In the process of mechanical processing and assembly, broken teeth of internal thread is a relatively common fault,
which can seriously affect the connection strength and service life of parts. Today, let's talk about the common causes
of broken teeth of internal thread and some repair techniques.
I. Analysis of the cause of broken teeth in internal thread sections
There are many reasons for the breakage of the inner hole threads. They can be mainly summarized
as the following aspects:
1. Material issue: If the material of the threaded holes is too hard or too brittle, it is prone to breakage when subjected
to force. For instance, the threaded holes of cast iron parts are more likely to break.
2. Processing technology issues: If the processing accuracy of the threaded holes is not high enough,
such as incomplete thread profiles or excessive surface roughness, it will also reduce the strength of the threads
and increase the risk of fracture. Additionally, if there is insufficient cooling and lubrication during tapping,
the threaded holes may overheat and eventually fracture.
3. Assembly Issues: During the assembly process, if the bolts are tightened too tightly or if the fit between the bolts
and the threaded holes is not precise enough, the threaded holes will be subjected to excessive force and may break.
Additionally, if the material or strength of the bolts is inappropriate, it can also cause the threaded holes to break.
4. Operating Environment: If the parts are exposed to extremely high temperatures, high pressure, or strong corrosive
conditions for a long time, it will accelerate the wear and corrosion of the threaded holes, thereby increasing
the risk of fracture.
II. Repair Techniques for Broken Teeth in Inner Grooves
1. Using the wire removal tool: For bolts that break inside the threaded holes, a professional wire removal tool
can be used to remove them. The usage method of the wire removal tool is quite simple. Insert it into the central hole
of the broken wire, and then rotate counterclockwise to remove the broken wire.
2. Electrical Discharge Machining: For bolts that are broken deep within the threaded hole and cannot be removed
using a broken wire removal tool, electrical discharge machining can be employed to remove them.
Electrical discharge machining is a highly precise and non-contact processing method that can effectively remove
the broken wires without damaging the threaded hole.
3. Inserted screw sleeve: If the damage to the threaded hole is severe and the original thread cannot be restored,
an inserted screw sleeve can be considered. The inserted screw sleeve is a commonly used method for thread repair,
which can effectively enhance the strength and wear resistance of the threaded hole.
4. Re-threading: If the damage to the threaded hole is not severe, you can try re-threading. Select a drill bit slightly
larger than the original one to re-thread, which can repair the damaged thread.
III. Measures for Preventing Breakage of Internal Hole Threads
1. Select the appropriate material: Choose materials with high strength and good toughness to make the threaded holes.
2. Enhance processing accuracy: Ensure that the processing accuracy of the threaded holes meets the requirements,
such as complete thread profiles and surface roughness reaching the standards.
3. Standardize assembly procedures: During the assembly process, it is necessary to control the tightening torque
of the bolts to avoid over-tightening. At the same time, ensure that the mating accuracy between the bolts
and the threaded holes meets the requirements.
4. Regular inspection and maintenance: Regularly check for wear and corrosion of the threaded holes,
and promptly carry out maintenance and upkeep.
IV. Handling Methods in Different Circumstances
1. Broken teeth protruding from the socket: They can be removed using pliers or a wire removal tool.
2. Broken teeth level with the holes: This can be achieved by using a drill bit or through electrical discharge machining.
3. Broken teeth are lower than the surface of the hole: It is recommended to use electrical discharge machining
or insert a threaded sleeve.
V. Selecting the Appropriate Repair Solution
1. Based on the condition of the broken tooth, the significance of the threaded hole, and the cost of restoration,
select the appropriate restoration plan.
2. During the repair process, be sure to follow safe operating procedures to avoid causing any further damage.
