Weft Accumulator or Feeder in Weaving

What is Weft Accumulator?

Weft accumulator or feeder is used to wind a predetermined yarn length to make it ready for insertion. It plays an important role in the weaving machines for supplying weft yarns at high speed to ensure high productivity and high-quality fabrics. Even though the weft packages are dispensed with in a shuttleless system, it becomes necessary to measure the weft yarn required for each pick and kept ready for inser­tion. For this purpose, weft accumulators are used in shuttleless weav­ing. The main function of the weft accumulators is to unwind the yarn from the larger yarn package and supply to the weaving machine smoothly at constant and proper tension. Maximum speed of weft insertion depends on the yarn count range. The weft insertion velocities for various insertion systems are given in Figure 1.

Weft is inserted during a fraction of the pick cycle. Ever since the successful introduction of the different weft insertion systems without shuttle, the prime aim has been to increase the speed of the loom to achieve higher weaving productivity. As the speed of the loom increases so does the weft velocity. The weft velocity depends on its driving force which again, is determined by the type of weft insertion system and the structural design of the machine.

High insertion speeds of weft associated with the different types of shuttleless weaving machines impose high stresses on the weft yarns and at certain phases undesirably high tension peaks. The consequent effects of these are increased weft breakage and/or disruption of the surface layer of the weft package if the yarn is drawn directly from it. Moreover, if the weft is made to be withdrawn directly from the package, withdrawal tension of the weft will be influenced significantly by the package parameters and the resultant variations in weft tension will affect the insertion of the pick. All these will have adverse effects on the weaving performances of the looms and the qualities of the fabrics produced and much of the purpose of the shuttleless picking system will be foiled. To solve these problems a suitable weft storage system known as weft accumulator or weft feeder is interposed between the weft package and the weft picking mechanism of the shuttleless weaving machine. A weft accumulator is shown in Figure 2.

Purposes of Weft Accumulator System in Weaving:

Their main purpose is to supply filling yarn to the weaving machine smoothly and at a constant and proper tension. Weft accumulator system should fulfill the following purposes :

1. As the weft is unwound from its supply package a minimum suitable tension, free of impacts, must be applied to it,
2. The system must allow an easy withdrawal of the weft from the prepared weft supply package, and
3. The passage of the weft through the feeder must be smooth and continuous and it must allow easy rethreading of the weft when it breaks between the package and the accumulator.

It should, however, be remembered that a weft accumulator with proper adjustments and settings can minimize the problems of weft tensions associated with weaving machine or yarn or package but cannot resolve them on its own. Leaving the weft accumulator as the yarn enters the picking area of the weaving machine, it is still subjected to increased tension due to yarn guides, tensioners or braking units and also yarn acceleration. etc. Moreover, all types of weft accumulator cannot control the weft tension variations in identical manner.

Characteristics of Weft Accumulator:

Typical characteristics of these machines are:

1. One-step pneumatic threading up
2. Integrated yarn break sensor
3. Floating element yarn store sensors
4. Stepless yarn separation adjustment
5. Microprocessor controlled speed and motor effect
6. Sealed spool body
7. S/Z rotation shifting
8. Insertion speeds up to 2000 m/min
9. Serial communication interface

The selection of a feeder depends on several factors:

• Maximum speed delivered
• Yarn count
• Winding direction (S or Z)
• Yarn reserve control

Types of Weft Accumulator in Weaving:

There are basically two types of weft accumulator in weaving:

1. Drum storage accumulator
2. Loop storage accumulator

1. Drum Storage Accumulator:

The weft yarn from the supply package is drawn at a constant rate and wound on a highly polished metal cylindrical body. During weft insertion, the coils are free to be pulled off. A tensioner is provided between the drum and the supply package. A stopper is provided between the weft insertion element and the drum to prevent extra supply of weft yarn over than necessary for one pick. Figure 3 shows the schematic of drum storage–type weft accumulator.

When yarn guide 7 rotates around storage drum 4, yarn is taken from supply package 1 through tensioner 3 and wound on the storage drum. As the yarn is with­drawn during picking, the tension in the yarn is controlled by the braking device. Different types of braking devices, such as bristle, metal lamella, fex brake and endless beryllium copper tensioning strips, are used.

2. Loop Storage Accumulator:

In a loop storage accumulator, a measuring roller draws the weft from the supply package at a constant rate, and this yarn is stored in the form of a loop in a tube with the help of suction. Figure 4 shows a loop storage type accumulator. This type of accumulator is not used anymore.

The loop storage is suitable for air-jet picking, but it requires a large space, especially for wide looms and faces some problems in controlling the wefts of high twist or high stiffness. For these reasons weft accumulator of drum type is more universally accepted in the shuttleless looms of all types of weft insertion systems.

Advantages of Weft Accumulator in Weaving:

By maintaining proper coordination with weft insertion, the weft accumulator ensures high weaving performance by reducing the chances of weft break and lowering the yarn waste. The weft storage system assists particularly the jet picking where the weft is inserted by drag force of air or water and the weft velocity is so high that the jet cannot have the ability to pull the weft intermittently from the supply package overcoming the severe retarding force to its own velocity.

Advantages of weft accumulator are:

1. A decrease in the average tension during weft insertion.
2. Fewer weft breakages.
3. Equalization of unwinding yarn tension due to the diminishing diameter of weft supply package.
4. The equalization of uneven unwinding characteristic of weft package of dif­ferent types.
5. Compensate for different withdrawal conditions when using different weft packages, and
6. Prevent sloughing-off of the yarns from the package.

References:

1. Fabric Manufacturing Technology: Weaving and Knitting by K. Thangamani and S. Sundaresan
2. Role of Yarn Tension in Weaving by Samir Kumar Neogi
3. Handbook of Weaving by Sabit Adanur

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