# Experimental Study on In Situ Storage of Grease-Lubricated Ball Screws
## 3 Test Results and Analysis
### Changes in the Performance of Lubricating Grease before and after In-Situ Storage
From the above analysis, it can be inferred that under long-term storage, the lubricating grease thickener in the screw pair undergoes an oxidation reaction, causing a change in its chemical structure  
Figure 6: Infrared spectrogram of Grease 7014.  
and resulting in a decrease in the thickener content and oil storage capacity. The base oil seeps out and oxidizes, resulting in a decrease or loss of lubrication performance. Overall, during the lubrication and storage process, the grease thickener may be affected by oxidation-reduction reactions or structural damage, which can affect its oil storage and drainage capacity, resulting in a decrease or failure of the lubrication performance. (4) Rheological Testing  
The rheological properties of Grease 7014's original sample and the sample after storage were tested, and the test results are shown in Figures 7 and 8. The blue line represents the original sample, and the red line represents the sample after storage. From Figure 7, it can be seen that the trend of the viscosity-temperature curve of the original sample and the sample after storage is consistent. The viscosity first decreases and then stabilizes with the increase in temperature. After the temperature reaches 100 \({}^{\circ}\)C, the viscosity of the lubricating grease increases slightly. The starting viscosity of the sample after storage at \(-40\)\({}^{\circ}\)C is significantly higher than that of the original sample, and the viscosity difference increases with the increase in temperature. The viscosity of the sample  
Figure 8: Shear curve of Grease 7014. Figure 7: Viscosity–temperature curve of Grease 7014.  
after storage at 25 \({}^{\circ}\)C is about 10 times that of the original sample, and the viscosity of the sample after storage at 70 \({}^{\circ}\)C is about 1000 times that of the original sample. This might be because, during storage, the base oil in the lubricating grease precipitates and loses, or its components evaporate, resulting in an increase in its viscosity. From Figure 8, it can be seen that the trend of the shear force versus shear rate curve of the original sample and the sample after storage is basically consistent. PDSC testing was conducted on the original sample and the sample after storage of Grease 7014, and the test results are shown in Figure 9.  
From Figure 9, it can be seen that the original sample of PDSC (210 \({}^{\circ}\)C) > 60 min has a good high-temperature antioxidant performance. After in situ storage, the PDSC (210 \({}^{\circ}\)C) of the sample was 1.59 min, indicating poor high-temperature antioxidant performance. This might be due to the gradual consumption of antioxidants during storage, resulting in a decrease in the antioxidant performance of lubricating grease. SRV testing was conducted on the original sample and the sample after storage of Grease 7014, and the test results are shown in Figure 10. Due to the poor lubrication performance of 7014 lubricating Grease after storage, it can only be maintained for 70 s. After 70 s, the test results exceeded the testing range of SRV, so the experimental results were only retained for 70 s.  
From Figure 10, it can be seen that both the original sample and the sample after storage failed to complete the SRV test, with the original sample lasting approximately 47.9 s while the sample after storage lasted for about 22 s after the start of the experiment. The friction coefficient of the sample sharply increased, exceeding the limit set by the instrument, and the experiment was forced to terminate. From the SRV results, it can be seen that the anti-fretting wear performance of the sample still needs to be improved. The decrease in the anti-friction and wear performance of lubricating grease affects the intensification of friction and wear in the transmission mechanism. For rolling screw transmission mechanisms, the debris formed by wear accumulates in the raceway to a certain extent, causing serious failure modes such as mechanism jamming.