Two very different materials for caps and plugs: nylon and PVC

Nylon and PVC are just two materials used to manufacture caps and plugs used for protection. Both share some similarities, and both can be very dissimilar. Before you can choose between nylon and PCV caps and plugs, however, you need to understand what makes each material unique. You’ll find that most times, caps and plugs in these materials have widely different applications.

Here’s a look at the characteristics of each:

A look at nylon

Nylon is a thermoplastic used in a variety of applications, and can easily be used as a material for injected molding and 3D printing.

The two most common nylons are nylon 6 and nylon 6/6, which account for nearly all of the nylons manufactured. The difference between the two is in their structures.

Both are easy to process, provide fantastic strength and are very tough. Nylon 6/6 – also known as nylon 66 – is more crystalline in nature than Nylon 6. This improves stiffness and flexural modulus.

Nylon 6 absorbs moisture, which makes these components increase in size if used in damp environments. As a result, the material is ill-suited for parts that operate in tight tolerances. Nylon 6/6 – also known as nylon 66 – has a more compact molecular structure, so it’s a little better at resisting moisture, but it’s still considered to have a high moisture absorption. In general, nylon is sensitive to moisture, losing up to 30% of its tensile strength and 50% of tensile modulus, according to California State University.

Nylon 6/6 is tougher than nylon 6, however, and as good as nylon 6’s abrasion resistance is, nylon 6/6 is even better. Nylon 6/6 is also better at resisting sunlight, which can cause nylon 6 to discolour.

Typical applications for nylon include:

• Fasteners
• Insulators
• Fiber cables
• Switch housings
• Ball bearing caps
• Electrical equipment
• Rocker covers
• Conveyor belts
• Bearings
• Rollers

Advantages of nylon

• Incredibly strong and can be used in place of low-strength metals. For instance, it’s used to reinforce rubber in tires
• Especially popular with the automotive industry, used to make gears, bushings and other components
• Additives can strengthen the characteristics that you want in nylon. For example, on its own, nylon has very low impact strength compared to say, poly-carbonate (PC). Adding other materials can significantly solve the problem. In injection molding, Nylon is sometimes filled with glass fibers – typically between 10% and 40% – to increase its tensile strength.

Disadvantages of nylon

• Needs UV stablization
• High shrinkage in molded section
• High moisture absorptivity, which degrades electrical and mechanical properties
• Vulnerable to oxidizing agents
• Lacks resistance to strong acids and bases
• High notch sensitvity

Another reason why the construction industry uses PVC in abundance is because the heat it releases when ignited is lower than the temperatures released by other plastics, such as polyethylene (PE) and polypropylene (PP). This lessens the chance that a fire will spread to other materials.

PVC’s versatility derives from the fact that it has to be combined with additives before it can be made into any product. This allows the manufacturer to essentially customize the material’s properties to their needs. It can be formulated to be flexible or highly rigid and anywhere in between, along with a host of other characteristics.

Typical applications for PVC include:

• Window frames
• Drainage pipes and water service pipe
• Cable and wire insulation
• Roofing membranes
• Automotive interiors
• Seat coverings
• Packaging
• Cling film

PVC advantages

• High density means it resists impact deformation as compared to most other plastics
• Durable, resisting weathering and corrosion, which makes it an excellent choice for outdoor applications. According to a measurement taken by the Japan PVC Pipe and Fittings Association showed no deterioration in 35-year-old underground pipes
• Excellent cost-performance advantages, with long life span and low maintenance
• Low thermal conductivity
• Good dialectic strength. Does not conduct electricity, making it an excellent material for electrical applications, e.g. insulation sheathing for cables, especially when combined with its fire-retardant properties

Disadvantages

• Limited thermal capability, though additives can stabilize PVC at higher temperatures
• Higher density than many plastics, which can be an advantage if that’s what you want. If it’s not, consider another material
• Emits toxic fumes when melted, which makes it less than ideal as a material for injection moulding
• Not a good material for CNC machining unless the cutter is made from stainless steel. PVC is corrosive and abrasive and can cause any other cutter to deteriorate over time

General Characteristics

	Nylon	PVC
Tensile Strength	90 - 185 N/mm²	2.60 N/mm²
Notched Impact Strength	5.0 - 13 Kj/m²	2.0 – 45.0 Kj/m²
Thermal Coefficient of expansion	90 - 20/70 x 10-6	80 x 10-6
Max Cont Use Temp	150˚C - 185 ˚C / 302˚F - 365 ˚F	60˚C / 140˚F
Density	1.13 - 1.35/1.41 g/cm3	1.38g/cm3

 

Resistance to chemicals:

	Nylon	PVC
Dilute Acid	Poor	Very good
Dilute Alkalis	Moderate	Very good
Oils and Greases	Excellent	Good (Variable)
Aliphatic Hydrocarbons	Excellent	Very good
Aromatic Hydrocarbons	Excellent	Poor
Hydrogenated Hydrocarbons	Excellent	Very good
Alcohols	Varies	Good (Variable)

If your application’s environment is outside, then you want PVC. PVC is also preferred if you’re dealing with irregular shapes or need to easily access the cavities due to wires and cables.

The rigidity of nylon makes it ideal for threaded fittings that require long lasting, or permanent, protection.

For masking, PVC’s properties give you more options for protecting your application, as seen here:

Application	Nylon 6/6	PVC
Powder Coating		✔
E coating		✔
Anodising		✔
Plating		✔
Wet Paint	✔	✔
Blasting

 

It’s worth noting that if you’re masking application is blasting, then consider ethylene propylene diene monomer (EPDM), thermoplastic rubber (TPR), or silicone. Those are the materials that can handle all six masking processes.

Nylon caps and plugs

Threaded sealing plugs’ nylon material absorbs paint to keep flakes at a minimum, while the hex head prevents trapping of liquid. A double sealing ring on the underside of the flange provides a positive seal. These are usually available to fit metric or UNF threads.

Like metric and UNF, BSP/Gas threaded sealing plugs’ solid design prevent the trapping of liquid. The underside of the flange also has a double sealing ring, which provides positive seal. Five complete threads reinforce a secure fit.

Threaded o-ring plugs are available in different materials for both UNF and metric threads. The nylon version is nylon 6/6. The compressing flange lip and o-ring, along with the 6/6 version of nylon, provide a watertight seal and outstanding protection against leakage.

Solid Locking Plugs close access holes, giving sheet metal panels a finished look. They’re usually used on automotive and other vehicles. The locking feature snaps to hold the plug in place for easy installation.

Vent Plugs are useful for functional and aesthetic reasons. They provide ventilation for fans, components that emit heat, and moving parts. They’re especially suitable for the electronics industry.

PVC caps and plugs

The flexibility of PVC makes it ideal for different applications. Flexible end caps, as the name says, are flexible, which gives you a tight fit for metric, BSP and UNF threads. This makes them perfect for protection during masking.

Pull tab caps are quick and easy to remove with a large pull tab. Available in different materials that provide good tensile strength and toughness, PVC’s flexibility makes it especially easy to use.

Round end caps work great as a decorative end cap. They stretch to fit larger dimensions without tearing, splitting or shredding, providing a snug fit.

The same can be said of tapered caps & plugs, which are soft and flexible, yet durable. You can cap multiple O.D.s or plug multiple I.D.s for protection during transit and storage.

Pump stator-rotor caps is an example of PVC’s durability. Used in the oil industry, the flexibility of these caps creates a snug fit on pipe stators and rotors on progressive cavity pumps.

Easy pull masking caps provide great protection for end tip profiles during the masking process. The internal seal prevents paint from seeping in, while the flange allows for easy removal.

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