Before reaching the spun yarn, the grip of the roller jaws is stable and does not slip, that is, there is no "hard head", which seems difficult to achieve under the existing conditions. From the perspective of drafting theory, the “hard head” is to deal with the contradiction between holding force and drafting force or guiding force and control force. During the drafting process, as long as the minimum holding force is always greater than the maximum drafting force, the guiding force of the planktonic fiber on the front jaw line is always greater than the control force, which is a relatively ideal drafting state. High elasticity is the basis for the low hardness of rubber rollers, otherwise plastic deformation will occur; but according to the existing technology, nitrile rubber cannot achieve elastic recovery at a lower hardness (currently lower than Shore A60 degrees). The hardness of the polyurethane rubber roller can reach Shao A55 degree, the elastic recovery is better than the existing nitrile rubber rubber roller and it is more wear-resistant. The regrinding cycle can be increased by 3 to 4 times. The surface roughness can be appropriately high without affecting the dryness. And anti-winding effect. For concentrated spinning, this kind of performance is more demanding, because the concentrated spinning equipment does not have cleaning rollers, so the winding has a greater impact on its yarn quality.
How to strengthen the grip of the front roller and rubber roller in actual production?
At present, the widely used low-hardness and high-elastic rubber rollers can basically meet the requirements under the flexible process. However, some factories take too tight a gap to balance the drafting force, and make the front rubber roller over-pressurized. The abnormal phenomenon that the thicker the coating ratio mentioned in some papers is, the better it is. This kind of gripping force increases too much and the drafting force does not increase synchronously, but it causes poor recovery of the elasticity of the rubber roller. The reverse encircling arc extension changes the shift of the shift point, destroys the dry CV value, and increases the spindle difference. In addition, the existing drafting device often has too large a feeding amount and a too large drafting multiple, which results in a corresponding increase in yarn defects and hairiness. Too small a spacer block or a control rod of the spacer block will also cause a short thick knot. increase.
The ideal gripping state is that under the premise that the front rubber roller is "light, smooth, cool, and dry," the surface roughness can be grasped. The surface roughness Ra value is less than 1.0 μm, which is the rubber roller. The hardness meets the requirements for elastic recovery in drafting, such as using low hardness polyurethane rubber rollers. In addition, if the breakthrough of the manufacturing technology of the front rollers: change the existing helical teeth to herringbone teeth to balance the friction transmission force of the front rubber roller, or cover the working surface of the jaw with a wear-resistant semi-elastic body, so that the upper and lower sides are elastically gripped Holding, the front pressure can be reliably held under lesser conditions. Another important condition for maintaining the stability of the front jaw is the stability of the fibers controlled by the upper and lower aprons, that is, the use of reliable equipment to achieve synchronous operation of the upper and lower aprons without slippage can meet the requirements of spinning draft stability .
