ABSTRACT
In any process, if there is something wrong with its working, it leads to defects. In combing, there are basically three factors that when develop faults lead to defects in the product or in its functioning. These are: combing preparation, process parameters and shortcomings in carrying out certain settings.
A lot depends upon how a comber lap is built. There are two important factors in lap preparation. First, it is required to arrive at a minimum number of doublings – of slivers in the first preparatory machine and laps in the second preparatory machine. Along with this and equally important is the amount of draft involved in lap preparation. This is because the drafts decide the fibre orientation and parallelization. If both draft and doublings are inadequate, there will be excessive waste extracted at comber, without improving the quality.
The process parameters involve the timings and settings of important parts. Some of the following settings are important in this regard. The step gauge deciding the closeness of nippers with detaching rollers decides the boundary distance below which the fibres are supposed to be short fibres. There are some other settings which have a parallel effect – viz. quadrant setting or bowl gauge setting. The other important areas are: settings related to the top comb. These are responsible for preventing short fibres from going into sliver. There is another setting which decides the depth to which the cylinder needles can penetrate the lap fringe.
Defects such as curling of fibres in the web, holes in the web, plucking or cutting across may be owing to bad maintenance practices, wrong atmospheric conditions or top comb interference. The web not coming through the head or lap running slack may have their origin in improper feeding of the lap. Flocking of waste on cylinder needles may be due to inefficient cleaning by the brush. There is another typical defect called lap licking. It is basically due to either over-parallelization in preparatory or less humidity in the department.
Lastly, there are technological defects such as long fibres in the comber waste or short fibres in the comber sliver. They are due to bad maintenance practices or inadequate gripping of lap fringe during combing. The comber sliver has its inherent irregularity due to piecing. In addition, owing to extra softness, there is often sliver stretching. Irregularity in the sliver may also be due to the limitations of the draw-box. A good inspection can always help in noticing these defects. If detected earlier, they can save a lot of faulty material.
