Formulation of cutting fluids

In order to realize the lubricating process of cutting fluids water miscible and non-watermiscible metalworking fluids have to be carefully formulated. These will be discussed separately.

Non-Water Miscible Cutting Fluids

The general composition of non-water miscible cutting fluids can be characterized as follows.

Base oil + Extreme pressure/Antiwear additives + Other additives

The most important components of these fluids are base oil (mostly mineral oils, in certain cases esters and polyalphaolefines), "lubricating" additives (antiwear and extreme pressure additives), oil fog reducing additives, corrosion inhibitors (only in specific cases) and oxidation inhibitors.

Some lubrication improving additives, mostly defined as antiwear additives, are fatty oils (animal and plant oils) and synthetic fatty acid esters or fatty alcohols. The most important extreme pressure additives belong organic chlorine, phosphorous and sulfur compounds.

Organic Chlorine-Containing Substances

As they are highly effective and relatively cheap, chlorinated paraffins were widely used as antiwear and extreme pressure additives.

A 1986 German law on the use and disposal of wastes divides used oils into three categories which have to be collected separately. The regulation contains the following limiting data for used oils which are suitable for recycling.

0.2 % total halogenes; 4 ppm polychlorinatcd biphenyls

Used oils containing higher amounts of halogens, especially chlorine are treated as special waste causing extremely high costs of disposal.

In older to reduce the risk of nitrosamine generation, the "Technical Regulation for Dangerous Products (TRGS/611)," released in April 1993, specifics the following.

• Metalworking fluids must not contain nitrosamine generating components. This applies to nitrites as corrosion inhibitors as well as to a few organic nitrogen-containing components used as biocides.

• Secondary amines like diethanolamines as corrosion inhibitors must not be used any longer.

• This ban does not apply if by selecting special amines or

using effective inhibitors, it is impossible, for carcinogenic nitrosamines to form.

• The content of secondary amines brought in as by-products with other components must not exceed 0.2 %. A result of the production process, mono- and triethanolamines may contain small amounts of diethanolamines.

Organic Phosphorous-Containing Substances

Organic phosphorous containing substances, such as tricresylphophate, are used as antiwear and extreme pressure additives. For toxicological reasons, one should take care that the tricresylphosphate is free of O-cresol.

Other Substances

Lead containing components were used as antiwear and extreme pressure additives, and boron containing components are currently in use as corrosion inhibitors.

• Lead containing components

Lead naphthenates have been used in the past for some special applications, but in coolants only as an exception. Due to their long term effect of increasing the lead
content in blood, lead based lubricants are hardly used any more.

• Boron containing components

Boric acid esters, as well as boric acid alkonolamine condensation products have gained certain importance as corrosion inhibitors, because they are biologically stable.

This property can result in certain disadvantageous effects as far as the disposal of coolants is concerned. As boron impairs the growth of certain plants, some countries released regulations that define maximum boron concentrations in waste water.

In addition to technical requirements, aspects of toxicology and industrial medicine will continue to exert an important influence on the development and formulation of cutting fluids. Higher fluid disposal costs will dictate a greater
emphasis upon fluid maintenance, and the use of products with longer service life and consistent long term performance.

It will become more and more difficult to find a balance between economic possibilities and ecological requirements. Of course, toxicologically and ecologically questionable products must be excluded from further use in metalworking fluids, if they pose any significant health risk under the conditions of application. On the other hand, it has to be taken into account that if unnecessary restrictions are, legislated, the technological performance of metalworking fluids will decrease. Today's formulations exhibit a good example to prove a reasonable balance between economic needs and ecological requirements.

Дата добавления: 2015-07-26