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APPLICATION ARTICLES

 

Cartridge Style Power Steering Valve (Load Sensing Flow Control Valve)

The power steering valve, which is well known outside the cartridge valve industry, is asimple priority type spool valve, combined with a remote load sensing orifice, used forprecision flow control on demand. Up until recently, all Priority On Demand Spool (PODS) valves were large, heavy, cumbersome, cast iron valves with ports that were fixed in size and location.

In an effort to advance cartridge valve technology, Command Controls Corp. has introduced a small, lightweight, flexible, cartridge style PODS valve, which can be designed into just about any circuit or any size manifold requiring priority-on-demand. This type of valve, even though it has been in use for over forty years, commands even more attention than ever, due to rising energy costs.

The load sensing flow control is used on many applications, especially power steering circuits where priority flow is needed. The valve functions in all systems: open center, closed center and load sensing. It provides flow and pressure to a controlled circuit on
demand. A fluid linked power steering system is used for this illustration, but the same principles can be applied to any circuit requiring a load sensing four-way valve.

A known performance characteristic in both an open and closed center hydraulic system is that the flow rate is affected by the resistance of the load, when a valve is opened to move the load. However, with a load sensing flow control valve, the flow will depend on the amount the valve is opened, independent of the load. By sensing the load, pressure demand is compensated, and the flow rate is actually insensitive to load. Therefore, the flow and the pressure in the controlled circuit, provided by the pump, will only be what is needed to move the load, plus a small amount for control. Any surplus pump capacity is usable in other circuits. In short, a load sensing system provides maximum energy savings.

In a load sensing system, such as the one mentioned above, the load sensing priority valve is typically used to give priority to steering and braking. In each case, the same load sensing hydraulic flow control is used, and the function remains the same. Maximum energy savings can be achieved by using more than one priority valve for more than one stage of priority. This allows for a multi-circuit system with the use of only one pump – a significant cost reduction!

The load sensing, flow control valve can function to build pressure or reduce pressure to the controlled circuit, as needed, in any type of system. It also gives priority to the controlled flow circuit as needed without cutting off flow to the excess flow circuit. The controlled flow circuit relief is set lower than the main system pressure, so that the controlled flow circuit can hold relief pressure, while the excess flow is still available up to the maximum system pressure. The controlled flow circuit relief will also limit the controlled flow circuit pressure, should the system pressure exceed the controlled circuit relief setting. This is especially true in a closed center system, where the system pressure could be set at 350 bar (5000 psi), while the
steering circuit is limited to 70 bar (1000 psi).

Let’s consider the operation with a fixed displacement pump. When there is no flow from the pump, the spring will move the spool to the right until it engages the stop. The “P” port will then be open to the “CF” controlled flow port and the “EF” excess flow port will be closed. Now, consider the controlling orifice closed when the pump is started. Inlet flow will now enter at the “P” port and exit at the “CF” port. However, with the orifice closed, the only open passageway is to the closed end of the spool. The inlet flow pressure will then move the spool against the bias spring until port “EF” is open, and all of the flow will exit at this port as excess flow. This flow will be from port “P” to port “EF” with a pressure drop (rP) of 7,0 bar (100 psi), as determined by the bias spring.

If we want flow in our controlled flow circuit (priority flow), the controlling orifice of the steering wheel is opened. If there is no load (zero pressure) downstream of the orifice, and there is a 7,0 bar (100 psi) pressure upstream of the orifice (determined by the bias spring), then the flow in this circuit will be that which can be pushed across the orifice by a 100 psi delta P.

Now consider that the controlling orifice is open, but the load passageway is blocked downstream. The pressure at port “CF”, 7,0 bar (100 psi), can pass through the orifice, and to the spring end of the spool, to add to the force at the left end of the spool. The spool will now move to the right, to close off port “EF” at port “A”. With the controlled flow circuit blocked, there is no flow across the orifice, and the pilot pressure at both ends of the spool is identical. The spring force will now hold the spool to the right, regardless of how high the pressure rises. As such, the circuit now has priority. Pressure will continue to rise until the relief setting of the pump is reached, and the flow will spill over the relief valve and go back to the tank. There will be no flow at port “EF” and no flow at port “CF” with the circuit blocked. If the controlled flow circuit is not blocked, but is opened to a load that will move at, for example, 100 bar (1500 psi), the action will be the same up to 100 bar (1500 psi). In other words, the 7,0 bar (100 psi), caused by the spring, will pass through the orifice and to the load sense “LS” pilot line to the left end of the spool, and will cause pressure build up until 100 bar (1500 psi) is reached. At this point, the load will start to move. With flow, there will also be a pressure drop across the orifice. The pressure will continue to rise and move the load until the flow through the orifice causes a pressure drop across the orifice equivalent to the bias spring setting, which in this case is 7,0 bar (100 psi). The flow will then level off at this setting, and the pressure will vary as needed.

In the active mode, the spool is balanced between the forces at its ends. Restated, the force of the bias spring must be reacted by the pressure difference at its ends, which is
caused by the pressure drop across the controlling orifice. Load pressure can also act on both ends of the spool, so the difference in pressure caused by orifice, is the only pressure that is effective to control the flow rate. Flow rate in the controlled flow circuit will be according to the orifice area, and the delta P caused by the bias spring regardless of load.

Lastly, consider a load being applied to the Excess Flow (secondary or auxiliary) circuit, while no load, and only flow, is applied to the Controlled Flow (primary) circuit. The flow rate in the primary circuit will be as determined by the orifice area, and the 7,0 bar (100 psi) bias spring setting. When the load in the secondary circuit exceeds 7,0 bar (100 psi), the pressure at the controlling orifice will start to exceed 7,0 bar (100 psi) and the flow rate will tend to increase. However, the pressure at the right end of the spool will also increase, and move the spool to the left. The control has now switched from “A” to “B”. “A” will now be wide open or non-controlling, while the restriction at “B” will reduce the pressure, and consequently the flow in the primary circuit. The pressure and flow in the primary circuit will remain almost unchanged by the loads in the secondary circuit. Any change that occurs will be the result of the difference in the bias spring force, which is caused by the change in length as the spool moves to close off “B”. The spring force changes slightly during all control whether the control is at “A” or “B”. It is important to note that when the load in the secondary circuit exceeds the bias spring setting, which is 7,0 bar (100 psi), the restriction at “A” is very low; it is basically a passageway loss. With a fixed displacement pump and an open center system, this means that there will always will be a 7,0 bar (100 psi) pressure drop from port “P” to port “EF”, but once the load in the secondary circuit exceeds this pressure drop, it is very low, and is on the order of line and fitting losses. Any bank of valves, along with lines, fitting and filters in the secondary circuit, will probably cause a load large enough to shift the spool, and the through flow pressure loss in the valve will be very low as well. If the load in the secondary circuit is high, or the circuit has blocked the pump pressure, it will rise to the relief setting, while the pressure in the primary circuit at port “CF” will still be at 7,0 bar (100 psi). The flow in this circuit will still remain as determined by the spring force and the orifice area, and the pressure and the flow will be restricted at “B”. Or, if there is a load in the primary circuit, the pressure will rise as needed, while the flow rate will be unaffected by the load in either circuit. Note that this same condition exists in a closed center system with a pressure compensated pump, but instead of flow being forced over a relief valve, the pump de-strokes at a high operating pressure. In the area of the load sensing flow control, and in the primary circuit, the operation is identical whether it is in an open or closed center system. The primary circuit also functions the same with a load sensing pump, pressure compensated pump or a fixed displacement pump.

In summary, the advantages of the load sensing flow control valve (PODS valve), when used in a fluid linked power steering system or other similar system are: 1) only the flow demanded by a steering maneuver, by the vehicle operator, goes to the steering circuit; 2) the steering function has priority over other functions in the system; 3) flow not demanded for steering is available to other circuits; 4) improved steering control exists regardless of the steering load pressure; and 5) four sizes are available with regulated flows up to 30 gpm (115 lpm).
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Written by Connie Kosarzecki of Command Controls Corp., Elgin, Ill. Kosarzecki has worked in the fluid power industry since 1958. Command Controls Corp, established in 1993, manufactures a complete line of state-of-the-art, high-pressure (5,000 psi/350 bar), high-performance, screw-in, cartridge-type, hydraulic control valves and manifold systems for the fluid power industry. For more information, please visit www.commandcontrols.com.

Wide Range Temperature, Pressure, and Fluid Resistant Hydraulic Cylinder Sealing Systems

Joel Johnson Ben Westbrook
Simrit Division of Freudenberg-NOK
Noriyuki Matsui
NOK Corporation

ABSTRACT
Excessive temperature and fluid compatibility often create problems for hydraulic cylinder sealing. Overall, new materials and designs are necessary to meet the increasing requirements of the industry. Smaller packages with higher pressures combined with hotter ambient temperatures (often directly linked to new environmental standards) continue to drive the demands for better performing seal systems. The new advancements presented in this paper help the fluid power engineer design a more robust cylinder that can be used in a wide variety of applications while providing longer life and lower warranty.

INTRODUCTION
Failure analysis indicates that the main sealing challenges for cylinder makers today are excessive temperature and fluid compatibility (including hydrolysis and glycolosis).
The latest demands (listed below) exceed the capabilities of most off-the-shelf sealing solutions.
•Capable of 42 MPa (6000 psi) @ 0.5mm diametrical extrusion gap
•Handle continuous 110º C or 120º C temperatures
•TR10 of -30º C; - 40º C actual application capability
•Compatible with biodegradable and standard hydraulic fluids
•Hydrolisis and glycolosis resistant
•Retrofit in existing standard grooves

The changes to the temperature range are especially concerning as they affect a broad range of applications. Bench testing has shown that increasing the system temperature by 10º C can decrease the seal life by 5 times (or greater). To narrow the scope of this paper, we chose to use our best-in-class sealing system (fig. 1: buffer seal + asymmetrical rod seal + vented rod wiper) produced in our Disogrin 9250 (urethane) as a baseline.




Baseline Sealing System
This system in Disogrin 9250 has decades of proven field experience, but an upper temperature limit of 100º C and is not hydrolysis or bio-fluid resistant. This paper centers mostly on materials, and will show the results of several new urethane and elastomeric blends in designs equivalent to our baseline sealing system.It should also be noted that many of the results concentrate on the residual interference that remains after test. This is a measurement of the remaining interference the seal
has with the bore and shaft, which takes into account not only wear but also the physical state of the material. This is a strong indicator of remaining life as a design is as dependant upon the material resiliency to ensure that it seals at low (or no) pressure as it is the material strength to ensure that it does not extrude at high loads.

MAIN SECTION
For several years we have supplied a proprietary blend of urethane into the market (NOK U641) that is capable of handling 110º C. As part of the material development, the baseline configuration was successfully lab tested to 500km (0.5million cycles) at 32MPa / 0.4mm/s / 110º C without leakage. Our experience indicates that the results of this accelerated test correlate well with actual field results. In this case the NOK U641 change allows our sealing system to provide similar hours to what was provided by Disogrin 9250, but at an elevated temperature (see figure 2). NOK U641 was also developed to be hydrolosis and glycolosis resistant.





NOK UH05 – 120º C Urethane.
In many cases NOK U641 is all that is needed to meet the application needs. It does not meet our initial high and low temperature requirements though, thereforeNOK UH05 was developed. NOK UH05 improves our cold temperature resistance, while increasing the high temperature capability (see figure 5). The trade off with NOK UH05 is that it is more difficult to process, and therefore only suitable for the thinner cross section of the buffer seal.



ELASTOMERS: G928=120ºC HNBR; A505=110ºC
NBR
As a complement to urethanes, we develop specially formulated elastomers for use in pressure applications. The advantage elastomers can offer is that they takeless of a compression set than urethanes (see figure 6), but they require back up support to prevent extrusion at pressures above 12MPa (see figure 7). Lowercompression set equates to improvements in residual interference which is advantageous where longer life is required. Extrusion is not an issue as we have
successfully used filled / reinforced PTFE back up rings to reach 40+MPa.




ELASTOMERIC ROD SEALING SYSTEM
We have successfully used combinations of urethane and elastomer in Asia for numerous years. A U641 buffer with A505 NBR rod seal system (fig. 8) meets allof the design goals except for the 120º C upper limit (max is 110º C). To meet the 120º C requirement, we substitute UH05 for the buffer seal, and HNBR G928 forthe rod seal.



BIODEGRADABLE OIL COMPATIBILITY
Immersion testing was conducted for 500 hours at 100º C and 110º C in numerous biodegradable oils to determine their effect on all previously mentionedmaterials. Panolin HLP Synth46 was chosen as our baseline biodegradable oil, and lab testing was conducted on the systems shown in figure 8 at 80º C,100º C, 110º C, and 120º C for 125km @ 42MPa. The results are shown in figure 9. All materials performed well, with U641 starting to take a set at its upper limit of110 deg C (as expected).



SYSTEM FOR N.A. AND DIN STANDARDS
The JIS standard groove sizes allow for a back up ring independent of the rod seal material, where as the North American and DIN standard groove sizes do not. Thiscreates a problem with retrofit of the new solutions into existing grooves. We have developed a design that integrates the back up into the seal (referred to as anIUY design – see figure 10) as a solution to this.



The IUY system was tested at 110º C and 120º C for 500km @ 32MPa (0.4mm/s) against a NOK U641 rod seal (both using a NOK U641 buffer), and the residualinterference results are shown in figure 11.



Although neither of the systems actually leaked, the HNBR G928 has significantly higher residual interference overall (especially at 120º) This can bedirectly correlated to longer system life.

CONCLUSION
NOK U641 is a hydrolisis / glycolosis resistant option for 110ºC systems with standard and bio hydraulic oils provided 100% sealing at extreme cold temperature isnot needed. If 100% sealing at extreme cold temperature is needed, A505 NBR can be used in combination with a back up ring for the rod seal.

NOK UH05 (buffer) in combination with G928 HNBR (rod seal) is a hydrolisis / glycolosis resistant material option for 120ºC systems with standard and biohydraulic oils. The HNBR rod seal does require a back up ring to prevent extrusion though. Base on our testing, this is the best sealing solution for long life atany temperatures.

Field test show that the A505 (NBR) system can go 8,000 hours in and excavator application, and based on the improvement in seal residual interference we expectthe G928 (HNBR) system could last 5X longer even at elevated temperatures. The life of any system is influenced by factors such as contamination, rod damage, and oil degradation which greatly effect seal life in actual applications. Every system should be tested in the actual application.

Standard Design Validation Test Fixture Example


Simrit

Simrit Division of Freudenberg-NOK,
2250 Point Blvd.,
Suite 230, Elgin, IL 60123
847.428.1261
Floating Cage Pressure Controls

Pressure control is a major factor in the design and operation of safe, efficient and reliable hydraulic systems. Limiting the operating pressure to prevent damage to hydraulic components and other expensive equipment due to the resultant forces is one of the most important functions of pressure control valves. Pressure control valves may also be used to control sequence of operations, maintain critical holding forces, and prevent loads from "running away" due to the effects of gravity.

Types of Pressure Controls

Pressure controls are typically 2-way or 3-way valves, which are either normally closed (non-passing flow) or normally open (passing flow). The majority of them are infinite positioning, which means they can assume an infinite number of positions between their fully open and fully closed positions, depending on flow rates and pressure differentials. Some pressure controls are also available as pressure breaker valves, commonly referred to as kick-down valves. These valves are only two position, and are either fully open or fully closed. They open or close at a pre-determined pressure, set by the spring, then reverse their position when pressure to the valve is reduced to near zero.

There are four common types of pressure controls, three of which are discussed in this article: reliefvalves, pressure-reducing valves, sequence valves and counterbalance valves.

Relief Valves

The relief valve is the safeguard that limits maximum pressure in a system by diverting flow back to the tank when the valve’s setting is reached. Relief valves are normally closed, while, in contrast, pressure-reducing valves are normally open. Various types of relief valves include: direct acting, differential area, piloted and bi-directional.

Pressure Reducing Valves
Pressure reducing valves are used to reduce pressure in certain parts of a hydraulic circuit that may not be able to withstand the maximum system pressure established by the relief valve. With a pressure-reducing valve in the system, pressure can be reduced to an actuator downstream of the valve, without affecting the pressure in the rest of the system. Pressure-reducing valves are normally open, and are available in 2-way (non-relieving) and 3-way (relieving) types.

Sequence Valves

As its name implies, a sequence valve causes operations in a hydraulic circuit to take place in a given sequence, without the use of electrical switches and controls. Sequence valves can be normally open or normally closed, depending on the application in which they are used, but are typically 2-way normally closed valves, and are either internally or externally piloted. Some sequence valves are 3-way, and can be normally open or normally closed.

Counterbalance Valves

Counterbalance valves are used when there is a need to control a load. They maintain a set pressure opposite of the load, to keep it from free falling. They may also serve as a full-flow relief valve. Pleaseread our article on Counterbalance Valves for more information.

The Problems

Due to the nature of most cartridge-type pressure control valve designs, they typically require a very precise forming of the valve cavity to ensure reliable operation. If the valve cavity is not machined within required tolerances, the valve tends to bind against the walls of the valve cavity. This can cause distortion of the cage and subsequent valve failure due to binding or sticking of the spool or poppet. Often, the cartridge valve is removed, assumed to be defective, and a different valve is installed in the cavity with the same results.

After a number attempts with different valves it may be determined that the cavity must be reworked to solve the problem. It should be noted, however, that reworking a cavity might also create another problem in that the cavity may become oversized, and will not provide enough squeeze on the o-rings to ensure a proper seal.

Another problem with cartridge type pressure controls is that they are often used in an environment that is prone to significant changes in temperature. This causes thermal expansion and contraction of the manifold and valve parts. Valves with a minimal margin of concentric clearance between the cage and the cavity may function properly with cold oil, but when exposed to hot oil, will experience binding and sticking failures because of the thermal expansion of parts in the hot fluid.

And last, but certainly not uncommon, over-torqueing the cartridge into the cavity during installation is another problem that will cause a valve spool or poppet to stick. Naturally, it is desirable to torque the cartridge into the manifold as much as possible to prevent it from backing out.

The Solution

The patented floating cage concept, designed by Command Controls Corp. of Elgin, Illinois solves the age-old problem of valve spool binding in pressure control valves caused by cage distortion. The floating cage, used in many of Command Controls’ flow controls, allow the cartridge to be flexible enough to conform to the contour of the valve cavity independently of the cartridge valve threads. This allows the cartridge to fit into the cavity without putting any side load on the valve, even in
cases where the cavity may be non-concentric or out-of-round, thereby allowing the spool to move freely without binding. Distortion of the cage, due to the effects of thermal expansion, is also eliminated by the floating cage design.

In the floating cage concept, since the retainer and cage are not physically connected to each other, torque applied to the threads when installing the cartridge in the manifold is not transferred to the cage. This yields another side-benefit: Command Controls floating-cage cartridges can be torqued into manifolds with higher torques than most other cartridge valves, and as such, are less likely to vibrate loose and cause external oil leakage. The floating cage design, along with other unique designs and innovations, put Command Controls’ cartridge valves on the leading edge of cartridge valve technology.
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Written by Connie Kosarzecki of Command Controls Corp., Elgin, Ill. Kosarzecki has worked in the fluid power industry since 1958. Command Controls Corp, established in 1993, manufactures a complete line of state-of-the-art, highpressure (5,000 psi/350 bar), high-performance, screw-in, cartridge-type, hydraulic control valves and manifold systems for the fluid power industry. For more information, please visit www.commandcontrols.com.
Rexroth Hydrostatic Regenerative Braking System (HRB) Makes Commercial Vehicles Up to 25 Percent More Economical

 Rexroth hydrostatic regenerative braking system (HRB) reduces fuel consumption by up to 25 percent and can be retrofitted as an add-on system even in vehicles without hydraulics.

Hydrostatic regenerative braking system (HRB) stores brake energy in a hydraulic pressure reservoir and relieves the load on the main drive when the vehicle is accelerating – potentially reducing fuel consumption by up to 25 percent.

(Bethlehem, PA - www.boschrexroth-us.com) Bosch Rexroth’s hydrostatic regenerative braking (HRB) system includes a hydrostatic hybrid drive which uses the considerably higher performance of hydraulics compared with available batteries to substantially reduce fuel consumption even in heavy commercial vehicles.

When the driver presses the brake pedal, a hydraulic unit integrated in the drivetrain presses the hydraulic fluid into a high-pressure reservoir. The resulting resistance makes the vehicle decelerate. When accelerating, the hydraulic pressure reservoir is controlled electronically to release the pressure and it relieves the load on the diesel engine. As a result, the engine consumes less fuel, generates less exhaust gases, and functions more quietly.

The compact Rexroth HRB is ideal for use in various commercial vehicles. The HRB can be integrated and even retrofitted in the chassis as an add-on system, without major modifications.

The system reduces fuel consumption by up to 25 percent in vehicles used for very short distances such as urban buses, garbage trucks, fork lift trucks, or delivery vehicles driven in city traffic. Fuel consumption can also be reduced considerably in other commercial vehicles and trucks used for intercity service.

Each time a driver brakes, the HRB system stores energy which would otherwise be lost. The hydrostatic hybrid drive functions almost maintenance-free and wear-free compared with electric hybrid drives. For example, it is not necessary to regularly change the battery. In addition, the HRB also improves the acceleration of the vehicle. The additional drive energy allows vehicles to be equipped with smaller diesel engines and therefore further reduce fuel consumption and emissions.

All Rexroth HRB components are based on standard components from the manufacturer's current product portfolio. Prototypes of the Rexroth hydrostatic hybrid drive are currently being tested in on-road vehicles.


CONEXPO-CON/AGG 2008 and IFPE 2008
set records for attendance and exhibit space
Construction, construction materials and power transmission industry leaders unveil latest product technologies and innovations

CONEXPO-CON/AGG 2008 and the co-located IFPE 2008 expositions have set records for attendance, exhibit space and number of exhibiting companies. In addition, CONEXPO-CON/AGG 2008 is the largest trade show in North America of any industry in 2008.

CONEXPO-CON/AGG and IFPE are known as global showcases of the latest equipment, product innovations and technological advances for the construction, construction materials and power transmission industries.

More than 144,600 industry professionals from around the world attended CONEXPO-CON/AGG 2008 and IFPE 2008 during their five-day run March 11-15, 2008 at the Las Vegas Convention Center in Las Vegas, USA.

CONEXPO-CON/AGG 2008 covered more than 2.28 million net square feet of exhibits (211,966 net square meters), taken by 2,182 exhibitors, and was 21 percent bigger than the last show, held in 2005.

IFPE 2008 was also the largest in its history with more than 129,000 net square feet of exhibit space (11,994 net square meters) used by 469 exhibitors – a 16 percent increase in space compared to 2005.

International Attendance
A record number of international industry professionals visited the shows – more than 28,000, which is more than 19 percent of total attendance and represents more than 30 percent growth compared to the last edition of the shows. International attendance increased by more than 50 percent from the Latin America and Caribbean marketplace, and doubled from China, India and Turkey. There were also significant increases from Canada, Australia, Russia and the Middle East, to name just a few.

International visitors to the shows hailed from more than 130 non-U.S. countries. There were more than 60 official international customer delegations organized by the U.S. Department of Commerce as well as in-country trade associations and related groups.

Exhibit Features
The show floor included a record number (14) of international exhibit pavilions highlighting products and services developed outside the United States - CONEXPO-CON/AGG 2008 with 10, from Brazil, Canada, China, Finland, Germany, Italy, Korea, Spain, Turkey and the United Kingdom, and IFPE 2008 with four, from China, Italy, Spain and Taiwan. -more-
IFPE 2008 hosted a new exhibit pavilion sponsored by the American Gear Manufacturers Association (AGMA), welcomed back a Power Transmission Distributors Association (PTDA) pavilion, and set up a new pavilion to highlight the expanded presence of sensors at the show.
CONEXPO-CON/AGG 2008 featured a new Safety Zone of exhibits and demonstrations from industry and government groups, including the U.S. Occupational Safety and Health Administration, Mine Safety and Health Administration, National Institute of Occupational Safety and Health, and the Aerial Work Platform Training/International Powered Access Federation.

Education Highlights
The CONEXPO-CON/AGG 2008 seminar program offered a record 130 sessions. Show education expanded in 2008 to include a special seminar on best practices for small fleet management. Also new: select education sessions were offered via LiveCasts and podcasts to extend the value of show education. Education session registrations totaled more than 22,850.

IFPE 2008 also expanded its educational offerings with an electronic controls symposium added to the show’s renowned Technical Conference. The conference offered a record 111 papers from industry experts from around the world. A new IFPE Innovation and Solutions Center, on the show floor, provided real world insights into future design applications. IFPE education session registrations totaled more than 1,700.

Industry Support
The shows were the industry gathering place in 2008. Some 105 allied industry groups were “supporting organizations" of CONEXPO-CON/AGG 2008 and IFPE 2008, bringing their memberships to the shows. In addition to U.S-based groups, these included international industry-related organizations from Brazil, Canada, Chile, China, Finland, Germany, India, Japan, Korea, Mexico, Spain, Taiwan, Turkey, United Kingdom and Venezuela.

A record number of 11 associations held annual conventions or board meetings at the shows, and overall a record number of more than 530 industry-related meetings were held in conjunction with CONEXPO-CON/AGG 2008 and IFPE 2008.

Other Highlights
CONEXPO-CON/AGG 2008 hosted a visit by Admiral Woody Sutton, the U.S. Department of Commerce Assistant Secretary for Manufacturing and Services, on March 12. Sutton toured the show and met with show officials and exhibitors to discuss global trade issues.

CONEXPO-CON/AGG 2008 was also the site of the first ever Construction Challenge competition, initiated by show organizer Association of Equipment Manufacturers (AEM). The creative problem-solving competition was designed to interest teens in construction careers, while calling attention to industry workforce shortages and infrastructure renewal needs.

The next edition of the triennial shows will be March 22-26, 2011 at the Las Vegas Convention Center in Las Vegas, USA. Check online for details: www.conexpoconagg.com, www.ifpe.com.



SENSING HYDRAULIC CYLINDER

Polygon Company, Walkerton Indiana, March 2008

Ever since the inception of composite materials an engineering conundrum has developed regarding the process of how to integrate composites and metals into a working relationship, which benefits upon each constituents performance properties. For composite applications to gain any real traction within traditional metallic OEM markets, a significant bridge needs to be crossed with respect to making them manufacturing friendly within existing metallic manufacturing infrastructures.

Polygon has taken a significant step in that direction through the creation of a composite sleeve inserted within ametallic tube for hydraulic cylinder applications. In addition to this manufacturing friendly concept the added feature of electronic sensing and positioning is included. This new sensing hydraulic cylinder contains a composite/metallic barrel, which can have ends that are attached using existing welding or threading techniques. This patented process allows the composite inner tube to carry almost the entire hydraulic pressure force while the outer metallic tube keeps the structure round. This engineering feat was possible by incorporating the anisotropic expansion characteristics of composites while simultaneously being constrained within the isotropic properties of a metallic shell. The circumferential pressure properties within a composite tube can be altered or manipulated through fiber path geometry.This feature allows the composite tube to slightly expand under pressure, which is in turn immediately contained by the metallic outer structure. It also eliminates the metallic tubing producers concern that the tolerance interface conditions between inserting two tubes together without any machining as a practical impossibility.

A serendipitous side benefit is that now hydraulic cylinder manufacturers can use thin walled, low-grade tubing to
make this technology work. The metallic outer tubing does not have to be honed or plated. Because the composite inner tube does most of the pressure work; low cost aluminum tubing can now even become an option as well. The non-magnetic properties of aluminum also afford new possibilities for additional externally mounted andpre-existing positioning devices to be used. This tube insertion technology is creating new opportunities to attack a very mature market with many new possibilities.

To take this technology to a whole new level is the additional potential of relaying the sensing
signal, via existing asset management or control systems, to a centralized location via wireless access or
even satellite tracking. In real time Polygon can supply this new sensing cylinder technology for
construction OEM manufactures that might have the need for such interpretative data or situational
awareness such as a cylinder requiring maintenance for safety purposes.

The Case for Safety Catchers

Ken Davis, Business Development Manager, Advanced Machine & Engineering Co.

The Europeans have the answer to safeguarding hydraulic and pneumatic presses from catastrophic failure. The good news: now it’s available here in the U.S.

An ounce of prevention is worth a pound of cure…the old adage rings especially true for the thousands of press operators today trying to reduce their production costs and stay competitive with higher speeds, smaller batches and – keep your fingers crossed – greater machine uptime. The cost today for a catastrophic press failure? On the low end, certainly thousands of dollars in lost production time and die replacement costs. On the high end, the loss of a key operator due to injury or a customer that takes his business elsewhere rather than run the risk of falling behind schedule again.

Sure, today’s most modern hydraulic and pneumatic presses have a variety of OSHA mandated protection systems in place to ensure operator safety. Guards, interlocks, electro-sensitive and opto-electronic devices, emergency stop devices and other redundant systems have helped make presses safer in recent years. But when it comes to safeguarding the presses themselves from expensive damage to the press or dies, standards in the U.S. fall well short of their European CEN counterpart, which states in prEN 693 Machine tools Safety Hydraulic Presses: “Where there is a risk…from a gravity fall of the slide /ram a mechanical restraint device, e.g. a scotch, shall be provided to be inserted in the press…On presses with an opening stroke length of more than 500 mm and a depth of table of more than 800 mm, the device shall be permanently fixed and integrated with the press.” A similar CSA Standard (Z142-02) exists in Canada…

‘Faulty’ vs. ‘failsafe’. For most American press operators, however, a ratchet bar, locking bolt or latch is all that’s standing between them and a catastrophic crash should hydraulic or pneumatic pressure be lost suddenly or the lifting mechanism experience a mechanical breakage. When functioning properly, the ratchet system -- usually running the length of the press stroke-- does an adequate job of arresting the fall of the ram and preventing a catastrophic crash. A spring latch will automatically extend to engage the teeth of the ratchet at some point before a crash can occur. Unfortunately, the ratchet is a wear part that after hundreds, even thousands of press cycles can begin to exhibit signs of wear that are difficult to detect visually, and probably can’t be heard, by even the most experienced operator. Over time, the ratchet teeth, spring and latch typically begin to wear, since the spring latch makes contact with the teeth (but doesn’t engage) on the upstroke of the ram every time the ram is raised for the next part. The ratchet, and even the end of the spring latch, can wear to the point where a fall can’t be prevented.

In addition, locking bolts and latches often operate only at the top of the stroke, and ratchet bars at fixed interval positions. Consequently, the ram must often be retracted to its full stroke position each and every part, despite the fact that the part requires only a short opening stroke. This can add considerable, and very expensive, non-productive time to the cycle.

But in Europe, Canada and elsewhere in the world, most presses are equipped with a SITEMA Safety Catcher, which satisfies the requirements of CEN and CSA safety standards, foolproofs presses from a catastrophic crash, and allows the operator to optimize the stroke for any size part. The SITEMA Safety Catcher works a little like the ‘Chinese Finger Trap’ you probably played with as a child. You could easily put your finger in one end of the paper cylinder, but it was very difficult to retract it. In fact, the harder you pulled the more clamping power the simple paper cylinder seemed to exert on your finger. The SITEMA Safety Catcher works in similar fashion. If hydraulic or pneumatic system pressure fails, or if a rope, chain, belt or toothed drive breaks, the SITEMA Safety Catcher prevents the load from crashing down at any position of the descent. Better yet, the system is ‘self-intensifying’, so that as downward force increases, so too does the Safety Catcher’s clamping force.

Here’s how it works (see Fig. 2 and 3):

1) A cylinder rod is mounted to the top of the platen extending through the press crown and the Sitema safety catcher housing (Figure 2). The safety catcher housing is securely fixed to the machine crown / frame and surrounds the rod which is free to move during normal operation. Wedge shaped clamping jaws inside the housing are held with hydraulic or pneumatic pressure to keep the wedges in position so that the rod can move freely.

2) This Safety Catcher instantly becomes effective when hydraulic or pneumatic pressure is lost or released. A spring causes the clamping jaws to firmly contact the rod. As a result, any downward movement of the rod initiates the “self-intensification” feature securing the load.

3) Significantly, the energy of the falling or sinking load is used to apply additional clamping force if needed. In other words, ‘self-intensifying’ friction created between the clamping jaws and the cylinder rod draws the jaws into their maximum clamping position after only a few millimeters of movement.

4) If the load continues to increase, the Safety Catcher will continue to hold the rod in a fixed position until a pre-determined static holding force limit is exceeded – (approximately 3-4 times the retain force). Beyond that point, the Safety Catcher continues to safely hold the rod, with a braking action dissipating the kinetic energy of the falling mass while it continues to resist the downward movement of the platen.

5) Only when hydraulic or pneumatic pressure is restored in conjuction with the equivalent reverse movement of the rod are the clamping wedges released, making the SITEMA Safety Catcher inherently failsafe.


SITEMA is ‘catching on’ everywhere. From presses to large hydraulic elevators to stack loaders to machine tools – in almost any application where a large load is traveling and the potential for a catastrophic mechanical failure exists – SITEMA Safety Catchers have been applied successfully and in increasing numbers, as safety standards toughen around the world. They are available in a variety of sizes to meet most common press sizes, including the very largest. Most importantly, they are readily available today in the United States through Advanced Machine and Engineering Co.

About AME

AME is a global manufacturer and distributor of precision machine components, fluid power components, fixturing/workholding, power drawbar and spindle interface components, and saw machines and blades. The company also designs and builds special machines for a variety of industries, and provides machine rebuilding, retrofitting and contract manufacturing services. AME has partners and customers around the world and across the U.S. To learn more, visit www.ame.com.
Bob and Dan's "boring" adventure

Cutting two eight-mile subway tunnels through varying Santa Monica Mountain rock formations is a dirty business. But someone had to do it.
 
Construction & Tunneling Services, Inc. (CTS), Kent, WA, an established design engineer and supplier of mechanical excavation equipment for the construction and mining communities, has kept two tunnel boring machines (TBMs) over 25 years old in service with the help of Bosch Rexroth.

The two TBMs were used by specialty underground contractor Traylor Bros., Inc., of Evansville, Indiana, on the Red Line Metro project owned by the Los Angeles County Metropolitan Transport Authority.

The Red Line Metro project required the construction of two 12,500-meter subway tunnels traversing the Santa Monica Mountains near the famous Hollywood sign. The final tunnel was a cast-in-place concrete lining of 5.44-meter diameter, so the job required two tunnel boring machines with a bore diameter of 6.3 meters.

CTS had to engineer and remanufacture two existing TBMs, resizing them with new cutterheads and shields and adding a hydraulic drive, taking advantage of Bosch Rexroth's broad technical product line.

"Hydraulic components consisting of pumps, motors, and valves were integrated with custom gearing and specialty hydraulic cylinders to provide the bulk of the critical pieces that the tunnel machine requires to operate at its peak," said Dan Nowak, CTS president. "Our experience with this job reaffirmed what we have known from previous work with Bosch Rexroth - they make good products that fit in major areas of machinery design, they understand how these parts perform and where they should be applied for best results. I don't think you will find an operating tunnel machine that doesn't have a Bosch Rexroth part on it."

The job was not without surprises. The first reach of these tunnels traversed soft rock, then encountered a soil-like material, almost plastic in places. Other materials included squeezing shales, sandstones, conglomerates, and granodiorites.

"The opinion of both the operating contractor and the CTS staff at the end of the job was that without the variable speed features and the higher torque capacity offered by the Rexroth hydraulics, the project would not have had such a mechanical success," according to Nowak.

If you've got a mountain of dirt to uncover and an unyielding deadline to meet, talk to the people with big ideas and the brawn to back them up. Bosch Rexroth.

Bosch Rexroth Corporation
2315 City Line Road
Bethlehem, PA 18017-2131
Telephone (610) 694-8298
Fax (610) 694-8339
When Morrell Inc, Schuler Inc and Bosch Rexroth teamed up, they proved that global manufacturing of auto parts with local control in Michigan was the right path for helping the Big Three achieve more productivity.

The world's first crossbar transfer press, developed by Schuler AG, in the early 1990's, revolutionized auto parts stamping plants throughout the auto industry.

Today's compact crossbar transfer press is used not only for large unstable auto body panels, but also for production of mid-sized parts such as doors and engine hoods.

Through the use of a compact transfer press and the unique partnership of Morrell, Schuler and Bosch Rexroth, both Ford Motor Company and General Motors are able to produce new hoods and doors while improving productivity, design flexibility and a reduction in costs.

Critical to the success of this global-local team effort was the teams ability to meet the scrutiny of design engineers in Germany, while also providing local installation and testing in Auburn Hills, Michigan. Schuler was also able to work with a single rep for all technologies while supplying contact for everyone.

If you would like to forge an application engineering partnership, across technologies, continents, companies, Bosch Rexroth can help.