Condition One: Random Grasping Loads
Field work in a tea mountain is not a laboratory duty cycle. The source describes the first condition as random grasping load: stable contact stress typically sits at 30-50% of the rated value, but transient spikes can reach 2-3 times the rated load when the hand grips an uneven branch, a basket handle, or a hot tool. These spikes compress the micro-pitting initiation window, because each overload event pushes the contact deeper into the fatigue regime while the film is still thin. A grease rated for steady load gives no indication of how it behaves during these transients.
Condition Two: Irregular Direction Changes
The second condition is irregular direction changes. When the joint reverses frequently without a fixed pattern, the tooth-root stress alternates with a stress ratio near R = -1, meaning fully reversed loading. The source notes that under this alternating stress the bending fatigue limit drops by 20-40% compared with one-directional loading, and the root stress concentration factor lies in the 1.5-2.0 range. Every reversal therefore counts as a much more damaging cycle than a designer might assume from a one-directional fatigue curve. The grease cannot prevent the stress, but it must keep the film present on both stroke directions so that no reversal runs dry.
Condition Three: Charcoal Roasting Heat
The third condition is ambient heat from charcoal roasting, with surrounding temperatures above 50°C. At sustained elevated temperature, oil separation from the grease increases, and the lubrication regime can degrade in a progression from mixed lubrication to boundary lubrication and eventually to dry friction. The film that was marginal at room temperature becomes inadequate in the roasting environment, and the same heat accelerates oxidation of the exposed oil.
The Three Balances Required
Given these conditions, the source concludes that the grease must hold three balances. First, an EP load margin sufficient for the 2-3x rated transients without sacrificing the base film. Second, consistency stability after shear, so that thousands of reversals do not permanently soften or harden the grease. Third, oil-separation and evaporation control at sustained high temperature, so the grease does not bleed out during a long roasting shift. Each balance is easy to achieve in isolation; the difficulty is holding all three in one formulation.
Validation / Selection Conclusion
Validate candidate grease with an overload cycling test that includes periodic 2-3x rated spikes, a reversal test that tracks fatigue-related wear, and a sustained high-temperature soak that measures oil separation and evaporation. The acceptance profile is: EP margin for transients, shear-stable consistency, and controlled bleed at elevated temperature. A grease that passes bench tests at constant rated load will miss all three field conditions; only a test matrix that mirrors random loads, reversals and heat is meaningful.
