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Both series of aluminium alloys are difficult to machine because of high tool wear and cutting-edge build-up. Due to the copper content the 2000 series alloys tend to stain or discolour when they come into contact with unsuitable metalworking fluids.

Composites: A composite material is a combination of two or more materials, usually a reinforcement which is embedded in a matrix. In contrast to metallic alloys, each material retains its separate chemical, physical, and mechanical properties. The main advantages of composite materials are their high strength and rigidity, combined with low density. Typical composites are metal matrix composites (MMC), ceramic matrix composites (CMC) and polymers reinforced by glass fibre (GFRP) or carbon fibre (CFRP). Many composites contain abrasive components which make them very difficult to machine. This results in short tool life but also in an often dissatisfying quality of the machined parts. The structure or properties of composites with polymer or resin matrix like CFRP or GFRP can be affected by some cutting fluid components.

Requirements on machining fluids for new materials Most of the described new materials are very difficult to machine because of factors such as high strength, toughness, abrasiveness or the proneness to form built-up edges. They represent specific challenges on the metalworking fluids and thus on the additives’ properties which have to be adapted to fulfil the specific demands of these materials. This includes the application of additives with adjusted activity that are able to prevent cold welding at high machining temperature or to avoid the adhesion of workpiece material on the tool without having a negative influence on the surface of the machined part. Synergistic combinations of different types of additives can be used to increase machining quality and tool life.

• Category 1 - Hydraulic fluids and tractor transmission oils • Category 2 - Greases and stern tube greases • Category 3 - Chainsaw oils, concrete release agents, wire rope lubricants, stern tube oils and other total loss lubricants

• Category 4 - Two-stroke oils • Category 5 - Industrial and marine gear oils

According to the ecological properties (aquatoxicity, biodegradability and potential to bioaccumulate) of lubricant additives, different maximum treat rates are applicable for every lubricant category. Suitable additives which have been assessed for the formulation of EEL lubricants can be found on the Lubricant Substance Classification (LuSC) list. The LuSC list also provides condensed information on biodegradability and aquatic toxicity by assigning a biodegradation/bioaccumulation class (A, B, C, X) and a aquatoxicity class (D, E, F, G) to the listed products.

For the near future however the European Commission plans to extend the scope of these categories by implementing other product groups in order to cover a higher market share. The new category 1, for example, will probably cover lubricants for hydraulic systems but also metalworking fluids.

The current evaluation criteria include the effect of the lubricants on water and soil during its use, the content of toxic or restricted substances as well as the content of renewable raw materials and a demand for a minimal technical performance. The scope of the revised EU Ecolabel is proposed to be enlarged in order to include: - health and safety concerns - concerns regarding disposal - lubricants with high market share and/or target end-consumer

Metalworking fluids (MWF) are not supposed to enter the environment except as accidental loss, however they could be important due to the impact on human health for the worker exposure. Also the impact linked with waste (disposal of used oil, aqueous waste carrying chemicals or metal ions) are relevant from an environmental point of view.

Figure 1. Turbine blades are typically made of titanium (compressor section) and nickel based alloys (high temperature section)

Implementation of metalworking fluids into the EU Ecolabel system

The EU Ecolabel (EEL) is a voluntary scheme, established in 1992 to encourage companies to market products and services that have a low ecological impact during their entire life cycle. It is part of the sustainable consumption and production policy of the European community, which aims at reducing the negative impact of consumption and production on the environment, health, climate and natural resources. Currently the product group “lubricants” of the Ecolabel describes evaluation criteria for the following 5 categories:

The LuSC list already includes several extreme pressure and antiwear additives, lubricity improving additives, corrosion inhibitors and antioxidants which are suitable for metalworking applications. Depending on the future requirements for an Ecolabel category “metalworking fluids” these additives can be combined to various formulations which are able to meet the demands of the miscellaneous metalworking processes.

Further toxicological aspects of metalworking fluid additives Biocides: The contamination of bacteria and fungi in water mixed metalworking fluids is a serious problem. Water diluted MWF contain many substances that bacteria and fungi can use for their metabolism like hydrocarbons (mineral oil), esters, emulsifiers, corrosion inhibitors and others. The growth of micro-organisms leads to a degradation of metalworking fluid components which has a negative influence on e.g. its stability, anticorrosion performance or anti-wear properties. To prevent the growth of bacteria and fungi several types of biocides and fungicides have been used.

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