Radial Stacking Conveyor Product

Overview

A radial stacking conveyor is a mobile or stationary device that distributes crushed stone, sand, or aggregate into multiple stockpiles. The machine consists of a long conveyor belt mounted on a rotating boom that can sweep through a full 360° arc. Material fed to the base of the boom is carried upward by the belt and discharged from the boom tip into a stockpile. By automatically rotating the boom, a single radial stacker can create multiple product stockpiles (typically 4–6 piles in a ring around the machine) without requiring material to be manually repositioned. Radial stackers dramatically improve quarry and aggregate plant efficiency, reducing labor and equipment requirements.

How it works

Material (typically 50–300 mm aggregate) is fed onto a conveyor belt at the boom base via a chute. The belt, inclined 3–5° above horizontal, carries material upward along the boom length (typically 20–40 m). A motor drives the belt at speeds producing 200–600 t/h throughput. At the boom tip, material is discharged from the belt into a chute and falls into the stockpile beneath. The entire boom rotates about a vertical axis using a large slewing bearing and a separate rotation motor (5–10 kW). An automated PLC control system positions the boom at preset angles (e.g., every 60° or 45° to create 4–8 product piles). As each pile reaches target height or size, the operator selects the next pile angle on the HMI, the boom rotates automatically, and material is diverted to the new pile.

Components and subsystems

Boom Arm Assembly

The boom is a welded steel truss (60–100 mm diameter main tubes, 20–40 m length) extensively braced with diagonal members to achieve high torsional and bending stiffness. The large span and slender profile require careful structural design to keep boom sag and deflection minimal (typically <50 mm at the tip). The boom base is bolted to a rotating inner race of the slewing bearing. Motors, gearboxes, and electrical controls are mounted directly to the boom structure, creating a self-contained, rotating system.

Conveyor System

A rubber belt (1–1.5 m wide, 20–40 m long) runs up the boom from the base to the tip. The belt is inclined 3–5° above horizontal, a gentle slope that minimizes energy loss while allowing material to climb steadily. The belt is supported by dozens of idler rollers (typically spaced 0.5–1 m apart) positioned both above and below the belt to handle the weight and ensure smooth running. A powered pulley at the boom tip drives the belt at speeds of 2–4 m/s, producing 200–600 t/h throughput depending on material bulk density and belt width. The return (empty) side of the belt is typically guided by rollers beneath the boom structure.

Drive System

Two independent motors power the machine: (1) a belt drive motor (20–40 kW) that runs continuously while material is being stacked, and (2) a boom rotation motor (5–10 kW) that operates intermittently to move the boom between stockpile angles. The belt motor connects to a gearbox (typically 3:1–5:1 reduction) and then to the belt drive pulley. The rotation motor drives a pinion gear that meshes with ring gear teeth cast or machined onto the inner race of the slewing bearing. This allows the 5–10 kW motor to rotate a machine weighing 80–200 tons at steady 0.5–1.5 rpm.

Slewing Bearing

The heart of the rotating system. A massive spherical or roller bearing (1–2 m bore) is mounted vertically, with the outer race fixed to the base frame and the inner race attached to the boom base. The bearing contains 100–200 rolling elements (rollers or balls) that handle both radial loads (boom and material weight) and thrust loads (belt tension). Ring gear teeth are machined or welded onto the inner race to mesh with a pinion gear on the rotation motor. The bearing must be periodically greased through a Zerk fitting, typically once per week under normal operation.

Boom Rotation Motor

An electric motor (5–10 kW, 900–1500 rpm) with a planetary or helical gearbox (20:1–50:1 reduction) produces slow, torque-rich rotation suitable for the slewing bearing. The pinion on the gearbox output meshes with the ring gear on the bearing inner race. As the motor runs, it slowly rotates the boom through the selected angle (e.g., 60° or 45° from the current position). An incremental encoder on the bearing rotation provides position feedback to the PLC, allowing automatic stopping at preset angles. Manual controls and limit switches provide safety backup.

Mobile Base Frame

The base frame is a welded steel structure (W-beams, typically W12x65 or larger) that forms a rectangular footprint (5–10 m × 5–10 m). The slewing bearing is mounted at the center of this frame. On stationary stackers, the frame is bolted to a concrete foundation. On mobile units, the frame sits on four large wheels (often pneumatic, 0.8–1.2 m diameter) with brakes and optional self-propulsion. Hydraulic or mechanical leveling pads (adjustable jacks) on each leg allow the frame to be leveled on uneven ground before operation begins. Some mobile stackers include a traction motor and gearbox for self-powered movement between sites.

Control and Positioning System

An industrial PLC with a touchscreen HMI (7–10 inch color display) automates boom rotation and material flow. The operator inputs the target stockpile angle, and the PLC commands the rotation motor to move the boom to that angle. An incremental encoder provides position feedback; when the boom reaches the target angle, the rotation motor stops and material continues to be fed to the current pile. An optional wireless remote pendant allows the operator to control pile selection and emergency stop from ground level, avoiding the need for an elevated control cabin. The system also typically includes horn alerts and warning lights for safety.

Discharge Chute

At the boom tip, material exits the conveyor belt through a simple fixed or articulated chute that directs material downward into the stockpile. The chute prevents material from scattering and focuses the discharge stream, allowing for controlled stockpile building and improved material containment.

Engineering considerations

Slewing bearing life and maintenance: The bearing is critical and expensive (often $50K–$150K for large units). Bearing life is extended by proper lubrication (weekly greasing), correct alignment, and load balance. Overloading (operating with undersized material or overfeeding) accelerates wear. Bearing replacement is a major maintenance event, typically requiring 2–4 weeks and specialized technicians.

Boom deflection and material distribution: Long boom arms deflect (sag) under their own weight and material load. Typical maximum deflection is 50–100 mm for a 30 m boom, but even slight sag causes material to concentrate near the center of the stockpile pile rather than spreading evenly. Good design minimizes sag; poor design results in tall, pointed piles rather than uniform cone-shaped stockpiles.

Throughput and power: Throughput depends on belt speed, belt width, and material bulk density. Lighter, fluffier material (e.g., newly crushed limestone) occupies more space at the same tonnage and may not achieve advertised throughput. Conversely, dense materials (iron ore, heavy basalt) can achieve higher t/h on the same belt speed. Power consumption is roughly 0.1 kW per ton/hour of throughput for the belt drive.

Stockpile angle control: Most radial stackers are programmed to rotate in fixed angle increments (45°, 60°, 90°) creating symmetric piles. Some advanced systems allow variable angle increments and continuous rotation, providing more flexible stockpile management. However, operator skill is required to avoid overloading one pile or creating unstable slope angles.

Weather protection: Open-air stackers expose material to weather (rain, dust). In regions with heavy rainfall, roofing or covers are sometimes added, but this increases capital cost and reduces rotational freedom. Most quarries accept weather exposure as a normal operational cost.

Dust control: The high discharge point (boom tip at 20–40 m elevation) and material fall can generate dust. Water spray systems on the boom or dust suppression cannons at the pile base are often added in populated areas or for dust-sensitive materials.

Mobility and portability: Mobile radial stackers (typically 80–150 tons) can be transported on low-bed trailers and moved to different sites. Stationary units are heavier (200+ tons) and are bolted to concrete foundations, making relocation impractical. Mobile units are preferred for contract operations or temporary quarries; stationary units serve long-term, high-volume facilities.

Capital and operating costs: Radial stackers range from $500K–$2M in capital cost depending on boom length and automation. Operating costs include belt replacement (3–5 years), bearing maintenance, motor and gearbox service, and occasional structural repairs. Payoff comes from labor savings: one operator can manage 4–8 stockpiles automatically, whereas manual bucket-and-conveyor methods require multiple operators and more equipment.