How Convolute Tubes Enhance Performance in Harsh Environments

Convolute tubes play a critical role in protecting cabling, wiring, and other sensitive components from abrasion, mechanical stress, and harsh environmental conditions. These tubes are engineered with precision and reinforced using advanced composite materials such as aramid, carbon fiber, and fiberglass. This robust construction provides exceptional durability, flexibility, and strength, ensuring essential components remain safeguarded even in the most demanding operational environments.

Composite convolute tubes deliver reliable performance and enhanced protection and are designed to meet the rigorous requirements of industrial applications. Their ability to withstand extreme conditions makes them an optimal choice for industries seeking high-quality, long-lasting solutions.

Composite Convolute Tube Performance in Harsh Conditions 

Composite convolute tubes are wound spirally to provide flexibility and help the tubing better withstand twisting forces. These qualities, in turn, allow the tubing to resist hoop stress, which affects the walls of cylindrical structures like convolute tubes. The layers of overlapping fibers create patterns that help the tubing resist radial expansion and better handle torsional forces.

Benefits provided by composite convolute tubes include:

• Chemical resistant: Corrosive substances can quickly break down tubing, so being able to resist chemicals prevents damage to the delicate components the tube protects.
• Flexibility: The helical or spiral configuration of the wrapping makes convolute tubes particularly flexible, enabling them to move and bend without breaking or losing strength.
• Good strength: Convolute tubes made from composites are stronger than many other materials, making them useful for multiple applications.
• Lightweight: Composites generally weigh considerably less than materials with similar strength, making them suitable for aerospace and automotive applications where weight is a factor.
• Temperature resistant: Composites can be designed to resist extreme temperatures, some even better than metal, so convolute tubing made from composites
• UV resistant: Ultraviolet light can break down many types of polymers, though many composites can be engineered to be UV resistant, which offers a significant benefit for outdoor applications.

Composite convolute tubes are incredibly resilient, offering both flexibility and structural integrity. The overlapping and uninterrupted construction of composite convolute tubes allows greater flexibility in design. The angle at which fibers are oriented can also be easily adjusted to alter mechanical properties to suit the application better. Composite convolute tubes also allow for variation in wall thicknesses along their length and can easily accommodate differing diameters. Compared to filament wound tubing, convolute wound tubes allow for smaller threads and grooves.

How Convolute Tubes Are Made 

The process for winding convolute tubes involves a mandrel spinning continuously at a set speed while the material is wound in a spiral around it. This material is rich in resins and reinforced with fibers, while the prepreg sheet typically integrates a thermoset like polyester, phenolic, or epoxy into the composite structure. Multiple layers are wound until the preferred thickness for the tube wall is achieved. Once wound, the composite convolute tube is cured using pressure and heat to cure the resin.

Detached after the curing stage from the mandrel, the composite convolute tube is then ready to accept and protect tubular or cylindrical items. Convolute tubes made from cotton phenolic are often machined into bearings and bushings for industrial purposes, which include articulating tandem axel pivots on road graders and axel-pinion style bearings for frontend loaders. Specific composite convolute tube grades feature excellent dielectric and flexural strength characteristics. Other materials are used in the oil and gas industry to make artificial lift components.

Composite Convolute Tube Structure

The structure of a composite convolute tube starts with a woven prepreg, which fits into the composite similarly to sheets positioned under blankets in a bed. The filaments used can include cotton, glass, polyester, and other materials. The prepreg is wound in a pattern that overlaps previously wound material as it spirals around the mandrel. These fibers usually orient to the convolute tube’s axis to more readily resist hoop stress and provide better torsional strength.

Fibers in the convolute tubes are wound more loosely to enable greater flexibility, as with tubing made from paper phenolic. Design options can include reinforcement with carbon and glass fibers supplemented by fabrics and mats. The actual fabrication of a convolute tube is often referred to as a layup, with these layups performed to ensure the composite has specific properties. Curing under pressure and heat hardens these different layers into a single block of composite material.

Considerations for a convolute tube layup might involve: 

• Mats help the convolute tube resist fracture and measure stiffness, often referred to as flexural or transverse strength.
• Mechanical strength depends on how the fabric’s weave is angled.
• Veils over the resin can provide smoother surfaces and deeper coloration.
• The strength and stiffness of the tubing can be reinforced through cross-winding.
• Undirected fibers that provide strength along the axis.

Due to the plethora of options available for layering, hybrid composite tubing is often advisable. Hybrid composites are normally based around a fiberglass structure, with purposefully placed carbon fiber reinforcement. Convolute tubes made from hybrid composites offer improved mechanical characteristics and are more cost-efficient than those that only utilize carbon fibers.

Applications for Composite Convolute Tubes 

The structures and advanced composite materials integral to their design allow convolute tubes to tolerate difficult environmental conditions better. Due to their ability to withstand these forces, convolute tubes are used by an array of industries.

Common applications for composite convolute tubes:

• Aerospace: Composite convolute tubes offer much greater strength than conventional tubing, and they are often used for fuel and hydraulic lines, along with providing cables and wires with structural support.
• Automotive: Engineers use this type of tubing to organize and protect fuel lines, hydraulic hoses, and wire harnesses within vehicle systems.
• Defense: With their high strength-to-weight ratio, these tubes can better resist all types of corrosion and other difficult battlefield conditions.
• Industrial applications: Manufacturing settings often use composite convolute tubes to protect cabling and hoses in pneumatic, fluid transfer, and other systems exposed to abrasive conditions, chemicals, corrosion, and heat.  
• Marine: The corrosive saltwater omnipresent in ocean environments makes composite convolute tubing particularly useful for marine vessels and undersea cabling and pipeline systems where durability is key.  
• Medical devices: Biocompatible composites benefit medical equipment like catheters, flexible endoscopes, and other tubing systems in healthcare applications by providing greater durability and hygiene.
• Motorsports: Composite convolute tubes work well in high-performance engines and exhaust systems because they can withstand the higher vibrations, temperatures, and chemicals present in racecars and other sporting vehicles.

Convelute tubes’ resilience and flexibility help prevent component failure under demanding conditions in these and other applications.

Convolute Tubes from Spaulding Composites

Spaulding Composites Inc. has considerable expertise in designing and fabricating convolute tubes. Of the highest quality, Spaulding’s convolute wound tubing can be engineered to up to four feet (about 1.22 m) in length, with internal diameters down to a quarter inch (6.35 mm) for garolite (G10 and G11) and an eighth of an inch (3.175 mm) for fabric composites. Additionally, outer diameters as large as 18 inches (45.72 cm) can be designed. Let our team work with you from the design stage to delivery. For more information on our convolute tubes and other capabilities, contact the composite experts at Spaulding today.