In the extrusion of clay bricks and blocks, the vacuum degree of the extruder significantly affects the quality of the green body as detailed below:

Improved Green Body Density:
High vacuum effectively removes air and moisture from the clay raw material, resulting in a denser internal structure of the green body. Reduced porosity increases the density, thereby enhancing the strength and forming precision of the green body. This helps minimize cracking and deformation during subsequent firing.

Enhanced Green Body Plasticity:
During vacuum extrusion, clay particles align more closely under low-pressure conditions, and moisture in the raw material is distributed more uniformly. This improves the plasticity and forming performance of the green body, making it easier to shape during extrusion, with smoother surfaces and more stable dimensions.

Reduced Internal Defects:
Low vacuum or non-vacuum extrusion may lead to residual air bubbles or microcracks in the green body. These defects can expand during drying and firing, causing cracking or reduced strength in the fired bricks. High vacuum significantly reduces such internal defects, improving the quality of the finished bricks.

Impact on Drying and Firing Performance:
Green bodies with high vacuum have fewer internal pores and more uniform moisture distribution, leading to more even shrinkage during drying and a lower risk of drying cracks. Additionally, denser green bodies exhibit more uniform heat conduction during firing, resulting in higher strength and durability of the fired bricks.

Production Efficiency and Cost:
Appropriate vacuum levels can improve extrusion efficiency and reduce defect rates in green bodies, thereby lowering scrap rates and production costs. However, excessively high vacuum may increase equipment energy consumption and maintenance costs, necessitating a balance between quality and cost.

Practical Considerations:
The vacuum degree is typically controlled within the range of -0.085 to -0.1 MPa, depending on the properties of the clay (e.g., plasticity, moisture content) and the type of brick.
The particle size, moisture content, and impurity levels of the clay raw material affect the vacuum extrusion outcome, requiring optimization of the raw material formulation to match the vacuum degree.
Equipment sealing and vacuum pump performance directly influence vacuum stability, requiring regular maintenance.
In summary, higher vacuum levels generally lead to better green body quality; however, the vacuum level should be optimized based on specific raw materials and process conditions to balance quality, efficiency, and cost.