Primary Motions of Loom:
These are fundamental or essential mechanisms of loom. Without these mechanisms, it is practically impossible to produce a fabric. It is for this reason that these mechanisms are called ‘primary’ weaving loom mechanism.
The primary weaving loom mechanism are three in number:
- Shedding mechanism
- Picking mechanism
- Beat-up mechanism
1. Shedding Mechanism
The shedding mechanism separates the warp threads into two layers or divisions to form a tunnel known as ‘shed’. The shed provides room for passage of the shuttle. A shed may be formed by means of tappets, dobby and jacquard.
Tappet shedding mechanism:
Generally there are two types of shedding
- Negative tappet shedding
- Positive tappet shedding
a. Negative Tappet Shedding:
In a tappet shedding mechanism, if the tappet controls only one movement, either an upward or downward movement of the healed shafts, then the shedding is known as “negative tappet shedding”. The healed shafts are returned by some external devices like springs, dead weights, rollers, etc.
b. Positive Tappet Shedding:
In a tappet shedding mechanism, if the tappet controls both upward and downward movements of the healed shafts, then the shedding is known as positive tappet shedding.
There are two types of dobby mechanisms, the negative dobby, and the positive dobby, are mainly used. In negative dobby shedding, the dobby lifts the heald frames, which are lowered by a spring motion. In positive dobby shedding, the dobby raises and lowers the heald frames, and the springs are eliminated.
When a big or complicated design is to be made in weaving, jacquard shedding is used. In this shedding, the warp ends are controlled individually by harness cords, and there are no heald frames. There will be as many cords as there are ends in the warp, which enables unlimited patterns to be woven. Jacquard machines can be mechanical or electronic with single or double lift mechanism.
2. Picking Mechanism
The process of propelling the weft yarn through the open shed by a weft insertion element continuously across the width of the loom is called picking. It is the second primary motion of loom, which is mainly classified according to the weft insertion system. In early manual looms, weft yarn was inserted by an oblong-shaped wooden element called a shuttle. Over pick or an under pick mechanism is used in conventional shuttle loom. But this picking system suffers many drawbacks such as low speed, high power consumption, high noise level, and low-quality fabric. A lot of researches have been conducted to avoid the use of shuttle in picking system to overcome this problem. The result of this is the innovation of air-jet, projectile, rapier, water jet, multiphase weft insertion system, which are also called the shuttleless loom. By using a picking mechanism, different types of yarns can be selected one after another. For making delicate cotton fabric, the conventional picking mechanism is still used with air-jet, rapier and projectile picking mechanism.
The picking mechanism passes weft thread from one selvedge of the fabric to the other through the shed by means of a shuttle, a projectile, a rapier, a needle, an air-jet or a water-jet. The inserted weft thread is known as “pick”.
Classification of picking mechanism:
Picking mechanism can be classified in different ways. Classification of picking is give below.
Following types of picking mechanism widely used:
3. Beat-up Mechanism
Beating or the beat-up mechanism beats or pushes the newly inserted length of weft thread (pick) into the already woven fabric at a point known as “fell of the cloth”. The main objective of beat-up is to maintain the proper tension of the overall fabric by letting the inserted weft yarn proceed forward with the progress of the weaving cycle.
Beat-up includes several portions of the loom, including mainly race board and sley. The lower portion of the warp yarns is in between the race board and the shuttle. The reed and race board are assembled, and it is called a sley.
These three weaving loom mechanism namely shedding, picking and then beat-up are done in sequence.
You may also like:
- Loom Motions: Primary, Secondary and Stop Motions of Loom
- Motions of Loom and Their Functions in Weaving Machine
- Different Parts of Loom and Their Functions with Pictures
- Over Picking Mechanism | How to Increase PPM
- Differences between Tappet Shedding, Dobby Shedding and Jacquard Shedding Mechanism
- Dobby Shedding Mechanism | Scope of a Dobby
- Jacquard Shedding | Jacquard Shedding Mechanism
- Beat-up Mechanism in Weaving Motion
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.