Clay sand processing technology

Clay sand processing technology
The clay sand processing technology is a crucial step in the casting production process, directly influencing the quality of the castings, production costs, and environmental protection. The following provides a systematic and detailed introduction to this technology. Core objective
The used and old sand (containing failed clay, coal powder, impurities, etc.) will be processed to restore its properties, and then mixed with new sand, binder (bulky clay), and additives (coal powder, etc.) to prepare a new type of sand that meets the molding requirements. This is a recycling process.
Process flow diagram (closed-loop cycle)
Sanding → Crushing → Magnetic separation → Screening → (Cooling and pre-treatment of old sand) → Sand regeneration (key stage) → Addition of new sand/auxiliary materials → Mixed sand → Molding sand performance testing → Molding use
Detailed explanations of each process
1. Pre-treatment stage
Before the old sand enters the regeneration core, it needs to be prepared.
Sanding and crushing: Separate the castings cooled by pouring from the sand mold, and large sand lumps are crushed.
Magnetic separation: Use magnetic separation equipment (magnetic drum, belt) to remove iron beans, iron nails, flying edges and burrs, etc. that are ferromagnetic in nature, protecting subsequent equipment.
Screening: Remove core bones, wood blocks, sand blocks, etc. that are non-magnetic by using a vibrating screen or multi-angle screen.
2. Cooling and pre-treatment of old sand (key stage)
The temperature of the old sand is usually 80-120℃. High-temperature sand can cause many problems (adhesion to equipment, water evaporation, affecting the quality of mixed sand). Cooling methods:
Vibrating boiling cooling bed: The most common and efficient. Air is blown in, and the sand is in a boiling state on the vibrating plate, while cooling and removing some dust.
Double-disc cooler: Cooling through stirring and air is used, and it also has a pre-mixing function.
Rolling cooling machine: Cooling through air cooling and water mist evaporation in a rotating roller.
3. Sand regeneration (core stage)
The purpose is to remove the failed clay film (dead clay) on the surface of the sand grains, which is the key to restoring the sand grain properties. According to the regeneration intensity, it is divided into:
First-level regeneration (basic regeneration): Only partially remove the failed clay through friction. Common equipment: Centrifugal rotor regeneration machine. The sand is vigorously rubbed and collided between the rotating rotor and the liner plate, causing the clay film to peel off. Suitable for small-scale, less demanding casting factories.
Second-level regeneration (powerful regeneration): On the basis of first-level friction regeneration, add impact or grinding.
Air flow impact regeneration: Use high-speed air flow to accelerate the sand particles and impact the target plate, resulting in a better stripping effect.
Mechanical powerful regeneration: Such as vertical or horizontal mechanical regeneration machines, combining friction, impact and grinding.
Second-level regenerated sand has high quality and can be used for manufacturing complex sand cores or as surface sand.
4. Wind separation and dust removal
Wind separation: The regenerated sand enters the wind separation device, using air flow to separate the fine powder (mainly dead clay and coal powder ash) from the qualified sand particles.
Dust removal: The entire system is equipped with a powerful central dust removal system, collecting dust generated at various locations to ensure environmental protection and workshop cleanliness.
5. Mixed sand and ingredient
Mix the regenerated sand, supplementary new sand (about 5-15%), bentonite (clay), coal powder (or other carbonaceous additives), and water in precise proportions.
Key equipment: Rotating mixer (efficient, uniform).
Control core: Online sand performance testing instrument (such as compactness rate, moisture content, strength controller), adjusting the water addition amount and auxiliary material addition amount in real time based on the test results to achieve closed-loop automatic control.
6. Sand homogenization and transportation
The mixed molding sand needs to be left to homogenize (allowing moisture to penetrate evenly) and then transported through belt or pneumatic conveying systems to the molding workshop.
Process type and selection
According to different production scales and sand demand, there are mainly two layout methods:
Centralized processing system: Suitable for large-scale, single-product production lines (such as automotive castings). All old sand is centralized processed, with a compact process and high automation, and convenient management.
Unit processing system: Suitable for multi-variety, small-batch workshops (such as machine tools, heavy machinery castings). Each molding line is equipped with an independent sand processing unit, with strong flexibility and no interference.
Key technical indicators and quality control Effective bentonite content and effective coal powder content: Regular testing is required (such as methylene blue titration method), to guide the replenishment amounts of new bentonite and coal powder.
Mud content (fine powder content): Should be controlled below 12%-16%, as excessive content will affect the performance of the molding sand.
Loss on ignition: Reflects the total amount of combustibles in the molding sand, and needs to be controlled below 3%-5%.
Particle size distribution: Maintain stability to ensure the透气性和 surface finish of the molding sand.
Water content： Usually controlled at 2.0%-3.5%, which is the "soul" of the molding sand and needs to be precisely controlled.
Compaction rate： The most intuitive online control parameter, reflecting the dry-wet and viscosity state of the sand, generally controlled at 35%-45%.
Development trend
Intelligentization and big data： Utilizing sensors and Internet of Things technology, real-time monitoring of all process parameters, through big data analysis to predict the state of the molding sand, achieving preventive maintenance and optimal control.
High efficiency and energy saving： Equipment is developing towards large-scale, low energy consumption, and low wear. Utilization of waste heat from hot sand.
Enhanced environmental protection： Collection and treatment standards for dust and exhaust gases (such as VOCs) are becoming increasingly strict.
Flexibility： Unitized and modular design, adapting to the market demand for multiple varieties and small batches. Summary
The clay sand processing technology is a complex system engineering that integrates mechanics, fluids, automation control and materials science. Its core concept is "circular economy", aiming to reduce new sand consumption and solid waste emissions through efficient regeneration.