What is torsional strength in baling wire?

Torsional strength measures a material’s ability to resist twisting forces without permanent deformation or breakage. It measures the baling wire’s capacity to withstand rotational stress during baling. A wire with a higher torsional strength is generally less ductile.

The torsional strength of baling wire is influenced by the type of steel, the manufacturing process, and the wire's diameter or gauge. Galvanized and black annealed wire, for example, exhibit different torsional properties due to their manufacturing processes and surface treatments.

Tensile strength and load strength are more important metrics to understand when choosing baling wire, but torsional strength can affect the wire at its tying point, since the baling wire is looped back and twisted against itself. A wire with sufficient load and tensile strength should also have sufficient torsional strength, making torsional strength a minor consideration for baling applications.

Normal baling and storage conditions shouldn’t place much torsional stress on baling wire, because the wire shouldn't be twisting during the baling process.

Torsional strength and carbon content

A wire’s carbon content affects its torsional strength. Higher carbon content means the wire has a stronger molecular structure, which enhances its torsional strength. Our black annealed wire features a 1016 carbon grade. This low carbon grade enhances its ductility and ability to stretch. Our high-tensile wire and double loop bale ties are made from 1060 and 1080 grade carbon steel respectively, providing them with superior torsional strength.

Torsional strength and manufacturing

The manufacturing process impacts a wire’s torsional strength through the following processes, which alter the wire's physical properties:

• Drawing the wire through dies to reduce its diameter and work-hardens the steel, increasing its torsional strength by aligning the lamellar cementite along the wire axis. This realignment enhances the wire's ability to withstand twisting forces.
• Annealing involves heating the wire and then slowly cooling it. This process relieves drawing stresses, increasing ductility but reducing torsional strength.
• Quenching and tempering can further refine the wire's microstructure, enhancing its torsional strength. Quenching rapidly cools the wire after it has been heated, locking the steel in a harder state. Tempering can tweak the balance between hardness and ductility, altering torsional strength.

Our baling wire is manufactured to perform beyond the normal torsional strength demands of industrial recycling machinery and storage conditions.

Torsional strength and wire gauge

The gauge (or diameter) of baling wire impacts its torsional strength. In general, as the wire gauge decreases (thicker wire), the torsional strength of the wire increases. This relationship can be explained by the following factors:

1. Polar moment of inertia. The polar moment of inertia is a geometric property that represents a material's resistance to torsional deformation. It is proportional to the fourth power of the wire's radius (r⁴). As the wire diameter increases, the polar moment of inertia increases rapidly, leading to higher torsional strength.
2. Torsional stress distribution. When a wire is subjected to torsional forces, the stress is distributed across its cross-section. In a larger diameter wire, the stress is distributed over a greater area, reducing the maximum stress experienced at any given point. This allows the wire to withstand higher torsional loads before deforming or breaking.
3. Material volume. A larger diameter wire contains more material volume, which contributes to its overall strength and resistance to torsional forces. The increased volume of steel in a thicker wire provides more resistance to twisting and deformation.

Thicker wire is generally stronger and more resistant to torsional force.

How do you calculate torsional strength?

To calculate the torsional strength of baling wire, you can use the following equation:

τ = (T × r) / J

Where:

τ (tau) = Torsional stress (Pa or psi)

T = Torque (N·m or ft·lbs)

r = Wire radius (m or ft)

J = Polar moment of inertia (m⁴ or ft⁴)

The polar moment of inertia (J) for a round wire can be calculated using:

J = (π × r⁴) / 2

Example calculation:

Let's calculate the torsional strength of a galvanized baling wire with a diameter of 3.5 mm (0.1378 in) subjected to a torque of 10 N·m (7.376 ft·lbs).

Given:

T = 10 N·m (7.376 ft·lbs)

d = 3.5 mm (0.1378 in)

r = d / 2 = 1.75 mm (0.0689 in) = 0.00175 m (0.00574 ft)

Step 1: Calculate the polar moment of inertia (J)

J = (π × r⁴) / 2

J = (π × 0.00175⁴) / 2 = 2.337 × 10⁻¹² m⁴ (1.917 × 10⁻⁹ ft⁴)

Step 2: Calculate the torsional stress (τ)

τ = (T × r) / J

τ = (10 × 0.00175) / 2.337 × 10⁻¹² = 7.486 × 10⁹ Pa (1,085,801 psi)

Baling wire with a diameter of 3.5 mm (0.1378 in) subjected to a torque of 10 N·m (7.376 ft·lbs) has a torsional strength of approximately 7.486 × 10⁹ Pa (1,085,801 psi), meaning it can resist that torsional force before permanent deformation or breakage.