Belt grading with perforated screens is the most widely used and technologically mature grading method among blueberry belt size grading machines. Its core design combines flexible conveying with gradient perforated screens, achieving efficient grading while maximizing the protection of blueberry fruit. It is particularly well-suited to the dual requirements of grading accuracy and fruit integrity in large-scale post-harvest blueberry processing. The following is a detailed analysis from aspects such as structural design, workflow, key technical details, advantages, and suitable scenarios:

I. Core Structural Components

The core component of the sieve belt grading system revolves around the "sieve belt." All components work together to achieve uniform feeding, precise screening, and stable discharge. Specifically, it includes:

**Graded Sieve Belt (Core Component):** As the key carrier for grading, the belt is made of food-grade flexible material (such as food-grade polyurethane or silicone composite material), typically 1.5-3mm thick, combining flexibility and wear resistance. Its smooth, burr-free surface prevents friction damage to the blueberry bloom. Circular sieve holes are machined onto the belt according to preset specifications, with rounded edges (radius ≥ 0.5mm) to prevent sharp edges from scratching the fruit. The sieve hole distribution follows a "gradient increase" principle—from the belt input to the output, the sieve hole diameter gradually increases. Common gradient combinations are 12mm→15mm→18mm→21mm (any specification within the range of 10-25mm can be customized according to market demand). The center-to-center distance between adjacent sieve holes is ≥ 2 times the sieve hole diameter to prevent fruit from getting stuck or overlapping during screening.

Drive and Tensioning System: Equipped with a variable frequency speed-regulating motor (power 0.37-1.5kw, speed adjustable range 5-20m/min), the belt is driven by a synchronous belt to ensure stable grading rhythm. Automatic tensioning devices (spring or cylinder type) at both ends of the belt compensate for belt tension in real time, ensuring accurate sieve hole positioning and preventing grading errors caused by belt slack.

Grading Channels and Receiving Devices: Independent receiving channels (usually 3-6, customizable) are set below the belt according to the sieve hole gradient. The inner walls of the channels are made of food-grade stainless steel or PE material, with an inclination angle of 15-25° to ensure smooth sliding of graded blueberries along the channels. The low drop (≤10cm) design further reduces the risk of fruit bruising. Each channel can be connected to a receiving box, conveyor belt, or directly to packaging equipment for rapid transfer of graded fruit.

Feeding and averaging device: The belt input end is equipped with a vibrating trough or spiral distributor, which uses low-frequency vibration (5-10Hz) to evenly spread the blueberries to be graded on the belt, ensuring a single-layer distribution of fruit (avoiding overlap and obstruction of the sieve holes). The spreading thickness is controlled within the range of "single fruit diameter + 5mm", laying the foundation for accurate screening. A baffle plate is installed at the end of the averaging device to prevent blueberries from falling off the sides of the belt, while simultaneously controlling the feeding speed to match the belt running speed (feed rate ≤ 110% of the equipment's rated capacity).

Machine body and protective structure: The machine body is made of 304 stainless steel, meeting food hygiene standards and facilitating cleaning and disinfection. A dust cover (optional) can be installed above the belt to prevent dust or foreign matter from entering, while also reducing the impact of direct sunlight on fruit freshness. Some models have adjustable baffles on both sides of the belt to adapt to belts with different sieve hole widths (common belt widths 500-1200mm), improving the equipment's versatility.