Impact of Wet-End Chemistry on Paper Mold Equipment and Product Molding

Wet-end chemistry has a dual impact on the operation of paper mold equipment and the molding of products:

• Positive impacts:
  • Enhance water drainage
  • Reduce air intake and eliminate foam
  • Maintain mold cleanliness
  • Keep the solid content in white water
• Negative impacts:
  • Equipment operates abnormally
  • Mold screen clogging, plugging, and scaling are severe
  • Products develop spots and bubbles
  • Reduce water drainage
  • Decrease production efficiency

The characteristics of paper stock flow:

• Critical concentration: Below 0.05%, the interaction between fibers is minimal, and the flow state is similar to water.
• Above the critical concentration, fibers intertwine to form flocs, and the flow state differs from water.
• As the paper pulp concentration increases, the opportunity for flocculation increases, and long-fiber pulp is more prone to flocculation.
• Turbulence can disperse fibers and flocs, but also promote the formation of flocs, with the degree of flocculation depending on the balance between turbulence and flocculation.

Wet-end molding process:

• The key to the wet-end molding process of paper mold products lies in the dehydration of product molding.
• Dehydration of wet paper mold blank is the primary process, removing the vast majority of water from the paper stock on the mesh mold.
• Dehydration methods: filtration and suction dehydration, accounting for more than 95% of the total dehydration on the mesh mold.

Molding machine dehydration stations:

1. Suction Dehydration:

The formation process of pulp from the storage tank to the wet paper mold blank on the mold mesh is a complex process:

• Pulp injection stage: This stage is from the start of pulp injection from the storage tank to the end of injection.
• Molding and dehydration stage: The first half of this stage is filtration dehydration, and after the injection is completed, the pulp is diluted with a certain amount of backwash water. Relying on the gravitational force of the pulp, it naturally settles through the pores of the mold to dewater.
• The second half is natural settling dehydration plus suction dehydration. At this stage, the wet paper mold blank has basically formed and has a certain wet strength. The suction dehydration at the suction station should not be too fast to improve the retention rate of fillers and pulp.
• If the dehydration is too fast, the fine substances and chemical aids in the pulp are likely to be lost in large quantities, and premature molding will affect the uniformity and double-sidedness of the finished product. The degree of filtration will be affected by the flocculation between fibers and fine fibers.

2. High-Pressure Dewatering (Cold Pressing Stage):

This stage further dewaters the wet paper mold blank transferred from the suction station by mechanical force, increasing the binding force between fibers on the basis of suction molding, and then transferring to the hot pressing drying station for further drying and shaping.

After high-pressure dewatering and strong suction, the water content of the wet paper mold blank is reduced from over 90% to about 55%, thus completing the dehydration task of the wet paper mold blank. High-pressure dewatering serves as a transition from the suction station to the hot pressing station, and also reduces the energy consumption of drying by maximizing dehydration.