Increasing compressed air plant efficiency
Compressed air is one of the least efficient forms of energy that is used in modern manufacturing plants. It takes seven to eight times more electricity to produce one horsepower with compressed air than with an electric motor. Compressed air is often the largest end-use of electricity in a plant.
There are many actions a plant manager can take that will quickly and easily increase efficiency of their compressed air system and decrease compressed air energy usage by 20% or more. Here, I will discuss only one of these actions, that is, installation of a Dewpoint Demand Switching system for the heatless desiccant dryer (HDD). The HDD is typically a major use point of compressed air and some of these dryers will use up to 18% of the compressor capacity just to operate the dryer.
How does a desiccant dryer operate?
In order to understand how we can improve efficiency, we must first understand the basic operation of this type of dryer. The HDD operates to maintain the compressed air at a specified pressure dewpoint; usually 400 or 700C.
The dryer utilizes two vertical pressure vessels (sometimes called dual towerss) filled with a desiccant such as activated alumina, silica gel, or molecular sieve. The compressed air passes through the desiccant bed before being distributed to the plant.
As the air passes through the desiccant, water vapor is removed from the air through a process called adsorption. Adsorption is defined as the binding of molecules or particles to a surface. The binding to the surface is usually weak and reversible.
Regeneration consumes energy
As the compressed air is passing through one vessel where water vapor is being adsorbed, the desiccant in the other vessel is undergoing regeneration where the water vapor that was previously adsorbed is removed.
Regeneration is accomplished by extracting a portion of the dry air as it exits the active vessel, expanding this air to atmospheric pressure and passing it over the desiccant that is to be regenerated.
The air that is extracted as it exits the active vessel is called purge air. As the purge air is expanded to atmospheric pressure it becomes very dry and will easily separate the water vapor molecules from the desiccant beads causing the regeneration of the desiccant bed.
Purge air and the energy required to produce the extra compressed air to fulfill the regeneration requirement is the direct energy cost that is required to operate the heatless desiccant dryer.
A savvy plant manager can capitalize on energy savings by installing a Dewpoint Demand Switching system.
Switching based on worst case conditions
The cycle of the dryer refers to the time between switching from one tower to the other. A typical cycle time is some ten minutes. During this ten-minute cycle, the dryer will switch one time so that each tower is online for five minutes and regenerates for five minutes. The cycle time is determined by the manufacturer and will depend on the dewpoint that is specified and the amount of desiccant in the vessels. The cycle time and amount of desiccant is determined based on worst case conditions;
full rated air flow of the dryer, 35 C air temperature, 100% relative humidity, and 100 psig (7.9 bar) pressure. The dryer is constantly demanding purge air based on this design. For example, if a dryer is rated to provide a 40 C dewpoint at a maximum flow of 1000 cfm (28 m3/min) and requires 15% purge air, it means that the dryer will continuously consume 150 cfm (4 m3/min) of the output from the compressor, regardless of the actual conditions and actual compressed air flow. In this specific example, the purge air requirement is equivalent to running a 35 horsepower compressor just to
provide purge air to the dryer. With such a fixed cycle, the dryer will demand 150cfm (4 m3/min) purge air every minute of the day, regardless of the actual conditions and demand of the plant and regardless cassapaf the real capacity of the desiccant bed.
Dewpoint demand switching optimizes the cycle
As we know, it is rare that a plant operates in such a way that it requires 100% of the compressor/dryer capacity 24 hours a day, seven days a week. The demand for air will vary throughout the shift and from day-to-day, depending on shift and plant operation, etc. The inlet air conditions will also vary depending on the ambient temperature and relative humidity.
This is where a savvy plant manager can capitalize on energy savings by installing a Dewpoint Demand Switching (DDS) system. With a DDS system installed, rather than the towers switching every five minutes and demanding constant purge air, the towers switch based on the dewpoint temperature as measured at the outlet from the dryer. Savings can be made because the towers will not switch back and begin using purge air until the hygrometer senses a degrading dewpoint temperature.
The DDS system ensures the full use of the desiccant bed, increasing efficiency and thus reducing the use of purge air, which in turn reduces the use of electricity.
A DDS system consists of a hygrometer that can reliably measure the dewpoint of the compressed air as it exits the active tower, and which is also able to generate an output signal that can be detected by the dryer operating system.
Retrofit your dryer for DDS
Is it possible for an existing dryer to be retrofitted with a Dewpoint Demand Switching system? The answer is yes, as long as the dryer operating system allows for controlled tower switching. If you are not sure, consult the dryer manufacturer or read the operating manual.
Retrofitting a dryer with this type of system is relatively easy. The first step is to confirm that the dryer will accept a signal and operate the switching process based on that signal. The second step is to find the correct type of hygrometer that will operate accurately, provide a suitable output signal, is easy to install, offers low maintenance and is resistant to contamination. There are several different types on the market, each with different pros and cons, and it is important to know what questions to ask the manufacturer to ensure that you reap rewards and not headaches from installing a Dewpoint Demand Switching system.
Vaisala DRYCAP Dewpoint Transmitter technology is the reliable choice. The DMT142 and DMT242 transmitters are compact and rugged. The DMT340 series transmitters, with a variety of options, provide the user with a complete solution, and the hand-held DM70 is a practical tool for spot measurements.
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This Article is Courtesy of Vaisala
Vaisala Inc.
10-D Gill Street
Woburn, MA 01801, USA
Phone:1-888-VAISALA (824-7252)
+1 781 933 4500 International Calls
Fax:+1 781 933 8029
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Shakin all over...
Burkert pneumatics control pharmaceutical tablet production
Buck Systems, part of GEA Pharma Systems based in Birmingham UK is using Burkert to sub-contract supply pneumatic control systems for itts leading edge powder processing plant equipment used in one of the worldds largest and most advanced tablet manufacturing plants in the Far East.
Burkert Fluid Control Systems has designed and manufactured a complete pneumatic control system for vibrating pharmaceutical powder mixing and delivery systems. The control system is built around Burkertts innovative AirLINE pneumatic valve islands that allow a variety of digital and analogue I/O signals to be combined with Profibus DPV1 connection and external vendor PLCs. The complete panel systems are supplied fully built in stainless steel cabinets, tested and with a certificate of conformity.
Also supplied for this project Burkert Side Control, electro-pneumatic positioners are used to control patented double seated hygienic Buck butterfly valves used to control the flow of powder from large hoppers. The control units are mounted remotely from the process valve bodies and provide the rotary actuators with precise positional control signals, using an integral process controller (PID) and an external position sensor. They also provide a digital status display and manual programming override controls from an integral keypad.
The hoppers are vibrated to ensure a smooth powder flow and no stickingg to the sides, the control cabinets are isolated from the majority of the vibration equipment, but are exposed to some continuous vibration, and had to be designed to cope with this tough operating environment. The electro-pneumatic control panels contain a variety of ancillary equipment: filter regulators, pressure switches, and various DIN rail mounted terminals and Wago I/O blocks, all of which had to be firmly attached and tested. Weighing equipment and HMIs form Mettler Toledo were also integrated into the control cabinets along with Siemens PLCCs.
Neil Saunders, who oversaw the project from Burkert UK comments, We were given a precise working requirement for the control systems and were able to go away and design a complete solution, I believe this was the overriding factor in Burkert being selected to complete this project. Hygienic processing is a market space that Burkert is very comfortable in and represents a large part of our turnover globally. Both GEA Pharma Systems and its customer are corporate accounts of Burkert, and it was vital to the end customer that comprehensive engineering and technical support was available locally; this didnnt pose a problem for us as we have a substantial sales and support business in the Far East..
The control cabinet layout is extremely neat and rationalised, thanks mainly to the flexibility of the AirLINE valve island system. All the typical benefits of using a fieldbus system, DeviceNet in this instance, are gained by using AirLINE, it plugs directly into I/O modules, Wago in this case, and DIN rail mounted PLCs from the main vendors. This cuts down on wiring massively and ensures that we can talk to a wide variety of sensors, positional control feedback, HMIs and other equipment producing a variety of digital and analogue signals that can be brought into one place and integrated with the latest pneumatic valves. The islands also allowed for the control of air for actuation and piloting for the lower pressure, higher flow rate valves used to control the air that carries the powders around the system.
The AirLINE 8644 system overcomes plant standardisation and communication protocol issues by integrating Burkert high performance solenoid valves with analogue and digital I/O modules and fieldbus communications from all market-leading PLC vendors, including Siemens, Rockwell, WAGO, GE Fanuc, Bosch-Rexroth, Beckhoff, Phoenix Contact, WAGO and Hitachi.
Calculated to save up to 40% on total system costs through the engineering efficiencies achieved, the series 8644 provides users with a remote field I/O network which is compact, reliable and not exclusive to any specific communication protocol.
The remote process actuation and control system combines digital I/O, including a full complement of solenoid pilot valve outputs, digital and analogue I/O, including direct RTDs and T/Cs, and speciality signals (RS232, high speed counters, etc) into a single node. The system enables pneumatic solenoid valves to be electrically connected directly to a remote I/O module, without any individual coil wiring, numbering or termination required; each valve is simply a digital output addressed by the network. Depending upon the application, the system can incorporate up to 13 modules (2x and 8x module types), with a maximum of 64 valves accepted.
This GEA Pharma Systems - Buck Systems project has been an ongoing one, with final deliveries due at the end of 2008, the very first control cabinet units in this project were installed over two years ago and have performed perfectlyy from the outset. Strong evidence as to why the pharmaceutical industry trusts Burkert hygienic processing products and the systems it designs around them.
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Non-contact gripping protects fragile workpieces
Very thin objects such as solar cells or wafers pose the most stringent requirements when it comes to handling technology. Such substrates are very fragile and, with diameters of up to 300 mm, they have a thickness of merely 0.6 to 0.8 mm. The thickness of thin wafers can even be less than 100 m. Extremely sensitive objects can nevertheless be securely handled, as SCHUNK demonstrated at Automatica 2008 with a machine from its partner Zimmermann&Schilp Handhabungstechnik GmbH that was especially designed for trade show exhibitions. This involves a robot handling solar cells using a non-contact gripper. It picks up the eight-inch large, 160 m thick cells from a depositing unit and places them on the linear transfer unit where they can be further transported without any mechanical contact.
The working principle of the ultrasonic gripper used here is based on so-called "near-field levitation". This involves an ultrasonic generator being moved close to the workpiece and creating a pressure as a result of the cyclic compression and decompression of a thin film of air between the ultrasonic generator and the workpiece. The pressure protects the workpiece from direct mechanical contact.
To apply this reaction to the construction of grippers, air is simultaneously extracted through holes on the gripper face to create a vacuum. While the vacuum is holding the workpiece, the pressure created by ultrasonic waves in the layer of air prevents the workpiece from coming into contact with the gripper face. Equilibrium is created between the weight of the workpiece, the suction force of the vacuum, and the back pressure of the film of air, in which even the thinnest substrate can be safely held. The workpiece is gripped without friction, and yet securely, without the need for compressed air. The distance between the ultrasonic gripper and workpiece can be between 0.05 and 0.5 mm, and since there is neither friction nor particle contamination, the process is also suitable for use under clean-room conditions.
When the shape of the gripper corresponds to the shape of the component, a fluid-mechanical effect generates a centering force in the case of small components. This force makes it possible to have fast accelerations or to turn the gripper together with the component. When larger parts are to be handled, there are lateral stops that prevent the workpiece from slipping when the gripper moves. Since these stops are only in position to absorb lateral acceleration, there is only minimal mechanical clamping required for the component.
This process, which is generally suitable for all reverberant workpieces made from metal, plastics, or ceramics, can be used for constructing universal grippers and transfer tracks as well as for the non-contact stabilizing of workpieces with unstable forms. Such ultrasonic components are easily integrated into existing machines and can have different sensors added to them. By avoiding mechanical contact between component and workpiece, non-contact gripping reduces losses due to handling damage and leads to an increase in profits.
SCHUNK Inc.
211 Kitty Hawk Drive
Morrisville, NC 27560
Phone: 919.572.2705 or
800.772.4865
Fax: 919.572.2818
www.schunk.com
info@us.schunk.com
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Keep Your Compressed Air High And Dry
Proper selection and application of air dryers maintains system reliability and longevity.
By Rick Hand, Parker Hannifin Corp., and Mark White, Domnick Hunter Ltd.
Desiccant dryers remove liquid from compressed air systems through the use of chemical beds.
Most maintenance and production engineers would say that oil is the major contaminant in their compressed air system. Wrong. Nearly all of the total liquid contamination found in a compressed air system is water, with oil being a small part of the overall contamination problem. Filter systems can remove oil and dust, but dryers are required to remove water and adjust humidity.
How much water is actually in your compressed air system? The answer might surprise you. A small 100 cfm compressor and refrigeration dryer combination, operating for 4000 hours in typical northeastern U.S. climate conditions, can produce approximately 2200 gal of liquid condensate per year!
Failing to remove this moisture from a compressed air system can result in condensation in piping, pneumatic tools, and instruments, leading to damage and premature failure.
Water, water, everywhere
Simply put, atmospheric air contains water vapor. The air's ability to hold water vapor is dependent upon its temperature. As temperature increases, the level of water vapor held by the air increases.
During compression, air temperature is increased significantly, which allows the air to retain incoming moisture. It takes 7.8 ft3 of free air to generate 1 ft3 of compressed air at 100 psig. After the compression stage, air is typically cooled to a usable temperature, reducing the air's ability to retain water vapor. A proportion of the water vapor condenses into liquid water and is removed by a drain fitted to the compressor after-cooler.
Further condensation occurs as air is cooled by the air receiver, piping, and as it expands in valves, cylinders, tools, and machinery. Condensed water and water aerosols can cause corrosion to the storage and distribution system, as well as damage to production machinery and an application's end products. Liquid water can also wash away pre-lubricants on the cylinders and valves, decreasing their operational life. Water in a compressed air system also reduces production efficiency and increases maintenance costs.
Benefits from using dryers
Low-pressure dew points derived from implementing air dryers helps prevent corrosion and inhibits the growth of micro-organisms within the compressed air system. Corrosion causes rust and pipe scale that, over time, breaks away and causes damage or blockage in production equipment and, in some cases, can contaminate final product and processes. Moist air provides an ideal environment for the growth of micro-organisms. If only a few of these bacteria or viruses enter a sterile process or clean production system, damage may result, diminishing product quality or rendering a product unfit for use.
A few examples of pneumatic applications that benefit from the use of dryers in the compressed air system, from chemical processing to blow molding, include:
Paint spraying that requires the removal of water from the air to eliminate blemishes in the painted surface increasing quality at body shops and large auto plants alike
Folding and either taping or gluing cardboard boxes water could affect adhesives and/or damage the boxes
Semiconductor processes that populate circuit boards would be compromised if moisture reached component contacts
Chemical or pharmaceutical compound mixing must eliminate moisture to maintain batch integrity
Automated pharmaceutical dispensing operations must ensure that moisture doesn't contaminate drugs
Food industry processes must remove moisture that may contaminate the product
Blow molding as varied as making plastic bottles or camera lenses requires the removal of moisture.
The right dryer for the application
Selecting the right dryer requires a combination of evaluating technical factors with actual field experience. Factors include the type of system, size of connecting lines, water capacity, flow capacity (system size), filtration capability, construction materials (i.e., steel or copper), and safe working pressures.
Two common types of dryers are refrigeration and adsorption (desiccant). When choosing a dryer, a general rule is to first select a pressure dew point that meets the requirements of the application and is 155 to 200 below the plant's lowest ambient conditions. (A dryer's efficiency is measured as the dew point, which is the level of dryness in a compressed air system.)
Dew point determines the major difference for selecting either refrigeration dryers or desiccant models. Refrigeration dryers cool air to a pressure dew point of 355 F, which is the effective limit on this type of dryer, as water freezes at 322 F. This style is ideal for general industrial applications in light assembly, including those that use air motors, air tools, valves, cylinders and rotary actuators, and painting and welding equipment. When piping is installed in ambient temperatures below the dryer dew point (i.e., systems with outside piping), refrigeration dryers are not suitable.
Adsorption dryers pass air over a regenerative adsorbent material that strips moisture from the air. These types of dryers are extremely efficient and can provide a pressure dew point as low as -1000 F, with a typical range of -400 F. Desiccant dryers remove liquid from the compressed air system through the use of chemical beds. Three styles are commonly used:
Silica gel: Very good for water vapor removal and produces a dew point of approximately -400 F. Liquid water can damage this style.
Activated alumina: Very food for water removal and produces a dew point of approximately -400 F. This style provides strong resistance to liquid water.
Molecular sieve: This material is excellent for water vapor removal and can produce a dew point of -1000 F. Liquid water can easily damage this style.
It should be noted that refrigeration and adsorption dryers are designed to remove water vapor, not water in liquid form. They require the use of coalescing filters, installed in front of them in the compressed air system, to work efficiently. In fact, coalescing filters are probably the most important purification equipment in a compressed air system. They are designed to remove aerosols (droplets) of oil and water using mechanical filtration techniques.
Coalescing filters have the additional benefit of removing solid particles as small as 0.01 m. When filters are installed in pairs, most users believe one is an oil removal filter and the other is a particulate filter. Actually, the filters both perform the same function, with the first filter (a general-purpose filter) used to protect the second filter (a high efficiency filter) from bulk contamination. This dual filter installation ensures a continuous supply of high quality compressed air with low operational costs and minimal maintenance requirements.
Cost-effective system design
To achieve the stringent air quality levels required for today's production facilities, a careful approach to system design, commissioning, and operation must be employed. Air treatment at one point alone within a system is not enough; a system-wide approach should be taken. Compressed air should be treated prior to entering the distribution system to a quality level suitable for protecting air receivers and distribution piping. The size of piping should be considered as well. Many existing systems have piping that is too small, so it restricts air flow.
Our dryers are not the same
Products for the filtering and drying compressed air are often selected because of their initial lower purchase cost, with little regard for the air quality they provide or the cost of operation and maintenance throughout their life cycle. Dryer equipment with a low purchase price may turn out to be a costly investment in the long run. While initial purchase costs are important, air quality, energy efficiency, and lifetime costs are the real issues.
Poor air quality with too much moisture can damage components in the air system, as well as to end products costing a manufacturer in terms of both money and reputation. Quality air dryers also minimize pressure loss, a major contributor to operational costs, thus reducing energy consumption. And finally, quality air dryers last longer than lower priced models, reducing downtime and maintenance costs while contributing to increased output.
By improving air quality, lowering energy consumption, and minimizing maintenance, air dryers from leading providers can reduce the total cost of ownership and improve a manufacturer's bottom line through improved production efficiencies.
Rick Hand is with Parker Hannifin, Pneumatic Div., Richland, Mich., and Mark White is with Parker's Domnick Hunter Ltd., Tyne and Wear, England. Contact them at rhand@parker.com and mark.white@parker.com
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A new twist on pipingg
The standard black iron pipe is no longer the standard. It stands to reason that as many new innovations are developed to overcome obstacles and issues that it is only a matter of time until plant piping systems evolved. Although black iron piping has been the norm for many years it has caused many head aches for plant maintenance personnel. From installation that requires pipe fitters and special machinery to build each section piece by piece the task is both time consuming and difficult. Once installed, itts only a matter of time for the burrs and other contaminants to find there way into critical locations. This may be flaking particulate or cutting oils but whatever does make it down stream may cause some serious damage.
The main contenders to replace the black iron pipe are aluminum or composite piping.
Each have there value based on installation, environment and personal preference. Some may prefer the aluminum as itts an easier mental transition from black iron pipe but it too has limitations. Length of pipe and special machinery are still required to cut and smooth each piece to length and corrosion although minimal may still occur. Due to the limited lengths of the aluminum pipe it will be necessary to piece each length together with a fitting which not only requires additional time but also adds to an increasing leakage rate based on the size of the installation.
Composite piping systems have been used for some time but with pressure restrictions and safety code requirements hasnnt always been a viable choice. Until recent advances by which these materials have been re-engineered to meet such stringent safety codes as are required by ASME and OSHA these materials are slowly becoming the new standard. The composite piping systems are manufactured with two main materials, high impact ductile ABS (Acrylonitrile butadiene styrene) for larger diameters and HDPE (High-density polyethylene) for smaller diameters.
The latest, most interesting, product has been designed to have the HDPE encapsulate a flexible aluminum pipe essentially sandwiching the pipe between layers of composite HDPE. Commercially available from IPEX, the Duratec product line this product combines the best of all current options building on the flexibility and chemical prowess of HDPE with the strength of aluminum. Another distinct advantage this product has over aluminum, ABS or Black iron, for that matter, is the length of the material available. Coil lengths of 100 to 300 ft in length are available which not only decrease the time required to pipe a plant but also reduces leakage rates by not requiring an additional fitting every 8-12 feet.
When the final decision has to be made on what material will be used in a plant piping system the materials described above along with material cost and labour need to be considered. Some materials may work well and are relatively inexpensive but cost considerably more to install and maintain. Some average installation times are as follows:
Black Iron 6ft/hr
Aluminum 45ft/hour
High impact ductile ABS 45ft/hour
Duratec HDPE 100 ft/hour
The choice is definitely yours to make, each application is different and requires considerable planning and effort. But before a decision has been made consideration should be given to the latest materials and there capabilities. All decisions should be verified by a professional engineer to assure that all safety requirements have been considered.
Barry Chadwick, CET
Pneumatics Online
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E/P Positioner Success Story by Bosch Rexroth Pneumatics
Mixing It Up:
Rexroth Electro-Pneumatic Positioner Helps RMC Pacific Materials Combine Aggregates While Controlling Gates
By Bob Atchison, Bosch Rexroth Pneumatics District Sales Manager and Certified Fluid Power Specialist
Manufacturing five different types of cement to meet various building requirements, RMC Pacific Materials, headquartered in Pleasanton, CA, is a key supplier in the building materials industry. Aggregate (sand and gravel), a main ingredient in concrete, is used in RMC's ready-mix operation and marketed to other ready-mix concrete producers and manufacturers of products such as concrete block, interlocking pavers and lightweight roofing tiles. These building products have been used in such high-profile projects as the San Francisco Giantss Pacific Bell Stadium and the Monterey Bay Aquarium.
Recently, with the help of Randy Mull, a professional engineer with Eichleay Engineers, Inc., a Concord, CA-based full-service design and services firm specializing in the life sciences and high-tech markets, distributor Motion Industries and Bob Atchison of the Pneumatics business unit of Bosch Rexroth Corporation, RMC automated its aggregate mixing operations at two of its California plants: RMC Pacific Materials in Pleasanton and Harbor Sand and Gravel in Redwood City. Using Rexroth electro-pneumatic, or E/P, positioners, RMC is now able to monitor and control gate positions and protect its mixing lines from overfeeding in case of power failure or malfunction.
Fail-Safe Solution
The basic process of aggregate mixing begins with mined aggregate which is washed, crushed and segregated into various components according to size. These components are then recombined according to ASTM specifications to create products used in making concrete, asphalt and aggregate. The mixing processes at each of the RMC locations employ Rexroth E/P positioners to open and close the gates that discharge material directly onto conveyor belts, which transport the material to predefined locations within the plants. Depending on the material being produced, from one to four different gates can be opened to blend ingredients.
This is the first time this type of automation has been used in aggregate mixing,, notes Bosch Rexrothhs Atchison. Once we tackled the size issue we needed a five-inch bore, which was a larger unit than we generally offer the main challenge was the unit had to be fail-safee in the extended position..
At RMCCs Harbor Sand and Gravel plant, the E/P positioner opens and closes a gate to control the amount of material released onto a conveyor to maximize the tonnage being transported without overloading the system. Feedback from a belt scale downstream opens or closes the gate controlled by the E/P positioner to maintain a tons-per-hour flow set by the operator. Once the E/P positioner is given a set point by a PLC, it moves the gate to the given position and then monitors the position, making adjustments as necessary. Feedback information from the E/P positioner is monitored by the PLC and alerts the operator in the event of a malfunction.
Quality control samples are taken daily, and the results are used to fine-tune positioner settings,, notes Richard Butchh Kelly, project and resource manager for RMCCs Aggregate Division. These are then periodically updated to make a more consistent blend, with fewer operator adjustments. Also, less out-of-specc material means less re-work and less re-purchasing of unsatisfactory material..
Tony Fuentes of RMCCs quality control department agrees with Kelly that the automated positioners have improved the reliability of the aggregate products made through the load-out system.
We have noticed a marked improvement in our operating band, and we have tightened our operating ranges on several products,, says Fuentes. The new system has taken a lot of the guesswork out of the gate positions, and one of the biggest benefits is that we can make changes with little or no effect to our product or operating parameters. We can also offer custom blends with more accuracy, which is a huge benefit for special projects..
According to Eichleayys Mull the E/P positioners replaced existing air cylinders at each aggregate mixing location, making installation easier and less expensive since air was already available. A push-button station was already being used to interface with the existing air cylinders, so it was a relatively simple task to integrate the new cylinders into the system while the plant maintained normal day-to-day operations.
Without the positioner,, says Mull, additional I/O slots from the PLC would have been required to open and close solenoids on the cylinder to maintain the set point..
Whatts more, the size of the cylinders was big enough to stop the flow of material when closing, move the gates and control the flow of material. Typically, the actuators default to the retracted position upon signal failure, or stay where last commanded upon total loss of power.
We needed to reverse this operation because the gate closed only when the cylinder was extended,, explains Atchison. We couldnnt risk leaving the chute gate even partially open, as the silo could completely empty on a stalled conveyor and create a costly clean-up operation..
By reversing signal wires and plumbing lines, adjusting command signals accordingly and adding a normally open 3/2 valve, which overrides the pilot pressure to the directional valve that extends the cylinder, the team was able to achieve the desired effect. The system is also equipped with an air reservoir to allow cylinder actuation even after a power failure stops the air compressors.
The E/P positioner was the only device on the market that could provide feedback on its actual position after it had been told to go to a particular position,, says Mull. In this way, we could send a signal to the positioner telling it the position we wanted it to go to, and then look at the return date to verify that the gate in fact moved and was in the correct position..
Power failures occur an average of three to four times per year at the plant. In the past, each time the power failed, the cylinders remained in their last position, as the solenoids were electrically actuated. This allowed the contents of the bunker to spill onto the stopped conveyor belt, burying the belt and requiring several hours of cleanup before the belt could be restarted.
By developing a fail-safe strategy, the cylinders are set up to fully extend in the event of power failure,, describes Mull. Upon power failure, any residual air pressure in the lines is used to extend any open cylinders to their fully extended position, thus closing any open gates and eliminating the associated spills and cleanup..
Atchison noted that E/P positioner technology can be used with any application in which discharge of material onto a conveyor must be metered to accurately monitor flow.
In addition to being a very cost-effective solution, it can handle very extreme external conditions such as dirt, dust, water or other liquid or solid contamination. The cylinder and valves used in this system are designed to withstand these elements. The control card is the only part of the system that must be in an enclosure, but it doesnnt necessarily need to be located at the cylinder; it can be several feet away and still function as well,, he adds.
The Rexroth E/P positioner provides strokes available in any length, from one inch to 10 inches, or in two-inch increments between 10-inch and 18-inch strokes. Strokes up to 600 can be special ordered (as in this case.) The positionerrs accuracy is +/- .050 inch or one percent full stroke, whichever is greater; and its repeatability is +/- .050 inch. Stroking speeds range from .5 inch/second to 2 inches/second, and operating temperatures range from 41 degrees F to 122 degrees F. The unitts feedback device is an internally mounted linear potentiometer for applications in which infinite positioning requirements allow electrical analog control signals. The positioner interfaces with a computer, PLC or simple potentiometer (in this case a PLC) and comprises a cylinder with an integral sensor, optimized valving and an electronic controller. The basic concept involves a cylinder with integral feedback potentiometer in conjunction with a controller and matched solenoid valves.
The Pleasanton plant has been using the Rexroth E/P positioner for approximately four years, introducing the positioners in an aggregate blending application about two years ago where units are used to divert the effluent from a rock crusher onto two conveyors.
Since then, it has been bombarded with gravel, sand, dirt and water and harsh air quality, yet the unit has functioned daily with only minimal maintenance requireddan important factor in the selection of this technology. In the final project, 25 units were installed at the Pleasanton plant, and the Redwood City facility is currently in test operation with one unit at each plant.
Summarizes Kelly: Ultimately, the positioners have helped improve the quality and reduce the cost of material being shipped to our customer, which allows RMC to remain very competitive in the marketplace..
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Norgren delivers peace of mind
Faced with sticking valves in a hazardous environment, Woodside Energy in Australia turned to Norgren and were rewarded with peace of mind and the correct solenoid valves for a demanding safety system application.
Woodside Energy in Australia is a leading company in the exploration, development and production of oil and natural gas resources. Their successful major development of the North West Shelf Project places them as a substantial supplier of energy with further large potential for growth in the home and Asian export energy markets. At their 200 hectares LNG (liquid natural gas) processing plant at the Burrup Peninsula, in the inhospitable north of Western Australia, they are expanding the plant with its fourth LNG production train. With an initial commitment of $2.4 billion the fourth production train is approaching completion and will be the largest single LNG production train in the world. Its output will add a further 4 million tonnes of LNG production each year. Future commitment of $7.8 billion is expected for expansion of onshore processing and pipelines.
Within a LNG processing plant there are many large process valves that use pneumatically controlled actuators to open and close them. For the safety shutdown system, it is imperative that operation of key process valves and their systems are totally reliable in their shut off action. Pneumatic solenoid valves are used to control the large process valvess actuators. These solenoid valves are likely to be located in harsh and hazardous environments, where there is an explosive atmosphere risk. It is hot, often in excess of 40O in the shade and dusty.
Briefed with the facts, the technical applications experts at Norgren were able to quickly specify a solenoid valve from the Herion range, series 24011, fitted with an EEx me II explosion proof coil and designed for operation in these extreme conditions. In co-operation with Woodside the Norgren engineers were further involved with the design of mounting hardware to allow direct replacement of the installed solenoid valves. From the initial resulting order of 55 pieces, the valves have successfully proven themselves over the past few years. Further orders have now been received for new plant, underlining the confidence afforded by accurate selection and quality manufacture. The Herion 24011 series valve from Norgren is now specified as a site standard.
From a comprehensive range of process control valves from Norgren, the 24011 series is a direct solenoid actuated 3/2 poppet valve. With an orifice size of 5mm diameter excellent flow is assured. Solenoid coils are available in a choice of voltages and protection classes. Suitable for outdoor installation. The body selected for Woodside is constructed of 316 Stainless Steel, although the valve is available in many options. Internal parts include a stainless steel spring for corrosion protection and long life .A version with a NAMUR interface is an ideal choice for direct mounting to compatible actuators. For use with compressed air or aggressive gaseous and liquid fluids from 0 to 10 bar, the valve is truly wide ranging in application.
Norgren.com
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Recipe for Success for Plastics Processing Applications
Short cycle times and reliable, high repeatability are top requirements of manufacturers of plastics processing machines. Bosch Rexroth meets this requirement with the SY.DFE, an electro-hydraulic closed-loop control system with 100,000 units installed worldwide. The SY.DFE uses a variable displacement axial piston pump for controlling pressure, displacement and power without throttling losses in the power branch.
The SY.DFE provides the ultimate in hydraulic energy efficiency, electronically controlling both flow and pressure with exceptional speed and precision. A proven combination of a variable displacement axial piston pump of swashplate design and innovative proportional control electronics, the SY.DFE provides efficient, reliable controlling of the pump.
The SY.DFE was launched at the plastics processing trade fair in DDsseldorf in 1989, and with 100,000 units installed, it demonstrates the exceptional value it has provided in multiple plastics processing applications since its debut. Primarily used in injection molding machines, the system is based on a Rexroth A10VSO or A4VSO axial piston pump. By adjusting the pumpps swashplate, flow and pressure can be infinitely varied, and the required flow and pressure can be generated fast and accurately for specific machine functions.
In addition, functional sequences in an injection-molding machine can be precisely controlled with the help of the SY.DFE. The flow control works without pressure losses in the power branch, which significantly increases the hydraulic efficiency within the machine. Moreover, the total efficiency of the machine is increased due to the high repeatability of the control.
Rexroth offers this system in three versions: SYDFE1 with external closed-loop control electronics, the SYDFEE, with analog, integrated functions, and the SYDFEC, which offers integrated, digital closed-loop control electronics and the optional field bus controlling via CAN, so that users in the plastics processing industry can benefit from a proven plug-and-play system.
Bosch Rexroth Canada is the Canadian partner company of Bosch Rexroth AG, the worldwide leader in Drive & Controll. Under the brand name of Rexroth the company supplies more than 500,000 customers with tailored solutions for driving, controlling and moving machinery used in industrial and factory automation as well as in mobile applications. As The Drive & Control Company, Bosch Rexroth develops, produces and sells components and systems in more than 80 countries. In 2006 the company of the Bosch Group achieved sales of approximately 4.9 billion Euro with more than 29,800 employees.
Company Information:
Bosch Rexroth Canada
Ontario, CANADA
www.boschrexroth.ca
info@boschrexroth.ca
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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 itts available here in the U.S.
An ounce of prevention is worth a pound of cureethe 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, todays 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 riskkfrom a gravity fall of the slide /ram a mechanical restraint device, e.g. a scotch, shall be provided to be inserted in the presssOn 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. failsafee. For most American press operators, however, a ratchet bar, locking bolt or latch is all thatts 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 cannt 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 doesnnt 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 cannt 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 Trapp 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-intensifyingg, so that as downward force increases, so too does the Safety Catcherrs clamping force.
Herees 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-intensificationn 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-intensifyingg 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 onn 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.
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