I. Stripped Thread Failure
This is the most common quality problem, directly resulting in loss of fastening function, causing parts to loosen and produce abnormal noise.
Root Cause: Insufficient screw thread strength, or the breaking torque that the connected part can withstand is less than the torque applied by the tool. Commonly seen in three scenarios: plastic nut seats, plastic parts with direct holes, and sheet metal holes.
Symptoms: The screw cannot form an effective engagement after being screwed in; it slips under slight force, failing to achieve its fastening function.
II. Fracture/Bending Damage
Causes: Improper manufacturing process, insufficient strength of raw materials, rough surfaces, or substandard heat treatment processes, resulting in poor overall toughness and high brittleness of the screw.
Symptoms: The screw breaks directly from the shank during screwing, or shows significant bending deformation under force, completely losing its load-bearing capacity.
III. Surface Corrosion Failure
Causes: Inadequate plating thickness, or the selection of materials incompatible with the operating environment. In harsh environments such as acid rain and high humidity, the surface rapidly oxidizes and corrodes.
Symptoms: Rust spots appear on the screw surface, plating peels off, and the material degrades after long-term use, eventually leading to seizure and breakage.
IV. Machining Dimensional Defects
Symptoms: Uneven thread pitch, missing tips, inconsistent head groove depth, or overall outer diameter and length not meeting standard tolerance requirements.
Impact: Difficulty in smoothly driving the screw into the material during installation; the bit easily slips and scratches the groove; insufficient effective thread engagement; and a significant decrease in tightening force.
V. Thread Overheating Deformation
Cause: Insufficient hardness of the screw material itself; the heat generated during high-speed driving causes thread deformation.
Symptoms: Plastic deformation occurs in the thread during screwing, preventing the formation of a complete internal thread, ultimately leading to loosening and detachment.
