The lifespan of tablet press dies is primarily influenced by six factors: materials and heat treatment, structure and tablet shape, materials and processes, equipment and lubrication, operation and maintenance, and environment and storage. Among these, materials and heat treatment, pressure and speed, and cleaning and lubrication are the most critical controllable factors.
Detailed Explanation of Each Factor
1. Materials and Heat Treatment
- Material: Hard alloy (WC) offers the best wear resistance and is suitable for highly abrasive materials; High-speed steel (HSS) has good toughness and is suitable for general materials; Surface coatings (such as DLC, TiN) can improve wear resistance/corrosion resistance.
- Hardness and Toughness: Hardness should be ≥ HV1200 (WC), toughness ≥ 4 J/cm², and fatigue strength ≥ 800 MPa. Avoid "hard and brittle" or "tough but soft" results.
- Heat Treatment: Quenching, tempering, carburizing, and other processes directly affect hardness, toughness, and fatigue strength. Poor heat treatment can lead to premature failure.
2. Structure and Tablet Type
- Cavity Depth: Flat tablets have an allowable load of approximately 800 N/mm², while deep recesses have only about 300 N/mm², making them more prone to damage.
- Engraving/Patterning: Depth ≤ 0.15 mm, angle ≥ 15°. Avoid sharp corners and excessive depth to reduce stress concentration and die sticking.
- Anti-rotation Structure: Improper installation of semi-circular/flat keys (too low to wear the sealing ring, too high to disengage from the keyway) can cause die rotation, leading to uneven loading and wear.
3. Materials and Process
- Pressure: Controlled within allowable load according to tablet type: flat tablets ≤ 800 N/mm², deep recesses ≤ 300 N/mm².
- Speed: High-speed tableting (>60 rpm) requires increased lubrication frequency to avoid overheating and wear.
- Lubricant: Use appropriate amounts of magnesium stearate, etc., avoiding excessive use which can lead to die sticking or tablet weight fluctuations.
- For abrasive materials (e.g., high-fiber traditional Chinese medicine): Use a carbide alloy-lined die or a WC die.
- For corrosive materials (e.g., effervescent tablets, Vitamin C tablets): Use a WC or surface-coated die, and enhance cleaning and drying.
- For viscous materials (e.g., high-sugar tablets): Use a shallow concave/flat die, and optimize the amount and type of lubricant.
- Material characteristics
- Process parameters
4. Equipment and Lubrication
- Equipment accuracy: Regularly check the parallelism, perpendicularity, and pressure roller condition of the equipment to avoid uneven loading and impact.
- Lubrication: Use food-grade lubricating oil, adding it every 8 hours, focusing on lubricating the punch head, guide post, guide sleeve, and pressure roller.
- Automatic lubrication system: Regularly check for blockages and leaks to ensure adequate lubrication.
5. Operation and Maintenance
- Daily: Visual inspection (chipping, scratches, sticking).
- Weekly: Dimensional inspection (punch length, die inner diameter), replace when wear > 0.1mm.
- Monthly: Accuracy calibration (weight difference ≤ ±2%), check the condition of the anti-rotation structure and springs.
- Cleaning: Clean within 30 minutes of each machine downtime. Soak in alcohol/kerosene and wipe with a soft cloth, avoiding scratches from hard objects.
- Installation/Disassembly: Handle with care, avoiding impacts to the cutting edge and cavity; ensure the anti-rotation key is properly installed and bolts are tightened evenly.
- Regular Inspection.
6. Environment and Storage
- Temperature and Humidity: Operating temperature 20–25℃, relative humidity 45%–65%, avoid humidity and drastic temperature changes.
- Storage: After cleaning, apply anti-rust oil, place in a dedicated storage box, store separately, avoiding stacking and collisions.
- Corrosive Gases: If present, isolate and purify to prevent corrosion of the die surface.
Key Measures to Extend Service Life
1. Material Selection
- Select WC, HSS, or surface-coated dies according to material characteristics to ensure hardness, toughness, and fatigue strength meet standards.
2. Process Optimization
- Pressure should be controlled within allowable load limits: flat plates ≤ 800 N/mm², deep concave plates ≤ 300 N/mm².
- Speed ≤ 60 rpm; increase lubrication frequency at high speeds.
- Optimize material particle size (D90 ≤ 150 μm), moisture content (2%–5%), and lubricant usage.
3. Lubrication and Cleaning
- Lubricate every 8 hours, and clean promptly after each shutdown to prevent material residue and corrosion.
4. Regular Maintenance
- Establish a daily, weekly, and monthly inspection system; replace the die promptly when wear exceeds 0.1 mm.
5. Equipment Calibration
- Regularly check the parallelism, perpendicularity, and pressure roller condition of the equipment to ensure uniform force on the die.
Summary and Actions:
Recommended priority controls:
- Materials and heat treatment (select the right material and heat treatment), pressure and speed (strictly operate according to allowable load limits), and cleaning and lubrication (regular cleaning and standardized lubrication).
Immediate Action:
- Verify the existing die material and heat treatment parameters to ensure hardness ≥ HV1200 (WC) and toughness ≥ 4J/cm².
- Adjust pressure according to sheet type: flat sheets ≤ 800N/mm², deep concave sheets ≤ 300N/mm², speed ≤ 60rpm.
- Establish a system for daily cleaning, lubrication every 8 hours, and weekly dimensional checks.
Long-Term Planning: Optimize die selection based on material characteristics, establish a full lifecycle management file for the die, recording usage frequency, maintenance status, and failure causes to provide data support for future selection.