##The Enduring Solution to Angel Hair: Over 45 Years of SPIRA/flo® Dominance in Pellet Conveying

Malvern, PA – In the world of plastics production and processing, the efficient and gentle conveying of polyethylene and polypropylene pellets is paramount. However, a persistent challenge plagues pneumatic conveying systems: the formation of "angel hair," "streamers," or "snakes." These undesirable byproducts, resulting from friction and heat, can lead to product contamination, system blockages, reduced throughput, and increased maintenance downtime, ultimately impacting quality and profitability. For decades, Delta Ducon, a leader in pneumatic conveying innovation, has offered a proven solution: the SPIRA/flo® pipe. This uniquely engineered pipe has demonstrated its superior performance in minimizing angel hair, a claim substantiated by rigorous testing and decades of real-world application by major industry players.

This white paper delves into foundational test data from 1977, conducted by a leading polyethylene pellet producer, which established SPIRA/flo® (then under Ducon Fluid Transport, now Delta Ducon, LLC ) as the premier choice for reducing angel hair formation.  The results of this comparative testing remain as relevant today as they were over four decades ago, underscoring a legacy of performance that continues to benefit processors worldwide.

The Challenge: Understanding and Combating Angel Hair

Angel hair formation is a common issue in pneumatic conveying systems that handle plastic pellets, particularly in smooth wall pipes. As pellets travel at high velocities, they interact with the pipe wall. This interaction involves several phenomena:

• Friction: Pellets rubbing against the pipe surface generate frictional heat.

• Static Electricity: The movement of dielectric plastic pellets can create significant static charges, causing pellets to be attracted to the pipe wall, further increasing friction and heat.

• Localized Melting: The combination of friction and static-induced heat can cause the surface of the pellets to melt slightly. These molten strands are then stretched and elongated by the airflow and pellet movement, solidifying into the characteristic "angel hair," streamers, or ribbon-like formations.

The consequences of excessive angel hair are significant:

• Product Contamination: Angel hair can contaminate the final product, leading to defects, rejects, and customer dissatisfaction.

• Reduced System Efficiency: Accumulations can narrow pipe diameters, clog filter receivers, and impede flow in elbows and diverter valves, leading to pressure drop increases and reduced conveying rates.

• Increased Maintenance & Downtime: Systems must often be shut down for cleaning to remove angel hair blockages, leading to lost production time and increased labor costs.

• Damage to Downstream Equipment: Angel hair can wrap around rotary valves, interfere with level sensors, and damage other sensitive downstream equipment.

Recognizing these pervasive issues, a major polyethylene producer undertook a comprehensive testing program in 1977 to identify a pipe interior that could effectively minimize these formations.

The 1977 Landmark Test: A Quest for Cleaner Conveying

In January 1977, a series of competitive tests were conducted at a major polyethylene producer's facility to evaluate various pneumatic conveying pipes with roughened interiors, aiming to recommend a particular pipe to reduce angel hair formation.  Among the pipes tested was DUCON's SPIRA/flo® pipe.  The original test report, transcribed verbatim, highlights the methodology and findings that solidified SPIRA/flo®'s reputation.

Test Methodology and Conditions:

The producer meticulously designed the test program to ensure competitive and comparable conditions for each pipe type, with the primary variable being the pipe itself.  Key parameters of the test included:

• Material Conveyed: TR635 polyethylene pellets were used for all tests.

• System Configuration:

  • The test unit operated as a push-pull system for continuous operation.

  • A total of 225 equivalent feet of 2-inch pipe was used.  This comprised 50-foot straight sections and four (4) 90° bends.

  • Two of the bends were heat-taped.

  • All piping was insulated with a 1-inch layer of fiberglass.  This was likely to maintain consistent temperature conditions and exacerbate angel hair formation for clearer differentiation.

• Test Duration: Each test run was five (5) hours in duration.

• Conveying Parameters:

  • 235 SCFM of conveying air was used.

  • This resulted in a pick-up velocity of 7,000 feet per minute and a discharge velocity of 8,260 feet per minute.

  • These high velocities were intentionally used to ensure the production of angel hair, especially during the cold weather experienced during the test period, allowing for a more distinct comparison of pipe performance.

• Pressure Readings (No Load): 0.4" Hg vacuum at the blower inlet and 1.25 PSIG at the blower discharge.

• Angel Hair Measurement: Due to the unavailability of equipment to quantitatively measure angel hair production by weight or volume at the time, the assessment was conducted through careful visual observation of the pipe walls and the discharge from an angel hair remover.

  
  

Comparative Test Results: SPIRA/flo® vs. Smooth Wall Pipe

The transcribed report details the performance of smooth aluminum pipe and DUCON's SPIRA/flo® pipe:

1. Smooth Aluminum Pipe Run:

   • Conveying Rate: 4,800 pounds per hour.

   • Operating Pressures: 3 PSIG blower discharge and 2" Hg vacuum blower suction.

   • Outcome: After the five-hour run, the piping was disassembled. Approximately 90% of the straight sections and 40% of the bends were found to be coated with a layer of angel hair.  This represented a significant level of formation, typical of smooth wall pipes under such conditions.

2. DUCON SPIRA/flo® Pipe Run (Full System):

   • The SPIRA/flo® pipe was installed using the same piping configuration and blower RPM as the smooth pipe run.

   • No-Load Pressures: Consistent with previous setups at 0.4" Hg vacuum (blower inlet) and 1.25 PSIG (blower discharge).

   • Conveying Rate: 4,000 pounds per hour.

   • Operating Pressures: 2" Hg vacuum at the blower suction and 3 PSIG at the blower discharge.

   • Outcome: A "dramatic reduction in formation of angel hair" was observed.  Approximately 25% of the SPIRA/flo® pipe interior was coated, not with tenacious layers, but with angel hair in the form of approximately 1/4" x 1/4" flakes.  Crucially, these flakes were described as "very light and loosely attached to the pipe," indicating they could be easily separated from the pellets in a cyclone or similar separation device.

   • Tester's Conclusion: "I feel this pipe would be satisfactory for plant operation."

     
     

3. Hybrid System Run (Smooth Aluminum Straights, DUCON SPIRA/flo® Bends):

   • To understand the contribution of different sections to angel hair formation, a run was made with smooth aluminum pipe for the straight sections and SPIRA/flo® for the bends. The pipe configuration and blower RPM were consistent with other runs.

   • Conveying Rate: 4,000 pounds per hour.

   • Outcome: After the run, approximately 50% of the smooth straight sections were covered with angel hair.  The SPIRA/flo® bends showed approximately 25% coating with the characteristic 1/4" x 1/4" flakes.

   • Tester's Insight: This configuration "affectively demonstrates angel hair is produced in the straights as well as the bends."

   • Tester's Conclusion: "I feel that this level of angel hair production would be unsatisfactory for plant use."  This highlights that while SPIRA/flo® bends helped, the smooth straights still generated significant unwanted material.

     
     

The SPIRA/flo® Advantage: Mechanism and Impact

The 1977 tests clearly demonstrated the superior performance of a full DUCON SPIRA/flo® pipe system.  The results indicated not only a significant reduction in the quantity of angel hair formed but also a critical difference in the nature of the formations – light, easily separable flakes instead of adherent layers.

While the original report doesn't delve into the fluid dynamics, the effectiveness of SPIRA/flo®'s unique, pressed groove design is understood to:

• Create a Boundary Air Layer: The spiral grooves gently disrupt the conveying stream, thought to create a cushioning boundary layer of air or slower-moving pellets along the pipe wall. This reduces the direct, high-velocity impact and friction of the core flow of pellets against the pipe surface.

• Minimize Frictional Heat: By reducing direct contact and friction, the localized heat generation responsible for melting pellet surfaces is minimized.

• Alter Pellet Trajectory: The spiral pattern may also influence pellet trajectory, promoting a more gentle, rolling, or spiraling motion rather than direct impingement, especially in bends.

  
  

The test comparing smooth straights with SPIRA/flo® bends powerfully illustrated that addressing only one part of the system is insufficient.  Angel hair generation is a system-wide problem, occurring in both straight sections and bends, necessitating a comprehensive solution like SPIRA/flo® throughout the conveying path for optimal results.

A Legacy Validated: Over 45 Years of Preferred Performance

The conclusions from this 1977 report were unequivocal: DUCON'S SPIRA/flo® pipe, used in both straights and bends, was deemed "satisfactory for plant use," with the explicit expectation that "the productions of angel hair would be significantly reduced and the angel hair that would be formed would be of such configuration that it could readily be separated from the pellet stream."

This foundational performance is not just a historical footnote. Delta Ducon proudly notes that this impressive performance has made SPIRA/flo® the preferred choice for that same major polyethylene pellet producer for over 45 years  – a remarkable testament to its enduring effectiveness and reliability.

Conclusion: Specify SPIRA/flo® for Cleaner, More Efficient Conveying

For plastic pellet producers and processors grappling with the costly consequences of angel hair formation, Delta Ducon's SPIRA/flo® pipe offers a time-tested and highly effective solution. The meticulous comparative tests conducted in 1977, and validated by over four decades of continuous industrial use, confirm SPIRA/flo®'s ability to:

• Dramatically reduce the formation of angel hair and fines compared to smooth wall pipes.

• Produce angel hair in a less problematic, flaky form that is easier to separate from the product stream.

• Improve overall plant operational efficiency by minimizing blockages, reducing cleaning downtime, and protecting product quality.

  
  

Delta Ducon's SPIRA/flo® pipe is more than just a component; it's an investment in smoother operations, higher product quality, and a cleaner conveying environment. As a Delta Ducon innovation, SPIRA/flo® continues to be a cornerstone of efficient bulk material handling systems worldwide.

If you are experiencing challenges with angel hair or other pneumatic conveying inefficiencies, we invite you to connect with the experts at Delta Ducon  to explore how SPIRA/flo® can optimize your operations.