A cooling lubricant or cooling lubricant ( KSS ), also drilling milk , or grinding milk is used in production technology when cutting and forming on machine tools to dissipate heat and reduce the friction between tool and workpiece through lubrication . In addition, it is used in some machining processes to remove chips by rinsing them from the work environment, ensures better dimensional accuracy of the workpiece, better surface quality , reduces the formation of built-up edges on the tool and binds the dust (e.g. when grinding). The side effect of the cooling lubricant is the corrosion protection of the workpiece.
In the manual processing of metallic materials, drilling or cutting oils, pastes or gels are often used, since water-based cooling lubricants do not wet the cut surfaces as well and usually have to be continuously replenished.
Mixed friction occurs primarily during machining and forming . Cooling lubricants reduce the friction through lubrication and thus reduce tool wear, heating of the workpiece and the energy requirement. Additives can be added to the cooling lubricants in order to adapt them to a wide variety of requirements. For example, EP additives (Extreme Pressure Additives) react at high pressures and temperatures with the material to be machined and thereby prevent roughness peaks, AW additives (Antiwear additives) form an adhesive film on the surface of the tool and workpiece.
Cooling lubricants should remove the heat from the point of action as quickly as possible in order to avoid changing the structure in the edge layers of the tool and material. The machining accuracy also benefits from good cooling. In the case of water-miscible cooling lubricants, in addition to the evaporation of the water, the high heat capacity of the water content also contributes to cooling.
In addition to water and oils, additives that are added before and during use are also used. These include, for example, defoamers, biocides ( bactericides / fungicides ) for pre- and post-preservation, disinfectant cleaners , stabilizers , emulsifiers , corrosion protection additives, high-pressure additives.
Cooling lubricants and their preparations are usually mixtures within the meaning of Regulation (EC) No. 1272/2008 (CLP) , therefore safety data sheets must be made available for them.
Types of cooling lubricants
A distinction is made between two types of cooling lubricants according to DIN 51385:
- Non-water-miscible (nw) cooling lubricants
- Water-miscible (wm) and water-mixed (wg) cooling lubricants
Non-water-miscible cooling lubricants
Unalloyed (without chemical additives) and alloyed oils. Mostly naphthenic or paraffin-based mineral oils, more rarely synthetic oils such as hydrocracked oils, ester oils, hydrogenating oils. A “pure” mineral oil is sufficient for very simple machining operations, but phosphorus, sulfur and, in very rare cases, chlorine additives are usually added to increase the oil's performance. Oils containing chlorine are highly effective, but very harmful to health and very expensive to dispose of. Further additives serve to protect against rust, reduce foam formation and oil mist, improve the flow behavior at low temperatures and improve the viscosity index. Non-water-miscible cooling lubricants are mainly used when a high lubricating effect is required.
Water-miscible cooling lubricant
Water-miscible concentrates or ready-to-use emulsions. Water-miscible cooling lubricants containing mineral oil contain emulsifiers and mineral oil as well as additives for better lubrication, such as ester oils and sulphurized additives, corrosion protection additives and additives that prevent foaming. Mineral oil-free, water-miscible cooling lubricants can be emulsions, for example based on rapeseed oil, but also solutions that contain, for example, polymeric alcohols instead of oil for lubrication. The properties of water-miscible cooling lubricants are good heat dissipation, but less lubricating effect. The oil content in emulsions is usually between 5 and 8 percent.
Cleaning the coolant
It makes sense to filter the cooling lubricants so that they can be used longer. Clean cooling lubricants result in a better surface quality. In machine tools with coolant supply through spindle and tool, a filter device is often mandatory by the manufacturer. Special cooling lubricant filters , settling basins or magnetic separators and oil separators ( skimmers ) are used for this. The use of cooling lubricants is important for improving the service life of the tools and the surface quality of the materials. Disposal takes place via all public disposal companies without any problems; the operator must ensure regular monitoring of the cooling lubricant (weekly measurements of the concentration, the nitrate and nitrite value, and the pH value).
Infestation by microorganisms
Water-miscible cooling lubricants in use are infected by microorganisms (fungi and bacteria). During longer work breaks (e.g. weekends), bacteria can multiply, which is noticeable in the form of a strong odor and possibly discoloration of the cooling lubricant. The infestation often results in health problems for workers who come into contact with cooling lubricants. In addition to the common slight inflammation of everyday wounds, skin rashes and allergic reactions can also occur. Technical problems can be caused by the clogging of pipelines by fungal threads and / or slime bacteria. To avoid this, biocides can be used. Non-water-miscible cooling lubricants are very rarely affected by germ infestation. Coolants containing mineral oil are particularly susceptible to bacteria and fungi, cooling lubricants free from mineral oil are less so because they contain less organic material. When using water-miscible cooling lubricants, the Biological Agents Ordinance must be observed.
Environment, work and health
A risk assessment is required by law for activities involving cooling lubricants . Based on their results, protective measures are to be derived according to the hierarchy of measures . In particular, the risks from skin and eye contact, emissions into the air, the risk from absorption into the body and the risk of fire and explosion must be eliminated or reduced to a minimum. For this, it is necessary to develop a concept of measures based on the special concerns of protection against cooling lubricants.
Particular attention must be paid to the air pollution in the workplace by aerosols and vapors . In closed rooms, there can be an accumulation of oils in the breathing air, which is why the oil content of the air must be controlled by appropriate measures and reduced if necessary. This can be achieved through procedural or organizational measures.
The use of cooling lubricants is associated with environmental pollution, which is why used or unusable cooling lubricants must be properly handled or disposed of, as otherwise there is danger to the environment and operating personnel. Disposal of the cooling lubricant is expensive and may only be carried out by specialized companies. Proper disposal must be proven.
In Austria, Huber KSS Service, the nationwide market leader in the field of cooling lubricant service, registered the common abbreviation KSS as a brand name in 2014 .
- Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA): Portal cooling lubricants
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- List of materials for cooling lubricants according to DIN 51385 for metalworking. (PDF; 548 kB) VKIS , Association of Lubricants Industry e. V., IGM , December 16, 2016, archived from the original on August 28, 2017 ; accessed on August 28, 2017 .
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- VDI 3397 sheet 2: 2014-06 Maintenance of cooling lubricants for cutting and forming manufacturing processes; Measures for maintaining quality, process improvement, and for reducing solid and liquid waste (Maintenance of metalworking fluids for metalcutting and forming operations; Measures for maintaining quality, process improvement, and for reducing solid and liquid waste). Beuth Verlag, Berlin, p. 44.
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- German Social Accident Insurance eV: IFA practical help: KSS portal - protective measures. Accessed June 20, 2018 (German).
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- VDI 2262 sheet 2: 2012-11 Air quality at the workplace; Reduction of exposure to air pollutants; Procedural and organizational measures (Workplace air; Reduction of exposure to air pollutants; Processing and organization measures). Beuth Verlag, Berlin, pp. 17-28.
- VDI 3397 sheet 3: 2016-10 Disposal of cooling lubricants (Disposal of metalworking fluids). Beuth Verlag, Berlin, p. 7.
- VDI 3397 sheet 3: 2016-10 Disposal of cooling lubricants (Disposal of metalworking fluids). Beuth Verlag, Berlin, pp. 14–15.
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