Low Closure Force
The force needed to compress an O-ring can be significant. Compressive load increases as
• The O-ring inner diameter increases
• The cross section increases
• The amount of compression (squeeze) increases
• The hardness of the material increases
Compressive force is generally not an issue for robust hardware materials, however it can be problematic for stamped hardware, molded substrates, and other lightweight metals.
The simple way to decrease the closure force of an O-ring is to:
1. Decrease the O-ring cross section. A look at the Compressive Load tables (listed in the eHandbook) for O-rings, we can compare the values for a .103” cross section to that of a .070” cross section. At 20% squeeze, the range for a .103” cross section is approximately 9 to 18 pounds per linear inch of O-ring. For the same amount of squeeze on a .070” O-ring, the range is roughly 5-18 pounds per linear inch of O-ring circumference.
2. Decrease the designed squeeze. For the same example of a .070” cross section, if we decrease the squeeze to 10%, we see the compressive load drops to a range of 2 to 5 pounds per linear inch.
The challenge many designers have with decreasing the O-ring cross section is that the O-ring groove needs redesigned to accommodate the smaller thickness. Many times it is easier to change the seal than the hardware.
The issue with decreasing the seal compression is that this can compromise the O-ring’s life due to increased compression set. Testing shows the optimum amount of seal compression for static seal is generally in the 25% range. By dropping much below this suggestion, the seal cross section is not fully energized for optimum resilience. Such a change may be favorable for reducing the load needed to compress or install, but it potentially accelerates compression set in the seal.
There are alternate seal options for reducing the compressive load force:
• Low durometer O-rings
• Hollow Profiles
• Lip Seals
• Diamond Seals
Low Durometer O-Ring
The simple solution to lowering the compressive load of an O-ring is to switch to a softer O-ring material. Changing to a softer material can reduce O-ring compression force up to 50%.
Extruded hollow profiles provide significantly reduced force without compromising seal height.
The simple solution to lowering the compressive load of an O-ring is to switch to a softer O-ring material.