With a very general expression of the circular knitting sector, “AbrajAlthough there are many more reasons for fabric faults, which he calls "", it is often difficult to distinguish these reasons from each other.
The faults called abraj in the sector are the traces that repeat on top of each other at equal intervals and in the width of the fabric seen in circular knitted fabrics. this error “Barre” Also called error. There are many reasons for this type of error. If we need to collect these reasons under two main headings, these are;
1-Knitting machine welded transverse tracks
2- Thread welded transverse traces.
Knitting Machine Welded Transverse Tracks
As it is known, in circular weft knitting machines, yarn direction and knitting direction are realized in the width of the fabric. It is possible to list the reasons for the formation of trace-shaped errors in the transverse direction that may arise from the knitting machine as follows.
1-loop setting differences,
2- shuttle misalignments,
3-Yarn tension differences
One of the causes of traces in the transverse direction originating from the knitting machine "loop setting differences" is coming. The knitting regions where circular knitting machines have performed the knitting process are in more than one amount. Yarn is fed to each knitting zone in the machine (the zones in which the needles are moved by the steel), that is, to each system separately. With the increase in the number of systems, the efficiency of the machine also increases. In order to obtain a smooth knitted surface, the heights of the rows of loops produced by each system must be exactly equal. If one or more of the systems produces rows of loops at different heights than other systems, there will be differences in the amount of yarn consumed by this system or systems and accordingly in the loop heights in the fabrics obtained. Generally, this error is detected in two ways.
Loop thread length measurement method
In this method, the fabric is cut with a certain number of stitches. Then, threads from this fabric width are ripped in order. Since these stripped threads stand in loop form for a long time, they are not in a straight state but in a curved shape. In order to eliminate this curved structure in the removed yarns and measure the actual length of the yarn, the yarns are stretched with a constant force and the lengths are measured with the help of a ruler. developed for this measurement. "HATRA" device helps to make the process easy and fast. These measured yarn lengths give us the length of yarn spent for one stitch divided by the number of stitches that have been removed. By applying these processes to faulty and defect-free areas on the fabric, it is determined whether there is a difference in the loop thread lengths between these areas. If the measured loop thread lengths in the faulty and faultless rows of loops are the same, the error is not caused by the loop setting difference.
loop height measurement
As a result of the different settings of the systems in the knitting machine, the stitch heights produced by the relevant systems will also be different. If the fabric is examined under a microscope with a suitable magnification, differences between faulty and defect-free areas can usually be detected.
However, as a result of the fixation process in elastomer material and fine knitted fabrics, the possibility of detecting the error with these two methods may disappear. In such cases, if the fabric we have is "full lycra” If it is a fabric that is produced by feeding elastomer material in each system, chemical methods are used to detect the defect. Fabrics produced with full lycra and cellulosic yarns are treated with special chemical mixtures under tension, and the cellulosic material in the fabric structure is dissolved and removed, leaving only a structure consisting of elastomer material. The view of this building;
The structure in the form of loops, which is obtained as a result of chemical melting in knitted fabric and consists only of elastomer material, gives us important information about the rows of loops. If there is a difference in setting in the rows of loops made by one or more systems, the traces in the elastomer material structure in the melted parts will be much more obvious and revealing than the traces before melting. In the photo above, the appearance of a structure in this direction is given. In this photograph, it is seen that the rows of loops in the marked places are at a different height from the other rows of loops.
Another error originating from the knitting machine is in yarn feeding systems setting differences.
As it is known, yarn delivery systems do not operate independently of each other. Movement is given to the yarn propulsion systems by means of belt-pulley device. And there are usually 2 or 3 of these systems, depending on the number of systems on the knitting machine. As an example is given in the figure below, yarn delivery systems on the knitting machine are fixed in layers at the top of the machine.
Yarn delivery systems arranged side by side on each floor are in the knitting machine. they are driven by a separate belt-pulley assembly. The yarns used in each system in circular knitting machines are delivered to the knitting zone by means of the yarn delivery systems on the machine. Due to the fact that the yarn feeding systems send different amounts of yarn from each other, even though the needles that are driven by the loop setting steels consume a constant amount of thread, the threads sent in different amounts will cause differences in the rows of loops produced by the related systems. However, it is not possible to produce without machine downtime for a long time in the machine, which is such an error. Because the belt-pulley assembly, which carries out different amounts of yarn delivery, will also cause differences between the tensions of the yarns. Therefore, over time, the tension differences between the yarns will change and as a result, the yarn will break as a result of excessive tension or the yarn control devices will stop the machine due to excessive slack. As a result, it will not be possible to carry out a production in this way for a long time.
Thread Welded Transverse Tracks
Another important factor in the formation of traces in the transverse direction in circular knitted fabrics is the differences between the yarns used in the knitting machine. However, although the differences mentioned here are very diverse, understanding the reason for this is much more difficult than detecting the transverse traces originating from the knitting machine.
If we need to examine the most common traces in the transverse direction that occur as a result of the differences between the yarns used in the knitting machine, it is possible to list the reasons as follows.
1-Traces in the transverse direction caused by the yarn number difference,
2-Traces in the transverse direction due to the difference in the number of yarn twists,
3-Traces in the transverse direction due to the difference in yarn twist direction,
4-Traces in the transverse direction due to the difference in yarn production method,
5-Traces in the transverse direction caused by the blending difference of the yarn,
6- Traces in the transverse direction due to the difference in the finishing processes between the yarns,
7-Traces in the transverse direction due to the difference in the filament numbers of the yarns produced with man-made fibers,
8-Traces in the transverse direction caused by the texture and/or center difference between the filament yarns produced as textured and/or centered,
It is seen that the formation of traces in the transverse direction seen in knitted fabrics is much more than the causes of machine-induced scars.
Traces in the transverse direction caused by the yarn number difference,
If one or more of the yarns fed to the knitting machine systems differ from the yarn count fed to the other systems, it will be inevitable to appear as traces in the transverse direction on the surface of the knitted fabric. Although this error is easily noticed during the knitting process, the difference between the yarn counts may not be noticed in the raw state if there is a slight difference. However, this error will reveal itself as a result of the painting process. Since the amount of dyestuff uptake of the wrongly fed yarns will be different from the amount of dyestuff uptake of the other yarns, the traces will be much more obvious than the raw fabric.
As a result of feeding the yarns with different yarn twist count and twist direction to the knitting machine, traces in the transverse direction are formed which are not very obvious in the raw fabric sample, but are more evident as a result of the dyeing process.
Traces in the transverse direction due to the difference in yarn production method
It is possible that such faults may have arisen with the feeding of yarns obtained by different production techniques (eg ring and open-end yarns) to the knitting machine. If one or more different yarns are fed to the machine one after the other, it is possible to show traces in the transverse direction on the fabric.
Traces in the transverse direction caused by the blending difference of the yarn
It is an error cause that causes traces in the transverse direction in knitted fabrics and is more difficult to detect than other errors. Especially in yarns obtained with cotton fibers, this type of error is encountered. Visual and microscopic examinations are not sufficient to detect this error. Detection of this error can only be possible by examining the yarn strength tests and the physical properties of the fibers in the yarn structure..
Traces in the transverse direction due to the difference in the finishing processes between the yarns,
This error group occurs when yarns with different paraffin content are used together with yarns that have been fixed and yarns that have not been treated, and yarns that have undergone yarn dyeing. If waxed and poorly waxed yarns are used together in a knitted fabric, it is possible to form traces in the transverse direction in the fabric obtained. However, as it is known, the paraffin material is easily removed from the yarn structure with the washing process. Therefore, while this error is evident in the raw fabric sample, the traces will disappear as a result of the dyeing process, since the paraffin on the yarn is removed during the finishing processes. If fixed yarns and non-fixed yarns are fed to the knitting machine together, it is possible to see traces in the knitted fabric in the transverse direction. However, depending on the degree of fixation applied to the fixed yarns, there are changes in the amount of defect remaining on the fabric surface as a result of the finishing processes. It is possible to see traces in the transverse direction because the yarns that have been exposed to different dyeing conditions during the knitting processes with dyed yarns (for reasons such as being dyed in different boilers) are used on the same machine. So much so that during the washing of fabrics with this type of production, the yarns leave dyestuff in the washing bath. These dyestuffs can also interact with other yarns and cause contamination of the fabric.
Traces in the transverse direction caused by the difference in the filament numbers of the yarns produced with man-made fibers
As a result of the different filament numbers in artificial yarns and feeding these different yarns to the same knitting machine, it is inevitable that traces will form on the fabric surface in the transverse direction. Although these traces are not usually evident on the raw fabric, the error appears much more clearly as a result of the dyeing process in the fabric finishing plant. The reason for this is that yarns with different filament counts have different amount of dyestuff uptake, and yarns dyed in different amounts appear as traces in the transverse direction as a result of the dyeing process.