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What Are The Causes Of The Taps
Jan 13, 2018

What are the causes of the taps

The fracture occurred mainly in the tap on (less die fracture), usually along the entire cross section split tap. Through the analysis of the failure cases of a large number of taps, the author believes that the main reasons for the taps fracture are in the following aspects.

(1) bad welding?


In order to save expensive high speed steel, the taper shank and blade are welded by friction between 45 steel and high speed steel. A large number of taps are broken because of the poor welding. The quality of the taps is mainly determined by the friction pressure, the time of friction, the pressure of the forging and the time of the forging. In the friction phase, the harmful impurities, such as the low melting point compound on the 45 steel and the high speed steel contact surface, are squeezed out and finally squeezed together under the appropriate pressing pressure. ?


When welding, because the strength of steel 45 under high temperature is very low, the friction pressure will produce big deformation, the formation of large and high speed steel flange; because there is enough strength of the flanging is small, low melting point compounds which makes the welding surface of high speed steel side was not completely out, easy to crack after welding. In the process of using tap crack cause fracture. ?


In addition, if the taps are welded, it is easy to break up in the heat affected zone if the stress is eliminated in time. ?


Therefore, in the production, we adopt a protective sleeve at one end of 45 steel to solve the above problems. Because the protective sleeve restricts the excessive compression of the 45 steel, it ensures that the friction pressure is transferred to the side of high-speed steel when welding, so that the flanging is increased, and the harmful impurities on the contact surface are extruded, and the welding is very firm. At the same time, the taps should be put into the annealing furnace immediately after welding in order to eliminate the welding stress.


(2) the structure is not reasonable?


If the design of the taps is not reasonable, it will cause fracture. ?

(1) the effective cross section of the taps is too small, which leads to the excessive bearing capacity of the unit section area, which exceeds the fracture of the taps when the strength limit is limited.

Secondly, the size of the taps is too large or the transition angle is not designed to lead to the stress concentration, and it is easy to break at the stress concentration. The transition area between the cross section of the handle and the blade is too close to the welding port, which leads to the complex welding stress and the stress concentration at the transition section, resulting in a larger stress concentration, resulting in the fracture of the tap.


(3) improper heat treatment process?


When the taps are heat-treated, the taps are likely to cause cracks without preheating, quenching overheating or overheating, untimely tempering and prematurely cleaning. ?


(4) improper use?


When taps are used, they will encounter high hardness parts, irregular sizes, or different concentricity between the taps and the machined parts, resulting in too much torque, or the tap will break. ?


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