The most common failure modes of thread rolling board mainly include: fatigue damage, abrasion, chipping, pile of teeth, spalling of teeth, etc.
The failure mode of the thread rolling board is mainly caused by cold working, hot working and improper use by users.
For cold processing:
(1) The thread is buckled in disorder, mainly because the helix is not straight, and the thread rolling board has axial displacement during manufacturing.
(2) The tooth profile is peeled off, and the thread is rolled and the thread is misaligned and the tooth profile clip and double cusps are caused. The main reason is that the rolling time is too long and repeated many times, or the tooth profile is unreasonable, such as teeth. Too sharp tip, tooth root or right angle and poor mechanical processing, or excessive grinding speed and feed rate, and poor lubrication and cooling, resulting in grinding and micro-cracks and other defects; The grains adsorb the fine iron powder, causing the tooth grains to grind each other, which will affect the service life.
Heat treatment:
(1) Oxidative decarburization-the final heat treatment after the thread rolling of the thread rolling board is finished. Heating in a non-protective atmosphere furnace will easily lead to oxidative decarburization. Decarburization of steel materials reduces the carbon content on the surface of steel materials due to oxidation. When the oxidation rate is lower than the diffusion rate of carbon (C) into the metal outer layer, decarburization will occur. On the contrary, when the oxidation rate is greater than the diffusion rate of carbon into the metal outer layer, oxidation will occur, resulting in scale exfoliation. The ferrite grain structure formed by decarburization has two forms: columnar grain decarburization and granular grain decarburization, resulting in reduced hardness, reduced wear resistance and fatigue strength, and caused piles of teeth and whole teeth peeling during service. Early failure. Due to the presence of O2, CO2, H2O and other gases in the furnace during heating, a chemical reaction occurs with iron (Fe) in the steel.
