Basic Weaving Operations
No matter what type of weaving is being done, four major operations are performed in sequence and are continuously repeated.
In shedding, alternate warp yarns are raised to insert the filling yarn into the warp to form a shed. Shedding is automatically performed by the harness on the modern weaving looms. Harness is a rectangular frame to which a series of wires, called heddles, are attached. As each warp yarn comes from the warp beam, it passes through an opening in the heddle. The operation of drawing each warp yarn through its appropriate heddle eye is known as drawing in.
As the warp yarns are raised through shedding, the weft yarn is inserted through the shed by a carrier device. A single crossing of the filling from one side of the loom to the other is called a pick. Different methods are used for carrying the filling yarn through the shed in different kinds of looms. There are many types of looms including shuttle loom, shuttle less loom, and circular loom.
This weaving operation is also called battening. In it, all warp yarns pass through the heddle eyelets and through openings in another frame that looks like a comb and is known as reed. With each picking operation, the reed pushes or beats each weft yarn against the portion of the fabric that has already been formed. It results in a firm and compact fabric construction.
Taking Up and Letting Off
As the shedding, picking and battening processes are being operated, the new fabric is wound on the cloth beam. This is known as 'taking up'. At the same time, the warp yarns are released from the warp beam which is known as 'letting off'.
The pattern of the weave depends on the manner in which groups of warped yarns are raised by the harnesses to allow the insertion of the weft yarn. These differences are responsible for producing different types of fabric weaves. Weave patterns can create various degrees of durability in fabrics apart from their utility and looks.
The warp threads wound on a beam (1) are bent on the back rest roller (2), support special drop wires (3), pass through the healds (5) and through the dents of the reed (8) fastened to the slay (7), along which the vehicle transporting the weft runs (9). The fabric produced is then drawn by a take-down roller(10) and wound on the cloth beam (11). Fig. 35 shows also the motor driving the warp let-off (4) and the motor driving the fabric take- down (6).
Actually the research work on the shuttle loom was dropped in the first half of the 70’s, with the arrival on the market and the prevalence of systems using for weft insertion other ways than the shuttle. The new shuttleless machines are simply called ″weaving machines″, this term implying looms working without shuttle.
The weaving machines present following advantages over traditional looms:
- Total elimination of any spooling operation
- Production increase, thanks to the fact that these machines can work at high speed, owing to the reduction or elimination of moving masses
- Reduction of the shed size, therefore lower tension of the warp threads and consequently reduction in the number of yarn breaks
- Noise reduction thanks to the elimination of the shuttle pick
- Automation of various devices.
On the basis of the system used for weft insertion, the weaving machines can be divided into:
- machines with mechanical weft
- by rigid rapiers
- by flexible rapiers
- by projectiles
- machines with non-mechanical weft
- by jets of compressed air
- by jets of compressed water
Furthermore the machines can be divided into:
- mono-phase weaving machines (inserting one weft at a time)
- multi-phase weaving machines (inserting several wefts at a time)