Water-miscible Metalworking Fluids Research Articles

Microorganisms in spent water-miscible metalworking fluids as a resource of strains for their disposal

Metalworking fluids (MWFs) are essential components for modern metalworking technologies. The volume of world consumption of diluted working solutions exceeds 20 million tons annually. Water miscible MWFs accounts to 90% of the global MWFs demand. Spent MWFs contain toxic xenobiotics and residues of biocides. They are hazardous to the environment and require complex processing and detoxification. Microorganisms are able to colonize MWFs and metabolize the majority of available substances (oils and additives). Microbial degradation is one of the most efficient ways to dispose of water-miscible MWFs. The species composition of microorganisms changes during the operation of the fluid. From the point of view of the selection of effective biodegradion agents, the composition of microorganism species at the end of the MWFs service life cycle is of high interest for the industry. The aim of this work is to study the fungal and bacterial diversity of the microbiota of the spent MWF both by the method of isolating axenic cultures of fungi and bacteria, and by NGS-based metagenomic profiling using 16S rRNA for bacteria and ITS for fungi, and evaluate the possibility of their growth in diluted to a working concentration MWFs that differ in composition. Multiplex sequencing revealed (share in the samples more than 0.01%) 18 bacterial genera: Achromobacter, Alcaligenes, Aquamicrobium, Bacillus, Bacteroides, Brevundimonas, Caulobacter, Chryseobacterium, Dechlorobacter, Desulfovibrio, Dysgonomonas, Ochrobactrum, Proteiniphilum, Pseudomonas, Ralstonia, Shewanella, Sphingomonas, Stenotrophomonas and 17 fungal genera: Alternaria, Aspergillus, Bjerkandera, Cadophora, Candida, Cladosporium, Cryptococcus, Cystobasidium, Didymella, Fusarium, Malassezia, Penicillum, Pithomyces, Saccharomyces, Talaromyces, Wickerhamomyces, Yarrowia. Six genera of fungi (Saccharomyces, Fusarium, Malassezia, Bjerkandera, Penicillum, Alternaria) were identified in all tested samples. Yarrowia, Saccharomyces, Cadophora and Fusarium dominated in different samples. The diversity of bacterial biota was significantly higher than that of fungi. There was no clear dominance of any kind of bacteria in any sample. The analysis of isolated axenic cultures revealed that bacteria Shewanella putrefaciens, Proteus sp., Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Aeromonas hydrophila, Pseudomonas pseudoalcaligenes and fungi Fusarium solani, F. oxysporum, Yarrowia lipolytica, Candida metapsilosis were capable of growing in water-miscible MWFs. The data on the microorganism's species composition of the spent MWFs will make it possible to select species-specific DNA regions and design specific and sensitive test systems that can be used for identifying and evaluating the concentration of potential agents for the biodegradation of MWFs intended for disposal.

Microbiology in Water-Miscible Metalworking Fluids

Water-miscible metalworking fluids (MWFs) are used in metal removal and forming operations. For end use, formulation concentrates are diluted in water, providing conditions conducive to microbial growth and metabolism and potentially causing fluid biodeterioration and microbiologically influenced corrosion. Microorganisms in the environment are highly diverse, and bacteria and fungi have been recovered from these fluids at population densities of >106 CFU mL−1. Thus, to control microbial bioburdens in MWFs, microbicides are often incorporated into MWF formulations, used as tankside additives, or both. Some microbicides are suspected as being responsible for adverse health effects. Consequently, their usage has been restricted in recently adopted regulations. Given the limited number of microbicides currently approved for use in MWFs, alternative microbial contamination control strategies are needed. Some of these strategies have already been employed in the market. Studies on microorganisms in MWFs are often hindered by the complexity of the media, especially when trying to examine in-use samples. Historically, microbiological analyses were primarily based on cultivation assays using nutrient-rich media. These analyses have severe disadvantages, and the adoption of more reliable test methods is of utmost importance. Here, we review MWF microbiology, discussing possible consequences and options for both control and condition monitoring testing.

Sustainable machining by energy- and resource-efficient application of metalworking fluids

Due to increasing demands regarding the sustainability of manufacturing processes, a long service life and an energy-efficient supply of mineral-oil-based metalworking fluids is of increasing relevance. In the context of this work, the influence of aging processes in water miscible metalworking fluids on their performance has been investigated. Furthermore, results are presented regarding the energy-efficiency of metalworking fluid supply, which can be increased by adapting the fluid supply conditions.

Investigation of the Influence of Aging on the Lubricity of Metalworking Fluids by Means of Design of Experiment

The influence of complex aging processes in water-miscible metalworking fluids on process performance is of high relevance for the metalworking industry. Because of the highly dynamic interactions in the complex “metalworking fluid” ecosystem, a distinct correlation between the aging process and the performance of the fluid in metalworking processes is hardly possible. Consequences of the aging process on physical, chemical, and biological properties of the fluid include aspects such as the decrease of the pH value, the increase of the droplet size in emulsions, the presence of bacterial cells, or the modification of the metalworking fluid composition. In the presented work, the influences of these aging aspects on the lubricity of metalworking fluids were investigated individually. A test series has been carried out, which was planned with a design of experiments method, to investigate interactions between the aging aspects regarding lubricity. In addition, the results enabled the development of an empirical regression model, which allowed an integrated description of the influence of the relevant aging aspects.

Influence of artificial aging on the lubricating ability of water miscible metalworking fluids

The understanding of the complex aging processes of water miscible metalworking fluids and their effect on the performance in machining processes is of high relevance for the metalworking industry. Nevertheless, only little knowledge is available in this context. Due to the highly dynamic interactions in the complex ecosystem “metalworking fluid”, a distinct correlating of the aging process with the performance of the fluid in metalworking processes is hardly possible. Consequences of the aging process on physical, chemical and biological properties of the fluid have been described in several research works. These consequences comprise aspects such as the decrease of the pH-value, the increase of the droplet size, the presence of bacterial cells or the modification of the metalworking fluid composition. The novel approach of the presented work aims to investigate the individual influence of isolated aging aspects on the lubricity of metalworking fluids. Therefore, selected aging aspects were artificially varied separately from each other and evaluated in tribological experiments. It could be shown that the physical presence of bacterial cells as well as extracellular polymeric substances have positive influence on the lubricating ability while the pH-value has no effect and the droplet size only a slight influence on the fluids performance. The results reveal essential knowledge for the design of future monitoring and maintenance strategies for water miscible metalworking fluids.

Performance evaluation of metalworking fluids based on microorganisms

For various industrial manufacturing processes metalworking fluids (MWFs) are of high relevance due to their cooling and lubricating ability. Water-based MWFs are prone to the colonization by microorganisms which leads to deterioration and a change of the chemical composition with increasing duration of use. A wide range of species is able to colonize MWFs and metabolize almost all available substances (base oil and additives). However, it is known that some microorganisms are able to stabilize emulsions in nature by releasing biosurfactants into their environment. Considering that most microorganisms are not pathogenic and some of them are able to synthesize equivalent metalworking fluid components, the potential of microorganisms to act as a sustainable source for MWFs (here emulsifiers) components is investigated. This work presents an overview of the current state of science and the systematic selection of organisms according to certain criteria. The microbially produced biosurfactants were used to generate mineral-oil-free metalworking fluid emulsions with rapeseed oil. Results are presented which indicate the ability of microorganisms to replace emulsifying components of conventional water-miscible MWFs. Moreover, further bacterially produced substances are considered as replacements of metalworking fluid components and results are shown for lubricants produced by microorganisms.

A differential adenosine triphosphate test method for differentiating between bacterial and fungal contamination in water-miscible metalworking fluids

A new variation of a method for quantifying cellular adenosine triphosphate (cATP) is described. The variation permits differentiation between cATP from bacteria and cATP from fungi. This paper describes the process by which the new differential cATP method was developed and validate in both laboratory and field tests. Laboratory tests using bacteria, yeasts and filamentous fungi demonstrated that cATP observed in ≥5 μm and <5 μm size-fractions, respectively were consistently within ±10% of predicted concentrations. The field evaluation during which four participating metalworking fluid (MWF) compounders collectively tested >250 used MWF samples, confirmed that the differential protocol reliably detected fungal contamination when it was present.

Comparative study of microbiological monitoring of water-miscible metalworking fluids

Microbial activity is one of the primary causes of water-miscible metalworking fluid (MWF) deterioration in application. Although it is impractical to maintain MWF under microbe-free conditions, timely, accurate and easily interpreted microbial contamination condition can substantially reduce the risk of MWF biodeterioration. This paper compares different condition monitoring methods detecting the microbial contamination of MWF related to their speed and precision in laboratory and field samples. Two culture tests (plate count and dip-slides) and two adenosine triphosphate (ATP) test methods were compared. Additionally the matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-ToF-MS) is introduced as a method for the identification of bacterial strains isolated from MWF. The results clearly indicate that MWF monitoring is in need of standardization concerning sampling, area of measurement, and analysis of determinable cell counts as well as species communities.

The influence of cell counts, cell size, EPS and microbial inclusions on the lubrication properties of microorganisms

Metalworking fluids (MWF) play an essential role in many machining applications and can be classified e.g. according to DIN 51385 in non-water miscible- and water miscible metalworking fluids. Most of the several billion liters of the worldwide and annually consumed MWF are water-based and thus exposed to a microbial contamination, which leads to a deterioration of MWF compounds and therefore to a loss of quality and technical performance. To maintain the MWF quality, biocides are used to reduce the microbial load, regardless of their potential risk for health and environment. A further limitation poses the high consumption of raw materials (mainly mineral oils) for the production of MWF, with approximately 50,000 t of raw materials consumed annually in Germany. To overcome these limitations, the paradigm shift of using microorganisms as a lubricant in a manufacturing process is investigated in this paper. Preliminary investigations on a Brugger-tribotester indicated the great potential of microorganisms as replacement for conventional metalworking fluid components. Against this background, the approach presented here intends to investigate the influence of cell counts, cell size, extracellular polymeric substances and microbial storage products on the lubrication properties of selected microorganisms. The results of the tribological tests show, that some microorganism exhibit superior lubrication properties (up to 68 % higher) compared to a highly concentrated conventional metalworking fluid. Therefore, the potential of microorganisms to substitute conventional MWF components can be derived.

Microorganisms in metalworking fluids: Current issues in research and management

The microbial contamination of water miscible metalworking fluids (MWFs) is a serious problem in metal industry. A good maintenance of MWF re-circulation systems can extend the lifetime of coolants and ensure the quality of the tools produced. In MWFs, as in the other water-based environments, microorganisms usually live in the form of biofilms, the communities of bacteria and fungi attached to the surface of sumps, metal parts and also to each other. Biofilms exhibit very high resistance to biocides. The effect of biocides that are used as additives to MWFs to control the growth of the bacterial and fungal microbiomes (microorganisms characteristic to the individual coolant system) have become the subject of research only in recent years. There are also only sparse reports on the impact of biocides on microorganisms growing in biofilms in MWF installations. Fast growing mycobacteria are important members of these biofilm communities. Their presence has recently been linked with the occurrence of cases of hypersensitivity pneumonitis, a serious respiratory disorder in the metal industry employees. The new, relatively fast and inexpensive techniques to assess the species diversity within MWF microbiomes and their population size should be developed in order to control the microorganisms' proliferation in MWFs and to diminish the occupational exposure to harmful bioaerosols in metal industry.

A combined cultivation and cultivation-independent approach shows high bacterial diversity in water-miscible metalworking fluids

Ten metalworking fluids (MWF) and seven water preparation basis samples (WPB) were taken from five industrial plants in Germany. Total cells (TCC) and colony forming units (CFU) were counted, strains were isolated and their 16S rRNA gene was sequenced. Additionally, DNA was extracted directly from the samples, and clone libraries of 16S rRNA genes were built and gene sequenced. TCC ranged from 7.6×104TCC/mL MWF to 1.6×108TCC/mL MWF, and from 4.6×102TCC/mL WPB to 7.8×107TCC/mL WPB. The CFU showed similar but often lower results. A total of 70 isolates and 732 clones were 16S rRNA gene sequenced and all isolates, as well as 183 of the nearly full length 16S rRNA of these clones, were gene sequenced. A total of 98 different genera were detected in all 17 samples. The number of genera within each sample varied highly, with 1–22 genera per sample. The dominant genera in MWF were Leucobacter, Desemzia, Sphingomonas and Wautersiella. From these, only Sphingomonas was detected in WPB as well. This study showed that MWF can harbour a high bacterial diversity, which differs significantly from the bacterial flora of the corresponding WPB.

Microbial degradation of water miscible metal working fluids

Water miscible metal working fluids (MWF) are prone to contamination by bacteria and fungi. In the present work it was investigated which components of a model MWF emulsion were most readily degraded by microorganisms and which are relatively resistant to biodegradation. The microbial community colonising an MWF emulsion, during its lifetime under in-use conditions was analysed up to species level. Shifts in the composition of microbial community were related to chemical changes in the MWF emulsion over time.

Respiratory Exposure to Components of Water-Miscible Metalworking Fluids

Water-miscible metalworking fluids (MWFs) are capable of causing respiratory symptoms and diseases. Recently, much emphasis has been put on developing new methods for assessing respiratory exposure to MWF emulsions. The air concentrations of ingredients and contaminants of MWF and inhalable dust were measured in 10 metal workshops in southern Finland. Oil mist was determined by infra red spectroscopy analysis after tetrachloroethylene extraction from the filter. Aldehydes were collected on Sep-Pak chemosorbents and analysed by liquid chromatography. Volatile organic compounds (VOCs) were collected on Tenax adsorbents and analysed by gas chromatography with mass spectrometric detection after thermal desorption. Endotoxins were collected on glass fibre filter and analysed by enzyme-based spectrophotometry, and viable microbes were collected on polycarbonate filter and cultured. Inhalable dust was collected on cellulose acetate filter and quantified gravimetrically. Associations between the different exposures were calculated with Spearman's correlations. The mean concentration of oil mist was 0.14 (range <0.010-0.60) mg m(-3). The mean total concentration of aldehydes was 0.095 (0.026-0.38) mg m(-3), with formaldehyde as the main aldehyde. The average total concentration of VOC was 1.9 (0.34-4.5) mg m(-3) consisting mainly of high-boiling aliphatic hydrocarbons. Several potential sensitizing chemicals such as terpenes were found in small quantities. The concentration of microbial contaminants was low. All the measured air concentrations were below the Finnish occupational exposure limits. The exposure in machine shops was quantitatively dominated by volatile compounds. Additional measurements of MWF components such as aldehydes, alkanolamines and VOCs are needed to get more information on the chemical composition of workshops' air. New air cleaning methods should be introduced, as oil mist separators are insufficient to clean the air of small molecular impurities.

Application possibilities of new AW/EP additive types in watermiscible metalworking fluids

Metalworking fluids are applied in metal working operations in order to decrease tribological effects and increase economy. Primarily they are used for cooling the tools and the workpieces and also for lubricating the cutting edges. The components of metalworking fluids responsible for decrease in friction are AW/EP additives. To comply with the very strong European legislation for human and environmental protection, important compounds for metalworking fluids formulation are reduced. Based on this, chlorinated paraffin, a widely used AW/EP additive, should be replaced with less harmful compounds. The application possibility of new types of AW/EP additives as chlorinated paraffin replacements is investigated in this paper. These additives are synthetic esters of carboxylic fatty acids, phosphoric and dithiophosphoric acid derivatives. Watermiscible metalworking fluids formulations are prepared with the new types of additives and examined at laboratory test machines–EP‐Four ball, Wear‐Four ball machine and Reichert balance machine.

Assessment of ep additives for water-miscible metalworking fluids

This paper presents a short overview of the background to EP additives and their operating mechanism in relation to temperature activation, in the formulation of water-miscible metal working fluids. The physical and chemical properties, determined using standard laboratory equipment, and dynamic tests, of different formulations of water-miscible metal working fluids are given. The main work reported here was to compare the EP performance of available commercial additives, looking particularly at commercial variations of phosphate esters as replacements for chlorparaffins. The paper concludes that the ‘tapping and drilling’ test, which is a relatively good simulation of practical conditions in metalworking operations, can be successfully used as a way of selecting the appropriate EP additives, and for formulation of the concentrate.