Rods/Pipes

Description

A rod is classically defined as a thin, straight cylindrical bar of material, usually wood or metal. In the 20th century, plastics became the the material of choice for most rods as they were readily available and light weight. New plastic materials offer strength and stiffness comparable to steel, and innovative processing capabilities allow us to machine plastic parts with tight tolerances. Combined with other benefits, many industries – particular medical and aerospace – are replacing their metal parts with plastic.

For art conservation, small and flexible tubes are mainly used as padding and interleaf over monofilament thread or metal rod mounts. Examples of tubing include heat-shrinkable tubing (made of Teflon, Polyethylene or Polypropylene) on metal wire, or silicone and polyethylene (surgical) tubing over monofilament lines to provide padding at points of contact. Polyethylene foam tubes and foam cylinders, sold typically as insulation to cover metal pipes, can also be used as padding and support in a variety of museum applications. Large and rigid tubes or rods are used primarily for display and for storing rolled flat textiles and similar objects. Tubing made of flexible PVC (Tygon), Vulcanized rubber or any rubber containing sulfur compounds should not be used.

A plastic rod is a solid plastic shape generally made by the process of plastic extrusion. Most plastic rods fall into the category of thermoplastic that can be reheated and harden when they cool. Thermoplastics have a wide range of properties and can be recycled. In contrast thermosets, can not be reshaped when heated and are not recyclable. However, the structural integrity of thermosets and their resistance to chemicals often make them preferable over metals because they have a higher strength to weight ratio. Thermosets are often used in composites. Due to the wide variety of plastics currently used in the production of plastic rods, the table below has been created to show some of their variations.

Materials	Tensile strength (psi)	Density (g/cm3)	Fabrication	Comments
Thermoplastic
Acrylonitrile-Butadiene-Styrene (ABS)	4,100	1.04	Easy to machine, can be welded (ultrasonic and thermal); easy to paint or glue	Low cost engineering plastic with good impact resistance and strength. Used for tubes and rods
Acetal (Delrin, polyoxymethylene)	10,000	1.42	Can be drilled, cut, sawed, sanded, maintains close tolerances	High-strength, semi-crystalline with low absorption in moisture; resistant to solvents
Acrylic (Plexiglas)	10,000	1.19	Cast rods have better optical clarity and machinability than extruded rods, but also more costly	Strong, stiff, with glass-like properties (clarity, transparency, and brilliance), but it is half the weight and has much more impact resistance than glass
Nylon	12,400	1.14	Easy to fabricate, lightweight	Stiff and strong engineering plastic containing outstanding wear and abrasion resistance; should be ne used for extened outdoor service
Polyamide imide (PAI)	21,000	1.41	Easy to fabricate and weld using thermoplastic welding equipment	Good wear and radiation resistance, inherently low flammability and smoke emission, and high thermal stability. The highest strength of any unreinforced thermoplastic,
Polycarbonate	9,500	1.20	Can be drilled, cut, sawed, sanded, maintains close tolerances; easy to join with adhesives	Semi-transparent, stiff, and strong with outstanding impact resistance and low moisture absorption.
Polyethylene (HDPE)	4,000	0.96	Easy to fabricate and weld using thermoplastic welding equipment	High-density polyethylene is a chemically resistant, strong, durable, lightweight plastic material
Polyetheretherketone (PEEK)	14,000	1.32	Readily machined maintaining close tolerances	Very high mechanical strength and dimensional stability (similar to Delrin, PTFE and Nylon)
Polyphenylene sulfide (PPS)	12,500	1.35	Easy to fabricate and weld using thermoplastic welding equipment	Good heat resistance, dimensional stability, rigidity, chemical resistance, flame retardance, and moist-heat resistance. It is also resistant to acids, alkalis, mildew, bleaches, aging, sunlight, and abrasion
Polypropylene	5,400	0.91	Easy to fabricate and weld using thermoplastic welding equipment	Chemically resistant plastic rod with excellent aesthetic properties at a cost that is low. The polypropylene plastic rod is easy to weld using thermoplastic welding equipment,
Polytetrafluoroethylene (PTFE, Teflon)	1,500-3,000	2.15	Easy to fabricate and weld using thermoplastic welding equipment; adhesion is difficult	Soft, low friction fluoropolymer rod that has outstanding resistance to weathering and chemicals
Polyurethane			Easy to fabricate and weld using thermoplastic welding equipment	can be bonded to metals fabrics and other plastics
Polyvinyl chloride (PVC, Vinyl, Tygon)		1.42	Easy to fabricate and weld using thermoplastic welding equipment	Strong and stiff; low-cost plastic material that is easy to fabricate and easy to bond using solvents and adhesives. The polyvinyl chloride plastic rod is also easy to weld using thermoplastic welding
Ultem (Polyetherimide, PEI)	15,200	1.27	Can be drilled, cut, sawed, sanded, maintains close tolerances	Properties similar to PEEK, but with a lower impact strength and usable temperature as well as a lower cost; excellent flame resistance
Thermoset
Fiberglass reinforced plastic (FRP)	30,000	1.07-1.20	Can be drilled, cut, sawed, sanded, maintains close tolerances	Thermoset; rigid polyester matrix reinforced with glass fibers; good insulator with low thermal conductivity; not electrically conductive
Filled phenolic	11,500	1.35	Machines readily with excellent dimensional stability	Can visually look appear like wood or metal; may emit formaldehyde
Reinforced Epoxy (FR-4 Glass Epoxy)	38,000	1.8
Other
Aluminum 6061-T6	45,000	2.70	Good machinability	Can cause galvanic corrosion; easily deforms under impact
Copper	28,000	8.93	Good machinability	May oxidize and/or corrode
Brass	45,000	8.5-8.8	Good machinability	May oxidize and/or corrode
Stainless Steel 304	90,000	7.7-8.0	May require welding or cutting torches	May oxidize and/or corrode; requires painting or galvanizing; can permanently deform under impact
Glass	1,000	2.4-2.8	May splinter or shatter	Transparent, stable in most environments
Wood	12,000	0.48	Easily fabricated, joined and adhered	Can warp, rot and decay, susceptible to attack by insects; low thermal conductivity; may emit acidic vapors when drying

Synonyms and Related Terms

dowel; stick; pole; wand; staff,

Resources and Citations

• Jean Tétreault, 'Products Used in Preventive Conservation', Canadian Conservation Institute, Technical Bulletin 32
• Industrial Quick Search: Plastic Rods
• EPlastics: Plastic Properties
• Curbell Plastics: Plastic Properties
• Bedford Reinforced Materials: FRP vs other materials
• The Free Dictionary: Definition