The Right Solutions for Coolant
Today's coolant-management technologies can clean up your processes
By Jim Lorincz
How important coolant management is in your shop will determine how high it will rank in your shop's capital and MRO budgeting process. The simple fact is that it may cost as much or more to dispose of used coolant than to buy it and maintain it properly.
Technologies that can help you deal appropriately with coolant range from the simplest devices such as refractometers to monitor coolant concentration in the sump, to coalescers and filters to clean coolant, to more complex devices like centrifuges that separate out and filter contaminating solids and debris, and return cleaned fluids to machines.
"Coolant management touches almost every area of the shop," says John Wiley, vice president, Blaser Swisslube Inc. (Goshen, NY). "Decisions about coolant management affect literally every aspect of running the business from purchasing and engineering to HR concerns for operator health and safety and the environment, not to mention its impact on production of quality parts and the maintenance of manufacturing processes," Wiley explains.
The rewards of good coolant management systems are many. They include longer tool life, improved part quality, reduced rejects and scrap, less machine downtime, and removal of odors, haze, and bacteria that are threats to operator health and safety.
The enemies of good machining processes are sumps (coolant tanks) contaminated with tramp oil and clogged with chips and fines that become excellent breeding grounds for dermatitis and rancidity-causing bacteria. It's not just sumps, either. Any and all parts, including spindles, bearings, and slides of machine tools can be contaminated, damaged, or worn excessively by dirty coolant.
Coolant management system design includes coolant/fluids, chemical additives, machine tools, metals and materials, tooling, and the equipment that delivers, filters, cleans, and circulates coolant through machines. Fluids are important because of their cooling and/or lubricating properties, as well as their ability to remove chips from the cutting zone. Straight oils (mineral oils) are better lubricants, while water-miscible semisynthetics and synthetic fluids are superior at cooling, requiring additives to ensure lubricity and other desirable properties.
Coolants are delivered in streams, as flood coolant, increasingly under pressures as high as 1000–1500 psi (6.89–10.34 MPa), or in minimum quantity lubrication (MQL) quantities that replace gallons with ounces of vegetable-oil-based, environmentally biodegradable fluids.
According to ChipBlaster Inc. (Meadville, PA), any mechanical device that is required to produce precision parts should be protected from contamination. Every part of the process is subject to excessive wear and loss of precision.
Metallic fines damage rotary couplings on milling machines, for example. Coupling manufacturers typically require from 5 to 25µm filtration. Fines and swarf cause poor repeatability and wear when tapers of milling holders or the mating surfaces of VDI and HSK tooling are contaminated. No tool is accurate or balanced when it is clamped against a 0.030" (0.76-mm) chip. The trend toward adopting quick-change tooling has increased the need for clean coolant.
Before manufacturers can reap the benefits of effective coolant-management decisions, however, they have to take stock of their shop's manufacturing environment and processes. David Philipbar of Alfa Laval Inc.'s Metalworking Equipment Div. (Salt Point, NY) suggests this checklist of questions as a starting point for sizing up a shop's manufacturing profile:
- What kinds of machine tools are being used and what processes are performed?
- What types of coolant are used?
- Is the coolant system centralized or decentralized?
- What metals (materials) are being machined?
- What tramp oils are entering the system, and how are they removed?
- What contamination levels are present, and how are they being handled, recycled, and/or disposed of?
Creating a profile of a plant's machining processes is a good starting point for evaluating system requirements and performance. For a new plant or new equipment installation, the evaluation process is relatively straight forward. For existing plants, especially large plants such as automotive facilities, getting to the bottom of coolant problems may be somewhat obvious, but changing out one coolant and/or system for another is far more complicated and involves tens of thousands of gallons of coolant that must be extracted and disposed of.
High-end systems like centrifuges make sense for central coolant systems where the customer might have a coolant capacity of 10,000–100,000 gal (37,900–379,000 L) of coolant in one location, or for individual machine tools with 500–1500-gal (1895–5685-L) capacity. "Based on technology that was invented more than 125 years for separating cream from milk, centrifuges offer the ability to remove solids down to a particle size of 5µm and tramp oil to less than a half a percent," explains Alfa Laval's Philipbar.
Alfa Laval offers its high-speed, disk-bowl centrifuges in two categories: the small flow 2.2 gpm (8.3 L/min) manually cleaned Alfie 500 for use on individual machine tools and the larger Z Series self-cleaning unit for central system cleaning. Both the Z series and the Alfie 500 perform a three-phase separation: clean coolant, tramp oil, and solids. The clean coolant is pumped back to the sump or central system. The tramp oil is sent to a collection tank; the solids are discharged to a buffer tank, and then pumped to a customer location (Z series) or held in the bowl (Alfie 500) for manual removal.
To put its centrifuge technology within reach of more metalworking facilities, about 15 months ago Alfa Laval introduced a rental/lease program that enables the user to upgrade or change system capability without capital expenditure. "There are literally tens of thousands of metalworking facilities, large and small, that can benefit from centrifuge technology in addressing their coolant-cleaning issues. Our rental/lease program is aimed at putting the technology in their hands, and allowing them to focus on their productivity," Philipbar says.
Sometimes, making a change to an established plant layout can yield unexpected benefits for the manufacturer. American Showa Inc., a Tier One supplier to the automotive, motorcycle, and marine industries, decided to modify the production floorplan at its Blanchester, OH, facility for logistical reasons. Two machines had to be moved that had been placed close to one another years ago because they were similar in design and machined similar parts through similar processes. The move entailed more than just physically relocating the machines. While each machine had its own auger mechanism for removing chips, they were tied together via a centralized drum-type filtering unit and overhead-pipe coolant system.
The move required a new chip and coolant-handling system. American Showa chose the ConSep 2000 chipseparator conveyor/coolant-filtration unit from Mayfran International (Cleveland). The machining process involved rough and finish boring of two different cast-aluminum housings. One major problem with the old chip and coolant system was its inability to handle long, stringy chips without tangling in the auger. When the filter drum became clogged with chips, foaming occurred in the overhead pipes.
Two ConSep 2000 units were installed, and after the first year results were even better than anticipated. Tool life expectancy increased about eight times, production doubled, and scrap was reduced by 20%.
Fluids used for machining and grinding come in many chemistries. Some like straight oils lubricate well, but don't remove heat. Semi-synthetics and synthetic coolants are water-miscible and adjusted in concentrations that are tailored for their machining use. They depend on additives to produce desired properties such as lubricity, antifoaming, anti-microbial, and anti-corrosive capabilities.
Formulating a cutting fluid is a complex proposition, BlaserSwisslube's Wiley says. "Many factors influence the interaction between the material, tool, machines, and operator/machinist. Products are designed to reduce operating costs by extending sump life, reducing downtime, prolonging tool life, and reducing disposal costs—all without harming operators or damaging machines."
BlaserSwisslube has introduced its Vasco 5000 coolant for cutting and grinding that extends tool life, provides faster cycle times, and improves surface finish. It's particularly well suited for machining titanium, stainless, cobalt chrome, and other difficult-to-machine materials. A water-miscible coolant, Vasco 5000 features vegetable-oil-based esters—renewable raw materials that are compatible with human skin.
"It's important to evaluate the overall impact on cost, and we have to be able to demonstrate a value to customers through greater metal removal rates vs. conventional coolants, savings through improved feed rates, reduced scrap, faster cycle times, and increased speed," Wiley says.
"Depending on the application and the customer, when we're testing fluids at a company we're talking a year minimum in terms of what we expect to see out of the sump if the customer is doing all the things that we expect them to do. A lot of it comes down to common sense and the kind of shop that they're running," he says.
"Within the flood-coolant area, semisynthetics are our fastest growing product lines," says Catherine Fuhr, business unit manager, ITW Rocol North America (Glenview, IL). "Within the last two years, we have launched two new biostable, semi synthetic products that enable smaller contract manufacturers to consolidate all of the fluids in the plant to one universal fluid."
Rustlick Ultracut 370R (the nonchlorinated version) and Ultracut 375R (the chlorinated version) can be used for both machining and grinding a wide range of ferrous and nonferrous metals. According to Fuhr, the products deliver lubricity and rust protection, corrosion protection, lubrication, and tolerance to contamination, with good biostability and sump life when compared with soluble-oil cutting fluids.
"Many of the product changes are due to raw materials changing, but also to a switch in customer demand. An example is the increasing use of high-strength steel in the automotive industry. And there seems also to be an increasing demand for biostable as well as chlorine-free formulas," says Fuhr. Selecting the best possible coolant for an application is a good start, but if the coolant is not properly maintained, it will fail," says Fuhr.
As an alternative to flood coolant, ITW Rocol North America offers its Accu-Lube line of lubricants and equipment. The Accu-Lube lines are often referred to as minimum quantity lubrication (MQL) or near-dry machining. The concept appeals to manufacturers looking for an environmentally safer alternative to flood coolants. Applicators deliver micro-droplets of lubricants to the cutting edge of the tool. Typical usage is 8 oz (236 ml) of fluid per 8-hr shift compared with conventional coolants measured in 55-gal (208-L) drums per machine. Lubricants are natural-based, biodegradable, nontoxic and nonirritating, won't cause contamination or discoloration of products, and can be cleaned up with soap and hot water. The net result is that lubricants are used in quantities of ounces rather than gallons, with all the accompanying benefits to plant cleanliness, safety, and maintenance.
Incorporating MQL technology right into the design of the machine tool is a necessary step to remove chips when there is no flood coolant to perform the task. According to Mark Ostraff of Horkos Technical Center of America (Canton, MI), about a third of the machines it delivers are specified for MQL cutting fluid applications. "The MQL technology has been around for a while, and there haven't been any great advances as far as chip management is concerned, other than those inherent in the design of the machine. A machine that is designed from the base up to accommodate MQL can be used equally well for conventional cutting fluid applications," he says.
Horkos has introduced a new series of machines in its "no-bed series." "The no-bed machines are designed for multiple-face machining and discharge chips like an HMC, but are said to offer the ease of control and operation of a VMC. Fixturing is on an NC direct-drive rotary table that rotates at 150 rpm to remove chips, and the fixture assembly is on a column that sits directly on the floor. The assembly above that sits on top of the column and has axis movements similar to those of an HMC. Typical applications include machining aluminum and cast iron, as well as crankshafts, camshafts, and connecting rods made from forged steel, and input and output shafts for transmissions."
The NS70 will be able to handle workpieces that fit into a 20" (508 mm) cube, including parts as large as cylinder heads or blocks. It's being touted for medium-sized companies.
Six Steps to Coolant Success
If the coolant is not properly maintained, it will fail. Here are six steps from ITW Rocol North America for maintaining it at peak operating performance:
Concentration Use a refractometer often. A simple test involves pouring some coolant into a plastic or paper cup, letting it sit for about 10 min, enough time for tramp oil to rise to the top and chips/debris to settle to the bottom and then using settled out fluid for the test.
Remove Tramp Oil Use a skimmer to remove tramp oil, which smothers and deoxygenates the coolant, allowing anaerobic bacteria to thrive and chemically attacking the coolant emulsion, causing coolant to split apart prematurely.
Aerate Your Coolant Running the machine a few hours a day will prevent premature rancidity. If this isn't possible, consider a small pump like those used in fish tanks to aerate the sump when the machine is not being used.
Mix Coolant Properly Remember the word, OIL (Oil In Last). Never put the coolant in first and then add the water to the coolant. It is always best (when possible) to mix the coolant outside the machine.
When Adding Make-up to the Sump Never add just coolant concentrate or just water to your sump. This will throw off the concentration of the coolant mixture. Always add a dilution of coolant and water based on your refractometer readings. If the coolant is slowly getting richer, use a make-up dilution that is leaner. If the coolant is slowly getting leaner, use a make-up dilution with a richer concentration. A good rule of thumb is the 15 principle. If you initially charge at one part coolant to 20 parts water, then make up at one part coolant to 35 parts water. Take refractometer readings to see which way you're going. If you're getting too lean, back off to 1:30 until a proper concentration is maintained.
Remove Chips and Debris From the Sump Chips and debris reduce the amount of coolant that you have in your sump, and reduce the coolant's ability to provide services such as lubricity, long tool life, rust protection, etc. it's designed for. Excess chips in the sump provide a breeding ground for bacteria and deplete rust inhibitors in the coolant.
This article was first published in the August 2007 edition of Manufacturing Engineering magazine.
Published Date : 8/1/2007