Plastic Connectors Benefit Critical ApplicationsRiley Phipps, Technical and Design Services Manager, Value Plastics, Inc., a Nordson Company
Industrial and laboratory OEM designers are constantly being challenged to come up with more versatile, user-friendly, lightweight, and cost-effective product solutions for their equipment and instrumentation. An important component in this design process is the selection of tubing connectors for the transfer and management of fluids and gases, particularly for mission-critical applications.
Although metal tubing connectors have been traditionally employed in industrial and laboratory markets, plastic connectors continue to supplant many that were previously metal, not only because of their increased options for design flexibility, improved ergonomics, reduced weight, and lower cost, but also for their ability to effectively meet stringent industry standards in diverse and harsh environments. Many features of plastic connectors, which have long been proven in critical medical equipment design, are now being integrated into a broad spectrum of industrial equipment and laboratory instrumentation.
But choosing the right plastic connector can be a challenge. Plastic connectors offer more options for material selection, user interface, and customized design than metal connectors. A basic understanding of the options available with plastic connectors will help the OEM to specify the most optimized features to achieve peak performance in the equipment or instrument being designed.
Application Driven
While plastic connectors effectively fill many roles, they may not be suitable for all laboratory and industrial uses. Brass, aluminum, die-cast zinc, and stainless steel connectors are designed for extreme durability and high-performance fluid handling, particularly when influenced by high pressures and high temperatures. Choosing the ideal connector first requires a careful assessment of the application. Following are the prime factors to be considered.
Temperature Range – the minimum and maximum temperature tolerances that the connectors will need to function within. Depending on connector material, temperature tolerances can range from -40 to 200°F and above; Pressure Range – determining the minimum, maximum, and working pressures that the connectors will be expected to tolerate; Flow Rate – assessing the required volume per minute, and the effect of fluid pulsation, and modulations from connect and disconnect forces; Media – the viscosity, sensitivity, and corrosiveness of the fluid or gas moving through the connection; Exposure – degree of impact from external or internal conditions, such as UV, wind, dust, vibration, radiation, gases, water submersion, chemicals or cleaning agents, and mechanical stress; Specialized Environments – for food and pharmaceutical grade manufacturing, including washdown, clean room and aseptic environments, and vacuums; User Interface – level of human contact expected with the system and connectors; Cycle Life – anticipated maintenance and changeability required to be performed on the system, and expected longevity of the system in operation.
The requirements of the application will then determine what materials would be best suited for the connectors.
Plastic Connector Materials
The material chosen for plastic connectors should be based on the mechanical requirements of the connector and the type of media that will be moving through the system.
Significant pros and cons need to be weighed in the selection of connector material. Mechanical properties such as toughness, ductility, impact strength, transparency, lubricity, temperature capability, ozone resistance, and UV compatibility need to be assessed when selecting the most functional material for the application.
The medium is critically important. The type of fluid or gas flowing through a connection can affect the strength, surface appearance, color, and performance of the connection. And conversely, the wrong material can adversely impact media.
Careful consideration needs to be given to chemical compatibility and the most appropriate plastic resin for the application.
Made from high-purity resin materials for use with aggressive chemicals found in most industrial and manufacturing plants, plastic connectors offer broad chemical compatibility. Many are manufactured from virgin resins, with accompanying certification of lot traceability.
A broad spectrum of plastic resins can be selected from which to produce connectors, each with different characteristics to match the needs of system designers. The following plastic resins are commonly used to produce connectors:
Polyethylene – chemically resistant, translucent or opaque thermoplastic with low temperature impact, which can withstand a variety of application environments; Polycarbonate – hard, transparent thermoplastic with moderate chemical resistance. It provides good impact resistance and superior dimensional stability; Polypropylene – soft thermoplastic that is highly resistant to chemical attack from solvents and chemicals in harsh environments; Polyamide (Nylon) – versatile thermoplastic with good wear and chemical resistance, low permeability to gases; it performs well at elevated temperatures; ABS – tough thermoplastic with good stiffness and impact resistance even at lower temperatures, as well as good dimensional stability and high temperature resistance; Acetal – strong, lightweight thermoplastic that provides high strength and rigidity over a wide range of temperatures; PTFE – fluoropolymer is resistant to most chemicals and solvents, with stability at high temperatures; PVDF – thermoplastic is mechanically strong, with good ductility over a broad temperature range, as well as having excellent chemical resistance.
After the most appropriate material for the production of the connector is determined, the type of connection that best suits the laboratory or industrial need can be assessed.
Connection Options
Connectors are designed to accommodate tubing of varying hardness (durometer), from soft and flexible like PVC, silicone, and C-flex®, to semi-rigid types like polypropylene, polyethylene, polyurethane, and ethylene vinyl acetate (EVA).
To facilitate these varying styles of tubing and their respective application needs, different connector types are used, including barbed connectors, check valves, luer connectors, quick connects, threaded luers, and tube-to-tube connectors. Of these, the most commonly used tubing connectors are tube-to-tube connectors, luers, and quick connects. These basic connector styles can cover a wide range of liquid and air applications in laboratory and industrial environments.
Tube-to-Tube Connectors – a popular choice for applications that do not require the disconnection of equipment or parts at any point during production or use. Tubing connectors are available in many different configurations, sizes, and material options to adapt different tube sizes or styles, reroute the flow direction without kinking, and act as a manifold.
Luer Connectors – delivery systems can employ conical or taper seal connectors, called luers, to link various system components. The male and female components of luer connectors join together to create secure, yet detachable, leakproof connections with no o-ring or gasket required.
Luer connectors come in a variety of configurations adapting to tube connections, threaded connections (UNF, NPT, metric) and other luer or quick-connect terminations. Some of those incorporate a tapered UNF thread, similar to a pipe thread, which can also seal on the thread due to interference on the pitch diameter, facilitating directional alignment with tees and elbows.
Quick Connects – quick connects/disconnects allow flexible tubing and/or equipment to be quickly and safely connected and disconnected. They may be preferred over general connectors for fluid control because they can incorporate built-in shutoff valves that prevent spillage and allow multiple disconnections and faster servicing.
A new and versatile plastic quick-connect solution available for laboratory and industrial applications is Series MQC from Value Plastics, a Nordson Company, which provides an intuitive push-to-connect design. With its large, ergonomic buttons providing an audible click on connection and grips for easy handling with gloves, combined with a wide selection of color-coding options, the MQC is unique for ease of handling and the prevention of misconnections.
Many of the latest quick-connect designs focus on the user interface, and are equipped with intuitively simplistic thumb latch and side latch mechanisms to make for easy handling in laboratory and industrial fluid management applications. Quick connects mitigate the prospect of accidental misconnections and create quicker and safer device connections.
Barbs
Plastic barb-style connectors provide designers with a capability to accommodate the widest possible range of tubing properties and application conditions, including a multitude of configurations such as tees, Ys, elbows, and manifolds. A number of barb designs – each with unique characteristics to tailor connection performance to specific needs – are available for handling assembly forces, tensile resistance, and blowoff resistance without the need for clamps.
Barbs derive their holding capability by expanding tubing above its nominal inside diameter (ID), creating some amount of interference for a secure seal and good mechanical retention. The tube expansion can vary dramatically, from lower profile, easier connections to much more aggressive interferences, depending on the pressure and tensile pull requirements.
Selection of the barb style is very important to the connector's tube holding capability. The cylindrical surface behind the barb should allow the tubing to relax against the connector. When choosing a barb style, ensure that the barb is designed with a sharp peak, allowing it to "bite" into the tubing for optimal retention.
Many plastic connectors and almost all metal connectors utilize a multi-barb, making for an inferior tube connection and seal. Multi-barbs cannot create a sharp bite on the tube, inhibiting retention, and do not allow the tube a chance to relax behind the barb, also resulting in poor tensile pull strength.
Multi-barbs are also relegated to a manufacturing process that leaves a parting line on the sealing surface, creating a potential leak path. This is an inherent design flaw, yet all multi-barb connector designs, including metal connectors, display this liability. In fact, many inferiorly crafted single-barb plastic connectors are also afflicted with a parting line, reducing the efficacy of the connector. An optimally designed and properly injection molded connector will incorporate a singular barb with no parting line, a sharp bite, and a clean sealing surface.
Design Optimization
Many factors can reduce the tubing's ability to perform under pressure including temperature, chemical degradation, mechanical stress, fluid pulsation, selection of connector type, and barb design.
The latest generation of plastic connector technology affords designers and manufacturers wide latitude of flexibility to design and set up applications that custom fit to their specific needs. Some connector manufacturers, including Value Plastics, provide comprehensive design centers to help instrumentation and equipment manufacturers achieve the highest level of performance from their connectors. With good consultation up front on the designer's application requirements and prospective off-the-shelf or custom solutions, the pitfalls can be avoided and optimal designs can be executed.
Benefits
Compared to metal, plastic connectors provide a considerable reduction in weight and much improved flexibility with regard to the equipment they serve. Uniquely equipped to do so, plastic quick connects allow rapid and easy servicing and maintenance of assembly line equipment, filling and packaging systems, which limits system downtime and speeds throughput. Color coding on plastic connectors also makes for quick tube identification and reconnection.
The cost difference between metal and plastic connectors is a major motivating factor pushing instrumentation, equipment, and system designers to further embrace plastic connectors in laboratory and industrial applications.
With project requirements and timelines becoming increasingly demanding, the need for precision fluid management solutions applicable to industrial processing and instrumentation design is critical to achieve a high efficiency ROI. Plastic connectors, particularly when custom designed for the application, are more frequently becoming the preferred solution in industrial and laboratory settings, due to their overall proven efficacy.
