A note of caution should be sounded for deep grinding where the long contact length allows substantial convective cooling from the grinding coolant. Also in high-rate grinding with low specific energy, the heat taken away by the grinding chips reduces maximum temperature very substantially [Rowe and Jin 2001].
Allowance can be made for convective cooling by subtracting the heat taken away by the coolant and chips as described by Rowe and Jin [2001]. Allowance for convective cooling is essential for creep grinding as shown by Andrew, Howes, and Pearce [1985]. It has also been found important for other high-efficiency deep-grinding processes as employed for drill flute grinding, crankshaft grinding, and cutoff grinding. If allowance is not made for convective cooling the temperatures are very greatly overestimated.
The maximum temperature equation modified to allow for convective cooling has the form
where Tmp is a temperature approaching the melting point of the workpiece material. For steels, the material is very soft at 1,400°C and this temperature gives a reasonable estimate for the chip convection term.
hf is the coolant convection coefficient that applies as long as the maximum temperature does not cause the fluid to burn out in the grinding zone. If burnout occurs, the convection coefficient is assumed to be zero. Burnout is a common condition in grinding but should be avoided in creep grinding and for low-stress grinding. Values estimated for convection coefficient when grinding with efficient fluid delivery are 290,000 W/m2K for emulsions and 23,000 W/m2K for oil.