Compression Limiters Information
Compression limiters are a type of insert or bushing designed to maintain joint integrity of a plastic assembly when tightening bolts or screws. They protect plastic parts from damage due to compression by limiting the force that gets applied to the plastic by the assembly fasteners. Compression limiters are designed for applications where the tightening load of the bolt or screw will compress, crack, or otherwise damage the plastic component. They provide a strong and reliable defense against the stresses caused by fastener torque.
Plastic does not have the compressive strength to withstand the force applied by the tightening of a screw or bolt. Plastic may crack or creep underload and allow the assembly to become loose. Compression limiters are designed to be inserted into a hole before the fasteners are inserted and tightened. These devices are non-threaded metal inserts made from materials such as brass, aluminum, stainless steel, or steel. They are designed in various configurations in order to meet the strength and alignment requirements and assembly techniques of the specific application. Compression limiters may be manufactured as solid or split down one side. They may also have knurled edges or undercuts for the purpose of retaining the insert in the part hole.
There are four techniques that are employed to install compression limiters. Typically the installation techniques used is dependent on factors such as production rate and plastic part tool design.
Compression limiters are also designed with specific installation methods in mind. When choosing a type of compression limiter the installation method must also be taken into consideration.
- Press in — Compression limiters are pressed in place with a pre-determined amount of interference to the hole.
- Mold in — Compression limiters are placed onto a core pin in the mold and the plastic is molded around the part.
- Thermal insertion — Compression limiters are placed into a molded or drilled hole that is slightly smaller than the diameter of the insert. A heated probe is used to handle heat and install the compression limiter. As the compression limiter is installed into the hole the plastic is melted in a localized area around the part. When properly located the probe is removed and the plastic re-solidifies around the compression limiter.
- Ultrasonic Insertion — Compression limiters are placed into a molded or drilled hole that is slightly smaller than the diameter of the insert. Ultrasonic energy is applied to the compression limiter with the use of an ultrasonic horn. The ultrasonic energy develops frictional heat and caused the plastic to melt as the compression limiter is installed in the hole of the plastic part. When properly located the probe is removed and the plastic re-solidifies around the compression limiter.