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Metalworking Fluid Chemistry & Tankside Additives

July 01, 2012
Neil Canter
Online Only Articles


In contrast to other lubricants, metalworking fluids are prepared with a large number of additives. This makes it a major challenge for the formulator to prepare products that meet the needs of end users.

The formulator is faced with the task of finding the right mix of additives and basestocks so that the resulting fluid can perform well in the diverse number of metal removal applications. Any additional challenge is that the formulator is required to prepare multiple fluid types ranging from straight oils to synthetic fluids.

There are at least 12 additives types used in developing metalworking fluids. In some cases, more than one additive of a specific type may be needed in a formulation further complicating matters. For example, emulsifiers (also known as surfactants) are essential to stabilizing the oil soluble components in an emulsifiable oil or semisynthetic fluid so that they will be stable in water. In many cases, at least two emulsifiers have been found to carry out this function better than one.

One of the most problematic additives is the antifoam agent. Foam (or entrained air) can be a major problem in metalworking fluid systems so there is need for using antifoam to minimize its outbreak during a machining operation.

The problem is that antifoam agents operating on the boundary between air and the fluid can readily become incompatible with the metalworking fluid or too compatible with the metalworking fluid. In the former case, they will either rise to the top of the fluid or precipitate to the bottom. In the latter case, they will become too soluble leaving the boundary area between the air and the fluid.

Rigorous testing is needed to make sure a specific antifoam will remain compatible with a particular metalworking fluid formulation and operate over a long period of time. This is usually difficult to achieve because antifoams tend to deplete rapidly. The result is that defoaming agents will need to be added to a depleted fluid in its end use application to rapidly cause foam to collapse.

Among the most challenging of the fluids to prepare is the semisynthetic fluid. This type contains both high percentages of mineral oil and water. In addition, there are oil soluble additives and water soluble additives.

The finished formulation contains tiny mineral oil droplets (typically ranging in size from 0.2 to 1 micron) dispersed in water. A semisynthetic fluid forms a translucent microemulsion that the user can see through with some difficulty. Due to changes in market conditions, use of the semisynthetic has also gained popularity because of it displays superior performance over a long operating time. In contrast to an emulsified oil, the semisynthetic is much more durable.

Keep in mind that the metalworking fluid must also be able to operate under a unique set of conditions at the end user’s facility. Parameters such as water hardness, the severity of the metal removal process, the metal alloys machined and the tooling used all must be considered when developing a product.

Cost effectiveness is a major driving force for the formulator. The end user may seek a low cost fluid but consideration must be made that such a fluid will only last for a short period of time. A more robust fluid that is more expensive initially may provide a better payback for the end user by performing at an optimum level for a long period of time. This will provide cost savings by extending the life of expensive tooling and minimize disposal costs.

The multifunctionality of a metalworking fluid necessitates that it be prepared with a large number of additives. The formulators must choose wisely to prepare a fluid that will operate effectively in a particular application.

This topic is covered in more detail in the Metalworking Fluid 115 course, Basics of Metal Removal Fluids. For more information on this and other education courses, click on the Annual Meeting link under the Events tab.

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