Coolant is a term generally used to describe grinding fluids used for cooling and lubrication in grinding. The main purpose of a grinding fluid is to minimize mechanical, thermal, and chemical impact between the active partners of the abrasion process. The lubricating effect of a grinding fluid reduces friction between the abrasive grains and the workpiece, as well as between the bond and the workpiece. A second requirement of a grinding fluid is direct cooling of the grinding contact zone through the absorption and transportation of the heat generated in the grinding process. Other functions of a grinding fluid are the evacuation of chips from the contact zone, bulk cooling of the workpiece and the grinding machine, and corrosion protection [Konig and Klocke 1996, Marinescu et al. 2004].
10.2 BASIC PROPERTIES OF GRINDING FLUIDS
10.2.1 Basic Properties
The selection of a grinding fluid is of crucial significance for the achievement of favorable cooling and lubricating conditions. Type, base oil, additives, and concentration of the fluid are all important for the efficiency of cooling and lubrication. Cooling and lubrication requirements are met in different ways by every particular grinding fluid. Depending on the contact conditions in the process, the cooling and lubricating properties of the applied grinding fluid have a substantial impact on the process and on the work result.
10.2.2 Basic Requirements
The basic requirements of a grinding fluid are good lubrication, good cooling and flushing performance, and high corrosion protection.
10.2.3 Secondary Requirements
Secondary requirements are economic and efficient operation, operational stability (long life), and environmental protection.
It is imperative for grinding fluids to be compatible with environmental and human health, as well as being reliable in operation. Additional requirements of the fluid are
• Easily filtered and recycled
• The residual film is easily removed from the workpiece, grinding wheel, and machine
• Provides solid particle transport for swarf removal
• Inhibits foaming and mist formation
• Exhibits low flammability
• Exhibits good compatibility with the materials of the machine tool system
In the case of water composite fluids, mixing behavior and emulsifiability must be considered (Table 10.1).
Important Properties of Cooling Lubricants
Usage Properties
Functional Properties Operational Behavior
Human and environmental compatibility (toxicity, odor, skin compatibility)
Resistance to aging and bacteria (stability)
Filterability, recycleability, mixing behavior, emulsifiability Washability, residual behavior, solid particle transport capability
Foam, fog behavior, inflammability Compatibility with different materials
Source: From Brucher, 1996. With permission.
The functional properties and the operational behavior of cooling lubricants are significantly influenced by physical-chemical properties. Thermal capacity and conductivity, evaporation heat, and viscosity are affected by the quantitative ratios of the base materials used. Additionally, the performance of a cooling lubricant can be adjusted by the addition of active substances and additives.