Tiny isolators solve frame stiffness problem

Dayton, OH--Engineers who build vibrating machinery often employ air springs in their designs. Because air springs have extremely low natural frequencies, they enable engineers to reduce the natural frequencies of vibrating systems.

But when Dean Blake of Quest Engineering set out to design a vibrating V-trough conveyor for a Pillsbury plant in Martel, OH, air springs were not available for his particular application. The reason: The V-trough conveyor, which vibrates food bags while they move over a distance of five feet, was only 12 inches off the floor. "To obtain the proper natural frequency, I knew that we needed an air mount," Blake says. "Unfortunately, the package size was too confining for ordinary air mounts."

Now, however, that's changing. As Blake learned, Firestone Industrial Products' new 2M2A air spring, also known as the Microactuator, solves such problems. The unit, which operates off pressures ranging from zero to 100 psi, can measure as little as 1.2 inches high and 2.2 inches in diameter. Designed for actuation and isolation applications in tight spaces, it has a stroke of about one inch.

The technical challenge to building such a small air spring was the curing process, say Firestone engineers. Conventional rubber air springs are cured in a press by employing an air and steam media. That enables the layers of rubber to bond together and perform as a single unit. For the Microactuator, Firestone engineers developed a proprietary new curing process. "We couldn't use the standard curing process for this size air spring," notes Brian Hoaglan, an applications engineer for Firestone. "So we developed a unique one based on the methods used on some of our earlier air spring styles."

The Microactuator played a key role in the design of the V-trough conveyor system for two reasons: First, it was small enough to fit the packaging constraints of the conveyor; second, it provided a low enough system natural frequency for the conveyor frame.

To meet the stiffness constraints, Blake designed the conveyor frame to be at least ten times as stiff as the vibratory frequency needed to settle the contents of food bags travelling along the conveyor. That meant that with a peak driving frequency of 58 Hz, the vibrating frame needed a frequency of at least 580 Hz.

Blake says that he considered other types of isolators, such as coil springs and elastomers, but only air springs could provide the necessary design reliability. "They offered low noise and low natural frequency," Blake says. "All the vibration energy was transmitted to the product and very little to the support frame."

The air isolators, he says, are ideal for vibratory applications. "The key to success for this vibrating system was that it had to have a low natural frequency," he says. "That required an Airmount isolator."

Additional details, Microactuator...Contact Brian Hoaglan, Firestone Industrial Products Co., 701 Congressional Blvd., Carmel, IN 46032, (317) 580-2300.

Additional details, vibrating conveyor equipment...Walter Dean Blake, Quest Engineering, 2325 Wrencroft Circle, Dayton, OH 45459, (937) 435-0500.

Pneumatic valve softens blow of sudden pressurization

Slow start feature is volume independent

by Charles J. Murray Senior Regional Editor

Englewood, CO--When turning on a delicate pneumatic instrument, it's best to start slowly, letting air in at a gradual rate before reaching full pressure. Problem is, many slow-start valves don't do that. They let air in slowly at the outset--reaching about 40 to 50% of line pressure--then they slam all the way open. Such harsh operation can damage valuable equipment. Worse, it can be a safety hazard in some applications.

Now, however, there's a better way. Engineers at the Wilkerson Corp. have developed a slow-start pneumatic valve that employs a gradual opening technique all the way to 100% of line pressure.

Key to the valve's operation is a design that allows it to be pressure dependent, rather than volume dependent. To accomplish this design objective, the slow-start portion of the valve employs a specially designed control volume and a pair of opposing pistons. During operation, air enters the system, causing pressure to build in the control volume. As that pressure builds, it pushes down on the uppermost of the two pistons. As a result, the unit's main valve opens, allowing air pressure into the outlet.

As pressure builds on the outlet side, however, it is channeled back to the lower piston, which tries to close the main valve. The resulting give-and-take between the two pistons accounts for the slow-start effect of the valve. "It's a balanc-ing act," explains Frank Bohenick, the Wilkerson engineer who de-signed the patent-pending system. "Pressures on the two pistons balance each other out until the valve is fully open."

The unit is designed such that the pressure on the upper piston ultimately overcomes the lower, and the valve fully opens. Full opening does not occur, however, until the unit reaches 100% of line pressure.

Operating in this way, the valve's performance is always independent of the application air volume. That's a critical distinction, because conventional slow-start valves typically are volume dependent. As a result, a change in the air volume on the downstream side of a conventional valve (caused by adding a new pneumatic application) changes the performance of the unit. But volume independence changes all that. "It really doesn't matter what you have downstream of the valve," Bohenick says. "You could have an open line downstream, or you could have a tiny air cylinder down there, and it will always pressurize at the same rate."

Wilkerson employs the feature on its E18/E28 Emergency Stop Valves. The unit can be used in a wide variety of applications, ranging from delicate instruments to those with safety-related needs. "It's helpful to the equipment and to the people using it," Bohenick says. "No matter what the situation is, it always opens slowly."

Additional details...Contact Randy Greenwood, Wilkerson Corp., 1201 W. Mansfield Ave., Englewood, CO 80110, (303) 761-7601.

Rapid Response quickly delivers custom fittings

by Charles J. Murray Senior Regional Editor

Cleveland--When engineers build a hydraulically based machine or a vehicle, they often run into connector-related dilemmas. Sometimes, to reach from one point to another, they must stack three or four special fittings. If they have eight or ten weeks, they can contact a specialist who builds custom fittings. If they don't have that much time, they usually must make due with a conglomeration of off-the-shelf products.

Now, however, there's another way. Parker Hannifin Corporation's Fluid Connectors Group offers a service that designs, builds and ships special fittings, sometimes as quickly as 24 hours. Known as Rapid Response, the service provides single custom fittings or larger volumes, which usually require slightly more time.

Key to the company's capabilities is a multiple-spindle, microprocessor-controlled CNC manufacturing technology that enables Parker Hannifin engineers to quickly set up for virtually any kind of fitting. Because the machine uses no cams, set-up can be as much as 20 times faster than for conventional machinery. "Most machines have cams," notes Don Smrekar, vice president of manufacturing technology for Parker Hannifin. "On those machines it can take 20 hours for total set-up. On this machine, we can often do the set-up in less than an hour."

Using the system, Smrekar says that the Rapid Response team can do small orders on a 24-hour emergency basis or larger orders, even as much as 1,000 items, within two weeks of a purchase order and approval of a drawing. Smrekar says that the Rapid Response systems can handle virtually any kind of fitting for applications including manufacturing, packaging, processing, transportation, agricultural equipment, construction equipment, and more.

Additional details...Contact Parker Hannifin Fluid Connectors Group, 17325 Euclid Ave., Cleveland, OH 44112, (800) 272-7537.