How to choose your plastic rivets: a guide

Plastic rivets are used in most things – from computers to panel fasteners in rockets. In most cases – not all – the rivet you use should have the same mechanical properties as the materials the rivets are intended to join. This means, for example, that plastic snap rivet fasteners can be used to join soft materials, such as other plastics, urethane and rubber.

We’ve put together this guide to help you better understand plastic rivets and their uses, their applications, the different types  of plastic rivets available and how to determine the correct size that you need. First, let’s start with types of rivets.

Push rivets

Perhaps no other rivet type gives you so many different styles. What they all have in common is the ease of use – as the name says, you simply push them into a panel hole, usually by hand. We said usually, not always. Push in blind rivets, so called because they can be installed when you can’t access the rear panel side – or “blind” side – require a pop rivet installation tool. Other types include removable push rivets, which allow you to quickly and easily access inside the panels if needed.

Example:

Ratchet Rivets

Typically available in natural colours or in black, the ratchet rivet comprises two identical parts. The two parts are pushed together, typically on a corrugated panel, during assembly to form a secure and tamper-proof fastening. Ratchet rivets usually have an appealing aesthetic, which gives design engineers another reason to use them.

Example:

Snap Rivets

These have male and female parts used for connecting flat panels together in a secure fashion. Plastic snap rivets are perfect for rigid or compressive materials where a finished head is needed on both sides. Snap on rivets are actually plastic push rivets and can vary in style. For example, barbed rivets snap in. These nylon snap rivets have teeth that grip together for quick fastening.

Example:

Three or Four Prong, Non Pre-Driven Rivets

These are non-removable rivets that come in a range of styles and sizes. Accommodating different materials and panel thicknesses, these plastic push rivets feature tapered prongs which snap into the fastening hole and expand to hold securely as the pin is driven into place. This type of rivet is often used to provide load distribution and panel spacing, and can usually be used on non-plastic materials.

Example:

Fir Tree Rivets

With a maximum panel thickness of 10mm, this type of plastic rivet is to secure two panels together, or to hold components to panels. Easy to install, this rivet contracts on entry, before relaxing to secure the two panels. Be aware that this rivet also goes by these names: pine tree button, Christmas tree fastener, or facing fixings.

Example:

Countersunk Rivets

The countersunk rivet is used to join work pieces together, where the head of the assembly driver will be flush with the top of the materials. The result is a tamper-proof panel with a clean, smooth finish. Once assembled, they can’t be removed.

Example:

Plastic materials

You need to know something about the characteristics different plastics give you, which will help you narrow your choice. It’s important to note that plastics can take on desired characteristics with the help of additives or stabilisers. For instance, nylon is especially vulnerable to UV rays, but stabilisers can give you a nylon that gives you high performance in outdoor applications, such as in components for an outdoor cable enclosure.

Here are the most popular plastics for rivets:

Low Density Polyethylene (LDPE)

As the name says, this plastic has low density. The reason is that its molecules are not tightly packed together, and it’s not as crystalline as say, high density polyethylene (HDPE). In fact, LDPE will float on water. Flexible, yet tough, LDPE can withstand the cold, specifically temperatures down to -58˚F (50˚C) before it becomes brittle.

Rivets with LDPE material:

• Load-spreading rivets
• Male/female ratchet rivets

Polypropylene (PP)

The packaging industry are the biggest users of polypropylene, but you’ll find this thermoplastic across every industry, from automotive to equipment manufacturing. It has good chemical resistance, which is another reason why it’s popular as packaging for household liquids and detergents. Polypropylene also resists electricity, making it valuable for the electronics industry.

Rivets with polypropylene material:

• Male/female ratchet rivets
• Fir tree rivets

Nylon

Nylon’s low-friction properties makes it ideal as a material for gears, bushings and bearings. It has poor resistance against dilute acid, but excellent resistance to oil and greases. There are different types of nylons, with nylon 6/6 perhaps the most widely used in manufacturing. Nylon snap rivet fasteners are especially popular. Nylons resist most chemicals, but can be attacked by strong acids, alcohols and alkalis.

Rivets with nylon material:

• Snap together rivets, male/female mini
• Unscrewing rivets
• Nylon rivets push in, knob head

Polysulfone (PSU)

Polysulfone is used in specialty applications due to its high thermal and mechanical capacity. It’s sometimes used as a replacement for polycarbonates. Polysulfone has good chemical resistance, which makes it popular as a material in medical technology, pharmaceuticals and food engineering and processing. It’s also used in the electronics industry.

Rivets with polysulfone material:

• Snap rivets

How to compare rivet materials

Properties	LDPE	Polypropylene	Nylon 6/6	Acetal	Polysulfone
Tensile strength – psi	1,400	3,800 – 5,400	12,400	9,800 – 10,000	10,200
Impact (notched), toughness – Min. – max. value, (J/m²)	no break	12.5 – 1.2	1.2	1.0 – 1.5	1.3
Dielectric strength (kv/mm)	16 – 28	20 – 28	20 – 30	13.8 – 20	15 – 10
Density (g/cm³)	0.917 – 0.940	0.900 – 0.910	1.130 – 1.150	1.410 – 1.420	1.240 – 1.250
Max. continuous service temp.	212˚F/ 100˚C	266˚F/ 130˚C	284˚F/ 140˚C	221˚F/ 105˚C	356˚F/ 180˚C
Thermal insulation, Min. – Max. value (W/m.K)	0.320 – 0.350	0.150 – 0.210	0.250 – 0.250	0.310 – 0.370	0.120 – 0.260

Find out more about how plastic fasteners compare to metal as fasteners, and how each has their place, but more and more, plastic is becoming the material of choice.

Determining the correct rivet size

A general rule of thumb, and perhaps the simplest approach, is to measure the thickness of the plates you need to rivet. The diameter of your rivets should be one quarter of that thickness, which is also called grip range.

Your formula will look like this: Diameter= ¼ x thickness of plates to be riveted

Note: The diameter of your rivets does not include the head but rather, the rivet’s shank.

 

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Questions?

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