Working Fluids (MWFs)
Back in 1990, newspapers in Iowa reported a milky-white, oily substance that someone had covertly dumped in the southeast-side storm sewer. Reports also said the substance did not pose any danger to the water supply near Emerald Avenue SE and 32nd Street Drive.
Authorities had nevertheless cited regulations that required the offender party to pay hefty penalties. Investigators later identified the whitish, innocuous looking culprit as waste cutting fluid alias metal working fluid (MWF) alias coolant.
Now, MWFs are an inseparable part of machining operations such as cutting, milling, and grinding, for they maintain the temperature of the workpiece and the tools while also flushing away the unacceptables born out of machining.
Most cutting fluids are water soluble and, with use, get loaded with chips, fines, swarfs, oils, greases, and microbes. Through all this, they lose their desired properties and have to be disposed. Nothing dubious about this.
The problem is, some machine shop operators do not always dump MWFs in the prescribed, environment friendly manner. Some shop operators acknowledge (off the record of course!) that ‘parking lot’ and ‘backdoor’ dumping is rampant in the industry.
And because professionals design coolant systems after setting up machines, you usually end up with an under-capacity system at an uncomfortable location that occupies more-than-necessary space. Enough for denting your plans for efficient floor space management!
Carrot & Stick Coolants
According to the findings of a recently released survey by Modern Machine Shop, more and more top machine shops in the U.S. are using high pressure coolant systems.
Using a highly directed coolant stream at the optimum pressure removes more heat from the cutting zone and facilitates easier chip removal to enable faster, more efficient, and more economical cutting.
Clear and pure cutting fluids enable the system to run at higher pressures and produce parts of superior accuracy, repeatability, and quality while extending the useful life of the machine and tools.
Remove contaminants, and you automatically cut down wear of all metal surfaces directly or indirectly associated with machining viz. pumps, tubes, motors, servo valves, gears, cylinders, bearings and the like. Tremendous strengths, wouldn’t you say?
But so is the nuisance value of neglecting them. While they cost a meager 1-2% of the part being machined, MWFs affect the manufacturing cost of the part by a stunning 95%. What is more, contaminated MWFs cause about 70-90% of machine tool wear and failures.
Functions & Design Parameters of Coolant Systems
Coolant Systems include the (undiluted) cutting fluid, local water, reservoir, pump, filtration system, sump, and skimmers. The following are the issues and challenges associated with cutting fluid systems:
• selection of the proper MWF(s) for a particular application(s)
• maintenance of the MWFs to derive optimum performance
• environment friendly disposal
Initial cost is not even the starting point in design, for a cheaper fluid might have a shorter life span than an expensive one. Furthermore, it might create disposal-related challenges that ensure you spend more than the price of the expensive variant for properly dumping it.
A coolant system performs the following functions:
• Cools the Workpiece and the Tool(s): if you cut down the tool temperature by 500F from 9500F to 9000F, for example, you boost the tool life by 5 times, from 19.5 minutes to 99 minutes
With a specific heat capacity of 4.186 joules/gram0C, water is a very effective coolant but facilitates rusting and microbial growth
• Lubricates the Workpiece and Tool(s): by slashing the tool-workpiece friction. With lubrication, you can use faster speed and feed rates that cut down the final time and cost of machining
While higher viscosity MWFs provide better lubrication, they stick to the workpiece. You thereby require more MWFs. This escalates the expenses for the coolant and for cleaning the part
Low-viscosity coolants compounded to provide higher lubricity are, therefore, a more pragmatic option
• Prevents Welding of Chips to Tools
• Flushes away Chips and Fines: produced in the machining operation
• Controls Rust: these days chemicals are added to MWFs for this specific purpose. As mentioned, water is a great coolant but it promotes rusting and hence the need for rust inhibiting chemicals
• Inhibits Rancidity: bacterial growth pushes up rancidity and obnoxious odors. The demerit of noxious odors more than offsets the merits of the coolant and may lead to a situation where the cost of safe disposal far outruns the purchase cost
Apart from the obvious properties needed to discharge these functions, cutting fluids also need to be:
• Transparent / Clear: so the operator can see clearly while machining
• Stable / Durable: to last through the machining operations
• Negligibly Viscous: to allow chips and fines to settle down and to flush them away rapidly
• Non-Inflammable
• Non-Toxic
• Non-Smoky
• Non-Promoters of Gummy Deposits: that block the circulation system and/or hinder the functioning of machine slides
In view of the above discussion, main design parameters for a cutting fluid system are:
• Capacity: calculate the required retention time and multiply it by the capacity of the pump. This gives you the minimum sump volume
Larger sumps allow the cutting fluid to cool down before you use it again. They also enable superior separation of tramp (lubrication) oil and improved settling of metal chips and fines
• Quality of Local Water: used to dilute cutting fluid concentrate is a prominent parameter, for final coolant mixes contain over 90% water and this water influences the coolant life, stability, tool life, corrosion control, foam properties, and product residue
If the quality of local water is unsatisfactory, you need special water treatment such as Reverse Osmosis (RO) or Deionization
• Removal Requirements: i.e. the kind of particles and oils that you have to remove. Based on this, you determine the required variants of baffled tanks, filters, and skimmers
Baffled Tanks enable particles to accumulate in areas away from the pump. Go for custom-built sumps if your sump volume is over 1,000 gallons. Pre-fabricated sumps do well for under 1,000 gallon sumps
• Location: depends on the type of machine and operations. Locate tanks slightly away from milling machines. This simplifies maintenance
• Required Additives: such as emulsifiers, anti-oxidants, stabilizers, anti-microbial pesticides, and defoamers
• Types of Metals / Alloys: you will machine in the shop
• Types of Machining Operations
• Type of Cutting Fluid
Finally
In machine shops, we are usually more impressed by the sophisticated machines operating on equally advanced technologies. Nothing objectionable about it. But we must learn to spare a thought for the not-so-visible but equally effective systems.
Authorities had nevertheless cited regulations that required the offender party to pay hefty penalties. Investigators later identified the whitish, innocuous looking culprit as waste cutting fluid alias metal working fluid (MWF) alias coolant.
Now, MWFs are an inseparable part of machining operations such as cutting, milling, and grinding, for they maintain the temperature of the workpiece and the tools while also flushing away the unacceptables born out of machining.
Most cutting fluids are water soluble and, with use, get loaded with chips, fines, swarfs, oils, greases, and microbes. Through all this, they lose their desired properties and have to be disposed. Nothing dubious about this.
The problem is, some machine shop operators do not always dump MWFs in the prescribed, environment friendly manner. Some shop operators acknowledge (off the record of course!) that ‘parking lot’ and ‘backdoor’ dumping is rampant in the industry.
And because professionals design coolant systems after setting up machines, you usually end up with an under-capacity system at an uncomfortable location that occupies more-than-necessary space. Enough for denting your plans for efficient floor space management!
Carrot & Stick Coolants
According to the findings of a recently released survey by Modern Machine Shop, more and more top machine shops in the U.S. are using high pressure coolant systems.
Using a highly directed coolant stream at the optimum pressure removes more heat from the cutting zone and facilitates easier chip removal to enable faster, more efficient, and more economical cutting.
Clear and pure cutting fluids enable the system to run at higher pressures and produce parts of superior accuracy, repeatability, and quality while extending the useful life of the machine and tools.
Remove contaminants, and you automatically cut down wear of all metal surfaces directly or indirectly associated with machining viz. pumps, tubes, motors, servo valves, gears, cylinders, bearings and the like. Tremendous strengths, wouldn’t you say?
But so is the nuisance value of neglecting them. While they cost a meager 1-2% of the part being machined, MWFs affect the manufacturing cost of the part by a stunning 95%. What is more, contaminated MWFs cause about 70-90% of machine tool wear and failures.
Functions & Design Parameters of Coolant Systems
Coolant Systems include the (undiluted) cutting fluid, local water, reservoir, pump, filtration system, sump, and skimmers. The following are the issues and challenges associated with cutting fluid systems:
• selection of the proper MWF(s) for a particular application(s)
• maintenance of the MWFs to derive optimum performance
• environment friendly disposal
Initial cost is not even the starting point in design, for a cheaper fluid might have a shorter life span than an expensive one. Furthermore, it might create disposal-related challenges that ensure you spend more than the price of the expensive variant for properly dumping it.
A coolant system performs the following functions:
• Cools the Workpiece and the Tool(s): if you cut down the tool temperature by 500F from 9500F to 9000F, for example, you boost the tool life by 5 times, from 19.5 minutes to 99 minutes
With a specific heat capacity of 4.186 joules/gram0C, water is a very effective coolant but facilitates rusting and microbial growth
• Lubricates the Workpiece and Tool(s): by slashing the tool-workpiece friction. With lubrication, you can use faster speed and feed rates that cut down the final time and cost of machining
While higher viscosity MWFs provide better lubrication, they stick to the workpiece. You thereby require more MWFs. This escalates the expenses for the coolant and for cleaning the part
Low-viscosity coolants compounded to provide higher lubricity are, therefore, a more pragmatic option
• Prevents Welding of Chips to Tools
• Flushes away Chips and Fines: produced in the machining operation
• Controls Rust: these days chemicals are added to MWFs for this specific purpose. As mentioned, water is a great coolant but it promotes rusting and hence the need for rust inhibiting chemicals
• Inhibits Rancidity: bacterial growth pushes up rancidity and obnoxious odors. The demerit of noxious odors more than offsets the merits of the coolant and may lead to a situation where the cost of safe disposal far outruns the purchase cost
Apart from the obvious properties needed to discharge these functions, cutting fluids also need to be:
• Transparent / Clear: so the operator can see clearly while machining
• Stable / Durable: to last through the machining operations
• Negligibly Viscous: to allow chips and fines to settle down and to flush them away rapidly
• Non-Inflammable
• Non-Toxic
• Non-Smoky
• Non-Promoters of Gummy Deposits: that block the circulation system and/or hinder the functioning of machine slides
In view of the above discussion, main design parameters for a cutting fluid system are:
• Capacity: calculate the required retention time and multiply it by the capacity of the pump. This gives you the minimum sump volume
Larger sumps allow the cutting fluid to cool down before you use it again. They also enable superior separation of tramp (lubrication) oil and improved settling of metal chips and fines
• Quality of Local Water: used to dilute cutting fluid concentrate is a prominent parameter, for final coolant mixes contain over 90% water and this water influences the coolant life, stability, tool life, corrosion control, foam properties, and product residue
If the quality of local water is unsatisfactory, you need special water treatment such as Reverse Osmosis (RO) or Deionization
• Removal Requirements: i.e. the kind of particles and oils that you have to remove. Based on this, you determine the required variants of baffled tanks, filters, and skimmers
Baffled Tanks enable particles to accumulate in areas away from the pump. Go for custom-built sumps if your sump volume is over 1,000 gallons. Pre-fabricated sumps do well for under 1,000 gallon sumps
• Location: depends on the type of machine and operations. Locate tanks slightly away from milling machines. This simplifies maintenance
• Required Additives: such as emulsifiers, anti-oxidants, stabilizers, anti-microbial pesticides, and defoamers
• Types of Metals / Alloys: you will machine in the shop
• Types of Machining Operations
• Type of Cutting Fluid
Finally
In machine shops, we are usually more impressed by the sophisticated machines operating on equally advanced technologies. Nothing objectionable about it. But we must learn to spare a thought for the not-so-visible but equally effective systems.
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