Super Absorbent Polymer, commonly referred to as SAP Powder, is a polymer product used in various applications due to its innate ability to absorb liquids. It can be used in diapers, soil remediation, or wires and cabling. To use SAP effectively, it is critical to control the particle size not only to achieve the highest performance but also to remove undesirable fines from the product.
A Brief History of The Tumbler Screener
The tumbler screening technology was developed in the 1950s, but since then, Allgaier has perfected the engineering and precision of this equipment, unlike any other tumbler screener company in the world. The Allgaier tumbler screener has been the preferred equipment for separating SAP polymer since its inception. Unlike traditional vibratory or ultrasonic screeners, the tumbler screener does not use vibrations to make separations but instead uses a 3D gyratory motion to separate particles. This more gentle approach resembles a “hand sifting motion” to screening that results in particles being finessed through hole openings rather than being shaken through them. For SAP polymer, this is critical to maintain particle integrity and effectively separate angular or misshapen particles. The intense energy produced by a vibratory sieving machine like the Hi-Sifter would not separate these particles efficiently.
The third dimension of the tumbling motion can allow these particles to stand up and pass through the mesh hole or lie flat and roll off the screen surface. The motion is similar to a lab sieve or Rotap but has an added “roll” that imitates more of a hand-sifting motion.
Why is Sieving SAP Important?
Sieving SAP is not merely a step in its manufacturing process; it is a vital measure to ensure the end products’ safety, efficiency, and performance. The necessity of sieving SAP is multifaceted here are the two main reasons:
- Size Consistency for Optimal Performance: The utility of SAP in diapers and other hygiene products mandates a precise particle size distribution. The ideal range spans from 1000 to 300 microns, with a critical lower limit of 100 microns to prevent the formation of lumps that could compromise product comfort, efficiency and clog up the manufacturing process .
- Dust Elimination for Safety: A significant hazard of SAP powder is the potential presence of ultrafine dust particles, primarily composed of clay used in the initial gel state to enhance flowability. As the polymer is milled, this clay, along with tiny SAP particles, can flake off. This dust not only poses a risk of reducing the product’s effectiveness by absorbing moisture prematurely, but also represents a severe health hazard if inhaled, potentially leading to fatal respiratory complications.
Operational Considerations of Sieving SAP Powder
As previously stated, implementing an air knife system for SAP sieving requires careful consideration of several factors:
- Humidity Control: Given that SAP’s absorbency is a defining feature, managing humidity levels during the sieving process is crucial to prevent premature swelling or clogging of the sieve meshes.
- Static Electricity Mitigation: The design of the air knife system must incorporate features to neutralize static electricity, ensuring that SAP particles flow freely without unwanted adherence.
- Efficiency and Yield Optimization: The system should be optimized to maximize the removal of undesirable fines while minimizing the loss of usable material, ensuring that the sieving process is both effective and economically viable.
Innovations in Sieving Technology: The Air Knife System
Addressing the challenges of SAP sieving required innovation. The air knife system, pioneered by Robert Grotto (Bradley Class of 1976) president of Elcan Industries an industry leading company in advanced sieving technologies, marked a significant advancement in the removal of fine dust particles from super absorbent powder. Traditional methods relied on mechanical screening with mesh sizes around 120 microns, which unfortunately led to substantial yield loss. The switch to a finer 90 micron mesh did not fully address the issue of fines without the risk of increased yield loss.
The air knife system introduced a novel approach to tackle the fines problem head-on. By employing a combination of air pressure and a small degree of humidity, the system effectively blows off the dust and breaks static bonds that cause particles to cling together. This method not only removes dust efficiently but also addresses the issue of “cling-on,” particles with adherent dust, often exacerbated by static electricity.
The mechanism involves a directional airflow that propels the SAP across the sieving surface in a controlled manner, ensuring that the material is evenly distributed and that dust is effectively separated. A vacuum system then removes the airborne dust particles, ensuring that they are safely collected and disposed of, preventing any risk of inhalation or environmental contamination.
Video Elcan Industries Allgaier Tumbler Screener
Screen Cleaning Devices Working Principle
The Allgaier Tumbler Screener can employ a wide range of screen cleaning devices that help prevent the screen mesh from blinding and increase efficiency while sieving SAP. These devices include balls, brushes, ultrasonics, and the unique Air-Jet cleaning device. Using an air jet to sieve or sift powders is an extremely efficient way to separate powders like SAP. It is similar to a Jet-Sieve that can be found in a lab setting, but in a production format. The Air-Jet-Sieve simultaneously blows out air while sucking powder through the screen to remove the fine particles. This method of sieving is ideal for light weight, or difficult to screen products like SAP.
Elcan Industries Experience with Sieving SAP Powder
Elcan dozens of machines for SAP separations across the world. Using a combination of technology and technique, methods have been developed to separate SAP at sizes ranging from 600,300,90 and 44um effectively. These separations can be made using a number of different approaches and Elcan has a full scale testing and toll processing facility where companies can sieve their powders. Check out our Case Study on processing SAP for an example of what can be achieved.
Call or email info@elcanindustries.com to find out more.
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