Rib circular knitted fabrics are a type of double-layered knitted fabric obtained by placing the cylinder and cover needles in a diagonal manner relative to each other in double-plate circular knitting machines. The biggest feature that expresses rib fabrics is that when the fabric is opened in the width direction, straight (R) and reverse (L) loops appear alternately depending on the knitting pattern on both sides. The structure of the fabric consists of consecutive straight and reverse loops in the vertical row direction. Rib fabrics are knitted fabrics with the most flexibility in the transverse direction.
Unlike single plate circular knitting machines, double plate rib circular knitting machines have two needle beds, two different needle groups and two lock systems. As at the beginning of all knitting, the machine must be prepared in order to produce RR Flat rib knitting. In order for the machine to be ready for knitting, needle selection, steel selection and may density adjustment, thread tension adjustment, machine speed adjustment and fabric drafting settings must be made.
Needle selection
There are two different needle groups in the circular rib knitting machine, a cover needle and a cylinder needle. The cap needles of the rib machines are short, and the cylinder needles are longer than the cap needles.
In addition, according to the number of steel ways, there are two different standing needles in the cover and cylinder, as well as the single type needle. The sizes of these two different-footed needles are the same, only the positions of the needle feet on the needle change. For the production of RR flat rib fabric, all needles must be lined up and in working condition on the cover and cylinder of the machine.
Steel selection and may frequency setting
The choice of the steel system is also important in knitting the RR rib fabric. The fabric to be produced is formed by completely looping the needles on the cover and the cylinder. Therefore, all steels of the machine should be adjusted as loop steel. Although it differs slightly in appearance according to the machine models, the general appearance of the loop steel is similar to a triangular shape. If there is a different steel on the machine, it should be replaced. If the machine has a double track steel system, both steels should be set as loop steel. Loop steel is also commonly called single jersey or knitting steel in the knitting industry. After the steel systems of the rib machine are adjusted and placed on the flat rib weave, the loop length (may) adjustments must be made from the loop setting steels on the steel (lock) covers. May adjustment cannot be made collectively on all knitting machines. On each steel cover, there is a may adjustment section for the steel belonging to that system. In circular knitting machines, the setting of may density (loop length) must be the same in all systems in flat knitting patterns. On the other hand, in double plate rib machines, adjustment must be made from both the cover and the cylinder.Adjusting the knitting frequency on the knitting machine is the most important factor in determining the number of rows of stitches per 1 cm. For example, on the same knitting machine, 1 rows of loops per 10 cm can be formed in the first of two different fabrics, and 20 rows of loops in the second.
Of these knits, the fabric with 1 loop bars in 20 cm will be harder and heavier in terms of weight. The way this process is done is by reducing and enlarging the may setting. The smaller the number on the indicator, the smaller the pressure applied to the heel of the needle and the smaller the loop size.
In other words, the number of rows of loops per unit size increases. As the number increases, the pressure on the heel of the needle will increase and the loop size will increase. The number of rows of loops per unit measure will decrease.
Thread tension adjustment
In all circular knitting machines, the tight or loose yarns coming to the systems affect the knitting. By adjusting the rotation speeds of the furniers that provide yarn delivery to the systems, the desired feature of the knitting can be achieved. If the speed of the furniers is slowed down, the yarn becomes more taut, and if the speed is increased, the amount of yarn transferred is greater and the yarn becomes loose. This situation has a great effect on the unit weight of the fabric. If the yarn is stretched, a tighter knitting surface is created and the fabric weight increases. In rib machines, as in all circular knitting machines, the yarn tension adjustment is made with the pulley adjustment. Enlarging the pulley diameter will cause more yarn delivery, and narrowing the diameter will cause less yarn delivery. This setting should be adjusted well according to the sample, fabric properties and knitting report.
Machine speed setting
Excessive speed in circular knitting machines causes wear of needles and steels. Especially since rib circular knitting machines work with double plate, they should be operated at a lower speed compared to single plate machines. In addition, the type of knitting is also effective in adjusting the machine speed. When knitting RR flat rib knit, the speed must be adjusted more carefully as all needles are working.
Fabric draft setting
In circular knitting machines, the setting of the fabric pulling device should be adjusted according to the knitting speed of the machine and the knitting principle. Because the setting of the fabric winding device also plays a role in determining the unit weight. For example, the number of loops per unit area will decrease in the fabric that is drawn more than the normal and the weight will decrease even more. Therefore, the fabric winding device should be adjusted well in order to match the fabric unit weights specified in the sample fabric or order form. After the machine is ready, some sample fabric should be knitted. The yarn used for this knitted fabric should have the same properties as the sample fabric. After some fabric is knitted, the machine is stopped and a piece of sample is cut from it. The cut sample is checked after waiting for a while. We need to check whether the knitted sample fabric has the desired properties. Here, the knitted fabric sample is compared with the sample fabric, if any. If there is no sample fabric, control is made by taking into account the desired features in the order form.
The first feature checked on the sample fabric in the production workshops is the unit weight of the fabric. Unit weight is the weight of one square meter of knitted fabric in kilograms. The fact that the unit weight of the knitted fabric is the same as the sample ensures that many of its properties are the same. We can weigh the unit weight with a precision scale, or we can measure the amount of yarn consumed for a certain number of loops by comparing the length.
Checking the sample with precision balance
After the knitted sample fabric is kept for a while, the piece is cut with a 10x10 sample cutting machine and weighed on a precision scale. Comparison of the yarn spent for a certain number of loops:
If you have a sample, we can reach some conclusions by measuring the length of the yarns used for a certain number of loops on the fabrics. For example, if the yarn length used in 100 stitches marked on the sample is 32 cm, the length of the yarn used for 100 stitches on the knitted fabric is 37 cm, it means there is a problem with the fabric. It is necessary to check the thread length settings again and make the adjustment again. Comparing the number of mays: In addition, some conclusions can be reached by comparing the number of may (loop bar) per unit measure of fabrics. After all these controls, if the desired properties are met, fabric production is started. If it does not have the desired feature, the necessary settings are made by going back to the settings.
Making the Production
After the desired settings on the machine and the sample fabric are knitted and checked, the production of the fabric can be started. During the production of the fabric, care should be taken for possible errors. For example, breaking even a single needle will cause longitudinal needle marks on the fabric. In addition, when arranging the bobbins on the creels, care should be taken that the yarns are in the same lot (lot) or bobbin according to the creel arrangement report.
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