Material rat holes are a common and costly issue in bins, hoppers, and other dry bulk storage vessels. They disrupt material flow, causes production delays, and lead to inefficient material discharge. NAVCO’s Bin Hopper Vibrators provide a proven solution to combat ratholing.
What is material ratholing?
Material ratholing occurs when material flows only through a narrow vertical channel directly above the discharge outlet, while the surrounding material remains stagnant against the vessel walls. Because of the way the rathole is formed, it can take some time before the rathole causes flow interruptions. Material will appear to be discharging normally, when in fact just the small vertical channel is. Once the channel reaches the top of the material, all flow stops. At this point a large volume of product remains stuck in the vessel, requiring intervention to restart flow.
Material ratholing is an issue that disrupts the manufacturing processes across every industry including:
Food
Plastics
Aggregates
Mining
Chemical
Petrochemical
Power
Trucking
Steel
Recycling
Construction
And many more
Yellow circle highlights the material rat hole that has formed
from the outlet up to the top of the vessel.
What causes material rat holes?
As in our article on material bridging, material ratholing can be broken down into two material characteristics – material strength and material friction.
Material Strength
Material strength is the ability of a bulk material to maintain its shape, even after it has been disturbed. For example, high material strength materials, like flour, are more prone to form ratholes because they tend to retain their shape, resist flow, and stick together. Whereas low material strength materials, like dry sand, are less likely to rathole. Additionally, the outlet size of the vessel plays a greater role in the formation of a rathole. When the outlet is sized too small for gravity alone to overcome the material strength, it will result in the formation of a rathole.
Sliding Friction
Ratholing is also affected by the friction between the material and the vessel walls. High wall friction can prevent material from collapsing into the flow channel once a rathole forms. Wall angle plays a role as well—steep, smooth walls reduce friction and promote flow, while shallow or rough walls increase the chance of rathole formation.
How NAVCO Bin Hopper Vibrators (BH Vibrators) Address Material Rat holing
NAVCO Bin Hopper Vibrators (BH Vibrators) are pneumatic piston vibrators that utilize vibration to reduce material strength and sliding friction.
Reducing Material Strength – Vibration Through the Material
Now imagine a Newton’s Cradle. The pneumatic piston vibrator acts like the swinging ball, delivering energy through the vessel wall and into the bulk material. This vibration breaks the bonds between cohesive particles, reducing material strength and enabling the rathole’s collapse. The result is improved material flow and less need for manual intervention (hammering on the bin).
Reducing Wall Friction – Vibration Through the Vessel Wall
Think of the vessel wall as a bell and the vibrator as the clapper. As the pneumatic piston vibrator operates, it causes the vessel wall to resonate. This vibration reduces the friction between the wall and the material, encouraging stagnant material to move toward the outlet and collapse the rathole.
Keep Material Flowing with NAVCO BH Vibrators
Material ratholing is a serious challenge for industries that rely on the smooth flow of dry bulk solids. NAVCO Bin Hopper Vibrators (BH Vibrators) offer a reliable, effective solution for poor material flow by addressing the underlying causes—cohesive strength and wall friction. By applying vibration strategically, these vibrators help eliminate ratholes, reduce downtime, and improve operational efficiency. Whether your application involves powders, granules, or cohesive materials, BH Vibrators are the ideal solution to keep material in bins and hoppers flowing.
