What types of impurities are found in sesame seeds? What are the functions of the cleaning machine used in a sesame processing line?

The first category is based on the origin of the impurities. The first type consists of impurities from the field and the harvesting process, such as straw fragments, branches, leaves, weed seeds, soil clods, sand, and stones—sesame seeds, in particular, are prone to trapping small stones and soil when their seed capsules split open. The second type consists of impurities introduced during processing and storage, including sand and dust picked up during sun-drying, as well as insect-damaged, moldy, or damp/clumped seeds, along with broken sesame hulls, fragments, and empty or shriveled seeds.

The second category is based on physical characteristics, which serves as the primary criterion for selecting processing equipment. First, there are "light" impurities—such as dust, chaff, empty or shriveled seeds, and lightweight weed seeds—which have a low specific gravity and a large surface area relative to their weight; these can be removed via air classification (aspiration). Second, there are "heavy" impurities—such as stones, sand, metal fragments, and soil clods—which have a specific gravity and particle size similar to sesame seeds; these cannot be easily removed by air classification or standard screening and require gravity-based separation. Third, there are "large" impurities—such as straw, long grass, pieces of twine, or large stones—which are significantly larger than sesame seeds and can be removed by screening. Fourth, there are "fine" impurities—such as fine sand, soil particles, and small debris—which are smaller than sesame seeds and can be removed through screening. Fifth, there are discolored or defective seeds—such as moldy, insect-damaged, or off-colored grains—which must be removed using optical sorting (color sorting). Finally, within the same batch, seeds can be categorized by their fullness and maturity; distinguishing between shriveled/small seeds and plump, mature seeds requires precise grading and gravity-based selection.

Precisely because sesame impurities are "diverse in type, small in size, and a mix of light and heavy particles," no single piece of equipment can handle the entire cleaning process. Instead, multiple machines must be arranged in a series to form a processing line, with each unit performing a specific, complementary role.

Functions of Equipment in a Sesame Cleaning Production Line

A standard sesame cleaning line is typically configured in the following sequence: "coarse cleaning → removal of heavy impurities → precision sorting → color sorting → weighing and packaging." The functions of the individual pieces of equipment are as follows:

First, the sesame seed Air Screen Cleaner (coarse cleaning and removal of light impurities at the intake). Function: This unit utilizes a combination of screening and air separation. The screen deck vibrates, causing the material to tumble across its surface; the upper screen layer traps and discharges large impurities—such as stalks, large stones, and pieces of rope—while the lower screen layer allows fine sand, soil, and debris to pass through. Simultaneously, a fan generates a directional airflow that extracts dust, husks, shriveled/empty grains, and lightweight weed seeds. Positioned at the start of the production line, this machine rapidly removes easily separable impurities in bulk, significantly reducing the load on subsequent processing stages; it serves as the first line of defense for the entire system. Outcome: A substantial initial improvement in sesame purity, characterized by high throughput and a low breakage rate.

Second, the Gravity Separator (removal of stones and heavy impurities). Function: Designed to target heavy impurities—such as stones, sand, and metal fragments—that are similar in size to sesame seeds and cannot be removed by an air-screen cleaner, this machine employs a three-in-one separation process: "fluidization via upward airflow + screen vibration + inclined conveyance." The material is fluidized by a uniform upward airflow; heavier particles, such as stones, sink to the screen surface and are directed toward a discharge outlet, while the heavier, plump sesame seeds float to the top of the material layer and flow toward the product outlet. Outcome: Highly efficient removal of "missed" heavy impurities. This is the core process for raising sesame purity to over 99.5% and is critical for ensuring food safety and preventing the risk of dental damage (from stones or hard debris).

Third, the grading sieve (for size-based classification and the removal of broken grains). Function: Utilizing multiple stacked screen layers with varying aperture sizes, the equipment allows sesame seeds to pass through different levels during reciprocating vibration. This process sorts the seeds into distinct size categories (large, medium, and small) while simultaneously removing broken or shriveled grains. Result: Ensures uniform particle size and an attractive appearance, thereby enhancing product grade and market value; it also creates a consistent size profile for subsequent color sorting and packaging.

Fourth, the color sorter (for the removal of discolored or defective grains). Function: Employs high-precision optical sensors to detect color variations on the surface of the sesame seeds. High-speed air nozzles then precisely eject moldy, insect-damaged, or otherwise discolored grains. Result: Eliminates residual discolored or defective seeds that are difficult to remove in earlier stages. This serves as the final quality-control step, ensuring the white sesame seeds possess a pure color and consistent appearance, meeting the rigorous standards required for export.

Fifth, the automatic packaging machine (for precise weighing and sealing). Function: Automatically weighs, bags, and seals the cleaned and sorted sesame seeds according to pre-set specifications. Result: Delivers accurate measurements, neat packaging, and high efficiency. It completes the closed-loop process—from initial cleaning to the final finished product—meeting the requirements for large-scale production and export logistics.

Sixth, auxiliary equipment. Elevators facilitate the vertical transport of materials between various processing units, while storage hoppers act as buffers to ensure a steady, uniform feed, preventing blockages and maintaining the continuous, stable operation of the entire production line. A dust collection system captures dust generated during air-separation and screening processes, ensuring compliance with environmental standards.

The challenge in cleaning sesame seeds lies in their small particle size, the presence of a complex mix of light and heavy impurities, and a high degree of color variation—difficulties that cannot be resolved by a single machine. Through a multi-stage, integrated process—using air-screen cleaners to remove bulk light and large debris; destoners and gravity separators to precisely eliminate stones and heavy impurities; grading screens to ensure uniform particle size; optical sorters to remove discolored or defective seeds; and automated packaging machines for accurate weighing and sealing—the purity of the sesame seeds can be consistently raised to over 99.5%. The resulting product features uniform color and consistent particle size, meeting both food-grade and export-grade standards.

The sesame cleaning line equipment from Hebei Taobo Machinery is engineered with high-airflow, low-breakage capabilities, featuring adjustable airflow and vibration amplitude, as well as quick-change screens. These systems allow for precise parameter tuning tailored to the specific characteristics of sesame seeds—namely their small size and high oil content. The entire line is fully enclosed and dust-proof, designed for high throughput and stable operation, making it a reliable choice for sesame processing enterprises aiming to achieve high purity, minimal breakage, and premium-grade output.