November 22nd, 2022 | Posted in General
Metal removal by machining and grinding creates friction and consequent heat. Excess heat can reduce tool life, affect surface finish and may affect finished dimensions due to thermal expansion of the parts being manufactured. In order to reduce friction and heat, coolants are frequently applied. These coolants or metal working fluids (MWF), are available in a number of formulations. These include:
Coolants may therefore be complex mixtures of oils, emulsifiers, anti-weld agents, corrosion inhibitors, extreme pressure additives, and buffers (alkaline reserve). This fluid complexity is compounded by other substances from the manufacturing process (such as tramp oils, hydraulic fluids, and particulate matter from grinding and machining operations).
One characteristic of the commonly used water based coolants is that they support microbial growth with consequent biological contaminants including:
“Historically, microbial contamination of metal working fluids has been a problem in the metalworking industries, primarily because of potential adverse health effects and microbial growth effects on fluid quality and performance.”[i]
“Metalworking fluids (MWF) are frequent causes of occupational irritant and/or allergic contact dermatitis in metalworkers. The most important allergens in water-based MWF are monoethanolamine (MEA) and oxidation products of resin acids. Resin acids are contained in distilled tall oil, which is a widely used basic MWF component. Other frequent sensitizers in MWF are formaldehyde, formaldehyde releasers, and other biocides such as isothiazolinones. Various other allergens have been described in individual case reports.”[ii]
A 2010 review of 227 reports in the peer reviewed literature directly relevant to regulation of MWF exposures was conducted. Of the papers reviewed, 26 addressed cancer; 58 respiratory effects; 32 skin effects or absorption; 45 microbial contaminants; and 76 exposure measurements and controls. Three major studies identified excess cancer including lung, liver, pancreatic, laryngeal, and leukemia associated with MWF exposures. Reports strengthened associations of asthma and hypersensitivity pneumonitis with recent exposure to MWF.[iii]
Research published in 2018 assessing coolant mist and cancer outcomes showed cancer sites contributing the most attributable cases were larynx, esophagus, brain, female breast, and uterine cervix. [iv]
In 1998 the National Institutes for Occupational Safety and Health (NIOSH) offered the following statement:
“To prevent or greatly reduce the risk of adverse health effects in exposed workers, NIOSH recommends that exposures to MWF aerosols be limited to 0.4 mg/m3 of air for thoracic particulate mass (or 0.5 mg/m3 for total particulate mass) as a time-weighted average (TWA) concentration for up to 10 hr/day during a 40-hr week.”[v]
Controlling exposures to the amines, oil products and formaldehyde associated with coolant mist is possible by use of specialized industrial air cleaning equipment. These exposure control tools may employ either electronic air cleaning or traditional media filtration. The choice of air cleaning technology may be driven by a number of factors that are best discussed with an air cleaning professional.
The capture of the coolant mist for MWF removal from the breathing zone is easiest when the machining and/or grinding operations associated with generation of coolant mist are enclosed in cabinets, as is the practice with CNC controlled processes. Cabinet-mounted air cleaners sized to fit various cabinet sizes are available with either electronic or media technologies. An example is the Air Quality Engineering MistBuster® product line.
It can be a challenge to capture coolant mist generated by machining or grinding processes which are not well enclosed. A number of possible solutions to this challenge are offered by the American Conference of Governmental Industrial Hygienists in “Industrial Ventilation: A Manual of Recommended Practice.” Your air cleaning professional can help you design a coolant mist capture solution for these applications.
[i] “Bacterial Microflora of Contaminated Metalworking Fluids” S. Bakalova, A. Doycheva, I. Ivanova, V. Groudeva, & R. Dimkov Pages 437-441 | Published online: 15 Apr 2014, https://doi.org/10.1080/13102818.2007.10817490
[ii] Geier, J., Lessmann, H. (2019). Metalworking Fluids. In: Johansen, J., Mahler, V., Lepoittevin, JP., Frosch, P. (eds) Contact Dermatitis. Springer, Cham. https://doi.org/10.1007/978-3-319-72451-5_36-1
[iii] “New evidence on the health hazards and control of metalworking fluids since completion of the OSHA advisory committee report”Franklin E. Mirer PhD, 08 July 2010, https://doi.org/10.1002/ajim.20853
[iv] “Risk assessment for metalworking fluids and cancer outcomes” Robert M. Park MS, 12 January 2018, https://doi.org/10.1002/ajim.22809
[v] Criteria for a Recommended Standard: Occupational Exposure to Metalworking Fluids. DHHS (NIOSH) PUBLICATION NUMBER 98-102, January 1998