Key Considerations for Ensuring Good Coverage on Knitting Machines

When utilizing a knitting machine with polyester and cotton woven fabric for covering, what are the key considerations during the transfer process to ensure optimal coverage?

Cause Analysis

The circular knitting machine employs a specialized fabric veil to cover the ground yarn. This fabric requires meticulous machine commissioning due to its unique characteristics. In theory, it falls under the category of one-sided coverage Tim yarn organization. However, there are distinctions in the knitting process compared to a single circular knitting machine knitting yarn Tim. Let's delve into a detailed analysis.

In a single circular knitting machine, when incorporating the covering yarn, both the ground yarn and the veil pass through the same yarn guide while being fed into the knitting region where the knitting needle hooks are located. However, there are variations in the feeding angles of the ground yarn and the veil. This results in differences in the positioning of the ground yarn and the veil relative to the knitting needle hooks. Specifically, the ground yarn and the veil may be positioned differently in terms of their distance from the needle bar, with the veil being either closer to or farther away from the needle bar compared to the ground yarn. Additionally, the veil may be positioned either above or below the ground yarn. Through precise yarn tension control, efforts are made to ensure that the positioning of the ground yarn and the veil remains stable throughout the knitting process. This stability ensures that the veil consistently remains at the front of the fabric, maintaining the desired appearance and structure.

On the sweater machine, ensuring the stability of the ground yarn and veil positions within the hooks is crucial for evaluating the quality of coverage. During the weaving process, the sweater machine utilizes three yarn feeders to supply yarn: the ground yarn (commonly referred to as the circle yarn), the veil, and the top yarn, completing a full course before fabric formation. As the needle passes through the woven veil triangle (known as the mountain triangle), the veil is inserted into the hook. However, during this process, only the stitch is formed, but the loop is not completed; the previous loop remains on the needle bar while the new veil loop remains in the hook without forming a coil.

Subsequently, the machine continues to operate, knitting the ground yarn triangle (known as the Hill triangle). As the needles rise, their height increase is restricted, reaching only the tuck height relative to the mountain triangle. This limitation ensures that the new veil loop fed from the needle tongue is not withdrawn and remains in the hook, as illustrated in the figure. Then, the needles begin to descend, and the ground yarn is inserted into the needle hook. At this point, the relative positions of the ground yarn and veil in the hook are as shown in Figure 2. The ground yarn is positioned over the veil, maintaining the arrangement for subsequent fabric formation with the veil in front of the fabric and the yarn at the back.



If the machine isn't properly adjusted, a particular scenario might arise. After completing a hill triangle and introducing new ground yarn, the veil may form a coil but remain within the needle hook without being lifted off. As the machine advances to the next course of liner yarn triangle, the needles are selectively raised, with one needle rising across two pins. During this phase, the coils on the needles may not be caught by the pin retainer ring during the rise. Consequently, a coil that isn't lifted by the rising needles may be pulled up, causing the ground yarn coil to catch on the inner needle hook and leading to variation in veil position, potentially resulting in an open field formation.

As the machine progresses after completing the mountains and hills triangle, the needles jack twice to close. This ensures complete lifting off of the old coil on the needle. However, the increased frequency and amplitude of needle reciprocation may raise the likelihood of the old coil hooking and sliding on the needle bar. This could extend beyond the veil and form a yarn roll, thereby increasing the probability of open formations.

Solution

To address these issues, two key aspects should be considered:

1. Adjusting the yarn and stitch length of the veil compared to the ground yarn can help mitigate problems. By making the veil stitches longer or shorter than the ground yarn, with a significant difference between them, the tension can be primarily exerted on the ground yarn rather than on the veil. This prevents the veil from being affected when unseating from the cloth, as the tension is focused on the ground yarn during the process of yarn off-circle to circle. As a result, the veil is less likely to extend beyond the yarn off-circle, minimizing the occurrence of unwanted phenomena during weaving. Typically, the loop length of the veil should be around 1.2 to 1.6 mm longer than the length of the yarn coils (applicable to polyester filament yarn).

2. Another solution involves addressing the issue of the veil rolling when some needles rise during the knitting yarn liner process, which may not increase the textured yarn pull on the needle. One common method to tackle this problem is by using the triangular depression of the spacer yarn path. This method aims to prevent the rising needles from catching and pulling the veil coil by utilizing the sedimentation woods jaw to maintain tension and prevent pulling. 



By implementing the adjustments outlined above, satisfactory results can usually be achieved in weaving sweater fabric with proper coverage. Additionally, when dealing with local yarn types like C yarn, polyester-cotton, and polyester filament that are prone to adhesion, attention should be paid not only to the two mentioned points but also to advancing the hill sinker triangle needles towards the center direction. This adjustment is necessary because when the veil is inserted, it can become bent and prone to sticking when in contact with the ground yarn (especially polyester yarn) due to the relaxed tension caused by the rise of knitting needles. Pushing the upper part of the hill sinker triangle sinker jaws tighter helps prevent sticking.

In summary, weaving this type of fabric requires meticulous attention to detail during the weaving process, with adjustments made based on the machine's technological characteristics. It's important to analyze every aspect carefully and make appropriate modifications to achieve the desired outcomes. However, if the machine's needle tract in the triangular flat needle is too broad, modifications to the flat needle on the triangle may be necessary.