Main Base Frame

Function

The rigidity of the base frame directly affects drum alignment, riding-ring wear pattern, and drive component life. Frame deflection greater than the design limit — typically L/1,000 of the frame span — causes misalignment between the two trunnion roller stations, producing differential wear on the riding rings and angular misalignment loads in the drive chain or friction wheel assembly. A well-designed frame also provides accurately located mounting pads for the thrust roller assembly that controls drum axial position. For mobile plants, the frame must resist racking loads during road transport, making diagonal bracing and fully stress-relieved all-welded construction essential.

Construction & quality

Fabricated from IS 2062 Gr B / ASTM A36 structural steel. Primary longitudinal beams: ISMB 450–600 or equivalent UB I-sections. Cross-members: ISMB 300–400 at 800–1,200 mm spacing. All primary joints are full-penetration butt-welded and double-fillet welded on all faces; after fabrication the frame is thermally stress-relieved or vibration stress-relieved. Trunnion-roller mounting pads are face-milled to ±0.5 mm co-planarity across all four pad surfaces simultaneously. Anchor bolt pockets and levelling jack pads are drilled and tapped to OEM specification. Frame is fully grit-blasted to Sa 2.5 and finished in an epoxy-polyurethane system: two coats primer (75 µm DFT each), one topcoat (50 µm DFT), rated to C3–C4 corrosivity category.

When to replace

• Visible cracking at cross-member-to-longitudinal-beam weld junctions from fatigue loading
• Trunnion pad deformation or surface indentation from overloading or improper trunnion bolt torque
• Frame sag or deflection measurable between support points exceeding the L/1,000 design limit
• Corrosion pitting at anchor bolt pockets or inside hollow cross-member sections in high-humidity environments
• Loose or fractured anchor bolts allowing frame movement relative to the concrete plinth