The plansifter is the core, the heart of the grinding section in a modern flour mill. If the roller mill is the "crushing expert," then the plansifter is the "master of precision separation." Its application level directly determines the flour extraction rate, yield, product quality, and production stability of the entire mill.
I. Core Tasks: Sifting and Grading
The primary task of the plansifter is to continuously, efficiently, and accurately sift and grade the mixture coming from the roller mills, which consists of particles of varying sizes including flour, bran, and endosperm.
Extracting Finished Flour: Separating the finest particles that meet flour specifications from the mixture to be sent as finished product to the next stage.
Grading Intermediate Stocks: Classifying larger particles that are not yet fine enough into different grades based on size and quality (e.g., bran content). These grades include coarse flour (dunst), semolina, middlings, and bran.
Establishing the Process Flow: Precisely conveying each graded stock to its designated next machine in the process (such as different roller mills or purifiers), thereby building the circulatory network of the entire milling system.
II. Position and Role in the Flour Mill Flow Sheet
The plansifter does not operate in isolation. It is paired with roller mills to form "grinding-sifting" units. The entire milling process is created by connecting multiple such units in series.
Typical Process Cycle:
Roller Mill (Grinding) → Plansifter (Sifting & Grading) → Graded Stocks → Respectively sent to next designated Roller Mill or Purifier → Reground → Enter next Plansifter...
This cycle repeats, progressively scraping the endosperm from the bran and reducing it to flour.
System Layout: In a 100-ton/day flour mill, multiple plansifters are typically used, each responsible for sifting tasks within different "systems," for example:
Break System Plansifter: Handles material from the break rolls. Its main tasks are extracting a large amount of high-quality flour and grading bran, coarse middlings, and fine middlings.
Reduction System Plansifter: Handles material from the reduction rolls. Its task is the fine grinding and sifting of relatively pure endosperm particles to produce high-grade, low-ash flour.
Scratch System Plansifter: Handles material from the scratch rolls. It processes endosperm particles with small bran attachments for further purification.
Tailings System Plansifter: Handles material from the tailings rolls. It processes stocks with higher bran content, aiming to extract as much flour as possible while maintaining flour quality.
III. Working Principle and Structural Features
Core Structure:
Sieve Casing: A tall steel housing, internally divided into several independent compartments or "sections."
Sieve Frames: The core working components. Each stack of frames contains sieves with different specifications (woven from silk or nylon mesh). The mesh aperture typically becomes finer from top to bottom, or is configured according to process requirements. The material moves in a horizontal rotary motion within the frames. Particles smaller than the aperture pass through ("throughs"), while larger particles remain on the sieve surface ("overtails").
Drive Mechanism: Typically driven by a vertical motor mounted on top. It generates a horizontal, plane rotary motion through counterweights. This motion evenly spreads the material across the sieve surface, causing it to move spirally outward for efficient contact with the apertures.
Working Process:
Feed: Ground material enters from the top of the plansifter and is distributed into different compartments and predetermined flow paths.
Progressive Sifting: The material, driven by the rotary motion, passes sequentially through the various sieve layers with different mesh sizes.
Grading & Collection: Each sieve layer separates the material into overtails (retained) and throughs (passed). Materials from different layers and flow paths are collected separately via internal channels.
Discharge: Finally, multiple outlets at the bottom of the plansifter simultaneously discharge various graded stocks. These are then precisely conveyed (often pneumatically) to their respective destinations.
IV. Key Technical Parameters and Impact
The performance of the plansifter dictates the efficiency of the entire milling process:
Sifting Surface Area: A larger sifting area means higher capacity and more thorough sifting. The plansifter's key advantage is achieving a massive sifting area within a small footprint by stacking multiple layers. A 100-ton/day mill needs sufficient sifting area configured according to its process design.
Sieve Configuration: The selection of sieve specifications (mesh count, material, weave density) is a core aspect of process design. It directly determines grading precision, the flow ratio of different stocks, and final flour quality parameters (like particle size, ash content).
Sifting Efficiency: The percentage of separable flour that is actually extracted from the stock. High efficiency ensures "maximum extraction," reducing unnecessary recirculation of material, increasing flour yield and capacity, and lowering energy consumption.
Motion Parameters: Rotational speed and eccentricity determine the speed and trajectory of material on the sieve surface. These need optimization based on stock characteristics and sieve specifications.
Sieve Cleaning: To prevent blinding (clogging), sieve frames often contain cleaning devices (e.g., canvas strips, rubber balls) that bounce against the underside of the mesh during operation, keeping the apertures clear.
V. Summary: The "Separation Hub" of the Milling Process
The role of the plansifter can be understood through analogies:
Traffic Control Center: It takes the mixed "traffic" (ground material from roller mills) and precisely directs each vehicle (particle) to its correct next destination based on its "type and destination" (size and quality).
Quality Gatekeeper: Through precise grading, it ensures that only pure endosperm enters the reduction system, enabling the production of high-quality specialty flours. It also prevents excessive bran breakage from contaminating the flour, ensuring flour purity.
Guarantor of Yield and Profitability: The sifting capacity of the plansifter is often a primary bottleneck in a mill's production. Its efficient and stable operation is fundamental to achieving the plant's designed capacity and extraction rate.
Without the plansifter, the efficient, precise, and continuous production of a modern flour mill would be impossible. It stands quietly in the mill, executing complex and precise "sorting commands" through its thousands of internal mesh apertures, representing one of the most technologically critical core components in the journey from "grinding" to "finished flour."
