Shake, Rattle & Roll

Shock and vibration in off-highway equipment can create a number of problems, from annoying rattling, to accidental storage compartment opening, to complete latch failure. The sources of these problems include extremely rough terrain, continuous operation of heavy-duty diesel engines, and intermittent vibration caused by auxiliary units installed on the equipment such as pumps, compressors, compactors, pile drivers and boring equipment.

Yet, regardless of the source or effects of that shock or vibration, the key to finding successful access hardware and fastener solutions to combat them is in understanding the nature of the force and identifying appropriate designs to handle it. This holds true in applications with cyclic loads that vary in frequency and amplitude, as well as those with a sudden acceleration in force in one axis or several.

Establishing the parameters

The effects of shock and vibration vary widely by the type of off-highway vehicle and the axis of force — fore/aft, side-to-side, or vertical. For example, the average fore/aft acceleration forces for back hoes and excavators (2 Gs) and excavators (2.5 Gs) are similar to those for off-highway trucks (3 Gs). However, the maximum fore/aft forces experienced by off-highway trucks (10 Gs) are two to three times higher than the maximum forces for backhoes (3 Gs), excavators (4 Gs), and on-highway trucks (4 Gs). Also, vertical acceleration forces typically exceed the fore/aft and side-to-side acceleration forces as a result of rough terrain. Having an idea of the magnitude of forces experienced in an application is the first step to specifying an appropriate solution.

Addressing the need

Once the shock or vibration problem is identified for the specific application, compare load ratings to identify more robust latch designs, or use multiple latch points to distribute the load. Gaskets can be used too dampen vibration, or modify the position of latches on the door to change the angle of the shock or the harmonics of the vibration. The size, weight, or shape of the door may also be adjusted to minimize torque forces on latches and hinges. For less critical applications, simply specifying a safety factor using a higher than normal multiplier of the static load rating for a particular latch or hinge mechanism might be acceptable.

For more complex applications — including those with sudden extreme shock or impact — consult with a hardware supplier about defining anticipated load forces, frequency of vibration and impact shock.

Consider convenience as well as safety

Nut-and-bolt fastening — using locknuts, lockwashers, or crown nuts with cotter pins — is certainly one way to ensure secure attachment of small components, accessories or panels in high-vibration applications where a full-size latch is impractical or unnecessary. But the time and effort to remove that type of fastener hardware for repetitive routine access, maintenance, or service can really dampen end-user satisfaction. Fortunately, there are other cost-effective options for promoting the convenience of quick-access without compromising shock- or vibration-resistant performance.

For lightweight compartment doors, swell latches provide a rubber bushing that expands when compressed by turning a wing nut or flipping a handle. That expansion creates the mechanical grip necessary to hold access panels fast, and provides a degree of shock absorption.

For heavier access panels, protective covers or noise-suppression panels in off-highway equipment, vibration-resistant quarter-turn fasteners reduce maintenance time and maintain consistent tension.

Numerous designs are available to provide varying degrees of economy, strength, and vibration-resistant performance that satisfy a wide range of requirements. Many of them have already proven their capabilities in demanding applications ranging from aerospace to high-performance automobiles to Class 8 trucks. (Figure A.)