Chutes are essential components in mining operations as they facilitate the efficient movement of materials. They are designed to minimise the damage to the material during transfer and reduce the likelihood of blockages.
In crushing plant design, a chute plays a crucial role as a steeply inclined trough facilitating the smooth transfer of materials onto a conveyor. There are two primary types of transfer feeding points: between a feeder and a conveyor and between two conveyors. Despite its simplicity and absence of moving parts, the chute requires careful design to ensure efficient operation. Here are key considerations and principles in the design of chutes:
2. Chute Functionality
- Chutes are positioned between feeders and conveyors or between two conveyors.
- Commonly of rectangular cross-section, chutes can also be circular or elliptical.
- Unlike conveyors, chutes do not rely on power for operation, leading to lower maintenance costs.
3. Chute Design Objectives
Chutes must be designed to feed material:
- In the direction of belt travel.
- At the center of the belt.
- Minimizing impact on the belt.
- At a speed equal to the belt speed.
4. Influencing Factors in Chute Design
- Capacity, size, and characteristics of the handled material.
- Speed and inclination of the belt.
- Single or multiple positions at which the belt is fed.
5. Principles of Chute Design
- Prevent Plugging at Impact Points: Ensure smooth material flow without blockages at impact points.
- Ensure Sufficient Cross-Sectional Area: Design chutes with an adequate area to accommodate the material flow.
- Control Stream of Particles: Manage the trajectory of particles to avoid erratic or disruptive flow.
- Minimize Abrasive Wear of Chute: Implement measures to reduce wear and tear on chute surfaces.
- Control Generation of Dust: Address factors contributing to dust generation during material transfer.
- Minimize Particle Attrition: Design chutes to minimize the wear and breakdown of transported particles.
While chutes are simple and cost-effective, they require careful planning to prevent downtime and ensure a seamless material transfer process. By following the above principles, operators can enhance the efficiency and longevity of chute systems.
6. Chute Angle
- The feeding chute must be inclined to facilitate the desired forward material flow.
- For fine, moist materials, a steep chute ensures rapid sliding, while a low angle prevents excessive bouncing of lumps on the belt.
- A low chute angle, combined with proper load direction and speed, minimizes impact on the belt, reducing the risk of damage, material degradation, and dust generation.
- An excessively low angle can slow material flow which will lead to chute blockage.
- Chute angle calculation considers lump size, material flowability, and atmospheric conditions.
- The chute angle should be 5°–10° more than the angle of repose of the material.
7. Chute Dimensions
- Chute widths are designed to match downstream equipment.
- Feeding chute width should be no longer than two-thirds of the receiving belt width and not less than 2–3 times the largest lump size dimension.
- Cross-sectional area should be at least four times the largest lump size to prevent blockages.
8. Chute Construction
- Metal chutes, typically mild or stainless steel, are common and cost-effective.
- They can be shaped in various ways and sizes, with options for abrasion-resistant linings for abrasive materials and corrosion-resistant coatings for corrosive materials.
- Chutes can be bolted or welded, with considerations for assembly/disassembly trade-offs.
- Rubber edging prevents material leakage and lump blockages.
9. Lining of Chutes
- Chute lining may be required for repair, performance improvement, resistance to wear, impact, noise, dust, or chemical reactions.
- Selection of lining material, including rubber, manganese steel, hardox steel, high-chrome steel, chrome–molybdenum steel, plastics, synthetic elastomers, and ceramics, is crucial.
- Liners can cover the entire chute or be applied strategically based on wear patterns.
- Hard-Wearing Steel Liner:
- Carbon content defines wear resistance in steel chute liners.
- Selection based on application, price, and required hardness.
- Collaboration with equipment manufacturers to determine specifications.
- Ideal for handling heavy ores and providing durability.
- Hardox steel is one of the most frequent used option.
- Ceramic Chute Liners:
- Installed for the toughest applications with coarse-textured materials.
- Ceramic liners designed to handle high impact wear without degradation.
- Combination of rubber and ceramic for high wear and tear resistance.
- Reduces annual maintenance cost and minimizes shutdown risks.
- 12 times more efficient and durable than steel wear liners.
Proper chute design, considering angles, dimensions, construction materials, and linings, is essential for ensuring efficient material flow, minimizing downtime, and extending the life of the chute system.