Mori Press Repair & Refurbishment

Hydraulic Cylinder Scoring

Mori's cylinder design uses a chrome-plated piston rod running in a cast iron bore with bronze guide bands. After 12-18 years of operation — particularly in environments where lubrication maintenance has been inconsistent — the chrome plating develops longitudinal scoring from particulate contamination in the hydraulic fluid. The scoring accelerates seal wear, creating a feedback loop: scored rod damages seal, damaged seal allows fluid contamination, contaminated fluid accelerates scoring. The visible symptom is a 10-15% force drop at rated pressure, accompanied by visible hydraulic fluid weeping from the cylinder gland.

Our cylinder rebuild addresses both the symptom and the root cause. The rod is removed, stripped of remaining chrome, inspected for base metal damage, re-plated with hard chrome to the original Mori specification (typically 0.05-0.08 mm plating thickness), and finish-ground to the original surface roughness (Ra 0.2-0.4 µm). The cylinder bore is honed to restore surface finish and remove any wear ridges. All seals — piston seal, rod seal, wiper, and guide bands — are replaced with Mori-compatible kits using NOK or Trelleborg seal specifications.

Mori presses use an 8-column guiding system — four corner columns plus four intermediate columns — that provides exceptional ram stability under off-center loading. This architecture is one of Mori's engineering strengths, but it also means eight bushings and eight columns must all be within tolerance simultaneously. A single worn bushing creates ram tilt that degrades part quality across the entire die area.

Our guiding restoration begins with measuring all eight columns for diameter, roundness, and straightness using a precision micrometer and dial bore gauge. Columns with light wear (under 0.05 mm) are reground in-place. Columns with deeper scoring are removed, reground, chrome-plated, and finish-ground at our Huangshi facility. All eight bushings are measured for clearance; any bushing exceeding 0.03 mm clearance is replaced with a bearing-grade bronze bushing machined to match the reground column diameter.

After guiding restoration, ram parallelism is measured and adjusted to 0.015 mm/100 mm — tighter than the original Mori factory specification of 0.02 mm/100 mm, because our refurbishment allows us to match each bushing to its specific column rather than using batch-produced tolerance pairs.

After any hydraulic or control system work, we verify tonnage accuracy using strain gauge calibration. Strain gauges are bonded to the press frame at calibrated positions — typically on the crown and bed tie-rods — and connected to a data acquisition system that records frame strain at each stroke phase. The strain measurements are converted to force using the frame's calibration factor, providing an independent verification of the hydraulic system's force transducer readings.

The calibration target is ±1% accuracy across the full tonnage range — from 20% to 100% of rated force. This means a 400-ton press verified at 80 tons, 200 tons, 320 tons, and 400 tons, with each measurement within ±4 tons of the commanded value. The calibration report documents the measured force at each test point, the hydraulic system pressure, and the frame strain, providing a baseline for future condition monitoring.

Tonnage verification is not optional in our refurbishment scope — it is the final sign-off that the rebuilt press delivers the force it claims to deliver. A press that produces 360 tons when the operator sets 400 tons will produce parts with inadequate V-ring impingement, resulting in die-roll and tear fracture — problems that are expensive to diagnose when the control system reports "400 tons achieved" but the frame strain tells a different story.

Mori's OEM spare parts supply for MFB-series presses has been progressively reduced as production focus shifted to newer platforms. Components that were standard catalog items 10 years ago — Mori-specific hydraulic manifold blocks, cylinder glands, guide bushings, PLC I/O modules — now require special order with lead times of 12-20 weeks, if available at all.

We manufacture replacement parts for discontinued Mori components in our Huangshi facility. Our reverse-engineering process begins with 3D scanning or precision measurement of the original part, followed by material analysis (spectrometer for chemical composition, hardness testing), CAD model creation, and manufacturing to the original specification. Every replacement part ships with a material certificate (EN 10204 3.1) and dimensional inspection report.

Common Mori replacement parts we manufacture: Hydraulic cylinder glands and pistons, guide bushings (bearing-grade bronze), seal plates, manifold blocks, ram components, ejector assemblies, and die cushion components. Stocked parts ship within 3-5 business days; custom manufacturing from measurement requires 2-4 weeks.