Annually the world produces millions of tons of wood waste. This waste could be made up of anything from tree branches and logging waste, through to pallet prunings and bamboo culms. It gets turned into useful wood chips using one main “work horse” the drum wood chipper. If you‘re considering purchasing a drum wood chipper for a biomass fuel plant, paper mill or landscaping operation, you should understand how they work first.
In this comprehensive guide you will understand the whole mechanical process step by step, piece by piece and learn about what sets Drum chippers apart from disc ones, the applications that use them most, and what you need to know to run and keep one up and running.
What Is a Drum Wood Chipper?
A drum wood chipper is one of the most powerful and robust industrial machinery for turning unprocessed wood material logs, branches, pallets, slabs and other by-products into consistent-sized woodchips. This equipment is characterized by a rotating cylindrical drum (also called a knife roller or cutter roller), on which many blades (steel cutters) are radially attached.
Compared to a disc chipper where cutting blades are fixed to a flat rotating disc, the drum chipper has its blades located flush to a drum which rotates in the same plane as the feed direction. This flat design results in the distinctive high dump and high capacity of the drum chipper.
Key point: Industrial drum wood chipper mill can crush between 0.8 and 25 metric ton wood per hour, which also rely a lot on models, organization and dimension of machinery.
Core Components of a Drum Wood Chipper
It is useful to understand the function of the different parts of the machine before describing the chipping process. A typical drum wood chipper is made up of the following main elements:
- Infeed Hopper / Feeding Chute
The large rectangular opening at the front of the machine used for loading raw materials. The chipper‘s diameter limit is set by its dimensions – the commercial drum chippers range from 25cm (10in) diameter to 60cm (24in).
- Upper and lower feed roller
A series of forcible (by hydraulics or by machinery), rollers or rolls that grip the feed stock and draw it into the chipping chamber at a rate that is uniform and consistent. The upper roller (s) is capable of floating of itself (themselves), in the vertical plane to adjust for various thicknesses of stock. This adjustment is hydraulically controlled to prevent burning of logs and maintain a uniform feed rate.
- The Rotating Drum (Knife Roller)
The cutting ‘thing’ in the machine This is a large steel cylinder — 36cm to over 90+cm diameter on commercial machines — which rotates rapidly on its axis carrying between 2 to 4 (sometimes more) mounted knives. The drum rotates in a horizontal plane toward the hold.
- Chipping Knives (Flying Blades)
Blades (wearing plates) of high quality steel mounted to the face of the drum by means of pressure blocks. Thes knives establish the chipping action and, being hardwearing alloy steel, can be resharpened and turned over. A larger drum will have four knives while a smaller one will have two.
- Counter Blade (Anvil / Bottom Knife)
A stationary, non rotating blade. Located at the mouth of the chipping chamber. As the blades in the drum rotate past the counter blade, the wood is sheared cleanly at the edge of the chip (like scissors cutting paper). In many mills, this is the most important knife for chip consistency.
- Discharge Outlet and conveyor
Once the wood has been chipped, it is blown out of the cutting chamber by a blow pipe or moved by conveyor belt to a storage bin or a downstream process stage (dryer, pellet mill).
- Hydraulic System
Powers the feed rollers and allows the upper roller assembly to open. This feature permits quick blade inspection, the ability to change the blade gap and even change the comb plate without having to strip the entire machine.
- Base Frame and Power Unit
The machine is welded to a rigid and high strength steel frame. It is powered by an electric motor or a diesel/gas engine that drive the drum through a set of belts and pulleys.
How a Drum Wood Chipper Works: Step-by-Step
Here is the complete operational sequence from raw log to finished wood chip:
Step 1: Raw Material Loading
All wood material (any log, brush bundle, waste pallet or slab) is fed through the in feed hopper. For many sizes of machine the wood material is manually fed into the machine by the operator, either by way of a simple flat belt or through an automated flat belt conveyor system. In some industrial applications a crane or wheel loader is used to deposit the bulk material directly into the hoper.
Step 2: Feed Roller Engagement
When material is dropped into the hopper, it encounters the top and bottom feed rollers. Also driven hydraulically, the rollers grab the wood on both sides and draw it into the chipping chamber at an optimal rate of feed. The industry standard is roughly 30 m (100 ft) of material per min into the chipper.
Constantly alters the position and pressure of the upper roller according to the thickness of the material. In extra stubborn or knotty timber, the system will adapt to prevent them kicking out and stopping (this is why highly modern, hydraulically fed drum chippers have replaced their older, conventionally fed, predecessors you can imagine why the hazards of these were looked upon with such disgust; the industry called them “chuck-and-duck” machines for a reason).
Step 3: Drum Rotation and Knife Engagement
The material delivered to the cutting chamber is introduced to the rapidly-spinning drum. The drum is aligned parallel to the infeed chute, and is spinning rapidly in a direction towards the discharge. The drum has mounted on it, at an angle, a series of blades.
For every revolution of the drum, each blade cuts a ‘slice’ from the incoming Wood. The thickness of this slice is dependent on how far the Wood moves forwards between the blades cutting (which is dependant on feed speed, and drum RPM). Several blades (say four) at a lower RPM may produce the same quantity of chips as a two blade Drum at a higher RPM.
Step 4: Counter Blade Shearing
Anvil, or counter blade, serves as the cutting edge upon which the knives do the scoring. A perfect knife-to-anvil clearances is vital with blade not too tight that the anvil and knife become worn rapidly and too loose that the chips are ragged and poor. Anvil setting after each Knife sharpening, and or changing is an integral part of the maintenance.
Step 5: Chip Sizing and Screening
In some (though not all) industrial drum chippers a screen (perforated plate) is placed below/behind the cutting zone. Only material small enough to fit through the screen holes will pass through the plate and out of the machine. Larger pieces will stay in the cutting chamber and will be hit by the rotating knives until they are chipped to the desired size. This screening is another factor responsible for the quite steady product sizes of drum chippers.
Step 6: Chip Discharge
The discharge chute discharges any chips which have been segregated from the machine as being of the correct quality. The drum‘s rotation and sometimes the addition of special wind blades, or fan paddles on the knife roller causes an airflow in the drum which pushes the chips out of the machine. This flow of outgoing chips may be directed into a truck bed, collection bin or conveyor, or stored as a pile. In process lines handling biomass, the chip stream may flow directly into a rotary-dryer or pellet press.
Key Technical Specifications to Understand
When evaluating drum wood chipper performance, these are the numbers that matter:
| Specification | Typical Range |
| Material diameter capacity | 100 – 600 mm (4 – 24 in) |
| Processing capacity | 0.8 – 25+ metric tons/hour |
| Number of knives | 2 – 4 (or more on industrial models) |
| Drum diameter | 360 – 900+ mm |
| Motor power | 15 kW – 700+ kW |
| Chip size output | Adjustable: typically 10–50 mm |
| Feed speed (target) | ~30 m/min (100 ft/min) |
Drum Wood Chipper vs. Disc Wood Chipper: Key Differences
One of the most common questions buyers get, other than “what kind of oil do I use?”, is the drum vs. Disc debate. For a simple answer to this question:
Cutting mechanism: drum chippers cut in a radial, scooping motion as the drum passes the counter blade. Disc chippers mount blades on the face of a spinning disc, which cuts across the grain at about a ninety degree angle. The cutting plane of a disc chipper is stationary, which typically yields marginally more consistent chip length however the screening of a drum chipper can actually be more effective.
Feed throat opening: Drum chippers tend to have larger infeed openings, which will benefit in processing larger, tougher or deformed objects such as brush, palm fronds, coily branches, and whole logs. Disc chippers are more adapted to straighter, more consistent material.
Volume of processing: drum chippers are designed for heavy-duty processing. They are designed for industrial operation and will turn out 50% more wood per hour than comparable disc chippers. The surface area of the drum and its hydraulic fed feed make this possible.
Chip quality: Disc chippers output chip of slightly more uniform length, and tend to blow chip slightly faster (more critical for loading trucks). Variance in shape of drum chipper chips, although generally uniform due to screen size, may be slightly higher.
Energy efficiency: using a Disc chipper gives a fly wheel effect advantage – once the large Disc builds up to speed it‘s momentum is effectively maintained. Than for a Drum chipper as it has a larger drum diameter and four -k nife arrangement with a lower rpm per cut.
Best use case:
Drum chippers: Large tonnage, industrial scale operations such as high volume processing, converting biomass into fuel, paper/particleboard mills, tree care companies with large equipment, land clearing, moving large or living trees.
Disc chippers: Moderate volume work, (for example, street tree work and landscaping) or situations in which the use of a portable chipper and uniform chip presentation are important
Industries That Rely on Drum Wood Chippers
Drum wood chippers are essential equipment across multiple industrial sectors:
Paper and pulp mills apply drum chippers to efficiently chip logs and logging residues into uniform-sized wood chips, which then feed a pulping process. The uniformity of the chips is reflected in the quality of the pulp, and its here that the screening system of the drum chipper is of the most benefit.
Biomass energy plants utilize drum chippers to prepare the wood fuel to be burned or converted into other formats such as gas or pellets. Since drum chippers can handle such a large diversity of input materials, including branches, bark, waste wood, bamboo, and farm stalks, they are the most popular machinery used in biomass feedstock preparation.
Particleboard and MDF manufacturers: Wood chips in certain sizes are needed as feed to particleboard and MDF plants. Fabricators providing drum chippers with adjustable screen opening to enable the customer to set the chip profile to the dimensions needed for its pressing and bonding profile.
Tree care and municipal services: The use of truck mounted or trailer mounted drum chippers for municipal and tree care work effectively processes tree waste at the job site. The large infeed throat of the drum chipper is more capable of handling the brushy and ragged material common to urban forestry work than any disc chipper.
Landscaping companies use drum chippers in order to shred green waste. It is then turned into mulch: for disposal or as a saleable product quite where all green waste ends up.
Drum Wood Chipper Maintenance: What Operators Need to Know
Without correct maintenance, a drum chipper that operates optimally for ten years could just as easily be a chipper that never gets to that point and is always down. Make sure you do following:
Chipping knives/ Blades should be inspected after each time the machine has been used as there will be enormous stresses on the blades. Check for chips and nicks and check blades for dullness after each run. Dull blades won‘t just lower the quality of output they also cause the machine to work harder leading to increased fuel use and more pressure on the bearings and belts.
Grease drum bearings while the machine is warm. Re-grease up to the point where old grease is expelled, this flushes away any dirt and water which could cause corrosion to the bearings. Advice from a Vermeer technician: never miss this step at the end of a shift!
You must re-adjust the anvil each time the blades are replaced or sharpened. Blade-to-anvil clearance is also very important. If the blade-to-anvil clearace is not set correctly there will be poor chip quality, more vibration and higher wear rates on the blade and counter blade. Re-set the anvil gap each time a knife has been serviced before starting again.
Monitor belt tension at intervals. Belts and pulleys transfer power from the motor to the drum in a drum chipper. Worn or frayed belts will slip when under load. Slipped belts will decrease the efficiency of the chipper. Manually inspect and/or replace when necessary.
Material moisture. Although drum chippers are more tolerant of wet material than other types, very wet material tends to cause the chips to stick together, reducing throughput and chip quality. Material that is too dry causes dust and fines. The best moisture content in terms of efficiency and quality of output is:
Maintain the hydraulic system. The hydraulic feed roller system needs to have clean, correctly leveled hydraulic fluid. Check for leaks in oil levels and the hoses and cylinders every so often.
Safety Considerations for Drum Wood Chipper Operators
A word of warning about drum wood chippers: they are heavy-duty and should be treated with the respect they deserve. As a 2005 report in the Journal of the American Medical Association details; between 1992 and 2002 thirty-one Americans had been killed in wood chipper accidents and this record has been much improved upon in the modern hydraulically fed drum chippers, but safety rules are no less imperative!
Must always be hydraulically fed. Conventionally fed older drum chippers (chuck-and-duck style) used the drum as the feed, sucking the material in directly and with a lot of force. The hydraulically fed units are continuously variable, in a safe controlled flow, and if necessary they can quickly stop or reverse the flow of material.
Never put your hand into the infeed chute. The force pulling on the drum is so great that the machine will not stop if clothing, part of your hand or a tool is caught. Always use push sticks and other mechanical devices to feed material.
Test the emergency stop switch prior to each use. It is the last ‘Safeguard’ of the operator.
Use the required PPE. It is essential to wear hearing protection the noise from drum chippers can be loud. Safety glasses and gloves should be worn.
Never try and clear a jam while the machine is running. Disconnect the power supply (spark plug, ignition or circuit breaker) before opening any part of the cutting chamber.
Frequently Asked Questions
Q: What‘s the difference between a drum wood chipper and a disc wood chipper?
A: A drum wood chipper consists of a horizontally mounted rotating cylindrical drum that has blades attached to the upper outside. A disc wood chipper has blades attached to a face on a steel disc that is spinning. Generally drum chippers are better if you are processing a large volume of irregular material while disc chippers will give you more uniform chip length and are good for smaller capacity requirements.
Q: What materials can a drum wood chipper work with?
A: Drum wood chippers work with different types of logs (most often up to 450 mm in diameter), branches, twigs, board skins, waste veneers, pallets, round wood cores, bamboo, cotton stalks, sugarcane, or other non-wood fiber materials. The ability of a drum chippers to work efficiently and flexible with a large variety of irregular-type material is one of their advantages.
Q: How many blades does a drum wood chipper have?
A: Most drum wood chippers have between 2 and 4 cutting blades (Knives) the mounted on the drum. Smaller drum chippers work with 2 knives and bigger (industrial) work with 4. The bigger the diameter of the drum and the more knives it has, the slower they can spin (in RPM), while still getting the same effective production as a smaller drum with less knives, spinning faster.
Q: What chip size does a drum wood chipper generate?
A. Chip size depends on the type of screen fitted in the machine and the rate of feed, most industrial drum chippers generate in the region of 10 to 50mm chips. Chip size is can be varied by fitting different screens and manipulating feed rate. Studies indicate that doubling the cut length increases average chip length by about 50% whilst net productivity can be increased by around 15%.
Q: How much does a drum wood chipper cost?
A: Commercial drum chipper prices range from a few thousand dollars for the entry-level equipment to hundreds of thousands of dollars for industrial models with higher capacities, power unit, and configuration. Drum chipper blades–an initial major consumable cost–last about 400 to 800 operating hours and are priced at about $100 to $300 a piece.
Q: Is the drum wood chipper electric or diesel?
A: There are both electric and gas/ diesel powered drum wood chippers. Stationary industrial drum wood chippers are electric because they have lower operating costs and are cleaner. Portability is achieved using gas/ diesel motors. The decision is based on your power supply, electricity costs, operational needs.
Q: How do I reduce jams in a drum wood chipper?
A: Use hydraulically fed machines with automatic feed regulation. Maintaining sharp blades is critical to reducing jams. Babcock recommends ‘if the blades go blunt, replace before exceeding the 110 hours between grinding’. Avoid chipping ‘wet, string bark material’, and feed in a steady, uniform flow consistent with the drum‘s speed. If a jam occurs, turn the machine off before clearing.
Conclusion
A drum wood chipper is one of the most versatile and high capacity machines in wood processing. Its main operating principle a series of knives on an axially rotating drum that feeds, shears and screens wood into clean standard chips makes it the ideal workhorse in high speed industrial operations where capacity, range of feedstocks and longevity are the paramount considerations.
No matter if you are comparing a drum chipper for a biomass fuel line, a paper mill‘s wood prep stage or a large tree care operation, the goal is always the same making certain that the fact the capacity, number of knives, screen size and feed mechanism are appropriate for the types of material you are working with and your production needs.