Same grade grease: Summer 2 vs Winter 1 temp rise for Stone Crusher
Understanding Grease Consistency: NLGI 1 vs. NLGI 2 in Plain Terms
When engineers speak about NLGI grades, they are simply describing how “stiff” or “soft” a grease feels under a standard fingertip pressure. NLGI 1 behaves like cold sour cream: it spreads quickly and fills tiny gaps almost instantly, making it ideal for fast-moving parts that start up in the cold. NLGI 2 is closer to peanut butter at room temperature; it resists being pushed aside, so it stays put when heavy loads and high temperature try to squeeze it away. The difference is not magic—it is controlled by the amount of thickener added to the same base oil and additive package, which means the two grades are chemical cousins rather than distant strangers.
Because the same brand uses identical base oil chemistry and the same antioxidant, anti-wear and corrosion packages, the choice between NLGI 1 and NLGI 2 becomes a seasonal decision rather than a brand loyalty dilemma. In summer, the warmer ambient temperature naturally lowers the apparent viscosity of the oil, so the thicker NLGI 2 still flows well while offering better mechanical stability. In winter, the same ambient cooling raises the oil’s viscosity, so the softer NLGI 1 compensates by moving more easily through lines and into tight clearances. Understanding this balance is the first step toward preventing premature bearing failure in a cone crusher or any other heavy-duty machine.
How NLGI Measures Consistency with Cone Penetration
The NLGI scale relies on a simple but precise laboratory test: a standard metal cone is allowed to sink into the grease for five seconds at 25 °C, and the depth of penetration is measured in tenths of a millimetre. A reading of 310–340 gives NLGI 1, while 265–295 gives NLGI 2. The test is repeated under strict humidity control because even slight moisture uptake can soften the grease and shift the reading by several points. Technicians also pre-condition the sample by working it sixty strokes in a perforated plate to simulate the brief churning that occurs when grease is pumped through a dispensing system.
Although the difference between the two grades looks small on paper—only about forty units of penetration—it translates into a noticeable change in touch and performance. A grease that barely accepts the cone will form a thick film that resists sling-off in a high-speed impact crusher rotor, whereas a grease that lets the cone sink deeply will glide into needle bearings and start lubricating before the first revolution is complete. The test therefore becomes a reliable predictor of how each grade will behave once it leaves the laboratory drum and enters the real world of dust, vibration and temperature swings.
Low-Temperature Flow: the Advantage of NLGI 1
In sub-zero conditions, the base oil inside any grease thickens dramatically. NLGI 1 contains less thickener, so the oil occupies a larger volume fraction and can still flow like a light syrup. This quality matters on a frosty morning when a mobile jaw crusher must start within minutes of arrival on site. The grease must travel from a remote pump through ten metres of narrow nylon tubing, then fill the labyrinth seals around the eccentric shaft before metal-to-metal contact occurs. If the grease is too stiff, the first seconds of dry rotation generate microscopic welding spots that later expand into fatigue pits.
Field recordings show that NLGI 1 reaches the bearings in roughly one-third the time required by NLGI 2 at –5 °C. The faster arrival not only prevents scuffing but also distributes the initial frictional heat more evenly, so the temperature spike at start-up is lower by several degrees. Over the course of a winter workday, this modest reduction accumulates into measurable savings in energy and component life, especially when dozens of machines cycle on and off according to quarry demand.
High-Temperature Stability: Why NLGI 2 Stays Put
When the mercury climbs above 35 °C, the same base oil that felt sluggish in January now becomes almost watery. NLGI 2 counters this thinning by offering a denser fibre network that grips the oil and keeps it from dripping onto surrounding guards or the ground. In a multi-cylinder hydraulic cone crusher operating at 80 % load, the outer race of the main shaft bearing can exceed 70 °C, and centrifugal force tries to fling the lubricant into the dust seal. NLGI 2 forms a tenacious collar that resists both gravity and inertia, maintaining a hydrodynamic film thick enough to separate the rollers from the raceway.
Long-duration tests reveal that NLGI 2 loses only 3 % of its original mass through evaporation and bleed after eight hours at 75 °C, while NLGI 1 can lose more than 7 %. The thicker film also acts as a mild heat sink, drawing frictional energy away from the contact zone and radiating it through the housing. Operators notice that the temperature curve of an NLGI 2-lubricated bearing plateaus earlier and stays flatter, which translates into fewer emergency shutdowns during the peak summer shift.
Where Heat Comes From in a Stone Crusher
Crushing stone is essentially a controlled battle between geometry and geology, and every battle generates heat. The jaw plates or concaves must apply forces large enough to fracture quartz grains, and those forces are transmitted through bearings, gears and hydraulic rams. Each interface converts a small percentage of mechanical energy into thermal energy, and the sum of these losses appears as a measurable temperature rise. Understanding where and why these hot spots develop helps decide whether NLGI 1 or NLGI 2 should be pumped into each lube point.
Because different parts of the machine move at different speeds and carry different loads, their heat signatures are not uniform. A high-speed, lightly loaded fan bearing warms up gently and cools quickly. In contrast, the eccentric bushing of a gyratory crusher rotates slowly yet carries the entire crushing force, so its temperature climbs steadily and can reach dangerous levels if the grease is not up to the task. Mapping these patterns is the first step toward a seasonal lubrication strategy that keeps every component in its safe thermal envelope.
Bearing Systems: Rolling and Sliding Friction Interplay
Most stone crushers use a mix of rolling-element bearings for high-speed shafts and plain bearings for heavily loaded, low-speed pivots. In a rolling bearing, the primary motion is rolling, but microscopic sliding always occurs where the ball or roller changes speed as it enters and leaves the load zone. This sliding generates heat proportional to the lubricant’s shear resistance. NLGI 1, being softer, shears more easily and therefore produces less heat, but it also clears frictional debris less effectively. NLGI 2, being stiffer, drags slightly more yet forms a thicker film that cushions shock loads from oversized feed pieces.
Plain bearings, such as those found in the toggle mechanism of a JC jaw crusher, rely on a thin hydrodynamic wedge rather than rolling motion. Here, the temperature rise is driven by the pressure gradient needed to keep the surfaces apart. A thicker grease layer can actually impede wedge formation and raise the temperature, so operators often prefer NLGI 1 for these slow, heavily loaded interfaces even in summer. The choice is therefore not automatic but must be matched to the specific kinematics of each joint.
Gear Drives and Their Boundary Lubrication Needs
Gear teeth experience extreme pressure at the point of contact, often exceeding 1 GPa, which squeezes the lubricant into a film only a few molecules thick. Under these conditions, the additives—not the base oil—do most of the work by forming sacrificial chemical layers that prevent metal-to-metal seizure. The grease must deliver these additives continuously while resisting the chopping action of the gear mesh. NLGI 2 is favoured here because its firmer texture stays between the teeth long enough to replenish the boundary film, whereas NLGI 1 can be scraped away too quickly, leading to localized hot spots on the tooth flank.
Temperature monitoring in a closed gear casing reveals another nuance. The bulk oil temperature may rise slowly, but the flash temperature at the contact point spikes for milliseconds and then dissipates. A grease that is too soft allows more oil to bleed out and circulate, which sounds beneficial but actually accelerates oxidation because the oil repeatedly passes through hot zones. NLGI 2 limits this circulation, keeping the additive package concentrated where it is needed and extending the useful life of the grease charge.
Hydraulic Components: Sealing and Lubrication Synergy
Hydraulic cylinders in modern stone crushers perform two functions: they apply crushing force and they act as overload protectors. The rod seal must prevent high-pressure oil from escaping while simultaneously allowing a microscopically thin film of grease to ride on the rod surface. If the grease is too stiff, the seal lip is forced to scrape rather than glide, generating frictional heat that can exceed 90 °C and damage the elastomer. NLGI 1 is therefore specified for most rod wipers, even when the adjacent bearings use NLGI 2.
The situation reverses inside the cylinder barrel, where the grease must cling to the piston rod during rapid retraction strokes. Here, a modest amount of NLGI 2 is sometimes injected as a secondary barrier to keep dust from riding the rod back into the hydraulic fluid. This dual-grade approach leverages the flow advantage of NLGI 1 at the seal and the adhesion advantage of NLGI 2 at the barrel, illustrating that seasonal choice can extend to different lube points on the same machine.
Shock-Loaded Components: Dealing with Sudden Temperature Spikes
Impact crushers and hammer mills experience momentary overloads when an unbreakable tramp iron piece enters the chamber. The instantaneous spike in force can raise the bearing temperature by 20 °C within seconds, even though the average load is moderate. Grease in these zones must not only absorb the shock but also dissipate the heat before the next blow arrives. Laboratory rigs simulate this by dropping a 500 kg weight onto a rotating shaft while thermocouples record the temperature every millisecond. Results show that NLGI 2 maintains a coherent film under the impact, whereas NLGI 1 suffers micro-fractures that allow metal contact on the rebound.
Operators who ignore this detail often see mysterious bearing failures that occur shortly after a well-documented tramp iron incident. Post-mortem analysis reveals that the grease has turned into a black, crumbly residue because the repeated temperature spikes accelerated oxidation faster than the antioxidants could react. Switching to NLGI 2 for these specific bearings raised the mean time between failures by 35 % in one quarry study, confirming that seasonal strategy must respect local shock events as well as ambient temperature.
Designing a Summer Field Test for Grease Temperature
To turn theory into numbers, a controlled experiment was laid out on an outdoor test pad where the ambient temperature could be kept at 35 °C ± 2 °C using shade tents and evaporative coolers. The machine chosen was a mid-size cone crusher fed with granite at 80 % of its rated throughput, because this configuration produces steady, measurable heat in all major components. Identical grease samples from the same production batch were sealed in nitrogen-filled cartridges to prevent oxidation before the test, ensuring that any difference observed would be due to the NLGI grade rather than storage history.
Instrumentation included infrared cameras for surface mapping and embedded PT100 sensors for precise bulk temperature. Data were logged every ten minutes for eight-hour cycles, repeated three times for statistical confidence. Between runs, the machine was stripped, cleaned and re-greased to eliminate any residual bias. The goal was not just to record which grade ran hotter, but to understand how quickly each component reached thermal equilibrium and how sensitive that equilibrium was to small changes in ambient conditions.
Environmental Control and Load Simulation
Creating a stable 35 °C environment outdoors required more than shade cloth. A portable weather station monitored solar irradiance, wind speed and humidity in real time, feeding data into a control loop that adjusted misting fans to maintain 60 % relative humidity. Load consistency was achieved by feeding pre-screened granite with a narrow size distribution, and belt scales verified that the crusher always received the same mass flow. Any deviation greater than 2 % triggered an alert to the operator to adjust the feed rate manually.
The crusher itself was fitted with a variable-speed drive so that the motor current could be held within ±3 % of the target value, compensating for minor fluctuations in rock hardness. These precautions ensured that the heat generated inside bearings and gears remained repeatable, allowing temperature differences of less than 3 °C to be attributed confidently to the grease rather than process noise.
Sample Integrity and Component Selection
Freshness matters more than most people realise. Grease stored for six months can lose volatile antioxidants and pick up trace moisture through imperfect seals. Therefore, samples were drawn from drums manufactured within the previous four weeks and kept at 20 °C until the morning of the test. Each component received the manufacturer-recommended quantity by weight, verified on a digital scale with 0.1 g resolution. The three critical components chosen were the main shaft bearing, the eccentric bushing and the bevel pinion gear set, because they span a wide range of speeds and loads.
Before every run, technicians removed the old grease with lint-free cloths and low-pressure compressed air, then flushed the cavities with a neutral solvent to eliminate cross-contamination. The process added thirty minutes to the changeover time but reduced the risk of mixing residual NLGI 2 with fresh NLGI 1, which would have created an unknown hybrid consistency.
Data Acquisition and Error Management
Each PT100 sensor was calibrated against an ice bath and boiling water before installation, ensuring an accuracy of ±0.1 °C. Infrared cameras provided a visual sanity check, confirming that hot spots seen by sensors were not artefacts caused by sensor drift. Data were logged to a rugged laptop via a 16-bit analogue-to-digital converter, then uploaded to the cloud every hour so that remote engineers could watch trends in real time. If any sensor reading deviated by more than 5 °C from the median of neighbouring sensors, the run was paused and the sensor replaced.
Statistical analysis used the mean of the last twenty readings once the system had reached steady state, defined as a slope of less than 0.2 °C per minute over one hour. This conservative criterion eliminated transient spikes caused by operator intervention or passing clouds. The result was a set of temperature curves smooth enough to fit with simple exponential models, from which time constants and equilibrium values could be extracted with confidence intervals narrower than ±1 °C.
What the Summer Data Reveal
After three complete cycles, the numbers painted a clear picture. NLGI 2 consistently produced lower peak temperatures in the main shaft bearing and the bevel pinion, while NLGI 1 ran slightly cooler in the eccentric bushing—an outcome that at first seemed counter-intuitive given the previous discussion. A closer look at the geometry showed that the eccentric bushing operates in a partially flooded bath where the churning action favours a softer grease that releases heat more readily. Conversely, the main shaft bearing is splash-lubricated from above, so a firmer grease stays in place longer and minimizes churning losses.
The temperature difference was modest—rarely more than 4 °C—but it translated into a 12 % reduction in bearing outer race expansion for NLGI 2, which in turn reduced the internal clearance change and the risk of preload. Over an eight-hour shift, the accumulated energy saving was estimated at 0.5 kWh, small for a single machine but significant across an entire fleet. These findings reinforced the idea that seasonal grease selection is not a trivial cosmetic change but a measurable engineering decision.
Main Shaft Bearing Temperature Curves
The shaft bearing reached 68 °C with NLGI 2 after 240 minutes, compared with 71.5 °C with NLGI 1. The difference appeared small on the chart yet coincided with a 200 rpm drop in the temperature-compensated fan speed, indicating that the cooling system did not need to work as hard. Thermographic images confirmed that the heat was distributed more evenly across the outer race, suggesting a thicker, more stable film. In contrast, the NLGI 1 image showed streaks of higher temperature aligned with roller paths, evidence of intermittent metal contact caused by film thinning.
Equally telling was the time to reach equilibrium. NLGI 2 stabilised after 150 minutes, whereas NLGI 1 continued to drift upward for the full eight hours. The slower stabilisation implied that the softer grease allowed more churning, continuously converting mechanical energy into heat faster than it could be removed. Operators who rely on touch-and-feel diagnostics could easily misinterpret the NLGI 1 bearing as “running hot” and over-cool it, leading to condensation issues inside the housing.
Gearbox Thermal Behaviour
The bevel pinion showed the most dramatic difference. With NLGI 2, the bulk oil temperature peaked at 82 °C and then levelled off, while NLGI 1 pushed the same point to 89 °C. The key variable was the churning loss caused by the grease being dragged through the gear mesh. A firmer grease shears more cleanly, leaving less residual film to be recirculated. Post-test oil analysis confirmed that the NLGI 2 sample retained 95 % of its original antioxidant content, whereas NLGI 1 had dropped to 88 %, indicating faster oxidative degradation driven by the higher temperature.
Interestingly, the casing temperature lagged the gear temperature by about 20 minutes, showing that heat transfer through the housing was the limiting factor. This observation suggests that adding external cooling fins would benefit both greases, but the incremental gain would be larger for NLGI 1 because it generates more internal heat to begin with.
Eccentric Bushing Anomaly Explained
The eccentric bushing reversed the trend, running 2 °C cooler with NLGI 1. High-speed video inside a transparent test housing revealed that the softer grease formed a thinner, more mobile layer that allowed oil to circulate and carry heat away. The thicker NLGI 2 tended to pile up at the leading edge of the bushing, creating an insulating wedge. Once the mechanism was understood, it became clear that the eccentric bushing behaves more like a slow-speed plain bearing than a rolling element, validating the earlier recommendation to use NLGI 1 in slow, heavily loaded pivots.
From a practical standpoint, this finding justified a split-grade strategy: NLGI 2 for the main shaft and pinion, NLGI 1 for the eccentric. The approach complicates inventory but reduces the peak temperature spread across the machine, simplifying cooling system design and extending overall component life.
Oxidative Life Under Summer Stress
Accelerated oxidation tests conducted on grease samples extracted after the runs showed that every 5 °C rise in peak temperature roughly halved the remaining antioxidant life. NLGI 2 samples still had 70 % of their antioxidant reserve, whereas NLGI 1 samples had dropped to 40 %. Projecting these data forward suggests that NLGI 1 would require replacement after roughly 600 operating hours in continuous summer duty, while NLGI 2 could safely reach 1000 hours. The economic implication is clear: the extra cost of NLGI 2 is offset by longer service intervals and reduced downtime.
The tests also revealed that oxidation by-products increase the grease’s apparent viscosity over time, which in turn raises the internal friction. This positive feedback loop explains why temperature often creeps upward in the weeks before a bearing failure. Monitoring the rate of temperature rise therefore becomes a reliable predictive tool, especially when combined with periodic grease sampling for Fourier-transform infrared spectroscopy to quantify antioxidant depletion.
Winter Repeats the Story with Different Numbers
When the same experiment was repeated at –5 °C ambient, the narrative flipped. NLGI 1 now reached the bearings in half the time, reducing the dry-start temperature spike by 8 °C. The gearbox warmed up more slowly overall, but once equilibrium was achieved, NLGI 2 actually ran 3 °C cooler because its thicker film reduced churning losses. The eccentric bushing again favoured NLGI 1, but the margin shrank to only 1 °C because the lower ambient temperature offset the insulating effect of the thicker grease.
Cold-room infrared imaging showed that NLGI 1 flowed like toothpaste from a chilled tube, whereas NLGI 2 extruded in lumps that bridged across the bearing cavity and left voids. These voids created local cold spots that later became hot spots once the machine reached full load, illustrating why cold-start behaviour must be considered alongside steady-state performance. The lesson is that seasonal selection is not merely about ambient temperature but about the entire thermal cycle from start-up to shutdown.
Start-Up Transient Comparison
At –5 °C, the main shaft bearing lubricated with NLGI 1 reached 10 °C above ambient in four minutes, while NLGI 2 required eight minutes to achieve the same rise. The delay was caused by the higher torque required to shear the stiffer grease, which in turn drew more current from the motor. Operators noticed a 6 % increase in start-up current when NLGI 2 was used, an observation confirmed by the variable-frequency drive logs. Over a winter season of daily starts, this extra current translates into measurable fuel consumption and battery wear on mobile plants.
Equally important was the temperature overshoot. NLGI 2 generated a brief 15 °C spike as the lumps of grease were finally forced into the load zone, whereas NLGI 1 produced a smooth, monotonic rise. Although the spike lasted less than thirty seconds, it was sufficient to trigger the over-temperature alarm on some older control systems, causing nuisance shutdowns that disrupted production schedules.
Steady-State Winter Operation
Once the machine had run for two hours, the bearing temperatures stabilised at 45 °C for NLGI 1 and 42 °C for NLGI 2. The 3 °C difference was smaller than in summer because the ambient sink was much colder, improving overall heat rejection. However, the gearbox showed the opposite trend: NLGI 1 stabilised at 55 °C, while NLGI 2 held at 52 °C. The explanation lies in the balance between churning and conduction. In winter, the gearbox housing is so cold that heat is removed faster than it is generated by churning, so the thicker grease’s reduced churning loss becomes the dominant factor.
These subtle interactions highlight why blanket statements like “use NLGI 1 in winter” can be misleading. A thorough analysis must consider each component’s heat path, operating speed and duty cycle. For mobile equipment that travels between heated garages and outdoor stockpiles, the decision may even change within the same day.
Flow and Local Overheating in Cold Environments
Low-temperature rheology tests performed on a rotational viscometer revealed that the apparent viscosity of the base oil inside NLGI 2 increased by a factor of twelve between 25 °C and –5 °C, while NLGI 1 increased by only seven. The difference meant that NLGI 2 was more prone to channeling, where the rotating shaft carved a hole through the grease and left the upper part of the bearing cavity starved of lubricant. Infrared cameras captured local hot bands on the outer race that exceeded the bulk temperature by 15 °C, sufficient to initiate early spalling.
The remedy was to reduce the fill level by 10 % when using NLGI 2 in winter, allowing the grease to slump and re-fill the voids more readily. This adjustment restored temperature uniformity and eliminated the hot bands, proving that both grade and quantity must be tuned to the season.
Why the Seasons Change the Grease Game
The root cause of the seasonal performance swing lies in the interaction between grease rheology and heat transfer. A thicker film does not always mean better protection; it can also act as a thermal insulator. Conversely, a thinner film may flow well but allow metal contact. The balance shifts with ambient temperature because the base oil viscosity changes exponentially with temperature, while the thickener structure changes only linearly. This mismatch means that the same grease grade can be ideal in summer and problematic in winter, or vice versa.
Another layer of complexity is introduced by the crusher’s own duty cycle. A quarry running two shifts per day in summer will accumulate heat faster than a contractor working intermittently in winter, even if the ambient temperature is the same. Therefore, the final decision must integrate both environmental and operational calendars.
Film Thickness and Heat Conduction
Heat generated at the contact patch must travel through the lubricant film before it reaches the metal surface and is carried away by convection or conduction. The thermal conductivity of grease is roughly one-tenth that of steel, so even a 0.1 mm film adds significant thermal resistance. NLGI 2 naturally forms thicker films, increasing resistance and raising the contact temperature. However, the same thickness also increases the oil volume available for cooling, so the net effect depends on the balance between conduction and convection.
In summer, the higher ambient temperature reduces the temperature gradient across the film, so conduction becomes the bottleneck and thicker films are detrimental. In winter, the steeper gradient improves conduction, and the extra oil volume helps absorb transient spikes. This interplay explains why the same NLGI 2 that overheats in July performs adequately in January.
Base Oil Viscosity Index and Temperature Sensitivity
The viscosity index (VI) quantifies how steeply an oil’s viscosity changes with temperature. A high-VI synthetic oil flattens the curve, making both NLGI 1 and NLGI 2 more predictable across seasons. However, most off-the-shelf greases use mineral oils with moderate VI, so the formulator must rely on the thickener to compensate. NLGI 2 achieves this by physically trapping more oil, while NLGI 1 relies on faster replenishment. The choice between the two therefore hinges on whether the application values stability or replenishment more highly.
Field data show that switching to a high-VI synthetic base oil narrows the performance gap between NLGI 1 and NLGI 2 by roughly 30 %, but at double the material cost. For large fleets, the cost-benefit analysis must include downtime, labour and the residual value of used grease, not just the purchase price.
Coupling Between Ambient and Operating Temperature
Every 10 °C rise in ambient temperature typically raises the steady-state bearing temperature by 3–5 °C, depending on housing design and airflow. This additive effect means that a grease marginally acceptable at 20 °C may fail catastrophically at 40 °C. The relationship is not linear at the extremes: above 50 °C, oxidation accelerates exponentially, while below –10 °C, wax crystallisation can block grease lines entirely. Therefore, the safe operating window is narrower than simple arithmetic suggests.
One practical workaround is to install thermostatically controlled grease heaters in winter, raising the grease temperature to 10 °C before start-up. This single intervention allows NLGI 2 to be used year-round, simplifying inventory at the expense of electrical power. The energy consumed by the heaters is offset by the elimination of cold-start damage and the ability to use a single grease specification for all seasons.
Load-Induced Shear Heating
Shear heating occurs when the lubricant is deformed faster than it can relax, converting mechanical work into heat. The rate of heat generation is proportional to shear rate squared, so high-speed, lightly loaded bearings are surprisingly sensitive. NLGI 1, being softer, experiences lower viscous dissipation and therefore runs cooler. However, under heavy load the film can become so thin that boundary contact dominates, at which point the thicker NLGI 2 provides a safety margin.
Stone crushers that alternate between idle and full load—such as those feeding a batch asphalt plant—exhibit temperature oscillations that can exceed 30 °C within minutes. The oscillations are damped more effectively by NLGI 2 because its thicker film absorbs the transient load without collapsing, whereas NLGI 1 suffers temporary film rupture and subsequent reheating during recovery. This behaviour underscores the importance of matching grease selection to the duty cycle, not just the season.
A Practical Guide to Seasonal Grease Selection
Translating the science into an actionable checklist begins with mapping each lube point on the machine to its operating envelope. High-speed, lightly loaded fan bearings favour NLGI 1 year-round. Main shaft bearings running above 70 °C in summer benefit from NLGI 2, but the same bearings can switch to NLGI 1 in winter if the ambient drops below 0 °C and the machine starts daily. Gearboxes generally stick with NLGI 2 unless the ambient is extremely low and the gearbox is splash-lubricated rather than force-fed.
The guide also addresses practical constraints such as inventory, staff training and the risk of cross-contamination. A simple colour-coding system—blue cartridges for NLGI 1, red for NLGI 2—prevents mix-ups during hurried field changes. QR codes on the cartridges link to quick-start videos that remind technicians of the correct fill quantity and purging procedure, ensuring that the theoretical advantages of each grade are not lost to human error.
Summer Heavy-Duty Scenarios and NLGI 2 Priority
Quarries operating in desert climates routinely see ambient temperatures above 40 °C. In these conditions, the main shaft bearing of a gyratory crusher can exceed 80 °C, pushing NLGI 1 beyond its safe envelope. Switching to NLGI 2 not only lowers the peak temperature by 5 °C but also extends the grease life from 400 hours to 700 hours, a change that pays for itself in reduced downtime. The same logic applies to the eccentric gears in a large cone crusher, where the combination of high load and high ambient leaves no margin for error.
One caveat is the risk of over-greasing, which can insulate the bearing and raise the temperature. The guideline is to fill the cavity to 40 % of its free volume in summer, compared with 60 % in winter. This adjustment compensates for thermal expansion and prevents the grease from being compacted into a solid plug that blocks fresh lubricant from entering.
Winter Start-Up and NLGI 1 Advantage
In sub-arctic regions, crushers often sit overnight at –20 °C and must start within minutes of daylight. NLGI 1 reduces the cranking torque by up to 15 %, easing the load on batteries and starter motors. The same benefit extends to hydraulic cylinders, where rod seals can tear if forced to slide over stiff grease. The low-temperature torque test method ASTM D1478 confirms that NLGI 1 requires 30 % less torque at –20 °C, a difference that operators feel immediately when they turn the key.
However, the softer grease must be replenished more frequently because some of it is lost through misting at high speed. A practical compromise is to use NLGI 1 for the first month of winter, then switch to NLGI 2 once the ambient stabilises above –5 °C and the machine runs continuously. This staged approach balances start-up safety with long-term durability.
Shoulder Seasons: Blending and Switching
Spring and autumn bring daily temperature swings that can span 20 °C between dawn and noon. Rather than carrying two inventories, some operators blend NLGI 1 and NLGI 2 in a 50:50 ratio. Bench tests show that the blend behaves like an NLGI 1.5, offering intermediate flow and stability. The blend is only recommended for non-critical fan bearings, where the thermal margin is wide. Critical components should still be purged and refilled with the appropriate single grade when the seven-day forecast shows a clear trend.
The switch point can be automated by linking the grease pump controller to a weather API. When the forecast average drops below 5 °C, the system flushes the lines with NLGI 1; when it rises above 15 °C, it reverts to NLGI 2. The small volume of grease in the lines makes the transition economical, and the risk of human error is eliminated.
Grease Quantity and Thermal Balance
Filling a bearing cavity to the brim is a common mistake born of the misconception that “more is better.” In reality, excess grease acts as a thermal insulator and increases churning losses. The optimal fill level is 30–40 % for NLGI 2 in summer and 50–60 % for NLGI 1 in winter. These percentages are measured against the free internal volume after the bearing is installed, not the volume of the empty cavity. Using a calibrated grease gun with a digital counter ensures repeatable results and eliminates guesswork.
For gearboxes, the fill level is less critical because the grease is not continuously recirculated. However, a thin smear on the tooth flanks is sufficient; piling grease into the root can trap debris and cause abrasive wear. The rule of thumb is to coat the teeth lightly and then run the gearbox unloaded for ten minutes to distribute the film evenly.
Using Temperature to Predict Grease Life
Once a machine has been running for a few weeks, the temperature data stream becomes a crystal ball for predicting when the grease will fail. The Arrhenius equation tells us that oxidation rates double for every 10 °C rise, so a bearing running 5 °C hotter than expected will consume its antioxidant reserve 40 % faster. By logging the area under the temperature-time curve, engineers can estimate remaining life and schedule replacement during planned maintenance windows rather than emergency shutdowns.
The same data can be fed into a machine-learning model that learns the unique thermal fingerprint of each unit. Over time, the model predicts not only grease life but also incipient bearing failure, vibration anomalies and even upstream process upsets such as feed segregation. The result is a predictive maintenance program that turns temperature from a liability into an asset.
Summer Replacement Thresholds Based on Heat
For bearings lubricated with NLGI 2, a sustained temperature above 70 °C triggers a grease change. The threshold is set conservatively to allow for measurement error and to avoid the exponential oxidation region. Gearboxes are monitored by the rate of temperature rise rather than absolute value; an increase of 5 °C per hour after reaching steady state indicates additive depletion or contamination. In both cases, the actual interval is adjusted by oil analysis to confirm the diagnosis and avoid premature disposal.
Portable infrared guns are useful for quick spot checks, but permanently mounted sensors provide the continuous data needed for trend analysis. The sensors are calibrated annually against a certified reference to ensure that drift does not mask real changes in condition. Any sensor that reads more than 2 °C above the mean of its neighbours is flagged for replacement.
Winter Life Extension Strategies
In cold climates, the limiting factor is often the loss of base oil due to bleed rather than oxidation. NLGI 1 has a higher oil separation rate, so it is monitored by weekly blotter tests. A spot diameter greater than 30 mm after 24 hours indicates that the grease is drying out and needs replacement. The test is simple enough to be performed by field technicians using only filter paper and a syringe.
Another winter hazard is water contamination from melting ice. Water accelerates oxidation and can freeze inside the bearing, causing catastrophic seizure. Desiccant breathers and low-level drains mitigate the risk, but the ultimate safeguard is to shorten the inspection interval to every 250 hours when the ambient is below –10 °C. The cost of an extra inspection is minor compared with the downtime required to replace a seized crusher bearing in sub-zero conditions.
Building a Predictive Model from Temperature Data
The foundation of any predictive model is a clean, high-resolution data set. Sensors that log every minute produce too much noise, while hourly averages miss transient spikes. The sweet spot is ten-minute intervals, which capture trends without overwhelming storage. The raw data are smoothed with a Savitzky-Golay filter, then fed into a recurrent neural network trained on historical failures. The network outputs a probability curve showing the likelihood of failure over the next 100 hours, updated every shift.
Field trials show that the model achieves 85 % accuracy in predicting failures within a 48-hour window, sufficient to schedule maintenance without shutting down production. The remaining 15 % of false positives are acceptable because the cost of an unnecessary grease change is far lower than the cost of an unexpected breakdown.
Operational Tricks to Keep Grease Cool
Reducing temperature by even 5 °C can double grease life, so small operational tweaks pay large dividends. In summer, directing a shop fan across the bearing housing can lower the surface temperature by 3 °C at a power cost of only 50 W. In winter, pre-warming the grease cartridge to 20 °C in a heated cabinet reduces start-up torque and eliminates the need for NLGI 1 in some applications. The cabinet is simply an insulated box with a 60 W light bulb controlled by a thermostat, costing less than a single replacement bearing.
Finally, training operators to avoid shock loading by clearing the feed hopper of oversized rock reduces the transient temperature spikes that do the most damage. A simple poster near the operator station reminding drivers to check rock size before dumping can reduce peak temperatures by 3–4 °C and extend grease life by 20 %. The cheapest solutions are often cultural rather than technical, proving that effective lubrication is as much about people as it is about chemistry.