Pneumatics Gets Lumber Mills Rolling
In the lumber industry, productivity demands are staggering; output is often measured in lugs per minute, a unit that describes how quickly a machine can process logs and boards. OEMs and timber-processing end users also need machines that can withstand harsh mill problems where temperatures fluctuate, dust damages equipment, and vibrations stress and grate machinery.
Traditionally, heavy-duty steel pneumatic cylinders were the only long-lasting hardware used in lumber production. However, over the past few years, pneumatic solutions combined with lighter and less expensive aluminum have improved sawmill production.
Mills resisted using aluminum because failure of aluminum pneumatic cylinders was common on equipment such as trim saws, where high speed and shock overstressed the units. Even though aluminum cylinders are less expensive than steel, the steep cost of downtime made sawmill operators question their use. Downtime in a mill is about $1,000 an hour, says lumber industry consultant Bill Bowlin. So if a trimmer stops for some reason, the whole mill stops because all the boards have to pass through the trimmer to get out of the mill.
Now, a new combination of pneumatics, aluminum, and ideal cushioning increases cylinder longevity and performance. The latter is a solution developed by Bosch Rexroth Corp., Lexington, Ky., that gently decelerates the pneumatic piston as it reaches end of stroke inside the cylinder to eliminate bounce and end-cap slamming, two main culprits of cylinder wear.
It is particularly useful for eliminating excess piston movement and bounce on quickly cycling, highly kinetic sawmills, especially in trim saws where pneumatic cylinders constantly drive blades up and down. Piston velocity at its maximum speed throughout the stroke sequence is exactly zero when it reaches the end cap. Vibration and noise are reduced and cycle time is improved, boosting machine speed as much as 30%. Cylinders with ideal cushioning are also lighter to further improve acceleration and cycle times.
Advanced Sawmill Machinery Equipment Inc. (ASM), Holt, Fla., worked with Bosch Rexroth to incorporate aluminum cylinders with ideal cushioning in its Series 140 Trimmer. The machine builder wanted to offer faster cycle rates and more durability.
ASM president David Seffens says the cylinders make their high-speed trimmer competitive and play a big role in opening up the 140 to 200 lugs-per-minute market for ASM. Seffens also notes that all the saw ladder surfaces on the Series 140 Trimmers are machined, keyed, and require no alignment by the customer. With the aluminum cylinders, each machine is customized for speed at the request of the end user.
Posted at 09:46AM Jan 25, 2010 Read More... by Rebecca in pneumatic |
12 Steps to Troubleshooting Pneumatic Systems
Troubleshooting a pneumatic system has been considered an art, a science, or just hit-or-miss luck. In the minds of maintenance personnel, production managers, and plant managers, the word troubleshooting conjures up images of hours of downtime and lost production.
However, when reduced to its basic elements, troubleshooting a pneumatic system is a step-by-step procedure. Using this process can speed up the ability to determine what the problem is, the probable cause of the malfunction or failure, and a solution.
Every pneumatic circuit has a logical sequence of operation that can involve timing logic, pressure sensing, position sensing, and speed regulation. Troubleshooting is initiated when the circuit does not operate properly.
Certain general diagnostic and testing steps can be applied to any troubleshooting problem, whether the problem occurred at startup of a new system or at a breakdown of an existing system.
Think safety first
Safety should always be a prime concern of maintenance personal. Compressed air is a volatile element in a pneumatic circuit. Air receiver tanks have exploded, causing severe injury to personnel and damage to property. It is imperative to relieve pressure in a receiver tank prior to making any repairs.
Air is also highly compressible, which is another reason to be cautious in the approach to troubleshooting a pneumatic system. When working with overhead loads that are supported by cylinders, but not mechanically locked into position, block the load before servicing the system to prevent falling or drifting.
Many pneumatic systems are controlled by electrical or electronic devices. Before attempting service or repair on these components, be sure the electrical power supply has been turned off.
Pneumatic directional control valves that use electrical solenoids to operate the valve spool are often equipped with manual overrides (Fig. 1) that can be used during troubleshooting to operate the system.
Pneumatic lockout valves (Fig. 2) are excellent safety devices that, when used properly on pneumatic systems, can prevent accidental operation. Ensuring a safe condition should always be the first step in troubleshooting pneumatic systems.
Ask the three Ws
When a breakdown in the system occurs, the pressures of downtime loom large in the minds of all concerned. Before beginning repair of a system, stop and ask these three questions:
What is or is not occurring in the system's operation?
When did the problem begin? Was it a sudden failure or a gradual failure?
Where in the machine cycle does the problem occur? Was it at startup or after the system has been operating for a while?
What is or is not occurring in the system can often be answered by the system operator. Answers to questions such as slow actuator speed or inability of the actuator to move could lead to looking for a low flow rate or low pressure.
Asking, "When did the problem begin?' can often lead to troubleshooting steps looking for worn components or leaks. Sudden malfunctions can point to breaks and possible mechanical problems, ruptures in lines, or other catastrophic failures. By determining the when, the problem search can be narrowed in its scope.
Asking, "Where in the machine cycle does the problem occur?" can reveal a reoccurring condition.
If good maintenance records have been kept, reoccurring problems should have been recorded. This information makes the troubleshooting process much easier.
A maintenance person who stops and asks the three Ws can reduce downtime by not having to guess at what is wrong. However, if these questions do not yield a satisfactory diagnosis the maintenance person must begin the mechanics of troubleshooting by visually inspecting the machine.
Make a visual inspection
Walking around the machine will often uncover problems such as worn or burst hoses, loose components, and broken components. This is the time to become familiar with the components contained in the pneumatic system.
If unfamiliar with the components, or if unfamiliar with the machine operation, ask as many pertinent questions about the system as possible. Before trying to operate the system or attempt repairs, understand the interrelations of all the components and the sub-systems found on the machine.
Read the schematics
Every pneumatic system should have two forms of documentation that will assist in troubleshooting. One document is a schematic drawing of the pneumatic circuit (Fig. 3). The schematic is a road map. It not only explains the operating function of the components but also is a valuable diagnostic tool.
The schematic contains useful information about pressure test point locations; pressure settings of regulators and other pressure valves; flow rates within the system; cylinder stroke lengths, and air motor speeds as well as a bill of materials for the system. This type of information can aid in determining if the system is operating within its design parameters.
Along with schematics supplied by the manufacturer, another set of documents, the service/maintenance manual and its service bulletin updates, may be available to assist in the diagnosis and repair of the machine. These may contain information about the problem that has occurred.
Operate the machine
After becoming familiar with the components and operation of the pneumatic system, start the machine and operate it to get a first-hand view of the malfunction. See if the malfunction that has been reported occurs again. While operating the machine, perform a visual inspection.
Some questions to ask during the inspection:
Is there any excessive air leakage?
Are system pressures at the levels specified on the schematic or in the maintenance manual?
If there are manual controls for the machine, do they feel stiff or loose in their operation?
Are components that move, moving smoothly or erratically?
By operating the machine, any abnormalities may become obvious, shortening troubleshooting time.
Recheck all services
Before attempting repair on the machine after it has been operated, once again check to see if power supplied to the machine has been turned off. Check to see if any stored pressure remains in the system, because this stored pressure can cause premature actuation of the system's actuators and cause injury to personnel and damage to the machine.
Isolate subsystems
A malfunction in one part of the machine can be caused by a malfunction in a different subsystem on the machine. Isolating the subsystems, can help focus on one system at a time. Narrowing the diagnostic area by isolation of subsystems requires extra precaution while operating the machine.
Any lines that have been disconnected and any ports that have been opened should be plugged properly to prevent unnecessary air leakage and the entrance of contaminants.
While operating the machine, a close watch should be kept on the pressures within the system, so maximum allowable pressures are not exceeded. Caution and safety are the two keys to this diagnostic step.
Make a list
During the previous step, the immediate problem may be quite obvious. However, in troubleshooting, the obvious may not be the root cause.
As an example, the obvious problem may be slow actuator speed but the root cause of the problem could be insufficient lubrication, no lubrication due to a faulty lubricator (Fig. 4), or bad seals within the directional control valve that controls the actuator.
After making a list of possible causes, check those items on the list and eliminate them without going back over ground previously covered. This list will also reduce the time required for troubleshooting and can eliminate the parts exchanging syndrome that often accompanies troubleshooting.
The example of slow actuator speed shows why a thorough understanding of component and system operating principles is required to accurately match the problem to the cause.
After making a list and narrowing the possible causes, it is now time to make a decision on which one of the remaining causes is most likely to be the reason for the malfunction. Reaching this conclusion may, at first, appear difficult but this step is essentially the starting point for the repair portion of troubleshooting. Up to now the system has been evaluated, now it is time to test the conclusion.
In the example, testing the conclusion may be merely the need to add lubricant to the lubricator or make an adjustment to the drip rate of the lubricator.
Conducting various tests such as pressure checks with an accurate gauge, checking actuator alignment, checking flow rate in the system with a flow meter, or temperature checking of the air system, can further reduce the number of causes remaining on the list and accurately pinpoint the cause.
Repair or replace
Testing the conclusion automatically leads to deciding whether to repair or replace a component. Many factors can influence this step. Repairing parts immediately for reinstallation on the machine increases downtime, and the cost factor of this downtime is a significant consideration.
To simply replace the part with a new or rebuilt component would reduce the amount of downtime; however, the question of inventory cost now becomes a factor.
Another point that may influence the repair-or-replace question is component availability. Obviously if the component is not readily available, then repairing may be the only alternative. Still another aspect may be the inhouse capability to make repairs.
After the malfunction has been corrected, one final step remains, the need to report the findings.
Report what you did
Paperwork is often neglected, but in the case of pneumatic troubleshooting it is a vital part of the procedure. This paperwork helps to maintain a record of changes, problems, and solutions that have occurred to individual machines.Pneumatic updates are necessary to keep this diagnostic tool current and accurate. Report making also serves as a good reference should any problems reoccur in the future.
Posted at 11:00AM Jan 21, 2010 Read More... by Rebecca in pneumatic |
Pneumatic Actuator Accessories Direct Mount To Namur Standards
Pneumatic Actuators are available with full line of accessories. The 4- and 3-way solenoid valves provide electrical operation of on-off functions, while pneumatic positioners automatically position output shaft to valve angles between 0-90[degrees].
Electro-pneumatic positioners offer direct or reverse operating modes. Valve status monitor signals actuator and valve position to local and remote stations. Proximity position indicator provides 2 inductive proximity switches in sealed enclosure.
Houston, TX-Augst 12, 2004-Ultraflo has introduced new accessories for their complete line of pneumatic actuators. New accessories include 4 and 3-way solenoid valves, pneumatic positioners, electro-pneumatic positioners, valve status monitor and proximity position indicator. All pneumatic actuator accessories from Ultraflo mount directly to Ultraflo pneumatic actuators and comply with NAMUR recommendations (VDI/VDE 3845) as standard.
4 and 3-way solenoid valves provide electrical operation of pneumatic actuator on-off functions. 4-way solenoids are direct mounted to the actuator by a NAMUR interface, with no external tubing required. Both waterproof (NEMA 4) and explosion proof (NEMA 4,7,9) housings are standard. NPT and IP65 DIN connections are offered with both single and dual coils. The air supply connection is 1/4" NPT and the electrical connection is 1/2" NPT. A manual override is located on the top of the valve body. A 3-way solenoid is also available.
Modular pneumatic positioners automatically position the output shaft to precise valve angles between 0[degrees] and 90[degrees] with a standard positioner input signal of 3-15 psi. They function with double acting or spring return actuators and feature selectable speed control, fast and accurate calibration, 2 NPT conduit entries, reversible and split range functions. Waterproof and intrinsically safe housings are available.
Electro-pneumatic positioners feature a modular design that allow actuators and accessories to be freely combined. For use with either double or single acting actuators, they provide direct or reverse.
Pneumatic actuators are selected by their ability to do work and the most common factor that limits productivity is using an undersized actuator. Follow these tips to select the right actuator for the job:
* Determine the force
* Subtract the piston rod area, if applicable
* Know the true operating pressure
Pneumatic actuators are available in a variety of shapes, sizes, and types, as well as with a multitude of standard options. At first glance, the number of permutations can be overwhelming. The good news is that each actuator type and configuration has a place in today's automation environment.
Posted at 02:56PM Jan 20, 2010 Read More... by Rebecca in pneumatic |
Pneumatic or servo? Choosing the right gripper for your automated laboratory process
The demand for speed to market requires that drug discovery, biotechnology and clinical diagnostics labs work faster, more accurately and more efficiently than in the past. Increasingly, lab technicians and scientists seeking greater levels of automation are turning to gripper solutions that mechanize what have traditionally been manual and mundane tasks, allowing them to work on more value-added activities.
Currently, a wide variety of pneumatic and servo grippers are available, each with its own set of unique attributes. It is critical that manufacturers select the appropriate gripper for their process. By understanding the specific advantages of servo and pneumatic grippers, life scientists can make smarter choices in selecting the best tool for any given application--as well as maximize the benefits in accelerated research and development processes, reduced human error, increased volumes of sample tracking and improved sterile conditions.
The majority of grippers utilized by manufacturers today are pneumatic grippers. These low-cost end-of-arm tools are cost effective and have the ability to produce and maintain considerably more force than servo grippers. While more expensive, servo grippers are necessary when more control is required for more delicate and complex assembly and handling applications.
Servo grippers, with their human-hand-like design, offer greater degrees of freedom and are appropriate for many medical applications. With the added expense of servo grippers, manufacturers need to carefully analyze their needs in order to make an educated decision on which gripper to design into their workcell. Applied Robotics, Inc., a global supplier of end-of-arm tooling solutions, conducted a thorough comparative analysis and has formulated the following application questions based on flexibility, control and environmental requirements to help manufacturers make that decision.
Posted at 03:56PM Jan 19, 2010 Read More... by Rebecca in pneumatic |
