Monday, December 17, 2018

STARTING MARKS, CRACKS IN THE FABRIC, DENSE MARK, A FABRIC DEFECT, A WEAVING DEFECT, CAUSES, AND REMEDIES

STARTING MARKS, CRACKS IN THE FABRIC, DENSE MARK, A FABRIC DEFECT, A WEAVING DEFECT, CAUSES, AND REMEDIES:

Starting mark is a fabric defect which appears along the weft direction and across the full width of the fabric. Sometimes it can appear in partial width of the fabric too. "The starting mark in  the fabric can be defined as a defect appearing in the fabric either across the full width of the fabric or partial width of the fabric just after restarting the loom due to the variation of the pick density at the place where loom was stopped. This defect appears in the form of weft bars in the fabric".

Normally, this defect does not appear in the heavyweight fabrics (high cover factor). When the fabric is woven with low ends per inch and picks per inch, then there is always a chance of appearing the starting marks in the fabric during weaving.

There are two kinds of starting marks appeared in the fabric during weaving:

Dense mark:  

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.



Cracks (open marks): 

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.



Now a question arises in the weaver’s mind why does this defect appear in the fabric? This defect occurs in the fabric due disturbance in the position of the fell of the cloth during the starting period or even stopped position of the loom. The position of the fell of the cloth either displaced toward the reed or away from the reed. If the position of the fell of the cloth displaces toward the reed, then the dense mark appears in the fabric. If the position of the fell of the cloth displaces away from the reed, then a crack (open mark) in the fabric appears.

"Please note that the starting marks can appear in the fabric during continuous working condition too. The problem of the starting marks generally appears in the old looms due to the aging of the bearings, gears, and other loom parts. This problem may also occur in the new looms due to incorrect loom settings".

The major factors influencing the starting marks frequency are being given below:

Loom brake efficiency: 

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.
If the loom does not take extra empty revolution after stoppage but it stops at different loom angles after each stoppage. In this case, the warp tension influences up to some extent. This warp tension variation results starting marks in the fabric.

A weaver should always be aware of this kind of situation. He should make sure that loom is being stopped at a correct angle after each loom stoppage. If any type of deviation is observed in the loom stopping angle, or the extra empty revolutions after loom stoppage identified, then loom brake setting should make correctly. Sometimes the loom brake liner is worn out due to aging and it is not possible to achieve desired settings. In this kind of situation, the brake liner should be replaced by a new one. When the loom stops after yarn breakage, the slow motion motor always helps to bring the loom at correct loom angle position automatically. Weaver should always make sure that this automatic function is working properly.

Efficiency of warp let-off motion: 

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.

If loom is too old, the bearings can get worn out. The clearance between gears is increased due to friction after a long time. This problem results starting mark in the fabric. The bearings and gears should be lubricated regularly as per loom manufacturer’s recommendations. The bearings and gears should be replaced if required. The bearings of beam adopter should be lubricated before each beam change. The beam gear should be tightened properly. The beam adopter shaft key should not have more clearance in beam gear slot than required.

Efficiency of cloth take-up motion: 

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.

The setting of temples: 

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).

Efficiency and setting of easing motion: 

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.
There is not any fixed setting of spring tension of easing motion. If the starting mark problem occurs, the spring tension can be either increased or decreased according to the nature of the starting mark. If you observe that spring mounted on the easing motion is not suitable for the fabric quality which you are weaving, then you can replace it with a heavy or light spring.

The setting of height and depth of backrest rollers also helps to prevent starting marks. Technician requires a lot of patience to achieve the correct setting. The height of the warp stop motion stand is also adjusted as per requirement to prevent the starting marks.
The technician should make sure that there is no bear and tear in the bearings of easing motion. The backrest rollers should rotate freely.

Shed opening and crossing: 

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.

Irregular beating motion: 

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.


"Please note that today’s looms are equipped with computerize starting marks preventing the procedure. This system is very useful and effective. The programme is configured as per the nature of the starting mark. The warp tension can be programmed separately for weft stop or other stops. The warp tension can be increased or decreased automatically with the help of the starting mark preventing procedure as per requirement just before the restarting of the loom. This warp tension is adjusted according to the observation taken by a loom technician.The take-up roller can move forward or backward direction as per nature of the starting mark. It can be programmed separately for weft stop and other stops. The setting of the reverse or forward pick is selected according to the observation of the loom technician. The automatic warp tension recovery and automatic movement (reverse or forward) of take-up motion can be selected together if required". 

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

Abrasion Marks in the fabric        

Size marks in the fabric, a fabric defect    

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