1️⃣ The Common Problem of “Bridging”
When handling powders, one of the most frequent problems in production lines is that the material simply doesn’t flow out of the hopper as expected.
In many cases, the cause is “bridging”—a phenomenon where powder forms a solid arch near the hopper outlet, blocking the discharge.
Once this happens, powder stops flowing even though the hopper looks full, often leading to production stoppages and poor feeding accuracy.
Bridging is one of the most common yet serious issues in powder handling systems.
2️⃣ How Bridging Occurs
Bridging is mainly caused by the cohesive and frictional forces between powder particles.
It tends to occur more frequently under the following conditions:
- The powder is very fine or tends to absorb moisture
- The bulk density is low and the powder traps air easily
- The hopper wall angle is too shallow, reducing the powder’s ability to slide down
- The material has been compacted due to long storage or external vibration
Once a bridge forms, an empty cavity appears beneath it, so although the hopper appears full, the outlet remains clogged.
3️⃣ Consequences of Bridging
Bridging does not only stop the material flow; it can also cause various secondary problems in the system:
- The feeder runs empty, putting extra load on the motor and screw
- The feed rate becomes unstable, leading to inaccurate mixing ratios
- Operators may attempt to clear the blockage manually, increasing safety risks
In short, bridging impacts both process reliability and operator safety.
4️⃣ How to Prevent Bridging
Preventing bridging requires both design improvements and operational management.
(Design measures)
- Increase the hopper’s wall angle to help powder slide more easily
- Use smooth inner surfaces such as stainless steel or fluorine coating
- Install an agitator to keep the powder loose and moving
- Add an air vibrator near the outlet to prevent material adhesion
(Operational measures)
- Avoid leaving powder static for long periods; move it periodically
- Control humidity during storage and operation
- Check screw rotation and hopper flow before starting the feeder
5️⃣ Practical Examples
Fine powders such as titanium dioxide and silica are notorious for bridging.
For these materials, using a hopper with an agitator can greatly improve powder flow near the outlet and ensure stable feeding.
Even modifying the screw shape or pitch can significantly enhance performance for poor-flowing powders.
6️⃣ Seiwa Giken’s Solutions
At Seiwa Giken, we design screw feeders that specifically address bridging and flowability problems.
- Mini Screw Feeder – A compact tabletop model for small-quantity feeding. Equipped with an agitator hopper, it maintains a steady flow even for cohesive powders.
- Standard Screw Feeder – Designed for continuous production lines. The built-in agitator inside the 20L hopper prevents bridging and rat-holing during long operations.
Both models can be customized according to powder type, screw geometry, and feeding rate requirements—significantly reducing downtime caused by bridging.
👉 Learn more about Seiwa Giken’s Screw Feeders↓↓
