When designing equipment for handling and processing bulk materials, it’s essential to understand their characteristics. Bulk material processing is critical in nearly every industry. Using such equipment limits the need for labor-intensive processing, and, as a result, using materials in bulk saves manufacturers time and money.

All sorts of solid materials are bought and sold in bulk. These materials include cement, coal, food ingredients, grains, pharmaceutical powders, plastic flakes or pellets, processed chemicals, rubber, and other raw materials. Regardless of the type, the characteristics of bulk materials help define how they’re transported before, during, and after processing. These qualities help manufacturers develop conveying and processing equipment and systems.

What are Bulk Materials? 

Bulk materials come in granular, lumpy, or powder form and then are packaged for end use. During processing, these dry, solid substances flow like liquids, so equipment that transports them needs to be designed to deal with their physical characteristics. Typically, these materials are stored in bins, heaps, or silos, depending on the type and characteristics of the bulk material.

Types of bulk materials include: 

The characteristics of bulk materials also define how they’re contained during shipping, and this is especially true when it comes to transporting finely ground grains or powders. Bulk packaging or containers for these must be sealed to prevent contamination and spillage.

Understanding the Characteristics of Bulk Materials

How bulk materials are handled during production depends on their characteristics and end-use. For example, pneumatic conveying systems are the most efficient for transporting bulk materials. Regarding food-grade products, bulk materials require sanitary equipment and procedures while being conveyed.

The distinctive properties of bulk materials affect their behavior under certain conditions. Bulk materials' characteristics determine whether they stick to surfaces, wear machinery, present hazards to factory employees, and how it flows. Material characteristics like temperature, flow rate, corrosiveness, bulk density, and abrasiveness all contribute to the type of equipment and systems necessary for processing the material.

Material characteristics directly impact how a product flows through a manufacturer’s processing system, helping to determine system design. By establishing the characteristics of bulk materials and their end use, makers of industrial processing machinery can, in turn, recommend the best equipment for specific applications. These characteristics may also affect regulatory compliance; for example, manufacturers that utilize material that produces combustible dust must follow specific OSHA guidelines. This means designing equipment to prevent leaks and minimize dust escaping into areas that can endanger workers.

Main Characteristics of Bulk Materials 

Understanding a material’s characteristics and production conditions helps determine the equipment and systems required for the material's application.  


Material abrasiveness affects how quickly production equipment wears down, with the velocity and speed of conveyed particles also contributing to equipment wear. This characteristic of bulk materials is particularly important when determining the size of the rotary airlock and other process equipment needed for the application. For more abrasive materials, it’s best to utilize protective coatings that give machinery better abrasion resistance.

Attrition or friability

Attrition and friability can play into the design of chutes and hoppers, pneumatic convey systems, and certain process equipment to either limit or enhance particle fracture during handling.

Coefficient of sliding friction

This applies to the surface on which a bulk solid is stored or moving across. The coefficient of friction will define the angles of storage hoppers, dust collectors, and silos, ensuring that the bulk material can sufficiently break friction with the surface to discharge from those vessels.


This refers to the stickiness of bulk material. Characteristics of particles that cake or stick together often plug up machinery. This characteristic of bulk materials leads to ratholing or arching in silos, hoppers, or bins. Certain rotary equipment with proper coatings can help keep material from sticking while making cleanup easier.


When working with potentially explosive bulk material like sugar, dust explosions are a real worry. They result from an ignition source combined with oxygen and fuel. Bulk processing systems handling explosible dusts should be designed to contain the dust and control or prevent an explosion thru the application of vent panels, indoor flameless vents, isolation valves, and chemical suppression systems., especially if it can become a potential fuel source.

Particle size, distribution, and shape

These characteristics of bulk materials directly link to their flowability, with industrial equipment design promoting material flow. This means using shear protectors for flakes, pellets, and other coarse materials. Additionally, larger inlets should be used on machinery that processes lighter material, while equipment that handles heavier material should feature robust shafts.

Characteristics of Bulk Materials and Conveying

Conveying systems are designed to handle various kinds of bulk materials. For example, food and pharmaceutical processing requires that equipment that handles bulk materials is built with hygiene in mind to keep end products free of impurities or pathogens. In contrast, bulk materials like coal won’t normally require this.

The components of conveying systems depend largely on the size of the particles they must process. Equipment for processing ores and other dense materials must have a robust design for handling heavy impacts and loads. Lighter materials and substances that can be reduced to very small particle sizes often utilize pneumatic conveyancing systems, which are the most efficient for such applications.

Which Machine Do I Need?

Bulk Material Processing Equipment by Prater

Prater Industries has provided solutions to industries that process bulk materials, regardless of their application or characteristics, for nearly a century. Bulk material handling and processing equipment we make can serve a variety of applications. With our expertise in designing custom industrial systems and machinery, Prater helps ensure your production process will achieve the desired outcome.

Prater equipment for bulk material processing includes: 

  • Air Classifiers create narrow particle size distributions ensuring uniform results when handling a variety of feedstock size variations.
  • Air-classifying Mills offers dual-stage grinding within a closed circuit and feature internal air classification, which outperforms single-stage mills when handling difficult-to-grind material.
  • Fine Grinders are ideal for grinding heat-sensitive and free-flowing dry material, with features that reduce the need for maintenance and improve reliability.
  • Hammer Mills include a rugged, enclosed design well-suited for use with pneumatic conveyancing systems or mills built for high-capacity grinding.
  • Lump Breakers offer an economical and compact means for reducing bulk materials that have densified or agglomerated.
  • Rotary Airlock Valves, with various optional features, help minimize air loss within systems.
  • Rotary Sifters scalp and sift at higher rates than conventional sifters, with a design that ensures smooth operation and a long lifecycle.
  • Rotary mills from Prater’s subsidiary IPEC called the Rotormill, grind, and mill through extreme internal turbulence that creates particle-on-particle collisions.
  • Rotary Dryers by IPEC incorporate a combined Rotormill and dryer system to allow milling and drying of slurries and high-moisture materials.

To learn more about the products and services Prater provides customers, we invite you to contact us or request a quote today for those ready to order.