Design Engineering Capabilities Blogs Archives - Page 4 of 4

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.

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.