Doff transfer rate refers to the percentage of fibers transferred to doff by one rotation of cylinder to the total fibers on the cylinder needle before transfer. Doffer transfer rate directly affects carding strength and is closely related to yarn quality. When the doffer transfer rate is too high, the average number of times that the fiber passes through the carding area of the cylinder cover plate is less, the carding strength of the cylinder cover plate is weak, and the fiber carding is not sufficient and mixed unevenly, the yarn strength and the sliver dry and kilometer thick details will obviously deteriorate; when the doffer transfer rate is too low, the average probability that the fiber dimension is repeatedly combed by the needle cloth is higher, and the carding strength of the cylinder cover plate is too strong, which will cause the fiber The damage and short fiber increase sharply, and even cause the fiber to be rubbed continuously during carding to form neps, which will also affect the yarn evenness and strength, kilometer thick and thin section, kilometer neps, etc.
Factors affecting the transfer rate of doff
01
Needle cloth model and specification
Fiber transfer occurs between cylinder and doffer clothing, so the type, specification and surface state of cylinder and doffer clothing directly affect their grasping and holding ability, and then affect doffer transfer rate.
The large front angle of the needle cloth and the weak holding ability to the fiber are conducive to improving the fiber transfer rate; the large front angle of the needle cloth and the weak grasping ability to the fiber are not conducive to improving the fiber transfer rate.
When the depth of the needle cloth teeth is large, the fibers are easy to sink, which increases the holding ability of the needle cloth to the fibers, which is not conducive to the cohesion of the fibers to doff and reduces the transfer rate; when the depth of the needle cloth teeth is large, the fiber capacity in the teeth can be increased, and the air flow generated by the high-speed rotation of the needle cloth teeth can overflow smoothly from the tip of doff teeth, which is conducive to improving the transfer rate of the fibers.
Increasing the density of the teeth of the needle cloth will increase the number of teeth affected by each fiber, increase the friction resistance, and reduce the fiber transfer ability; increasing the density of the teeth of the doffer will enhance doffer's grasping ability of the fiber, which is conducive to the improvement of the transfer rate.
02
The cohesion ratio of cylinder and doff
Under high-speed rotation, the carding fiber on the cylinder clothing is thrown at one end under the centrifugal force and held by the relatively low-speed rotating doffer clothing, and the fiber is transferred from the cylinder clothing to the doffer clothing and condensed into a fiber network.
The cohesion ratio of cylinder to doff refers to the ratio of the surface linear velocity of cylinder to that of doff. When the coagulation ratio of Schilling and doff is small, the doff transfer rate is high.
Under the condition of constant output at set time: ① if the speed of cylinder is constant and the cohesion ratio is reduced, the increase of doff's speed will reduce the number of fibers agglomerated on doff's unit area, which will help to improve doff's ability of grasping fibers and increase the transfer rate; ② if the speed of cylinder is constant and the cohesion ratio is reduced, the increase of cylinder's speed will increase the centrifugal force of fibers on cylinder and the velocity of air flow boundary layer. It is beneficial to the transfer of the fiber to doff and the transfer rate is increased.
03
Cylinder doff separation
The interval between cylinder and doffer is relatively small: ① the depth of doffer's needle cloth penetrating into the fiber layer is large, and there are many fibers in contact with doffer, which is conducive to the transfer of fibers; ② the length of fibers held by doffer's needle cloth is large, and the holding capacity of doffer's needle cloth to fibers increases; ③ the number of fibers suspended between cylinder and doffer's needle surface decreases. Therefore, when the distance between cylinder and doffer is small, doffer's ability of grasping fibers can be enhanced and the transfer rate of fibers can be increased.
04
Output of carding machine
When the speed of cylinder is fixed, the output of carding machine increases, that is, the output of doffer fiber increases in unit time, which requires the increase of fiber quantity transferred from cylinder to doffer and the increase of doffer transfer rate.
05
Cylinder speed
When the speed of cylinder is slow, with the increase of the speed of cylinder, the amount of fibers on the unit area of cylinder decreases, so the doff transfer rate decreases; when the speed of cylinder increases to a certain value, the centrifugal force on the fibers on the needle cloth increases, which is conducive to the fibers being thrown onto or grabbed by doff, so the doff transfer rate begins to increase with the increase of the speed of cylinder. 。 The influence of cylinder speed on doffer transfer rate has a critical value, which is related to the type and specification of card fabric, the output of carding machine, process configuration and other factors.
06
Fiber properties
The larger the friction coefficient between the fiber and the needle cloth, the more unfavorable the smooth transfer of the fiber; the larger the fiber length, the larger the contact area with the needle cloth and the larger the friction coefficient, the more unfavorable the smooth transfer of the fiber.
07
The air flow state of Xilin and doff triangle
The air flow in the triangle area of cylinder and doffer is smooth, and the air flow goes down through the needle gap of cylinder and doffer in an orderly manner, which is conducive to the condensation of fibers from cylinder to doffer and improve the transfer rate; on the contrary, the air flow here is disordered and the fiber orientation is poor, which is not conducive to the transfer of fibers.
