Apparatus for and methods of stabilizing and regenerating metalworking fluids

Metalworking fluids (MWFs) could be regenerated and stabilized by the controlled addition of a chelating agent. The consequent sequestration of the dissolved metals at the MWF has been proven to decrease incidence of dermatitis, to restrain the growth of microbes including bacteria and parasites, and also to decrease the production of odors, all with no further addition of new (virgin) MWF or even a conventional biocide. Apparatus useful for this control includes tracking means for determining the presence of free metal ions at the MWF, analyzing means of determining the concentration of free metal ions if existing, and addition means for adding, in a controlled manner, a chelating agent for sequestering the free metal ions.

 

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BACKGROUND

 

 
The present invention relates generally to metalworking fluids and, more particularly, to methods of using additives to regenerate and stabilize metalworking fluids and to diminish dermatitis and other health problems associated with the usage ofmetalworking fluids. This invention also relates to a wholly or partly automated system for executing these methods.
 

 
From the fabrication of metal parts by machining and from various cold forming processes, a lubricant can be utilized. In a machining operation that entails cutting or other removal of material from the workpiece, the lubricant assists in removing heatgenerated by engagement of the cutting tool, in removing chips, turnings, and penalties generated through such machining, and in lubricating or protecting newly exposed part surfaces. In cold forming operations, a lubricant may be put on the slug surfaceto decrease friction through deformation and also to lubricate recently exposed surfaces. For cutting operations, the fluid may be dispersed continuously over the workpiece.
 

 
Notably for similar and turning lathe operations, the lubricant is usually known as a”metalworking fluid.” Metalworking fluids (MWFs) are used throughout the production sector to supply a more efficient material removal or formingoperation. Such fluids are selected generally for the purpose of cooling the workpiece and the tool through cutting operations, and also to ease removal of chips through turning, grinding, and similar operations. MWFs are an important facet of manymanufacturing operations in that they supply the essential heat and chip elimination properties essential to achieve increased production outputs, improved tool life, and also enhanced machined-surface complete and part quality.
 

 
MWFs are usually categorized as oil-based, artificial, or semisynthetic. Oil-based MWFs might be comprised of straight (neat) oils derived from oil and/or paraffinic hydrocarbons, natural oils like vegetable oils, or might be contained ofa synthetic oil like a siloxane or dibasic ester. Water-based MWFs may include a water-soluble oil, a synthetic composition, or even a semisynthetic composition. Water-based artificial fluids are free from mineral oils, and their aqueous environment canspawn bacterial and/or fungal growth. Semisynthetic fluids and water soluble oils generally combine the benefits of emulsifiable oils and synthetic fluids, and they’re typically provided as a oil-in-water emulsion. View generally, T. Cole,”KnowYour Coolants,” Cutting Tool Eng., October 1990, p. 59f.
 

 
Conventional additives for MWFs include corrosion inhibitors, such as alkaline and alkanolamine salts of amino acids, sulfonates, amines, amides, natural borate compounds, and others. Corrosion inhibitors are generally added to the hydrophobicportion of this MWF. Polar compounds, such as certain vegetable or animal oils (e.g., castor oil, olive oil, peanut oil), esters of amino acids, and the like are regarded as biologically inactive MWF ingredients. Polar additives function throughelectrostatic fascination in which the small polar group adsorbs on the metal surface, and the larger hydrophobic group is solubilized from the oil phase. These characteristics produce a firmly anchored mono-molecular film (a metallic soap) on theexposed metal surface that serves as a protective barrier.
 

 
“Intense pressure” additives are just another type of conventional additive and typically contain chlorine, phosphoroussulfur or sulfur compounds. These additives may be used in heavy duty machining operations where the temperature is greater than thattolerated by polar additives, so which is more than about 390. degree. F. (about 200. degree. C.). Other conventional additives include solubilizers (e.g., long-chain alcohols), colorants, fragrances, anti-oxidants, anti-foaming brokers, as well as the like.See, e.g., Keith Bienkowski,”Waste Minimization During Improved Coolant Management,” Technical Paper No. MRR92-12, Soc. of Mfg. Eng., Dearborn, Mich.. (1992).
 

 
MWFs are susceptible to microbial attack by bacteria, parasites, or yeasts (collectively termed herein”microbes”), inducing one or more symptoms like odor development, a drop in pH, a reduction in dissolved oxygen concentration, changes inemulsion stability (for water soluble oils and semisynthetic fluids), greater incidence of psoriasis, workpiece surface-finish blemishes, clogged filters and traces, greater workpiece rejection prices, diminished tool life, and also generally unpredictablechanges in coolant chemistry. See, e.g., Frederick J. Passman,”Microbial Problems in Metalworking Fluids,” Lubrication Engineering, pp. 431-3, May 1988. See also I. Mattsby-Baltzer et al.,”Microbial Growth and Accumulation at IndustrialMetal-Working Fluids,” Applied and Environmental Microbiology, October 1989, pp. 2681-2689.
 

 
Biocides are generally added to the MWF to fight microbial contamination. 1 traditional biocide is o-phenylphenol (accessible as DOWICIDE 1 antimicrobial fluid from Dow Chemical USA, Midland, Mich.). Hernandez (Canadian Pat. No. 1,161,026)describes inherently bactericidal MWFs which include a combination of boric acid, an alkali tetraborate, pelargonic acid (also referred to as normal ennoic acid or nonanoic acid, CH.sub.3 (CH). sub.7 COOH), a nonionic surfactant, and water. Biocides typically havea limited lifetime of only a few or a couple of days and, accordingly, are replenished weekly or even daily according to traditional manufacturing protocol.
 

 
While reported opinions differ regarding whether MWFs can transmit communicable disease, and regarding the general viability of germs in MWFs, it’s fairly well-established that used MWFs are correlated with outbreaks of dermatitis. Two potentialsources of MWF-induced dermatitis are compounds intentionally added to the MWF (for instance, biocides) and solubilized metal ions from metal chips, dust, and fines, typically collectively known as”swarf”, deposited in the MWF from the machining orforming operation.
 

 
Metal ions can become solubilized in the MWF on account of the generation of friction, heat, oxidation, along with other physical and chemical processes which happen in the MWF environment. Just about any metal ion, including nickel, iron, chromium, cobalt,cadmium, copper, manganese, or zinc may lead to contact dermatitis in a certain machine operator. Iron, nickel, and chromium are usually found in swarf generated from machining various types of stainless steel. Cobalt is generally encountered whenmachining with cutting tool steel and tungsten carbide cutting tools.
 

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