METALWORKING
Environmental advantages of sulphur carriers in metalworking
Wilhelm Rehbein, Senior Manager Application Technology, LANXESS Deutschland GmbH, Cologne, Germany
Introduction The reduction of global warming and climate change by minimising or avoiding greenhouse gas emissions is essential to protect our planet and to take care about our future generations. Apart from using energy from renewable sources, the reduction of energy consumption is the most effective way to achieve this goal. However, saving energy is not only possible by for example insulating buildings, optimising heating or lighting or using energy efficient transportation. One additional element is to reduce the energy consumption of manufacturing processes. Particularly the different procedures of cutting or forming metals have a high energy demand. Depending on the specific metalworking process and machining parameters like machining speed, applied force, material removal rate or feed rate, the energy consumption can exceed 50% of the energy consumption of a machine tool in heavy duty cutting, deep drawing or massive forming processes (figure 1).
that are essential to prevent adhesive wear and cold welding under boundary lubrication conditions. Most EP additives are based on chlorine or sulphur.
Chlorinated paraffins Chlorinated paraffins (CLPs) were one of the earliest EP additives used in lubricants and are still widely used as additives in metalworking fluids for a broad variety of manufacturing processes.
Short chain chlorinated paraffins (chain-length C10 C13
– ), however, were already banned and eliminated
from metalworking fluid formulations in many countries due to their persistency in the environment with a high potential for bioaccumulation and because of their classification as toxic to aquatic organisms, carcinogenic to rats and mice, and possibly carcinogenic to humans. Medium chain chlorinated paraffins (chain-length C14
– C17 ) are also due to be
banned within the next few years because of their risks to the ecosystem and to human health.
Figure 1: Energy consumption of components of a CNC machining center on a percent basis. The main spindle drives the cutting tools [1]
Extreme pressure additives Metalworking fluids are complex mixtures of base fluids and additives, used to reduce friction and prevent abrasive and adhesive wear in metalworking processes. Further functions are cooling of the manufacturing process and the removal of chips in metal cutting. They usually contain extreme pressure (EP) additives
46 LUBE MAGAZINE NO.176 AUGUST 2023
Chlorinated paraffins are able to prevent adhesive wear between metal surfaces by forming pressure stable adsorption layers under standard metalworking conditions. Though with increased machining speeds, resulting in higher temperatures of workpiece and tool surfaces, they tend to decompose and cause tremendous chemical wear. They are also sensitive to moisture and can easily evolve hydrogen chloride which causes severe corrosion of metal surfaces.
Sulphur carriers
Nowadays, the most commonly used EP additives in metalworking applications are sulphur carriers. “Sulphur carrier” is a frequently used generic name for sulphurised natural or synthetic esters or olefins. Due to their broad variety in sulphur content,
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