by Justin Singleton, Field Applications Engineer and Michael Morehouse, Shims Estimator
Angular roller bearings and ball bearings in an assembly typically require preloading in order to maintain a minimum designed axial force in the assembly. This minimum force is called the bearing preload and is designed to overcome the stack up of tolerances within the assembly and to ensure no slop or gaps exist for a smooth and tight rotation.
There are many options available to the designer to compensate for the assembly’s tolerances and achieve the desired preload force. The options and benefits to be considered are:
Threaded Systems are preload adjusted by a threaded stop nut or bolt. The advantage is that the preload is infinitely adjustable and can be serviced in the field with minimal stocked parts. However, the drawback is that the preload amount is limited and dependent on torquing to specification. Threaded systems are also comparatively expensive.
With Springs (Conical, Coil/Compression, Wave), the preload achieved by a spring and is dependent on the spring constant “K”. It is only adjustable by replacing the spring with a different strength or configuration. The benefits are a simple design and the allowance of a small yield during impact. The drawbacks are a dissipating preload as the spring fatigues and the fact that the spring allows yield during impact – this may be detrimental to assembly (such as with a ring and pinion meshing gear set). The preload is also difficult to adjust.
Stop Nuts, Wave Spring, Belleville Washer and Coil Spring. Preload is critical to ensure the proper function and prolonged life cycle of a bearing. Shim packs, or sets, are used for preloading bearings and positioning for proper gear tooth meshing.
With Single Thickness Shims, preload is adjusted by displacing the gaps with a shim of the required thickness during assembly. The advantages are a simple and inexpensive design and the maintenance of a constant preload between service intervals. The disadvantages are that this approach requires multiple stocked shim thicknesses to achieve the proper force during assembly.
With a Surface Bonded Laminated Shim Pack the preload is achieved using the same method as a single thickness shim, but a glued, multiple-layer shim pack is used to adjust the thickness at the point of assembly. The benefits are that it is a simple and inexpensive design and that it maintains a constant preload between service intervals. It also allows for easier service in the field with less parts stocking. However, sometimes it is difficult to peel layers and discarded layers must be scrapped.
With an Edge Bonded Shim Set preload is achieved with multiple layers of shims, but the shims are held together only by their edges making peeling to the desired thickness relatively simple. The advantages are easy to peel layers and it is a simple and inexpensive design. A constant preload between is maintained between service intervals and this approach allows for the easiest service in the field with less parts stocking. Unused layers may be used in a different assembly.
Edge Bonded Shim Sets are ideal for bearing preload applications and have distinct benefits over conventional and laminated shims. The key distinction between an Edge Bonded Shim Set and a Laminated Shim Pack is the method of attachment between each layer of material:
• Laminated Shim Packs are adhered throughout the entire surface between each layer of material and the layers are pressed together to cure much like how particle board is manufactured.
• The layers of an Edge Bonded Shim Set are first pressed together, and then adhered by the edges of the Shim’s profile. This allows for a much easier separation of the layers in the field.
Furthermore, in a Laminated Shim Pack, the unwanted layers must be discarded due to their deformation during peeling. Since Edge Bonded Shim Sets are easier to peel, the layers that are not needed are preserved and can be used for a later application.
An additional benefit of Edge Bonded Shim Sets over conventional preloading techniques is more versatility with size and shape. With spring or threaded preload systems, the preload force must be distributed in a circular design, while with Edge Bonded Shim Sets, the shims can be manufactured to any shaped design — large or small.
Additionally, Edge Bonded Shim Sets provide a more accurate and consistent preloading throughout the service life of the assembly without requiring a precise torque set, such as with a threaded system.
In most cases, Edge Bonded Shim Sets offer the most cost-effective solution to any angular bearing preload system, especially during repair or service in the field.
In other applications, SPIROL Edge Bonded Shim Sets can provide cost-saving advantages over surface-bonded Shims because the materials are less expensive. Edge-Bonded Shim Sets offer safe adjustment in seconds, rather than time consuming and difficult to peel surface bonded laminates. Safety improvement is realized because no knife is needed to remove the edge-bonded layers. Cost savings can also be realized because removed layers are reusable functional parts.
SPIROL Edge Bonded Shim Set Case Study
A military ground assault vehicle manufacturer approached SPIROL to provide quick delivery of adjustable shim packs for spacing of armoured vehicle door hinges.
The spacing is critical to the welding process, providing proper sealing and locking engagement of the door systems.
The customer designed an adjustable shim pack based on surface bonded shim material requiring 94 layers of 0.05 mm thick laminates. Because of the size and configuration of the parts, surface bonded materials were problematic in cost, the amount of time needed for dimensional adjustment, as well as a long lead-time required for manufacturing.
SPIROL Application Engineers worked with the customer to determine the required adjustment and developed three Edge-Bonded Shim Set proposals. The customer evaluated the advantages and selected a proposal offering safe, quick adjustment, a 70% cost reduction and a short manufacturing lead-time. SPIROL provided the solution without tooling cost using SPIROL’s tool-less manufacturing technology.
SPIROL offers free samples and application engineering support. SPIROL manufactures non-threaded types of bearing preload systems including Disc Springs, Shims, Laminated Shims, and Edge Bonded Shims.
SPIROL Application Engineers will review a customer’s application needs and work with their design team to recommend the best solution. For more information, visit SPIROL’s Shim Applications in the Optimal Application Engineering portal at www.spirol.com