5 differences between wet press and dry press molded pulp

Table of Contents

Wet press molded pulp uses more water and pressure, creating finer, smoother products suitable for detailed packaging, but is slower and less energy efficient than dry press, which is faster and more suitable for robust, utilitarian items due to its higher temperature and lower water content process.

Process

The wet and dry press molded processes are rooted in turning paper slurry into a shaped, finished product. In the case of the wet press mold, the process starts by mixing the recycled paper fibers in large quantities of water. The resulting mixture is 95% water to 5% fiber, which allows it to be manipulated in the desired shapes and forms. This mixture is then poured into molds that create the shapes for it with the help of hydraulic presses, used for squeezing out the water in the mixture. The result is a more defined and smooth surface of the product. The dry press molded begins with the paper mixture, but its consistency is different – it is 60% water to 40% fiber. As a result, this mixture has a more solid form that keeps its shape within the heated molds. The tires almost 250 degrees Celsius, which allows it to evaporate the water quickly and cure the pulp, creating a strong type of the final product.

Both types of molding used to shape the paper pulp allow the resulting products to be utilized in the real world. Wet press molded which is more visually pleasing and allows for greater detail, is often used in end applications that require packaging and storing products in a protected manner. As a result, product packaging for such products as sensitive electronics, where the container must offer protective properties for the electrical components and be attractive to the consumer. The dry press, molded which has the advantages of a quick process and a strong final product that is relatively difficult to break or collapse, is commonly used to craft the packaging materials for various foods – egg cartons and trays are the best examples of the use of such presses. The matter of firmness is critical however, the energy, and as a result, the cost waste that is associated with the two forms of molded presses. Around five units are required to produce the finished material with the wet press torture. The creation of the finished product requires twice as much energy with the use of the dry molded torture – ten units.

Density and Precision

Products made of molded pulp must have a particular density and level of precision to ensure their performance and suitability to a particular application. Wet press molding typically produces products that have a density of 1.2 to 1.4 g/cm³, which makes them smoother and denser. These products should be used for creating protective packaging for items requiring an elegant finish, such as makeup compacts or smartphone cases. The undesirability of wet press molded pulp for other applications allows it to be highly precise, to the point of serving for uneven embossing for non-regular products. As such, the wet press method can produce less dense, but highly functional products that both look good and work perfectly.

Dry press molded pulp typically has a lower density of 0.7 to 1.0 g/cm³. It retains the rougher texture typical for the product, which can be easily felt by people touching it. It is lighter than wet press molded pulp, lowering the final product’s cost and making shipping and handling cheaper. Lower density also allows products made by dry press molding to be less expensive and faster to produce. As such, these products are generally limited to relatively robust applications for this rougher description, and they are used, for instance, for molding disposable trays for school cafeterias. They are also used for packaging less delicate agricultural products with plenty of air circulation, such as fruit or vegetables. The density and precision required for these applications ensure cost and speed efficiency for both forming and production.

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Drying and Strength

The primary way to differentiate between a wet press molded pulp product and its dry press counterpart is the drying process that takes place as well as the resultant strength of the item. When creating something using wet press molding, it is a high-pressure production method that provides for the effective removal of a significant amount of water from the pulp slurry during the initial molding step. The production method is followed by a drying phase when the produced items are placed in an environment designed to dry them. The perfect result in this technique means that the end products retain the shape they were molded into and have a high enough strength or integrity of the structure. Also, this shows that the average time spent on drying in a wet press molding device is about 10-20 minutes per batch, adjusted for the thickness and complexity of the new product. It is an ideal technique to use when the goal is to design packaging for something fragile, like glass or electronics, but they cannot be placed into there without a certain level of strength to prevent breakage or damage, for example, during transportation or shipping.

A dry press molding is the type of technique that uses both heat and pressure in the exact manner during the creation steps, mainly the molding of new pulp items. From the start, however, the technique uses significantly less water while employing a high-temperature product of the form. Also, the high temperature of the molds implies that they take less time to complete the drying process, with the average time to complete it on a new product being about 5-10 minutes. It is suitable when the produced items need a strength-level of a high enough level to serve as protection during shipping and long-term storage, for example, industrial parts or produce that may be placed in some boxes for further transportation. The materials used in the device at the dry press molding produce a tensile strength of the products that allows stacking and further handling. The strength of products made in the wet press variant will usually be higher, as well as with the added benefit of a more even, denser structure. These items are likely to last longer than items produced by other methods, although the dry-pressed items, while strong, will have a coarser texture and possible less uniform density.

Applications

Both wet press and dry press molded pulp has its own specialization, as it can be seen by their characteristic features, which are their superioritiy in density, precision, and durability. Wet press molded pulp is targeted to the fields where better quality of production and its more precise details are needed. Thus, a higher rate of the minority of this production is the retail packaging of better electronics, such as smartphones, cameras, and even high-end laptops. The structure of the pulp is dens er and thus smoother, that is why the fit is more precise and the equipment is saved better against shocks. This type of the production is also used in the medical industry for packaging equipment, as well as wet press molded pulp can show its best features in packing the most sensitive instruments. The molded pulp is denser, the molding may be effectively fitted to any slots for the equipment’s fixation. Thus it is used in the medical sphere in order to secure the preciseness of the equipment fitting in the casings.

Dry press molded pulp is more often used in solving transport or bulk handling problems, where the high quality of the bright design is out of any considerations. Thus dry press molded pulp is used for packaging food by producing less presentable production which may be quite roughly used, like disposable plates or cups, glasses or even clamshell food containers, as well as making one of the fundamental environmentally-friendly kinds of packaging. Moreover, It is also used in the production of light transport trays or even egg delivery boxes or trays for packing plants, being a very breathable kind of the production, it also gives additional protection being moisture-resistant. Thereof, in most cases, the choice of wet press or dry press molded pulp production is done according to the requirements of the equipment’s usage, where the wet press is definitely used for the production of better quality production, and on the contrary, the dry press is used for more efficent packaging where the requirements of the cost do matter. The reason is usually the greater complexity of the wet press thus making the production of wet press molded pulp to be a rather more expensive thing due to a greater amount of time needed for moulding the product and longer time of the product’s drying.

Efficiency

The main aspects that are usually used to compare the efficiency of molded pulp via wet press and dry press methods are the production times, energy consumption, and possibilities to satisfy large-scale demand. The main advantage of the dry press molding is speed. Once the pulp pieces are formed in the device, they can be produced within approximately 5-10 minutes per cycle because of the lower water content and the application of heat that creates rapid drying. Therefore, the dry press molding can be beneficial if a large order must be pressed in a very short timespan. For instance, if a producer needs to create a large amount of egg cartons or packaging for some merchandising operations. Both require a lot of boxes and pallets to be laid out in a short timespan, which is why a fast turn-around could make the difference in satisfying the requirements distributed. The above difference can be put into figures, i.e. a very rough calculation shows it to be 2 times faster than wet press molding.

The major benefit of wet press molding, in turn, is the ability to exercise a better control of product quality. Such a procedure on average takes approximately 10-20 minutes. Despite it being multiple times slower in terms of ensuring the available number of cycled products, wet press proves to be better when regarding the final product as being more important than the pace of processing. High-quality finish and detail characterize the products made in this way. They are usually used for more delicate applications such as the packaging of premium electronics where not only sufficiency of the products to its intended use but also how it reflects the brand and creates an added value to it. One more difference is that the wet press molding consumes more energy per unit because of the need to use more intensive hydraulic pressing to get rid of water as well as use extra energy to dry ultimately denser materials. Contrary to it, the dry press molding utilizes heating that is directly integrated into the machinery pressing the products into shape. This results in a better energy expenditure balance respectively for the dry press molding.

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