Life Support For Cutting Fluids

Feb. 20, 2007
Managing cutting fluids, and extending their life, pays dividends in lower operating and disposal costs.

A mineral-oil based, chlorine-free fluid from Blaser Swisslube ( is formulated to reduce instability, separations and short fluid life when cutting magnesium.

Although cutting fluids account for only a small fraction of the cost of metalworking operations, disposal of spent cutting fluid can be expensive and troublesome. In past years, shops simply disposed of their metalworking fluid as soon as it showed signs of degradation and decreased performance. It was easier to get rid of and replenish fluids than to extend their life. Now, with more stringent environmental regulations, stricter rules for sanitary sewer discharges, increasing costs for cutting fluids, and higher costs for disposal, shops have become increasingly aware of the advantages of prolonging cutting fluid life. Besides the direct economic benefits, more effective and longer lasting cutting fluids and the development of efficient coolant-cleaning technologies has made coolant management and maintenance beneficial for the environment. New coolant management and maintenance programs can minimize contamination, prolong cutting fluid life and reduce operating costs.

The basic components of an effective coolant management program include:

  • Cooperation between the user and supplier to administer the program.
  • The correct selection of a cutting fluid.
  • Close monitoring and control of the cutting fluid.
  • Removal and prevention of contaminants in the fluid.
  • And, careful fluid inventory management and handling.

Program Administration
Cooperative support of management, employees, fluid suppliers and equipment vendors is necessary to ensure the success of a cutting fluid — or coolant — management program. Shop management has to commit to acquiring the equipment and resources necessary to sustain the program, and employees must be committed to the program. Management helps employees to commit to the program by teaching them the importance of the program. Shop employees must be included in making decisions about the implementation and upkeep of the program, and in record keeping for the program.

Record keeping is necessary. Data has to be kept on the types and volumes of fluids used, the machine tools in which the fluids are used and sump capacities. For each machine, a detailed log should be kept to document fluid usage information and, besides the type of fluid that is being used, it should note the mixing ratios with which it was prepared, data on the quality of water used to prepare the cutting fluid, the concentration of the fluid, its acidity (pH), biological agents that are added to it and their concentration, and the dates and quantities of coolant as they are changed or added. Information also should be kept on the cleaning and maintenance equipment used on the machine tool.

By collecting complete information on the use of cutting fluids for an entire facility, the quantity of fluid purchased, recycled or disposed in a year can be compiled and analyzed. Such an analysis provides a check on the effectiveness of a fluid management program and helps to identify where improvements need to be made.

Choosing the Right Coolant
Selecting the proper coolant depends on the type of metal and machining operations that it will be used for. Coolant manufacturers formulate different grades of products for all types of machining operations, but some products can be used for multiple purposes, such as grinding and milling.

Using coolant that is not suited for the specific job can lead to premature tool failure, and can produce undesirable surface finishes on parts. Also, the life of the coolant can be reduced if it is not made for the job.

Minimizing the number of cutting fluids used in a shop is a good shop practice. Many metalworking facilities require only two types of coolants: one for machining, one for grinding. Using more types of coolants requires extra storage space, adds to inventory and maintenance needs, and increases the chances that the fluids would be mixed up and contaminated by each other.

Higher priced coolants tend to perform better and last longer than low-priced coolants, but selecting a coolant solely on the basis of its initial cost can lead to problems. A cutting fluid should be selected to match the function for which it is needed. Then, the true cost of the fluid can be determined based on its cost per gallon divided by its life expectancy. Once performance parameters and the true cost of a cutting fluid are determined, the fluid's long-term cost and effectiveness can be determined.

Cutting fluids commonly are oil-based or water-based. The oil-based fluids include straight oils and soluble oil, and water-based fluids include synthetics and high-oil, semi-synthetics. Joe Purnhagen, metalworking market manager at Lubrizol ( said the increased use of semisynthetics fluids is growing in the industry. "These are a hybrid between petroleum-based fluids and synthetics, and offer a mix of advantages of each," Purnhagen said. "Oilsbased on petroleum have the highest lubricity potential, while semi-synthetics offer good lubricity, greater cleanliness and longer life." For example, a semi-synthetic machining and grinding fluid from Blaser Swisslube Inc. ( rejects tramp oils, requires no biocide additives and has rinsing characteristics designed to leave parts and machines clean.

Bio-based lubricants, such as soybean oil or methyl soyate formulations, match the price and performance of petroleum or semi-synthetic oils but offer other advantages that include the promotion of better surface finishes on the workpiece and reduced risk of fire, smoke and misting while they are in use. Additionally, these coolants are biodegradable, and do not contain chlorine or sulfur, so they are more easily disposed of.

Monitoring and Control
It is necessary to monitor and control coolants to anticipate problems that could arise and to allow remedial action to be taken to prevent premature fluid degradation and failures. The heat generated during machining and the introduction of contaminants can change the composition and performance of a coolant while it is being used. Monitoring fluid parameters, including concentration, the growth of biological contaminants and pH, will detect changes from optimal fluid quality and allow for appropriate remedial action. Remedies could include adjusting the fluid concentration or the pH, adding a biocide or removing contaminants.

Keeping Coolants Clean
Removing contaminants, or preventing contaminants from getting into cutting fluids reduces costs because it extends the effective life of coolants. Metal chips and fines, tramp oil, bacteria and dissolved salts are the most frequent contaminants that affect coolants. Chips and fines from metalcutting provide surfaces on which bacteria can grow. Tramp, or free oils are a food source for bacteria and often develop into surface films that prevent oxygen from dissolving into the coolant. These oils also reduce the cooling capability of metalworking fluids, contribute to the formation of oil mist and smoke, and deplete the oil-soluble components in a coolant.

The excessive accumulation of metal chips reduces sump volume while depleting coolant ingredients and providing an environment for bacterial growth. Chips and fines can be particularly troublesome in systems that direct the coolant under pressure to the working area, such as through-thetool and through-the-spindle coolant delivery systems.

Inventory Control
Coolant inventory and management practices promote a clean working environment and reduce the chance of mixing problems. Centralized fluid dispensing systems allow storage of fluids close to the work area and eliminate the chance of spills from fluid-drum tipping, cleaning and switching. When transferring fluids, personnel should always use spigots and funnels to reduce spills and provide spill kits for quick clean up should a spill occur. Mixing should always be done in a container outside the sump. Water purified through deionization or reverse osmosis before mixing helps to reduce corrosion and microbial problems due to water hardness and dissolved solids.

Advantages Disadvantages
Straight Oils Excellent lubricity; good rust protection and sump life; easy maintenance; rancid resistant Poor heat dissipation; increased risk of fire; limited to low-speed cutting
Soluable Oils Good lubrication; improved cooling capacity; limited to light and medium-duty applications More susceptible to rust problems and bacterial growth; tramp-oil and evaporation losses
Synthetics Excellent microbial control and rancid resistance; relatively nontoxic; good cooling qualities; easy maintenance; long service life; heavy-duty cutting Reduced lubricity; may cause misting, foaming and dermatitis; may emulsify tramp oil; easily contaminated by other machine fluids
Semi-synthetics Good microbial control and rancid resistance; relatively nontoxic; superior cutting qualities; easy maintenance; long service life Water hardness affects stability; may emulsify tramp oil; easily contaminated by other machine fluids

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