Are You Playing the Clean Manufacturing Game?
A 10 part blog series discussing important aspects of clean manufacturing technology and implementation strategy.
Look, but Don’t Touch – Part 8 of 10
Contamination is a relative term and can be defined as any foreign substance contained on a surface at a level that prevents the production of reliable, complex hardware. Examples of surface contamination include particles, soils, oxidation, electrostatic charge, radioactivity, and heat. The purpose of cleaning or modifying a surface is to produce a surface free of, or with acceptable levels of, contamination.
In conventional cleaning operations, products are typically removed from a (contaminant-generating) manufacturing process (and line) at a certain point, cleaned to remove contamination to an acceptable level, inspected to verify cleanliness, and returned to the production line for further value-add manufacturing steps. Example iterations include machining-cleaning-inspection, assembling-cleaning-inspection, cleaning-inspection-bonding, and cleaning-inspection-welding. A variety of analytical methods may be employed to verify surface cleanliness, all of which generates space, labor, and transport wastes.
A new non-contact surface inspection technology called Optically Stimulated Electron Emission (OSEE) offer a unique way of addressing these manufacturing wastes. Optically Stimulated Electron Emission (OSEE) inspection is a unique CleanTech for non-invasive, non-contact analysis of surfaces to determine contamination levels. This technique utilizes a tool which utilizes ultraviolet radiation to create electron emission from a surface, resulting in a small current detected by the inspection tool. Electron emission is dependent on the substrate's surface chemistry; hence the electron emission characteristics will change with the presence of a contaminant on the surface, generally by attenuating the signal. OSEE inspection combined CO2 CleanTech is a dynamic duo that provides a number of clean manufacturing benefits.
David Jackson is President/CEO of Cleanlogix LLC and serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
Part 9 of this series discusses robot CleanTech.
Wednesday, June 16, 2010
The Clean Manufacturing Game Part 9 of 10
Are You Playing the Clean Manufacturing Game?
A 10 part blog series discussing important aspects of clean manufacturing technology and implementation strategy.
Robots to the Rescue – Part 9 of 10
Robot CleanTech has become a mainstay due to their flexibility, reliability and repeatability. Prior to robots, material handling and machine tending applications were purely a manual task. Operators transporting material from one fixture or machine to the next, waiting on the equipment to finish its task, and then relocation of the processed part or parts to another tool or process fixture; these were some of the most common manual tasks that required several operators to manufacture the product. These material handling and machine tending tasks are now almost always accomplished using robots, especially in operations requiring high speed and accuracy.
The advantages of Robot CleanTech include:
• No wait time for operators since the robots are performing material handling and wait times could be absorbed by having them perform additional processing operations if possible.
• Robots have negligible downtime resulting in limited production loss
• Robots are inexpensive to operate in the long run compared to manual labor and the return on investment can be fast based on the demand for the manufactured product.
• Robots are repeatable to a high degree of accuracy which results in lowered scrap parts once the robot tasks are optimized.
While standard off the shelf robots have one arm to which you can mount tooling, the advent of tool changers and dual equipment end-of-arm tool (EOAT) design have helped make robotic operations more flexible and lean in terms of higher per cycle utilization. In the die cast industry, robots are currently being used for material handling parts as well as de-gating and finishing operations like deburring and grinding. In the Automotive industry, robots in body shop applications are in some cases used for material handling of parts as well as welding or sealant application through the use of dual application end-effectors or floor mounted pedestal equipment. In applications involving multiple product models, tool changing equipment can be used for robots to disengage/engage new EOATs. Servo motor driven external axes allow robots to be more flexible by acting as auxiliary axes of motion to ensure maximum robot utilization.
This flexibility that allows engineers to process as many operations as possible within the given cycle time and feasibility constraints helps make manufacturing processes lean. Robot vendors have already developed robots with multiple arm configurations. In the future, these multi-arm robots will be more of the norm with operations that are faster, more efficient and lean.
Vision systems are being used in combination with robots to help inspect parts for feature existence and feature sizes. Vision systems are more commonly used on robots to act as dynamic guidance systems that allow robots to vary their motion targets based on vision generated guidance information. Vision technology and robots are a natural pairing and the combination has resulted in making robotic operations leaner than ever before.
Operations such as racking and de-racking of parts, part picking from bins, visual inspection of parts, which were normally handled by human operators, are now being performed by robots with higher consistency, accuracy, repeatability and speed due to vision systems used in conjunction with the robots. Finishing operations such as routering, grinding, sealing are now being applied more accurately with fewer imperfections and scrap parts thereby contributing solidly to lean manufacturing. In the inspection arena, robots are utilized heavily in Flexible Measurement Systems (FMS). Robots mounted with vision cameras to collect feature information for multiple inspection locations have resulted in a drastic reduction in the number of vision cameras and fixtures required to inspect parts. In the past, the same inspection would have been performed with several fixed vision cameras.
One of the primary drivers to automate a manufacturing process using robots is the safety factor. Most manufacturing operations have a degree of human injury risk. Some simple part transfer operations may be safe for humans to perform while others like unloading parts from a press/die or foundry operations with molten metal are definitely not fit for manual operations. In these cases, robots are invaluable in lowering risk to humans.
An unsafe workplace leads to human inefficiency driven by fear. This in turn leads to lowered production rates and employee retention. A safe and secure workplace improves morale and lowers costs, which in turn improves the bottom line. Unsafe working environments can lead to waste in terms of effort and time.
The above cases are just a few examples of how robots, if used correctly, can contribute to cleaner manufacturing. Robots help achieve higher production quality at a reduced operating cost compared to manual manufacturing. They help produce more parts with fewer defects using less equipment while maintaining their flexibility for future changes.
The most significant impact to clean manufacturing related to robot CleanTech lies in their ease of use. Programming robots to perform manufacturing operations has evolved into an easy-to-use PC-based process that can be easily understood and applied by engineers as well as skilled trades at the plant floor.
CO2 CleanTech utilizes robots to provide reliability, accuracy, consistency and capacity. Robot CleanTech is also used to transport product through combination processes involving spray, immersion and plasma treatments, and production operations such as assembly, machining, soldering, and bonding.
David Jackson is President/CEO of Cleanlogix LLC and serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
Part 10, the last part of this series, discusses thinking clean.
A 10 part blog series discussing important aspects of clean manufacturing technology and implementation strategy.
Robots to the Rescue – Part 9 of 10
Robot CleanTech has become a mainstay due to their flexibility, reliability and repeatability. Prior to robots, material handling and machine tending applications were purely a manual task. Operators transporting material from one fixture or machine to the next, waiting on the equipment to finish its task, and then relocation of the processed part or parts to another tool or process fixture; these were some of the most common manual tasks that required several operators to manufacture the product. These material handling and machine tending tasks are now almost always accomplished using robots, especially in operations requiring high speed and accuracy.
The advantages of Robot CleanTech include:
• No wait time for operators since the robots are performing material handling and wait times could be absorbed by having them perform additional processing operations if possible.
• Robots have negligible downtime resulting in limited production loss
• Robots are inexpensive to operate in the long run compared to manual labor and the return on investment can be fast based on the demand for the manufactured product.
• Robots are repeatable to a high degree of accuracy which results in lowered scrap parts once the robot tasks are optimized.
While standard off the shelf robots have one arm to which you can mount tooling, the advent of tool changers and dual equipment end-of-arm tool (EOAT) design have helped make robotic operations more flexible and lean in terms of higher per cycle utilization. In the die cast industry, robots are currently being used for material handling parts as well as de-gating and finishing operations like deburring and grinding. In the Automotive industry, robots in body shop applications are in some cases used for material handling of parts as well as welding or sealant application through the use of dual application end-effectors or floor mounted pedestal equipment. In applications involving multiple product models, tool changing equipment can be used for robots to disengage/engage new EOATs. Servo motor driven external axes allow robots to be more flexible by acting as auxiliary axes of motion to ensure maximum robot utilization.
This flexibility that allows engineers to process as many operations as possible within the given cycle time and feasibility constraints helps make manufacturing processes lean. Robot vendors have already developed robots with multiple arm configurations. In the future, these multi-arm robots will be more of the norm with operations that are faster, more efficient and lean.
Vision systems are being used in combination with robots to help inspect parts for feature existence and feature sizes. Vision systems are more commonly used on robots to act as dynamic guidance systems that allow robots to vary their motion targets based on vision generated guidance information. Vision technology and robots are a natural pairing and the combination has resulted in making robotic operations leaner than ever before.
Operations such as racking and de-racking of parts, part picking from bins, visual inspection of parts, which were normally handled by human operators, are now being performed by robots with higher consistency, accuracy, repeatability and speed due to vision systems used in conjunction with the robots. Finishing operations such as routering, grinding, sealing are now being applied more accurately with fewer imperfections and scrap parts thereby contributing solidly to lean manufacturing. In the inspection arena, robots are utilized heavily in Flexible Measurement Systems (FMS). Robots mounted with vision cameras to collect feature information for multiple inspection locations have resulted in a drastic reduction in the number of vision cameras and fixtures required to inspect parts. In the past, the same inspection would have been performed with several fixed vision cameras.
One of the primary drivers to automate a manufacturing process using robots is the safety factor. Most manufacturing operations have a degree of human injury risk. Some simple part transfer operations may be safe for humans to perform while others like unloading parts from a press/die or foundry operations with molten metal are definitely not fit for manual operations. In these cases, robots are invaluable in lowering risk to humans.
An unsafe workplace leads to human inefficiency driven by fear. This in turn leads to lowered production rates and employee retention. A safe and secure workplace improves morale and lowers costs, which in turn improves the bottom line. Unsafe working environments can lead to waste in terms of effort and time.
The above cases are just a few examples of how robots, if used correctly, can contribute to cleaner manufacturing. Robots help achieve higher production quality at a reduced operating cost compared to manual manufacturing. They help produce more parts with fewer defects using less equipment while maintaining their flexibility for future changes.
The most significant impact to clean manufacturing related to robot CleanTech lies in their ease of use. Programming robots to perform manufacturing operations has evolved into an easy-to-use PC-based process that can be easily understood and applied by engineers as well as skilled trades at the plant floor.
CO2 CleanTech utilizes robots to provide reliability, accuracy, consistency and capacity. Robot CleanTech is also used to transport product through combination processes involving spray, immersion and plasma treatments, and production operations such as assembly, machining, soldering, and bonding.
David Jackson is President/CEO of Cleanlogix LLC and serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
Part 10, the last part of this series, discusses thinking clean.
The Clean Manufacturing Game Part 10 of 10
Are You Playing the Clean Manufacturing Game?
A 10 part blog series discussing important aspects of clean manufacturing technology and implementation strategy.
Thinking Clean – Part 10 of 10
Clean manufacturing is a change of mindset - changing the conventional production paradigm using non-traditional lean and green manufacturing game rules. This is thinking clean. A clean manufacturing strategy involves training in the relevant CleanTech, followed by proper planning, assessment, and analysis of the various manufacturing wastes produced. The new clean manufacturing game involves a skillful and diligent waste auditing process that overlays state-of-the-art CleanTech onto a conventional production model – line, tool and process – to produce a new clean-enabled line, tool and process. Winning the clean manufacturing game is experiencing improved productivity and profitability.
For example in manufacturing operations that produce high reliability hardware, a product may be cleaned several times through the production cycle (build-clean). Manufacturing and assembly operations requiring a product cleaning include cutting, drilling, trimming, micromachining, bonding, dicing, abrasive finishing, polishing, stamping, welding and inspection. Conventionally, precision cleaning is performed as an “island” operation using, for example, a stand-alone spray cleaner, vapor degreaser, ultrasonic cleaning system, rinsing and drying stations. Segregation of the cleaning process from the assembly tool has been a necessity due to the inherent chemical and physical (space) incompatibilities between conventional cleaning operations and most assembly processes and tools. CleanTech changes this conventional paradigm.
CO2, Robot and OSEE Inspection CleanTech can be integrated with virtually any production tool or process to produce numerous new and advanced clean-enabled tools; Clean-Assembly™ tools. Clean-Assembly tools are much more productive because two or more assembly processes are be performed simultaneously within the same work cell. Products don't have to be transported from, cleaned, inspected and transported back to the production line - resulting in reduced labor, higher throughput, increased quality and decreased production space. The Clean-Assembly CleanTech model changes the game rules by incorporating the non-value add (although necessary waste), processes with the value-add production operations. This significantly reduces manufacturing waste and improves both productivity and profitability.
Conclusion
In today’s manufacturing environment, there is a need to reduce waste and improve profitability. This is accomplished using flexible and adaptable production methodologies, cleaner, leaner and drier process chemistries, and an increasing use of clustered production processes (cells). Production steps previously performed as separate operations using separate tools, space, transport, time, and labor) may now be integrated into modular lean cells using CO2 technology. Space and time saving hybridized forms of assembly processes integrated with CO2 technology may be used. In-situ clean-assembly tools may be clustered with manufacturing operations in modular production cells in which two or more steps can be performed simultaneously, thereby increasing throughput and yield and reducing human interaction and cost of ownership.
The bottom line is that CleanTech, and CO2 CleanTech in particular, reduces manufacturing waste and reduces operational costs in a number of unique ways. It's worth the effort to employ CleanTech where possible to improve productivity and profitability.
David Jackson is President/CEO of Cleanlogix LLC and serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
Select Clean Manufacturing References:
1. An Introduction to Environmental Accounting as a Business Management Tool, United States Environmental Protection Agency, EPA 742-R-95-001, June 1995.
2. Lean Manufacturing and the Environment: Research on Advanced Manufacturing Systems and the Environment and Recommendations for Leveraging better Environmental Performance, United States Environmental Protection Agency, EPA 100-R-03-005, October 2003.
3. The EPA Manual for Waste Minimization Opportunity Assessments, United States Environmental Protection Agency, EPA/600/2-88-025, April 1988.
4. How to Be Green and Stay in the Black, Department of Navy, NAVSO P-3680, October 1997.
5. Schwendeman, T., “Pollution Prevention Can Pay”, Industrial Heating, December 2003.
6. Jackson, D. et al, “Today’s Forecast – It Looks like Snow”, Precision Cleaning, Volume VII, Number 5, May 1999.
7. Darvin, C. et al, “ Demonstration of Liquid CO2 as an Alternative for Metal Parts Cleaning, Precision Cleaning, Volume IV, Number 9, September 1996.
8. Chittick, R.C., “Using CO2 Snow to Correct Drive Level Dependence in Quartz Crystal Resonators”, Precision Cleaning, Volume V, Number 6, June 1997.
9. Jackson, D., “Liquid CO2 Immersion Cleaning- The Users Point of View”, Parts Cleaning, pp 32-37, April 1999.
10. Jackson, D., “Making the Case for CO2”, CLEANTECH, February 2004.
11. Jackson, D., “CO2 in the Miniature Manufacturing Process”, MicroTEC, October 2004.
12. The Role of Robots in Lean Manufacturing, http://www.robotics.org.
13. Chawla, M., “Measuring Surface Cleanliness”, Precision Cleaning, June 1997.
14. Jackson, D, “Setting the Record Straight: CO2 Technology is Part of the Solution”, EHS Today, August 2009.
15. Jackson, D., “CO2 for Complex Cleaning”, Process Cleaning, July/August 2009.
16. Jackson, D. et al, "Advanced CO2 Cleaning and Machining Options for Rolling Element Bearings", ASTM Rolling Element Bearings Workshop, May12-14, 2009.
17. Jackson, D. et al, “Automated CO2 Composite Spray Cleaning System for HDD Rework Parts”, Journal of the IEST, V. 52, No. X, 2009.
18. Jackson, D. et al, “CO2 Cooling for Thermal Spray Advances”, SprayTime – Thermal Spray Association, First Quarter 2009.
19. Jackson, D., “A Versatile Manufacturing Technology for Thermal Spray Operations”, ASM/TSS Aerospace Coatings Symposium 2008.
20. Jackson, D., “Changing the Game Rules with CO2 – CO2 Machining Fluid Technology”, SME/IMTS September 2008.
21. Jackson, D., “CO2 Composite Spray Technology for Probe Card Cleaning”, SW Test Workshop, June 2008.
A 10 part blog series discussing important aspects of clean manufacturing technology and implementation strategy.
Thinking Clean – Part 10 of 10
Clean manufacturing is a change of mindset - changing the conventional production paradigm using non-traditional lean and green manufacturing game rules. This is thinking clean. A clean manufacturing strategy involves training in the relevant CleanTech, followed by proper planning, assessment, and analysis of the various manufacturing wastes produced. The new clean manufacturing game involves a skillful and diligent waste auditing process that overlays state-of-the-art CleanTech onto a conventional production model – line, tool and process – to produce a new clean-enabled line, tool and process. Winning the clean manufacturing game is experiencing improved productivity and profitability.
For example in manufacturing operations that produce high reliability hardware, a product may be cleaned several times through the production cycle (build-clean). Manufacturing and assembly operations requiring a product cleaning include cutting, drilling, trimming, micromachining, bonding, dicing, abrasive finishing, polishing, stamping, welding and inspection. Conventionally, precision cleaning is performed as an “island” operation using, for example, a stand-alone spray cleaner, vapor degreaser, ultrasonic cleaning system, rinsing and drying stations. Segregation of the cleaning process from the assembly tool has been a necessity due to the inherent chemical and physical (space) incompatibilities between conventional cleaning operations and most assembly processes and tools. CleanTech changes this conventional paradigm.
CO2, Robot and OSEE Inspection CleanTech can be integrated with virtually any production tool or process to produce numerous new and advanced clean-enabled tools; Clean-Assembly™ tools. Clean-Assembly tools are much more productive because two or more assembly processes are be performed simultaneously within the same work cell. Products don't have to be transported from, cleaned, inspected and transported back to the production line - resulting in reduced labor, higher throughput, increased quality and decreased production space. The Clean-Assembly CleanTech model changes the game rules by incorporating the non-value add (although necessary waste), processes with the value-add production operations. This significantly reduces manufacturing waste and improves both productivity and profitability.
Conclusion
In today’s manufacturing environment, there is a need to reduce waste and improve profitability. This is accomplished using flexible and adaptable production methodologies, cleaner, leaner and drier process chemistries, and an increasing use of clustered production processes (cells). Production steps previously performed as separate operations using separate tools, space, transport, time, and labor) may now be integrated into modular lean cells using CO2 technology. Space and time saving hybridized forms of assembly processes integrated with CO2 technology may be used. In-situ clean-assembly tools may be clustered with manufacturing operations in modular production cells in which two or more steps can be performed simultaneously, thereby increasing throughput and yield and reducing human interaction and cost of ownership.
The bottom line is that CleanTech, and CO2 CleanTech in particular, reduces manufacturing waste and reduces operational costs in a number of unique ways. It's worth the effort to employ CleanTech where possible to improve productivity and profitability.
David Jackson is President/CEO of Cleanlogix LLC and serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
Select Clean Manufacturing References:
1. An Introduction to Environmental Accounting as a Business Management Tool, United States Environmental Protection Agency, EPA 742-R-95-001, June 1995.
2. Lean Manufacturing and the Environment: Research on Advanced Manufacturing Systems and the Environment and Recommendations for Leveraging better Environmental Performance, United States Environmental Protection Agency, EPA 100-R-03-005, October 2003.
3. The EPA Manual for Waste Minimization Opportunity Assessments, United States Environmental Protection Agency, EPA/600/2-88-025, April 1988.
4. How to Be Green and Stay in the Black, Department of Navy, NAVSO P-3680, October 1997.
5. Schwendeman, T., “Pollution Prevention Can Pay”, Industrial Heating, December 2003.
6. Jackson, D. et al, “Today’s Forecast – It Looks like Snow”, Precision Cleaning, Volume VII, Number 5, May 1999.
7. Darvin, C. et al, “ Demonstration of Liquid CO2 as an Alternative for Metal Parts Cleaning, Precision Cleaning, Volume IV, Number 9, September 1996.
8. Chittick, R.C., “Using CO2 Snow to Correct Drive Level Dependence in Quartz Crystal Resonators”, Precision Cleaning, Volume V, Number 6, June 1997.
9. Jackson, D., “Liquid CO2 Immersion Cleaning- The Users Point of View”, Parts Cleaning, pp 32-37, April 1999.
10. Jackson, D., “Making the Case for CO2”, CLEANTECH, February 2004.
11. Jackson, D., “CO2 in the Miniature Manufacturing Process”, MicroTEC, October 2004.
12. The Role of Robots in Lean Manufacturing, http://www.robotics.org.
13. Chawla, M., “Measuring Surface Cleanliness”, Precision Cleaning, June 1997.
14. Jackson, D, “Setting the Record Straight: CO2 Technology is Part of the Solution”, EHS Today, August 2009.
15. Jackson, D., “CO2 for Complex Cleaning”, Process Cleaning, July/August 2009.
16. Jackson, D. et al, "Advanced CO2 Cleaning and Machining Options for Rolling Element Bearings", ASTM Rolling Element Bearings Workshop, May12-14, 2009.
17. Jackson, D. et al, “Automated CO2 Composite Spray Cleaning System for HDD Rework Parts”, Journal of the IEST, V. 52, No. X, 2009.
18. Jackson, D. et al, “CO2 Cooling for Thermal Spray Advances”, SprayTime – Thermal Spray Association, First Quarter 2009.
19. Jackson, D., “A Versatile Manufacturing Technology for Thermal Spray Operations”, ASM/TSS Aerospace Coatings Symposium 2008.
20. Jackson, D., “Changing the Game Rules with CO2 – CO2 Machining Fluid Technology”, SME/IMTS September 2008.
21. Jackson, D., “CO2 Composite Spray Technology for Probe Card Cleaning”, SW Test Workshop, June 2008.
Tuesday, January 6, 2009
High-performance dry machining fluid options for the tool room
The work performed on tool room machines is prototype or short run jobs and there is rarely the opportunity to optimize tooling, feeds or speeds. The machine and cutting tools must be able to absorb punishment from processes that are much less refined than can be achieved on longer runs using automated machines. Over the years there has been a continuous evolution in metalworking tool room equipment capabilities, with the exception being coolant-lubricant options.
Equipping manual or CNC-enabled open machining platforms such as knee-mills, bed-mills, drills, tool grinders and lathes with flooded coolant systems leaves the tool room equipment, operators and floors awash. When flooding is not possible or desired, this leaves air-oil or air-only lubricating and cooling options. However these near-dry and dry machining fluid options are very limiting, in particular for hard machining applications and work requiring only dry machining and producing lots of tool heat.
Portable and adaptable dry and near-dry CO2 composite spray machining fluid technology offers the tool room machinist with productivity and machining quality improvements as good as or better than those achieved with high pressure flooded coolants, but without the mess. CO2 composite sprays offer a unique set of cooling and lubricating capabilities to enable machining of harder, more abrasive materials and using more capable and expensive cutting tools. Cutting tools last longer and parts are machined cooler, quicker and cleaner with improved surface finishes. Tool room machines, floors and air stay clean.
David Jackson serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN.
Equipping manual or CNC-enabled open machining platforms such as knee-mills, bed-mills, drills, tool grinders and lathes with flooded coolant systems leaves the tool room equipment, operators and floors awash. When flooding is not possible or desired, this leaves air-oil or air-only lubricating and cooling options. However these near-dry and dry machining fluid options are very limiting, in particular for hard machining applications and work requiring only dry machining and producing lots of tool heat.
Portable and adaptable dry and near-dry CO2 composite spray machining fluid technology offers the tool room machinist with productivity and machining quality improvements as good as or better than those achieved with high pressure flooded coolants, but without the mess. CO2 composite sprays offer a unique set of cooling and lubricating capabilities to enable machining of harder, more abrasive materials and using more capable and expensive cutting tools. Cutting tools last longer and parts are machined cooler, quicker and cleaner with improved surface finishes. Tool room machines, floors and air stay clean.
David Jackson serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN.
Dimensional grinding using composite CO2 machining fluids
During dimensional machining of a polymer-coated precision valve spool, a Norton 80 grit grinding wheel generates temperatures of up to 450 degrees F. A traditional coolant-lubricant approach requires interrupted processing to provide substrate dimensional control due to thermal expansion, in particular the polymer-metal interface.
A composite CO2 machining fluid spray (Air, MQL-Soy oil and carbon dioxide particles) directed into the grinding zone is able to maintain substrate temperatures to under 90 degrees F. Efficient removal of excess heat with minimal oil lubrication during precision grinding allows the machining operation to proceed to completion in a single and continuous step with reduced cycle time and improved dimensional stability.
An additional benefit of using this unique machining fluid technology with precision grinding includes a potential for significantly reducing wheel dressing intervals. In this particular application a 50% increase in parts production was realized between wheel dressing intervals.
David Jackson serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
A composite CO2 machining fluid spray (Air, MQL-Soy oil and carbon dioxide particles) directed into the grinding zone is able to maintain substrate temperatures to under 90 degrees F. Efficient removal of excess heat with minimal oil lubrication during precision grinding allows the machining operation to proceed to completion in a single and continuous step with reduced cycle time and improved dimensional stability.
An additional benefit of using this unique machining fluid technology with precision grinding includes a potential for significantly reducing wheel dressing intervals. In this particular application a 50% increase in parts production was realized between wheel dressing intervals.
David Jackson serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
CO2 Composite Spray Machining: An Introduction (Part 2)
In the previous blog, CO2 composite spray technology was introduced with a focus on basic components and operational characteristics of a spray system. This blog completes the introduction with a description of various performance aspects of a CO2 composite spray and includes initial laboratory test results for this new machining fluid technology.
Managing Heat
A CO2 composite spray manages machining heat through both physical (thermal transfer) and chemical (i.e., Rehbinder) effects. Frictional heat generated at the cutting edge is eliminated indirectly using chip-tool-workpiece temperature control and directly through juvenile surface reactions using a suitable lubricant chemistry, including carbon dioxide itself. Efficient heat removal is achieved through adjustable heat capacity, phase change phenomenon and reactive chemistry within the spray.
Penetration and Sticking Power
For CO2 composite sprays of the second kind, the combination of sublimating solid coolant and subcooled lubricants (mass) with near-sonic air flow (velocity) creates significant surface penetration power (Force = mass x velocity), which allows the coolant and lubricant particles to penetrate deeply into cracks and crevices and intimately contact machining surfaces. Particle velocities of between 50 m/s and 300 m/s are easily obtained with CO2 composite sprays. Upon entering the cutting zone, the cooling lubricant spray provides chip cooling and chip evacuation during sublimation or evaporation of the CO2. During expansion, electrostatically-charged CO2 gas and lubricant uniformly coat and penetrate cutting interfaces. Compared to conventional high pressure flooding techniques, CO2 composite sprays operating at 120 psi can exert particle-fluid impact stresses of over 8,000 psi.
Cutting Performance
In standardized cutting tests (see Table 1 below) performed by an independent testing laboratory (TechSolve, Inc., Cincinnati, Ohio), it was demonstrated that CO2 composite sprays using a bio-based oil additive outperformed conventional flood processes using standards: synthetic oil, soluble oil, and semi-synthetic fluids with extreme pressure agents, in terms of both uniform tool wear and cutting force (see CO2 Composite Spray data line 1 in the cutting force figure below).
Hard Machining Advantages
CO2 composite sprays offer several technical advantages and opportunities for challenging machining applications involving superhard tools and hard or abrasive substrates. These include:
• Supercharge existing cutting fluid chemistries in minimum and bulk amounts with increased coolant power and cutting zone penetration
• Increase machining efficiency for harder and more abrasive materials
• Improve surface finish
• Test new advanced coolant-lubricant additives in minimum quantities on-the-fly without having to change-out coolant sumps
• Optimize challenging machining processes with customized combinations of coolant, lubricant and advanced cutting tool coatings such as PCD, CBN and coated HSS
Another advantage provided by CO2 composite sprays is that they are a very clean and lean technology. Implementing CO2 composite spray technology can reduce or eliminate the use of flood coolants. This conserves fossil fuels, water and energy, and eliminates (or reduces) the generation of nonproductive outputs, hazardous wastes, air emissions, wastewater, or other pollutants.
Wrap-Up
CO2 composite spray technology improves machining productivity while reducing operating costs and environmental pollution. CO2 composite spray technology can be implemented along side many older and newer machining and metalworking processes, including machinery, materials, methods, processes, cutting tools and fluids, augmenting a successful conversion to a clean and lean metalworking operation.
Future blog articles will focus on specific commercial machining applications and challenges which have been addressed with CO2 composite technology.
David Jackson serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
In the previous blog, CO2 composite spray technology was introduced with a focus on basic components and operational characteristics of a spray system. This blog completes the introduction with a description of various performance aspects of a CO2 composite spray and includes initial laboratory test results for this new machining fluid technology.
Managing Heat
A CO2 composite spray manages machining heat through both physical (thermal transfer) and chemical (i.e., Rehbinder) effects. Frictional heat generated at the cutting edge is eliminated indirectly using chip-tool-workpiece temperature control and directly through juvenile surface reactions using a suitable lubricant chemistry, including carbon dioxide itself. Efficient heat removal is achieved through adjustable heat capacity, phase change phenomenon and reactive chemistry within the spray.
Penetration and Sticking Power
For CO2 composite sprays of the second kind, the combination of sublimating solid coolant and subcooled lubricants (mass) with near-sonic air flow (velocity) creates significant surface penetration power (Force = mass x velocity), which allows the coolant and lubricant particles to penetrate deeply into cracks and crevices and intimately contact machining surfaces. Particle velocities of between 50 m/s and 300 m/s are easily obtained with CO2 composite sprays. Upon entering the cutting zone, the cooling lubricant spray provides chip cooling and chip evacuation during sublimation or evaporation of the CO2. During expansion, electrostatically-charged CO2 gas and lubricant uniformly coat and penetrate cutting interfaces. Compared to conventional high pressure flooding techniques, CO2 composite sprays operating at 120 psi can exert particle-fluid impact stresses of over 8,000 psi.
Cutting Performance
In standardized cutting tests (see Table 1 below) performed by an independent testing laboratory (TechSolve, Inc., Cincinnati, Ohio), it was demonstrated that CO2 composite sprays using a bio-based oil additive outperformed conventional flood processes using standards: synthetic oil, soluble oil, and semi-synthetic fluids with extreme pressure agents, in terms of both uniform tool wear and cutting force (see CO2 Composite Spray data line 1 in the cutting force figure below).
Hard Machining Advantages
CO2 composite sprays offer several technical advantages and opportunities for challenging machining applications involving superhard tools and hard or abrasive substrates. These include:
· Supercharge existing cutting fluid chemistries in minimum and bulk amounts with increased coolant power and cutting zone penetration
· Increase machining efficiency for harder and more abrasive materials
· Improve surface finish
· Test new advanced coolant-lubricant additives in minimum quantities on-the-fly without having to change-out coolant sumps
· Optimize challenging machining processes with customized combinations of coolant, lubricant and advanced cutting tool coatings such as PCD, CBN and coated HSS
Another advantage provided by CO2 composite sprays is that they are a very clean and lean technology. Implementing CO2 composite spray technology can reduce or eliminate the use of flood coolants. This conserves fossil fuels, water and energy, and eliminates (or reduces) the generation of nonproductive outputs, hazardous wastes, air emissions, wastewater, or other pollutants.
Wrap-Up
CO2 composite spray technology improves machining productivity while reducing operating costs and environmental pollution. CO2 composite spray technology can be implemented along side many older and newer machining and metalworking processes, including machinery, materials, methods, processes, cutting tools and fluids, augmenting a successful conversion to a clean and lean metalworking operation.
David Jackson serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
Managing Heat
A CO2 composite spray manages machining heat through both physical (thermal transfer) and chemical (i.e., Rehbinder) effects. Frictional heat generated at the cutting edge is eliminated indirectly using chip-tool-workpiece temperature control and directly through juvenile surface reactions using a suitable lubricant chemistry, including carbon dioxide itself. Efficient heat removal is achieved through adjustable heat capacity, phase change phenomenon and reactive chemistry within the spray.
Penetration and Sticking Power
For CO2 composite sprays of the second kind, the combination of sublimating solid coolant and subcooled lubricants (mass) with near-sonic air flow (velocity) creates significant surface penetration power (Force = mass x velocity), which allows the coolant and lubricant particles to penetrate deeply into cracks and crevices and intimately contact machining surfaces. Particle velocities of between 50 m/s and 300 m/s are easily obtained with CO2 composite sprays. Upon entering the cutting zone, the cooling lubricant spray provides chip cooling and chip evacuation during sublimation or evaporation of the CO2. During expansion, electrostatically-charged CO2 gas and lubricant uniformly coat and penetrate cutting interfaces. Compared to conventional high pressure flooding techniques, CO2 composite sprays operating at 120 psi can exert particle-fluid impact stresses of over 8,000 psi.
Cutting Performance
In standardized cutting tests (see Table 1 below) performed by an independent testing laboratory (TechSolve, Inc., Cincinnati, Ohio), it was demonstrated that CO2 composite sprays using a bio-based oil additive outperformed conventional flood processes using standards: synthetic oil, soluble oil, and semi-synthetic fluids with extreme pressure agents, in terms of both uniform tool wear and cutting force (see CO2 Composite Spray data line 1 in the cutting force figure below).
Hard Machining Advantages
CO2 composite sprays offer several technical advantages and opportunities for challenging machining applications involving superhard tools and hard or abrasive substrates. These include:
• Supercharge existing cutting fluid chemistries in minimum and bulk amounts with increased coolant power and cutting zone penetration
• Increase machining efficiency for harder and more abrasive materials
• Improve surface finish
• Test new advanced coolant-lubricant additives in minimum quantities on-the-fly without having to change-out coolant sumps
• Optimize challenging machining processes with customized combinations of coolant, lubricant and advanced cutting tool coatings such as PCD, CBN and coated HSS
Another advantage provided by CO2 composite sprays is that they are a very clean and lean technology. Implementing CO2 composite spray technology can reduce or eliminate the use of flood coolants. This conserves fossil fuels, water and energy, and eliminates (or reduces) the generation of nonproductive outputs, hazardous wastes, air emissions, wastewater, or other pollutants.
Wrap-Up
CO2 composite spray technology improves machining productivity while reducing operating costs and environmental pollution. CO2 composite spray technology can be implemented along side many older and newer machining and metalworking processes, including machinery, materials, methods, processes, cutting tools and fluids, augmenting a successful conversion to a clean and lean metalworking operation.
Future blog articles will focus on specific commercial machining applications and challenges which have been addressed with CO2 composite technology.
David Jackson serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
In the previous blog, CO2 composite spray technology was introduced with a focus on basic components and operational characteristics of a spray system. This blog completes the introduction with a description of various performance aspects of a CO2 composite spray and includes initial laboratory test results for this new machining fluid technology.
Managing Heat
A CO2 composite spray manages machining heat through both physical (thermal transfer) and chemical (i.e., Rehbinder) effects. Frictional heat generated at the cutting edge is eliminated indirectly using chip-tool-workpiece temperature control and directly through juvenile surface reactions using a suitable lubricant chemistry, including carbon dioxide itself. Efficient heat removal is achieved through adjustable heat capacity, phase change phenomenon and reactive chemistry within the spray.
Penetration and Sticking Power
For CO2 composite sprays of the second kind, the combination of sublimating solid coolant and subcooled lubricants (mass) with near-sonic air flow (velocity) creates significant surface penetration power (Force = mass x velocity), which allows the coolant and lubricant particles to penetrate deeply into cracks and crevices and intimately contact machining surfaces. Particle velocities of between 50 m/s and 300 m/s are easily obtained with CO2 composite sprays. Upon entering the cutting zone, the cooling lubricant spray provides chip cooling and chip evacuation during sublimation or evaporation of the CO2. During expansion, electrostatically-charged CO2 gas and lubricant uniformly coat and penetrate cutting interfaces. Compared to conventional high pressure flooding techniques, CO2 composite sprays operating at 120 psi can exert particle-fluid impact stresses of over 8,000 psi.
Cutting Performance
In standardized cutting tests (see Table 1 below) performed by an independent testing laboratory (TechSolve, Inc., Cincinnati, Ohio), it was demonstrated that CO2 composite sprays using a bio-based oil additive outperformed conventional flood processes using standards: synthetic oil, soluble oil, and semi-synthetic fluids with extreme pressure agents, in terms of both uniform tool wear and cutting force (see CO2 Composite Spray data line 1 in the cutting force figure below).
Hard Machining Advantages
CO2 composite sprays offer several technical advantages and opportunities for challenging machining applications involving superhard tools and hard or abrasive substrates. These include:
· Supercharge existing cutting fluid chemistries in minimum and bulk amounts with increased coolant power and cutting zone penetration
· Increase machining efficiency for harder and more abrasive materials
· Improve surface finish
· Test new advanced coolant-lubricant additives in minimum quantities on-the-fly without having to change-out coolant sumps
· Optimize challenging machining processes with customized combinations of coolant, lubricant and advanced cutting tool coatings such as PCD, CBN and coated HSS
Another advantage provided by CO2 composite sprays is that they are a very clean and lean technology. Implementing CO2 composite spray technology can reduce or eliminate the use of flood coolants. This conserves fossil fuels, water and energy, and eliminates (or reduces) the generation of nonproductive outputs, hazardous wastes, air emissions, wastewater, or other pollutants.
Wrap-Up
CO2 composite spray technology improves machining productivity while reducing operating costs and environmental pollution. CO2 composite spray technology can be implemented along side many older and newer machining and metalworking processes, including machinery, materials, methods, processes, cutting tools and fluids, augmenting a successful conversion to a clean and lean metalworking operation.
David Jackson serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
Monday, February 4, 2008
CO2 Composite Spray Machining: An Introduction (Part 1)
- David Jackson, Cool Clean Technologies
Background
Carbon dioxide (CO2 gas, solid, liquid) as a machining fluid and its beneficial impacts on machining operations with regards to both lubricating and cooling qualities has been studied for the past 60 years. One of the earliest documented metal cutting processes utilizing a carbon dioxide spray is described by Thompson Products (later TRW) in the early 1950’s (1). The literature contains several good examples of the benefits that can be realized with a CO2 based machining fluid. With regards to tool wear, a reduction in CBN tool wear has been noted when CO2 gas is admitted to the atmosphere of the cutting zone, removing oxygen and reducing oxidation (2). With regards to tungsten carbide tool wear, it has been observed that liquid CO2 sprayed at base of carbide tool tip retards crater wear (3). In another investigation, it was observed that CO2 gas increases tool life by allowing a larger, protective BUE to form on HSS (4). Gases such as CO2 not only lubricate, but also cool. This point has been illustrated with cooled gases in many applications (5). For example, tool life increases when CO2 gas is cooled to -40° C to -60° C, even when cutting forces rise (6-8).
Limitations and shortcomings associated with conventional carbon dioxide machining fluid sprays of the past include, among others, a lack of fluid compositional control, limited lubrication ability, lack of temperature and penetration control, and limited machine-tool adaptability. These issues are being addressed with a new CO2 machining spray technology – CO2 Composite Spray Machining comprising gas-solid, gas-solid-liquid and gas-liquid compositions.
- David Jackson, Cool Clean Technologies
Background
Carbon dioxide (CO2 gas, solid, liquid) as a machining fluid and its beneficial impacts on machining operations with regards to both lubricating and cooling qualities has been studied for the past 60 years. One of the earliest documented metal cutting processes utilizing a carbon dioxide spray is described by Thompson Products (later TRW) in the early 1950’s (1). The literature contains several good examples of the benefits that can be realized with a CO2 based machining fluid. With regards to tool wear, a reduction in CBN tool wear has been noted when CO2 gas is admitted to the atmosphere of the cutting zone, removing oxygen and reducing oxidation (2). With regards to tungsten carbide tool wear, it has been observed that liquid CO2 sprayed at base of carbide tool tip retards crater wear (3). In another investigation, it was observed that CO2 gas increases tool life by allowing a larger, protective BUE to form on HSS (4). Gases such as CO2 not only lubricate, but also cool. This point has been illustrated with cooled gases in many applications (5). For example, tool life increases when CO2 gas is cooled to -40° C to -60° C, even when cutting forces rise (6-8).
Limitations and shortcomings associated with conventional carbon dioxide machining fluid sprays of the past include, among others, a lack of fluid compositional control, limited lubrication ability, lack of temperature and penetration control, and limited machine-tool adaptability. These issues are being addressed with a new CO2 machining spray technology – CO2 Composite Spray Machining comprising gas-solid, gas-solid-liquid and gas-liquid compositions.
Conventional Coolants and LubricationLiterally thousands of different cooling lubrication formulations are available on the market for the many different types of machining processes, equipment, cutting tools and materials. Besides machinability issues related to cooling lubricants, selection factors include machine/tool compatibility, sump stability, foaming characteristics, filterability, toxicity, biodegradability, odor, misting, surface wetting, staining, surface cleanliness and disposal issues. Cooling lubrication formulations are tested and selected based on its ability to provide the best mix of all of these characteristics, the tradeoffs being between machining and non-machining performance characteristics.
Alternatives to current practices are getting more serious consideration in response to environmental and operational cost pressures. Alternatives to flood machining include dry machining, near-dry machining (NDM) or minimum quantity lubrication (MQL) machining. The MQL approach utilizes a small amount of an oil of one type or another which is entrained as microscopic droplets in an airstream and delivered as a coherent dry (air only), near-dry, and wet machining spray. Bio-based lubricating oils derived from soybeans or other vegetable products are also being utilized successfully with MQL. Natural oils have numerous MQL advantages, including a polar chemistry which reacts more favorably with metal surfaces, unsurpassed lubricity, and an abundant U.S. agricultural growing capacity. MQL performance studies in machining processes such as milling, grinding and drilling show great promise. However issues related to tool adaptation and cooling capacity continue to be barriers to widespread adoption of MQL and other near-dry or dry machining technologies.
CO2 Composite Spray Machining
A new carbon dioxide (CO2) based cooling lubrication technology – comprising CO2 composite sprays - has been developed and is in its early market introduction period. CO2 composite spray technology employs robust spray compositional and energy control capability which have been developed to resolve many of the limitations found in more advanced cooling alternatives such as LN2 and CO2 machining sprays, while delivering beneficial physicochemical machining actions and benefits provided by conventional MQL. CO2 composite spray machining employs unique and beneficial combinations of lubrication and cooling technologies:
- Minimum amounts of carbonated coolants and lubricants
- Coanda effect for additive injection and spray trajectory control (see figure below)
- Precise machining spray temperature control
- Precise cooling lubrication composition control
- Electrostatic charging (Passive/Active) of cooling lubrication compositions for improved droplet formation and cutting zone deposition
- Pressure and flow control for enhanced penetration, flushing and lubricant deposition
CO2 composite spray technology includes three general kinds of compositions:
1st Kind (Dry): Gas (Air)-Solid(CO2)
2nd Kind (Near-Dry): Gas (Air)-Solid(CO2)-Liquid(MQL)
3rd Kind (Flood): Gas (CO2)-Liquid(Coolant/Lubricant)
This paper focuses primarily on CO2 composite spray systems of the second kind – a gas-solid-liquid composition – and fluid phenomenon associated with same. A gas-solid-liquid composition combines a source of propellant gas (i.e., compressed air), lubrication additives (i.e., soy oil), and solid and/or gaseous CO2 (i.e., coolant) in various proportions to form an infinitely adjustable cooling lubricant spray. For lubricant-based CO2 composite sprays, a Coanda-Coaxial lubricant injector and spray applicator are applied as an external spray. Spray applicators employ a passive electrostatic charging mechanism to enhance droplet uniformity, spray force and machined surface deposition. Alternatively, an electrostatic charging system may be employed to provide combination spray charging capability. An important performance aspect associated with composite CO2 machining sprays, and unlike conventional LN2 and CO2 (flood) machining sprays, is that dilute mixtures containing solid coolant particles and subcooled lubricants more easily access and interact (high frequency impacts) with cutting surfaces and interfaces. Concentrated particle or fluid streams tend to “pack” the surface during impact which retards physical actions such as outflow velocity and heat exchange.
1st Kind (Dry): Gas (Air)-Solid(CO2)
2nd Kind (Near-Dry): Gas (Air)-Solid(CO2)-Liquid(MQL)
3rd Kind (Flood): Gas (CO2)-Liquid(Coolant/Lubricant)
This paper focuses primarily on CO2 composite spray systems of the second kind – a gas-solid-liquid composition – and fluid phenomenon associated with same. A gas-solid-liquid composition combines a source of propellant gas (i.e., compressed air), lubrication additives (i.e., soy oil), and solid and/or gaseous CO2 (i.e., coolant) in various proportions to form an infinitely adjustable cooling lubricant spray. For lubricant-based CO2 composite sprays, a Coanda-Coaxial lubricant injector and spray applicator are applied as an external spray. Spray applicators employ a passive electrostatic charging mechanism to enhance droplet uniformity, spray force and machined surface deposition. Alternatively, an electrostatic charging system may be employed to provide combination spray charging capability. An important performance aspect associated with composite CO2 machining sprays, and unlike conventional LN2 and CO2 (flood) machining sprays, is that dilute mixtures containing solid coolant particles and subcooled lubricants more easily access and interact (high frequency impacts) with cutting surfaces and interfaces. Concentrated particle or fluid streams tend to “pack” the surface during impact which retards physical actions such as outflow velocity and heat exchange.
Chemistry and Control
CO2 composite spray chemistries combine several chemical and physical cooling and lubrication ingredients and are formed and delivered on-the-fly. The sprays are infinitely adjustable and may include liquids, extreme pressure solid additives, and reactive gases which are combined with a propellant gas and injected into a metered flow of charged CO2 gas-solid aerosol. Each ingredient contributes a specific physical and/or chemical dimension, including cooling capacity, penetration power, boundary layer reactivity, lubricity, viscosity, spray particle size and density. CO2 composite sprays have variable geometry including adjustable physical spray characteristics from dry to wet composition, room temperature to near-cryogenic temperature, and spray pressures ranging from 10 psi to 150 psi, or much higher if desired.
Unlike simple atmospheric gases like nitrogen and oxygen, CO2 demonstrates very strong hydrocarbon fluid and water solubility. For example, CO2 gas exhibits greater than 600% higher solubility in oils (i.e., mineral oil) as compared to compressed air. CO2 modifies lubricant and coolant MQL or flood properties to produce mixtures having lower surface tension, lower viscosity, and increased heat capacity. Moreover, CO2 itself behaves as a reactive boundary layer lubricant, forming carboxylic acid functional groups during tribochemical reactions.
CO2 composite spray technology provides infinitely adjustable cooling-lubricant compositions of CO2 coolant, propellant gases, and minimum quantities of any type of lubrication additive(s). Adjustable spray pressure, temperature, coolant particle size and lubricant additive concentration allow a machinist to customize a cooling lubricant composition for a particular machining application. One or more individually controllable machining spray applicators may also be employed.
The next blog article will cover performance aspects of CO2 composite spray technology including heat management, spray characteristics and laboratory test results.
I may be reached via e-mail at david.jackson@coolclean.com. For more information on CO2 composite spray technology, visit http://www.2cooltool.com/.
References
1. U.S. Patent No. 2,635,399, West, April 21, 1953
2. V.N. Ponduraev, Russian Eng. J., 59 (3), 1979, pp. 42-44
Study of Cubic Boron Nitride (CBN) Tools
3. W.S. Hollis, Int. J. Mach. Tool Des. Res., 1, 1961, pp. 59-78
Study of Carbide Tool
4. N.N. Zorev and N.I. Tashlitsky, Machinability, ISI Spec., Rep. 94, Iron Steel Institute, London, 1967, pp. 31-34
5. Tribology in Metalworking, Friction, Lubrication and Wear, John Schey, American Society for Metals, 1983, pp. 624-625
6. I. Ham, K.Hitomi and G.L. Thuering, Trans. ASME, 83, 1961, pp. 142-154
7. L.Walter, Can. Mach. Metalwork., 76(8), 1965, pp. 94-97
8. F.A. Monahan et al, Am. Mach., 104 (May 16), 1960, pp. 109-124
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