Every year, the world generates 16 million tons of wood scrap. Though most of this scrap wood can be recycled, only 15 percent of it is. This occurs even though recycling costs far less in energy and materials than utilizing virgin lumber. In many places, recycling wood scrap is even cheaper than dumping it in landfills.
This has increased recycling efforts by businesses that generate wood scrap, who can then process it themselves or sell this valuable resource to a recycling company. Recycling wood scrap often requires breaking it down to turn it into a readily usable material like wood fibers or flour, which usually involves reduction equipment like rotary mills and hammer mills.
Applications for Wood Fibers & Wood Flour
Wood scrap, like other waste, has the potential to be recycled and turned into valuable products. It can be used as a building material for landscaping, paper production, and other uses. Two byproducts made from processed wood scrap are wood fibers and wood flour. These two derivatives of processed wood waste are beneficial for various applications.
Wood plastic composites made from wood fibers are used for outdoor benches, cladding, decking, doors, window frames, fencing, railings, and other products needing to withstand weathering. These composites are also used in construction materials like fiberboard, hardboard, particleboard, and waferboard.
Other applications wood fibers can be used for include:
- Decorative baseboards.
- Façade paneling and trim.
- Production of glues, paints, and varnishes.
- Pulp for paper, along with paperboard.
- Substrate for hydroponic farming.
- Wood plastering and cement composites.
Scrap wood flour can be used in animal feed and food processing industries. Animal feed often includes wood flour to optimize the digestion process in livestock, contributing to better animal health. Human food processing is used to aid filtration when processing glucose or starches.
Wood flour can also be used for applications that include:
- Auto manufacturing, including both interior and exterior uses.
- Bioplastics for flooring products.
- Fabricating fuses in the electronics industry.
- Filler for epoxy or wood when mixed with resin.
- Firework manufacturing.
Most wood scrap can also be made into biofuels. To make biofuel effectively from scrap wood, it needs to be reduced to bits of 1/8 inch (3 mm) or less. The particles within processed wood fibers, especially wood flour, tend to be considerably smaller. Additionally, the water content must be 15 percent or lower.
Processing Wood Fibers & Wood Flour from Scrap
As per lumber, scrap wood made into wood fibers or flour is separated into grades. It’s important when processing wood scrap to understand these different grades, which correspond roughly to their source. For example, sources like pallets, crates, construction scrap, and wood from tree servicing are easier to recycle than those recovered from wood used for discarded furniture or demolition. Grading also helps determine the products that can be made from the scrap.
The different grades of scrap that can be made into wood fibers and flour are:
- Grade A is pre-consumer scrap wood mainly used for products like animal bedding and surface landscaping, though it’s sometimes used for biofuel and briquettes for barbecuing. Typically, grade A scrap wood comes from manufacturers of wood products and the logistics, retail, and packaging industries. Including soft and hardwoods, it comes from sources like offcuts of either sawed or virgin timber, untreated boards, scrap pallets, packing cases, packaging waste, and cable drums.
- Grade B is industrial scrap wood that’s received non-hazardous treatments, and it’s generally used for making panelboard, though it too can be used for biomass. Sourced from places like a construction site, demolition operations, skip operators, or transfer stations, grade A scrap includes building materials and solid-wood furnishings
- Grade C is municipal waste wood, treated similarly to grade B scrap and used for biomass or panelboard. It often comes from household waste and municipal waste collections. It can include all types of scrap wood as per grades A and B, plus DIY materials and furniture made from board products.
- Grade D is considered hazardous waste, requiring disposal at a special facility. It includes utility poles, railroad ties, cooling towers, and agricultural fencing, though it can include sources from any other grades of scrap wood.
Regardless of the grade, scrap wood requires a reduction to be correctly recycled and used for other products. This requires milling and grinding, for which rotor and hammer mills work particularly well. Let’s look at how each of these mills handles scrap wood.
Using RotorMills to Process Scrap into Wood Fibers
Whether it’s to produce fiberboard or other types of composite wood products for construction, for making paper, or for another application for processed wood fibers, the wood chips, shavings, or other scrap requires a milling process. Depending on the application, wood fibers need to be of precisely defined lengths, which influences the quality of the end product.
The concept of rotary milling is ancient, going back to Carthage in the 6th century BCE. Modern-day rotary mills operate similarly, and today rotary mills are often used to recycle wood scrap by preparing secondary wood fibers that are then used to make various products. Rotary mills are especially useful for processing fibrous materials like wood into varying degrees of fineness.
Processing of wood fibers by Rotormill follows this general process:
- Wood scrap is fed thru a hopper into the bottom section of the mill.
- A fan wheel attached to the rotor distributes material into the grinding chamber
- In the main section of the grinding chamber is a rotor containing rows of grinding plates that accelerate the air, causing it to react with grooved linings of the rotormill body.
- Miniature pockets of air rotating at high velocities cause particles to collide with each other and disintegrate against the lining.
- Pneumatic air “sweeps” the product up the gap between the grinding plates and grooved lining, which is conveyed to a dust collection system at the top.
IPEC Rotormill for Processing Wood Fibers
A subsidiary of Prater Industries, IPEC offers its own version of the rotary mill. The Rotormill has a long gap design that reduces downtime, as it doesn’t require screens that can wear out or plug/blinds over during production. Its rotor design is more balanced, featuring particularly robust bearings at the machine’s top and bottom.
Some key benefits of IPEC’s Rotormill include:
- Allows high throughput fine milling continuously.
- Enables easy access to the mill’s interior for maintenance and cleaning operations.
- Handles a variety of types of wood scrap to produce wood fibers.
- Offers the ability to “fluff” wood fibers.
- Reduces processing time and costs as it simultaneously does several operations, including deagglomerating material and coating surfaces.
IPEC offers eight models of its Rotormill, which range from 15 to 750 horsepower. The Rotormill’s sturdy carbon or stainless steel construction also allows it to operate under harsh conditions, while its compact design enables flexible positioning on a production line and means it requires no special foundation.
Using Hammer Mills to Process Wood Flour
When it comes to breaking down and grinding wood scrap into flour, the effectiveness of hammer mills is nearly unparalleled. Their versatile configurations make them perfect for processing scrap wood. For this reason, they’ve become essential for wood recycling efforts, including biofuel production.
Hammer mills grind wood scrap into wood flour in the following manner:
- Wood scrap is fed through a transition chute or tray into its grinding chamber.
- In the chamber, hammers attached to a rotor swing at high speeds, pulverizing the scrap into smaller particles.
- As the rotating hammers strike the scrap wood, the fragments are swept across this screen.
- Once particles are small enough, they pass through the screen, dropping through a discharge chute into the collection chamber.
Rotor speed, screen opening size, and hammer type determine the size of particles a hammer mill produces. Flat-edged hammers are the best for producing wood flour, as they pulverize scrap wood into a fine powder, though knife-edge hammers may be used initially to break down larger pieces of wood scrap.
Prater Hammermill for Processing Wood Flour
The Prater Full-Screen Hammer Mill is one of the most useful equipment for processing scrap into wood flour. Able to handle high capacities and produce uniform particle size distributions, Prater’s hammer mills are designed to enhance the quality of the final product. A durable piece of equipment, this Prater hammer mill handles oddly sized wood scrap, which makes it perfect for wood recycling operations.
Features the Prater Full-Screen Hammer Mill includes:
- Allows various configurations of screen openings, patterns, and hammer sizes depending on the application.
- Enables balanced horsepower to screen area to maximize power efficiency.
- Features rotors that are precision balanced, reversible, and symmetrical.
- Grants easy access to screens for removal and replacement.
- Makes cleaning and maintenance easier with large access doors.
- Permits uniform hammer-to-screen clearance with its rigid-frame mounting for the screen.
- Requires no tools for screen changes.
- Utilizes 100 percent of the screen to maximize efficiency.
The full-screen hammer mill’s durability stems from its heavy-duty design, which includes sturdy pillow-block bearings to extend its lifecycle. Its lifespan can be extended further with optional stainless steel or armored construction.