Chippers and shredders
Most of our industry refers to chippers or chipper-shredders as pieces of equipment that can handle both wood and leaves. These machines have both a chipping device and a leaf-shredding mechanism. This mechanism is basically a hammer mill, cylinder or drum with a series of pivoting flail-type knives. The chipper-shredder usually is a smaller machine and may include a vacuum to clean up leaves. These machines can be self-propelled or stationary. Most chippers are disc-type, consisting of a large, heavy, rotating disc with knives mounted to it and are for chipping wood only.
Stand-alone or PTO-driven Stand-alone units are more expensive because they require their own power source. However, these units have an advantage because they do not require a tractor (which could be used for another project) as a power source. They are mounted on a trailer, and you must consider whether you'll be towing them at highway speeds. Before purchasing one of these units, tow it behind your vehicle to make sure it tracks properly at various speeds. For safety reasons, you may need to install separate trailer brakes for some of the larger units if they aren't standard.
Most companies offer a choice of unit size determined by the diameter of limbs or trees that it can handle. For larger diameter material, you'll need a unit with fast chipping speed and larger power plant. The price tag also goes up with these larger units. The higher horsepower units equipped with diesel engines provide more torque and can sustain more hours of operation than gasoline-powered units. Some manufacturers of medium to smaller units offer a choice of horsepower, makes and models for gasoline engines.
PTO-powered units are less expensive and may serve your needs if you don't need to transport them far. In addition to being more affordable, these units are well suited for fixed-site work if you already have a PTO-equipped tractor there. Your determining factor will be the size of debris you need to chip.
Chipping unit Because knives cause the highest amount of maintenance concerns, choose a chipper that allows you to quickly and easily remove these knives and their anvil (back-up plate or bed knife). Pay attention to the number of knives on a machine, whether you can reverse them and how many times you can sharpen them before replacement. Knives should be made of high-quality steel, so you may want to avoid installing generic-brand replacement knives. Do a little research and find out how many times you can sharpen the knives before they will need replacement. Some manufactures sell a sharpening machine for their chippers.
Another feature to look for in chipping units is the ease with which you can change the size of the discharge screens that control chip size. This allows you to make chips for various landscaping needs.
Self-feeding units The self-feeding option usually is available only for machines greater than 20 hp. These chippers feed at a more constant rate, cut down on operator fatigue and offer higher production. These units consist of an additional hydraulic motor (or motors) and a feed wheel or dual feed wheels that pull the material into the machine. You usually can add these later to most machines if purchased without. Typically, a bar at the outside edge of the feed chute controls the feed rollers. You can set this bar in neutral, forward or reverse and also adjust the feeding speed with it. Some machines have flow-control valves that can further change the range of the feed rates for lighter and heavier material.
Main-shaft bearings The next component that you need to closely examine before selecting a unit is the quality and type of main bearings for the rotating shaft. These need to be of high quality because they perform most of the workload. They should be easy to maintain, and you also should consider their ease of replacement.
Feed and discharge chute When assessing the chipper's ability to accept branches, you must consider the width of the feed chute. Some feed chutes rotate to accept branches from different sides of the machine without moving the unit. Chutes take a lot of abuse and are subject to wear. So, be sure that the unit you select has a chute made of heavy-gauge material. The height of the feed chute is also important because an inappropriate height will cause operator fatigue.
Take note of the discharge chute's degree of rotation (the maximum being 360 degrees), discharge height and how far the machine will throw material from the discharge chute.
Capacity The largest material that you will need to chip determines the size of chipper you'll need. This is determined by diameter of the wood and the species of the wood to be chipped.
Maintenance (excluding the power plant) Your primary maintenance concern with chippers and shredders is their knives. You can re-sharpen chipper knives, whereas you can reverse shredder flail-type knives when dull but you can not re-sharpen them.
You must sharpen chipper knives with special sharpening equipment because they are made of high-carbon steel. Maintaining sharp knives can lengthen their life and the life of the machine by keeping power requirements low. An over-dulled or chipped chipper knife will need extensive sharpening, which will remove a large portion of the blade. This obviously will shorten its life. As soon as a blade is slightly dull, you should sharpen it to minimize the amount of blade-material that you remove. All knives need sharpening at the same time to keep them in balance-even if only one is worn or chipped. Also, you must use matched sets to keep the knife the same distance from the anvil for proper chipping and feeding. After removing the knives, clean the area where they are fastened with a wire brush to make sure they will align correctly. Be sure to torque the knife bolts to their proper specifications. You will need to examine the anvil and be sure it maintains a good, square edge. Occasionally, you may need to remove and sharpen it.
Other maintenance issues include proper lubrication of all moving parts at intervals recommended by the manufacturer. Do not over-grease. This will only cause excess grease to pile up and collect dust and dirt. If a power-feed unit has its own hydraulic system, you'll need to check the hydraulic-oil level and its condition daily and change it at recommended intervals. If the chipper is PTO-mounted, keep the hydraulic couplers clean. Examine the hydraulic-drive motors and hoses for leakage. Check drive belts daily for proper tension and cracks. Replace them, if necessary. Know your machine and be aware of unusual vibration. Excessive vibration usually means something is out of balance, loose, or knife-blades or bearings are too worn. Feel the bearings to see if they are excessively hot after operation. If so, replace them both-even if only one is hot.
Safety Operators of chippers or chipper-shredders-as with all power equipment-need to be aware of safety requirements and potential hazards. Safe operation requires effort and concentration. Any piece of machinery that can shred an entire tree demands the operator's full attention. Before operation, be sure to read the safety manual and all warning decals. If you are responsible for others working with the equipment, make sure they are familiar with the safe operation of the equipment. Wear eye protection (safety glasses or face shields) at all times while operating the equipment. Always wear appropriate clothing-it should fit snugly. Do not wear scarves, loose-fitting shirts or pants with cuffs, or gloves with gauntlets. Tuck-in shirts completely and button or zip up coats because limbs can snag these and pull you in the machine. With tow-behind units, check that you've properly secured the hitch and the safety chains are attached. When you store tow units, block-up the tongue and put chocks behind the wheels to prevent movement. Before starting the chipper, visually inspect bolt tightness, condition and tension of belts, sharpness of cutting knives and anvils and that the feed chute is clear of debris. Make sure that on automatic feed units (usually equipped with a rear safety-control bar around the feed chute), the safety bar is in neutral so that the feed rollers are not turning. Before operation, set up the machine in an area where the ground is level, stable and not slippery. While operating the chipper, the single most important rule to follow is never break the plane of the front of the feed shoot with hands or feet. If the machine becomes jammed or clogged always shut the machine off before unclogging it. It is important that your operator knows how to control the forward and reverse motion of the machine's feed rollers. If an operator is accustomed to these functions working in a certain way, he or she can easily change directions simply by reversing the hydraulic hoses on the hydraulic-drive motor. In other words, if a left-handed operator is assigned a machine that is designed for right-handed preferences, you can reverse the hoses to accommodate him or her.
Make sure that the machine has come to a complete stop before removing access panels. When performing maintenance on the machine, shut off the engine, remove the key (if electric start) or temporarily disable the machine.
Always feed material butt-end first. Feed shorter material into the machine by laying it on top of longer material. Do not feed material that you've raked up or scraped off the ground. You should simply place this material on top of the material that you've already chipped, as it may contain dirt and rocks that may damage the chipper. Chippers with dull knives and anvils do not feed well. This becomes a problem with any machine but especially on manual-feed units. If your operator then tries to force the material into the feed shoot, he or she creates a greater danger of slipping and getting too close to the chipper knives.
Do not operate the chipper alone. Always be prepared for a fire or injury by having a fire extinguisher attached to the machine and a first-aid kit handy. It is the operator's responsibility to make sure that flying chips and debris will not harm bystanders.
Following these safety rules will help ensure your operator's safety and protect your chipper from damage.
Michael McCaskey is a professor in the College of Agriculture and Technology at State University of New York-Cobleskill (N.Y.).
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