What Are Plies and Ply Adhesion?

Some conveyor belting is manufactured with one ply of fabric. This fabric layer can be coated with rubber, polymer or elastomer. Yet, most conveyor belting is manufactured using two or more plies of fabric that are adhered to each other by using inner layers of rubber, polymer or elastomer.

In addition, there can be top or bottom surface covers of rubber, polymer or elastomer.

While ply adhesion is defined as the force required to separate two adjoining plies, the reality is that ply adhesion is the force required to pull apart the adhesion that joins the plies. This is measured in pounds per inch or newtons per millimeter.

In the context of conveyor belts, “plies” refer to the layers of fabric or reinforcement material used to compose the belt carcass. Ply adhesion, on the other hand, is the bonding strength between these layers. Understanding these terms is crucial when evaluating the construction and performance of conveyor belts.

Plies: Conveyor belts consist of multiple layers, and these layers collectively form the belt carcass. Each layer, known as a ply, serves a specific purpose in providing strength, flexibility, and durability to the conveyor belt. The primary components of a conveyor belt include:

1. Cover: The outer layer that comes in direct contact with the conveyed material. It protects the belt carcass from external factors such as abrasion, impact, and environmental conditions.
2. Carcass (Ply): The core structure of the belt, comprising layers of fabric or other reinforcing materials. The carcass provides the tensile strength required to withstand the forces involved in conveying materials.
3. Bottom Cover: The inner layer that protects the carcass from contact with the pulleys and other mechanical components of the conveyor system.

Ply Adhesion: Ply adhesion is the measure of the bond strength between the individual layers (plies) within the conveyor belt carcass. It is crucial for the overall durability and performance of the belt. Adequate ply adhesion ensures that the layers remain securely bonded under various operating conditions, preventing delamination and maintaining the structural integrity of the belt.

Factors Influencing Ply Adhesion: Several factors contribute to the ply adhesion of conveyor belts:

1. Adhesive Quality: The type and quality of adhesive used in bonding the plies play a significant role. High-quality adhesives are essential for ensuring strong and durable ply adhesion.
2. Fabric Type: Different types of fabrics, such as polyester, nylon, or aramid, are used in conveyor belt carcasses. The choice of fabric can impact the overall strength and adhesion properties.
3. Manufacturing Process: The methods and processes used during belt manufacturing, including curing and vulcanization, can influence ply adhesion.
4. Environmental Conditions: Factors like temperature, humidity, and exposure to chemicals can affect the adhesion properties over time.

Importance of Ply Adhesion:

1. Durability: Proper ply adhesion is crucial for the long-term durability and reliability of the conveyor belt. Weak adhesion can lead to premature failure and delamination of the belt.
2. Operational Safety: Adequate ply adhesion is essential for maintaining the structural integrity of the belt under the stresses and loads imposed during conveyor operation, ensuring safe and efficient material handling.

Conveyor belt manufacturers pay close attention to achieving optimal ply adhesion during the manufacturing process to deliver high-performance belts that meet the demands of various industries. Regular inspection and maintenance practices also help monitor the condition of the ply adhesion to ensure the continued reliability of conveyor belts.

Conveyor belts operate on equipment that requires flexing over pulleys on the conveyor. This repeated flexing action will stress the ply adhesion of conveyor belts. As a result, it is important for the belt to have adequate ply adhesion to resist ply separation.

(the bottom ply bends over a smaller radius)

The test for ply adhesion is a “pull test” and can be accomplished with a simple clamping device and a fish scale. The test for ply adhesion is usually done on 1” wide x 8” long samples. Multiple samples of the product should be tested and tests should be conducted on the samples from both directions in order to achieve statistical measurements. Belt manufacturing processes can produce different measurements depending on direction of pull

In general terms, ply adhesion of less than 13-lbs per inch of width is considered unacceptably low. Ply adhesion of more than 50-lbs per inch of width is considered very high and can create challenges in belt fabrications where the plies need to be separated manually.

Synthetic fabrics (i.e. polyester, nylon) are often treated with RFL (resorcinol formaldehyde latex) during manufacturing in order to increase the ply adhesion because, without this treatment, the synthetic fabrics are too smooth and too resistant to effectively absorb the polymer, elastomer or rubber in a manner that achieves acceptable ply adhesion. Cotton, by contrast, is coarser and more absorbent, therefore not requiring RFL treatment to achieve acceptable ply adhesion.

Examples of Minimum Adhesion Standards in Umar Farooq Belting’ Belts

• 14-lbs/inch Untreated Polyester- Poly Flake, Sno Cone, TevTex 22M & 32M
• 18-lbs/inch Untreated Cotton/Nylon – HSW, 144 TevTex
• 18-lbs/inch Untreated Cotton Polyester – 28 NOS, Nytop
• 22-lbs/inch RFL Treated Polyester Econo- Rough Black, Food King 3W
• RFL Treated Polyester/Nylon- 3XLN, 143 Ruff Tex, 415-N, Food King 1W