4 Types of Sheds in Weaving Loom: Easy Explained
What is Shed in Weaving?
In weaving, the separation of warp threads into two groups to allow the insertion of weft threads is called a shed. Different types of sheds are used depending on the loom type, yarn quality, and fabric structure. Proper shed formation helps to increase weaving efficiency. Additionally, it also helps to improve fabric quality. So, it is crucial to know the types of sheds used in the weaving loom. This article will briefly discuss the types of sheds in weaving loom and their advantages and disadvantages. Besides, one can know the uses of different types of sheds.
You may read: 3 Types of Motions of Loom: Simple Description
Types of Sheds
Basically, a shed is divided into two classes, namely, 1) a closed shed and 2) an open shed. Each type of shed is divided into two groups. Broadly, Sheds are classified into four groups. They are:
- Bottom closed shed
- Centre closed shed
- Open shed
- Semi-open shed
Now, let’s learn about the types of sheds one by one, including their advantages and disadvantages, and uses.
1. Bottom Closed Shed
| A | Represents the bottom line of warp. |
| B | The rising and falling line. |
| C | An arrow showing the space passed through. |
A bottom closed shed is formed when the warp yarns are at the same moment, forming the top/upper line. As a result, to form a top shed, it is necessary to move some threads twice as deep as the depth of the shed, once up and once down, before a fresh section is made. This type of shed is often referred to as a stationary bottom with a rising and falling top.
By reversing the order of the bottom close shed, sometimes a shed is formed with a stationary top line, imparting motion to those warp threads which are to form the lower line of the open shed. This is called a “top closed” shed.
Advantage of bottom close shed
- Bottom close shed is suitable for fine fabrics like silk fabric.
- Besides, bottom closed shedding produces cloth with good cover due to the altered tightening and slacking of warp threads.
Disadvantages of bottom close shed
- Bottom close shed takes a long time to make a change and is unsuitable for high speed.
- Further, by moving the warp threads through an excessive space, great and unequal strain is placed on them.
- The waving machine consumes a lot of power.
Uses of bottom close shed
There are certain tappets, single lift dobby, and single life jacquards that produce bottom closed shedding. But in handlooms, ordinary springs, dead weights, and bows to produce top closed shedding.
2. Centre Closed Shed
| A | The closed warp line |
| B and C | Respectively, the upper and lower lines of a divided warp |
| D and E | An arrow shows the movement of each thread to equal the depth of a shed, namely, half the distance in an upward and half in a downward direction. |
A centre closed shed is created by imparting an upward movement to the threads that form the top line and a downward movement to the threads that form the bottom line. Upon inserting the pick, both lines will then meet in the middle between the highest and lowest lines of a divided warp.
Advantages of centre closed shed
- In a centre-closed shed, every thread moves to form every shed, yet the strain is less.
- In general, it takes approximately half the time to open a shed, as the distance travelled by a thread is 1:2.
- The speed is high because rising threads are partially balanced by falling lines.
- The weaving machine uses less power.
Disadvantages of centre closed shed
- There is a high risk of yarn breakage due to rubbing.
- There is a beating up that takes place in the condition of a closed shed.
- In the formation of sheds, yarn is more strained as a result of movement.
Uses of Centre Close Shed
Many wood croft tappet, the Jamieson tapet, the Oscillating and certain other tapes, all centre shed dobbies, Jacquares and most handlooms form centre closed shed.
3. Open Shed
| A and B | The two stationary lines of warp |
| C and D | An arrow which shows the movement of rising and falling warp to equal the distance between A and B. |
| E | The fell of the cloth |
| F | Lease F form two ends of the open shed |
Open sheds have two stationary lines, a top line and a bottom line, and threads are carried from one fixed line to the other to change the fabric. There are ascending and descending threads moving from one fixed line to another. Because there is no unnecessary movement given to the warp and the falling threads help to lift the rising threads, a shed is formed in a short period of time with the least strain on the warp.
Advantages of open shed
- Stain upon the warp is less.
- It is capable of running at a high speed.
- Ascending threads help to rise the descending ones as they move simultaneously.
- It requires a minimum of time to form a shed and there is no unnecessary movement of warp threads.
- Less power is consumed.
Disadvantages of open shed
- This shed is troublesome to weavers because the two fixed shed lines make it more difficult to repair broken ends. Some effective apparatus know as “levelling apparatus” should be added to all open shedding motions to place the healds in one plane, whenever repairs become necessary, and replace them in their original postion before starting the loom.
- When the number of healds used is great, the warp in the back healds is strained and broken more than in the form one.
- As the shed always remains open, breakages may result, especially when the yarn is weak.
Uses of Open Shed
- Open shedding is obtained by the use of ordinary tappets, the Hattersley, the Climax and Knowles dobbies. Besides, this type of shed is used in double-lift Jacquards.
4. Semi-open Shed
| A | The stationary bottom |
| B | The top line |
| C | The point where downward movement ceases in threads that are to form part of the top line for the succeeding pick |
| D and E | An arrows showing the movement of through heals |
| F | F that of threads which are to lift for the next pick |
This shed retains a stationary bottom, but threads for the top line either pass to the bottom at one movement, or they pass mid-way, and then they pass to the top again. Closed and open sheds occurred simultaneously in this shed. The bottom is retained, but the top line threads are either carried to the bottom or arrested halfway and carried to the top again. As fast as an open shed, such a shed can be constructed, since upward movement begins and ends with downward movement, and the arrested downward movement is converted into upward movement as soon as the falling threads are in the same plane as the rising ones. The strain is not equally distributed among them even though they all reach the top together.
Advantages of Semi-open Shed
- Top and bottom warp lines are tensioned equally
- Every pick does not require all warp yarns to move up and down
- The beat up occurs in a cross-shed environment
- There is a possibility of running the loom faster
Disadvantage of Semi-pen shed
- It is difficult to find breakage yarn.
- There is difficulty in leveling heals.
- The strain on yarn is not evenly distributed.
Uses of Semi-open shed
Many double-lift Jacquards and certain double-lift dobbies are used semi-open shed.
These are the types of sheds used the weaving loom machine. If you have any questions about types of sheds, feel free to ask me in the below comments box.
FAQs
- What is shed in weaving?
- A shed is the opening formed between warp threads in weaving for the weft thread insert.
- Which shed is used in high-speed loom?
- Open shed is commonly used in high-speed loom.
- Why is shed formation crucial in weaving loom?
- Shed helps to insert the weft thread smoothly through the two pars of warp thread. Besides, shed also reduces yarn breakage in weaving loom. Hence, shed formation is important in weaving loom.
- Which shed consumes more energy?
- A closed shed consumes more energy owing to more yarn movement.
Reference
- Banerjee, N. (2000). Weaving Mechanism. West Bengal: Smt. Tandra Banerjee and Sri Apurba Banerjee.
- Gokarneshan, D. N. (2009). Weaving Preparation Technology. Delhi: Abhishek Publicaions.
- Gupta, R. S. (1977). Weaving Calculations . Bombay: D.B. Taraporevala Sons & Co. Private Ltd.
- V. Gordeev, P. V. (1982). Cotton Weaving. Russia: Mir Publishers Moscow.
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