T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y N O V E M B E R 2 0 0 7 59

Lubrication Fundamentals

here’s a pretty catchy title. Themanure spreader, invented a fewhundred years ago (an early horse-

drawn John Deere version is shown in figure1.), is yet another tantalizing tribologicaltaste of our industry at work.

I recognize that more than a few of youmay be exclusively urbanophiles, but for theagrarianly inclined this is an excitingmachine of great importance to society thatovercomes tribological challenges in a cost-effective manner. Once again, I’m constant-ly intrigued by the wide diversity of applica-tions that engage the tribologically orientedmind. So, here we go!

First, a manure spreader manages a sig-nificant hygienic issue in an ecologicallysound manner by recycling nutrients to thesoil and increasing the amount of top soilsuch that more nutrients can be grown tofeed livestock. Left to accumulate, manurecan pose serious runoff problems and canresult in bacterial, fungal and insect infesta-tion, odor and an absolutely displeasinglandscape. This is not trivial, as the averagehorse generates 25 lbs. per day plus anyurine soaked bedding, left over hay, etc. Youcan soon create a small mountain of verybiologically live material in no time at all—great for the garden and flower beds,though.

For people with livestock, this task is car-ried out 24/7, every month of the year,

weather most certainly notwithstanding. Figure 2 shows amanure spreader in action on agood day—it is only raininglightly.

So what about the tribologyof a manure spreader? As youcan see, it is essentially a two-wheeled wagon. The wheelbearings are sealed bearingsfrom the manufacturer and,thankfully, require little maintenance—that’s just about all the good news. In Figure3, looking into the bed, we see two chainson either side with simple angle iron piecesspaced evenly running from chain to chain.As the chain is pulled toward the back of thewagon, the manure is fed slowly intowhirling paddles that spread and dispersethe manure evenly out the back.

These chains are in-expensive metal stampings.This means that they have rel-atively sharp edges that pre-clude coatings or most lubri-cants to protect them fromcorrosion. Further, the bear-ing surfaces are also rough,adding to friction and wear,but they are inexpensive (seeFigure 4 on page 60).

These chains have another

By Dr. Robert M. Gresham

Contributing Editor

T

The fascinating world ofmanure spreader tribologyA little horse sense is all you need to deal with this

product’s unique lubrication challenges.

Figure 2.

Figure 1.

Figure 3.

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remarkable proper-ty: they only seemto break at below20 F, especially ifit’s windy andsnowing. As timegoes on, constantexposure to theelements, manure,urine and wet bed-ding eventuallycorrode and weak-en the chain. Thestresses of winter,frozen “pay load,”ice, etc., put morestrain on the chain,increasing the

probability of failure. Repair is simpleenough, the tension on the chain isreleased, the chain is bent into positionwhere with just a few light taps of a hammerthe old link is removed and the new oneinstalled. This repair, of course, happensonly out in the field, only on a cold, windy,snowy day—hopefully duringdaylight.

The manure must first bedug out of the spreader, byhand, to get access to the chain.The “light taps” of the hammerare actually a bare-handed,knuckle-busting, expletive-deleted opera-tion that takes only a few seconds. Yeah,right!

Interestingly, while I was working for E/MCorp. some years ago, we developed a heavyasphaltic product, containing a high level ofcorrosion inhibitors, for the mining indus-try. This product actually works pretty wellon these chains to slow their rate of failure,both from friction and corrosion. The mate-rial was diluted in a solvent that made itsapplication by aerosol practical and afterthe solvent evaporated left a relatively dry-to-the-touch, self-healing coating that themanure did not overly stick to. It never oc-curred to us at the time to try to sell it to theagricultural community.

The next area of scintillating tribologicalinterest is the ratcheting mechanism thatpushes the manure into the whirling pad-dles to spread the manure. As shown in Fig-

ure 5, this mechanism is driven, in this caseby another chain, like a big bicycle chainthat, when engaged, runs off a large gearattached to the wheel of the wagon—as thespreader is moved, the chain is moved. Themechanism has a large ratchet gear and acouple of smaller sprockets (all iron cast-ings) that turn on stationary journals. Eachof these must be regularly greased with agood molybdenum disulfide-containinggrease, preferably also containing corrosioninhibitors.

Fortunately with regular maintenance,these greases perform well, and failures arerare. There are normally shrouds that coverthis mechanism. Nonetheless, manure, rainand related detritus get in and around themechanism. Indeed, in the picture (Figure 5)you can readily see the corrosion on the for-ward shroud (to the right) that covers the bicy-cle chain running to the drive gear wheel.

Finally, there is an idler sprocket (see Fig-ure 6) at the front end of the conveyor chainthat needs regular lubrication, as well. Thissprocket runs on a solid stationary journal

and is allowed to float alongthe journal, as lateral stressesare put on the chain by clumpsof manure, ice, etc. Again, thegrease performs well in this rel-atively clean environment.

Clearly, manure spreadersaren’t designed by “rocket scientists,” other-wise they would all be made of titanium orperhaps a mix of aluminum, stainless steeland composites. All bearings would besealed for life. The cost of the thing mightbe over $100,000. Thus, if rocket scientistshad existed back then, we would still beusing our great-grandfather’s sempiternal,mint condition manure spreader.

Nevertheless, a manure spreader repre-sents another victory for tribology. With sig-nificant moving parts that operate in a veryharsh environment, the spreader works reli-ably day-after-day with minimal mainte-nance and is relatively inexpensive to pur-chase. <<

You can r each Bob Gre sham, STLE’s d i r e c tor o f pro f e s s i ona l deve lopment , a t rgresham@stle.org.

Figure 4.

Figure 5.

Figure 6.

A manure spreader

manages a significant

hygienic issue in an

ecologically sound

manner by recycling

nutrients to the soil

and increasing the

amount of top soil

such that more nutri-

ents can be grown to

feed livestock.

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