Developing Easier-to-Assemble Linkage Pin for Fire Doors
An OEM designer and manufacturer of emergency exit fire doors and related hardware was searching for a more consistent method of assembling their main push-pad product line, often called “panic bars,” which unlock doors immediately when depressed.
Specifically, the emergency exit firm wanted to redesign the internal mechanism for the assembly of the main control link to the control linkage, to make it easier to assemble, but without risking reliability or durability. In a case study detailed at Machine Design magazine, the exit door maker called on Pivot Point Inc., a Hustisford, WI manufacturer of non-threaded fastener solutions, to develop a solution.
Pivot Point met with the OEM at their facility to view the application, discuss project needs, and review the current assembly process. Being a safety critical application, it was clear that minimizing failure of the unit after installation was a top priority. Due to the high volume being assembled each year, maintaining efficiency of assembly was also critical to the OEM’s bottom line.
The existing fastener design consisted of a cold-formed clevis pin with a head on one end, and a circumferentially machined groove on the other. The pin would be inserted through the hole of the main control link and control linkage. A special tool was used to grab a ring from the cartridge and then push the ring over the groove in the pin until it snapped into place. This method was slow and allowed for the possibility of improperly installed units or failures in the field. Pivot Point came up with a new approach, using a self-locking implanted cotter pin (or SLIC pin) as an alternative to the clevis pin. The solution is described in detail at MachineDesign.com.