A chipwood block press turns dried wood particles and a thermosetting resin into a dense, uniform block that replaces a sawn solid-wood block in a pallet. The most common machine type is the extrusion press, in which a reciprocating ram pushes a resinated particle mat through a heated channel so that the profile cures as it travels, after which it is cut to length. Output is a consistent, moisture-stable block made largely from sawmill residues and recycled wood.
What a chipwood block is
Chipwood (also called pressed, compressed or chip blocks) is a particle-based material close to particleboard in structure, but formed as a thick, square or rectangular section rather than a thin panel. It is used mainly as the block in block pallets, where it separates the decks and carries the compressive load. The wider choice between solid and pressed blocks is covered in pallet blocks: solid wood vs chipwood.
The appeal is practical. Solid blocks require clean, defect-free cuts of timber, while chipwood can be made from planer shavings, sawdust, edging chips and cleaned recycled wood. Properties are uniform from block to block, there are no knots or splits, and dimensions are held within tight tolerances.
A research study published in 2025 in BioResources tested chip block pallets made from mixed forest sawdust and reported block densities of 0.50–0.56 g/cm³, which is in the range of light to medium solid softwood. Density, binder choice and pressing conditions together determine compressive strength and nail-holding ability.
Raw materials and binders
The particle furnish is typically shavings, sawdust and fine chips, screened to a defined size range. Oversized pieces are re-ground, and contaminants such as metal, stones and plastics are removed before drying. Moisture content going into the press is controlled closely because water must evaporate during curing and too much steam can cause blows or internal splits.
The binder is a thermosetting resin that hardens under heat. The main families are:
| Binder | Typical position |
|---|---|
| Urea-formaldehyde (UF) | Low cost and fast curing; limited moisture resistance; emission control needed |
| Melamine-urea-formaldehyde (MUF) | Better moisture resistance than UF at higher cost |
| Phenol-formaldehyde (PF) | Strong and moisture resistant; slower curing, darker color |
| Polymeric MDI (pMDI) | Isocyanate binder, formaldehyde-free; sensitive to handling and more expensive |
In the 2025 BioResources study, phenol-formaldehyde gave the highest compressive strength (6.93 MPa) among the three adhesives compared, while a low-emission urea-formaldehyde variant had lower mechanical strength. Urea-formaldehyde performed adequately at shorter pressing times but declined when pressing was prolonged. Results from one laboratory setup do not transfer directly to a production line, but they show the trade-off between strength, cure time and emissions.
Press types
Extrusion presses
An extrusion press has a forming channel (die) with the cross-section of the finished block, often heated by thermal oil or electric elements. A ram compresses a measured charge of resinated particles into the channel at regular strokes. Each stroke pushes the earlier material forward, so the strand moves slowly and cures as it passes through the heated section. At the exit the continuous profile is cut by a saw into blocks of the required length.
Because the strand is formed along its length, the particles in extruded material tend to lie in a particular orientation. Extruded blocks are therefore normally installed with the pressing direction aligned to the load direction recommended by the producer.
Mould (platen) presses
In a platen or mould press, a charge of particles is pressed in a closed mould between heated plates, which makes it possible to produce blocks of different shapes and densities, including blocks with chamfered edges or holes. Cycle time is longer per block, and the 2025 study used 60 minutes at 180°C for laboratory chip blocks, so production presses normally form many blocks per cycle. Mould pressing is related to the technology used for full moulded pallets, described in moulded wood pallet presses.
A typical production flow
- Particle preparation: shredding or chipping, hammer-milling, screening and metal removal.
- Drying: the particles are dried to a target moisture content, usually in a rotary or flash dryer fed by a biomass burner.
- Blending: resin, hardener and often a hydrophobic wax are metered onto the particles in a blender.
- Pressing: the mixture is extruded or molded under heat and pressure.
- Cutting: the strand or board is cut to block length with a cut-off saw; dust is extracted.
- Cooling and conditioning: blocks are cooled and stacked so that stresses and residual steam can equalize.
- Inspection: dimensions, density and surface quality are sampled before packing.
The overall layout resembles a small particleboard plant, and capacity is limited by the press stroke rate, the die cross-section, the heated channel length and the cure time of the resin. Dryer and resin-dosing capacity must be matched to the press, otherwise they become the bottleneck.
Quality parameters
Producers check a small set of properties routinely:
- Density and density profile across the section.
- Compressive strength parallel to the load direction.
- Screw or nail withdrawal resistance, which affects how well a pallet holds together.
- Moisture content after cooling.
- Water absorption and thickness swelling, which show how the block behaves in damp storage.
- Formaldehyde emission class, relevant for buyers and regulators.
- Dimensional tolerance, because block height controls fork opening height.
Block specifications for exchange pallets, such as the EPAL pallet, are controlled by the licensing body's technical rules, so a producer who supplies blocks for such pallets must meet the current approved specification. Chipwood is made of processed wood, but pallets that use it with solid-wood boards still count as wood packaging unless made entirely of processed material; see what is exempt from ISPM 15.
Economics and planning
A chipwood block line is a process plant, not a single machine. The investment covers particle preparation, dryer, resin storage and dosing, press, saw, dust extraction and fire protection. It therefore makes sense mainly where a producer has a steady supply of residues and consumes blocks in volume, or sells them to other pallet makers. Smaller pallet plants usually buy blocks rather than make them. Comparing offers requires asking for the resin type, density range, test certificates and the allowed moisture on delivery. The role of blocks in plant layout is covered in block pallet (EUR) production lines.
Frequently asked questions
What is the difference between a chipwood block and a solid block?
A solid block is cut from sawn timber, while a chipwood block is made from wood particles bonded with resin under heat and pressure. Chipwood is more uniform and avoids defects such as knots, but quality depends on the binder, density and press control.
Which resins are used for chipwood blocks?
Urea-formaldehyde, melamine-urea-formaldehyde, phenol-formaldehyde and isocyanate (pMDI) binders are all used in wood-based materials. The choice balances cost, cure time, moisture resistance and formaldehyde emissions.
Why is the press heated?
Heat starts the chemical curing of the thermosetting resin and drives off moisture. Without sufficient temperature and time the binder does not fully cure and the block loses strength and stability.
How is block capacity determined?
Capacity depends mainly on the die cross-section, stroke rate and the length of the heated channel, which together set how long the material needs to cure. Upstream dryer and blender capacity must be matched, or they limit the output.
Sources
- Effects of adhesives on the physical and mechanical properties of chip block pallets from mixed forest group wood biomass (BioResources, 2025) — BioResources, North Carolina State University
- The manufacture of presswood pallets — Racklify Encyclopedia
- EPAL Euro Pallet (EPAL 1) technical data — European Pallet Association
- ISPM 15 Regulation of wood packaging material in international trade — IPPC / FAO