Designing With Inflatable Seals - Pawling - #5

eight times as higher. Even then, the expansion height at the corner will be a slightly lower than on straight sec­tions. Often, it's better to put the seal around the door than around the opening.

For sharp corners, use a fil­let pad to create a sealing curve. The pad can be

mounted to the seal or the opening.

Large-circumference seals: Seals must sometimes be joined end to end to form a large hoop. These cases can be handled by combining one or more seals into a larger one. The most common method of doing this is to in-

Inflatable bladders have solved a variety of actuating problems, especially when some "softness" is required. For example, small annular bladders have been used for decades to hold round bar stock and tubing in place during production. Because inflated bladders are gentle and easy to keep clean, they are often relied upon to handle fragile, glass containers in food and pharmaceutical equipment. Heavier-duty bladders assist in short-stroke liftin holding, and temporary positioning in fabrication shops and construction sites.

One machine builder reworked the conveyor brake on a plate-glass cutting machine for soft stops and reliability. The previous setup jerked the belt to a stop and was a leading source of service calls. Jerky stops also caused glass sheets to shift on the conveyor, creating scrap and wasting material.

The new brake consisted of a footed seal running beneath the conveyor. When inflated, it presses against the drive belt under the main conveyor belt and stops it friction. The seal is quickly inflated and deflated on command through two pressurizing connections, meeting the cycling requirements. When inflated, the tube expands and gently, but quickly, stops and holds the conveyor in position. When deflated, the tube's top surface falls ³/a in., letting the drive belt move the conveyor belt forward. Other than expansion and contraction of the bladder, the brake has no moving parts.

Though the functions differ, designing bladders for clamping or

actuating follows the same approach

as designing seals, as outlined in the main article. The main difference is that engineers must define the forces, required displacements (strokes) and duty cycles in greater detail.