Study on Tappet Shedding Mechanism

The tappet shedding mechanism is one of the primary methods of shed formation used in traditional and modern looms, especially for creating simple weaves. This mechanism is integral in controlling the movement of warp yarns to form the shed – the opening that allows the shuttle (or other weft insertion devices) to pass through and interlace the weft with the warp. The tappet shedding mechanism is widely used in producing plain and twill fabrics, offering efficient, reliable, and straightforward operations that are ideal for high-speed weaving.

This article will explore the tappet shedding mechanism, its components, working principles, advantages, and applications in weaving. Understanding this mechanism provides insight into how looms produce basic woven structures and how modifications can enhance textile production efficiency.

 

Importance of Shedding Mechanisms in Weaving

In weaving, shedding is the first step of the primary motions, allowing the loom to create an opening in the warp threads for the weft insertion. Proper shed formation is essential for efficient weaving, as it enables smooth shuttle passage, reduces yarn breakage, and ensures consistent fabric quality. Shedding mechanisms, like the tappet mechanism, help achieve controlled movement of warp yarns to create patterns and maintain uniform interlacing of yarns throughout the weaving process.

 

Components of the Tappet Shedding Mechanism

The tappet shedding mechanism has several key components that work together to move the warp yarns up and down in a predetermined pattern. The main components include:

1. Tappets:
• Tappets, also known as cams, are the heart of this mechanism. These are disc-like structures with specially designed profiles or shapes. The tappet's profile determines the movement of the heald shafts, dictating the weave pattern. The shape and contour of the tappet decide the lifting and lowering of specific warp threads, allowing patterns like plain and twill weaves.
2. Cam Shaft:
• The cam shaft is a rotating shaft on which the tappets are mounted. It provides the rotational motion that drives the tappets, which in turn move the heald shafts. The cam shaft’s speed and rotation synchronize with the other parts of the loom, maintaining a seamless flow in the weaving cycle.
3. Rollers and Followers:
• Rollers (also called followers) are attached to the tappets. As the tappet rotates, the roller or follower follows the contour of the tappet, translating the rotating motion into vertical movement. This vertical motion is then transferred to the heald shaft, raising or lowering it to create the shed.
4. Heald Shaft (or Harness):
• The heald shaft holds the heald wires, which have eyelets through which individual warp yarns pass. Each tappet controls a specific heald shaft, raising or lowering it based on the tappet’s contour. This vertical movement of the heald shafts results in the opening or closing of the shed.
5. Connecting Rods and Levers:
• The motion generated by the tappets is transmitted to the heald shafts through connecting rods and levers. These connecting parts ensure that the movement from the tappets is precisely transferred to the heald shafts, maintaining accurate shed formation.

 

Working Principle of the Tappet Shedding Mechanism

The tappet shedding mechanism operates by converting rotational motion into linear motion to raise or lower the heald shafts and form the shed. Here’s how the tappet shedding mechanism works:

1. Rotation of Cam Shaft:
• The cam shaft rotates continuously during the weaving process, driven by the loom’s main motor. As it rotates, it causes the tappets mounted on it to turn, creating movement in the followers or rollers that rest on the tappet profiles.
2. Contour-Based Motion of Tappets:
• Each tappet has a unique contour that corresponds to a specific pattern. As the tappet rotates, its profile moves the roller or follower up and down. This motion pattern directly influences the vertical movement of the heald shaft, creating either an open or closed shed depending on the tappet’s shape.
3. Heald Shaft Movement:
• The movement generated by the tappet is transferred to the heald shaft via levers and connecting rods. The heald shaft, which holds the warp yarns, then moves up or down to form the shed. This action is synchronized with the shuttle’s movement so that the weft yarn can pass through the shed without any interference from the warp threads.
4. Shed Formation:
• As the tappet-driven heald shafts raise and lower warp yarns, they create an alternating shed for each weaving cycle. The tappet design determines the lifting pattern, enabling specific weave designs like plain or twill weaves. The shed closes after each weft insertion, locking the weft yarn in place and preparing for the next cycle.

 

Types of Tappet Shedding Mechanisms

The tappet shedding mechanism can be customized to produce different types of weave patterns. Some common types of tappet shedding mechanisms are:

1. Plain Tappet:
• A plain tappet is designed for simple weaves like the plain weave, where each warp yarn alternates over and under each weft yarn. This tappet has a straightforward contour that enables regular, equal raising and lowering of warp threads, making it ideal for basic fabrics.
2. Twill Tappet:
• Twill tappets have a more complex profile, allowing them to lift warp threads in a sequence that creates diagonal lines, characteristic of twill weaves. The shape of the tappet contour is designed to produce a specific lifting order, creating the distinctive twill pattern in the fabric.
3. Multiple-Shaft Tappet:
• For more intricate patterns, multiple tappets can be used to control additional heald shafts, allowing for variations in patterning. This setup is common in looms producing small repeat designs that require more than two shafts but do not necessitate advanced shedding mechanisms like dobby or jacquard.

 

Advantages of the Tappet Shedding Mechanism

The tappet shedding mechanism offers several advantages, especially for simple weave structures:

1. Cost-Effectiveness:
• Tappet shedding mechanisms are relatively simple in design and low in cost, making them a budget-friendly option for producing basic weaves.
2. High-Speed Weaving:
• Tappet mechanisms are highly efficient at high speeds, allowing for fast fabric production rates. This makes them ideal for bulk manufacturing of plain and twill weaves.
3. Durability and Low Maintenance:
• Due to their simple design, tappet mechanisms are durable and require less maintenance compared to more complex shedding systems. This contributes to reduced downtime and lower operational costs.
4. Consistency in Fabric Quality:
• The tappet mechanism provides consistent shed formation, which ensures uniform fabric quality and reduces the likelihood of weaving defects.

 

Limitations of the Tappet Shedding Mechanism

While the tappet shedding mechanism is highly effective for basic weaves, it has some limitations:

1. Limited Design Capabilities:
• Tappet mechanisms are best suited for simple patterns like plain and twill weaves. For more complex designs, such as intricate geometric or large-scale patterns, more advanced mechanisms like dobby or jacquard are needed.
2. Shaft Limitations:
• Tappet mechanisms typically control only a limited number of heald shafts (usually between 2 and 8), restricting the variety of patterns they can produce.
3. Mechanical Wear:
• Continuous high-speed operation can lead to wear in the tappet contours, affecting the accuracy of the shed formation over time. Regular maintenance is required to prevent degradation in pattern precision.

 

Applications of the Tappet Shedding Mechanism

The tappet shedding mechanism is widely used in the production of:

• Basic Fabrics: Plain weave fabrics, which are widely used in various applications, from apparel to home textiles.
• Twill Fabrics: Twill weaves, known for their durability and diagonal structure, are used in denim, workwear, and upholstery fabrics.
• Bulk Production of Simple Weaves: Tappet looms are highly productive, making them suitable for large-scale manufacturing of basic fabric types.

 

Conclusion

The tappet shedding mechanism is an essential component in textile weaving, enabling the efficient and high-speed production of simple weaves like plain and twill fabrics. Its straightforward design, durability, and cost-effectiveness make it an ideal choice for bulk manufacturing applications. However, while the tappet mechanism excels at basic patterns, its limitations in design complexity mean that more intricate fabric patterns require advanced shedding mechanisms.

Understanding the tappet shedding mechanism's principles, components, and advantages allows weavers and textile professionals to optimize loom operations, maintain consistent fabric quality, and make informed choices when selecting weaving equipment for specific production requirements. With its balance of simplicity and efficiency, the tappet shedding mechanism remains a valuable tool in the textile industry, supporting a wide range of everyday fabric applications.