Refining Strategies for Recycled Fiber
Refining recycled fiber comes with its own set of challenges. One must look at the contaminants inherent in the furnish and the intricacies of developing already refined fiber. If not, over-refined fiber, short plate life and slower paper machine speeds can result.
By choosing the correct refiner plate design, refining can maximize fiber strength development, make the fiber more flexible by hydrating the fiber, and minimize the freeness drop. The trick is to refine the fiber to develop strength while limiting the amount of power applied and not cause a reduction of fiber length and unwanted freeness drop.
What happens when you refine the “already refined” fiber again? The answer comes from understanding how the recycled fiber was treated in the past. What was the specific energy applied, refining intensity, and how much potential the fiber has for developing additional strength.
Various contaminants are found in recycled fiber that complicate the ability to refine recycled fiber at low intensity. Possible contaminants are tramp metal, stones, plastic, baling wire and sand, each is a potential cause of reduced plate life. Excessive bar breakage can be caused by tramp metal and stone, plastic and baling wire can lend itself to plugging, and sand/grit can cause accelerated bar wear.
In order to combat these issues, it is necessary to look at the refiner plate design. Selecting the right pattern is essential to addressing stock contaminants. Choosing the correct alloy can determine the best balance between the risk of bar breakage and wear resistance. For example, J&L’s Reverse Flare™ patterns minimize plate plugging by eliminating the potential to wedge a contaminant into a groove that narrows toward the outer diameter of the plate. J&L’s Powercast™ designs allow the use of lower intensity plates for improved quality and offers improved hydraulic capacity and longer life through zero-degree draft angle technology.
In addition to the challenges of contaminants, already refined fiber characteristics are often less than desirable. The recycled fiber’s strength is reduced due to previous fiber length reduction and fibrillation. The usual range of applied energy (HPD/T) is less than for the same fiber in a virgin state. It is necessary to minimize the refining SEL intensity (W-sec/m) in order to utilize the energy applied and not generate further fines, fiber cutting, or freeness reduction.
J&L’s Six-Step System Analysis combines the understanding of recycled fiber with the needs of the paper machine to find the best plate design that will meet all the specific guidelines for your recycled fiber. Specific energy must be minimized while still developing the full potential of the fiber. Intensity also must be minimized as low as possible to achieve proper fiber characteristics. Contaminants will dictate the pattern design used to minimize intensity. Consistency should be considered, and specific freeness drop should be calculated and compared to objectives for recycled fiber.
When setting the plate parameters, information gathered using the analysis process is essential. The result will be a plate design optimized for recycled fiber that has low intensity, doesn’t plug, and has a long life. The optimum pattern will have the proper groove width, low Km/rev (Intensity), ReverseFlare design, PowerCast technology and one of J&L’s low carbon stainless steel alloys. The ReverseFlare design and PowerCast technology are great solutions for addressing stock contaminants. J&L’s C90, C91 or C96/C97 alloys provide good wear resistance and are virtually unbreakable… a great defense against contaminants.
Click the following link to view J&L’s Six Step System Analysis process, Refining tips