Modern Weaving

Modern Weaving - Shuttleless Weaving

Modern weaving machines stand out as an expensive class compared to conventional machines in terms of capital investment. This basic difference requires certain prerequisites to be considered while planning to venture into modern weaving machines.

The quality of yarn used on shuttleless looms is the prime criteria considered for quality weaving. The machine parameters to be controlled for an optimised preparatory operation have been dealt with respect to winding, war ping and sizing operations. Guidelines for machine stoppages corresponding to warp and weft breakages in weaving are considered as important in deciding the efficiency of a shuttless weaving shed.

Introduction

For the successful installation of shuttleless looms, it becomes inevitable to go for quality yarn and optimization of the preparatory operations prior to weaving. A better quality yarn leads to a quality war p and sized beam which consequentially gives and efficient weaving operation both qualitatively and quantitatively. The parameters to be checked as regards yarn quality, winding of warp and weft yarns, warping and sizing are dealt with in some detail in the following sections.

Advances In Weaving Technolgy And Looms

Advances in Weaving Technology

The emphasis on productivity and quality has developed the weaving technology very much and as a result the working hours required to weave fabric from loom have been reduced from about 20 to 0.25 during the last 125 years, and in the last 50 years there has been a reduction of 95% in operative hours per standard unit produced. Majority of the developments are taking place on the shuttleless looms in the following directions :

• To increase productivity of the loom.

• To make the looms more flexible for different kinds of fabric.

• To reduce the down time for changing style, etc.

• Application of electronic control mechanisms to increase automation

• Development of accessories such as dobby, jacquards, etc.

In addition to these, the newer looms are simple in design, the motions are more reliable, consumes less energy and have lower maintenance cost.

The Principles Of Weaving

The Major components of the loom are the warp beam, heddles, harnesses, shuttle, reed and takeup roll. In the loom, yarn processing includes shedding, picking, battening and taking-up operations

Shedding

Shedding is the raising of the warp yarns to form a shed through which the filling yarn, carried by the shuttle, can be inserted. The shed is the vertical space between the raised and unraised warp yarns. On the modern loom, simple and intricate shedding operations are performed automatically by the heddle or heald frame, also known as a harness. This is a rectangular frame to which a series of wires, called heddles or healds, are attached. The yarns are passed through the eye holes of the heddles, which hang vertically from the harnesses. The weave pattern determines which harness controls which warp yarns, and the number of harnesses used depends on the complexity of the weave. Two common methods of controlling the heddles are dobbies and a Jacquard Head.

Picking

As the harnesses raise the heddles or healds, which raise the warp yarns, the shed is created. The filling yarn in inserted through the shed by a small carrier device called a shuttle. The shuttle is normally pointed at each end to allow passage through the shed. In a traditional shuttle loom, the filling yarn is wound onto a quill, which in turn is mounted in the shuttle. The filling yarn emerges through a hole in the shuttle as it moves across the loom. A single crossing of the shuttle from one side of the loom to the other is known as a pick. As the shuttle moves back and forth across the shed, it weaves an edge, or selvage, on each side of the fabric to prevent the fabric from raveling.

Battening

As the shuttle moves across the loom laying down the fill yarn, it also passes through openings in another frame called a reed (which resembles a comb). With each picking operation, the reed presses or battens each filling yarn against the portion of the fabric that has already been formed. The point where the fabric is formed is called the fell. Conventional shuttle looms can operate at speeds of about 150 to 160 picks per minute.

With each weaving operation, the newly constructed fabric must be wound on a cloth beam. This process is called taking up. At the same time, the warp yarns must be let off or released from the warp beams. To become fully automatic, a loom needs a filling stop motion which will brake the loom, if the weft thread breaks

For all this to happen, the yarn has to be prepared. The weft, or filling must be wound tightly on the correct size pirns, quills or bobbins. Weaving happens at great speed so the yarn must be at the correct tension when it leaves the shuttle. The warp passes through the heddles which stretch it at each pick, and through the reeds which are abrasive. The warp is thus sized, that is coated with a mixture that can include china clay and flour, to give it extra strength and to act as a lubricant. It is dressed or wetted while passing through the loom. The warp, hundreds of ends of yarn rolled in parallel, comes on a wooden beam. Before weaving can commence each end must be passed through the heddles and and reeds, a process known as looming.

Overview of Weaving

The weaving is a process of formation of fabric with interlacement of two or more sets of yarns using a stable machine called loom. Human beings have started using the woven fabrics since the drawn of history. If we exclude the stone age period, we may conveniently say the history of civilization is also, to some extent, the history of weaving. Aitken says there is evidence that the Egyptians made woven fabrics over 6000 years ago. Though primitive civilizations used coarser threads to make fabrics which were crude and coarse, there are references of fine fabrics made from filament of silk in China. Silk was one of the most important product in China 4000 years ago. In India too, there existed some of the finest hand woven fabrics.