In the cigarette manufacturing industry, enhancing product quality and achieving cost savings through reduced waste are perpetual goals. The filter rod supply system plays a critical role in this endeavor, and many systems in use today are derived from imported technology localized by manufacturers such as Xuchang Tobacco Machinery. The YF215 filter rod receiver, a key component, often operates at high speeds for extended periods, leading to significant challenges. Specifically, the compact design of its transmission box, small gear modules, high operational speeds, inadequate lubrication, and excessive loads contribute to unstable gear operation. This instability can damage internal components, including the gear shaft, and even the box itself, resulting in erratic transverse roller movement, substantial filter rod waste, and, in severe cases, complete receiver failure. Through detailed analysis and iterative learning, we focused on modifying the intermediate gear shaft within the transmission box to enhance stability and reliability in filter rod supply. This article documents our first-person perspective on the structural issues, failure analysis, redesign process, and outcomes, incorporating tables and formulas to summarize key aspects.
The YF215 filter rod receiver comprises two primary drive systems: a longitudinal drive and a transverse drive. The longitudinal system uses a servo motor connected via a flat belt to acceleration-deceleration discs, which slow down and then re-accelerate high-speed filter rods from the pipeline. In contrast, the transverse drive system employs a servo motor coupled to a gearbox that outputs six distinct speeds. These speeds drive two guide rollers and four transport rollers to convey filter rods parallelly into the cigarette machine’s filter rod reservoir. The transverse gearbox is constructed from two cast aluminum housings, housing 13 spur gears with high machining precision, assembled using fastening screws. The servo motor transmits rotation through various gear reductions to the rollers, operating at speeds up to 2800 RPM. Specifically, shafts 1 and 2 rotate at equal speeds, as do shafts 3 and 4, and shafts 5 and 6. Shafts 1 and 2 drive smooth rollers via elastic couplings, while shafts 3 to 6 utilize gear-type couplings for transport rollers. The gearbox features a modular design with a gear module of 0.5, and to prevent oil contamination of filter rods, grease lubrication is used throughout. Each cigarette-making unit integrates two receiver units, with individual units handling approximately 1200 filter rods per minute. Given that a cigarette machine produces 7000 cigarettes per minute, requiring 1750 filter rods, the receiver operates about 73% of the machine’s runtime. This prolonged, high-speed operation under typical lubrication conditions makes the gearbox prone to failures, with repairs causing significant downtime.
To quantify the failure modes, we analyzed data from 2018, identifying four primary categories of gearbox malfunctions. Gear wear accounted for 11% of incidents, largely due to the small gear module of 0.5, which, under poor lubrication or heavy loads, accelerates deterioration. Bearing failures constituted 22% of cases, involving various small bearings such as 6001, 609, 607, and 608 types, which are susceptible to damage under continuous high-speed operation. Shaft neck wear represented 11% of failures, often resulting from uneven force distribution caused by bearing or gear issues. Housing wear was the most prevalent at 44%, primarily affecting the bore holes for the intermediate gear shafts, leading to ovalization and loosening of the gear shaft. Other miscellaneous faults made up the remaining 11%. Regular maintenance, synchronized with cigarette machine schedules, involved disassembling the gearbox, replacing worn bearings, lubricating components, and addressing minor gear wear. However, housing wear persisted, necessitating full housing replacements and incurring substantial costs—six housings were discarded in the first half of 2018 alone due to irreparable damage.
| Failure Type | Number of Incidents | Percentage | Primary Causes |
|---|---|---|---|
| Gear Wear | 2 | 11% | Small module (0.5), lubrication issues, high load |
| Bearing Damage | 4 | 22% | Continuous high-speed operation, excessive load |
| Shaft Neck Wear | 2 | 11% | Uneven force distribution from other components |
| Housing Wear | 8 | 44% | Ovalization of bore holes for intermediate gear shafts |
| Other Faults | 2 | 11% | Miscellaneous issues |
Further investigation revealed that housing wear concentrated on the bore holes for the intermediate gear shafts, which were designed as cantilevered installations with short engagement lengths. These intermediate gears each meshed with three other gears unevenly, leading to complex radial force distributions. For instance, intermediate gear 1 experienced radial forces \( F_{r2} \), \( F_{r2′} \), and \( F_{r2”} \), while intermediate gear 2 faced \( F_{r5} \), \( F_{r5′} \), and \( F_{r5”} \). The resultant force \( F_r \) on each gear shaft can be expressed as the vector sum: $$ F_r = \sqrt{ (\sum F_{x})^2 + (\sum F_{y})^2 } $$ where \( F_x \) and \( F_y \) are the force components in orthogonal directions. This resultant force acted on the gear shaft, transmitting stress to the aluminum housing bore. Given the material’s lower strength, prolonged high-speed operation caused deformation and wear, enlarging the bore holes and leading to gear misalignment, accelerated wear, and eventual failure. The gear shaft’s role in transmitting torque and forces is critical; thus, any instability directly impacts the entire system.
To address these issues, we formulated a redesign strategy focused on the intermediate gear shaft. The original design featured a short engagement length with the housing, resulting in high localized stress. We proposed lengthening the shaft’s engagement portion to distribute forces over a larger area and adding an external thread at the shaft end. This modification allows for securing with a nut and washer outside the housing, increasing frictional resistance and reducing point loads on the bore. The new gear shaft design ensures that the contact area between the shaft and housing is maximized, thereby decreasing the stress concentration. The stress \( \sigma \) on the housing bore can be approximated by: $$ \sigma = \frac{F_r}{A} $$ where \( A \) is the contact area. By increasing \( A \) through a longer shaft, \( \sigma \) is reduced, enhancing durability. Additionally, the threaded end with nut fixation provides axial constraint, preventing loosening under dynamic loads. We verified that this design would not interfere with adjacent components through spatial analysis during prototyping.
| Parameter | Original Design | Improved Design |
|---|---|---|
| Engagement Length (mm) | Short (approx. 10 mm) | Extended (approx. 20 mm) |
| Shaft End Feature | Plain | External Thread with Nut |
| Contact Area (mm²) | Low | High |
| Stress Concentration | High | Reduced |
| Assembly Complexity | Simple press-fit | Requires nut tightening |
The implementation of the improved gear shaft began in early 2019, with upgrades applied to six receiver units across three cigarette machines. During routine maintenance, we replaced the original intermediate gear shafts with the new design. Post-modification, we monitored the systems for over six months, observing no gearbox failures. The receivers operated smoothly, with no instances of unstable roller movement or filter rod waste. Upon disassembly after nearly eight months—aligning with the standard maintenance cycle—we found no signs of gear wear, shaft loosening, or housing damage. The gear shafts remained securely fixed, and the bore holes retained their cylindrical form, confirming the effectiveness of the redesign. This improvement significantly reduced downtime and spare part costs, as housing replacements were eliminated. The successful application underscores the importance of optimizing the gear shaft in high-speed transmission systems to enhance overall machine reliability.
In conclusion, the modification of the intermediate gear shaft in the YF215 filter rod receiver’s transverse gearbox has proven highly effective in mitigating failures related to housing wear and gear instability. By extending the shaft engagement and incorporating a threaded end with nut fixation, we distributed radial forces more evenly, reduced stress concentrations, and improved the longevity of the gearbox. This approach not only ensures stable filter rod supply but also aligns with industry goals of waste reduction and operational efficiency. Future work could explore material upgrades for the gear shaft or advanced lubrication techniques to further enhance performance. The tables and formulas provided here summarize the key aspects of our analysis and redesign, emphasizing the critical role of the gear shaft in transmission systems.