Pulp and Paper Industry Overview: Processes and Equipment

Intensive processing is required to turn wood fibers into graphic paper, cardboard, packaging, and a variety of other paper-based products.

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This blog examines the basics of the process and equipment required to get the job done.

The article below is part of our series examining some of the biggest challenges for pulp and paper equipment manufacturers (and how the right materials can help). For a deep dive on this topic, please see our guide here.

A Complex Industry Process Full of Challenges for Pulp and Paper Equipment Manufacturers

Pulp and paper processing is one of the most varied industries around, so the process below is necessarily generalized. It represents a prototypical modern paper-making process (we provide a look at the history of the industry in our blog here).

Paper products can be made from a variety of different wood pulps, fibrous plants, recycled materials, and more. Wood chips, the most common source today, can be made from logs but are also commonly sourced as a residual product of sawmills, furniture factories, and other timber-related industries. Any object that becomes embedded in a tree can ultimately become a contaminant within woods chips. Old fence posts, metal bolts, and even bullets have been known to emerge in pulp and paper processing facilities.

Industry equipment must be ready to process any of these inputs into quality pulp. To accommodate all this variation, the industry uses a variety of intensive processing techniques. All of them share the same goal: separating the cellulose fibers used to make paper. This processing can be accomplished using chemical pulping, mechanical pulping, or some mixture of both. Within these two broad categories, operating parameters can vary substantial from mill to mill—pulp and paper companies are always looking for opportunities to employ more aggressive processing techniques that enhance yield. More aggressive downstream processing can also drive savings by limiting the amount of filtering and cleaning required for raw inputs.

1. Mechanical Pulping: rather than using chemicals, a grinder is used to press against woodchips and physically separate cellulose fibers. This process tends to result in shorter fibers which exhibit less strength, a typical base for newsprint paper. After being finely ground, techniques like steaming can be used to further process the wood material.
2. Chemical Pulping: the most common process in the United States, wood chips are cooked in a “digestor” machine (see below) at an elevated temperature and pressure. This digestor also includes a special chemical mix designed to dissolve lignin, a substance which binds wood fibers to one another. This process preserves longer wood fibers, enabling stronger paper products ideal for applications like photo-paper and paperboard.

By the time wood fibers are separated, they have become a mix of fibers and water called pulp. Pulp forms the base ingredient for almost any paper product. Pulp is then thoroughly washed and decontaminated to ensure no processing chemicals remain in the paper. For white paper, the pulp is bleached to remove any color.

Finally, the wet pulp must be drained. This is typically accomplished by pumping the pulp onto rolling, wire-screen mats that allow water to drain as the fibers press down and become interwoven into sheets. Altering the thickness of the pulp, the length of the drying process, and other key parameters results in paper with different final qualities.

The final step is passing through a long series of rollers and heated drums which remove any remaining moisture. Dried paper can then be polished, smoothed, and wound onto rolls or cut into individual sheets.

Examples of Pulp and Paper Equipment

These are just a few examples of the solutions offered by pulp and paper equipment manufacturers.

1. Chippers: woodchippers are used to turn pulpwood into evenly sized chips, which will allow for cooking or grinding processes to work effectively and uniformly. Stationary chippers are employed at paper mill facilities, and mobile units are also used directly at timber yards.
2. Pulpers: “pulper” also describes a different type of equipment used for food products, but a paper pulping machine is very different. Mechanical pulping machines are essentially large (usually cylindrical) grinders where wood chips can be ground into pulp.
3. Digesters: Digesters are the key piece of chemical pulping equipment. They essentially look like large tanks—inside, chips are processed using caustic chemicals, rapid pressure changes, and heat.

4. Refiners: refining processes paper fibers through brushing, cutting, and hydrating, all of which can help determine different final paper qualities. This is accomplished using hydraulic refining machines that utilize high-speed rotating discs to treat pumped-in paper slurry.
5. Fourdrinier Machines: originally developed in England by the French Fourdrinier brothers, this basic design has become so commonplace (with some evolution) that these machines are now often simply called “paper machines.” They use a conveyor belt, traditionally made of wire mesh, to continuously drain water from paper as it moves down the line.

Learn About Key Challenges for Pulp and Paper Equipment Manufacturers

The process described above is full of challenges for pulp and paper industry OEM’s. Caustic chemicals are used to break down pulp, wood chips and paper dust can be highly abrasive to the wrong materials, and intensive water use drives a need for non-absorbent materials. Relatively high heats are commonplace. Any of these issues demands careful component engineering. When all of these challenges are present in the same paper mill, selecting the right materials can be like threading a needle.

That’s why, in our experience, pulp and paper industry applications are typically best served by carefully engineering materials and components to reflect specific operating challenges.

We take a deeper look at some of these challenges in our free downloadable in-depth guide:

When it comes to producing high-quality molded pulp packaging, the journey from slurry to finished product involves a series of precise, interconnected components. Among these components, the wire mesh you incorporate into your molds stands as the unsung hero.

It’s easy to assume that something as simple as wire mesh—specifically the mesh count you use—is relatively insignificant to the overall success of your operation. That is, until you uncover issues with things like fiber retention, drainage efficiency, and mold consistency.

Now, let’s say you are overseeing two production lines.

One is facing constant disruptions—plagued with inconsistent mold thickness, high energy consumption, and a slew of rejected batches. The other is running smoothly, producing molded pulp products you can proudly stand behind.

The key difference? The mesh count used in each set of molds.

Here at W.S. Tyler, our mission is simple: to leverage our 150 years of wire weaving experience to provide innovative solutions that empower the molded pulp industry and help make the world cleaner and safer.

With that in mind, we’ll take a detailed look into 24 mesh and 50 mesh—mesh counts that we believe offer the best bang for your buck when it comes to molded pulp applications. This article will cover:

• The importance of mesh count in the pulp molding process
• The qualities that make 24 mesh ideal for molded pulp applications
• The qualities that make 50 mesh ideal for molded pulp applications
• How to determine which mesh count is right for you

Why Mesh Count Is Important To Molded Pulp

When molding pulp into various molded pulp packaging, mesh count is a critical wire mesh specification as it impacts the opening size of the weave’s pores. This ultimately influences fiber retention, drainage capacity, and the quality of the end product.

A higher mesh count indicates more openings per linear inch, resulting in the retention of more valuable fibers. Naturally, this means a lower mesh count has fewer openings per linear inch, allowing for better drainage times.

To ensure your pulp molding process is running as efficiently as possible, you will want to find the perfect balance between fiber retention and drainage requirements. This will allow you to pinpoint a mesh count that promotes consistent molded pulp products.

That said, after extensive research and application testing, W.S. Tyler has discovered that our 24 mesh and specialized 50 mesh specifications work to streamline production and improve overall consistency.

Want more information on the role mesh count has during the pulp molding process? Look no further:

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• Molded Pulp Fiber Mesh Specifications: Mesh Count
  
  

What Makes the 24 Mesh a Good Fit for Molded Pulp?

The 24 mesh has grown in popularity among the pulp and fiber industry as it delivers the ultimate balance between open area percentage and durability. This means that molds outfitted with a 24 mesh screen afford efficient water drainage and peak fiber retention while minimizing the need for frequent replacement.

24 mesh delivers predictable results that you can count on, working to facilitate consistent mold thickness and reduced drying time. This is critical when it comes to managing operational costs.

Not to mention, its sturdy weave structure combats everyday wear from constant cycles of pressure and heat variations. This longevity is key to operations that must keep their pulping machines running.

Now, those opting for the 24 mesh are often focused on high-output production. Their operations often prioritize efficiency and reliability.

In short, 24 mesh is, more or less, implemented to keep production lines running smoothly while accommodating basic quality standards.

What Makes the 50 Mesh a Good Fit for Molded Pulp?

With more openings per linear inch, W.S. Tyler’s 50 mesh is a standout option for those seeking extra precision. Outfitted with scientifically altered oblong openings, this custom specification retains more fibers, only allowing the smallest particles to pass.

This is critical to advanced thermoforming and high-specification wet pulp systems, as it removes unwanted particles from your slurry. As a result, a denser, more refined mold is possible.

Despite its finer specification characteristics, this 50 mesh weave can handle the heat and pressure of the pulp molding process with ease. The resulting effect? A uniform, higher-quality surface that the end consumer will love.

In other words, 50 mesh is ideal for applications that call for aesthetically pleasing end products and must operate under stringent standards.

24 vs. 50 Mesh: How Do I Know Which Mesh Count Is Right for Me?

Choosing between the 24 and 50 mesh specifications starts with understanding your priorities. Do you want to achieve a premium finish? How much do you value cost over aesthetics? What’s your production volume and cycle speed? Are you dealing with a thick, coarse slurry or a finer mix?

These are all questions you should be asking yourself to gain a true understanding of whether your target goal(s) favor affordability and throughput or precision and aesthetics.

Now, looking at the specifics of your process parameters, there are several things you should be mindful of. This includes the material consistency, throughput rate, and moisture levels.

Taking a deeper dive, let's say your slurry has a relatively chunky consistency. The 24 mesh would combat clogs and allow efficient water flow, making it the better fit.

On the other hand, if your slurry contains very fine fibers, the 50 mesh will ensure eco-friendly fiber retention.

Your throughput requirements will ultimately determine the pore opening profile of your mesh. Naturally, this means the throughput you need will dictate whether 24 mesh or 50 mesh is the better fit.

If you require high-speed production, the percentage of open area provided by the 24 mesh weave will offer desirable drainage. Conversely, the 50 mesh specification will be a better fit for those looking for smoother, more elegant surface finishes.

As moisture level is critical to reducing energy costs associated with the drying process, it is key that your mesh delivers the right level of drainage capacity.

Wetter slurries will take more effort to drain to moldable levels. Thus, the 24 mesh is often recommended as the moisture level increases. But if the moisture levels in your slurry are lower and more controlled, the 50 mesh will most likely be your best bet.

Having said all this, it should be noted that the use of both 24 and 50 mesh in your system is often recommended. 24 mesh is typically used in conjunction with the 50 mesh.

In these instances, the 50 mesh serves as a filter layer, with the 24 mesh serving more as a support layer. Nevertheless, proper integration of these mesh counts will ensure sufficient pulp formation.

You Chose a Mesh Count That Performs - Now Ensure Your Wire Mesh Holds Its Form

Regardless of whether you integrate 24 mesh to achieve high throughput or W.S. Tyler’s custom 50 mesh to capture the refined look the end consumer will love, selecting the right mesh count is just the tip of the iceberg. Consistent, long-lasting performance requires looking beyond mesh size alone and ensuring the mesh is properly prepared to capture every detail of your molds.

This is where heat treatment—specifically the annealing process—shines. This value-added step alters the physical properties of the mesh in a way that improves its formability, ensuring a glove-like fit for your molds.

Combining our 150 years of woven wire mesh experience with a deep understanding of the pulp molding process, W.S. Tyler is committed to delivering tailor-made solutions that eliminate the roadblocks standing in the way of your operational success.

Read the following article to gain invaluable insight into the benefits annealed wire mesh can bring to your molded pulp operation:

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