Prestressed PC Bar Button Heading Dies for Spun Pile Upsetting Machines

1. Common Failures

Hydraulic cold upsetting of high-tensile PC bars subjects solid forming punches to extreme axial crushing loads (50 to 200 kN). Standard tool steels frequently suffer rapid working-face deformation, premature wear, or brittle structural splitting. Flawed punching surfaces lead to eccentric button head expansion, edge flash, or material shortage, failing critical high-tonnage tensioning inspections.

2. Technical Features

ALAS button heading dies are forged from high-purity GB Cr12MoV cold-work tool steel. Vacuum heat treatment combined with precision CNC machining ensures exact concentric alignment and balanced core toughness, preventing cavity cracking during continuous high-volume production.

3. Key Technical Standards

Carbide Microstructure: Forged from vacuum-degassed Cr12MoV steel with uniform carbide distribution to prevent micro-cracking and structural failure under cyclic mechanical stress.

Coaxial Alignment: The punch cylinder holds a strict ≤0.03 mm coaxiality and perpendicularity tolerance relative to the wire axis, preventing uneven material displacement and eccentric heading.

Working Face Surface Finish: Precision ground to a standard Ra 0.8 μm to Ra 1.6 μm profile (custom mirror finishing up to Ra 0.4 μm available upon request). This eliminates dynamic tool marks, ensuring smooth button-head release without material sticking and delivering clean upset heads (1.5 to 2.0 times the bar diameter).

4. Specification Matrix

• Component Type: Button Heading Die / Pier Head Set

• Substrate Metallurgy: Forged GB Cr12MoV Steel

• Hardness: 54–58 HRC (Vacuum Quenched)

• Target Wire Range: Φ7.1 mm, Φ9.0 mm, Φ10.7 mm, Φ12.6 mm

• Primary Function: Cold-forges wire ends into concentric, full-profile anchoring button heads under 200 kN hydraulic loads.

5. Technical Troubleshooting (FAQ)

Q: What causes splitting or punch face chipping on heading dies, and how does ALAS prevent it?

A: Splitting and tool-face chipping result from excessive material brittleness or carbide segregation typical in standard box-furnace treated alloys. Under full hydraulic pressure, internal stress concentrations cause fracturing. ALAS utilizes vacuum-degassed, high-purity Cr12MoV billets combined with multi-cycle gas quenching and tempering. This refines grain boundaries and stabilizes hardness at 54–58 HRC, providing the required dynamic impact toughness to eliminate brittle cracking.

Q: Why do finished button heads occasionally display flashing, eccentricity, or material shortage?

A: This indicates that the coaxial alignment between the heading punch face and the clamping jaw V-groove has drifted, or that the mounting slot has accumulated compressed scale. A wire offset of even 0.05 mm causes asymmetrical plastic displacement, forcing material past the die split-line to form sharp flashing.
Remedy: Clear scale debris regularly with compressed air, verify clamping coaxiality within ≤0.03 mm using standard test pins, and replace clamping jaws if internal tooth wear allows wire slippage.