoric acid solution forms a phosphate coating which provides a level of corrosion protection.
Acidic cleaners are poor at removing oil, grease and rosin flux. Other contaminants —especially inorganics— are either removed or dissolved by acidic cleaners.
Alkaline aqueous solutions are the most common form of cleaning chemistry. They are water-based mixtures with a pH of greater than 7. Most range in pH from 10 – 24. This does not mean however, that they can be easily disposed of down the drain; pH adjustments to neutralize are required before disposal.
Alkaline cleaners are blended from alkaline hydroxides such as borates, carbonates, phosphates or silicates and often contain additives such as sequestering agents, emulsifiers and surfactants to improve cleaning. Inhibitors are also necessary with some metals, especially aluminum.
Alkaline cleaners can be anionic, caustic or neutral. Nonionic cleaners are lower foaming and are generally better for applications using agitation or sprays and require less rinsing.
Since these cleaners may be used in a wide range of temperatures they have an increased suitability as general purpose cleaners. Alkaline solutions are used with all types of liquid processes such as sprays, ultrasonics, immersion systems and power washers.
Alkalines are most useful in removing grease, lubricants, coolants, cutting fluids, shop dirt, fingerprints, cosmolene, petrolatum, wax, rubber, drawing compounds, rust, scale, salts, fingerprints, polishing and buffing compounds, most protein-based stains, and some water-soluble paints, inks and adhesives.
Alkaline cleaners are available for most metals, chrome, polycarbonates and plastics, vinyl, glass, mirrors, plexiglass, ceramic coatings and other materials and coatings.
Some metals are very susceptible to etch from alkaline cleaners. To reduce this possibility, particularly with high pH cleaners, inhibitors such as silicates, chromate, sodium zincate, are added. Inhibitor materials must be thoroughly rinsed to avoid problems with coating or plating operations.
Aqueous alkaline cleaners have been used successfully to clean mild and stainless steel and irons. Flash corrosion may be a problem with some materials. Materials which require inhibitors or are susceptible to etching include aluminum, brass, magnesium, tin, lead and terneplate. Strong alkalines do not attack Titanium unless chelating agents are present.
Neutral solutions are mixtures of water and other chemicals with a pH near 7. The chemicals may include surfactants, corrosion inhibitors and other additives and work well when a high degree of chemical solvency is not needed.
Neutral solutions are used in spray and ultrasonic equipment but are not ideal for immersion processes which depend more on chemical action.
The major issues with a neutral solutions are the possible requirement of a drying system to prevent corrosion and water quality. Hard water cleans differently than soft water.
Depending on the chemicals in solution, neutral aqueous solutions may be used to remove chlorides and other salts, organic contaminants and particulate.
The important thing to remember when choosing a cleaner is “Like Cleans Like”.
Try to identify the contaminant to select the best cleaner for the job. Petroleum-based residue is best cleaned with an alkaline or solvent-based cleaner, followed by a water rinse.