Conveying velocity is the speed at which material travels across the screen surface of a vibratory screener, measured in feet per minute (ft/min) or meters per second (m/s), and directly determines residence time and throughput capacity. It is the kinetic result of the screener's vibration pattern, G-force, weight angle settings, and screen inclination working together to move material from the feed point to the discharge.
In round vibratory separators using circular motion, material follows a spiral path from the center feed inlet to the peripheral oversize discharge. The conveying velocity has two components: a tangential component (the circular path) and a radial component (the outward movement toward the edge). The radial component determines how quickly material reaches the discharge. In linear-motion screeners, conveying velocity is a simple straight-line speed from inlet to outlet. In both cases, faster conveying velocity means less time on the screen and a direct tradeoff between throughput and screening efficiency.
Conveying Velocity Control Methods
| Control Method | Screener Type | Effect on Conveying Velocity | Adjustment Ease |
|---|---|---|---|
| Lead angle (weight offset) | Round separators | Primary control — wider angle = faster | Quick (5–15 minutes) |
| G-force adjustment | All types | Higher G-force = faster conveying | Quick (5–10 minutes) |
| Screen inclination | Linear screeners | Steeper angle = faster (gravity-assisted) | Moderate (mechanical adjustment) |
| Throw angle | Linear screeners | Lower throw angle = faster horizontal movement | Moderate (motor repositioning) |
| Motor speed (VFD) | All types | Higher RPM = faster (caution: avoid critical speed) | Quick (electronic) |
| Feed rate | All types | Higher feed = faster (bed pressure effect) | Quick (feeder adjustment) |
Typical Conveying Velocities
| Application | Screener Type | Typical Velocity (ft/min) | Corresponding Residence Time |
|---|---|---|---|
| Safety screening | Round | 3 – 6 | 3 – 8 seconds |
| General classification | Round | 1.5 – 3 | 8 – 15 seconds |
| Fine screening | Round | 0.5 – 1.5 | 15 – 30 seconds |
| High-volume scalping | Linear | 15 – 40 | 3 – 10 seconds |
| Dewatering | Linear | 10 – 25 | 5 – 15 seconds |
Why This Matters
Conveying velocity is the operational parameter that directly links the screener's mechanical settings to its production output:
- Residence time relationship — Conveying velocity and residence time are inversely related. Doubling the conveying velocity halves the residence time. This is the fundamental tradeoff in screening: faster material movement means higher throughput but fewer opportunities for undersize particles to pass through the screen.
- Throughput control — Conveying velocity, combined with bed depth and screen width, determines the volumetric flow rate across the screen. Increasing conveying velocity is one of three ways to increase throughput (the others being increased bed depth and larger screen area).
- Efficiency optimization — For a given feed rate, reducing conveying velocity (by adjusting the lead angle) increases residence time without changing bed depth, improving screening efficiency. This is the preferred first adjustment when carry-over is too high.
- Uniform distribution — Conveying velocity must be uniform across the entire screen surface. If material moves faster on one side than the other (from an unlevel machine or unbalanced vibration), one sector of the screen is underutilized while the other is overloaded, reducing overall performance.
Related Glossary Terms
- Residence Time — Inversely proportional to conveying velocity
- Lead Angle — Primary control of conveying velocity in round separators
- G-Force — The driving force behind material conveying
- Feed Rate — Combined with conveying velocity to determine bed depth
- Circular Motion — Creates the spiral conveying pattern in round separators
- Linear Motion — Creates the straight-line conveying pattern in rectangular screeners
Conveying Velocity FAQs
What is conveying velocity in vibratory screening?
Conveying velocity is the speed at which material moves across the screen surface from feed to discharge. In round separators, it is the radial speed from center to edge; in linear screeners, it is the straight-line speed from inlet to outlet. Faster velocity means higher throughput but less residence time and potentially lower efficiency. It is controlled by lead angle, G-force, and screen inclination.
How do you control conveying velocity on a round vibratory screener?
The primary control is the lead angle setting (angular offset between top and bottom counterweights). A wider lead angle increases radial conveying velocity; a narrower angle slows it. Increasing G-force also increases conveying velocity. These two adjustments give operators precise control over how fast material crosses the screen. On ScreenerKing, Sweco, Kason, and similar round separators, weight adjustments take 5–15 minutes.
Fine-Tune Conveying Velocity for Maximum Productivity
ScreenerKing vibratory screeners — the SiftPro, SiftPro 48, and SiftPro 60 — feature tool-free weight adjustment for fast conveying velocity optimization. Need help finding the right balance of throughput and efficiency? Our application engineers have 30+ years of experience optimizing screening operations across every industry. Parts and screens for Sweco, Kason, Midwestern, Cleveland Vibratory, Russell Finex, and Rotex.
