What is the difference between a straight pivot pin and the Expander System?
Pivot pins are one of the most important components in machinery with rotating joints, but the design of straight pivot pins has a flaw that leads to lug wear, loss of precision and costly downtime. This technical explainer details the engineering behind the Expander System, showing how an Expander pin eliminates the wear and downtime associated with standard straight pivot pins.
Why straight pivot pins cause lug damage (where Expander pins do not)
A straight pivot pin cannot fit into the lugs of a machine unless the lug holes are slightly bigger than the pin itself. This means that there is always a gap between a straight pin and the lugs. Although this gap is necessary to mount a standard pivot pin in the lugs, it is also problematic, as it affects the precision of the machine.
This also allows the axle to hit the lugs with full speed and force when the direction of the machine changes. Contrary to some misconceptions, flat washers, locking rings and other fasteners do not actually fix the pivot pin in the lugs – they only prevent it from rotating and falling out.
The result of this design flaw in standard pivot pins is that when a machine is exposed to heavy loads and vibration, the pin slowly wears down the lug holes. This then leads to loss of precision and control from the machine, making it necessary for the lugs to undergo repairs. These repairs usually take place every 3,000 to 5,000 hours, depending on the load intensity on the machine.
The play between the lugs and the pin is not the only reason why straight pivot pins make lugs more prone to damage. When these pins are loaded, all the pressure is forced onto a small area, deforming it permanently. In addition, the lugs are also typically made from a softer material than the pin, and easily lose their shape after repeatedly coming into contact with the harder pin. Expander pins solve all of these issues through clever engineering.
How the Expander System improves the pivot pin design to prevent lug wear
The Expander System consists of a pivot pin tapered at both ends, two expansion sleeves, two tension washers, and two fasteners. The pin is installed directly into the existing mounting. Upon tightening the fasteners, the washer presses the slotted expansion sleeve further up the tapered ends of the pin. The sleeves then expand, conforming to the pattern in the lugs and locking the system in place. Once retorqued, the system locks from both sides.
Days of downtime with standard pivot pins vs a simple repair with Expander
Traditional straight pivot pins and the Expander System also have different repair procedures. When using traditional pins, welding and line boring are used to repair worn lugs. This not only takes time, but also necessitates an experienced mechanic with specialized equipment. Since complex repairs like these are difficult to carry out in the field, the machine is usually moved to a workshop causing costly and time-consuming downtime.
The Expander System, by contrast, can be mounted directly into an already worn lug, so there is no need for welding and line boring. In many applications, the Expander pin can easily be installed on-site, with operations resuming after a few hours.
Finally, the pressure from an Expander System pivot pin is well distributed over the whole contact area in the direction of the force, so the lugs do not become damaged from the pressure as they would with a standard pivot pin. This system permanently prevents lug wear and eliminates the need for repairs.
KEY TAKEAWAYS:
- Standard pivot fins are flawed in their design as they unavoidably cause lug damage
- Unlike an Expander pin, this makes repairs necessary in order to continue operating the machine
- The Expander System’s design resolves these problems to permanently prevent lug wear
- The Expander System can be installed quickly on-site, while standard pivot pins require complex maintenance in a workshop
