handbook for crusher
Handbook for Crusher: A Practical Guide to Selection, Operation, and Maintenance
Overview
This handbook consolidates fundamental knowledge for crushing equipment used in mining, aggregate production, and recycling industries. It covers crusher types, selection criteria, operational parameters, wear management, and common failure modes. The content is based on industry standards (ISO 21873, ASTM D75), manufacturer guidelines (Metso, Sandvik, Terex), and field data from aggregate plants. It is intended for plant operators, maintenance crews, and project engineers who need a reference that bridges theoretical design and daily practice.
1. Crusher Types and Their Application Scope
Crushers reduce large rocks into smaller fragments through compression, impact, or attrition. The choice of crusher depends on feed size, product gradation, hardness (abrasiveness), and capacity. Below is a comparison of the four primary types:
| Crusher Type | Principle | Typical Feed Size | Reduction Ratio | Best For | Limitations |
|---|---|---|---|---|---|
| Jaw Crusher | Compression (single toggle / double toggle) | Up to 1,200 mm | 4:1 – 6:1 | Primary crushing of hard, abrasive rock | High wear on jaw plates; not for slabby material |
| Gyratory Crusher | Compression (conical) | Up to 1,500 mm | 5:1 – 8:1 | High-capacity primary (above 2,000 t/h) | High capital cost; requires heavy foundation |
| Cone Crusher | Compression (eccentric gyratory) | 50 – 400 mm | 3:1 – 6:1 | Secondary/tertiary crushing, hard rock | Sensitive to feed distribution; requires stable feed |
| Impact Crusher (HSI / VSI) | Impact (high-speed rotor) | Up to 500 mm (HSI), 50 mm (VSI) | 10:1 – 20:1 | Soft to medium-hard rock, recycling (concrete, asphalt) | Higher wear cost per ton; not for abrasive rock (quartzite, granite) |
Selection rule of thumb:
- If the material’s abrasion index (AI) > 0.5 g/ton, prefer compression crushers.
- If the material is limestone or recycled concrete, impact crushers offer lower operating cost per ton.
- For a plant producing 500 t/h with feed of 800 mm, a jaw crusher (primary) + cone crusher (secondary) is the conventional configuration.
2. Key Operational Parameters That Affect Performance
2.1 Closed Side Setting (CSS) and Open Side Setting (OSS)
CSS is the smallest gap between the crushing liners at the discharge end. It directly controls the top size of the product. Reducing CSS increases fines but also increases power draw and wear. For a cone crusher, a 10 mm reduction in CSS can increase power consumption by 15–20% while improving the reduction ratio.
2.2 Feed Distribution
A crusher must be fed with a well-distributed, continuous stream. For cone crushers, the feed must be evenly distributed around the crushing chamber (360°). If feed is biased to one side, uneven wear occurs, and the crusher may vibrate excessively. The recommended feed segregation index (max particle size / min particle size) should be less than 3:1..jpg)
2.3 Moisture Content
Moisture above 5% in fine fractions (< 10 mm) causes clogging in the crushing chamber and reduces throughput by up to 30%. In such cases, a scalping screen before the crusher is mandatory.
2.4 Speed and Stroke (for Cone Crushers)
- Eccentric speed (rpm): Higher speed increases fines but reduces capacity.
- Stroke (throw): Larger stroke increases reduction ratio but increases power draw and wear.
Typical values for a 300 hp cone crusher: speed 360 rpm, stroke 25 mm.
3. Wear Management and Liner Life
Wear parts (jaw plates, mantles, concaves, blow bars) are the largest consumable cost in a crushing plant, often accounting for 30–50% of operating cost per ton. The following practices extend liner life:
- Rotate liners: For jaw crushers, flip the fixed and movable jaw plates when the wear reaches 50% of the original profile.
- Monitor wear profile: Use a wear gauge or laser scanning. A worn mantle in a cone crusher changes the crushing angle, leading to higher power draw and lower throughput.
- Match liner material to feed:
- Manganese steel (12–14% Mn) for impact and compression.
- Chrome steel (high Cr, 20–28%) for impact crushers on abrasive feed.
- Ceramic composite for VSI rotors when processing river gravel.
Real case (from a granite quarry in Jiangsu, China):
A 200 t/h granite plant used a jaw crusher (PE-750×1060) with standard manganese jaw plates. The original liner life was 180 hours. After switching to a high-manganese (18% Mn) alloy with a thicker cheek plate design, liner life increased to 320 hours. The cost per ton of wear parts dropped from USD 0.12 to USD 0.08, while downtime for liner change was reduced from 12 hours to 8 hours per change.
4. Common Failure Modes and Troubleshooting
| Symptom | Possible Cause | Corrective Action |
|---|---|---|
| Excessive vibration | Loose foundation bolts; unbalanced rotor (impact crusher); worn bearings | Tighten bolts to torque spec; rebalance rotor; replace bearings |
| Overheating of bearings | Insufficient grease; wrong grease type; misalignment | Grease per schedule (e.g., every 4 hours for jaw crusher); check alignment |
| Product too coarse | CSS too wide; worn liners; feed too large | Adjust CSS; replace liners; check feed size against crusher opening |
| Sudden power spike | Tramp iron (metal) in feed; feed segregation | Install magnetic separator; improve feed chute design |
| Low throughput | Moisture > 5%; feed not continuous; crusher running at reduced speed | Install pre-screening; adjust feeder speed; check V-belt tension |
5. Safety and Maintenance Checklist (Daily)
- Check oil level and temperature (for oil-lubricated crushers).
- Inspect drive belts for tension and wear.
- Listen for abnormal knocking sounds (indicates loose liners or broken springs).
- Verify that all safety guards are in place before starting.
- After shutdown, clean the crushing chamber of accumulated fines to prevent cold-start jamming.
6. Case Study: Upgrading a Secondary Crushing Circuit
Background: A limestone quarry in Vietnam operated a 250 t/h plant with a jaw crusher (primary) and a single cone crusher (secondary). The product P80 was 45 mm, but the asphalt plant required P80 of 25 mm. The quarry was forced to run the cone crusher at a very tight CSS (12 mm), causing frequent liner changes (every 90 hours) and high power consumption (1.8 kWh/t).
Solution:
- Added a VSI crusher (Barmac B7150) after the cone crusher.
- The cone crusher CSS was opened to 22 mm, and the VSI was set to produce the final 25 mm product.
- Installed a vibrating screen (2-deck) to close the circuit.
Results (after 3 months of operation):
| Parameter | Before | After |
|---|---|---|
| P80 product size | 45 mm | 24 mm |
| Liner life (cone) | 90 hours | 220 hours |
| Specific energy | 1.8 kWh/t | 1.2 kWh/t (total circuit) |
| Production rate | 250 t/h | 280 t/h |
| Wear cost per ton | USD 0.15 | USD 0.09 |
The payback period for the VSI and screen was 11 months, based on reduced wear cost and increased saleable product (higher price for finer aggregate)..jpg)
7. Frequently Asked Questions (FAQ)
Q1: How often should I change the oil in a cone crusher?
A: For a standard oil-lubricated cone crusher, change the oil every 500 operating hours or every 3 months, whichever comes first. Use the oil grade specified by the manufacturer (usually ISO VG 150 or 220). Always take an oil sample for analysis at each change to detect metal particles indicating bearing wear.
Q2: Can I use an impact crusher for hard granite (Mohs 7)?
A: Technically yes, but it is not economical. The blow bars and impact plates will wear out extremely fast (often less than 50 hours), and the cost per ton will be 3–5 times higher than a cone crusher. For granite, use a jaw crusher + cone crusher combination. Impact crushers are best for limestone (Mohs 3–4) or recycled materials.
Q3: What is the correct way to adjust the CSS on a jaw crusher?
A: For a single-toggle jaw crusher, use hydraulic shims or mechanical wedges. Always adjust with the crusher stopped and locked out. Measure the CSS with a lead wire or a laser device. Never adjust the CSS while the crusher is running, as this can damage the toggle plate.
Q4: Why does my cone crusher produce flat and elongated particles?
A: Flat/elongated particles are caused by a low reduction ratio per stage, a worn crushing chamber profile, or a feed that is too coarse relative to the CSS. To fix this: (1) reduce the CSS, (2) ensure the feed is well-graded (not all large lumps), and (3) consider adding a third crushing stage or a VSI for cubical shaping.
Q5: What is the maximum feed size for a cone crusher?
A: The maximum feed size is typically 80–85% of the feed opening (the distance between the mantle and concave at the feed point). For example, a cone crusher with a 200 mm feed opening can accept a maximum feed of 160–170 mm. Feeding larger material will cause blockages and damage the upper frame.
8. References and Standards
- ISO 21873-1:2015 – Building construction machinery and equipment. Mobile crushers. Part 1: Terminology and commercial specifications.
- ASTM D75/D75M – Standard Practice for Sampling Aggregates.
- Metso Crushing and Screening Handbook (6th ed.), 2020.
- Sandvik Rock Processing Guide, 2019.
- Wills' Mineral Processing Technology (8th ed.), Chapter 6 – Crushers.
This handbook is a practical reference. Always consult the specific equipment manual for torque values, lubrication schedules, and safety lockout procedures before performing any maintenance.