How does a screw press work？

1. The Working Principle of the Twin-Screw Press

1. Synergistic Action of Twin Screws
   The twin-screw press consists of two counter-rotating screw shafts (the conveying screw and the pressing screw). After the material enters the hopper, it is first pushed towards the pressing screw by the conveying screw. Due to the opposite rotation directions of the two screws, the material experiences its first pressing and forms an initial compression when changing direction.
2. Pressing Process

• Pitch and Shaft Diameter Changes: The pitch of the pressing screw gradually decreases while the shaft diameter gradually increases. As the material is pushed, it is subjected to both axial and radial pressures, forcing the liquid (such as juice) to pass through the screen holes of the screen cylinder and collect in the juice collection pan.
• Screen Wall and Conical Resistance: The design of the inner wall of the screen cylinder and the end of the conical body further increases resistance, enhancing the pressing effect and ensuring thorough liquid separation.

1. Sludge Regulation
   The size of the discharge opening at the rear of the conical body is regulated by springs or hydraulic systems, changing the discharge resistance to control the dryness or wetness of the material. For example, increasing the pre-tightening force of the spring can enhance the pressing strength, making the sludge more dry.

2. Working Principle of Single-Screw Press

1. Spiral Structure and Segmentation
   Single-screw presses typically divide the screw into three sections: the feed section (transmission), the pressing section (compression), and the discharge section (squeezing). After the material enters through the feed hopper, it is gradually pushed forward by the rotation of the screw blades.

2. Pressure Increment Mechanism

• Pitch and shaft diameter changes: In the pressing section, the screw pitch gradually decreases while the shaft diameter increases, forming an incrementally larger compression space, which forces the liquid in the material to be discharged through the screen holes.
• Forced Feeding Device: Some models are equipped with a forced feeding plate to prevent material slippage or backflow, ensuring continuous pressing.

1. Sludge Control
   The thrust valve or pressure regulating device at the discharge end controls the slag discharge resistance by adjusting the size of the annular gap, achieving flexible adjustment of the sludge moisture content.

3. Key Components and Adjustment Mechanisms

1. Sieve Drum and Filter Screen
   The sieve drum is typically made of stainless steel, with sieve hole sizes designed according to the characteristics of the material (such as specialized small hole sieves for goji berries). The filter screen is removable and washable to ensure hygiene.

1. Hydraulic/Spring System

• Hydraulic Adjustment: Controlled by piston oil pumps and relief valves to regulate oil pressure, which adjusts the pressure at the discharge outlet. This is suitable for high-precision pressing requirements.
• Spring Adjustment: Manually or automatically adjusted spring preload, which is cost-effective but has a limited adjustment range.

1. Transmission and Drive
   The motor drives the screw shaft via a reducer, with some models featuring a friction-reducing design that omits the shaft.
   Four, Application Scenarios and Advantages
2. Applicable Materials
   Primarily used for materials containing fibers or viscosity, such as grape pomace, goji berry fruit, Chinese herbal waste, and kitchen waste, particularly suitable for scenarios requiring high solid-liquid separation.
3. Advantages and Features

• Efficient Dehydration: The double-spiral design allows for dual pressing, resulting in high juice yield and low moisture content in the residue (typically around 60%).
• Corrosion Resistance: The contact parts with materials are mostly made of 304 stainless steel, making it suitable for acidic and alkaline environments.
• Flexibility: It can adapt to different material characteristics by adjusting pressure and sieve hole size.
  Five, Matters to Note

1. Operating Procedures

• Adjust the slag discharge outlet to the maximum before startup to avoid overload; empty the material before shutdown to prevent residue blockage.
• Regularly inspect the wear of the screen mesh and replace it promptly to ensure separation efficiency.

1. Maintenance and Care

• Lubricate the bearings and gearboxes; the hydraulic system requires regular oil filter replacement.
• Avoid using hard objects to scratch the screen drum during cleaning to prevent affecting its sealing performance.

Summary
The screw press achieves efficient solid-liquid separation of materials through the rotational motion of the screw shaft and its design. The double-screw model has an advantage due to its two-stage pressing process, while the single-screw model is simpler in structure and lower in cost. The key lies in achieving dehydration requirements for different industrial scenarios through pressure increment, screen mesh filtration, and dynamic adjustment.