PSM Compression rings are spring steel components used in assemblies, especially with plastic parts, to clamp or secure parts by radial pressure. Unlike rigid fasteners, compression rings deform elastically when installed, exerting force against adjacent components or housings. In many cases, they’re used to secure knobs, handles, or other rotary elements onto shafts without needing adhesives or keys.
Advantages
- Easily applied
- Low in place cost due to speed of assembly
- Will not damage surface of hose
- Easily removed
Method of Assembly
Simply push compression ring over split knob end and then push whole assembly over shaft.
When specifying, please state:
- Quantity
- Prefix (CBCR)
- Part No.
- Finish code (e.g. 5000 CBCR-0940-00)
How Compression Rings Work
A compression ring fits over a shaft (or within a hub), and when installed into a housing or onto a split shaft, its spring action forces the ring segments outward or inward, creating frictional grip. In knob or handle assemblies (particularly with thermoplastics), the compression ring grips the bore of the plastic knob and simultaneously locks into the split shaft, acting as a captive retaining ring.
The design allows removal and re-engagement, so the knob or part can be pulled off or repositioned without damaging the plastic. The ring’s elasticity makes it forgiving to small tolerances and differential thermal expansion between plastic and metal.
Design Application and Guidelines
Geometry & Sizing
The ring’s inner diameter (ID) and outer diameter (OD) must match the shaft and housing tolerances, respectively, to ensure the right preload. The ring cross-section thickness and width must provide enough spring force without exceeding material yield.
Material & Surface Treatment
Spring steel is the usual choice for its fatigue strength. Coatings, such as zinc plating or phosphate finishes, help reduce corrosion and friction against plastic. The contact surfaces may be polished or ground to limit abrasion on mating plastic surfaces.
Clearance, Tolerances & Fit
Ensure minimal radial clearance between ring and housing bore so the ring doesn’t buckle or distort. The plastic hub or knob bore should allow slight flexibility to conform to the ring’s grip. Control run-out and coaxiality of shaft-to-knob alignment so preload is evenly applied.
Installation & Handling
Slide the compression ring into its seat (slot or bore) gradually; avoid twisting or damaging ring legs. For split shafts, ensure ring expansion or compression is balanced to avoid eccentric clamping force. During installation, monitor torque or axial force so the ring isn’t overstressed or plastically deformed.
Advantages & Common Use Cases
Compression rings provide quick, tool-free assembly for knobs, handles, and rotating parts on plastic or composite housings.
Suitable in situations where adhesives are undesirable (e.g. serviceability, disassembly).
Good for mismatched thermal expansion between steel and plastic, since the elastic ring can maintain grip across temperature cycles.
Frequently used in instrument knobs, control shafts, valves, and low to moderate torque rotary connections.
Dimensional Data & Sizes
