Net Shape Thermoplastic PEEK Seals

August 24, 2016  |  , , , , , , ,

Proprietary Tool Design Software Contributes To Precise Sealing Surface

  • Market: Oil & Gas
  • Project Requirement: Produce an “out-of-mold” net shape fiber reinforced PEEK seal holding dimensional tolerances of .0003 inches.

Overview

Mating parts providing a fluid or gas seal are critical components in most mechanical systems. We commonly think of them in valves and connector assemblies, but they are also found in pressure vessels, compressors, pumps, motors, engines, transmissions, and almost all mechanical power trains. Seals, especially those that mate to moving parts, have a demanding set of quality requirements. Each application has its own specific needs, but all seals are characterized by tight dimensional tolerances and excellent surface finish.

 

compressor valve plate with thermoplastic seals

Dresser-Rand is among the largest global suppliers of custom-engineered rotating equipment solutions for long-life, critical applications in the oil, gas, chemical, petrochemical, process, power, military, and other industries worldwide.  Their industry leading Magnum™ valves are used in all brands of reciprocating compressors, where they are known for operating at high compressor speeds and pressure differentials. The product contains 30 to 100 valve elements manufactured from a fiber reinforced PEEK thermoplastic, providing the high strength and low inertia necessary for reliability at high operating speeds.

 

Challenge

Dresser-Rand engineers wanted to improve the usable life and leakage profile of their Magnum valve without absorbing any increase in component cost.  The sealing surface specifications were tightened to 0.0005 inches (12.7 µ) which was key to accomplishing the performance improvements.

thermoplastic sealing valve

Dresser-Rand’s then current supplier of this component was unable to meet the more stringent sealing surface dimensional tolerances “out of the mold” necessitating a finish machining operation to bring the part into tolerance.  However, machining the sealing surface removed the resin-rich surface of the part creating micro-cracks in the surface and exposing reinforcing fibers. Both of these unavoidable consequences of machining negatively impacted component performance, useful life and cost. While it’s never easy to get “something for nothing”, Dresser-Rand knew the right people to talk to, the injection molding thermoplastic experts at Performance Plastics, LLC (PPL).

Solution

Performance Plastics knew eliminating the machining operation would improve strength, reduce trapped impurities, and lower manufacturing cost.  Thus, PPL’s engineering team focused on producing a “true net shape” part directly out of the mold.   Key to accomplishing the customers goals involved leveraging the Company’s proprietary, iterative tool design process.  It required making a 3D CT scan of preliminary molded parts measuring, in this case, approximately 1 million critical part dimensions.  This analysis identified minute distortions.  Utilizing internally developed proprietary software, PPL integrated the CT scan data with CAD/CAM software to make exacting mold modifications eliminating the out of tolerance conditions.  This process contributed to producing a best in class “out-of-mold” conforming part.

The manufacturing process also had to be optimized to produce the desired performance results.  Although the material posed molding challenges, PPL decided to direct gate the part at the top to ensure symmetry of material flow throughout the cavity, critical in achieving roundness to the sealing surface.

Results

The results of development program surprised everyone. PPL achieved “out of mold” net shape parts with a seal surface capable of meeting sealing ranges of 100 psi to 3,000 psi, with no porosity and consistently meeting dimensional tolerances of 0.0003 inches, or 7.62 µ. Eliminating the need for subsequent finish machining dropped the leakage rate for the valve by 50%, from 1.0 scfm to 0.5 scfm. At the same time, Dresser-Rand reported a doubling of estimated lifetime from 10M to 20M cycles between valve element replacement. Lastly, PPL’s direct gating approach improved material efficiency, by eliminating the sprue and runner system, resulting in a lower price per part.  Dresser-Rand’s customers benefitted from improved performance, increased service life and lower maintenance costs.

For more information about our net shape molding process please contact us.

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Metal To Plastic Conversion

May 24, 2016  |  , , , , , ,

PPL Races To Solution With Thermoplastic Gear

  • Market: Automotive
  • Project Requirement:  Develop a longer lived, more efficeint drop in replacement for a metal component
  • Project Requirement:  Develop a material with a low coefficient of friction not needing lubricating fluids

Overview

Metals have been the first choice of design engineers for almost three centuries. Developments in highly engineered thermoplastics materials are challenging that dominance. The aerospace and automotive industries have led the charge in this dramatic changeover, initially driven by the need to reduce weight to gain fuel efficiency. Advanced thermoplastic and thermoset systems, including fiber reinforced compositions, are now finding their way into almost every industry.

Some of the benefits arising from metal to plastic conversion are:

  • Reduced part weight and inertia;
  • Net shape (or near net shape) manufacturing, improving material efficiency;
  • Simplified manufacturing processes, with higher repeatability and less scrap;
  • Higher tensile strength with proper part design;
  • Increased part lifetime in corrosive and/or abrasive environments;
  • Greater conformability, providing improved sealing characteristics;
  • Increased lubricity;
  • Greater design flexibility.

Challenge

Race car engineers are always looking for a performance edge with their drive trains. Keeping power output up at maximum level is critical racing success. So when engine mechanics noticed their bronze distributor gear showed noticeable wear by race end, they knew vehicle performance was significantly degraded. The key question was whether or not material substitution could provide them with a longer lasting, higher performing gear.

Fortunately, the designers turned to Performance Plastics, LLC (PPL) for help. Working with Victrex plc, a supplier of high performance thermoplastic polymers, PPL developed an injection molded replacement for the conventional bronze alloy gear. As with most metal to plastic conversions, the first and most critical step is material selection. In this application, the part had to maintain structural rigidity at 120°C (250°F) operating temperatures while being subjected to oil and gasoline vapors.

Solution

PPL teamed with Victrex® technical development engineers to create a custom resin able to survive the high under hood operating temperatures and the abrasion from material to material contact.  Our collective efforts resulted in a unique carbon fiber filled PEEK compound embedded with additives obviating the need for additional lubricants.  PPL injection molds gear blanks to near net shape which are then finished by machining the gear teeth to the desired involute shape.  The injected molded PEEK gear is capable of maintaining a high level of its physical properties while operating close to its melt temperature of 343°C (645°F), well in excess of the requirement.

Results

The new gears were tested in a number of cars before being used in actual races. The gears were examined for surface cracks, chemical attack, distortion and abrasion. Initial testing showed no detectable wear in over twenty-four hours of racing. Additionally, the new gears provided an 81% reduction in part mass and inertia, helping to deliver faster throttle response and more horsepower to the drive wheels. After multiple years on the racing circuit, a single gear is now being used for an entire season, as opposed to being replaced after every race.

For more information about metal to plastic conversion please contact us.

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Biocompatible Fluoropolymers

April 3, 2016  |  , , , , , ,

Injection Molding Biocompatible Fluoropolymers For Medical Device Industry

Biocompatible Fluoropolymers And Advances In Injection Molding These Materials For Medical Devices, Drug Delivery Systems And Storage Components

Abstract

Injection molded fluoropolymers provide the chemical resistance and material performance needed for the manufacturing, storage and delivery of next generation cancer and biologic drug technologies. Fluoropolymers barrier properties, thermal properties and low surface adhesion characteristics offer advantages for powder and viscous liquid manufacturing, storage and delivery components.

In the past, fluoropolymer were not often considered for high volume parts with complex geometries due to injection molding process limitations. Developments in mold design and tooling steels combined with new manufacturing equipment and processing techniques now allow the use of these biocompatible materials for high volume drug storage and delivery components.

Introduction

Polyethylenes, polypropylenes and polycarbonates currently used for drug storage containers and delivery components will struggle to meet future efficacy requirements. Next generation drug technologies are bringing new handling and dispensing challenges because of increased chemical resistance and cytotoxicity issues. Long-term storage  solutions that  maintain performance and extend shelf life will be required. Improvements in dosage control and minimizing or eliminating the use of silicone coating operations in drug delivery components have also become industry wide concerns. Because of the elimination of traditional injection molding process limitations, product design engineers can now cost- effectively use fluoropolymers inherent material property benefits to address these issues.

Fluoropolymer Material Benefits

Fluoropolymers are chemically inert and pure generally containing no additives that could contaminate liquids or solids during storage or delivery. Fluoropolymers barrier properties resistance to chemical, enzyme and microbiological attack also eliminate biodegradation issues.

Barrier Properties of Thermoplastics

 

Figure 1. Barrier Properties of Thermoplastics

Compared to current plastics, the barrier properties of fluoropolymers (Figure 1) are exceptional. Aging, even at high temperatures and in the presence of solvents, oils, oxidizing agents, ultraviolet light and other environmental agents, is minimal because fluoropolymers do not use any leachable or degradable stabilizing additives. Fluoropolymers  also  have  a  low  refractive  index  and visual  appearance  that  is  unchanged  after  exposure  to light. Applications include drug containers and delivery systems components including bottles, vials, syringes and specimen trays.

Low Surface Energy Material Comparison

 

Figure 2. Low Surface Energy Material Comparison

Fluoropolymers have one of the lowest coefficients of friction of any solid material (Figure 2). Low surface energy in its solid state provides an anti-stick, non-wetting contact surface that is hydrophobic and completely resistant to hydrolysis. For sprays and inhalers, fluoropolymer manifolds can minimize drug delivery buildup to assure consistent dosing. Other applications include medical devices, surgical equipment, syringes, plungers, valves and connectors.

Fluoropolymer Processing

Concerns about fluoropolymer material application and processing limitations are prevalent.  It is still generally thought that sintering or machining are the only viable alternatives because of corrosion and thermal issues during the traditional injection molding process.  Temperatures of molds and equipment can range from 300°F to 800°F.

Highly toxic gases produced have an extremely corrosive effect on both molds and machines. Mold deterioration, runner system scrap rates, melt fracture, delamination and dimensional limitations of traditional gating methods. New fluoropolymers, processing equipment and manufacturing methods have been developed to address both by-product and material waste issues.

Continue reading by clicking, Performance Plastics white paper on fluoropolymers for the medical device industry or contact us to learn more.

 

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Proprietary Fluoropolymer Injection Molding Process

February 12, 2016  |  , , , ,

Cost Effective Fluoropolymer Molding

  • Market: Medical/Life Science
  • Project Requirement:  Manufacture a cost effective, conforming fluoropolymer part

Fluoropolymers (PFA, PEF. ETFE, PTFE, PVDF) are ideal for many medical applications due to their desirable attributes including biocompatibility, lubricity, sterilization, chemical inertness, stability over a wide temperature use range, barrier properties and high-purity with low extractables and leachables. However, fluoropolymers are relatively expensive and are difficult to injection mold (shear sensitivity, high melt temperature, and fluorine outgassing when melted).

Overview

Our customer, a manufacturer of diagnostic lab equipment, developed a new system automating a critical, but time consuming, manual diagnostic process. This system greatly reduced processing time, but utilized PFA, an expensive material, in its small (features as small as 0.20 mm), thin-walled (down to 0.30 mm), highly complex consumable parts. In fact, prior to contacting Performance Plastics (PPL), the customer had worked with other high end molders, who while even ignoring cost, were unable to manufacture the part.

Challenge

As mentioned above, fluoropolymers by their nature are difficult to mold. Further complicating the challenge was the highly complex, thin walled design of the part. The customer was looking for a way to cost effectively manufacture a compliant part.

Solution

The customer, on advice from its material supplier, contacted PPL to develop a cost effective injection molding solution. PPL leveraged its extensive fluoropolymer expertise in designing a solution to this challenging component. Our solution began with a hot runner system and mold designed to greatly reduced shear forces inherent in the injection molding process. Mitigating shear is key to preserving the mechanical properties inherent in the resin. Further, PPL utilizes proprietary metallurgy highly resistant to corrosion from fluorine gas. This significantly extends the useful life of the hot runner system, tooling and all other wetted component coming in contact with the melted resin. Lastly, PPL engineers incorporated a direct gated multi-cavity tool design eliminating the sprue and runner associated with traditional injection molding processes. Employing a direct gated tool design removes the material waste associated with the sprue and runner, particularly important when utilizing expensive resins such as fluoropolymers.

Results

PPL was able to produce a compliant part within 60 days while meeting their cost target. This allowed the customer to successfully introduce its new automated diagnostic system. The multi-cavity mold has reduced the production cycle and lowered the amount of required raw and finished goods inventory. Additionally, the advanced metallurgy developed has been leveraged to produce longer life/lower maintenance molds for other chemically reactive or abrasive resin systems.

For more information about our proprietary molding process please contact us.

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