Key points of internal thread tapping of stainless steel pipe fittings

1 Design and manufacture of taps

(1) Choose a better tap material. Adding special alloy elements to ordinary high-speed tool steel can significantly improve the wear resistance and toughness of the tap.

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

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

(4) Appropriately increase the amount of tap shovel back. However, it should be noted that if the amount of 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 is not smooth.

(5) Reasonably select the tool heat treatment method to take into account the hardness and toughness of the tap.

2 Pre-Jjn-r of the bottom hole of the workpiece

(1) According to the principle of tapping processing volume as small as possible, the bottom L size of the pre-processed workpiece, especially the American standard NPT thread and the British standard f, r thread, the taper is 1:16, and most stainless steel manufacturers are A straight hole is cast according to the diameter of the small end of the thread as the bottom hole of the tapping, resulting in a large amount of processing in the latter half of the tapping.

(2) The L size of the bottom hole is best to be the minor diameter size of the thread being machined plus a margin of 0.1-0.2mm.

(3) It is best to use a custom reamer before tapping. For the American standard Nf, r thread, and the British standard f, r thread, the taper bottom hole L should be processed. At present, many companies use waste taps to manually grind the threads to make reamers, so that the waste taps can be reused.

3 Reasonable use of taps

(1) Different chip trends should be considered when processing different types of workpieces. New taps also need to be ground when necessary. The principle of grinding is to try to discharge the chips from the chip pocket when tapping to prevent scratches on the processed threads.

(2) The non-concentricity of the tap and the workpiece is also an important factor affecting the service life of the tap. It will cause uneven force on the tap during the tapping process, causing premature fatigue damage, or even breakage of the tap. The main factors that affect the concentricity include the spindle of the machine tool, the tap joint, the tap shank, the workpiece to be processed, the manufacturing quality of the fixture, and the adjustment quality of the fixture and the machine table. The solution is to use qualified tap joints and fixtures and adjust the machine carefully. Besides, during the machining process, the tap joint and the tie rod of the machine tool should not be pulled too tightly to make the tap joint a little bit movable; the top screw should not be too tight when connecting the tap and the tap joint so that the tap can self-center.

(3) The service life of the tap is closely related to the regrind quality of the tap.

4 Selection of tapping oil

When tapping stainless steel pipe fittings, the selection of tapping oil is also essential. The tapping oil must have good cooling, lubrication, and anti-rust functions. If the lubrication effect of the tapping oil is not good, the tapped threads will have a poor finish and the tapping resistance will be large. If the cooling effect of tapping oil is not good, the tap is easy to stick to the teeth, that is, it is easy to bond stainless steel chips on the tap thread and the rake surface. It is better to use special tapping oil for stainless steel and can be used directly. You can also use tapping oil and engine oil to configure yourself, but the ratio must be appropriate. The choice of machining tools in the slurry pump industry. Domestic companies engaged in the production of slurry pumps and the processing of their accessories are all facing the problem of choosing machining tools. The main feature of the slurry pump is that the transportation fluid path has high wear resistance or corrosion resistance, so it is suitable for transporting abrasive or corrosive slurry. Its products are widely used in mining, metallurgy, petroleum, coal, transportation, Electricity, building materials, and municipal engineering industries, used for mining, dredging, conveying tails, concentrated ore sand, ash, coal slime, iron powder, and other strong abrasive, high-concentration slag transportation.