Dummy Bar Bolt

Product Description

In the continuous casting process of steel manufacturing, a dummy bar bolt (also known as a disconnecting bolt or starter bolt) is a specialized, sacrificial fastener. It serves as the critical link between the dummy bar head and the newly solidified steel strand during the initial start-up phase of the caster.

The Role in Continuous Casting

The dummy bar acts as a "starter" to plug the bottom of the mold. As molten steel is poured, it solidifies around the dummy bar head and the protruding dummy bar bolt. Once the strand is sufficiently cooled and reaches the withdrawal unit, the dummy bar must be separated from the hot steel strand so the steel can continue to the cutting station.

Key Functional Requirements

1. Sacrificial Design

The bolt is designed to be the "weak point" in the assembly.

• Mechanical Disconnection: In many systems, a hydraulic or mechanical "disconnector" applies a sharp force to snap the bolt or pull it out once the strand has reached a specific point in the machine.

• Thermal Fusion: The bolt must be made of a material that allows the molten steel to partially fuse with it, ensuring the dummy bar can pull the heavy strand through the cooling chamber without slipping.

2. Specific Material Properties

The material is often a medium-carbon or low-alloy steel that matches the thermal expansion properties of the steel being cast.

• Strength: It must have high enough tensile strength to pull a strand that can weigh several tons.

• Machined Weak Points: Many industrial dummy bar bolts feature a circumferential groove (a "neck") machined into the shank. This ensures the bolt breaks at a predictable location and at a specific force, preventing damage to the expensive dummy bar head.

3. High Temperature Resistance

The bolt must maintain its structural integrity while submerged in molten steel (approximately 1500°C) for the duration of the start-up sequence, which can last several minutes.

Common Variations

Selection and Maintenance

• One-Time Use: Because these bolts are either snapped or fused into the end of the steel strand (which is later cut off as "crop end" scrap), they are treated as consumables.

• Fitment: The bolt must fit perfectly into the dummy bar head to prevent molten steel from leaking into the head's internal mechanisms, which could cause the dummy bar to "freeze" or become permanently stuck to the strand.

• Sealing: Often used in conjunction with asbestos-free packing or specialized casting powder to ensure a tight seal at the base of the mold.