Criteria for Design of Steel Bins for Storage of Bulk Materials, Part 3: Bins Designed for Mass Flow and Funnel Flow
1980 Edition

According to IS 9178 Part 3, for plane flow hoppers with rectangular outlets, the hopper slope angle (fp) should exceed 30°, especially when the bulk solid has an internal friction angle greater than 40°. For pyramidal hoppers, the slope relates to the valley angle and must not exceed specified maximums to prevent doming, as illustrated in Appendix C. The slope angle must ensure first-in-first-out flow, complete emptying without flow aids, and remain within limits derived from bulk material friction properties.

The standard mandates that the outlet dimension must be at least six times the maximum lump size to avoid blockages. For free-flowing materials, outlet size is the greater of six times the lump size or the size required for the desired discharge rate. Additional factors such as preventing arching and piping are also considered. This ensures a smooth and uninterrupted flow of bulk solids from the bin.

IS 9178 Part 3 prescribes using shear testers (flow factor testers) to assess bulk material flow properties. These tests measure the major consolidating force, flow function (FF), and wall yield loci (WYL), reflecting the material’s behavior under different consolidation stresses. Samples should represent actual storage conditions, including particle size, moisture, temperature, and storage age, to provide reliable data for design purposes.

During filling, with the discharge closed, vertical 'peaked' pressure distribution occurs on the cylindrical walls following Janssen’s method, while hopper pressures vary linearly. The standard accounts for low-impact loading, with considerations for wear and impact if materials are dropped rapidly. During emptying, load distribution changes because of material deformation and possible dynamic effects from arch collapse. These load patterns guide structural design ensuring bin safety and performance.

Jenike’s theory tends to overestimate required outlet widths due to neglecting sliding arches and powder weight above arches. It inadequately predicts arching near hopper-silo transitions and does not consider impact loads during filling. The shear cell tests underlying the theory are limited to certain particle sizes and rely on assumptions about slip planes. These factors mean designers should apply the theory cautiously and consider additional research and alternative approaches.