Redesigning the Deflate Nip Roll Shaft for Heavy-Duty Packaging Manufacturing
Overview & Project Highlights
Industry:
Packaging manufacturing
Problem:
Journal fractures occurring every 1 to 4 months
Scope of Work:
Failure analysis, simulation, redesign, fabrication drawings
Equipment:
Rubber-covered nip roll (8.19 in. diameter, 67 in. overall length)
The Challenge
At a packaging manufacturing facility, a deflate nip roll experienced frequent and costly failures.
Every one to four months, a shaft journal would fracture, leading to:
Unexpected downtime and lost production time
Heavy burden on the maintenance team
Continuous temporary repairs
Although the failure location varied between ends, the root location was always identical: right next to the weld joining the journal to the shaft body. Solution Services was brought in to identify the root cause and engineer a permanent, fast-repair replacement.
Execution & Analysis
To identify the root cause and engineer a permanent solution, we performed a thorough inspection of the failed components followed by digital stress testing.
Failure Analysis
To understand the mechanism behind the breaks, we examined the failed journal, the unbroken end, and the operating conditions (two air cylinders applying ~1,000 lbf at 80 psi against a drive roll turning at ~400 rpm).
Key findings
- Evidence of incomplete weld fusion and fatigue failure
- Severe gouging from previous repairs
- A sharp 90-degree step between the weld and journal, which severely concentrated mechanical stress
Simulation & Stress Testing
Using SolidWorks FEA simulation, we modeled the operational forces (cylinder load, rotational torque, and gravity).
- Peak stress concentrated exactly at the 90-degree transition (~1,861 psi).
- The stress level was well below basic material yielding limits, confirming that failure was caused by fatigue from cyclic loading, compounded by stress concentrations and heat-affected metal from repeated weld repairs.
The Redesign Solution
We evaluated two potential avenues with the customer: a re-engineered welded assembly vs. a bolt-on assembly. The customer selected the bolt-on design to eliminate structural welds completely and enable quick field repairs.
Key Features of the New Assembly:
- No Structural Welds: Eliminates heat-affected weak zones.
- Optimized Geometry: Solid 4140 steel journals machined with a large, smooth transition radius into the flange to reduce stress points.
- Robust Bolted Joint: Journal bolts directly into a 1045 steel end-insert using six 1/2-13 wire-locked bolts and two dowel pins for precise alignment.
- Easy Maintenance: Integrated threaded jack-bolt holes allow quick unbolting and replacement of a damaged journal without requiring cutting or welding.
WE DESIGN.
WE ELIMINATE WELDING.
WE SPEED UP REPAIRS.
Zero weak points. Maximum uptime. Built for fast maintenance.
Before vs. After Comparison
Feature
Before Redesign
After Redesign
Joint Type
Partial-penetration weld with incomplete fusion
Bolted & doweled (no structural weld)
Geometry
Sharp 90° step at weld; rough repair machining
Large machined radius to distribute stress
Material
Unknown material weakened by repair welds
4140 steel journals & 1045 inserts
Repair Method
Re-weld upon failure (repeating the cycle)
Fast unbolt & swap replacement
Joint Type
Before Redesign
Partial-penetration weld with incomplete fusion
After Redesign
Bolted & doweled (no structural weld)
Geometry
Before Redesign
Sharp 90° step at weld; rough repair machining
After Redesign
Large machined radius to distribute stress
Material
Before Redesign
Unknown material weakened by repair welds
After Redesign
4140 steel journals & 1045 inserts
Repair Method
Before Redesign
Re-weld upon failure (repeating the cycle)
After Redesign
Fast unbolt & swap replacement
Final Result
The client received a custom-engineered shaft built around real-world failure dynamics. By removing the weld and sharp transitions, the underlying fatigue cause was resolved, giving the maintenance team a durable, modular component designed for long-term serviceability.
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