As a researcher focused on lubricant development, I have been deeply involved in the formulation of specialized oils for industrial applications. In this article, I will detail the comprehensive process of developing L-CKE680 worm gear oil, which is critical for the efficient operation of worm gears. Worm gears are widely used in power transmission between non-intersecting shafts, offering advantages such as high speed reduction ratios, compact design, and significant torque output. However, the sliding motion inherent in worm gear operation, combined with high relative sliding speeds and extended contact, poses severe lubrication challenges. With advancements in materials science and lubricant technology, modern worm gear systems have become more compact and load-bearing, demanding higher performance from lubricants. Thus, developing a worm gear oil with excellent properties—including superior viscosity-temperature characteristics, low-temperature fluidity, oxidation stability, anti-wear performance, and corrosion resistance—is paramount.
The development of worm gear oil adheres to strict standards to ensure reliability. For this project, we referenced the SH/T 0094–91 specification, which outlines key quality indicators for L-CKE680 worm gear oil. These include viscosity at 40°C ranging from 612 to 748 mm²/s, a viscosity index of at least 90, a pour point below -6°C, and requirements for oxidation stability, rust prevention, and foam resistance. Meeting these criteria is essential for protecting worm gears from wear, corrosion, and premature failure. The importance of worm gears in various industries—from automotive to heavy machinery—cannot be overstated, as they enable precise motion control and power transmission in confined spaces.
To begin the formulation, we selected base oils as the primary component, as they significantly influence the final product’s performance. We evaluated both in-house produced paraffinic high-pressure hydrotreated base oil (designated as 50-number white oil) and an externally sourced 680 white oil. Their properties are summarized in Table 1 below:
| Property | 680 White Oil | 50-Number White Oil | Test Method |
|---|---|---|---|
| Kinematic Viscosity at 40°C (mm²/s) | 729.7 | 54.04 | GB/T 265 |
| Kinematic Viscosity at 100°C (mm²/s) | 33.99 | 8.325 | GB/T 265 |
| Pour Point (°C) | -9 | -13 | GB/T 3535 |
| Viscosity Index | 72 | 126 | GB/T 1995 |
| Total Sulfur Content (mg/kg) | <1 | <1 | SH/T 0631 |
| Saturated Hydrocarbon Content (%) | 98.87 | 99.13 | SH/T 0607 |
From Table 1, it is evident that the 50-number white oil has a higher viscosity index (126) compared to the 680 white oil (72), making it beneficial for maintaining viscosity across temperature ranges—a crucial factor for worm gears operating under varying thermal conditions. However, the 680 white oil provides higher base viscosity. Therefore, we decided to blend these two base oils to achieve the target viscosity for L-CKE680, while incorporating viscosity index improvers to enhance the viscosity index further.
The viscosity index (VI) is a critical parameter for worm gear oils, as it indicates how viscosity changes with temperature. A higher VI ensures stable lubrication across operating temperatures, reducing wear in worm gears. The VI can be calculated using the standard formula based on kinematic viscosity at 40°C and 100°C:
$$ VI = \frac{L – U}{L – H} \times 100 $$
where \( U \) is the kinematic viscosity of the oil at 40°C, and \( L \) and \( H \) are reference values derived from tables based on viscosity at 100°C. For worm gear applications, we aimed for a VI ≥ 90 as per the standard. To achieve this, we evaluated two types of polymethacrylate viscosity index improvers, labeled A and B, by blending them with the base oil mixture. The formulations and results are shown in Table 2:
| Formulation | Base Oil Blend (680:50-number) | VI Improver A (%) | VI Improver B (%) | Kinematic Viscosity at 40°C (mm²/s) | Kinematic Viscosity at 100°C (mm²/s) | Viscosity Index | Shear Stability (% decrease) |
|---|---|---|---|---|---|---|---|
| 1 | 81.1:11 | 7.9 | 0 | 589.3 | 33.6 | 88 | 2.2 |
| 2 | 75.8:14.8 | 7.9 | 0 | 544.7 | 32.44 | 90 | 2.3 |
| 3 | 74.2:14.5 | 9.8 | 0 | 628.8 | 36.14 | 92 | 2.4 |
| 4 | 73.4:14.3 | 10.8 | 0 | 677.1 | 38.48 | 94 | 2.7 |
| 5 | 72.5:14.1 | 0 | 13.4 | 561.3 | 32.4 | 88 | 4.1 |
| 6 | 71.5:14.0 | 0 | 14.5 | 632.5 | 35.8 | 90 | 4.5 |
| 7 | 70.7:13.8 | 0 | 15.5 | 681.4 | 38.3 | 93 | 5.1 |
| 8 | 69.2:15.3 | 0 | 15.5 | 665.6 | 37.8 | 93 | 5.3 |
Shear stability is vital for worm gear oils because the mechanical shear in worm gear systems can break down polymer chains in viscosity index improvers, leading to viscosity loss. The shear stability is measured as the percentage decrease in kinematic viscosity at 40°C after testing, with a limit of ≤6% per SH/T 0094–91. From Table 2, Formulation 4 with VI improver A at 10.8% achieved the target viscosity (677.1 mm²/s at 40°C) and VI (94) with a shear stability decrease of only 2.7%, outperforming formulations with VI improver B, which required higher treat rates and showed poorer shear stability (up to 5.3%). Thus, we selected VI improver A for its cost-effectiveness and superior performance in maintaining viscosity under shear—a key consideration for worm gears.
Next, we focused on composite additives to enhance critical properties such as anti-wear performance, oxidation stability, and rust prevention for worm gears. We evaluated two high-performance composite additive packages: Package C (consisting of main agent C1 and reinforcement C2) and Package D, along with a saturated polyol ester Q and antifoam agent P. The goal was to identify the optimal combination that meets all standard requirements. The formulations based on Package C are detailed in Table 3:
| Property | Specification (L-CKE680) | Formulation 1 (C) | Formulation 2 (C) | Formulation 3 (C) | Formulation 4 (C) | Test Method |
|---|---|---|---|---|---|---|
| Base Oil (%) | – | 97.9 | 96.6 | 95.5 | 94.2 | – |
| C1 (%) | – | 0.8 | 1.0 | 1.1 | 1.3 | – |
| C2 (%) | – | 0.3 | 0.4 | 0.4 | 0.5 | – |
| Polyol Ester Q (%) | – | 0 | 2 | 3 | 4 | – |
| Antifoam P (mg/kg) | – | 200 | 200 | 200 | 0 | – |
| Neutralization Number (mg KOH/g) | ≤1.3 | 1.02 | 1.17 | 1.22 | 1.35 | GB/T 4945 |
| Sulfur Content (%) | ≤1.25 | 0.822 | 0.901 | 0.993 | 0.993 | SH/T 0303 |
| Saponification Value (mg KOH/g) | 9–25 | 1.2 | 9.0 | 11.5 | 14.5 | GB/T 8021 |
| Demulsibility (54°C, min) | ≤60 | 45 | 40 | 30 | 30 | GB/T 7305 |
| Copper Strip Corrosion (100°C, 3h) | ≤1 | 1c | 1b | 1b | 1b | GB/T 5096 |
| Foam Tendency/Stability (mL/mL) | ≤75/10 | 25/0 | 25/0 | 25/0 | 55/0 | GB/T 12579 |
| 24°C | – | – | – | – | – | – |
| 93.5°C | – | 0/0 | 0/0 | 0/0 | 500/0 | – |
| Post-24°C | – | 35/0 | 35/0 | 35/0 | 150/0 | – |
| Rust Prevention (Distilled Water) | No Rust | No Rust | No Rust | No Rust | No Rust | GB/T 11143 |
| Oxidation Stability (hours to reach 2 mg KOH/g) | ≥350 | 462 | 704 | 938 | 945 | GB/T 12581 |
| Shear Stability (% decrease) | ≤6 | 2.6 | 2.8 | 2.6 | 2.7 | NB/SH/T 0505 |
From Table 3, Formulation 3 with Package C (1.1% C1, 0.4% C2, 3% polyol ester Q, and 200 mg/kg antifoam P) showed optimal results: a saponification value of 11.5 mg KOH/g (within the 9–25 range), excellent oxidation stability (938 hours), and good shear stability (2.6% decrease). However, the foam performance was marginal without antifoam, highlighting the need for additives to suppress foam—a common issue in worm gear systems due to agitation. For comparison, we evaluated Package D in similar formulations, as shown in Table 4:
| Property | Specification (L-CKE680) | Formulation 5 (D) | Formulation 6 (D) | Formulation 7 (D) | Formulation 8 (D) | Test Method |
|---|---|---|---|---|---|---|
| Base Oil (%) | – | 98.75 | 96.35 | 95.25 | 94.15 | – |
| Package D (%) | – | 1.25 | 1.65 | 1.75 | 1.85 | – |
| Polyol Ester Q (%) | – | 0 | 2 | 3 | 4 | – |
| Antifoam P (mg/kg) | – | 200 | 200 | 200 | 0 | – |
| Neutralization Number (mg KOH/g) | ≤1.3 | 0.68 | 0.72 | 0.78 | 0.81 | GB/T 4945 |
| Sulfur Content (%) | ≤1.25 | 0.614 | 0.657 | 0.698 | 0.711 | SH/T 0303 |
| Saponification Value (mg KOH/g) | 9–25 | 1.5 | 9.0 | 11.5 | 14.5 | GB/T 8021 |
| Demulsibility (54°C, min) | ≤60 | 45 | 30 | 28 | 28 | GB/T 7305 |
| Copper Strip Corrosion (100°C, 3h) | ≤1 | 1b | 1b | 1b | 1b | GB/T 5096 |
| Foam Tendency/Stability (mL/mL) | ≤75/10 | 25/0 | 25/0 | 25/0 | 45/0 | GB/T 12579 |
| 24°C | – | – | – | – | – | – |
| 93.5°C | – | 0/0 | 0/0 | 0/0 | 450/0 | – |
| Post-24°C | – | 35/0 | 35/0 | 35/0 | 140/0 | – |
| Rust Prevention (Distilled Water) | No Rust | No Rust | No Rust | No Rust | No Rust | GB/T 11143 |
| Oxidation Stability (hours to reach 2 mg KOH/g) | ≥350 | 584 | 927 | 1105 | 1136 | GB/T 12581 |
| Shear Stability (% decrease) | ≤6 | 2.7 | 2.4 | 2.8 | 2.7 | NB/SH/T 0505 |
Comparing Tables 3 and 4, Package D demonstrated superior performance in oxidation stability (up to 1136 hours in Formulation 8), lower neutralization numbers (indicating better acid control), and reduced sulfur content, which is beneficial for environmental and equipment compatibility. For worm gears, oxidation stability is crucial because thermal degradation can lead to sludge formation and increased wear. The oxidation process can be modeled using an Arrhenius-type equation:
$$ \frac{d[Acid]}{dt} = k \cdot [Acid]^n $$
where \( [Acid] \) is the acid number, \( k \) is the rate constant dependent on temperature, and \( n \) is the reaction order. A higher oxidation stability time implies slower degradation, prolonging the oil’s life in worm gear systems. Formulation 7 with Package D (1.75% additive, 3% polyol ester Q, and 200 mg/kg antifoam P) emerged as the optimal choice, meeting all specifications with a saponification value of 11.5 mg KOH/g, excellent demulsibility (28 minutes), and robust foam control. The polyol ester Q enhances lubricity and helps achieve the required saponification value, which correlates with ester content and improves film strength in worm gears.
To delve deeper into the technical aspects, the anti-wear performance for worm gears relies on the formation of protective films under high pressure. The extreme pressure (EP) properties can be described using the Hertzian contact theory, where the contact pressure \( P \) between worm gear teeth is given by:
$$ P = \sqrt{\frac{2E^* F}{\pi R}} $$
Here, \( E^* \) is the equivalent Young’s modulus, \( F \) is the load, and \( R \) is the effective radius. Worm gears often operate under high sliding conditions, so the lubricant must reduce friction and wear. The composite additives in Package D likely contain sulfur-phosphorus compounds that form sacrificial films, preventing metal-to-metal contact. Additionally, the viscosity modifier A ensures that the oil maintains adequate film thickness across temperatures, as per the Stribeck curve relationship:
$$ \lambda = \frac{h}{\sigma} $$
where \( \lambda \) is the lubrication regime parameter, \( h \) is the film thickness, and \( \sigma \) is the composite surface roughness. For worm gears, a full-film lubrication regime (\( \lambda > 3 \)) is desirable to minimize wear, and the high viscosity of L-CKE680 supports this.
Furthermore, rust and corrosion prevention are vital for worm gears exposed to moisture. The additives in Package D provide passivation layers on metal surfaces, inhibiting electrochemical reactions. The mechanism can be expressed as:
$$ Fe^{2+} + 2OH^- \rightarrow Fe(OH)_2 \quad \text{(rust formation)} $$
Additives like rust inhibitors adsorb onto metal, blocking water and oxygen access. In our tests, all formulations passed the distilled water rust test, ensuring protection for worm gear components in humid environments.
Foam resistance is another critical factor, as foam can reduce lubrication efficiency and cause overheating in worm gears. The antifoam agent P works by reducing surface tension, causing bubble collapse. The effectiveness can be quantified by foam volume decay over time:
$$ V(t) = V_0 e^{-kt} $$
where \( V(t) \) is the foam volume at time \( t \), \( V_0 \) is the initial volume, and \( k \) is the decay constant. With 200 mg/kg of antifoam P, formulations showed minimal foam, meeting the standard’s limits.
In summary, after extensive testing, we formulated L-CKE680 worm gear oil using a blend of 73.4% 680 white oil and 14.3% 50-number white oil, with 10.8% viscosity index improver A, 1.75% composite additive Package D, 3% saturated polyol ester Q, and 200 mg/kg antifoam agent P. This formulation exceeds SH/T 0094–91 requirements, with a kinematic viscosity of 681.4 mm²/s at 40°C, viscosity index of 93, pour point below -6°C, oxidation stability over 1100 hours, and excellent shear stability. The oil provides superior protection for worm gears, ensuring reduced wear, corrosion resistance, and extended service life.
The development process highlighted the importance of balancing base oil properties, additive synergies, and cost-effectiveness. For future work, we plan to explore synthetic base oils like polyalphaolefins (PAOs) to further enhance low-temperature performance and oxidation stability for worm gears operating in extreme conditions. Additionally, field trials in industrial worm gear applications will validate the oil’s performance under real-world loads and speeds. Worm gears continue to evolve, and our lubricant development aims to keep pace with these advancements, ensuring reliable power transmission across diverse sectors.
Throughout this project, the focus on worm gears has been paramount, as their unique kinematics demand specialized lubrication solutions. By leveraging advanced additives and rigorous testing, we have created a worm gear oil that not only meets but exceeds industry standards, contributing to the efficiency and durability of worm gear systems worldwide.