Learn About Thread Repair

Why is the thread damaged?

There are many reasons, such as corrosion, wear, and excessive tightening torque.

How to repair the thread?

It seems that there are many methods, but by using threaded sleeves, this method may be the simplest and most economical to operate.

What is a screw sleeve?

As the name implies, the threaded sleeve is a threaded insert. After being installed correctly, it can provide a permanent internal thread with high strength and wear resistance for the connecting hole.

Why choose to use threaded sleeves?

The thread size is exactly the same as that of the original damaged thread by using the threaded sleeve, so that the previous bolt or screw can be used without consideration of enlargement or replacement of part specifications.

What are the types of threaded sleeves?

From the structure type, it can be roughly divided into two categories: spiral threaded sleeve and solid threaded sleeve.

What are the advantages and disadvantages of using threaded sockets for thread repair?

advantage:

Improve the strength of threaded connection by distributing the clamping force of the fastener to a larger area of the parent material;

When installed on a softer parent material, it can increase the pull-out resistance and wear resistance of the thread;

The embedded design of the screw sleeve makes it easy to replace in the case of thread peeling, wear, etc.

shortcoming:

The locking of some screw sleeves in the parent material requires damage to the parent material itself, which may weaken the strength of the parent material;

Need to control the installation accuracy, incorrect installation may cause the screw sleeve to break away from the parent material during use and cause the connection to fail.

Through the above questions, you must have an understanding of the application and precautions of screw sleeves. From the two shortcomings mentioned above, the spiral threaded sleeve seems to be a very ideal solution.

First of all, the installation of the spiral threaded sleeve will not cause any damage to the parent material itself, so there is no problem of weakening the strength of the parent material. Usually the cross section of this kind of threaded sleeve is not circular. The threaded sleeve wound by the spring will be compressed after being screwed into the mounting hole with a smaller diameter, and its outward tension can be guaranteed in addition to the fixed threaded sleeve. Maximum surface contact is obtained between the screw sleeve and the inner wall of the mounting hole, and the load is evenly transferred to the parent material.

Secondly, the installation of the spiral threaded threaded sleeve is also simpler, from hole making to tapping, and then to the screwing and fixing of the threaded sleeve are supported by special tools, which greatly improves the accuracy and stability of the installation. help.

There is a drill for making holes, and there are special screwing tools for screwing. These only need to be selected according to the diameter of the screw sleeve. Here I want to share some tools about tapping, that is, the choice of taps.

Taps are tools used to produce threads. They can be classified into cutting tools. The process of using taps to obtain internal threads in the mounting hole by cutting is called tapping. There are many different types of taps, which vary for different applications. The following three types are common:

Flat bottom tap

Flat-bottomed taps have almost no taper, and are especially suitable for tapping in blind holes to ensure that the minimum thread finish is obtained when tapping to the bottom of the blind hole.

Middle tap

The intermediate tap has a tapered cutting edge, which will help the tap to align into the untapped hole and is suitable for most applications.

Taper tap

The cutting edge of the tapered tap is also tapered, similar to the middle tap, but the taper is larger and more pronounced than the middle tap. Used for holes with higher precision and difficulty.

Sometimes in order to obtain better hole-making quality, multiple types of taps are used at the same time. When tapping on a softer parent material, such as aluminum alloy, you can usually use an intermediate tap to cut the thread; if it is a blind hole, when the tap is about to approach the bottom of the blind hole, switch to a flat-bottomed tap to continue cutting. When tapping in hard materials, taper taps with a larger taper can be used, which can effectively reduce the amount of torque required for cutting threads. If it is a blind hole, then replace the middle tap and flat bottom tap.

After the tapping is done, the screw sleeve can be installed. However, for aerospace manufacturing or maintenance applications that require precision threads, the quality of tapping is very critical. Therefore, it is recommended to check the accuracy of the thread through a gauge. If the accuracy of the tapping meets the requirements of the inspection, the threaded sleeve must be Meet the tolerance requirements of the thread. The principle of the inspection gauge is a pass-stop gauge, which detects the pitch circle diameter of the threaded hole. The pitch circle diameter on the side of the pass gauge is not too large, and the pitch circle diameter on the side of the stop gauge is not too small. Neither big nor small is correct.

Finally, I need to mention that it is not that the spiral threaded sleeve is better than other solid threaded sleeves, but from the perspective of thread repair, the spiral threaded threaded sleeve has its own advantages. If you consider from the perspective of structural strength, or you want to obtain higher thread connection strength on the softer parent material, all kinds of solid threaded sleeves with mechanical locking structure have more advantages.