Metalworking Fluids

What are metalworking fluids?

• context Metalworking fluid (MWF) is the name given to a range of oils and other liquids that are used to cool and/or lubricate metal workpieces when they are being machined, ground, milled, etc. MWFs reduce the heat and friction between the cutting tool and the workpiece and help prevent burning and smoking. Applying MWFs also helps improve the quality of the workpiece by continuously removing the fines, chips, and swarfs from the tool being used and the surface of the workpiece. Swarfs are small pieces of metal removed from a workpiece by a cutting tool.

Are there different types of MWFs?

Yes. While there are many different components and additives in MWFs, there are four basic classes. Although each class will vary greatly in composition, each may contain additives such as

• context Straight Oils: Also called "cutting" or "neat" oils. This type is made up of mineral (petroleum), animal, marine, vegetable or synthetic oils. Today, the mineral oils are "severely solvent refined" or "severely hydrotreated". These terms refer to refining processes that help reduce the amount of polynuclear aromatic hydrocarbons (PAHs). Straight oils are not diluted with water but other additives may be present.
• context Soluble Oils (emulsifiable oils): This category contains 30 to 85 percent severely refined petroleum oils, as well as emulsifiers to disperse the oil in water.
• context Semi-synthetic fluids: This category contains 5 to 30 percent severely refined petroleum oils, 30 to 50 percent water and a number of additives.
• context Synthetic fluids: This category does not contain petroleum oils. Instead, they use detergent-like components and other additives to help "wet" the workpiece.
• context Sulphurized or chlorinated compounds.
• context Corrosion inhibitors (e.g., calcium sulfonate, sodium sulfonates, fatty acid soaps, amines, boric acid).
• context Extreme pressure additives (e.g., sulfurized fatty materials, chlorinated paraffins, phosphorus derivatives).
• context Anti-mist agents (e.g., polyisobutylene polymer).
• context Anti-weld agents.
• context Emulsifiers (e.g., triethanolamine, sodium petroleum sulphonates, salts of fatty acids and non-ionic surfactants).
• context Alkanolamines.
• context Biocides (e.g., triazine compounds, oxazolidine compounds).
• context Preservatives.
• context Stabilizers.
• context Dispersants.
• context Defoamer.
• context Colourants.
• context Dyes.
• context Odourants.
• context Fragrances.

Does the composition of MWFs change with storage or use?

• context When stored, nitrosamines can form while the fluid is stored for long periods of time. Nitrosamines form slowly in the water-based MWFs and may be the result of the interaction of nitrites in the fluid, lining of the cans used for storage, or from nitrogen oxides in the air. Recycling MWFs can increase the problem if more reactants are added. The formation of nitrosamines in metalworking fluids is a concern since many nitrosamines are classified as carcinogens.
• context When MWFs are used, a primary concern is the presence of contaminants that encourage the growth of bacteria and fungi in water-based MWFs. The bacteria can degrade the emulsions and change the properties of the MWFs. While biocides are added to reduce the amount of microbial growth, the biocide products themselves have hazardous properties.
• context Other sources of contamination include "tramp" oil - oil used for lubrication of the machines, such as hydraulic oil, gear box oil, and other lubricants. Tramp oils that leak into the metalworking fluids can contribute to microbial growth in many ways, including by being a source of nutrients for bacteria, and by creating various conditions for anaerobic microbial growth.
• context MWFs are also contaminated by small particles of metal or alloy objects (e.g., fines, chips, swarfs) that come off the parts while they are being machined. Common metals used include steel or alloys containing nickel, cobalt and chromium.
• context In addition, while the extent of the problem is not clear, there is the potential for straight oils to be heated during use (usually at the site where the cutting tool works on the metal workpiece), and the temperature may increase high enough to cause the formation of polynuclear hydrocarbons (or polyaromatic hydrocarbons, PAHs).
• context MWFs may also be contaminated by water, cleaning products used for routine housekeeping, or other products at the work site. Improper recycling of materials or the addition of unspecified fluids (such as old lubricating oils) to the MWF will also change the composition of the fluid.

How do MWFs enter the body?

MWFs can enter the body when:

• context What kind of machining is being done?
• context How the fluid is applied (e.g., manually with an oil can; flooded through a hose or pipe, or atomized (aerosolized) and the mist directed where the tool contacts the workpiece).
• context The operator works close to the metalworking machine.
• context The operations involve high-speed tools or deep cuts.
• context The machines do not have an enclosed process.
• context The ventilation is poor.
• context How, or if, the machine is enclosed and ventilated. Higher exposures happen when:
• context The mist, aerosols, or vapour is inhaled. Exposure will depend on:
• context It comes into contact with the skin. The risk of absorption through the skin is high especially if there are cuts, rashes, cracks, or other breaks in the skin. Hands and arms are most at risk if adequate precautions are not taken. Fluids can splash onto the skin during machining, and can also occur when they are prepared or drained, when work pieces are handled, when tools are being changed and set, and during maintenance or cleaning operations. Rags or clothes soaked with MWF that are in constant contact with the skin are also a concern (including when rags are placed in the pockets of clothing).
• context Ingested if you eat, drink or smoke without washing your hands first.

What are health concerns about working with MWFs?

MWFs have been associated with several health concerns. Contact dermatitis is the most common skin condition reported. Symptoms include burning, itching, and blistery skin. Inhalation of the mists may cause asthma and lung irritation (hypersensitivity pneumonitis), chronic bronchitis, and impaired lung function. There is also evidence that some MWFs are associated with an increased risk of certain cancers such as the larynx, rectum, pancreas, skin, scrotum, and bladder. Since the time between exposure and the development of the disease is often more than 20 years, most of the cancer cases associated with the use of MWFs are due to exposure to MWFs used in the mid-1970s or earlier. In the past few decades, substantial changes to the composition of MWFs and reductions in the contaminants have occurred. As a result, the risk of cancer from more recent exposures is not as clear. Overall, the type and severity of the health problem depend on: The three major areas of concern (skin, respiratory and cancer) are described in more detail below.

• context What MWF is used.
• context Degree and type of contamination to the MWF.
• context The level (how much), duration (how long), and frequency (how often) of exposure.

Skin

All types of MWFs can cause skin irritation. If you had severe eczema as a child, there is a high risk that you will suffer dermatitis when exposed to MWFs. Exposure occurs when hands are dipped into the fluid, or when a person handles the parts, tools and equipment covered in fluid. Splashing is a concern if guarding is absent or inadequate. Clothing contaminated with MWF, poor housekeeping, and poor personal hygiene also contribute to skin exposure. Irritant or allergic contact dermatitis is reported to occur from exposure to soluble, semisynthetic, and synthetic MWFs. Dermatitis can be caused by: Skin conditions associated with straight oils include: In addition, the small metal particles (fines and swarfs) generated while parts are machined can damage the skin and make existing irritations worse. Skin conditions can become disabling if not treated or if the worker continues to work with the condition.

• context Bacteria and their by-products.
• context Chemicals added to control bacteria (biocides).
• context Chemicals added to control rust and corrosion.
• context Contact with metal contaminants such as nickel, cobalt and chromium, which are known sensitising agents.
• context Folliculitis (inflammation of hair roots or follicles). Caused by prolonged and regular contact with straight oils.
• context Oil acne (red bumps with yellow pustules/ blisters filled with pus). Caused by skin contact with oil-soaked clothing. Can develop on various body parts: face, forearms, thighs, legs, etc.
• context Irritation. The small metal particles (fines and swarfs), generated while parts are machined, can damage the skin and make existing irritations worse.

Respiratory

• context An increase in the number of work-related asthma, bronchitis, irritation of the respiratory tract and breathing difficulties has been reported among those exposed to MWFs. Exposure to mist, aerosol, and vapour can lead to the development of respiratory conditions or can aggravate the existing ones.
• context It is not clear whether respiratory problems are caused by specific fluid components, contaminants, products of microbial growth or degradation, or a combination of these factors. For example, metalworking fluid-induced asthma is reported more consistently with synthetic MWFs, but MWF-induced asthma can also occur with soluble and straight fluids.
• context Again, the severity of exposure depends on proximity to the machine, and if the operations involve high tool speeds and deep cuts, if the machine is enclosed, or if ventilation equipment is working properly. High pressure or excessive fluid application, contamination of fluid (with tramp oil), improper fluid selection, and poor maintenance will also result in higher exposures.
• context Bacteria contamination can cause irritation of respiratory tracts or flu-like symptoms, aggravate asthma, and irritate the eyes, nose and throat (causing a sore throat, red watery itchy eyes, runny nose, nose bleeds, coughing, wheezing, or shortness of breath). For example, hypersensitivity pneumonitis is an allergic-type reaction in the lungs that may be caused by exposure to microbial products. hypersensitivity pneumonitis is marked by chills, fever, shortness of breath and a deep cough - similar to a cold that will not go away. If left untreated, it can lead to irreversible lung damage.

Cancer

Cancers often associated with exposure to metalworking fluids include rectum, pancreas, larynx, skin, scrotum, esophagus, and bladder. The National Institute for Occupational Safety and Health (NIOSH) in the USA reports that studies were not highly consistent regarding the specific types of cancer associated with MWFs. This uncertainty is likely due to the wide variation in the types of MWFs and contaminants and the lack of detailed exposure information. Also, because the latency period (the time between first exposure and the discovery of disease) for cancer is often 20 years or more, it is likely that the diseases studied recently are associated with older formulations of MWFs (from the mid-1970s and earlier). For example, fluids used before 1985 may have contained nitrites, mildly refined petroleum oils and other chemicals which were removed because of health concerns. Areas of concern for risk of cancer currently include:

• context Unrefined mineral oils and contact with exposed skin (including oil-soaked clothing and especially oily rags kept in pockets, which caused cancer of scrotum).
• context Nitrites or nitrates and amines that cause the formation of nitrosamines when MWFs are heated or under pressure. Certain nitrosamines, such as N-nitrosodiethanolamines (NDELA), are known to be cancer-causing agents.
• context Some biocides release formaldehyde, a known carcinogen. Formaldehyde can also speed up the formation of nitrosamines.
• context Chlorinated paraffins are carcinogens (often used when extreme pressure is required). They also form dioxin, another carcinogen.

How do you find out about the composition of a MWF?

• context The fluid supplier or manufacturer can provide you with the Safety Data Sheet (SDS), which will provide information about the ingredients and health and safety hazards.
• context It is important to monitor the MWF for contamination and to have good work practices that help keep the fluids as free from contamination as possible.