Switching Fasteners Increase Durability and Efficiency in Exit Doors
A company widely known for its exit devices for buildings wanted a more consistent way to assemble the internal workings of its main push pad product line, a commonly used device used to open office doors and exits that can be used for up to 30 years. Specifically, it wanted a better way to assemble the main control link to the control linkage.
The original design used a cold formed clevis pin with a head on one end and a circumferentially machined groove on the other to secure the control linkage. The pin would go through a hole in the main control link and control linkage. Then a special tool grabbed a ring and pushed it over the groove in the pin until it snapped into place. This method was slow and risked mis-installation and failures in the field.
Although retaining rings and e-clips have long been used, they lack the consistency some applications require. The retaining rings are usually installed in relatively shallow grooves. Technicians or inspectors must be watchful to ensure each installed ring is properly seated in the groove. Additionally, in some cases, assembly technicians must be careful not to overstress the ring by opening it too far during assembly. Overstressed rings may not clip into grooves properly.
In this specific case, the ring was being seated in a groove only 0.020 in., which is in accordance with the ring manufacturer’s specifications for a 03/16 in. pin. As you can imagine, it would be difficult for installation technicians to determine if the ring is properly seated in such a small groove. It’s not surprising that failures would occur in the field due to improperly installed rings on a small pin like this, especially when high volumes are involved.
The company soon partnered with Pivot Pins on the redesign. The team determined that the latch held a safety-critical role, so minimizing failures after installation was a top priority. And due to the high volumes being assembled annually, the pin’s contribution to assembly efficiency was also critical to the OEM’s bottom line.
Familiar with the strengths and weaknesses of grooved clevis pins and retaining rings, Pivot Point has often seen self-locking implanted cotter pin (or SLIC pin) fill the void as a viable alternative for over a decade. It has the clip built in, referred to as a “plunger.” The spring-loaded plunger automatically ramps down upon installation and locks into place once it passes through the holes in the linkages.
Pivot Point also examined the application to ensure that the push pad’s stamped bracket had a mating hole with good bearing surface against which the wedge can engage and retain the pin. Additionally, the company noted it was a double-shear type application, which are ideal for SLIC Pins.
The material and finish of previous grooved clevis pin were easily used for the new pin, as both fasteners are cold formed. In addition to eliminating concerns about mis-installed clips, or clips that could fall out after years of use, the SLIC Pin significantly increased assembly efficiency by eliminating the need for an assembly tool.
SLIC Pins are only about double the purchase price of a grooved clevis pin and clip, so reducing the risks and increasing efficiency gave the pin a clear advantage. The updated assembly passed, UL testing and was approved for use, so it is now in production.