I. Small temperature difference, but significant damage

In the minds of many engineers, alternating high and low temperatures are problems that only need to be faced by aerospace engines, polar research, and deep-sea drilling. For "ordinary equipment" such as fans, compressors, pumps, and reducers - the dozens of degrees of temperature difference caused by the changing seasons do not seem to pose any threat.

 

But this is not the case.

 

In a cement factory, the bearing temperature of a high-temperature fan suddenly rose to 90°C during operation. The loaded-end bearing became stuck and burned out, and the rollers scattered. In a chemical plant, the bearing of the compressor for circulating hydrogen gas had a long-term abnormal temperature fluctuation of 20-30°C, with the highest temperature reaching 90°C. The annual fluctuation exceeded 40 times, accompanied by deteriorated lubricating grease and bearing wear, seriously threatening the continuous production of the plant. In a centrifugal pump, when used in an environment with a large temperature difference between the inside and outside, the hollow bearing housing with a cooling device underwent significant deformation, causing abnormal loads on the outer ring of the bearing, resulting in premature failure of the bearing. In a steel mill's sintering production line, the reducer due to improper adjustment of the bearing clearance caused the bearing to heat up and freeze, and the B granulator stopped for 76 hours. Six sets of high-speed shafts and 12 sets of bearings were replaced, resulting in direct economic losses of over 300,000 yuan.

 

These cases come from different equipment and different industries, but all point to the same conclusion: a temperature difference of several dozen degrees is sufficient to cause a set of bearings to fail, to paralyze a production line, and to present a maintenance bill of several hundred thousand yuan.

 

The temperature difference is not small, but each temperature change is consuming the lifespan margin of the bearings. Over time, the clearance drifts, the grease thickens, the seal cracks, and the shaft freezes. It is not a one-time "high-temperature burnout", but a long-term "boiling the bearing in warm water".

 

II. Fan: The "thermal expansion trap" behind the "90°C freezing"

Case: The tail high-temperature fan of the 2nd new line kiln of a cement group in Henan Province has been vibrating abnormally since its commissioning in July 2016. On July 24th, the loaded-end bearing froze and burned out, causing the fan to shut down. The central control data showed that the temperature of the bearing significantly increased during the accident, reaching 90°C. The vibration value of the unloaded-end was 6.4 mm/s, and the current of the motor jumped from 140A to over 170A. After disassembly, it was found that the rollers on the side of the bearing near the motor were scattered, and both the inner and outer rings were damaged to varying degrees. After the first accident, the bearing was replaced and restarted, but the unloaded-end again froze and shut down after only 5 shifts.

 

After the incident, it was determined that the direct cause of the burned-out loaded-end bearing was poor installation - during the process of adjusting the coaxiality of the main shaft and the motor reducer shaft, only one micrometer was used for reading, resulting in excessive bearing impact load. More importantly, the axial clearance of the unloaded-end was insufficient, and the bearing expanded due to heat, squeezing the loaded-end bearing, causing it to freeze and burn out.

 

The same fan had two freezing incidents, and the root cause was "heat" - the first time was due to the axial expansion of the shaft occupying the axial clearance, and the second time was due to the misalignment of the inner and outer rings of the damaged bearing under high temperature, causing it to freeze again. In the first few months after the fan was put into operation, every increase in the bearing temperature approached the freezing threshold.

 

The temperature variation test of the fan is not limited to this. The sudden change in vibration faults of the two-stage adjustable blade induced draft fan occurs more frequently when the environmental temperature is high. In a power plant, the first bearing temperature of the supply fan continued to rise above 110°C after starting in winter and was urgently shut down. The disassembly revealed that the inner ring of the bearing was jammed with the shaft. In a wind farm, the 3.6MW gearbox in operation initially had a critical problem with the bearing temperature on the motor side. In cold environments, air suspension blowers have difficulties in cold start, start jamming, overloading alarms, and large vibration problems are extremely common in northern projects.

 

The common feature of these cases is that temperature variation attacks the reliability of the fan bearings through three paths: thermal expansion, changes in lubricating grease viscosity, and drift in clearance. Most maintenance personnel only see "the bearing burned out", but fail to see "the temperature difference burned out".

 

III. Compressor: 40 times of torture at 20°C fluctuation Case: The drive motor of a hydrogen compressor in a chemical plant experienced abnormal temperature fluctuations of 20-30°C at the shaft extension end. The highest temperature reached 90°C, and the annual fluctuations exceeded 40 times. This was accompanied by deteriorated lubricating grease and bearing wear.

 

A temperature difference of 20-30°C may not sound significant in an industrial context. However, with over 40 fluctuations per year, it means that the bearing has to undergo a temperature climb from 60°C to 90°C every less than 10 days. Each climb accelerates the oxidation of the lubricating grease; each drop causes a sudden change in viscosity. Day after day, the lubricating grease turns from a paste to carbonized matter, and the bearing raceway becomes rough and pitted.

 

This is not a one-off incident but a chronic wear that lasts for a year.

 

The problem of temperature variation in compressor bearings is not an isolated case. The No. 3 oxygen production unit of Liuzhou Steel Gas Company's air compressor secondary thrust bearing operated continuously after being put into service. The temperature was consistently high, reaching up to 105°C. After a maintenance of a certain air compressor, the main thrust bearing of the gearbox temperature rose from 68°C to 100°C within one week. The bearing housing temperature of a certain hydrogen production plant's shaft bearing repeatedly increased and decreased after starting up. The support bearing housing of a certain ethylene plant's refrigeration compressor showed temperature fluctuations. The analysis revealed that the oxidation of the lubricating oil and the formation of a varnish film were the direct causes, while structural factors such as the lower limit of the bearing installation clearance and the small diameter of the oil inlet hole led to the temperature increase and accelerated the oxidation process of the lubricating oil.

 

The peculiarity of the compressor lies in the fact that it is itself a heat source. During continuous operation, the bearing temperature can reach 80-100°C. The lubricating oil oxidizes under high temperatures and forms carbon deposits, blocking the oil passage and accelerating wear. Each start-stop and each load change adds a temperature cycle to the bearing. The bearing is not "burned out" once, but "tortured" to failure.

 

IV. Pumps: Temperature Difference Forces the Bearing Housing to "Deform"

Case: A centrifugal pump was used for a long time in an environment with a large temperature difference between the inside and outside. The hollow bearing housing with a cooling device underwent significant deformation. This caused the outer ring of the bearing to receive abnormal loads during operation, resulting in local actual loads far exceeding the design load, causing the bearing to fail prematurely.

 

This case reveals an easily overlooked fact: Temperature variation not only acts directly on the bearing but also indirectly destroys the bearing by changing the shape of the bearing housing. The thermal deformation of the bearing housing due to the temperature difference caused the outer ring to be "pressed" into the deformed housing hole, resulting in excessive load on the raceway, and the bearing failed prematurely. This is not a problem with the bearing itself but a structural failure caused by temperature variation.

 

The problem of temperature variation in pump equipment is also widespread. At a certain petrochemical plant, the bearing temperature of a circulating water pump was high during operation. After investigation, the fault was determined to be due to thermal imbalance. During the summer high-load heating period of a 350MW supercritical thermal power generation unit's pre-pump, the temperature of the free-end bearing frequently exceeded the normal range, reaching up to 91°C. The motor of a condensate pump in a certain power plant suddenly showed a bearing temperature defect after operating for more than 600 hours. The pump was used in a humid environment for a long time, and the bearing surface oxidized and formed rust. Tests showed that only 0.002% of water contamination in the lubricating oil reduced the bearing life by approximately 48%.

 

Another characteristic of pumps is outdoor installation. In northern pump stations, the bearing lubricating grease hardens at -30°C, and the starting resistance increases sharply; under the summer sun, the pump body temperature exceeds 60°C, and the expansion of the inner and outer rings is not synchronized, causing the clearance to shrink or even get stuck. The same pump, frozen in winter and unable to rotate, and overheated in summer and stuck - the temperature difference forced the bearing to be at two extremes.

 

V. Reducer: 0.25mm Error, 76 Hours of Shutdown

Case: Five reducers in a steel mill's sintering production line experienced the same type of failure during operation. Taking one of them as an example, the high-speed shaft bearing of the reducer overheated and stuck due to improper adjustment of the clearance. The B granulator was shut down for a total of 76 hours. Six sets of high-speed shafts and 12 sets of bearings were replaced, resulting in direct economic losses of over 300,000 yuan. The bearing of a reducer is much more sensitive to thermal expansion than other general equipment. This is because the internal structure of a reducer is compact and the heat dissipation conditions are limited, so the temperature rise of the bearing is often more significant than in an open environment. The calculation of bearing clearance must be based on the working temperature - if the reserve is too little, the shaft will seize up when heated; if it is too much, the operational accuracy will decrease and the vibration will intensify.

 

This principle may seem simple, but it is frequently misapplied in practice. In a cement factory, the bearing of the secondary shaft of a rotary kiln in a reducer suddenly rose in temperature after the replacement of the gear pair. It exceeded 60°C at 18:00 and reached 95°C at 18:15, and smoke emerged from the upper ventilation hole of the reducer. The technicians later discovered that when installing, 0.208mm of expansion allowance was reserved based on the working temperature of 50°C. However, the actual working temperature reached 65°C, and the ambient temperature at night was only 10°C - re-calculation based on the actual conditions showed that the expansion allowance should be 0.458mm. A difference of 0.25mm led to a failure of seizing up.

 

The mechanism of temperature fluctuation-induced failure of reducer bearings is very clear: temperature fluctuation causes clearance change → clearance change leads to a change in the gear meshing state → the meshing state change leads to increased vibration and heat generation → heat further raises the temperature → clearance changes further. This is a self-accelerating vicious cycle. Once it starts, the lifespan of the bearing is calculated in hours.

 

Six. Temperature Fluctuation - The Greatest "Invisible Killer" for the Reliability of General Equipment

Overall, the failure of bearings in fans, compressors, pumps, and reducers, with temperature fluctuation being often the overlooked culprit.

 

The failure path of the reducer in a cold-feed extruder: temperature difference → thermal expansion occupying the axial clearance → clearance disappears → bearing seizing. The failure path of the compressor: temperature difference → repeated oxidation of lubricating grease → failure of the oil film → increased wear → temperature失控. The failure path of the pump： temperature difference → thermal deformation of the bearing housing → abnormal load on the outer ring → overload of the raceway → premature failure. The failure path of the reducer： temperature difference → calculation error of clearance → inability to release thermal expansion → seizing → shutdown.

 

These devices cover most scenarios in industrial production. They are neither "extreme" nor "minor"， but precisely because of their universality， temperature fluctuation becomes a systematically underestimated reliability hazard. Every fan， every compressor， every pump， and every reducer is subjected to invisible wear caused by temperature fluctuations in the course of the four seasons， day and night cycles， and start-stop cycles.

 

Seven. NMT's Solution： Make the Bearings Adapt to Temperature Differences， Not Passively Bear Them

The design logic of NMT's special high and low temperature fluctuation transmission bearings is precisely targeted at each of the failure paths mentioned above.

 

For thermal expansion seizure - special heat-stable treated steel will control the size change of the bearing's inner and outer diameters within a very small range， avoiding thermal expansion from occupying the clearance. Thermal balance simulation optimizes the structure by precisely calculating the expansion amount under working temperature， customizing the most suitable clearance group for each device.

 

For repeated oxidation of lubricating grease - wide temperature range special lubricating grease maintains stable viscosity characteristics in the range of -30°C to 120°C， does not solidify at low temperatures， and does not thin out at high temperatures， maintaining chemical stability in tens of temperature cycles， not oxidizing， not coking， and not losing.

 

For abnormal load on the outer ring caused by thermal deformation of the bearing housing - optimized fit design and thermal compensation structure ensure that the bearing maintains a reasonable operating clearance when the bearing housing undergoes thermal deformation， avoiding the outer ring bearing additional load. Regarding the deviation in clearance calculation - the engineering team of NMT conducted precise calculations based on actual working temperatures, ambient temperatures, shaft span and other parameters, providing customized clearance settings and thermal compensation solutions for each reducer.

 

The NMT high and low temperature alternating special transmission bearings transfer the technical capabilities verified in extreme environments to the general industrial field. This enables each piece of equipment to provide stable accuracy and long-lasting lifespan in the scorching heat of summer and the freezing cold of winter, eliminating the "temperature difference" from becoming an unnoticed efficiency killer in industrial transmission.