Thanks you for the question. This is a question a lot of people ask because by not owning one, they really do not know what the benefits are of a shredder versus a grinder.
First, the definition of a shredder via Wikipedia® is that shredders “are all slow-speed systems, in contrast to hammer mills which are generally high-speed systems.” That’s a fairly accurate statement. So if we assume that horizontal and tub grinders have hammermills that rotate at 700-1800 revolutions per minute(rpm), low speed shredders usually rotate at 0-50 rpm.
In addition, shredders most commonly have single or dual shafts, but can even have 3 or 4 on occasion. Some have screens that can create a determined particle size while others are strictly for size reduction.
So what are the benefits of shredding at low speed:
· Lower Fuel Usage
· Limits the amount of fines being produced
· Increased Wear Part Life
· Can shred contaminated materials
With all that being said, in general, what would it be used for?
· Any initially ground material- If you are grinding twice currently for mulch, fuel, etc., using a shredder on the first grind would certainly lower your production costs. While your production volume would probably be a little less than a grinder, the fuel savings would be in the 50% or better range and the wear part life would probably be five times greater. In addition, because the rpm is in the 30 or 40 range, the amounts of fines produced are significantly reduced. This will lower mulch bag weights, hauling weights and reduce mulch colorant usage.
· Landclearing Material–What happens when you throw stumps and big wood in a horizontal grinder? You produce fines, fines and more fines increasing hauling weights. Also the dirt from the stumps significantly wears the grinder tips while the shredder tips tend to break the dirt away from the stump because of the reduced rpm.
· Contaminated Materials- Materials like Railroad ties, storm cleanup and C&D are most likely contaminated with rock, concrete and steel and unable to be reduced with a grinder safely. A shredder turning at 30 or 40 rpm can pass contaminants without significant damage.
· Demolition- Reducing MSW, Demolition or C&D Recycling debris can create savings of more that can be estimated. Last month, at a C&D Recycling Site, we reduced the 1200 yards a day of already sorted material that is sent to a landfill, to 700 yards, while removing additional steel that was missed by the sorting system and more steel that was broken free from other materials. That equaled 500 less yards charged at the landfill, five less loads of paid transportation and an additional 5 ton of steel recovered. The cost of the shredder is able to be recouped in less than a year.
So, just like 10-15 years ago, when horizontal grinders were being introduced, it became obvious that larger operations needed a tub and a horizontal grinder to take advantage of the benefits of both. In today’s market, it is now obvious, that owning a shredder and a grinder are necessary.
Shredders are not all created equal obviously. Make your list of needs and try a few. Whether single shaft or dual shaft, without trying a shredder, you do not know how much money you are losing.
Questions? Dave Whitelaw, email@example.com