How to Avoid Streamers and Fines in a Pneumatic Conveying System

Pneumatic conveying systems are commonly used to transport plastics, but they can also transport something else entirely unwanted: streamers and fines. These products of plastic degradation in the system can not only decrease the overall quality of the product, but increase the operational costs of the system over time as well. Thankfully, there are ways to avoid, or at the very least reduce, the formation of fines and streamers.

What Causes Streamers and Fines in Pneumatic Conveying Systems?

Streamers and fines are formed when plastic pellets slide along the inner surface of the pipes and pneumatic conveying elbows. Friction creates heat that melts the pellets and leaves behind a polymer film inside the line. The film eventually tears off in strips, causing angel hair (fine, small strips) and streamers (thick, long ribbons) to fill the line. Fines (or fine particles, also known as dust) are created when the pellets suddenly crash into other pellets or sharp bends within an elbow, causing tiny fragments to break off.

How to Prevent Streamers and Fines in Pneumatic Conveying

One way to prevent streamers and fines is through a custom pneumatic conveying system specifically designed for plastics. Such a system can control the velocity and temperature of the plastics, preventing them from reaching levels of heat and friction that cause streamers and angel hair. This can be accomplished by keeping the air inside the system cool, around 86° Fahrenheit, and by keeping the pipelines away from outside heat sources.

Another option is to use a roughened or shot-peened pipe in conjunction with dilute phase conveying. This can stop the plastic from running against the pipes and instead, the plastic will bounce off of the roughened surface. Short radius bends can also be used to prevent the plastic from sliding along its length and melting. However, keep in mind that while this will reduce streamers, it will increase the number of fines in the line.

Additionally, angel hair screens can be installed to prevent streamers from clogging the system. These screens capture any angel hair that forms and prevent it from accumulating and causing blockages.

How to Reduce Plastic Degradation in Pneumatic Conveying Systems

There are several ways to avoid streamers and fines in a pneumatic conveying system, including using a custom system specifically designed for plastics, keeping the air inside the system cool, using roughened or shot-peened pipes in conjunction with short radius bends, and installing angel hair screens.

It is important to keep in mind that each method may have its own unique trade-offs, making it important to consider your specific needs before implementing a solution.

At Progressive Products, our team of experts are happy to listen to your challenges and help you find a solution that is tailored to you and your system. Contact us today and let's get started.

What causes streamers and fines in pneumatic conveying systems?

Streamers and fines are caused by friction and impact as plastic pellets move through pipelines and elbows. Friction creates heat that melts the surface of pellets, leaving a polymer film inside the line. This film tears off in strips — fine strips are called angel hair, and thick, long ribbons are streamers. Fines (dust) are created when pellets crash into other pellets or sharp bends in an elbow, causing small fragments to break off.

How does conveying velocity affect the formation of streamers and fines?

Higher conveying velocities increase friction between pellets and pipe walls, generating more heat and accelerating the formation of streamers and angel hair. Faster-moving pellets also experience more forceful impacts at bends, producing more fines. Keeping velocity as low as possible — while still maintaining sufficient airflow to move the material — is one of the most effective ways to reduce streamer and fines formation.

What is the difference between streamers, angel hair, and fines?

Angel hair refers to fine, small strips of melted and re-solidified plastic that form along the inner walls of pipes. Streamers are thicker, longer ribbons of degraded plastic that have torn away from the pipe wall. Fines (or dust) are tiny solid fragments that break off pellets upon impact with other pellets or sharp bends. All three are forms of plastic degradation, but each is caused by a slightly different mechanism — friction for angel hair and streamers, impact for fines.

How can elbow design help reduce plastic degradation during conveying?

Short radius bends can reduce streamer formation by preventing pellets from sliding along the curved surface — instead they impact and bounce, limiting frictional heat buildup. However, this trades streamers for more fines. Specialty elbow designs with roughened or shot-peened inner surfaces cause pellets to bounce rather than slide, reducing friction-based degradation. Choosing the right elbow design for the specific material and velocity is critical.

What role does temperature play in streamer and fines formation?

Temperature is a central factor in streamer formation. When the heat generated by friction between pellets and pipe walls exceeds the pellet's melting point, a polymer film forms on the pipe interior. Keeping the conveying air temperature cool — around 86°F — and routing pipelines away from external heat sources helps prevent pellets from reaching the temperature threshold where melting and streamer formation occur.

Which materials are most susceptible to streamers and fines in pneumatic conveying?

Plastic pellets — including polyethylene, polypropylene, PVC, and similar thermoplastics — are the materials most susceptible to streamers and angel hair because their melting points can be reached by frictional heat during conveying. Softer or lower-melting-point plastics are at greater risk. Harder, less heat-sensitive materials are less likely to form streamers, though they may still generate fines through impact.

What system modifications can reduce product degradation without sacrificing throughput?

Effective modifications include: designing a custom pneumatic conveying system calibrated for plastics with controlled velocity and temperature; using roughened or shot-peened pipe to cause pellets to bounce rather than slide; installing angel hair screens to capture streamers before they accumulate and cause blockages; and optimizing air cooling to keep pipeline temperatures below the plastic's melting threshold. Each approach involves trade-offs, so the best solution depends on the specific plastic, system layout, and throughput requirements.