by Matt Hagny
One of our competitors touts their use of SeedXtreme bearings. Are they in fact better?
The SeedXtreme bearing uses 6 seals per side (12 total), versus the typical 2 or 3 seals per side that are commonly used in ag bearings (such as gauge wheels and firming wheels). However, to make the bearing capable of turning under low drive conditions (e.g. soils are muddy or loose, and not imparting a lot of rotational force to the wheel, and/or not much downpressure is being applied to the wheel, or the wheel has encountered a gob of straw or rock and needs to climb over it), there cannot be too much drag from the seals. Drag is primarily from what’s called ‘contact pressure’ of the seal against whatever it’s pressed up against (the race usually). The sum of the contact pressure of the seals to a large degree determines drag, all else being equal (the viscosity of the lubricant also matters). Too much contact pressure, and the bearing won’t turn easily. Too little contact pressure, and the seals don’t hold out contaminants. It’s a balancing act.
When you double or triple the number of seals, the contact pressure of each seal must be decreased so much that they no longer seal up very well in abrasive, dusty ag environments. Indeed, the SeedXtreme has already undergone several iterations trying to get them to seal up decent. As far as we can tell, they still don’t have it right, because in the field, the SeedXtreme bearings are failing much more quickly than standard bearings with double- or triple-lip seals. (Peer’s mud slurry test apparently doesn’t replicate field conditions—partly because mud in the field is much higher viscosity, and dust is another matter entirely.)
Exapta works closely with many experts. Here’s what one sharp guy who’s spent much of his career working with bearings has to say: “The torque required to turn a standard ag bearing such as what’s in your Thompson wheel is 14.8 N-cm [Newton-centimeters][or 0.109 ft-lbs here]. The torque needed to make your DuraLok wheel turn efficiently is about 8.8 N-cm.
If you divide the N-cm required by the number of lips, you will find that having 12 lips means that you essentially cannot have any pressure on the inner race contact from the seals in order to allow the bearing to turn. This is the case with the SeedXtreme bearings. No matter how many lips you have, you still have to use [are limited by] the same amount of total torque, or your wheel will slide due to the seal interference.
The current amount of pressure applied per seal lip in most of these ag bearings results in about 3 N-cm of torque required per seal; the SeedXtreme would have available only about 0.75 N-cm of torque per lip—with such little torque available, the seal must exert very very little pressure against the race—not sufficient to seal contaminants [esp dust] out. The only advantage that I can see with the SeedXtreme is that it might take a slightly longer time for the contaminants to pass through all of the lips *if* there was no side pressure applied at all to the seal surface, but you and I both know that there is a lot of side force from the contaminants on the seal lips during operation of the firming, closing, and gauge wheels. Every wheel has a pinch point where the contaminants build up between the bearing mounting [e.g., bolt] and the wheel hub.”
As a further note, the side-load applied to any of these wheels (quite a lot on gauge wheels and closing wheels with toe-out; and whenever the seed-lock wheel is misaligned to the furrow) causes the seal contact pressure to decrease even further on one side of the bearing (due to the small amount of wobble that’s always present between the inner race and outer race, and which gets larger as the bearing wears the balls and races). If you start with very light contact pressure, there’s not much margin for the seals to remain in contact at all with side-load.
It’s not that Peer makes poor bearings in standard configurations—indeed, they’re one of the better brands. Instead, it’s simply that the basic concept of the SeedXtreme is seriously flawed. I’m not sure why they ever bothered messing with it, since the standard gauge-wheel bearings with double-lip seals have been lasting a very long time. Sometimes, less really is more!