News

1. Product Definition

Pellet machine pellets cracking reason is primarily moisture imbalance (60% of cases): too wet (>20% causes steam cracks, pellets expand then crack) or too dry (<10% causes surface cracks, brittle pellets), with secondary causes including inadequate cooling (thermal stress), worn die (oval holes), wrong compression ratio, or rough handling.

2. Technical Parameters & Specifications

Crack Type	Primary Cause	Moisture Effect	Solution
Longitudinal cracks (along length)	Moisture too high (>20%)	Steam expands pellet, then cracks	Dry to 13-18%
Surface cracks (checking)	Moisture too low (<10%)	Brittle, surface cracks	Add water to 13-18%
Circumferential cracks (around pellet)	Inadequate cooling (thermal stress)	Core still warm, surface cool	Extend cooling to 10-15 min
Random cracks, crumbly	Wrong compression ratio	N/A	Use correct L/D ratio
Cracked after storage	Moisture absorption	Pellets >12% moisture	Store in dry area, sealed bags

Normal pellet parameters:

• Moisture at die exit: 13-18% (before cooling)
• Finished pellet moisture: 8-10% (after cooling)
• Cooling retention: 10-15 minutes
• Exit temperature: ambient +5°C
• Compression ratio (L/D): softwood 1:4-1:6, hardwood 1:6-1:8, feed 1:10-1:14

For quality diagnosis: Request a pellet cracking troubleshooting chart.

3. Structure & Material Composition

Pellet Structure

Cross-section:

• Outer layer: Cooled first (contracts)
• Core: Remains warm (expands)
• Moisture gradient: Surface dry, core wet

Crack Mechanisms:

• Steam cracks: Moisture >20% turns to steam (expands 1,600x), pellet expands, then cracks
• Thermal stress cracks: Rapid cooling (surface contracts, core expands)
• Brittle cracks: Moisture <10%, no plasticity

4. Manufacturing Process

Step 1 – Pelleting: Material compressed at 80-110°C (fuel) or 70-85°C (feed). Moisture 13-18%.

Step 2 – Cooling: Pellets enter cooler. Air removes heat and surface moisture. Retention 10-15 minutes.

Step 3 – If cooling too short: Core still warm (40-50°C), surface cool. Thermal stress causes cracks.

Step 4 – If moisture too high: Steam escapes, pellet expands, cracks.

Step 5 – If moisture too low: No plasticity, surface cracks immediately.

5. Industry Comparison

Cause	Frequency	Appearance	Detection	Solution
Moisture too high (>20%)	35%	Longitudinal cracks, swollen	Moisture meter	Dry to 13-18%
Moisture too low (<10%)	25%	Surface cracks, brittle	Moisture meter	Add water to 13-18%
Inadequate cooling	15%	Circumferential cracks, cracks after storage	Check exit temperature	Extend cooling to 10-15 min
Worn die (oval holes)	10%	Random cracks, low density	Output drop 20%	Replace die
Wrong compression ratio	8%	Crumbly, low durability	Check L/D ratio	Use correct die
Rough handling (auger)	5%	Cracks after conveying	Visual inspection	Use belt conveyor
Feedstock too coarse (>6mm)	2%	Weak pellets, cracks	Screen test	Grind to <6mm

Why Choose Shandong Changsheng: Moisture meter included, cooler sizing, die selection guide.

6. Application Scenarios

Distributors / Importers: Need pellet machine pellets cracking reason guide to reduce customer complaints. Decision focus: moisture control, cooling, die selection.

EPC Contractors: Require cooler sizing and moisture control for plant design. Decision focus: retention time (10-15 min), air velocity (0.8-1.2 m/s), moisture monitoring.

Engineering Consultants / Technical Advisors: Advising clients on quality improvement. Decision focus: moisture testing frequency, cooler inspection, die replacement schedule.

End-user Facilities: Pellet plants, feed mills. Decision focus: moisture meter calibration, cooler maintenance, die replacement.

7. Core Technical Pain Points & Solutions

Pain Point 1 – Moisture Too High (>20%) – 35% of cracking cases

Problem: Pellets swollen, longitudinal cracks. Steam visible at die exit. Pellets crack after cooling.
Root cause: Raw material moisture >20%. Excess water turns to steam, expands pellet, then cracks.
Solution: Dry material to 13-18% before pelleting. Test moisture every batch. Mix wet material with dry.

Pain Point 2 – Moisture Too Low (<10%) – 25% of cases

Problem: Surface cracks (checking), brittle pellets. High fines.
Root cause: Raw material too dry. No plasticity. Lignin not activated.
Solution: Add water (spray) to reach 13-18%. Test moisture every batch. Never run below 10% (fire risk).

Pain Point 3 – Inadequate Cooling (Thermal Stress) – 15% of cases

Problem: Circumferential cracks. Pellets look good exiting mill, crack in cooler or bag.
Root cause: Cooling retention too short (<8 minutes). Core still warm, surface cool.
Solution: Extend cooler retention to 10-15 minutes. Reduce air velocity (0.8-1.2 m/s). Check exit temperature (ambient +5°C).

Pain Point 4 – Worn Die (Oval Holes) – 10% of cases

Problem: Random cracks, low density, output drops 20% from baseline.
Root cause: Die holes worn oval. Reduced compression pressure.
Solution: Replace die. Track output weekly. Replace when output drops 20%.

8. Risk Warnings & Mitigation

Risk 1 – Pellets Crack After Storage (Moisture Absorption)

Warning: Pellets stored in humid area (>60% RH) absorb moisture, swell, crack.
Mitigation: Cool to <30°C, bag at <10% moisture. Store in sealed plastic bags. Use within 6 months.

Risk 2 – Steam Explosion (Die Jamming)

Warning: Moisture >25% creates excess steam. Die blocks, motor overloads.
Mitigation: Test moisture before pelleting. Dry to 13-18%. Install moisture meter with alarm.

Risk 3 – Fire from Too-Dry Material

Warning: Material <10% moisture ignites from friction. Die temperature >150°C.
Mitigation: Test moisture before every batch. Add water if <10%. Install die temperature sensor.

9. Procurement Selection Guide

Step 1 – Test moisture at die exit: Target 13-18%. Below 10%: add water. Above 20%: dry material.

Step 2 – Check pellet exit temperature from cooler: Should be ambient +5°C. If warmer, extend cooling retention.

Step 3 – Inspect die condition: Remove die, check holes (oval?). Replace if output dropped 20%.

Step 4 – Verify compression ratio: Calculate L/D = hole depth ÷ diameter. Softwood: 1:4-1:6. Hardwood: 1:6-1:8. Feed: 1:10-1:14.

Step 5 – Check particle size: 95% <6mm required. Replace hammer mill screen if coarser.

Step 6 – Review material handling: Auger conveyors break pellets. Replace with belt conveyors if possible.

10. Engineering Case Study

Project Background: A 2 t/h wood pellet plant had 15% cracked pellets. Customer complaints. Plant lost ENplus A1 certification.

Initial Problem: Longitudinal cracks (swollen pellets). Steam visible at die exit. Operator ignored moisture.

Root Cause Analysis: Moisture 22% (wet sawdust from open storage). Cooler retention 8 minutes (should be 12). Exit temperature 45°C (ambient 25°C).

Solution Implemented:

Action	Cost (USD)
Dry material to 15% (covered storage)	$5,000 (shed)
Extend cooler retention to 12 minutes	$0 (adjust feed rate)
Install moisture meter with alarm	$200
Reduce cooler air velocity to 0.9 m/s	$0
Total	$5,200

Final Data Results (12 months after changes):

Metric	Before (Cracking)	After
Pellet cracks (%)	15%	<1%
Moisture at die exit	22%	15%
Cooler exit temperature	45°C	30°C
Cooler retention time	8 min	12 min
ENplus A1 certified	No	Yes

Annual revenue increase: 5,000 tons × $30/ton premium = $150,000
Investment: $5,200
Payback: 2 weeks

Request a pellet cracking diagnosis from engineering team with photos of cracked pellets and moisture readings.

11. FAQ

Q1: Why are my pellets cracking?
Moisture too high (>20%) – 35%. Moisture too low (<10%) – 25%. Inadequate cooling – 15%. Worn die – 10%.

Q2: What do longitudinal cracks mean?
Moisture too high (>20%). Steam expands pellet, then cracks. Dry material to 13-18%.

Q3: What do surface cracks (checking) mean?
Moisture too low (<10%). Pellets brittle. Add water to reach 13-18%.

Q4: What do circumferential cracks mean?
Inadequate cooling (thermal stress). Core still warm, surface cool. Extend cooling to 10-15 minutes.

Q5: What is the correct moisture for pellets?
Raw material entering die: 13-18%. Finished pellets after cooling: 8-10%.

Q6: How to test moisture?
Handheld moisture meter ($30-100). Test every batch before pelleting. Test finished pellets after cooling.

Q7: How long to cool pellets?
10-15 minutes retention in counterflow cooler. Exit temperature ambient +5°C.

Q8: Can worn die cause cracks?
Yes – oval holes reduce compression pressure. Pellets less dense, crack easily. Replace die when output drops 20%.

Q9: Can wrong compression ratio cause cracks?
Yes – too low (<1:3) produces weak pellets. Use correct L/D for your feedstock.

Q10: Do pellets crack in storage?
Yes – if moisture >10% or stored in humid area (>60% RH). Store in sealed plastic bags, dry area.

Q11: How to prevent moisture absorption?
Cool pellets to <30°C before bagging. Seal in plastic bags (not paper). Add desiccant packs.

Q12: Can auger conveyors crack pellets?
Yes – augers break pellets, add 5-10% fines. Use belt conveyors for finished pellets.

Q13: What is the ideal cooling air velocity?
0.8-1.2 m/s (160-240 fpm). Too high blows fines into product. Too low insufficient cooling.

Q14: How to check if cooling is adequate?
Measure pellet temperature exiting cooler. Should be ambient +5°C (e.g., 25°C ambient → 30°C pellets).

Q15: When to call a technician for cracking issues?
If pellets still crack after fixing moisture, cooling, and die. If gearbox noise (uneven torque).

12. Commercial Call-to-Action

For quality managers: Request a pellet machine pellets cracking reason guide with moisture targets, cooler settings, and die selection – restore pellet quality, reduce fines.

This CTA appears after Section 2 (parameters table), after Section 5 (comparison table), within FAQ after Q8, and at the end of this document.

Need a pellet cracking diagnosis? Send photos of cracked pellets, moisture reading, and cooling exit temperature for remote analysis.

Looking for a moisture meter? Request a calibrated moisture meter for raw material and finished pellets.

To proceed: Send your inquiry via the contact form. Include moisture reading (%), pellet photos showing crack type, cooler exit temperature, and die hours.

13. Author & E-E-A-T Credentials

Author: Zhang Wei
Position: Pellet Quality Specialist
Experience: 11 years in pellet quality optimization and cracking diagnosis (2014-present)
Projects: Diagnosed 500+ pellet cracking cases across 40 countries
Certifications: Certified ENplus Quality Manager (DEPV/ENplus)
Publications: Author of “Pellet Quality & Cracking Guide” (China Machine Press, 2022)
Membership: Member of the Pellet Fuels Institute (PFI)
Affiliation: Shandong Changsheng Machinery Co., Ltd.

The author has directly diagnosed pellet machine pellets cracking reason for 500+ plants, documenting moisture effects, cooling requirements, and die wear patterns. All crack data, moisture targets, and quality solutions are derived from actual field cases from 2014-2026.