Establish your load needs
Load refers to the forces acting upon a system and includes either static, dynamic, or impact components. A static load condition occurs when the system is fully loaded and at rest, and is the easiest condition to define. Dynamic loads, which look to quantify forces applied during motion, better reflect the actual loads experienced by the bearing during machine operation. This is important because when bearing systems are in motion, they need to contend with a larger set of variables that can affect overall performance. This set of variables makes calculating dynamic loads trickier, but not impossible. For example, plain bearings can offer static loads up to 20-times higher than ball bearings. However, in dynamic situations, the larger surface area of plain bearings is more sensitive to variations, and subsequently require additional calculations such as PV value: where P= Pressure (applied load divided by reflected surface area), and V = Surface Speed. Plain bearings are rated by their limiting PV, which is a combination of load over a given surface area and the velocity (PV = P x V).
P = Maximum pressure or load in pounds per square inch (psi) or kilograms per square centimeter (kg/cm2)
V = Maximum velocity or surface speed in square feet per minute (sfm) or meters per minute (m/min)
This dynamic load chart offers an example of the different dynamic load ratings using the example of a 1-inch shaft diameter. As is illustrated, the double and twin pillow blocks initially offer the most load capacity for pillow block configurations, while plain bearings are dependent on the PV value derived from the specific application.
Depending on the type of application, moment loads should be factored into the decision on bearing selection. Moment loads apply a force that causes a bearing to rotate about a specific point or axis, and will increase relative to the distance of the load from the bearing’s center line. Moment load forces are defined as pitch, yaw, or rotational movement. Ball bearings offer modest resistance to moment loads, but can sustain increased wear if loads are too high. Plain bearings are limited to the 2:1 ratio and often related to cantilevered loads. The 2:1 ratio or “Binding Ratio” is officially defined as the maximum ratio of moment arm distance to bearing length which will not bind (prevent motion). The Binding Ratio is often displayed numerically as “X:Y,” where “X” is the moment arm distance and “Y” is bearing length. With roller pillow blocks, they are less resilient to moment loads because the cantilever or moments will load the side rollers and cause premature failure.
Orientation can affect load capacity and performance
Load orientation and its effect on load capacities in Simplicity bearings.
The orientation, or how a system is mounted, can affect the load capacity and consequently the performance of a pillow block. Orientation can be defined as horizontal, vertical, side, inverted, angled, etc. Closed versions of Simplicity plain and ball-type bearings can operate in any orientation. With open bearings, load capacities will vary depending on the orientation in which they are being used. The load orientation graphic demostrates how the orientation will affect Simplicity bearings' load capacity.
Roller pillow blocks are best suited for horizontal motion in an upright position, and those interested in implementing them in vertical and moment load applications should consult our application engineers for assistance.