What are Core Tubes & Why are They Used in Water Purification Applications?

Purifying water through a technique known as reverse osmosis involves using extraordinarily high pressure to force water or other fluids through a membrane. Made semipermeable, these membranes filter out contaminants, allowing potable water to flow through them. An outer tube containing the membrane is key to this process, and it must be strong enough to resist pressure while also being unaffected by water or other contaminants. These tubes are known as core tubes. For water treatment, core tubes are essential to reverse osmosis and important in other types of water purification techniques.

What Are Core Tubes? 

Core tubes are cylindric assemblies that can be made from cardboard, composite materials, metals or plastics, depending on their purpose. These components facilitate processing in a range of systems and provide support for various industrial applications that utilize core tubes. For water treatment applications, they specifically aid filtration and transport of water while also providing physical support to the system. Generally, materials used to make core tubes for water treatment are made from thermoplastics, stainless steel or composite materials that provide both chemical resistance and durability.

General Applications for Composite Core Tubes

Composite core tubes are used for a variety of purposes due to their chemical resistance, corrosion resistance, customizable nature, durability and strength-to-weight ratio. Composites often replace metals or plastics due to these material traits, though a key reason for their use involves the ability to increase thickness. As composites tend to be of lower density, their use in core tubes can boost stiffness without also dramatically increasing weight. Essentially, composites create a sandwich-like structure with a matrix made from fabric and resin, with the core tubes acting similarly to how I-beams support structures in construction.

Basic applications for core tubes include: 

• Aerospace: For both civilian and military aerospace applications, composite core tubes are used for airframes and missile casings due to their high strength-to-weight ratio and thermal stability; their chemical resistance and durability make them a good choice for aircraft fuel systems and ducting as well. 
• Energy: Along with other sectors, the oil and gas industry uses composite core tubes as corrosion-resistant piping for handling fluids; core tubes also support blades for wind turbines and components within generators, improving their mechanical efficiency.
• Industrial processing: Textile manufacturing equipment, printing presses, conveyor belts, and other rotating industrial machinery all use core tubes made from composites to boost performance due to their wear resistance and low inertia rating.
• Medical: Composite core tubes are used in magnetic fields like MRI equipment because of their non-magnetic characteristics; due to their lighter mass and higher strength-to-weight ratio, they also suitable for orthotics and prosthetics well.
• Motor vehicles: Core tubes made from composites are used for structural reinforcement, drive shafts and components within exhaust systems to augment fuel efficiency through weight reduction; vehicles that run on hydrogen fuel cells utilize core tubes for their corrosion resistance and to enhance structural integrity.
• Sports: Bicycles, fishing rods, golf club shafts, hockey sticks and other sporting equipment often use composite core tubes due to their lighter weight and superior strength.
• Water filtration: Composite core tubes for water treatment are used in membranes for ultrafiltration, reverse osmosis and nanofiltration water treatment methods for structural support, while also optimizing the flow of water through the system.

The majority of composite layups for core tubs involve infusion, prepregs or wet layups. However, certain composite materials aren’t suitable within certain cure parameters or specific kinds of layups. Conventional layups or prepregs are sometimes designed specifically for the composite materials used, while other types work exclusively with infusion techniques.

How Composite Core Tubes for Water Treatment Applications are Made

Composite core tubes for water treatment applications are usually made through filament winding or pultrusion. Filament winding uses automated machines that wrap continuous strands of fiber around a mandrel as it rotates. This method coats fibers with resin into specific patterns, curing the core tubes via heat and hardening the resin until it becomes rigid. With pultrusion, a heated die is used to shape the material into a tube after pulling fibers through a resin bath. For smaller tubes, compression molding is used, which involves compressing prepreg fiber sheets into a mold before curing them with pressure and heat.

Using Composite Core Tubes for Water Treatment Applications 

Epoxy-based core tubes have been used increasingly for purifying water because of their ability to handle high pressures, while also removing more toxins than other thermoset composites. The use of epoxy in core tubes for water treatment offers greater environmental advantage. It also makes the construction of core tubes more cost-effective and extends their lifespans. Epoxy glass core tubes contain reinforced fibers that resist corrosion and provide strength for structural applications, which keeps operational and maintenance costs low.

Both desalination and wastewater treatment can benefit from composite core tubes. For water treatment of brackish groundwater or saltwater from the sea, reverse osmosis techniques are generally preferred. These use semipermeable membranes that can withstand the intense pressures involved, so are used for desalinating brackish or salty water. Reverse osmosis is preferred for many reasons, as the method saves energy and offers greater flexibility, as it allows for smaller facilities.

Often, core tubes for water treatment are used to reinforce the spiral wound membrane modules that filter contaminants out. Collecting the purified water once it passes through the layered membrane and prior to exiting the module, these systems cause water to flow into the center along the perforations of the core tubes. For water treatment techniques in ultrafiltration, reverse osmosis and nanofiltration systems, core tubes must be strong enough to handle internal pressures as water forces its way through the membranes. Composite core tubes for water treatment are ideal for these applications.

In summation, key uses of composite core tubes for water treatment include:

• Aiding even distribution of water within activated carbon media or ion exchange resin beds to for water deionization or softening systems.  
• Ensuring purification media and water maintain maximum contact to optimize activated carbon or ion exchange treatment processes.
• Guiding flow to enable sufficient exposure to ultraviolet light (UV) to disinfect water in certain types of UV water purification systems.
• Maintaining membrane filtration in nanofiltration, reverse osmosis and ultrafiltration systems to:
• Act as support structures in membrane modules to ensure longer filter life and proper distribution of water flow.
• Facilitate efficient flow of water while operating under high pressures.
• Structurally reinforcing membrane modules to enable purified water to pass through while maintaining the membrane’s fundamental integrity.
• Supporting largescale industrial and municipal distribution systems and filter housings in facilities with varying water conditions and high flowrates for water and wastewater treatment.

Core tubes for water treatment applications optimize filtration efficiency, flow distribution, and structural integrity of these systems. Composite core tubes have become a necessary part of many water purification systems for residential, industrial, and commercial purposes.

Spaulding Core Tubes for Water Treatment Applications

Spaulding Composites Inc. makes glass epoxy core tubes for water treatment systems that will meet or surpass our customers’ mechanical requirements. We can provide filament wound core tubes, as well as injection molded interconnectors to decrease the need to go through multiple suppliers. To learn more about our capabilities, contact the composite engineering experts at Spaulding today.