Twin screw extruder screw sleeve is commonly used in angle thread workpieces. In addition to being machined mechanically, the thread can also be obtained by tapping and threading in the method of wrench processing.
The tapping (also known as tapping) of screw sleeves for twin screw extruders is to machine internal threads on the cylindrical surface of the workpiece with a tap. The threading (also known as threading and buttoning) of screw sleeves is to machine external threads on the cylindrical rod with a die.
Tap
The tap of the twin extruder machine is a forming tool used to machine small diameter internal threads. It is usually made of alloy tool steel 9SiGr and is made by heat treatment. A set of taps for M6~M24 consists of two, called the taper tap and the second tap; a set for below M6 and above M24 consists of three, namely the taper tap, the second tap, and the third tap.
Each tap is composed of a working part and a shank part. The working part is composed of a cutting part and a calibration part. There are several (usually three or four) chip grooves axially, forming several blade edges (cutting edges) and front angles correspondingly. The cutting portion (the incomplete tooth portion) is an important part of cutting the thread and is usually ground into a conical shape to distribute the cutting load among several cutting teeth. The taper tap has a smaller cone angle and 5~7 teeth, while the second tap has a larger cone angle and 3~4 teeth. The calibration part has complete teeth and is used to polish the thread and guide the tap to move along the axial direction. The shank part has a square head, which matches with the reamer and transfers torque.
Reamer
The reamer is a tool used to clamp the tap, and the commonly used one is the adjustable reamer,which is one of the indispensable twin screw extruder elements. The rotation handle can adjust the size of the square hole to clamp taps of different sizes. The length of the reamer should be selected according to the size of the tap to control the torque during tapping and prevent the tap from breaking due to improper force.
Determination of the bottom hole diameter
During the tapping process, the cutting edges of the tap mainly cut the metal, but also have the effect of extruding the metal, resulting in the phenomenon that the metal protrudes and flows towards the tooth tip. Therefore, before tapping the thread, the drilled aperture (i.e. the bottom hole) should be larger than the inner diameter of the thread. The diameter of the bottom hole can be checked in the manual or calculated according to the following empirical formula: brittle materials (cast iron, bronze, etc.): drilling diameter d0=d (thread outer diameter) - 1.1p (pitch); plastic materials (steel, brass, etc.): drilling diameter d0=d (thread outer diameter) - p (pitch).
Determination of drilling depth
When tapping blind holes (non-through holes) of threads, because the tap cannot tap to the bottom, the depth of the hole should be greater than the length of the thread. The depth of blind holes can be calculated according to the following formula: hole depth=required thread depth+0.7d.
Chamfering of the hole mouth
Before tapping the thread, chamfering should be carried out on the hole mouth drilled to facilitate the positioning and cutting of the tap. The depth of the chamfer is greater than the pitch of the thread.
Correctly select the tap according to the specification of the thread hole on the workpiece, first use the taper tap and then the second tap, and cannot be used in reverse.
When clamping the workpiece, the center of the hole should be perpendicular to the chuck to prevent the thread from being skewed.
When tapping with the taper tap, after screwing in 1~2 turns, check whether the tap is perpendicular to the end face of the hole (it can be visually checked or checked with a square ruler in two mutually perpendicular directions). After the cutting part has cut into the workpiece, it should be reversed 1/4 turn every 1~2 turns, so that the chips can fall off; at the same time, no pressure should be applied (i.e. only rotating without pressure) to prevent the tap from breaking or the threaded teeth being thin.
When tapping internal threads on steel parts, lubricating oil can be added to make the thread smooth, save effort and prolong the service life of the tap; when tapping internal threads on cast iron, no lubricant or kerosene can be added; when tapping internal threads on aluminum and aluminum alloys, brass, emulsifiers can be added.
Do not blow chips directly with your mouth to prevent chips from flying into your eyes.
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