SECTION 3.10
Cleaning the Coolant System

Certain basic procedures should be followed to ensure thorough system cleaning. First, pump the dirty fluid out of the system. Inspect all sumps, tanks, and flumes for cracks and dead areas as well as debris and built-up chip dams that may create pockets of stagnant coolant or may trap dirt and swarf. These areas harbor bacteria that will quickly contaminate the fresh fluid. All blind risers or other dead areas in the coolant recirculation and distribution system must be drained to remove stagnant or contaminated fluid.

Next, inspect all machines supplied by a central system to make sure they don't have a similar problem. Ideally, machines will be purchased that do not have such dead areas. However, shop maintenance or the machine tool manufacturer can modify them so that all chips and coolant can be flushed from the machining area into the system for removal.

Similar procedures should be applied to free-standing machines, even though their fluid systems are less complex. Stagnant pockets of fluid are even more detrimental to individual machines than to machines in centralized systems, because free-standing machines have smaller sumps.

SECTION 3.10.1
Selecting the right cleaner

A cleaner specifically designed for system cleanouts will greatly improve the initial cleanliness of a freshly charged system and extend its life. If bacteria-contaminated fluid is quickly dumped and recharged without a good cleanout, the bacterial count will return to its original level in about four days. The biocides in the fresh coolant will quickly be consumed in fighting the multiplying growth of leftover bacteria in the system. As a result, fluid odor will recur quickly. This may require more frequent biocide treatment, which may cause operator skin problems. There will, of course, be increased costs for additives, more frequent dumping, and recharging.

A system cleaner formulated for complete removal of residual bacteria should meet certain basic requirements. It must be noncorrosive to all surfaces it contacts during cleanout. It should provide some degree of rust protection for these surfaces after cleaning and before rinsing with coolant. And of course, the cleaner should be compatible with the coolant to be recharged into the system, so that any remnants of the cleaner remaining will not affect the performance of the coolant.

A mild alkaline cleaner is recommended for coolant systems. Select a cleaner that can be applied effectively at temperatures from ambient to 180o F, so it does not require excessive thermal energy to use. Low foaming is desirable to prevent pump cavitation during recirculation of the cleaner.

SECTION 3.10.2
Maximizing cleanout benefits

The following precautionary steps can be extremely helpful in extending coolant life and minimizing problems.

1. Install outlet connections and hoses in the coolant-pumping systems of central-system and free-standing machines so that machine operators can flush accumulated chips into the system or sump daily.
2. On a daily basis, flush areas that catch and hold coolant with more coolant to prevent stagnation and resultant contamination.
3. Check flumes weekly. Break up chip dams and remove debris that can trap dirt and become a breeding pocket for bacteria.