# 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  
(1) Appearance  
Based on the designed testing scheme, performance tests were conducted on samples of Grease 7014 before and after storage. The appearance of the original sample and the sample after storage is shown in Figure 4.  
From Figure 4, it can be seen that the appearance of lubricating grease has undergone significant changes after in situ storage. The original sample is in a white uniform paste shape. After in situ storage, the color of the sample is uneven, showing a yellow-brown color, and some samples are black, which is related to the base oil of 7014 Grease, which contains ester oils with poor biodegradability. (2) SEM Testing  
SEM testing was conducted on the original sample and the sample after the storage of Grease 7014. The test results are shown in Figure 5.  
Figure 4: Appearance of Grease 7014. (**a**) Original sample; (**b**) sample after storage. Figure 5: Microscopic morphology of Grease 7014. (**a**) Original sample; (**b**) sample after storage from different tests. It is clear that the original sample in Figure 5a had a tightly connected overall structure, and the soap base of the thickener remained intact without any irregular broken structures. The overall structure of the sample after storage in Figure 5b was relatively loose, and the fiber skeleton structure was severely damaged. Only a small amount of irregular entanglement on the incomplete skeleton could be observed, with irregular block or sheet solid structures scattered around. Grease 7014 is a sodium-based lubricating grease; the thickener is a fiber-like structure; and its oxidation stability is relatively insufficient. Therefore, in a long-term in situ storage environment, the soap-based skeleton structure of the thickener of the sample after storage was severely damaged, which can affect the oil storage capacity of the base oil, cause the leakage and volatilization of the base oil and reduce the lubrication performance of the lubricating grease during storage. (3) FTIR Testing  
FTIR testing was conducted on the original sample and the sample after the storage of Grease 7014. The test results are shown in Figure 6, where the red line represents the original sample, and the blue line represents the sample after storage. From Figure 6, it can be seen that both the original sample and the sample after storage showed characteristic peaks of silicone oil at 1260 cm\({}^{-1}\), 1098 cm\({}^{-1}\), and 1023 cm\({}^{-1}\), and amide at 3260-3360 cm\({}^{-1}\). However, after in situ storage, the amide characteristic peak of the sample changed significantly, with a new characteristic peak appearing at 1740 cm\({}^{-1}\), which is a stretching vibration peak of C=O, the in-plane bending vibration characteristic peak of -OH in the carboxyl group was 1429 cm\({}^{-1}\), and the stretching vibration peak of C-O in the carboxyl group was displayed at 1260 cm\({}^{-1}\). The above characteristic peaks correspond to the presence of carboxyl groups in the lubricating grease thickener. The reduction in these three peaks in the screw grease may indicate that the carboxyl groups in the thickener participate in the oxidation reaction and generate other oxidation products, indicating that the lubricating grease undergoes oxidation during storage. At 2919 cm\({}^{-1}\) and 2851 cm\({}^{-1}\), asymmetric stretching vibration characteristic peaks and symmetric stretching vibration characteristic peaks of -CH2- are displayed, respectively. Due to the large amount of -CH2- in the base oil, an increase in the peak value here indicates an increase in the relative content of the base oil. It is speculated that there is precipitation of the base oil, which indirectly reflects a decrease in the content of the thickener, which is a relatively large proportion of the lubricating grease except for the base oil.