Most bearing manufacturers offer a wealth of bearing technical data and procedures. If you’re like me, you simply don’t have the time, patience, or interest to read all of this information, as profitability is not supported by the frequent need to outsource bearing maintenance, but you still have an interest in cost. of operation. reduction for your tree stump grinder. Replacement bearings cost over £100 each and represent a large part of the overall maintenance costs of the machine. This guide is intended for those who want to reduce costs by increasing bearing life. Failure or premature wear of bearings in stump grinders is primarily due to improper maintenance of clean lubricant. I use an air compressor powered pneumatic grease dispenser at the end of each day of stump grinding, with a refill of grease, in the field, using a conventional manual grease pump. I use a lot of grease, but it’s much cheaper than replacement bearings. When I re-grease the bearings, I completely purge the contaminated grease until clean grease comes out of the bearing. A high melting point EP-2 grease is essential. I prefer an EP-2 complex grease enriched with molybdenum disulfide (molybdenum) because it is a heavy-duty grease. So, to summarize this paragraph, there are three principles for maximizing bearing life when it comes to lubricants:
- select the correct grease
- apply the correct grease correctly, for example in the correct amount
- re-grease frequently
A second common reason for premature bearing wear on stump grinders is improper or incorrect bearing adjustment (for those machines with adjustable bearing wear compensation). Now, I know how inconvenient it can be to access bearings for adjustment on stump grinders. I made some specialized tools out of Allen wrenches, due to their high quality and strong steel content, as a solution to the awkward access problem I have on my grinder. I simply remove the excess material with a bench grinder to shape an Allen key into a right angle punch. If you feel comfortable doing this, be sure to frequently cool the Allen wrench in water. Don’t let it turn blue. I come from an engineering background and accept that many of you who can read this don’t. Many may feel that this is a bit out of their reach. That is why I am making this effort to avoid technicalities as much as possible with an emphasis on the minimum salient points. I’m not familiar with bearing access configurations on all brands of stump grinders, but I can’t stress enough how, with a little initiative and determination, it’s important to overcome a bearing access problem. It will save you money.
The detection and analysis of premature bearing failure is by nature a technical issue involving specialized equipment such as heat sensors, vibration sensors, infrared sensors, oil analysis equipment and ultrasound. All of this equipment generates a large amount of data, is very expensive, and totally impractical in the field. A non-technical tree stump grinder who relies on continuous operation of his stump grinder will be easily discouraged by this situation. The simplest, most practical and non-technical way to roughly monitor bearing performance is to rest your hand on the pillow block bearing after it has been run for a reasonable period of time, say at least an hour. If you must remove your hand because the bearing is too hot, this indicates a worn bearing. Adjustment to compensate for excessive play within the bearing must be made in accordance with the manufacturer’s instructions. If the sound of a bearing “banging or rumbling” is also heard, this usually means that it is excessively worn and needs replacement. For whoever may be interested, there are four stages of bearing failure that I will mention as it gets involved and does not fit within this scope and its objective:
- Stage 1. Vibration analysis detects the first sign of bearing failure. The signal data appears in the ultrasonic frequency range band around 250 to 350 Kilo Hz. At this point, there is 10 to 20 percent of bearing life remaining.
- Stage 2. The bearing failure begins to “resonate” at its natural frequency (500 – 2000 Hz). At this point there is 5-10% bearing life remaining.
- Stage 3. Bearing failure harmonics are evident with defects on the inner and outer races. Temperature rise is now evident with 1 to 5% life remaining
- Stage 4. The high vibration is clear with a considerable increase in random ultrasonic noise, the temperature rises rapidly. One hour to one percent remaining health.
It is unfortunate for all stump grinder operators, that when a bearing knocks, rumbles, or becomes noticeably hot, it is on its way to failure. There is no practical way for the average owner/operator to accurately judge the remaining service time on a stump grinder bearing while out in the field.
From this point of view, I try to collect some useful data in the field, which can be a practical and inexpensive way to monitor the serviceability of bearings. I will install thermocouples (heat sensors) in the bearings. If an average operating temperature gradient can be established, it can be useful for those stump grinders who are concerned with maximizing the bearing life of their machines, simply by adjusting their bearings, when temperature rise indicates the time to do so. . This will require some effort on the part of those concerned. They will also need to put thermocouples in their bearings to monitor temperature as the only cost-effective and practical way to know when to adjust their bearings.
This effort will be totally negative if a strict and sufficient regreasing program is not maintained. What would be the point of regular and timely bearing adjustments, if the bearings were regularly running in a bed of contaminated grease? I think the reader will agree, it’s a complete waste of time and effort.
