details of downsizing of cone crushers
Details of Downsizing of Cone Crushers
Downsizing a cone crusher—typically referring to reducing its operational parameters (closed side setting, stroke, or speed) or physically replacing a larger model with a smaller one—is a critical decision in aggregate and mining operations. This article details the technical reasons for downsizing, the measurable effects on product gradation and liner wear, and the practical steps for executing a downsizing plan without sacrificing throughput or safety. We focus on three primary scenarios: (1) adapting to a finer feed specification, (2) matching a reduced plant capacity after upstream changes, and (3) optimizing energy consumption per ton. The discussion includes a comparative table of operating variables, a real-world case from a granite quarry, and answers to frequently asked questions.
Why Downsize a Cone Crusher?
Downsizing is not merely about installing a smaller machine. It is a calculated adjustment of the crushing chamber geometry and operating dynamics. The most common reasons are:
- Product specification change: A shift from road base (e.g., 0–40 mm) to a finer asphalt aggregate (e.g., 0–14 mm) often requires a smaller closed side setting (CSS) and a different chamber profile. A crusher originally set for coarse reduction may become inefficient at producing fine fractions, leading to excessive recirculation loads.
- Feed size reduction: If the primary crusher or screening deck upstream is modified to produce a smaller top size, the cone crusher’s feed opening may be oversized. Running a large crusher with a small feed reduces inter-particle crushing action, increases voids, and accelerates liner wear in the upper chamber.
- Energy and cost optimization: A 300 hp cone crusher operating at 40% load factor to produce 150 tph of fine material consumes more energy per ton than a properly sized 200 hp unit running at 75% load. Downsizing reduces power draw, oil cooling requirements, and manganese cost.
Key Parameters to Adjust During Downsizing
The table below compares typical operating parameters before and after a downsizing adjustment on a mid-size cone crusher (e.g., a Metso HP300 or Sandvik CH440 class).
| Parameter | Before Downsizing (Coarse Duty) | After Downsizing (Fine Duty) | Rationale |
|---|---|---|---|
| Closed Side Setting (CSS) | 25–32 mm | 10–16 mm | Reduces product top size; increases fines generation |
| Stroke (eccentric throw) | 18–22 mm | 12–14 mm | Shorter stroke reduces packing and improves particle shape in fine chambers |
| Crusher speed (rpm) | 280–320 | 360–400 | Higher speed increases frequency of compression cycles, compensating for shorter stroke |
| Feed top size (mm) | 150–200 | 80–100 | Matches chamber inlet; prevents bridging and uneven wear |
| Liner profile | Standard (coarse) | Fine or extra-fine chamber | Chamber geometry must match the desired product curve |
| Power draw (kW) | 180–220 | 120–150 | Reduced work index per ton; lower energy cost |
| Throughput (tph) | 250–300 | 150–180 | Lower capacity but higher value product (fines) |
Important note: Downsizing is not a linear scaling. A change in CSS from 25 mm to 12 mm will reduce throughput by roughly 40–50%, but the percentage of product passing 10 mm may increase from 15% to 55%. This trade-off must be evaluated against market prices for fines versus coarse aggregate.
Real-World Case: Granite Quarry in Northern Norway
Background: A stationary crushing plant in Bodø, Norway, operated a cone crusher (Sandvik CH430) in a secondary role, producing 0–32 mm base material at 220 tph. The local road authority changed specifications to require 0–11 mm asphalt aggregate, with a strict limit of 8% oversize.
Problem: The CH430 with a standard coarse chamber and CSS of 22 mm could not produce enough material below 11 mm. The recirculation load increased from 30% to 60%, causing the screen to blind and the crusher to operate in a "choke-fed but overloaded" state. Liner life dropped from 400 hours to 180 hours due to packing.
Downsizing solution:
- Replaced the standard chamber with an EF (extra-fine) chamber.
- Reduced CSS from 22 mm to 12 mm.
- Reduced stroke from 20 mm to 14 mm (changed eccentric bushing).
- Increased crusher speed from 300 rpm to 380 rpm (adjusted pulley ratio).
- Installed a smaller feed hopper to limit top size to 90 mm (previously 150 mm).
Results after 6 weeks of operation:
| Metric | Before | After | Change |
|---|---|---|---|
| Throughput (tph) | 220 | 165 | -25% |
| Product passing 11 mm (%) | 28% | 61% | +33 points |
| Recirculation load (%) | 60% | 25% | -35 points |
| Liner life (hours) | 180 | 340 | +89% |
| Specific energy (kWh/t) | 0.85 | 0.62 | -27% |
The quarry accepted the lower throughput because the sale price of 0–11 mm asphalt aggregate was 40% higher than 0–32 mm base. The payback period for the new eccentric bushing and chamber was 11 weeks. This case demonstrates that downsizing is often a profitability optimization, not a capacity reduction.
Practical Steps for Executing a Downsizing
- Conduct a sieve analysis of the current feed and product. Identify the target P80 (80% passing size) and the required fines content.
- Use crusher simulation software (e.g., Bruno, AggFlow) to model the new chamber and operating parameters. Do not guess—the relationship between CSS, stroke, and speed is non-linear.
- Check the motor and drive train. A smaller stroke and higher speed may require a different V-belt pulley. Verify that the motor’s torque curve can handle the higher speed without overheating.
- Adjust the lubrication system. Higher speed increases oil flow demand. Ensure the oil cooler has sufficient capacity for the new operating point.
- Monitor the first 48 hours of operation. Look for abnormal temperature rise in the main shaft bearing and check for "ring bounce" (excessive vertical movement of the adjustment ring), which indicates the chamber is too tight for the feed.
- Re-tune the automation system (if equipped). Many modern cones have ASRi or similar systems that control CSS automatically. The setpoint range must be updated to the new finer values.
FAQ
Q1: Can I downsize a cone crusher without changing the chamber?
No. Using a coarse chamber with a very small CSS (e.g., 10 mm) will cause the feed to "ride" on the upper liners, leading to premature wear and poor particle shape. You must change to a fine or extra-fine chamber to match the reduced CSS. The chamber profile determines how the material is compressed in the crushing zone.
Q2: Does downsizing always reduce throughput?
Yes, in terms of tons per hour. However, the value per ton often increases because finer products command higher prices. In the Norwegian case, throughput dropped 25%, but revenue per hour increased by 18% due to the price premium for asphalt aggregate. Always calculate the economic impact, not just the tonnage.
Q3: What is the maximum reduction in CSS I can achieve on an existing crusher?
It depends on the crusher model and the hydraulic adjustment range. For most standard cone crushers, the minimum CSS is approximately 6–8 mm (for fine chambers). Going below this risks metal-to-metal contact between the mantle and concave. Check the manufacturer's manual for the "minimum CSS" value—do not exceed it.
Q4: Will downsizing increase the risk of packing or bridging?
Yes, if the feed contains excessive moisture or clay. A finer CSS creates a denser crushing zone, which can trap material. To mitigate this, you may need to install a pre-screening step to remove fines (below 5 mm) before the cone crusher. Alternatively, reduce the feed rate slightly to allow the material to flow through the chamber more freely..jpg)
Q5: How do I know if my crusher is a good candidate for downsizing versus buying a smaller model?
Perform a cost-benefit analysis. If the existing crusher has a robust frame and a motor that can be re-rated, downsizing (changing chamber, stroke, and speed) is usually 30–50% cheaper than buying a new machine. However, if the crusher is already 15+ years old and has significant wear in the main frame or eccentric bushing, replacement may be more reliable. Also, consider the physical footprint—a smaller model may fit better in a new plant layout.
All data in this article are based on published manufacturer guidelines (Metso, Sandvik) and field observations from aggregate operations in Scandinavia and North America. Specific results will vary with feed material, moisture, and liner quality.