When the picks per in the fabric is increased at a particular place (the place just after re-starting of the loom). A weft bar appears in the fabric. This weft bar is known as a dense mark. See below graphic.
When the picks per in the fabric is decreased at a particular place (the place just after re-starting of the loom). A weft bar appears in the fabric. This defect or weft bar is known a crack (open mark). See below graphic.
The efficiency of the loom brake is a major and very common reason of appearing the starting mark. When the weft or warp breakages occur, every loom stops just after one or two empty revolutions of loom according to the loom configuration. If the loom brake does not work correctly, then the loom stops at a different angle every time. The loom takes more empty revolutions than configured in the control software. Now weaver requires to recover the position of the fell of the cloth by pick – finding the procedure. The weaver needs to reverse the loom for more empty picks. Due to extra pick finding, the position of the fell of the cloth is disturbed. There is always a chance of appearing the crack or open mark in the fabric. These cracks appear prominently in the fabric.
Today’s looms are equipped with electronically controlled warp let-off motion. This kind of let- off motion is very effective and efficient. Since new loom has no bear and tear in the gears, bearings servo motor and warp tension sensor, therefore chances of warp tension variation are almost nil. If the starting marks still appear, then weaver should check and correct electronic settings in control software. Zero setting should always be carried after each beam change. Zero setting means the loom monitor should show zero warp tension when the warp beam is fully slackened. The total number of ends in the beam, warp count, beam width and other beam parameters should always be configured in the loom software after each beam change. Loom technician should always take extra care during each beam change.
The efficient working of cloth take-up motion always helps to prevent starting marks to be appearing in the fabric. Any kind of mechanical or electrical fault results starting marks in the fabric. The bearings, gears, emery of the take-up roller and rubber emery of pressure roller should be replaced when required.
loom temples setting is also responsible for the starting mark to be appearing in the fabric. The movement of the fabric should be free. The rings of the temples should clean and rotate freely without any interruption. If the fabric movement is interrupted by a temple, then the partial starting marks (near the selvedge of the fabric) may appear in the fabric. These partial starting marks appear in the form of cracks (open marks).
If all above-described factors are working efficiently and perfectly but starting marks are still appearing in the fabric, then the role of the easing motion comes into play. When the fabric is woven on the loom, the warp tension reaches to the minimum at shed leveling position and maximum at the fully shed opening position. When the tension reaches the minimum, the easing motion helps to maintain the required warp tension. When the warp tension reaches to maximum, the easing motion protects the warp yarn from excessive tension during the beating and other causes. When the loom stops for any reason, pick- finding device comes into action to recover the position of the fell of the cloth. Reverse pick- finding acts after each stops. Take- up and let- off moves in reverse direction. Due to the minimum required clearance among gears the take- up and let- off do not reach to the required position. Here, the easing motion tries to recover the warp tension up to the optimum limit and hence helps to prevent the starting marks to be appearing in the fabric.
The loom should be set for minimum possible shed opening position. The shed crossing timing is also adjusted. Early shed crossing timing gives a better result.
The beating motion always beat every last inserted pick regularly. If the clearance between cam and cam follower reaches to beyond than acceptable limit, it results in irregular beating action. This irregular beating generates full or partial staring marks during a continuous running situation of the loom. If the technician observes this problem, then he should replace the cam and cam follower immediately.
You may also interested in following articles:
New English count (Ne), an indirect yarn count system
Ring frame process and it's objectives
Woven fabric analysis