The truth about the pulp molding process

The pulp molding process of paper pulp molding products involves the transformation of paper pulp—a suspension of fibers in water—on the mold surface. The pulp molding process starts with dehydration and layering of the pulp, continuing until the structure of the paper mold is firmly set. Specific dewatering conditions and timing are applied to maintain the paper mold’s weight, with the moisture content serving as an indicator of the process’s completion.

Filtration and Concentration Mechanisms

The primary mechanism in up-and-down and drum-type molding machines is filtration, which ensures uniform distribution and layer-by-layer deposition. In contrast, injection molding machines utilize both filtration and concentration simultaneously.

Uniform Distribution and Layer Deposition

The filtration mechanism directs more mobile fibers to areas of least resistance, promoting even layer growth. It also facilitates the deposition of single-fiber states of the paper pulp suspension, resulting in a stratified structure with less fiber interweaving.

Concentration Mechanism’s Role

The presence of interwoven fibers in the paper mold’s structure indicates an instantaneous concentration effect following the filtration layer’s formation. This mechanism leads to the formation of a fiber network that deposits on the primary filtration layer, demonstrating the concurrent existence of the concentration process during dewatering.

Complexity in Filtration and Concentration

The complexity of filtration and concentration processes is heightened in a suspension system containing both solids and liquids. The liquid phase, production water, is integral, providing a medium for chemical or physicochemical reactions between fibers and additives during molding.

Molding Quality of Paper Mold Products

The quality of paper mold products is often described as good or poor, reflecting the uniformity of fiber distribution. The storage and transportation of paper pulp, along with the structure and performance of molding equipment, influence this distribution to a certain extent.

Characteristics of Good Molding

Good molding is characterized by uniform fiber distribution, an indicator of overall quality. This uniformity requires that any selected area of the paper mold product has an equal concentration of fibers, contributing to consistent product characteristics.

Factors Influencing Uniformity

• Fiber Distribution: Uniformity is key to achieving consistent product characteristics.
• Fiber Arrangement: A non-directional arrangement of fibers is ideal for enhancing uniformity.
• Pulp Concentration and Return Flow: Adjusting these factors is crucial for improving fiber distribution uniformity.

Structural Impact on Quality

The structural organization of fibers and other solid-phase substances significantly impacts the quality of paper mold products, influencing air permeability, bulkiness, strength, appearance, and performance.

Importance of Mold Design

Mold design plays a critical role in paper mold product quality. It should meet both product structural requirements and molding principles, facilitating reduced filtration resistance and improved fiber distribution uniformity.