Humanity has used simple sifting techniques to remove chaff from harvested grain since before recorded history. Farmers in ancient Egypt, for example, used manual sifting methods that utilized gravity, relying on agitating the grain with sieves made from reeds and palm leaves. Though mainly used to separate the chaff from the rest of the grain, Egyptian farmers also used these techniques to separate and grade grain by size. Not much changed with the basic manual methods for separation until the Industrial Revolution.

This period of innovation saw more sophisticated sifting processes developed. This included contraptions like the bin sieve, the first mechanical sifting machine used in the United States. The 19th century also saw advances in material handling technology, as Peter von Rittinger – an Austrian pioneer of modern approaches to mineral processing – introduced standardized sizes for sieve apertures, often referred to now as “mesh size”. The result of his work brought about Rittinger’s Law, one of the three physical laws now used universally to establish how much energy is necessary to reduce the particle size of a material. These advances eventually led to the development of the rotary sifter, machines that utilize a rotating action to produce centrifugal force to separate materials by particle size.

The early 20th century saw all manner of materials separated by what would become known as the rotary sifter. Machines that operated on the premise of centrifugal force increased in use throughout the past century. Modern designs saw innovative materials used for screens, greater control over rotational speed and enhanced mechanisms for feeding, among other technological developments that resulted in the modern rotary sifter. As machines are involved in a wide array of various applications, rotary sifters are now commonly seen in agriculture, chemical processing, food processing, pharmaceutical and many other industries.

The Rotary Sifter: Machines for Streamlining Separation Processes

Also known as a centrifugal sifter, rotary screener or rotary sieve, the rotary sifter is used primarily for separating and classifying dry powders and granulates according to particle size. Additionally, other solids, along with liquids and slurries, can be processed using various types of specially designed rotary sifters. 

Material is fed into one end of the sifter, subjecting it to centrifugal forces as the rotates. This in turn causes material to pass through the drum’s screen, thus separating the material by particle size. Smaller particles pass through to the bottom of the sifter, while larger particles exit the machine into a separate hopper.

 Machines designed for liquids or slurries use screening apparatus devised to separate solids from liquids rather than separating smaller from larger particles. 

The Development of Rotary Sifter Machine Technology 

The 20th century saw a great deal of innovation in the design of the rotary sifter. Machinery developed for the food industry during the early 1900s helped optimize flour processing, leading to the development of mechanical sifters and roller mills. The early 1930s saw changes in the shapes of screens, which tended to be square or rectangular, as the introduction of rotary sifters with circular screens allowed more efficient use of the sieving area.

The latter part of the 20th century saw a move towards automation to augment efficiency, materials that enabled better sanitation and the variable frequency drive (VFD) to enhance energy efficiency. All these improvements brought greater versatility, expanding the uses for the rotary sifter. Machined configurations have since been built to meet particular requirements for various industries and applications. This has improved particle separation of fines, led to higher throughputs and allowed narrower particle distributions during processing of bulk materials.

Currently, manufacturers are focusing on features like touchscreen interfaces that work with programmable logic controllers (PLC) to optimize the accuracy, efficiency and productivity of a rotary sifter. Machine features like these enable operators to control settings, monitor performance and regulate operations more easily. Materials like stainless steel that resist corrosion reduce the need for maintenance, provide greater durability and are easily cleaned are also becoming more popular among manufacturers that rely on the rotary sifter. Machinery designs these days can even be customized to meet any special requirements, such as the rotary sifter’s capacity or size.

Role of Rotary Sifters in Industry

The rotary sifter is a machine used by numerous industries for a variety of purposes related to the particle size of materials. Its use is often essential to ensure the quality of processed materials in many industrial applications. The machine’s main purposes are to separate particles by size, screen out any impurities before production processes, ensure product quality at the end of production and adjust the bulk density of a product.

Industries that utilize rotary sifters include: 

  • Agriculture: As per its forbears, the ancient Egyptian sieves made from reeds, and rotary sifters are still used for grading and sifting grains, along with other seed crops based on their size and shape.
  • Chemical processing: Used in the production of chemical fertilizers and plastics, the chemical processing industry uses rotary sifters for classifying and separating material by particle size.
  • Flour milling: Used to sift flour, rotary sifters are invaluable tools for removing impurities and classification of flour particles. 
  • Food processing: Used to grade and otherwise separate food products like sugar, spices, cocoa and other powdered products according to shape and size.
  • Pharmaceutical: When producing different types of drugs, medications and even nutraceuticals, particles are often classified with and separated by rotary sifters.

When it comes to processing powdered and granulated material, few pieces of equipment are as essential to production as the rotary sifter. Machinery capable of separating particles by shape and size, rotary sifters consistently achieve accurate results that make them valuable for material handling applications in many different sectors.

Rotary Sifter Machines by Prater Industries

With Prater’s various types of rotary sifter, machines utilize centrifugal forces that make materials flow like fluids, accelerating material into the screen’s surface. Our rotary sifters feature a distinctively placed auger within the inlet to move material in the machine’s screening area, where it then meets with rotor paddles that speed particles centrifugally. With a precise pitch, these rotor paddles force coarser material out into a separate discharge hopper, while finer particles pass through a screen into another hopper. This free flow of material results from natural vibrations in the screening surface during operation to classify both near-sized and oversized particles.

Prater manufactures several models of the patented Rota-Sieve® rotary sifter. Machines designed to handle high-capacity sifting for larger processing applications, the Prater Rota-Sieve® offers an efficient means for working with a wide variety of agglomerates, granulates, powders and other similar materials that flow freely during manufacturing. 

Additionally, existing material handling operations can easily incorporate a Prater rotary sifter. Machines within these systems be used for sifting material introduced from silos, before mixing processes, prior to packaging or even as a standalone process. Prater’s engineers can also set up sifters to work with pneumatic conveying systems. To learn more about our rotary sifters and other material processing solutions, contact the experts at Prater today.