How is the position of the sinker cam of a single jersey knitting machine determined during production? What effect does changing this position have on the final fabric?

The movement of the sinker in a Single Jersey machine is governed by its triangular design, with the sinker acting as a supplementary component for forming and closing loops during the weaving process. As the shuttle opens or closes loops, the sinker's jaws function similarly to the lateral walls of the needle groove found in a double-faced loom. They block the yarn, allowing the shuttle to create a loop and push the previous loop away from the shuttle's mouth once the loop is completed. To prevent the old loop from getting stuck at the top of the shuttle's needle during its ascent and retraction, the sinker's jaws must effectively push the old loop away from the fabric's surface while maintaining a firm grip on it throughout the shuttle's movement. This ensures that the loop is fully cleared. Consequently, the positioning of the sinker's jaws plays a crucial role in determining the technological positioning of the sinker during weaving, which directly influences the overall weaving process. 

From the sinker's function in weaving, it is evident that before the shuttle's ascent and loop retraction, the sinker's jaws need to push the old loop away from the needle's top. Regarding the distance from the thread to the loom, as long as the warp is positioned behind the needle, it can prevent new threads from piercing or breaking old threads during the needle's rise. However, if the sinker's jaws push too far, they can obstruct the descent of the new web, leading to disruptions in the weaving process.

1. Theoretically, during the weaving cycle, the sinker's jaws should only make contact with the back line of the needle as they move upward, facilitating a smooth descent. Any additional movement forward could disrupt the settling arc of the new loop, negatively impacting the weaving process. However, in practice, simply determining the position of the settling cam based on the point where the sinker's jaws meet the needle line is not enough. Various factors can influence the optimal placement of the cam.

2. Recently, the most common sinker for single jersey machines with curved corners can be divided into two categories. The dashed line represents an arc that intersects angle S on the sinker plate, with its center aligned with the needle's center. If the needle bar line is used as a reference for installing the drop-in cams, then throughout the entire curve depicted in the weaving needles complete their loop formation and begin to unwind until they reach their peak and finish unwinding—the jaws of the drop-in cams should remain aligned with the needle bar line. From a microscopic viewpoint, it becomes evident that the actual sagging arc of the new coil consistently exceeds the needle-back line in the tiger's mouth, resulting in the new coil's sagging arc being under constant tension during the weaving process. While the impact of large-diameter thread loops may not be significant when weaving delicate fabrics, it becomes problematic with thicker fabrics, as the smaller circumference of the loops can easily lead to defects such as holes. Therefore, the selection of this type of curved drafting cam technique should not solely rely on aligning the tiger's mouth with the needle and the thread behind it. In practice, a certain distance should be maintained outward from the line of the tiger's mouth and the needle during installation.

3.If the gauge is adjusted to align with the needle back line at point T, it should remain fixed in that position until the shuttle begins its ascent from the loop formation to its highest point. Throughout this movement, the gauge’s mouth should be positioned outside the needle back line, except at the moment it aligns with the needle back line as the shuttle starts to rise. At this point, the new coil’s sagging arc, even if briefly subjected to load, would not significantly impact the weaving process due to the mutual force transfer between the strands. Therefore, for the curve illustrated, the positioning of the trapezoidal plates for entry and exit should be determined based on the installation guideline that the trapezoidal plates align with the needle’s back line during workshop adjustments.

4.From a microeconomic perspective:
The shape of the tiger’s mouth in the sinker resembles a semicircular arc, with one end of the arc coinciding with the blade jaw. As shown in Figure 2, the weaving process involves a curve of the yarn along the plate jaw. Before the shuttle completes its loop and begins to rise to the level of the plate jaw, if the sinker is pushed down to align with the needle line, the descent arc of the new loop does not reach the deepest point of the sinker but instead lies somewhere along the curved surface between the sinker plate and the plate jaw. This point is positioned away from the needle line, and the sinker of the new coil experiences load at this location unless the cleft shape is rectangular, which may allow it to align with the needle line. The unaccounted descent of the triangular curve of the sinker is significant. Currently, the most common sinker curve cams for single jersey machines on the market can be broadly classified into two types. The dashed line represents an arc that passes through the center of the syringe and intersects cam S on the sinker.

5. If the needle bar line is used as the reference point for installing the sinker cams, then throughout the entire process of following curve 4a, from the moment the weaving needles complete their weft thread until they exit the loop and reach their highest point, the jaws of the sinker must consistently align with the needle bar line. From a microscopic perspective, it is evident that the actual sagging arc of the new coil consistently exceeds the needle knot line in the tiger's mouth, resulting in the new coil's sagging arc being under continuous load during the weaving process. While this effect may not be noticeable when weaving delicate fabrics due to the larger loop lengths, it can lead to issues such as holes when working with thicker fabrics, where the smaller loop lengths are more susceptible to imperfections. Therefore, when determining the sewing pattern for these curves, the alignment of the tiger's mouth with the needle line should not be the sole criterion. During installation, the needle should be positioned slightly outward from the tiger's mouth, aligning with the back line.

If the tiger's mouth is adjusted to align with the needle back line, from the moment the weaving needle begins to unwind the warp thread until it reaches its highest point before descending, the slotted mouth of the tiger should be positioned ten millimeters outside the needle back line, except when it coincides with the needle back line as the weaving needle starts to rise (at point T). At this stage, even if the new coil's sagging arc is momentarily subjected to force, it would not significantly impact the weaving process due to the mutual force transfer between the coils. Thus, for curve 4b, the positioning of the sinker cams for entry and exit should be based on the installation reference point where the sinker cams align with the needle line and the back line of the sinker at point T.

6. A change in the machine number indicates a variation in the needle pitch, which is reflected in the fabric as a change in the sagging arc of the weft threads. A longer settling arc length corresponds to a higher machine number, while a shorter settling arc length corresponds to a lower machine number. Additionally, as the machine number increases, the allowable line density for weaving decreases, resulting in lower yarn strength and shorter lengths. Even minor forces can alter the shape of the loop, particularly when weaving polyurethane fabrics.