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Key Points of Internal Thread Tapping of Stainless Steel Pipe Fittings

The main reason for the popularization of stainless steel is its nature of environmental protection. The internal threads on stainless steel pipe fittings are usually tapped with taps.  Stainless steel has high viscosity and poor property of chip breaking. Therefore, it is easy for chips to scratch the workpiece thread or tap chipping during the process of tapping, which affects the processing efficiency and thread quality. In order to extend the service life of the tap and improve the quality of thread processing, the following points should be paid attention to:

1. Design and manufacture of internal thread taps for stainless steel pipe fittings

(1) It is important to choose taps of good quality. The special alloy elements added to ordinary high-speed tool steels can significantly improve the wear resistance and toughness of the tap.

(2) The titanium nitride coating coated on the surface of the tap thread can significantly improve the peformance of wear resistance, heat resistance and lubricity of the tap.

(3) Properly increase the rake angle of the tap. However, it should be noted that if the rake angle of the tap is too large, it will be easy to cause the tap edge collapse and multi edge of the thread when the tool is retracted.

(4) Properly increase the amount of shovel back of the tap. However. It should be noted that if the amount of the shovel back is too large, it is easy to cause chips to jam into the rear angle of the tap when the tool is retracted, and the tapped thread will present poor finish.

(5) The heat treatment method of the tool should be chosen reasonably to take into account the hardness and toughness of the tap. At the same time, it is important to ensure the clarity and stability of the internal threads on the stainless steel pipe fittings.

2. Reasonable use of s internal thread tapping in stainless steel pipe fittings

(1) Different types of stainless steel pipe fittings welded or non-welded can be found in the market. When processing various types of stainless steel pipe fittings, it is necessary to consider different chip trends. If necessary,  the new taps also need to be ground. The principle of grinding is to try to discharge the chips from the chip pocket when tapping so as to prevent scratches on processed threads.

For example:

Processing Coupling (SPU):  A vertical tapping machine (or a three-head tapping machine) is the best choice for the tapping of the coupling. The grinding method of the tap is to:  ① Extend the front guide part of the tap, so that the tap can gradually enter the cutting to improve the service life of the tap.

② Grind the inclination on each blade of the tap, but the first grinding should not be too long (around 3-4mm) and can be gradually lengthened later. The standard for judging the quality of sharpening of the blade inclination is that during tapping the chip is discharged from the end face of the coupling in a horn shape without damaging the thread that has been tapped. If the quality of the tapped thread is not good after tapping for a period of time, the blade inclination can be increased.

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