Shock Absorbers and dampers work to provide smooth deceleration of a given payload. A pneumatic or hydraulic shock absorber will use fluid or gas power for deceleration, and a spring to return the piston to its initial position. However, linear dampers typically do not. They facilitate the smooth closing of hinged doors, such as garage doors.
Important parameters for the proper selection of a linear damper can be broken up into general, dimensional, performance, material and features.
What are the selection criteria?
The general criteria when selecting a shock absorber are the dampening method and damping direction. The dampening method can be elastomeric, pneumatic or hydraulic. The damping direction can be either in compression or extension.
When choosing a shock absorber, one must specify the stroke length, compressed length, extended length, cylinder diameter, and rod diameter. The stroke length is the distance between the compressed and extended length. The cylinder diameter is an important factor in determining whether the cylinder will fit into the desired housing, or what housing to use. The rod diameter is used to determine how the shock absorber will be affixed to a given component.
The performance of the shock absorber can be determined from the maximum force, energy per cycle and maximum cycles per minute. The maximum force, also called the P1 force, is the greatest rated force that the shock absorber can supply. The energy per cycle is the amount of energy that the component can absorb, and will also depend on the stroke length. The maximum cycles per minute is a measure of how quickly the shock absorber can return to its unstretched length.
Shock absorbers may be made from aluminum, steel and stainless steel, or thermoplastic. Steel is used when strength is required. The other materials provide varying balance between strength and corrosion resistance.
Additionally, the rods can be treated with chrome to provide corrosion resistance and increase surface hardness. Nitride will increase the hardness by introducing nitrogen into the outer surface of the rod.
There are also a number of important shock absorber features to consider. Adjustable shock absorbers allow the stiffness of the response to be monitored and fine-tuned. This is usually accomplished by adding or removing hydro/pneumatic medium from the shock absorber by way of a valve. Locking capability allows the position of the rod to be fixed at a given position.
Filed Under: Fluid Power Basics, Fluid Power World Magazine Articles