It’s a given that when you need to transmit tremendous forces for excavators and other types of heavy equipment, hydraulics is the only way to go. And although transmitting cylinder force to the machine’s structure may not be a “hydraulics” problem, a practical solution must be found to avoid premature bearing failure and other problems.
The way its been done
For decades, the most common viable solution for attaching the cap and rod ends of a hydraulic cylinder to a structure has called for a clevis pin — a high-strength bearing surface that usually is hardened and polished. Traditionally, the clevis pin pivots inside a journal bearing made of soft or hardened steel. The bearing-to-pin interface involves very high forces acting at very low speed.
A limitation to this traditional setup is the expense and labor required to install, remove, and replace the journal bearing. Because it involves an interference fit, the journal bearing generally requires very high axial force to press it into place. Whether this occurs at an OEM or a heavy equipment repair facility, installation cost usually far exceeds the cost of the bearing. Costs are even higher when a shrink fit is used. The shrink fit requires cooling the bearing and heating the structure, then quickly sliding the bearing into the cavity. This provides a permanent tight fit when the temperatures equalize, but makes costs to replace the bearing extremely high.
A cost-effective alternative
A trend among many machine builders and repair facilities is to use tension bushings as a cost-effective alternative to journal bearings. Tension bushings save money for OEMs because they cost less than journal bearings and requiring much less labor intensive installation. Repair facilities save even more because the tension bushings can be removed using a small press or even a drift and hammer instead of highly labor intensive removal techniques.
Tension bushings, offered by Vogelsang Corp., Lakewood, N. J., are split cylindrical bushings made of AISI 1074 or 6150 steel that is through-hardened to RC 45 to 50. The material is noted for its high elasticity, resilience, and wear resistance. The split can be wavy or straight, depending on the preference of the user. Standard sizes are ¾- to 3½-in. OD, with a ½- to 3-in. axial length.
The bushings have a relaxed OD that is larger than the cavity into which it will be inserted. They also have chamfered ends to facilitate insertion and removal. As they are pressed into the cavity, the interference fit reduces the width of the split.
The bushings are self-retaining, and the inherent elasticity of the material provides constant radial tension for a tight fit — even if the bore becomes enlarged. Although they can accommodate high load at low speed, they can also be a cost-effective replacement for bronze bearings, which typically support lighter loads.
Vogelsang Tension Bushings are cost effective bearings, ideal for high-load/low-speed operations in harsh, non-lubricated environments. These bushings are designed to replace solid steel (tubular) and case hardened parts.
After normal use, a clevis pin often elongates the bore of a journal bearing at the pivot point due to normal wear. When this occurs, the bore of the bearing can be reamed to accommodate a Tension Bushing properly sized for the same sized shaft.
For more information, contact Vogelsang Corp. here or email [email protected], or call (732) 364-0444.