The routine quality inspection of cooked bars in the factory mainly detects the three indicators of dryness unevenness, weight unevenness and weight deviation. Among them, the requirement for weight unevenness is through sufficient combination number and control. Quantitative differences are achieved. According to the needs of scientific research or mechanical and process performance research, there are also methods of testing the intrinsic quality of slivers, which will not be discussed here.
Quantitative control
The control of cotton (or chemical fiber blended) sliver sliver ration, that is, the average dry weight of spun cotton sliver (g/5m), is an important measure to ensure yarn quality and reduce the end-break rate. There are two types of sliver quantitative control and adjustment range: one is the sliver quantitative control for each eye of a single machine, and the other is the sliver quantitative control for all machines spinning the same linear density. The quantitative control of the entire machine is to control the weight deviation of the spinning machine and reduce the number of replacements and workload of the draft conversion gear of the spinning machine.
The quantitative control of a single machine can promptly eliminate the difference in spinning weight between the machines of the draw frame, which is beneficial to reducing the weight unevenness of slivers and spun yarns and the weight deviation of spun yarns. As for the allowable range of the difference between the average dry weight of sliver spun by a single machine and the whole machine and the designed standard dry weight, production practice has proved that if the difference percentage of the dry weight of slivers from a single machine is controlled at around plus or minus 1%, Then the difference percentage of the sliver dry weight of the entire machine (that is, the average dry weight of the sliver of each single machine) is generally controlled at around plus or minus 0.5%. At this time, the weight deviation and weight unevenness of the spun yarn are guaranteed to be within 2%. within the range. The quality requirements of fine special yarn are relatively high, so the control of the weight difference of cooked strips should be correspondingly stricter.
01 Test methods and steps for tampon quantitative testing
In order to be timely To control the spinning dry weight of cotton sliver, the production plant generally tests the cooked sliver (final sliver) of each variety 2 to 3 times per shift. The sampling method is to take a sample (5m) from both eyes of each machine. ). The total number of samples varies according to the number of draw frame cells used for this variety, and is generally in the range of 8 to 30 sections. At the same time, randomly sample a total of 50g of cotton slivers from each machine of the same variety to test the moisture regain of the cotton slivers. After weighing them separately, first calculate the average spinning weight (this is the wet weight containing water) per machine, and calculate the same The weight unevenness of each cotton sliver of each variety is then converted into the actual average dryness of this experiment based on the average weight (also wet weight) of all samples of the same variety and the tested moisture regain of the entire machine. Heavy. Generally, in order to obtain sample results quickly and adjust the conversion gear in time, the moisture regain rate of the previous shift of experiments can be used for calculation. Finally, calculate the weight difference percentage based on the actual average dry weight and the design dry weight to see if it is within the allowable range of the above control, and decide whether the draft conversion gear and draft fine-tuning gear (crown tooth) need to be replaced. When making quantitative adjustments to a single machine, some factories use the standard dry weight to first calculate the standard wet weight based on the cotton sliver moisture regain, and then compare the average wet weight of the sample with the standard wet weight to calculate and adjust the conversion gear. This is more convenient and timely. .
02 Adjustment method of changing gears
In order to control the entire machine The fluctuation value of the average dry weight of sliver should be controlled within the specified allowable range. The method of individual adjustment of single machines should be adopted, that is, the draft multiple of each single machine should be adjusted separately to control the fluctuation value of the average dry weight of sliver of single machine. Within the allowed range. In order to facilitate the timely adjustment of the spinning weight of the draw frame, the transmission system is equipped with draft conversion gears (light and heavy teeth) and draft fine-tuning conversion gears (crown teeth). The number of teeth will be changed depending on the specific situation.
According to the fluctuation range of the spinning weight, the method of changing the conversion gear can be: changing only the crown teeth (the fluctuation value is small, close to the weight controlled by 1 crown tooth when); only replace the light and heavy teeth (when the fluctuation value is large, close to the weight controlled by one tooth of the light and heavy teeth); replace the crown teeth and one tooth each of the light and heavy teeth at the same time (if the weight adjusted by changing the crown tooth is too small, But when the weight of changing the weight of each tooth is too large), there is a method to match each other.
03 Experience in quantitative control
How it affects cotton production in actual production There are many factors that affect the spun weight, and they often change. Therefore, the spun weight data obtained from the sample must be analyzed and judged before deciding whether the conversion gear should be replaced. The following factors need to be considered.
●Sliver standard control
In order to relatively reduce the number of exchanges of draw frame gears, To reduce the fluctuation of uneven weight of spun yarn, when single-machine adjustment is used, the control range of the sliver weight difference of a single machine can be appropriately relaxed. For example, if the average weight difference range of each unit in linear density is plus or minus 0.13g, and the average weight difference range of a single unit is plus or minus 0.2g, then the conversion teeth will not be exchanged if the average weight of a single unit does not exceed plus or minus 0.2g.
The weight control range of the whole machine and single machine for spinning the same linear density varies with the linear density and spun yarn weight requirements. Generally, the single machine control standard is about looser than the entire machine control standard. About 2 times. The control range of the sliver weight of a single machine is strictly controlled for low and medium special yarns, which is generally about plus or minus 0.5~0.75% of the standard weight. High special yarns are wider, generally about plus or minus 1% of the standard weight. This standard is roughly close to the sliver weight that can be controlled by one crown tooth of the draw frame, and one light and heavy tooth is approximately equivalent to the sliver weight controlled by two crown teeth.
●Cotton, pressurization failure and uneven pressure. A strict regular pressure testing system should be implemented to control the pressure difference range at both ends of the rubber roller and between the two eyes. The deterioration of the evenness caused by the pressure difference between the left and right sides of the same rubber roller is even greater than the impact caused by insufficient pressure. Attention should be paid to selecting the cradle spring of mechanical material and processing level, regularly detecting its elasticity decline, and the spring pressure should be aligned with the center of the rubber roller shaft.
The concentricity and installation quality of rollers and rubber rollers have a great impact on the quality of the whiskers and the life of the machine parts. The bending of the roller should be controlled within 0.05mm, the flatness and roundness of the rubber roller should also be within 0.05mm, and the hardness of the rubber roller should be suitable for the variety being spun.
Abnormal drafting transmission components are an important reason for the deterioration of the high-speed draw frame. If the gear mesh is too loose, the keyway or the shaft hole is worn and loose, it is easy to produce intermittent cotton webs, resulting in deterioration of the sliver or slub strips. The transmission gear on the fast shaft is loose, and its impact is greater than that on the slow shaft.
If the keyway and shaft hole are worn out and loose, you can turn the front roller by hand and check the rotation delay of the second or third roller and whether the cotton web has intermittent marks. To judge, because this is a concentrated reflection of the cumulative error of gear looseness in the transmission system.
Common mechanical failures that cause unevenness include: worn gears (prone to regular unevenness), loose gears (prone to irregularities) , The ball bearings are worn out (regular unevenness is prone to occur), the concave grip of the rubber roller is insufficient (unevenness is prone to occur), roller twisting, etc.
Auto-levelling device
Combining effect of draw frame Long segment weight deviations and short segment weight fluctuations cannot be solved. At the same time, combined drafting produces new additional drafting unevenness. The above-mentioned manual sampling test has limitations. Therefore, it is inevitable for the development of draw frame technology to control draw frame weight unevenness and weight deviation by combining merging and autoleveling in high-speed draw frames.
The auto-leveling device randomly detects and automatically detects the difference between the unit length weight of the fed or spun semi-finished products (when the density is uniform, it can be expressed as thickness) and the standard. Adjust the draft ratio to keep the weight (or thickness) of the spun semi-finished product per unit length at a relatively stable value. Equipping the high-speed draw frame with an auto-leveling device is an effective measure to further improve the quality of the strips.
Autoleveling devices can be divided into three categories according to control methods: one is an open-loop control system, which compensates for uneven evenness in medium and short segments; the other is a closed-loop control system, Compensate for product unevenness in medium and long segments; the third is the mixing control system.
According to the current situation, for ring spinning, general products of the carded system do not need to be equipped with leveling devices; for products with special requirements, leveling devices can be used in the first drawing pass. (If the carding machine has a leveling device, the head does not need to be used); for general products of the combing system, a leveling device can be used on the final draw frame after combing (if a draw frame is used after combing, it is best to use short segments Leveling device); for products with high quality requirements, it is best to install a long segment or long and short segment leveling device on the combing unit or carding machine. </p
