When considering which fastener is best for a particular task, you should evaluate your options using basic criteria such as strength, longevity, and ease of installation. Ideally, you want to choose a “no maintenance” fastener so you can set it and forget it, which is why blind bolts have become so popular. However, in order to get optimal performance from any blind bolt, you must install it correctly.Blind bolts are attractive for heavy-duty jobs, such as constructing buildings or manufacturing railway cars, because they are stronger than other fasteners and easier to install. Unlike nuts and bolts that require access to both sides of the joint and can loosen over time, blind bolts can be installed from one side for a strong and permanent joint. They also can be installed by anyone with very little training.
If you install a blind bolt incorrectly, it won’t deliver the lasting performance you need. For example, you have to ensure the bolt properly fits the pre-drilled hole to ensure a solid joint. If you fail to apply sufficient pressure upon installation, the bolt will not get a solid seal on the blind side. There are only a few things that could go wrong with blind bolt installation, but a poorly installed bolt could fail over time.
Blind Bolt Installation
You should follow the same basic steps when installing any blind bolt, no matter what type of bolt or the application.
Start by matching the size of the hole to the length of the joint, including the thickness of the materials to be joined. The strength of the blind bolt is determined by the length of the fastener—or, more specifically the grip length—to ensure a solid joint that will not loosen with time or vibration. The use range chart from the manufacturer will help you determine the hole size needed for the appropriate fastener. Most vendors also have grip gauges that you can insert into a pre-drilled hole to determine the best bolt size.
You should check the manufacturer’s performance chart to make sure that the bolt you choose has the right tensile strength and shear strength for the job. Tensile strength is the amount of force needed to pull the blind bolt out of its hole. Shear strength is the amount of lateral force along the plane of the bonded material to cause the bolt to fail or break.
Additionally, you should have the appropriate tools for proper installation. You want to use tools that have sufficient pull-through power to properly install the bolt. You also want to ensure that the bolt is swaged properly. Once the installation is complete, the blind bolt tool should be able to cleanly shear the bolt pin flush with the bolt collar for a smooth finish.
Blind bolt tools are typically hydraulic or pneumatic, powered by fluid or air that is delivered under pressure through a hose to the installation gun. These types of tools are appropriate for a factory setting or a location where dragging hoses around won’t create a problem. There also are battery-operated, handheld installation tools that are easier to use on job sites. You should ensure that a battery-operated tool is specified to deliver sufficient pull strength to properly seal the blind bolt.
Installing the Avdel Avbolt
The Avdel Avbolt is one of the most popular types of blind bolt and is used in heavy-duty, structural applications such as construction, automotive manufacturing, and the creation of mining equipment.
To install an Avdel Avbolt, you start by inserting the fastener into the pre-drilled hole and inserting the stem of the blind bolt into the installation tool.
The first step is to pull the pintail of the bolt to form a bulb on the blind side of the joint. Once the bulb is formed, apply the clamp-up force to the joint to pull the workpieces together. The collar material is then swaged into the pin lock grooves. This traps the load from the clamp-up and forms a lasting, tamper-proof joint.
When the pressure applied by the installation tools reaches a specified load, the pin will break at the pin-breaker groove and the join will be complete.
Avdel offers various hydraulic and pneumatic pullers, and a new family of XT blind bolt installation tools, each with different performance specifications.
Installing the Huck BOM
Arconic has a similar installation procedure for its Huck BOM® (Blind, Oversize, Mechanically locked) fastener, with a few distinct variations.
Installation starts in the same way as with an Avbolt, by fitting the fastener installation into the hole and then placing the installation tool over the pintail. Pressing the trigger on the installation tool starts the pulling action on the pin, continuing to draw the pin out to form the best possible bond on the blind side. The Huck BOM has a unique collar design that delays the swaging action until the largest possible bulb is created on the blind side.
The tool continues to pull the pintail, drawing the materials together, at which point the swaging anvil is released and moves the length of the collar to securely lock the collar to the pin. Once the collar is swaged, the tool ejects the fastener and releases the puller, thus completing the installation.
As you can see, blind bolt installation isn’t complicated, but it does require a basic understanding of how blind bolts work. When you match the right-size bolts for the task and use the right tools, the end result will be a strong, lasting join that will outlast any other type of fastener.