Miljøprojekt, 1039 – Mapping and development of alternatives to chlorinated lubricants in the metal industry (KLORPARAFRI)

Mapping and development of alternatives to chlorinated lubricants in the metal industry (KLORPARAFRI)

Summary and conclusions

Background

Medium-chained chloroparaffins are used in substantial amounts as extreme pressure (EP) additives in lubricants for metal working. Chloroparaffins are persistent and bio-accumulating substances. They are found widespread in the external environment and biota, including in food stuffs and human beings. The substances are toxic to aquatic organisms and may have adverse effects on human health. A health and environmental risk assessment has been performed by the EU Commission for short-chained chloroparaffins, while a risk assessment for medium-chained chloroparaffins is presently being prepared. Short-, medium- and long-chained chloroparaffins are included in the List of unwanted substances 2004 published by the Danish Environmental Agency due to their serious health and environmental properties.

In the past decade, a number of projects have been carried out in the Danish metal industry aiming at finding alternatives to chlorinated lubricants for metal working. Thus, there has been a substantial reduction in the use of chlorinated lubricants by Danish large-scale users in the metal industry. Chlorinated lubricants for cutting operations as milling, screw-cutting and drilling have been completely substituted. However, for non-cutting operations, particularly demanding processes such as forming in stainless steel and titanium, chlorinated lubricants are still widely used. This is due to a lack of technically satisfying alternatives so far. At the same time, the need for lubricants to be used under very demanding production conditions is increasing due to demands for material and energy saving, increased productivity and improved quality.

Objective

The overall objective of this project “Mapping and development of alternatives to medium-chained chloroparaffins in lubricants in the metal industry (KLORPARAFRI)” is to promote substitution of chlorinated lubricants for metal working. The focus of the project is on alternative lubricant systems for heavy-duty metal forming, including deep drawing, punching and extrusion, in stainless steel and titanium, where the use of chlorinated lubricants still persists. The specific objectives of the project are to map existing non-chlorinated lubricant alternatives for heavy-duty metal forming, to technically test the lubricating performance of selected lubricant alternatives, to assess the health and environmental properties of alternative lubricants and, if possible, to develop promising lubricant alternatives for production.

Mapping of non-chlorinated lubricant systems

A mapping of existing non-chlorinated lubricant systems for heavy-duty metal forming has been performed by contact to international lubricant suppliers, including both large companies and smaller, highly specialized companies. Approximately 50 lubricant systems have been proposed as alternatives to the specified metal forming operations.

Three types of lubricant systems have been mapped in this project.

The dominant type is traditional oil-based wet lubricants with extreme pressure components added. Chlorinated lubricants are normally of this type. Wet lubricants are applied to the metal surface without any drying step prior to the forming operation.

A second type of alternative lubricants is the so-called dry lubricants, which are also applied to the metal surface. However, they require drying prior to the forming operation. Dry lubricants are water-based emulsions and may contain polymers. The EP additives of wet and dry non-chlorinated lubricants are typically combinations of sulphur and/or phosphorous compounds. Some non-chlorinated lubricants may contain inorganic components as EP additives.

While the above-mentioned wet and dry lubricant systems require a single lubricant layer on the metal surface, a third type of lubricant system has been mapped which requires two lubricant layers on the metal surface: a carrier layer and a lubricating layer. Prior to application of a lubricant, a carrier layer is applied to the metal surface by phosphating or oxalating the metal surface. The lubricant to be applied subsequently on the carrier layer can be either a wet or dry lubricant as mentioned above or it can be soaps.

The mapping phase of non-chlorinated lubricants for heavy-duty metal forming has shown that substitution of chloroparaffins in metal forming lubricants requires a complete reformulation of the lubricant. It is not possible to substitute chloroparaffins in lubricants with a single component. Most often the composition of the lubricants becomes substantially more complex than the traditional chlorinated lubricant.

Technical testing of non-chlorinated lubricant systems

The lubricating qualities of 19 of the proposed non-chlorinated lubricants have been tested in simulating and process technical tests developed at the Technical University of Denmark (DTU). Four of the lubricants exhibited promising lubricating properties in these tests and were further tested in a full scale production test at Danfoss A/S. None of the four tested alternative lubricants exhibited sufficient lubricant performance. The production test comprised a several-step sheet forming of a work piece in stainless steel, including deep-drawing, extrusion and punching operations.

Not all proposed lubricant systems were technically tested in the project. This was due to either failure to comply with technical or health and environmental criteria established in the project or that the demands of application of the lubricant could not be fulfilled in the test system. The last-mentioned includes lubricants system that require an initial phosphating or oxalating of the metal surface prior to the test.

Health and environmental assessment of non-chlorinated lubricants

A health and environmental assessment has been carried out for selected components that typically occur in non-chlorinated lubricants. The objective has been to obtain an assessment of the inherent health and environmental properties of non-chlorinated lubricant components in addition to an overview of the data quality and availability for the substances.

As a substitution of chloroparaffins in lubricants normally implies a complete reformulation of the lubricant, it was estimated in this project that the most suitable frame of reference for comparison of the health and environmental properties of chlorinated and non-chlorinated lubricants respectively, is comparison of total lubricants. Thus, the health and environmental assessments of lubricant components has included not only components with a primary function as extreme pressure additives but also components with other functions as lubrication-enhancing additives.

The result of the health and environmental assessment of non-chlorinated lubricants indicates that especially the extreme pressure additives alkyl sulphides (polysulphides) and phosphorous compounds include substances which may cause adverse health and environmental effects. The result also demonstrates that substitution of chlorinated lubricants for heavy-duty metal working implies a movement from a reasonable data platform regarding potential health and environmental effects to a substantially poorer data platform.

A combined health and environmental screening for non-chlorinated lubricants has been performed for 14 of the 19 lubricants tested in the simulating and process technical tests. This has been done with the aim to establish an overview of the health and environmental properties of the lubricants at a screening level in addition to identifying and eventually sorting out lubricants with obvious unwanted health and environmental properties prior to a production test.

The result of the screening, based on the sparse available data, is that non-chlorinated lubricants seem to be better than chlorinated lubricants with regard to health and environmental properties compared to chlorinated lubricants. However, some of the lubricants suggested contain components exhibiting a sensitizing potential. In addition, many of the lubricants contain substances with an environmental hazard potential at the same level as chlorinated paraffins. However, the substances are present in the lubricants at substantially lower concentrations than chloroparaffins in the chlorinated lubricants.

Several of the proposed lubricants contain substances for which no or very limited data on potential health and environmental effects could be retrieved.

Worst case exposure assessments and risk characterizations in the working environment have been carried out at a screening level for two polysulphides and two phosphorous compounds considered to represent the most critical substance groups in non-chlorinated lubricants for metal forming regarding health and environmental effects. The result of these assessments indicate that worst case dermal exposure or inhalation of vapours may involve a risk of adverse effects on health for some compounds in these two groups. The risk of adverse effects by dermal contact is, however, quite easily reduced by use of personal protection equipment, especially gloves.

Discussion and conclusion

Four of the non-chlorinated lubricants have demonstrated promising lubricating qualities in an initial simulating test and a process technical test involving deep drawing and extrusion in stainless steel. However, none of the four lubricants showed satisfactory lubricating qualities in a full scale production test comprising a several-step forming of a work piece in stainless steel, including deep-drawing, extrusion and punching. Thus, under the test conditions given it was not possible to identify non-chlorinated lubricants capable of substituting chlorinated lubricants in full scale production involving several-step sheet forming operations in stainless steel.

Very often production of work pieces in the metal industry implies several-step operations, including various types of operations as in the full scale production test. However, the demands on the lubricating properties of a lubricant may vary considerably in various metal forming processes. It is known that non-chlorinated lubricant systems exist which operate with satisfying lubricating properties in individual forming operations. However, the limits for these lubricants are that they are specially designed for a certain forming operation and often also a certain customer. Thus, these lubricants can only work under a narrow set of production conditions.

Not all alternative lubricant systems proposed were technically tested in the project. In some cases, this was due to failure to comply with the testing conditions available in this project. Danfoss A/S has previously developed a lubricating system - the Extreme Pressure Lubricant System (EPL) - for cold forging of stainless steel. Cold forging involves high demands on the lubricating performance of the lubricant due to large plastic deformation rates with high energy release. The EPL system is a two-layer lubricating system comprising a carrier layer and a lubricant. The new technology in the system is the application of a phosphate carrier layer on stainless steel. A ordinary soap is subsequently applied on the metal surface as the lubricant. The EPL technique has previously demonstrated very good results in production tests at Danfoss A/S for the preparation of shell pipes in stainless steel. For financial reasons, Danfoss A/S has not implemented the EPL method as a standard technique in their production. Their production is estimated to be too small to establish the necessary production equipment. A market analysis of the sale of phosphated stainless steel demonstrated surprisingly low interest.

Thus, technically satisfying alternatives to chlorinated lubricants in heavy-duty metal forming may exist. However, they involve substantial costs due to large investments in production equipment.

By contrast, chlorinated lubricants are multi-functional and can be successfully added to most metal forming processes. They have well-documented lubricating properties and are cheap.

The health and environmental assessment of components in non-chlorinated lubricants and the screening of proposed alternative lubricants indicate that non-chlorinated lubricants seem to possess improved inherent health and environmental properties. However, they may contain substances that are potentially sensitising and substances that may have adverse environmental effects at a level corresponding to that for chloroparaffins though the substances occur in the alternative lubricants in substantially lower concentrations than chloroparaffins in chlorinated lubricants. Furthermore, substitution of chlorinated lubricants for heavy-duty metal working implies a movement from a reasonable data platform to a significantly poorer data platform.

The overall conclusion of the project is that further development of non-chlorinated lubricants for heavy-duty metal forming remains in order to obtain technically satisfying alternatives while simultaneously improving the health and environmental properties.