Wood Veneer Defects after drying: Causes and Improvement Solutions

Defect Name

Causes

Improvement Methods

Edge Cracks

1. Veneer damaged during loading.
2. Drying temperature too high.
3. Over-drying.
4. Conveyor stopped during drying.
5. Prolonged storage of wet veneer, edges dry.
6. Loose veneer quality or large cracks on the back.
7. Tight edges in veneer cutting for ash.

1. Follow operational procedures to reduce damage.
2. Adjust temperature to correct levels.
3. Check final moisture content meets process requirements.
4. Avoid stopping the conveyor to extend drying time.
5. Spray water on edges before drying.
6. Increase edge pressure with clamps.
7. Cut ash veneer with slightly loose edges.

Center Cracks or Brittle Veneer

1. Drying temperature too high or humidity too low, not suited to the wood species.
2. Incorrect upper belt speed.
3. Large cracks on the back of the veneer.

1. Adjust temperature and humidity for the species, close moisture exhaust valves, or reduce temperature.
2. Adjust speed of upper and lower belts; entry should be faster to allow free expansion.
3. Check middle knife clearance or wear on center clamps in wood peeling machine

Batch Too Dry or Wet

1. Process not followed.
2. Dryer malfunction.
3. Temperature measuring instruments inaccurate.
4. Variation in initial moisture content.

1. Strictly follow process specifications for temperature and speed.
2. Repair the dryer.
3. Calibrate temperature instruments.
4. Monitor initial moisture and adjust temperature and speed accordingly.

Partial Over/Under Drying

1. Dryer malfunction.
2. Inconsistent veneer thickness.
3. Variability in initial moisture content.
4. Uneven drying conditions across layers.
5. Different wood species or material characteristics.

1. Repair the dryer.
2. Check veneer thickness.
3. Inspect initial moisture content.
4. Stop for repairs.
5. For species with significant moisture variation (e.g., pine), dry separately.

Uneven Moisture Content

1. Dryer malfunction.
2. Initial moisture uneven.
3. Prolonged veneer storage.
4. Inconsistent compression during cutting.
5. Uneven veneer thickness.

1. Inspect the dryer.
2. Check initial moisture.
3. Dry in the order of cutting.
4. Adjust cutting clearance.
5. Improve thickness accuracy.

Discoloration

1. Drying temperature too high.
2. Conveyor stopped mid-operation.

1. Set temperature as per process requirements.
2. Avoid conveyor stoppages.

Wavy Veneer

1. Excessive drying temperature.
2. Low humidity in the dryer, over-drying.
3. Insufficient veneer compression.
4. Uneven compression or knife clearance during cutting.

1. Lower drying temperature.
2. Reduce exhaust vent opening, decrease moisture loss.
3. Check pressure rollers or belts.
4. Adjust knife clearance and improve veneer cutting quality. Ensure even compression for basswood.

Mechanical Damage

1. Indentations from debris.
2. Veneers stacked too closely, causing dents.
3. Tearing due to improperly adjusted rollers or belts.

1. Remove debris during loading and clean conveyor rollers and belts.
2. Leave gaps between veneers during feeding.
3. Ensure uniform pressure on upper/lower rollers and belts.