Quick Answer: Wood chipping is the first mechanical step in paper and pulp manufacturing. Logs are debarked, cut to length, fed into a chipper (drum or disc design), and reduced to uniform chips sized about 4 to 6 mm thick by 15 to 20 mm long per TAPPI wood preparation standards. Screening removes oversize and fines; accepted chips go to storage piles or directly to the digester. Chip uniformity controls cook quality downstream, which is why every chemical pulping line depends on this step running well.
1. What is the chipping process in paper making?
Chipping is the conversion of debarked logs into small, uniform wood chips that feed downstream pulping. It is the first step in any wood-based paper making process, and chip quality directly determines the efficiency of every stage that follows, including digester cooking, washing, screening, and bleaching.
The chipping line lives in the woodyard at the front of the mill. A typical kraft or sulfite mill consumes about 1.6 to 2.0 cubic metres of wood per air-dry tonne of pulp per FAO 2024 forestry statistics, so a 1,000 TPD mill processes roughly 1,800 m³ of wood daily and the chipping line must keep up without bottlenecking. Chip dimensions are tightly controlled because oversize chips under-cook in the centre while fines and pin chips over-cook and reduce yield.
Key Takeaways - Chipping is the first wood-prep step before pulping; it controls downstream cook quality. - Target chip size: about 4 to 6 mm thick, 15 to 20 mm long and wide (TAPPI reference). - Two main chipper designs: drum chippers (large mills, high throughput) and disc chippers (smaller logs, lower maintenance). - Screening removes oversize and fines, typically rejecting 5 to 10% of chip output. - Moisture content of fresh chips is 45 to 55%, which affects storage and pulping.
2. Raw material used in the chipping process
Most wood pulp mills run softwoods (pine, spruce, fir) for long-fibre kraft and tissue grades, or hardwoods (eucalyptus, birch, aspen, acacia) for shorter-fibre printing and writing grades. Choice of wood species is set by the final paper grade and by local forest supply per CEPI 2025 industry statistics.
Raw material arrives at the woodyard as full-length logs, short-bolts (2 to 3 m), or already-debarked roundwood. Some Indian and Southeast Asian mills also feed agro-residues (bagasse, wheat straw, rice straw) or bamboo through dedicated chipping or shredding lines (per IPPTA technical references on alternative fibres).
3. Drum vs disc chippers: when to use each
The two dominant chipper designs in pulp and paper mills are drum chippers and disc chippers. Both produce roughly the same target chip size but differ in capacity, knife geometry, and maintenance profile.
Most large kraft mills run drum chippers for the main softwood line and supplement with disc chippers for sawmill chips, branches, and reclaimed wood. The chipper selection is then matched to the rest of the woodyard equipment, which we cover in the paper mill equipment list for stock prep and beyond.
4. The 5 steps of the chipping process in paper making
The chipping operation runs in five sequential steps from log intake to chip storage. Each step has measurable quality targets that the operator monitors continuously.
Step 1, Debarking. Logs are tumbled in a rotating debarking drum or run through a ring debarker that strips bark. Target residual bark is below 0.5% by weight per TAPPI test methods, because bark carries colour, ash, and pitch that contaminate downstream pulp.
Step 2, Log cutting. Long logs are bucked to chipper-feed length, typically 1.0 to 3.0 m. Uniform log length helps the chipper hold consistent chip dimensions and reduces feed jams.
Step 3, Chipping. Debarked logs feed into a drum or disc chipper at a controlled angle. Rotating knives slice cleanly across the wood grain to produce chips with target dimensions of about 4 to 6 mm thick by 15 to 20 mm long and wide per TAPPI wood preparation references. Knife angle, log feed rate, and rotor speed are tuned to the wood species.
Step 4, Screening. Chips drop onto vibrating or gyratory screens with two or three deck levels. Overs (chips above 45 mm or thicker than 8 mm) are sent back to a re-chipper or hammer mill. Fines (below 3 mm) are rejected to bark fuel or hog fuel. Accepts typically run 85 to 95% of total chip output, with screening rejects of 5 to 15%. Acceptable chip uniformity is the single most important predictor of pulp yield per IPPTA chemical recovery technical paper.
Step 5, Storage. Accepted chips are conveyed to open chip piles (outdoor, weeks of inventory) or silos (indoor, days of inventory). Pile design controls air flow, moisture loss, and microbial activity. Fresh chips have moisture 45 to 55% which drops to 35 to 45% during outdoor storage.
This 5-step sequence feeds the paper mill digester where chips are cooked into pulp.
5. Chip quality specifications
Chip quality is graded on five measurable parameters. A mill that misses any of these by more than a few percent will lose pulp yield, increase chemical consumption, or produce off-spec pulp.
Pulp mills test these parameters every shift on representative chip samples per TAPPI standards. Failed samples trigger immediate corrective action at the chipper or screen.
6. Machinery for the chipping process in paper making
A complete chipping line includes:
- Log deck and cross-conveyor: receives logs from the woodyard
- Debarker: drum or ring design, sized to log diameter
- Slasher or chipper-canter: pre-cuts oversize logs
- Primary chipper: drum or disc, sized to throughput target
- Chip conveyor system: belts and pneumatic blowers to screens
- Chip screens: 2 to 3 deck vibratory or gyratory
- Re-chipper or hammer mill: handles oversize rejects
- Storage system: open piles, A-frame silos, or covered domes
- Reclaim equipment: bucket reclaimers or screw reclaimers to feed pulping
Most modern lines also include chip density meters, moisture sensors, and image-based size analysers for continuous quality monitoring. The machinery details for a full mill are catalogued in our paper mill equipment list.
7. Where chipping fits in the bigger picture
Chipping is one stage in a long process. Downstream of chipping, the chips enter pulping (mechanical, semi-chemical, or chemical), which produces pulp that is then screened, bleached if needed, and converted to paper. The two dominant chemical pulping routes are explained in our chemical vs mechanical pulping comparison.
For wood-fed kraft mills, the chip line directly feeds the digester for the kraft paper manufacturing process. For mechanical mills, the chips go to refiners. For recycled-fibre mills, this entire chipping section is replaced by a re-pulper that handles recovered paper from sorted waste paper grades.
Outside wood, alternative-fibre mills running bagasse, bamboo, or agri-residue use shredders rather than knife chippers, and the upstream prep looks different. For the bagasse route specifically, see the bagasse plate making machine guide.
