Section 13. qxd

CUTTING FLUIDS
Cutting fluids, frequently referred to as lubricants or coolants, comprise
those liquids and gases which are applied to the cutting zone in order to
facilitate the cutting operation. A cutting fluid is used (1) to keep the
tool cool and prevent it from being heated to a temperature at which the
hardness and resistance to abrasion are reduced; (2) to keep the work-
piece cool, thus preventing it from being machined in a warped shape
to inaccurate final dimensions; (3) through lubrication to reduce friction
and power consumption, wear on the tool, and generation of heat; (4) to
provide a good finish on the workpiece; (5) to aid in providing a satis-
factory chip formation; (6) to wash away the chips (this is particularly
desirable in deep-hole drilling, hacksawing, milling, and grinding); and
(7) to prevent corrosion of the workpiece and machine tool.
Classification
Cutting fluids may be classified as follows: (1) emul-
sions, (2) oils, and (3) solutions (semisynthetics and synthetics). Cutting
fluids are also classified as light-, medium-, and heavy-duty; light-duty
fluids are for general-purpose machining. Induced 
air blast
may be used
with internal and surface grinding and polishing operations. Its main
purpose is to remove the small chips or dust, although some cooling is
also obtained, especially in machining of plastics.
Emulsions
consist of a soluble oil emulsified with water in the ratio of
1 part oil to 10 to 100 parts water, depending upon the type of product
and the operation. Emulsions have surface-active or 
extreme-pressure
additives to reduce friction and provide an effective lubricant film under
high pressure at the tool-chip interface during machining. Emulsions
are low-cost cutting fluids and are used for practically all types of cut-
ting and grinding when machining all types of metals. The more con-
centrated mixtures of oil and water, such as 1 : 10, are used for
broaching, threading, and gear cutting. For most operations, a solution
of 1 part soluble oil to 20 parts water is satisfactory.
A variety of 
oils
are used in machining. They are used where lubrica-
tion rather than cooling is essential or on high-grade finishing cuts,
although sometimes superior finishes are obtained with emulsions.
Oils generally used in machining are mineral oils with the following
compositions: (1) straight mineral oil, (2) with fat, (3) with fat and sulfur,
(4) with fat and chlorine, and (5) with fat, sulfur, and chlorine. The more
severe the machining operation, the higher the composition of the oil.
Broaching and tapping of refractory alloys and high-temperature alloys,
for instance, require highly compounded oils. In order to avoid staining
of the metal, aluminum and copper, for example, inhibited sulfur and
chlorine are used.