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Issues in the Production Process of Pulp Molded Products

There are some common issues during the production process of pulp-molded products. These issues impact the final pulp molding products, so we should pay attention to these issues, to find out why they are important in the production process of pulp molded products.

Common Issues In the Production Process of Pulp Molded Products

Uneven Mold Filling

This issue can arise due to various factors such as improper pulp consistency, inadequate mold design, or uneven distribution of pulp slurry. It can lead to variations in product thickness and density, affecting the structural integrity and aesthetics of the final products. To mitigate this issue, precise control over the pulp consistency and optimized mold design with uniform flow channels are essential. When encountering uneven thickness in the same product or mold, consider the following issues:

  • Is the suction hole in the molding mold uniform? If it’s uneven, open or block holes as needed based on the actual situation.
  • Is the metal mesh clogged? If so, clean it promptly.
  • If it’s injection molding, check if the injection nozzle directly impacts the product. Adjust the position of the injection nozzle promptly to avoid direct impact.
  • Is there any vacuum leakage in the area? If so, repair and seal it promptly.
  • Check if the pulp discharge valve is stuck. If there is, repair it promptly. All four discharge valves need to work simultaneously for a more uniform result.
paper pulping products
paper pulping products

Poor Mold Release

Difficulty in releasing the molded products from the molds can occur due to insufficient application of release agents, improper mold surface treatment, or complexities in the product geometry. This issue can result in product damage during demolding, leading to production delays and increased scrap rates. Proper mold surface preparation and the use of effective release agents are crucial for smooth demolding operations.

Inadequate Drying

Proper drying is critical to ensure the desired strength, dimensional stability, and surface quality of pulp molded products. Inadequate drying time or improper drying conditions, such as high humidity or insufficient airflow, can lead to residual moisture content in the products. This can cause deformation, mold growth, or microbial contamination, compromising product quality and shelf life. Optimal drying parameters and adequate ventilation are essential to achieve uniform drying and minimize moisture-related issues. Generally, the moisture content of molded wet embryos is around 70%. If the moisture content is too high, it can lead to excessively long molding times, excessive energy consumption, and even phenomena like “edge blowing.” Therefore, if the moisture content is too high, considerations should be made regarding whether the wet embryos are too thick, whether the vacuum degree of the vacuum is too low, whether the suction time is too short, whether the molding molds are glued sealed, whether cushion seals are applied, etc. In case of emergencies, it’s essential to focus on checking for any leaks in vacuum pipes and valves.

paper egg trays
pulp molded box

Surface Imperfections

Surface defects such as cracks, wrinkles, or rough textures can detract from the visual appeal and functionality of pulp molded products. These imperfections may result from uneven fiber dispersion, improper molding pressure, or insufficient mold release. Addressing these issues requires optimizing molding parameters, ensuring uniform fiber distribution, and employing effective mold release techniques to achieve smooth and defect-free surfaces.

Dimensional Instability

Variations in product dimensions can occur due to factors such as inconsistent fiber distribution, inadequate compaction, or post-molding shrinkage. Dimensional instability can lead to challenges in product assembly, packaging, or compatibility with secondary processes. Achieving dimensional stability requires meticulous control over molding conditions, fiber consistency, and drying parameters to minimize dimensional variations and ensure product uniformity.

paper pulp molded products
paper pulping products

Excessive Pulping Time

For pulping chemical pulp into pulp boards, if the pulp cannot be sufficiently broken down, it’s essential to consider both the density of the pulp boards and the blades and speed of the pulping machine. Generally, high-consistency pulping machines are equipped with both helical blades and flat blades, while low-consistency ones typically use flat blades with additional side blades around the tank. If the pulping speed is too slow, the sharpness of the blades and the motor speed should be considered. A 6-pole motor has high torque but slow speed, while a 4-pole motor has fast speed but low torque. Therefore, motor speed adjustments can be made according to different pulping machines.

Mold Damage

Continuous operation and repeated use of molds can lead to wear and tear, resulting in mold damage or distortion. Mold damage can compromise product quality, increase rejection rates, and necessitate frequent mold replacements, leading to production downtime and higher costs. Regular maintenance, proper handling, and the use of durable mold materials are essential for prolonging mold lifespan and ensuring consistent product quality.

coffee carton
egg carton 6 cells

Fiber Migration

Uneven distribution of fibers within the pulp slurry can result in fiber migration during molding, leading to weak spots or inconsistencies in the final products. Fiber migration can compromise product strength, integrity, and aesthetic appeal, affecting its suitability for intended applications. Optimizing pulp formulation, refining processes, and molding techniques are essential for achieving uniform fiber distribution and minimizing fiber migration issues.

Environmental Impact

The production process of pulp molded products can have significant environmental implications, including water consumption, energy usage, and waste generation. Addressing environmental concerns requires adopting sustainable practices such as water recycling, energy-efficient technologies, and waste minimization strategies. Implementing eco-friendly production methods not only reduces environmental impact but also enhances the overall sustainability of the manufacturing process.

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