Inserts for Plastics

What are Inserts for Plastics

Inserts for plastics are designed by engineers for fast and quick installation into plastics using different methods. They are fastener elements that are inserted into plastic parts and assemblies to add a threaded hole. Plastic inserts can also be used to provide a durable threaded hole in a soft material and also to repair a stripped threaded hole.

The Advantage

In most cases, plastics are not strong enough to support the use of fasteners like bolts or screws. For example, the use of screw often ends with stripped threads, falling apart of parts, and failed housing. To get rid of this limitation, inserts for plastic are designed by engineers. These inserts are installed into plastic to give bolts and screw stronger metal thread to mate with.

Inserts for plastics are used for many reasons，they mainly include below:

1. It helps to preserve threaded joints

The main benefit of using a plastic insert is that it preserves the threaded joint integrity throughout the life span of the material. Besides, it allows for an unlimited reusable thread.

2. The use of inserts for plastic allows for proper seating torque

In the process of assembling the mating component, the screw to be used must be tightened with sufficient torque. To prevent loosening, this helps to introduce the recommended axial tension to achieve the required load between the insert threads and the screw. Also, the body design and the bigger body diameter of the insert are very important. They allow for appropriate installation torque to be applied to the screw.

3. Inserts for plastics don’t react to stress relaxation

In plastic applications, the problem common to bolted joints is that plastic is prone to stress or creep. Plastic loses its ability to maintain a load when exposed to loads below the elastic limits. At this point, the threaded connection may loosen. Inserts for plastics made up of brass and aluminum provide permanent resistance for the load path of the thread.

4. Improve Load Carrying capacity

Inserts for plastics features larger diameters when compared to screws. Due to the larger diameter, the load-carrying capacity of the joints becomes enhanced. This function is attributed to the fact that inserts are generally twice the diameter of screws. This helps to increase the shear surface by about fourfold.

Applications

Inserts for plastic provides sturdy reusable threads for plastic parts and assemblies. Inserts help to maintain the integrity of tensioned joints and eliminate creep. While they are made of varieties of materials their applications are found in electronic, automotive, communication equipment as well as other consumer product application.

Variations of Insert for Plastics

There are different variations of inserts for plastics. They include the threaded inserts and the compression limiters.

√ Threaded Inserts

Threaded inserts exist as cylindrical plastic and metal shapes placed in existing holes to provide a threaded track. These threaded inserts provide a threaded track for screws, bolts, and other fasteners for use in plastic parts and assemblies. The standard materials for manufacturing plastic inserts include;

• Aluminum (High strength alloys of aluminum)
• Brass (Free cutting)

√ Compression Limiters

Compression limiters are said to be non-threaded inserts. They are mostly used in applications that involve the application of compressive loads to a plastic assembly. The main benefits of compression limiters are to strengthen the plastic while it withstands the compressive force. This occurs when the mating screw is tightening into the plastic assembly which does not compromise with the integrity of the plastic when the load is applied. The features of compression limiters include:

• Can be custom designed in a vast variety of profiles and sizes
• Are available in stainless steel, lead-free aluminum, and brass
• Can be installed using molded-in installation, ultrasonic, or heat-staking methods
• Most common design types include: symmetrical, flange-head, non-knurled symmetrical, and full diamond knurl

Types of Inserts for Plastics

At RapidDone, we can offer different types of inserts, they mainly include below four types.

√ Press-in Inserts

These types of inserts are manufactured to reduce the cost of installation while sacrificing torque and pull-out performance. These inserts feature the helical knurls which are used to provide both pull-out resistance and torque. Besides this, the knurls help to ensure good plastic flow as the plastic insert rotates into the hole.

The helical knurl of the inserts is designed so that the direction of the torque of installation will possess a tendency to drive the insert into the hole. As a result, the installation torque to obtain sufficient tension between the threads poses no problem. Lastly, this type of insert features a pilot which is smaller than the hole with sufficient length. This makes it possible for a straight insertion into the hole.

√ Self-Tapping Inserts

This type of insert for plastic offers the best pull-out resistance for a post-mold installed insert. It features a thread that is designed with a thin profile to reduce induced stress into the material (plastic). Besides this, it features a relatively coarse pitch that offers the maximum plastic shear surface to resist pull-out.

It offers no installation torque problem. This is because there is an increase in friction between the thread and plastic during the tightening process. This can be attributed to the fact that the larger the diameter of the external the larger the frictional surface. It is important to know that the back-out torque is dependent on the large surface area of the external insert thread and the tension between the plastic and the threads.

√ Heat Staking or Ultrasonic Inserts

This type of insert is designed for post-mold installation in a plastic material such as thermoplastics. They yield outstanding performance and are result-oriented. The heat staking or ultrasonic inserts exist in vast varieties of variations including the long and short types. The short variations are for less stringent requirements with the advantages of reduced cost and reduced time of installation. On the other hand, the long variations are for pull-out resistance and maximum torque.

√ Molded-In Inserts

This variation of inserts for plastic is designed to feature torque performance and maximum pull-out. They have mostly inserted choices for engineered plastics with a great percentage of fillers and thermosets. Positive positioning and perpendicularity of the inserts on the core pin are ensured by controlling the minor thread diameter. This is done mostly during the molding process.

Plastic Materials Suitable for Inserts

Plastic inserts have a vast variety of usage with suitability for materials in the industry today. There are about four main categories of plastics used in the industries where insert applications are needed. They include:

• Thermoplastics
• Thermosets
• Elastomers
• Foam

However, the last two on the list have limited suitability for the installation of inserts. In a situation where an insert is needed for assembly, an application analysis is suggested.

√ Thermoset Plastics

This category of plastic is heat resistant and tough. They can’t be reformed using pressure and heat. Once thermoset plastics are formed, they undergo an irreversible chemical change. Examples include urea, Bakelite, vulcanized rubber, and polyester resins.  Molded-in, self-tapping, or press-in inserts are suitable for thermoset while heat/ultrasonic inserts are not suitable.

√ Thermoplastics

This category of plastic is solid and rigid at normal room temperatures. At higher temperatures, they begin to soften and melt. Examples of thermoplastics include nylon, polycarbonate, ABS, and PVC. For insert suitability, the heat/ultrasonic inserts as well as other types fit in perfectly. This category of plastics can also be further delineated into polymers including

• Amorphous polymers
• Semi-crystalline polymers

1. Semi-crystalline Polymers

This delineated category of thermoplastic possesses a highly ordered molecular structure. They feature a defined narrow melting point so they don’t soften as temperature increases. The melting temperature here is generally above the upper range of the amorphous polymers. Common examples are the PEEK and PET.

• Polybutylene terephthalate (PBT)
• Polyethylene (PE)
• Polyetheretherketone (PEEK)
• Polyethylene terephthalate (PET)
• Polypropylene (PP)

2. Amorphous Polymers

Amorphous polymers feature random molecular structures with a melting point range. As a result, they soften gradually as the temperature increases. Besides, the presence of hydrocarbons makes them more susceptible to stress failure. Common amorphous thermoplastics include PVC and ABS.

• ABS
• Polycarbonate (PC)
• Polymethyl methacrylate (PMMA / Acrylic)
• Polystyrene (PS)
• Polysulfone (PS)
• PVC

Suggested Installation Methods for Inserts

1. Installation of Heat Insert

A very versatile method of installation is heat installation. The only variable here is pressure and temperature. During this method, proper care must be taken to prevent the heated inserts from melting the plastic. The goal is to soften for easy access as it keeps the insert in place when it re-solidifies.

To guide the insert during the installation process, a piloted tip should be used. Also, an extended tip must be used because it provides access to recessed holes. The plastic insert should be installed flush with the plastic surface and this is mostly accomplished with a positive stop.

To carry out this process, there are two methods used in applying heat to plastic inserts. They include:

• Use of a heated tip that transfers heat to the plastic insert. Here the plastic inserts are placed manually into the hole.
• Use of a pre-heat chamber that heats the plastic insert to the appropriate temperature. Then the insert installation is done with a non-heated quill.

2. Installation of Ultrasonic Insert

This method is a very complex but effective way of installing plastic inserts. Its effectiveness can be attributed to technical expertise that helps to assure consistent quality. The variables of this technique include pressure, amplitude, weld-time, and down speed. To minimize wear in this method, a carbide-faced horn or special hardened steel is required.

For installation, the insert is placed in the hole while the ultrasonic inserter’s horn presses the inserter down. The inserter’s horn transmits an ultrasonic vibration to the insert. A thin film of plastic melts to the metal-plastic interface due to the friction that arises from the insert’s vibration. The horn’s pressure forces the insert into the hole. After the horn has been removed, the melted plastic solidifies next to the insert as it is installed flush with the surface.

3. Installation of Press-in Insert

Press-in inserts are an economical alternative as they are easily installed. They do not require the use of special auxiliary equipment for installation. This is done by using an arbor or harmer to press the insert to the seat while the pilot of the insert is placed into the hole. In recessed areas, a piloted extended punch can be used. This method is the simplest of all installation methods.

4. Installation of Self-Tapping Insert

In this case, the insert is driven by its internal thread. Therefore, a different driving stud is needed for each size of insert. An extension driver is mostly used for applications close to walls or recessed areas. By hand, the thread of the insert is threaded onto the driver, while the manual press is lowered to line the insert up with the hole.

To prevent rotation during installation, the plastic component must be located against a stop. Another way to prevent rotation is to fixture the plastic component and to ensure consistent alignment of the hole. To reverse and raise the driver after the insert has been seated appropriately, the pressure is then released. In this case, the insert must be installed flush or slightly below the surface.

Conclusion

As an experienced manufacturing supplier, we can offer different types of inserts of high quality at a reasonable price. We also are able to give important tips to help you choose the best manufacturing options.  Therefore, regardless of your application, you can trust us to get your inserts for plastic that meet your requirements.