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Between supply chain concerns and the desire to create a more environmentally friendly way of living, molded pulp products are as popular as ever. This ultimate guide was created to help you understand how you can leverage woven wire mesh to perfect your molded pulp process and keep up with demand.
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Molded fiber, also known as molded pulp, refers to products molded into 3D shapes and vacuum-formed from a slurry of virgin or recycled agricultural fibers. Fibers such as wood, sugarcane, and wheat straw are processed into pulp.
Molded fiber products are used to package a variety of food items and protective packaging.
Manufacturing molded fiber products involves a fiber slurry, a mold, a molding machine, and a drying method. The mold and slurry are two important variable items in the process. The mesh/screen attached to the mold surface largely determines the quality of a finished molded part as well as production efficiency.
The pulp, and in some cases, recycled paper, is mixed with water, producing the molding slurry with a fiber consistency based on the molding machine capability, the mold design, and the finished molded product requirements.
The molded part is formed on a screened, porous mold machined into a desired shape. The mold, immersed in a tank of slurry, is subjected to a vacuum, drawing fibers in the slurry onto the surface of the screened mold. The mold, with its layer of fiber, is removed from the slurry tank and drained. The molded part, depending on the machine type, is transferred using a mating mold or blown off with a blast of air. The molded part is dried either in a heated mating mold or a drying oven.
Woven wire mesh, or simply wire mesh, is a screening media that is fabricated using hundreds of individual metal wires. These wires are woven together using a heavily monitored weaving technique, forming pore openings that are precise and rigid.
The mesh is engineered to function as a controlled filter when fastened to the surface of molds in producing molded fiber products. Its unique design characteristics allow it to deliver the flexibility needed to deal with a variety of 3D shapes.
To that end, processes such as heat treatment and calendaring add value to mold function in forming a quality molded fiber part.
To address different needs, many forms of screening media are available, including wire mesh, sintered multi-layered mesh, perforated plate, and expanded wire. Considering the screened mold requirements of throughput, durability, and cost-effectiveness, woven wire mesh stands out as an integral part of producing molded fiber products.
These benefits are achieved by using thin wires, typically made of durable 304 or 316 stainless steel, and designed to withstand the high temperatures and pressures associated with the molded process.
Although brass, copper, and aluminum, each with their specific properties, have been used in the molded fiber industry in the past, stainless steel has proven to be the most suitable material for use in molds for producing molded fiber products.
Wire mesh screened molds are made by either pressing and attaching the wire mesh onto the surface of a porous metal mold body or fabricating the mesh to the shape of the mold body and attaching it in close contact with the mold body surface.
Implementing engineering and design technology, including wire diameters, alloys, and annealing levels, as well as wire mesh patterns that control water flow, ensures the screened mold results in efficient products and high-quality molded fiber products.
In order to ensure an even distribution of vacuum pressure and heat when manufacturing molded pulp products, the molds must be lined with formed wire mesh. As every detail of the molds will be transferred to the molded pulp, your wire mesh must be properly formed.
All forming processes should begin with the design of the mold. The design should accurately outline the shape, size, and fine details of the desired pulp product.
Once you have zeroed in on the design of the mold, you will want to take your wire mesh and cut it down into manageable pieces. These pieces are then deep drawn or pressed until the product's exact form is achieved.
To properly form your wire mesh molds into the profile of the molded pulp product, they must be deep drawn. Deep drawing is best defined as the process in which a flat piece of mesh is altered to take on the three-dimensional profile of the product.
To properly deep-draw your mesh, you must first cut and pre-form the mesh piece in accordance with the parameters of the final mold. The mesh can then be loaded into the press machine.
This press machine is furnished with a die that accurately depicts the profile of the molded pulp product the mesh mold will be producing. The mesh will then be pressed into the cavity of the die, embedding each detail of the die into the mesh.
After being formed, any unnecessary material is trimmed.
This deep drawing process works to maximize the amount of screening capacity of your process; however, it also ensures your wire mesh molds fit into your equipment perfectly. But as with any value-added process applied to woven wire mesh, the deep drawing of wire mesh must be fine-tuned based on the alloy of the mesh and the profile of the final mold.
NOTE: Once placed into the pressing machine, we have found that turning non-circular wire mesh pieces at a 45-degree angle enables the corners of the mesh piece to be deep drawn effectively.
The production of molded pulp products that deliver heavily relies on properly drawn mesh molds. For maximum efficiency, you must understand the issues you can encounter when deep drawing wire mesh and how to prevent them.
Cracked mesh, wrinkled mesh, deformation, and spring back are the most noteworthy issues that can hinder your molded pulp production line.
Cracked wire mesh describes the development of broken wires in concentrated areas of a wire mesh mold.
Cause: Drawing wire mesh beyond its limits or using mesh woven with low-quality wires..
Wrinkled wire mesh describes the development of folds, waves, or ripples in a wire mesh mold as it is being deep drawn.
Cause: Wire mesh often wrinkles when the die is not lubricated thoroughly, too much pressure is applied, or the mesh is not cut and pre-formed to accommodate the profile of the final mold.
Deformation is used to define a wire mesh mold that does not correctly form to the die.
Cause: Not providing enough support to the wire mesh piece as it is being drawn.
Spring back is a term used to describe a wire mesh mold that fails to hold the form of the die, springing back to a flatter orientation.
Cause: Implementing wire mesh that has not been properly annealed.
Once properly drawn and pressed, the edges of the molds are trimmed to remove any excess material. This serves two purposes:
In most molded pulp applications, a wire mesh mold is paired with support elements to provide additional reinforcement. This, of course, enhances the durability of the mold.
Now, prior to integrating them into the production line, you will want to test your wire mesh molds and subject them to a quality control inspection. This involves verifying proper drainage, consistent pulp formation, and confirming the mold performs desirably when processing your slurry blend.
Note: If you notice any warping or inconsistencies in the molded product, it’s a sign the mold needs to be adjusted before entering full production.
It is widely known that wire mesh is relatively flexible as is; however, having your mesh annealed is required for best results. Annealing is the heat-treatment process in which wire mesh is subjected to tremendous heat and pressure in an effort to reduce the internal stress of the wires.
The resulting effect is a wire mesh weave that is softer and easier to form.
Not only does this ensure every detail of the mold is captured without altering the integrity of the pore openings, but it helps the mesh hold its form after being deep-drawn. Using wire mesh that is not properly annealed—or annealed at all—increases the risk of mold spring back. Spring back is a term that describes the occurrence in which the wire mesh molds have minimal structural integrity, causing them to spring back to a flatter profile.
As annealing also makes the pore openings more rigid and permanent, wire mesh that is not annealed is typically more sleazy and flimsy. This heavily affects the fiber retention that occurs when forming the pulp, which results in inconsistencies in your final molded pulp products.
Ultimately, using wire mesh that is not annealed makes for a less efficient molded pulp process.
Looking for more information on annealing wire mesh for molded pulp applications? Refer to the following post:
There are several benefits associated with fabricating your wire mesh molds in-house. First and foremost, you can produce your particular specifications as needed.
As a result, costly downtime is reduced, and you can maintain desirable lead times.
Manufacturing your own wire mesh molds in-house will also make implementing elements of your brand much easier. Despite third-party companies having the capacity to create dies custom to your brand, the amount of proprietary labor would dramatically impact the cost and lead times of your molds.
While making your molds can be convenient, it can be a relatively daunting investment. It requires you to invest in all the tooling and any maintenance needed to keep your operation up and running.
With that, the machinery needed to properly press wire mesh into molds can have a large footprint. This can be troublesome when you begin to add in the other equipment needed to develop a comprehensive molded pulp production line.
Another factor of note is that pressing wire mesh molds can prove to be labor-intensive. In other words, a portion of your staff would not only have to be trained to use the equipment, but they would be spending less time contributing to more critical aspects of the molded pulp process.
So, to put it simply, if you must be mindful of your budget (especially unexpected expenses), are limited on space, or often face issues with staff volume, having a third-party company fabricate your wire mesh molds may be a suitable solution for you.
One of the more notable benefits of using woven wire mesh to fabricate your molds is the fact that virtually every aspect of the material can be customized to accommodate your needs. In the molded pulp industry, the mesh specifications you will need to fine-tune to perfect your process are mesh count and alloy.
Mesh count, or the number of pore openings in a linear inch, is critical to controlling what passes through the screen when forming molded pulp products. As a result, you are in complete control over fiber retention, water drainage, and the finish of the final product.
20 mesh and 40 mesh were once seen as the industry standard and are thus recommended by numerous pulper manufacturers. With this in mind, W.S. Tyler has discovered 24 mesh and 50 mesh to produce desirable results.
20 mesh and 40 mesh were once seen as the industry standard and are thus recommended by numerous pulper manufacturers. With this in mind, W.S. Tyler has discovered 24 mesh and 50 mesh to produce desirable results.
In the molded pulp industry, 24 mesh has grown a reputation for its balanced percentage of open area and durability. This harmony of mesh specifications makes it ideal for molded pulp operations looking to fine-tune drainage efficiency without sacrificing fiber retention or mold longevity.
Promoting consistent pulp molds and reduced drainage times, 24 mesh streamlines production. In turn, operational costs are lowered.
The robust characteristics of the 24 mesh weave combat the effects of daily wear caused by pressure and temperature fluctuations. In other words, 24 mesh is perfect for high-demand processes.
In short, 24 mesh will help keep high-volume production lines moving—often adopted by operations that rely on consistent throughput.
Outfitted with custom oblong openings, W.S. Tyler’s distinctive mesh was meticulously engineered to produce optimal fiber retention and selectively remove fine particles. Its one-of-a-kind properties make 50 mesh a go-to solution for high-precision thermoforming and advanced wet pulp systems.
This is particularly true when clarity, uniformity, and end-product aesthetics are of the utmost importance.
While a finer weave, W.S. Tyler’s 50 mesh molded pulp weave handles the heat and pressure fluctuations associated with continuous cycling with ease. As a result, 50 mesh molds yield molded pulp products that deliver a dense, smooth, and refined surface that will instill the feeling of high-quality craftsmanship.
During the molded pulp process, the pulp slurry is typically heated to varying temperatures while being subjected to vacuum pressure during forming. Distributing this heat and pressure is vital to producing a consistent product.
But as each molded pulp process features proprietary parameters, you must select an alloy that can accommodate the elements of your process. With that, the four main alloys used for molded pulp applications are stainless steel, brass, copper, and aluminum.
Stainless steel is possibly the most popular woven wire mesh material to date. With a manufacturing process based on centuries of research, the alloy has become known for delivering the perfect balance of durability, corrosion resistance, heat resistance, and formability.
It should also be noted that it won’t react with your pulp slurries. This is particularly beneficial when producing food-grade molded pulp packaging.
Brass is a wire mesh alloy often employed for its ability to retain and effectively distribute heat when forming molded pulp products. At W.S. Tyler, the brass wires used have a chemical composition of copper (85%) and zinc (15%).
This particular chemical blend works to ensure your wire mesh molds combat rusting.
Copper is a wire mesh alloy known for its ability to conduct heat and electricity. It also has poor resistance to cyanides, halogenides, and ammonia.
That said, copper can resist some of the common corrosive elements associated with molded pulp and features the tensile strength to withstand most forming processes.
Aluminum is a wire mesh alloy often used for its lightweight and corrosion-resistant characteristics. It should be noted that it is the weakest of the alloys listed and may need to be replaced more frequently.
Despite its weak traits, aluminum can accommodate the pressure and heat distribution requirements of most molded pulp processes.
Multi-functional in nature, woven wire mesh plays a critical role in several areas of the pulp molding process. This includes delivering peak performance when integrated into the drainage stage.
Paired with CNC-machined molds, wire mesh acts as a filtration layer used to shape the pulp slurry into high-quality forms without sacrificing drainage efficiency.
The high durability of the various alloys that can be used to weave wire mesh ensures your molds can perform when subjected to vacuum pressure, heat, and chemical variations. Adjacent, wire mesh’s formability affords a glove-fit solution.
Customizable weave options, such as W.S. Tyler’s 24 and 50 mesh, let you fine-tune parameters such as the weave’s pore size. This empowers you to create the perfect balance between water drainage and fiber retention.
The sheer level of optimization wire mesh offers also helps combat troublesome clogs. This further helps promote optimal drainage efficiency while also reducing downtime and maintenance.
With this in mind, you are encouraged to really hone in on the right wire diameter and mesh count combination. This will help you strike the percentage of open area/durability balance needed for peak drainage.
Over time, the various chemicals used in your pulp molding process will react with the surface of the wires used to weave your mesh, leading to pitting, compromised accuracy, structural weakness, and ultimately, product defects. This gradual degradation is often referred to as chemical wear.
Neglecting to address chemical wear dramatically increases the risk of product waste, frequent mold replacement, and unplanned maintenance expenses. It goes without saying that these risks can throw a wrench in operational efficiency and the reputation of your brand.
Now, there are several steps you can take when laying out the specifications of your wire mesh molds to prevent chemical wear.
Possibly the most important step is selecting a suitable alloy. Stainless steel alloy—typically 304 or 316—offers optimal resistance to chemical wear. In fact, 316 stainless steel stands as one of the most widely used alloys for corrosive environments.
That said, if your process is on the more extreme side in terms of corrosiveness, you will want to turn toward specialty alloys like Hastelloy.
Aside from the alloy of your weave, you will want to meticulously identify the perfect balance between wire diameter, mesh count, and percentage of open area. Finding harmony between these specifications will help facilitate optimal drainage and structural durability while also working to combat chemical pooling and surface degradation.
No matter where you begin to fine-tune your wire mesh mold design, chemical compatibility, operating temperatures, and mechanical stress loads should always be taken into consideration. This, paired with a consistent and dependable maintenance routine, will work in conjunction to facilitate the prolonged production of high-quality molded pulp products.
There are several instances in which molded pulp manufacturers turn to minerals to improve the products they provide. Concerns such as improving water drainage, improving molded pulp integrity, preventing the pulp from sticking to the molds, and more can all be resolved with the right mixture of minerals.
Generally, four minerals are used when forming molded pulp to enhance the process. These minerals are talc, kaolin, bentonite, and calcium carbonate.
Talc is considered the softest mineral on Earth and is typically reserved for applications where friction is a concern during the forming process. Additionally, it is used to make slurries with high pitch levels easier to manage.
These factors work together to create a smooth surface that can be easily printed on. Nevertheless, talc is predominantly used when working with a slurry created from wood or recycled paper.
Kaolin, often called china clay, is a mineral that creates a smooth, white finish. Much like talc, this makes for a finish perfect for printing color, labels, and graphics.
Having been used for over 100 years, kaolin is particularly known for allowing for more effective laser marking capabilities.
Naturally found in volcanic ash, bentonite makes slurries with high pitch and sticky levels easier to manage.
Calcium carbonate is one of the most widely used filler minerals and is a term that can be used to categorize marble, limestone, or chalk. On top of creating a bright, white finish, calcium carbonate can be used as a filler to reduce the amount of fiber in each mold.
Moisture is a prominent concern when forming molded pulp products. Fillers allow manufacturers to have more control over the dewatering process, reducing the amount of energy spent on drying wet molds.
Putting this into perspective, working with a pulp slurry that is 3% calcium carbonate will reduce the moisture present in the formed pulp. This, in turn, yields improved drainage times without substantially impacting the burst strength.
But mineral fillers are not limited to just improved drainage. Fillers, such as talc and kaolin, can also be used when struggling to properly detach molded pulp from the wire mesh molds. Additionally, fillers can be used to maintain the performance of your wire mesh molds. Mineral fillers, such as talc and bentonite, can reduce the amount of stickies and pitch within the pulp slurry. In other words, your pulp slurry will not easily stick and accumulate on your wire mesh molds.
As a result, you will spend less time cleaning your mesh molds while maintaining uniformity in the quality and dewatering of your molded pulp products. That being said, regardless of what fillers you use, it will change the density of the final molded pulp product.
A critical step in manufacturing high-quality molded pulp products is formulating an easy-to-manage pulp slurry that can accommodate the mold’s profile and level of quality needed. As stated above, mineral fillers can make this process much easier. But the individual mineral particles must be uniform for the fillers to work effectively and efficiently. This is where particle size analysis comes into play.
Particle size analysis is the process of determining the uniformity of material by analyzing the size distribution of a sample that represents the material’s presence in the production line. It is often employed in the molded pulp industry to analyze the particle size range of the mineral fillers, verifying that a specific amount of mineral filler will deliver the same effect with each use.
This will enable you to standardize your pulp slurries, ensuring customer expectations are met no matter who is operating the production line.
Woven wire mesh is a screening media known for being an open product. As wires with precise wire diameters are used during the weaving process, the amount of surface area closed off by the wires is reduced and controllable.
To that end, virtually every parameter of woven wire mesh can be customized. In regard to mesh count, more specifically, specifications as small as 400 mesh can be achieved.
This makes it extremely easy to achieve the finish and fiber retention needed to produce quality molded pulp products.
Perforated plate is a screening media constructed from a piece of sheet metal with hundreds of uniform pore openings created from laser, water jet, and plasma cutting. Its sheet metal characteristics make it one of the more durable screening media you can choose.
Additionally, it is known for its heat conductivity. This is critical as heat distribution is key to bonding the individual fibers of the slurry and initiating the drying process.
Expanded wire is a screen fabricated by taking a piece of sheet metal, cutting a specific number of slits at specific dimensions, and stretching the metal, creating diamond-shaped pore openings. Having comparable durability to perforated plate, it is widely used when extreme and continuous vacuum loads are placed on the screen.
What makes it stand out in comparison to perforated plate is that it can be fabricated to feature finer pore openings, though not as fine as woven wire mesh. It also has better flexibility than perforated plate, allowing it to be used in more complex mold designs.
Wire mesh laminate is a screening media fabricated from several layers of woven wire mesh that have been sinter-bonded together. The multilayer configuration allows the material to deliver optimal durability while maintaining the accuracy woven wire mesh is known for.
This leaves you with a mold that minimizes the need to be replaced, ultimately increasing production capacity.
W.S. Tyler has 50 and 24 mesh weaves that are optimized for molded fiber product production, and the cost depends on the needed specifications and requirements of the wire mesh. Today’s average cost, depending on volume, is $7 USD per square foot.
With this in mind, we understand that these specifications may not suit you. Your wire mesh supplier can work with you to determine a specification that will output the best results, but the price you can expect to pay will be dictated by the specifications you choose.
Regardless, the quantity of the order will also play a critical role in the cost.
Placing a purchase order for a set quantity of mesh to be released at specific intervals is the best way to manage costs when ordering wire mesh. This will allow you and your wire mesh supplier to lock in a price that best suits your operation while also helping you manage inventory.
Ordering mesh in bulk will also work to manage costs. To explain this further, let’s say you require 50 mesh rolls.
Buying 50 rolls would reduce costs to about $6.75 per square foot, whereas a 100-roll order would reduce costs to about $6.50.
Purchasing wire mesh will typically start with you requesting a quote from a reliable wire mesh supplier. To help make this process as quick and effective as possible, you should be prepared to tell the supplier about your operation as well as the following regarding your wire mesh needs:
Once it is determined that the wire mesh supplier can accommodate your needs, you will receive a quote reflecting the costs associated with the order. At this point, you will need to either accept the quote or submit any revisions.
After the quote is approved and returned, you must send in a purchase order. The supplier will confirm that the purchase order has been received, start production, and provide lead times as well as tracking information.
To gain a comprehensive understanding of what you can expect when inquiring about wire mesh for molded pulp applications, refer to the linked article:
To ensure you invest in the wire mesh specifications needed to excel, W.S. Tyler offers samples of all our molded pulp wire mesh. Samples can be obtained in 12” x 12” pieces.
While samples come at no cost to you, there is a limit of two samples per specification. To request a sample, simply reach out to our team of experts with your particular needs.
Contact W.S. Tyler at 800-321-6188 or via our contact us page for more information.