When this method is used to knead the pipe in reverse, the inner diameter of the kneading cylinder acts as a mold to confirm the outer diameter of the pipe, and the outer diameter of the kneading pad (reverse extrusion pad) acts as a puncture needle to confirm the inner diameter of the pipe. The operation procedure is as follows: sleeve shaft kneading (reverse extrusion) - kneading end - separation and pressing - pushing out pipe - finishing kneading cylinder. This kneading method is only applicable to extruding large-diameter pipes. Generally, the diameter is more than 60mm. The length of kneading products is limited by the length of kneading shaft. It is applicable to kneading metals with good plasticity. Its disadvantage is that the kneading operation is troublesome, the production efficiency of kneading machine is low, and the surface quality of kneading products is poor, but this reverse kneading method is still widely used.
The following points shall be paid attention to when selecting this reverse kneading method: (1) the reverse kneading shaft and the reverse kneading pad shall be reasonably selected according to the released product specifications, and the difference in diameter shall not be less than 15mm. (2) Before kneading, confirm the stroke direction of kneading shaft (according to the stroke scale on the equipment). (3) At the end of kneading, the residual thickness shall be 10-20mm. (4) When the cup bottom is flushed, the kneading shaft advances 40-50mm. (5) If the length of the kneading shaft is insufficient and the stroke does not reach the calibration position, it is allowed to add shims. The supplementary gasket shall be stably sleeved on the kneading shaft pin, and the thickness orientation of the supplementary gasket shall be confirmed together (confirmed on the scale of the equipment).
The surface quality of the pipes kneaded by this method is relatively poor. If it is used as the pipe blank for drawing, it is necessary to arrange the turning process in the drawing process. The detailed operation, control, requirements and precautions can be confirmed according to the specification of kneading products, alloy and tonnage of kneading machine.