What you need to consider when specifying a seal
Click here for typical profiles and details on other seals.
Design criteria
Cross-sectional Design - Several things need to be known about the application before you can properly determine what a good cross-sectional design will be.
Knowing the attachment system is important - how the seal will be applied to the substrate or to the application.
The gap or the opening the seal is going to fit into and be expected to seal. - This includes both the minimum and maximum amount of gap that exists throughout the application, taking into account tolerances of the enclosure and sealing material. In most cases, the amount of seal compression for sponge seals to be effective is 15% to 25% percent. For solid materials the general effective compression range is 2% to 10%. It is important to remember, that the end use always needs to be considered. For example, there is a very significant difference between sealing a box to keep out dust and taking that same box, and sealing it to keep out moisture when the box is submerged in ten feet of water.
The amount of closing force that will be tolerated in the application. - A seal requiring 50 lbs. of force to seal is not going to work in an application where only 20 lbs. of force will be tolerated. How much force is required on the seal, how much surface area, the type of material that is used and the size of the cross-section all need to considered.
- The direction in which the load is applied to the seal is also a critical factor. Very different results will occur if a 60° load is applied as opposed to a 90° load.
- There are also ways to help reduce or control the total amount of load required to get a good seal; 1) The shape of the cross section can be changed, depending on how the load is applied, and 2) holes or hollow sections can be introduced into the cross-section to help reduce the load required to compress the seal. For example, a solid "D" section will have a higher mechanical load deflection than one that has been "hollowed" out.
The Rubber Manufacturers Association has issued standard dimensional tolerances
-- Click here for RMA Tolerance Tables.
