Dry press technology recycling pulp molding tray 5 processes

Table of Contents

Dry press technology molds recycled paper pulp into trays by pressing under high pressure (200-500 psi) and drying at 100°C-150°C, ensuring trays are durable and cost-efficient.

Pulp Preparation

The dry press technology of recycling pulp with the purpose of molding trays requires the selection and preparation of raw material at the beginning of the process. Waste paper is the main material used for the purpose, which may include the discarded office paper, newspapers, and cardboard. The other issue to consider is waste paper collecting and sorting. For instance, it is important to remove non-paper components, such as plastics and metals, in order to ensure the appropriate quality of the pulp. Subsequent processing requires shredded paper, which enhances the sheet’s surface, increases the drying rate, and facilitates the penetration of the materials.

Soaked paper is known as pulp and is usually placed in large containers with water for soaking, and the process does not usually take more than 24 hours until the paper starts dissolving. Furthermore, authors note that natural binders such as starch or glue may be added to the mixture in order to make the final product more durable. This way, the water-to-paper ratio is an essential consideration, since the final consistency of the mixture should provide the most effective production. According to Schnabel, the optimal ratio is 5:1. The final product is mechanically beaten in order to further enhance the processing of the paper fibers and increase the bonding capacity of the pulp .

It should be noted that it is an essential step in the process, as it ensures that the trays will be strong and stay together. The energy consumed for the purpose is about 50 kWh per ton of pulp, which encourages production with energy-efficient equipment. The final product is placed in a mold. Overall, this stage plays an important role in the production process, as rubber trays are made with the purpose of producing stamped trays, and the quality and level of soaking are crucial for the production of rubber trays. References Schnabel, L. Process for Making Paper Pulp Moulded Articles and Product Produced Thereby.


Pulp Screening and Cleaning

After producing the pulp in the first stage of recycling trays using dry press technology, the next step of the recycling process, which is screening and cleaning, is critical. This is because it is necessary to remove any impurities that are present. The screening process is an effective solution for the purpose and it is performed by having the slurry pass through screens with different sizes of mesh. The screens that have holes of mesh size between 0.15 mm and 0.25 mm, are most effective at removing the impurities Allen. Typically, the screens have mesh of range 0.15 mm to 0.18 mm.

The screening process is completed at approximately 1,000 liter of slurry passed every hour Allen. The cleaning process involves the use of centrifugal cleaners, which rotate at different speeds and remove the impurities with higher density than the pulp of paper fibers that is passed, as the slurry of paper pulp is spun with it, through them. The centrifugal cleaners are most effective as they remove 99% of any particles with density higher than the pulp of paper fibers, including ash, grit, sand, glass, and staples. The cleaning process is most effective when the fibers of pulp are uniformly distributed and spun at higher speeds because the fast-spinning may not be effective in removing all of the particles. This, however, may also increase the energy needed for the cleaning process and add to the costs of the process.

The cost of the energy required for the cleaning process is an estimated 30 KWh per every ton of pulp produced. The cleanliness of the pulp is a major concern for the product because the final product is used for consumer goods. The final trays need to be both strong and have a good appearance. The hardness of the pulp is proportionate to the numerical discount of the particles in the pulp. Thus, the more the cleaning process is more effective, the stronger the trays because the greater the number of the fibers that are not broken. The quality of the pulp directly impacts the quality of paper pulp products that are produced using the trays. Examples of such products include egg trays, fruit trays, and packaging papers.


The molding stage in the dry press technology process which is used for recycling pulp into molded trays describes the process through which the prepared and cleaned pulp is given its shape as a solid object. This is the stage at which the pulp is turned into the final product, and it will thus play an important role in the efficiency and quality of production. Molding machines use appropriately shaped metal dies in which the pulp slurry is fitted in order for the tray, packaging, or egg carton to take its final shape. Once fitted into the “mold,” the pulp slurry is then put under high pressure from below in order for the water contained within it to be expressed, and the fibers within it to be packed together. The pressure can be as high as 200 to 500 psi, depending on the thickness and density of the product.

The pressing cycle lasts between 10 and 30 seconds, giving ample speed to the production processx. This way, a single machine can produce up to 5,000 trays per hour, as I did not know before. The molds used by the manufacturers are very precise. such as in the use of inductive heating by Pro-Finish. An important factor ensuring the quality of the trays is equal distribution of the pulp, which will prevent weak spots in the dry product.

If the product does not have weak spots, the quality of the final product is raised to a level which does not necessitate additional materials, such as extra pieces of cardboard. The product at this point is a molded tray of 50 to 60% moisture, and the next step is thus drying. The efficiency of the high-pressure drying process is critical both for the speed of production and for the energy consumption, which is one of the main buyout costs. If the equipment is properly calibrated and maintained, the energy wasted in the pressing cycle can be decreased by as much as 75%.



The drying of the pulp is the next important process that takes place after it has been molded into trays using dry press technology. This technology provides for the preliminary pressing of the material and makes it possible to carry out the process of drying. The importance of the drying process is that the trays should not be too moist – then they do not remain completely rigid to be able to use. The process should also be timely and should not take too much energy for productivity and profitability. Normally moisture content of trays of paper pulp right after they have been molded would be around 50% – 60%.

It should be taken down to 10% or less to allow for their use and storage. For this, there are a series of heated dryers standing in line to help manufacturers achieve this. Dryers are usually heated up to 100-150 degrees Celsius using electrical heaters and sometimes gas heaters slashing some of the energy expenditures. Time the process takes can vary but should be around 20 – 40 minutes per one cycle. While the results of the process are important to the finished product, also the efficiency of the process is key. The dryers used to be wasting up to 2,500 kilowatt hours per one DaN of processed pulp.

The drying of the later stages has then resulted in vast improvements to the technology, which allows manufacturers to reclaim 20% of that energy. The new technology of dryers allows for energy recirculation and for multi-stage drying zones. It also allows for the latest heat characteristic measurement sensors for accuracy. This process ensures that the form of the trays molded are resistent enough to break or unform during usage and transport. For instance, food industry trays molded for trays should always be moisture resistant – carrying water is meals but also it is always cool.


The finishing of production of recycled pulp molded trays with the use of dry press technology is the final stage of their production, and it is also an important factor defining the aesthetic and functional quality of the final product. This process involves several key steps during which the trays are refined to ensure they have attractive and smooth surfaces and are durable. After the trays are removed from the mold and dried, they have rough edges, and their surface is not as smooth as required, which has to be removed. Trimming is the first step, during which the parts of the formed and dried trays which are extra are trimmed along the edges using automatic cutting machines.

The trays are put into machines which are set for the dimensions of that type of tray. The precision with which this step is performed is important for ensuring the uniformity of the product dimensions, which is essential for customer satisfaction and usability; for example, trays of the same dimensions can be stacked. The subsequent step may involve smoothing the surface of the trays. This can be done using very fine sandpaper or rubbing the surface with soft brushes. In both cases, the purpose is to remove the very fine fibers sticking out of the surface as a result of the manufacture of the tray without removing any of the material comprising the tray, which would affect its strength.

Further coatings may be applied, and these may also be used to ensure even greater moisture resistance, strength, or other qualities depending on the intended use of the trays. The coatings are usually water-based to meet the sustainability goals of the manufacturing process, and they also have to be environmentally friendly to meet the requirement of using the recycled material, and, in this case as well, no formaldehyde etc. can be used.

Again, the coating applied to the trays is very often a food-safe barrier coating on the surface of food packaging trays and plates protecting food from contacting the surface of the container, and it has to ensure the transfer of no moisture, oil, or odor. Each batch of trays is then checked for uniformity in size, shape, color, and finish, with a visual check often complemented by durability and strength tests based on random sampling everything is packed and shipped to the costumer.

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