Original Post September 1, 2011
Well, let me ask you a question-
· What if you only had to fuel your grinder every 2 or 3 days?
· What if your tips lasted 3 months?
· What if you reduced weight gaining, color using fines?
· What if you could use contaminated materials?
If any of these would save you money, then absolutely. Is it for everyone? Probably not.
There are different types of slow speed shredders, dual shaft and single shaft, and they are getting more and more advanced in specialty operations. In general, the operations that can use a slow speed shredder include those in general volume reduction and most everyone sending waste for fuel.
Is it for a mulch operation? Not for finished product, but for a first grind it is.
How do they save money?
· RPM- They say speed kills in driving, but in this industry, speed costs. Most slow speed shredders turn at 30-50 rpm, not 1000-1800 rpm like grinders. This saves in multiple ways. Compared to more direct drive grinders, slow speed shredders use gearboxes to transfer the engine horsepower into torque to turn the shredder shafts reducing the extreme variation in engine rpm which in turn saves fuel. The gearboxes also allow for use of a smaller horsepower engine which reduces fuel usage. Because of the lower rpm, slow speed shredders will not create the same amount of fines which reduces weight and color usage for mulch, and the tips and screens last ten times as long in many cases.
· Contamination- Damage to high speed grinders is usually twice as bad because of the amount of downtime, repair hours and overtime associated with the breakdown. Slow speed shredders can impact contaminants at a slow enough rpm that they can reduce or eliminate damage. The shredder recognizes a contaminant by monitoring the pressure on the shafts and reducing speed and reversing, before finally shutting down or discharging to reduce or eliminate damage from contaminants. In addition, because of the slow rpm, the brittle carbide coating on the tips of the shredder will not damage like it would with a high speed impact, therefore the tips will last even longer.
· Materials- The slow speed shredder can shred many different types of materials without the wear and damage of a high speed grinder. By changing screens slow speed shredders are able to create large pickable size pieces of C&D, or reduce C&D to 6” minus for transfer. Shingles can be reduced for sorting plastic, paper and steel out, or made to 2” minus. Steel and aluminum can be reduced to a consistent size for an optimum price per ton. Logs and stumps will be reduced using half the fuel of a grinder.
Are slow speed shredders perfect? No.
· Production is generally lower than a high speed grinder. How much depends on materials and sizes. The fuel saved as compared to grinders is increased by the amount of increased shredding hours, but the total amount of grinding maintenance and repair hours on a weekly or monthly basis will be far less with the shredder. Also, the wear factor is considerable lower.
· Material sizing is an issue. It is very difficult to shred product smaller than 2” or 3” with any sort of production, but for first grind or fuel size, it would be difficult to beat the cost per ton.
Some things to consider and ask when purchasing a slow speed shredder-
· Sizing- Can you put in screens to make a several consistent size products and are they easy to change
· Replaceable tips- Are the wear tips replaceable? Some shredders do not have replaceable tips and you have to weld on the shafts constantly, jeopardizing the integrity of the steel shafts themselves.
· Protection- Do they have gearbox drives? Are they hydraulic for protection or direct drive with no protection? Do they have the same torque in forward and reverse? Do the shafts reverse individually? Does the shredder have the ability to release/remove contaminants?
· Magnets- Does the shredder have a crossbelt magnet which stays on for transport? Is it adjustable? For C&D a magnet is about 8”-12” or so away from the belt, but for wood, it is 4”-6”.
· Engine and Parts- Are the engines a common brand with the correct type of support in your area? Do they have field service? Are parts stocked locally or available overnight?
This is just one Grinder Guys opinion.
I have posted some videos of slow speed shredders shredding RR ties, C&D, tires and more at www.youtube.com/askthegrinderguy
Have a question or issue or need more help with slow speed shredders?