material bridging Archives - Control Concepts, Inc.

How to Prevent Bridging in Material Hoppers (aka The Ketchup Effect)

July 28, 2023 10:39 pm Comments Off

Ketchup in a factory getting packaged

Have you ever struggled to get ketchup or any thick sauce out of a bottle? That’s the same issue that production facilities face when they try to move solids or powders through bulk material hoppers. The bulk material gets stuck, and production stops.

Unlike liquids, bulk solids and powders will not flow readily without intervention. Even some thick liquids like ketchup are notoriously difficult to handle. The bulk material clings to the vessel walls, or becomes more compact – also known as bridging.

What is bridging?

Bridging in material hoppers refers to the phenomenon where bulk materials, such as powders, granules, or pellets form an arch-like structure over the outlet. It stops material from flowing freely, which leads to several material production problems:

Need for manual intervention to loosen the material
Lower productivity and machine downtime
Inconsistent product formulas
Stagnant bulk material that can spoil or contaminate the next batch
Bulk material waste from throwing away spoiled material or out-of-spec batches

What causes bridging in material hoppers?

Know your bulk material’s flow properties. Choose non-cohesive materials whenever possible. If cohesive materials are necessary, consider additives or treatments to reduce their cohesive properties.
Control moisture. Implement proper moisture control measures to ensure the bulk material remains within the acceptable range for smooth flow. This might include using desiccants, heaters, or dehumidifiers.
Select the right design of material hoppers. Select an appropriate hopper design based on the bulk material’s characteristics. Conical material hoppers with an angle between 50 to 60 degrees, and the right outlet size, can help promote steady material flow.
Consider hopper liners. Using hopper liners made of low-friction materials like Teflon can help reduce bulk material adhesion and bridging.
Use the right flow aid. Many manufacturers use industrial material flow aids to break up bulk material blocks and encourage regular, reliable flow. Aside from speeding up production, it prevents stagnant or spoiled material and the safety risks from manual intervention and cleaning.

Solve bridging in material hoppers with AirSweep

Preventing bridging in material hoppers is essential to ensure the continuous and efficient flow in industrial processes.

Both global brands and SMEs use AirSweep material flow aid to get smooth, on-demand flow. AirSweep is a pneumatic material flow aid that releases powerful, high-pressure air pulses that break up bridging and sweep the vessel walls clean. It is energy-efficient, requires very little maintenance, and has proven effective for even the toughest flow problems.

AirSweep can be installed on material hoppers as well as other process equipment like silos, chutes, conveyor belts, or any place where material tends to hang up.

Since AirSweep uses aeration rather than vibration, it does not cause metal fatigue and damage small or thin material hoppers. AirSweep is also certified safe to use in hazardous and flammable environments, and there are models that are specifically designed for sanitary applications.

What Causes Material Bridging in Hoppers and How AirSweep Can Help

December 12, 2022 5:54 pm Comments Off

material bridging inside of hopper

Material bridging in a hopper can slow down production and reduce bulk storage space. The stagnant material can spoil or become contaminated, and workers have to clear the vessel and throw out compromised batches.

What is material bridging?

Bridging is the material block that forms above the discharge outlet of a hopper, silo, or any bulk material handling equipment.

The bridge is caused by friction on the vessel walls which slows down the flow of material. Eventually, the material particles start to bind and interlock, until it partially or completely blocks the discharge outlet.

The bridge is so strong that it can support the weight of material above it. New material can condense the trapped material further and strengthen the bonds.

Types of bulk material bridging

Mechanical bridging. Particles mechanically interlock, like jigsaw puzzles. This usually happens for particles that are larger than 3mm.
Cohesive bridging. Particles compress until they bind together. This usually happens for smaller particles, especially those that attract moisture.

What causes material bridging in the hopper?

Material bridging can be caused by the hopper design, the bulk material’s flow properties, and the conditions in the plant.

Hopper Design

Ideally, the hopper design should reduce friction and encourage material flow. However, there is no one-size-fits-all solution. Solids and liquids behave differently, and materials have unique properties that can also vary in different conditions. These factors have to be considered while choosing the hopper’s angle, and the outlet’s shape and diameter.

Bulk Material Properties

Some bulk materials are simply more prone to bridging and arching. This includes:

Moist and sticky materials
Materials that tend to settle during storage
Materials with a high cohesive strength
Hygroscopic powders that attract moisture
Pellets that soften and form soft clumps
Fibers that can entangle
Irregular particles that can interlock
Heavy materials that can push down on stagnant material and cause it to compress

Plant Conditions

Fluctuating temperatures can affect the stress on the hopper walls and the material flow properties. Moisture in the air can cause materials to expand and compress. Gas in the air can also permeate through powders and fill empty spaces.

The best solution for material bridging in the hopper

Material flow aids solve bridging and other material blocks by breaking up the cohesive bonds in the bulk material. However, not all flow aids can do this safely or effectively.

Manual cleaning—where workers hammer the vessel or enter the hopper to clear the build-up with axes and shovels—is slow and dangerous. Some bulk materials release flammable or toxic gases during storage. Workers are also at risk for falls, sprains, health problems from direct exposure to the material, or being hit by falling material.

Vibrators can damage the vessel and can cause some materials to become more compact. Fluidizers can only activate light powders; air cannons are expensive and still leave material residue on walls.

AirSweep is the most cost-effective solution for material bridging in hoppers. It releases powerful air pulses that break up bridging and sweep stagnant material back into the flow stream.

AirSweep material flow engineers customize the system so the units are installed at key areas on the hopper to stimulate first-in/first-out flow. They select the right model for the bulk material and the vessel size. The AirSweep USDA-accepted model is also specially designed for sanitary applications like food, beverage, and pharmaceuticals.

The AirSweep material flow system is energy-efficient. It uses less air than air cannons, and the units pulse in sequence instead of running continuously like vibrators and fluidizers. The units also have a large area of activation and move more material with every pulse.

Find more information about AirSweep, or get a customized quote.

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