Should you go tanged or tang-free? This is an issue that manufacturers and others consider when looking at tanged helical inserts. There are applications and advantages for both tanged helical inserts and tang-free helical inserts, which become clearer once you understand the difference.
A helical insert is the ideal fastener solution if you are working with a stripped screw thread or soft materials that are likely to strip. A helical insert is a coil of wire that is inserted into a predrilled hole in order to accept screw threads to create a tight and lasting fastening. In the case of stripped bolt holes, the helical insert provides the thread necessary to accept a bolt or threaded fastener, and the pressure of the inserted bolt causes the insert to expand and bind against the hole, thus creating a stronger connection than the original drilled fastener. The same is true for softer materials, although when working with materials such as aluminum, wood, zinc, or plastics, the helical insert can accept a threaded fastener such as a bolt where the material itself would strip under stress.
Because the diameter of the helical insert is wider than the tapped drill hole, it compresses as it is inserted. When the fastening is complete, the locking torque of the bolt or other insert creates a secure, lasting connection. In fact, helical coils often are used for high-performance and high-stress applications, such as factory machinery, aerospace, automotive applications, railways, and other uses where vibration stresses fasteners. Helical insert coils also perform well in extreme temperatures.
Tang or No Tang?
To install helical inserts, you need to tap the hole to match the size of the helical coil, then screw in the coil using a tool for helical inserts. To screw the helical insert into the hole, you will need a means to secure the coil so it will rotate for proper installation. This is where you have to decide between tanged or tang-free coils.
A tanged helical insert extends the end of the coil wire across the radius of the coil. This provides a grip point for the helical insert tool so it can rotate the coil insert to snugly fit in the hole. Once the coil is inserted, the tang must be removed before you can screw in the fastener or bolt.
A tang-free helical insert is installed in much the same way, although instead of using a metal coil tang that has to be removed after installation, tang-free inserts have a drive notch in the helical coil that is used as a grip point for the helical insert tools.
Although both types of helical inserts are used across various industries, the tang-free insert eliminates a step—tang removal—which saves time and money. Kato estimates that eliminating tang removal can save from $0.15-$0.50 per hole in labor costs. It also eliminates the need for tang retrieval and the risk of loose metal getting into the machinery.
Free-Running and Screw-Locking Inserts
Free-running helical coils, for example, are extremely flexible inserts designed so that each coil in the helical insert can independently adjust to the fastener threads. This enables more surface contact between the coil and the parent materials, which creates a stronger and more reliable seal because the load is evenly distributed. One of the advantages of using a helical insert is it increases fastener strength and longevity. Free-running coil inserts reduce stress and fatigue while maximizing thread strength and increasing reliability. Free-running helical inserts are available in both tanged and tang-free designs.
Screw-locking helical inserts provide added strength. In a screw-locking insert, the coil includes one or more straight segments. When the bolt is inserted, these segments flex outward, placing added pressure on the bolt thread and the walls of the drill hole. These locking coils make for even stronger, longer-lasting connections.
Typically, these types of coils are made from stainless steel, which makes the coil thread corrosion-resistant and extends the life of the fastener assembly. Because they are designed for critical applications such as transportation and aerospace manufacturing, these inserts also can withstand extreme temperatures, from -320 degrees to +800 degrees Fahrenheit.
There are a wide variety of insert sizes and specifications, so you have numerous options when it come to choosing the right helical insert for the task. Be sure that you choose a distributor with industry expertise to advise you on the right tools for the job.