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When it comes to working with thermoplastics, ecosyn®-plast is the go-to thread-forming screw. Many lighting industry components are made of thermoplastic materials that must be assembled, which is where this type of screw comes in.

ecosyn®-plast is useful when dealing with thermoplastics due to its ability to be threaded directly into plastic, thereby removing additional components or inserts. This allows you to eliminate potential quality issues, such as deformation, which occur when threading into plastic with inappropriate threads.

Compared with tapping screws, which are used solely for metals, thread-forming screws like ecosyn®-plast have specifically designed threads for use in thermoplastic applications. These types of screws provide improved material flow and thread load-bearing depth, as well as lower drive torque, higher stripping torque, less risk of cracking, and self-locking capabilities. In contrast, the use of tapping screws in non-metals can increase the risk of cracking and lead to improper thread configuration, causing stress fractures in the plastic.

Another ecosyn®-plast advantage for use in thermoplastics is its optimized thread geometry for low-stress generation in joints. This type of screw is also a Bossard catalog part, meaning it is readily available and easy to acquire. It comes in various head styles and available materials to cover a wide assortment of projects.

When to switch from tapping screws to ecosyn®-plast

Certain projects may benefit from converting to ecosyn®-plast from tapping screws. Below is a list of conversion scenarios our customers have encountered in the past. In these situations, Bossard was able to immediately arrange samples, convert to appropriate thread-forming materials, and rectify the issue at hand:

1. Customer manufactured various lighting equipment, signaling devices, and switch gears.
2. Customer used imperial sized self-tapping screws for sheet metal to assemble plastic components.
3. Customer was experiencing base material distortion.

Inappropriate fastener selection, as highlighted in the above scenarios, can result in issues such as cracking, which can in turn lead to costly product recalls. Selecting a suitable thread-forming screw at the start of your project eliminates potential rework issues and reduces hassle by ensuring your product is assembled correctly the first time.

For more information, check out www.bossard.com or contact our engineering department at ProvenProductivity@bossard.com.

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Threaded inserts have many valuable uses, especially when it comes to the lighting industry. This type of fastener element creates precise, durable internal threads that are able to withstand higher axial and radial loads compared with self-tapping screws.

There are several factors that will influence the performance of threaded inserts. If you decide to use them and which type to use will depend on the installation method, the material you are using, and what kind of insert support you are looking for.

FASTEKS® makes steel or stainless steel threaded inserts guaranteed to create precise, durable internal threads in workpieces made of light metal alloy and other materials with low shear resistance. They are self-tapping, simple to install and come in six different types, depending on your needs and what kind of project you are working on.

Threaded Inserts Types and Uses

The list below highlights each type and what kind of projects each one is best used for:

1. The TRISERT®, made out of brass, has a regular head and is used for thermoplastic materials. It has a larger contact surface and can be used in drilled or molded holes. It also has a higher torque and axial forces.
2. The TRISERT-3®, made out of steel, has a reduced head and is used for light metal and plastics. It can be used in drilled or molded holes. It offers faster installation due to a greater helix angle of the thread flanks, and has corrosion resistance of up to 720 hours to red rust.
3. The FOAMSERT®, made out of brass, can be either double ended for bidirectional purposes, or have a reduced head. This insert was designed especially for expanded material and wood, and it can be used in drilled or molded holes.
4. The MULTISERT®, made of brass, is un-headed and particularly suitable for thermoplastic materials. It has a special plain location spigot and has three installation options: press-fitting, ultrasonic insertion or heat insertion.
5. The MICROBARB®, made out of brass, is particularly suitable for thermoplastics and thin section materials. It’s used especially for applications in electronics and can be installed via press-fitting, ultrasonic insertion or heat insertion.
6. The HiMOULD®, made of brass, has an open or closed ended design and is used for thermoplastic and thermoset plastics. It is very thin-walled, particularly suitable for applications with low wall thickness. This insert is designed for molded-in applications featuring precise locating pins that ensure proper shut off to prevent plastic flow into the threads compromising integrity.

For more information, check out www.bossard.com or contact our engineering department at ProvenProductivity@bossard.com.

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Rivet nuts were discussed in a previous blog, but what tools are required to install this type of fastener?

Hand Tools

Smaller rivet nuts can easily be set by hand using simple tools. The nuts are threaded onto a mandrel by hand, inserted into the hole and then using a mechanical lever action, the mandrel is pulled into the tool causing the nuts to collapse on the back side of the hole. The tool must then be manually rotated in reverse to disengage from the nut.

Spin/Spin Tools

These tools are typically pneumatic and have three stages. The first spin assembles the nut onto the threaded mandrel. The nut is then placed into the prepared hole, and the second stage spin collapses the nut on the backside of the hole creating a bulge. This bulge squeezes the material, and secures it into place. The third stage reverses the rotation and backs the mandrel out of the nut. These tools are the lowest cost power tools, but can be a bit fussy about hole size. Too large of a hole can allow the rivet nut to spin and not collapse. The pressure that the nut applies once the bulge is formed is controlled by the amount of torque that the gun creates, so consistency can be an issue if air pressure and/or friction in the threads varies.

Spin/Pull Tools

These tools also have two stages and are typically pneumatic over hydraulic. The first stage spins the nut onto the mandrel while the second stage does not rotate, but instead pulls the mandrel into the tool collapsing the rivet by force. This tool comes in two versions:

• Pull to pressure – the amount of setting force is set by hydraulic pressure, which can be adjusted on the tool. This style works best if the material thickness is not consistent.
• Pull to stroke – the amount of setting force is set by the distance of the stroke, which can also be adjusted on the tool. This type of tool works well for materials that are very consistent in thickness.

Some high-end tools incorporate both pull to pressure and pull to force.

For questions about rivet nuts and or tooling, check out www.bossard.com or contact Bossard directly at ProvenProductivity@Bossard.com.

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Doug Jones
Applications Engineer
djones@bossard.com

A rivet nut is a special type of nut that is installed into a prepared hole in a piece of sheet metal and secured prior to assembly of a bolt. A special installation tool is required to ‘set’ the nuts into the prepared hole. The nuts are placed into the hole and ‘upset’ on the backside (much like a blind rivet) which secures them, eliminating the need for a wrench.

Standard rivet nuts have been around for years, and work well as attachment points for low strength joints that do not see much stress. These standard nuts are not high strength and generally cannot support enough clamp load for structural joints.

Uses

Standard rivet nuts must be used with through holes in harder materials such as steel or aluminum and do not work as well in softer materials like wood or plastic. The bulge formed on the backside must have unrestricted space to form and will apply pressure to the plate which could overly stress plastic or wood.

Specialty type rivet nuts exist, such as the BCT®* which employ bulge control technology to allow them to work in blind holes and/or soft materials such as plastic. There is also a high strength version of BCT® which may be used in structural joints and can create high clamp loads for use with high strength bolts.

If you are currently using weld nuts, or have areas with limited access to one side, consider looking at rivet nuts. Contact us at ProvenProductivity@Bossard.com for more information. Look for a future blog discussing tools for the installation of rivet nuts.

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*BCT® is a registered trademark owned by BBA srl Italy

How many threads should protrude through a nut in an optimal joint?

The generally accepted answer is 1 to 3 threads. Most externally threaded fastener blanks are manufactured with a header point prior to thread rolling, which leaves the first 1 to 2 threads undersized for ease of assembly. To ensure full load carrying capability for a nut and bolt combination, this rule makes sure we have fully formed threads throughout the entire thickness of the nut.

One notable exception to this is for nuts with a locking feature at the top – or toplock nuts. This includes all nylon insert nuts. For these, it is best to have a minimum of 3 threads protruding through the nut to ensure that the locking feature is engaged on a fully formed external thread. Anything less could compromise the locking affect.

Is there a rule for the maximum number of threads protruding through a nut?

Too many threads is a waste of material, adds unnecessary weight and can be a hazard or cause interference with other components. However, functionally there is no downside to having too much thread protrusion.

When selecting fastener lengths, be conscious of the standard length increments. Metric fasteners are generally available in 5mm length increments up to 70mm and 10mm increments beyond this. Inch fasteners have similar standards. When choosing your fastener lengths, it is best to select the shortest fastener that will consistently give you 1-3 threads protruding through the nut.

For questions, please contact our Bossard engineering team at ProvenProductivity@Bossard.com.

Doug Jones
Applications Engineer
djones@bossard.com

Thread forming screws per DIN 7500 produce a chip-free, gage correct metric internal thread into ductile metals up to 160HV hardness. Thread forming screws may be reused up to 20 times, but care must be taken when re-starting screws to avoid cross threading. They are not intended for use in brittle metals such as gray cast iron; however, they can be used in non-ferrous metals and light metals, as well as steel.

Screw Hole Preparation

Hole preparation and hole size are key to trouble free assemblies with thread forming screws. In general, the material thickness should be 1xd minimum (for example, a 6mm plate for a M6 screw). Punching, drilling or laser cutting are common methods for creating through holes for thread forming screws. Different hole sizes may be required for each method based on the break-out of a punched hole, or the size of the heat affected zone of a laser cut hole, which makes the surface harder and more difficult to thread. Different material composition and thickness will also require different hole sizes.

Good design practice requires a countersunk hole as thread forming will slightly raise the surface of the mating part without the chamfer. This can cause mating parts to not sit flush against the tapped component creating a gap.

Assembly Torque

Recommended assembly torque is 80% of the breaking torque of the screw, and half way between the driving torque and the breaking torque. Drive torque and strip/break torque is recommended to select the optimum hole size for your application.

Check out www.bossard.com for more recommendations for thread forming screws, or contact us directly at ProvenProductivity@Bossard.com to perform a drive/strip torque test for your application.

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Doug Jones
Applications Engineer
djones@bossard.com

Are you thinking about using stainless steel fasteners in your next application but aren’t sure if it’s the right fit? Read on to see if it’s the right fit for your product.

Austenitic Stainless Steel

Austenitic stainless steel is by far the most common material used to manufacture stainless steel fasteners. It has a chromium content between 15 and 20 percent and a nickel content between 5 and 19 percent. It offers the highest corrosion resistance than martensitic stainless steel and ferritic stainless steel. It is also considered to be non-magnetic. The tensile strength may vary between 72,000 psi and 115,000 psi. Austenitic stainless steel is not heat treatable however the strength of this material may be improved by cold working or strain hardening.

18-8

The material that is commonly referred to as 18-8, is a type of austenitic stainless steel that contains approximately 18% chromium and 8% nickel. Austenitic stainless steel includes AISI grades 302, 303, 304, 304L, 316, 32, 347, & 348.

For more information about stainless steel fasteners and how you can use them in your applications, contact us at ProvenProductivity@Bossard.com.

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