Abstract
The issues of air and water leakage in steam ovens are among the core challenges in the industry, and the reliability of the door sealing system is a crucial indicator of product quality. This paper confirms the design scheme, conducts practical testing and verification, and repeatedly analyzes, verifies, and improves to resolve various anomalies encountered during testing. Each issue is interrelated. The sealing performance of the door is mainly related to the door structure, the flatness of the door glass, the riveting height of the front panel, the interference fit of the sealing ring design, the hardness of the sealing ring, the aging and deformation of the sealing ring, the size control of the sealing ring, and the internal air pressure of the cavity. Solving the problems of air and water leakage from the door is a systematic project that requires reasonable and effective solutions for each module. By controlling the flatness of the door glass, using inspection tools to check the dimensions of the sealing groove in the front panel, and maintaining the riveting height of the cavity within tolerance limits, we can address these issues. The sealing ring design is adjusted based on actual conditions, increasing the thickness of the sealing edge appropriately, selecting suitable hardness values for the sealing ring, determining reasonable opening forces, and using tooling to check and control the stability of the sealing ring’s dimensions in bulk production. Ultimately, this research addresses significant technical challenges related to air and water leakage in steam ovens.
Introduction
The reliability of the sealing system is one of the core technologies of steam ovens. Air and water leakage from the door is a common technical challenge in the industry. The product is benchmarked against top-tier brands, with extremely high quality requirements, particularly a lifespan requirement of 3,000 hours of aging, which is three times the industry standard. The door opening and closing lifespan is required to be tested for 30,000 cycles without any leakage. Achieving a true 10-year service life is a significant R&D challenge. The three main structural elements of the door sealing system are the cavity, sealing ring, and door assembly. The reliability of the door sealing system is related to many factors, including the structure of the door assembly, the flatness of the door body, the structure of the sealing ring, the internal air pressure of the cavity, and the locking force of the door. Each design confirmation is a challenge that requires repeated adjustments and testing to finalize. Better dimension stability results in lower defects such as burrs and flash, but at a higher cost. Considering the increased customer demands for sealing performance and the high-end positioning of the product, the final solution confirms that the sealing ring is made of liquid silicone rubber through molding and installed on the front panel. The cavity uses fully automated laser welding to ensure overall sealing. The sealing is achieved through the interference fit between the inner glass of the door and the sealing ring.
1. Research Purpose and Significance
The door sealing system of steam ovens is extremely important for ensuring product performance and quality, as its performance directly affects the product’s lifespan and user experience. This paper conducts in-depth research and solutions to the issues existing in the steam oven door sealing system, which is crucial for product optimization and improving user satisfaction. This study aims to explore the key factors of the steam oven door sealing system, including door structure, glass flatness, sealing structure, and materials. Through detailed testing and verification, we aim to improve sealing effectiveness and ensure product quality. Solving air and water leakage problems is significant for enhancing the quality of steam oven products and user experience. This research can also provide references and insights for the design of sealing systems in similar products.
2.Confirmation of Door Sealing System Design Scheme
The sealing ring is a key part of the door sealing structure, serving to fill the gap between the door and the cavity to prevent the loss of heat and humidity. When designing the sealing ring, factors such as material, shape, and size need to be considered. In the industry, there are generally two types of door sealing structures. One is to arrange the sealing ring on the door assembly, and the other is to place the sealing ring on the front panel. Each structure has its own advantages and disadvantages. A sealing ring installed on the door structure results in a simpler cavity structure but is inconvenient for disassembly. If the sealing ring ages, users cannot replace it themselves, and it mainly serves as an auxiliary seal. A sealing ring installed on the front panel results in a more complex cavity structure, incurs higher costs, and provides better sealing performance. The sealing ring can be treated as a consumable that users can replace freely. Given that the main function of this model is steam, which requires extremely high sealing performance, the second structural scheme was chosen after comprehensive evaluation. There are two types of silicone sealing rings in the industry: one is extruded, and the other is molded. Extruded molds have very low opening costs, while molded types include ordinary silicone and liquid silicone. Liquid silicone offers better dimensional stability, with very low defects such as burrs and flash, but at a much higher price. Considering the increased customer demands for sealing performance and the high-end positioning of the product, the final solution confirms that the sealing ring is made from liquid silicone rubber through molding and installed on the front panel. The cavity is constructed using fully automated laser welding to ensure overall sealing. Sealing is achieved through the interference fit between the inner glass of the door and the sealing ring.
3.3 Analysis and Solutions to Door Sealing System Issues
3.1 Analysis and Resolution of Air Leakage and Wrinkling at the Four Corners of the Sealing Ring
According to the overall scheme requirements, structural design was conducted, and parts were sampled to assemble prototypes for testing. Initial tests revealed significant air leakage at the four corners of the sealing ring, which also tends to wrinkle upon installation. Measurement and analysis of the product structure showed that there were indentations of approximately 0.5mm to 0.8mm at the corners where the cavity front panel and U-shaped frame were riveted. Detailed analysis and discussion indicated that the corner indentation issue was caused by material pulling at the R corners during the riveting of the front panel and U-shaped frame. Currently, there is no simple solution to improve the mold, and the cost of mold modification is extremely high—estimated to be at least several hundred thousand yuan. Therefore, from an efficiency perspective, optimization of the product structure was the only feasible approach. After repeated research and analysis, it was decided to add adhesive compensation at the collapsed areas where the sealing ring meets the front panel, while also shortening the length and width of the sealing ring to resolve the wrinkling issue caused by excessive material accumulation during installation. The cost of modifying the sealing ring mold is relatively low, estimated at 20,000 to 30,000 yuan. Drawings were outputted, and changes were immediately initiated. The newly sampled sealing ring after modifications was sent for testing and verification, significantly resolving the large area of air leakage at the corners, although some minor leakage issues remained, which will be analyzed and verified further.
3.2 Analysis and Resolution of Front Panel Sealing Groove Dimension Stability
3.2.1 Causes of Dimension Instability in the Sealing Groove
After trial production, products were tested, revealing that 20% of the machines still experienced air and water leakage issues. A comparative analysis of the dimensions of the leaking products was conducted. It was found that the riveting height of the front panel was very unstable, with a measured deviation of 0.4mm, while the design tolerance requirement was ±0.15mm, indicating poor dimension stability. Figure 1 shows the sealing groove surface. If the riveting height of the cavity is too high, it will press against the sealing ring when closing the door, causing the door not to close tightly and leading to air leakage. If the riveting height is too low, the sealing ring cannot achieve an interference fit, resulting in an inability to seal effectively and leading to air leakage. The cross-section of the sealing ring installation is shown in Figure 2. The cavity front panel and U-shaped frame are produced using fully automated laser welding, which should normally have high dimension stability. Each finished product undergoes dimension inspection, and data is collected. By collecting data and inspecting each production process, parameters were repeatedly adjusted and verified, ultimately revealing that the issue originated from the previous process. The instability of the stainless steel front panel sealing groove dimensions was found to be the cause. Some sealing groove dimensions were too large, while others were too small. To improve production efficiency, the front panel was produced using multiple machines in a connected line. However, the inspection during the production process was inadequate. After multiple productions, the mold deviated, and no mold repairs were scheduled. The sealing groove has an irregular structure, making measurement difficult. Various compounding factors led to the failure to detect abnormalities in the front panel dimensions.
3.2.2 Solutions for Dimension Instability in the Sealing Groove
Through detailed research discussions with relevant personnel, it was ultimately confirmed that additional measurement tools would be implemented to measure the width of the front panel sealing groove and the overall inner diameter of the front panel using specific gauges and stop gauges. If any abnormalities are detected during production, timely mold repairs will be arranged. Consequently, measurement tools were added to control the width of the front panel sealing groove, effectively stabilizing the dimension stability of the previous process. The tolerances for the riveting height of the cavity can be controlled within reasonable limits during bulk production inspections.
3.3 Analysis and Resolution of Water Leakage at the Bottom of the Sealing Ring
3.3.1 Analysis and Control of Glass Flatness
After approximately 500 hours of aging, water leakage was observed at the bottom sealing ring of the door. Machines exhibiting poor water leakage can easily cause the water collection tray to overflow, impacting user experience, and in severe cases, may even soak the cabinetry. A further measurement analysis was conducted on the machines with abnormal water leakage. It was found that the flatness of some inner door glass exceeded 1.0mm. Additionally, after a period of aging, the sealing edge of the sealing ring showed signs of collapse and deformation, with a maximum collapse height of 0.7mm, while the designed interference fit was 1.8mm. The insufficient sealing interference, combined with a certain micro-pressure during the steam cooking process, leads to the sealing ring being breached by air pressure, resulting in steam leakage and subsequent water leakage. This issue arises from the combination of two factors, both of which need to be addressed. The flatness issue of the inner door glass was communicated to the glass manufacturer. The inner door glass is low-radiation glass, which is relatively large, and the tempering process involves high temperatures, resulting in certain temperature differences that lead to glass deformation. From a design perspective, the supplier was required to control the flatness of the inner door glass to ≤0.4mm. The manufacturer responded that the current production process could not achieve this and suggested adjusting the flatness to ≤0.6mm. To evaluate whether the flatness met this requirement, a trial batch of glass was arranged for production, and the flatness of all glass pieces was inspected to collect data confirming compliance with the requirement. On-site confirmation during the trial production established that the flatness of the inner door glass could indeed be controlled to ≤0.6mm. Production process parameters were then solidified accordingly, and a production process card was generated, mandating adherence to this process during production.
3.3.2 Analysis and Resolution of Sealing Ring Deformation and Collapse Issues
The deformation and collapse of the sealing ring were analyzed using projected measurements. Significant deformation and collapse were observed in the middle of the long edge of the sealing ring. The primary reason for this is that after prolonged aging, the sealing ring becomes harder and loses elasticity. The thickness at the deformation site is too thin at only 0.8mm, causing the sealing edge to deform under long-term compressive stress. The corners, which had previously been thickened for compensation, showed minimal deformation. Considering that the deformation is most severe in the middle of the four edges, the design should appropriately increase the thickness in the middle while gradually tapering towards the sides. Therefore, the improvement plan involves designing a gradient of adhesive on the sealing ring, where the middle is thicker and gradually thins towards the sides, as illustrated in Figure 3. This plan theoretically addresses the water leakage issue caused by the collapse and deformation of the sealing ring. However, increasing the thickness of the sealing ring introduces a new challenge. A thicker sealing ring has greater overall strength,requiring a larger sealing force. The original opening force may be insufficient to counteract the deformation force of the sealing ring, potentially resulting in the door not closing properly and becoming uneven. Since the sealing ring is made from high-precision molds, it is impossible to use prototypes or other methods to validate the feasibility of the modification; thus, direct mold modifications are necessary. This presents a risk point, as excessive adhesive may prevent the door from closing, while insufficient adhesive may still lead to collapse and deformation. After research and discussion, it was confirmed to increase the thickness by 0.5mm. To maximize assurance against anomalies, the liquid silicone mold is a two-cavity mold; the first cavity will be modified and tested for compliance before modifying the second cavity. The opening force will be confirmed after the modified samples are sent for testing. Ultimately, the sealing ring after modification underwent aging tests and verification, successfully resolving the water leakage issue at the bottom, but a new problem emerged with minor air leakage at the top, and the door had a slight bulge, indicating that the sealing effect was not ideal, consistent with pre-modification predictions. This new issue remains to be addressed.
3.4 Analysis and Resolution of Minor Air Leakage at the Top of the Sealing Ring
As previously mentioned in section 3.3.2, the minor air leakage at the top of the sealing ring is caused by insufficient opening force. During the testing and verification process, manual application of closing force effectively resolved the top air leakage issue. This confirms that increasing the opening force is a viable direction for solving the problem. The opening force is crucial for user experience; it cannot be too high or too low. If the opening force is too low, it will lead to significant air and water leakage. Conversely, if the opening force is too high, users will find it very difficult to open the door. The initial design for the opening force was set at (35-45) N. The preliminary improvement plan is to adjust the opening force to (45-55) N. The opening force is measured using a dynamometer, with the measurement method being to open the door at a constant speed until the maximum opening force is reached, averaging five sets of data. The opening force is controlled through the door hinge, which is also a core component. The challenge lies in ensuring the door’s opening and closing life reaches the requirement of 30,000 cycles, while the industry standard is generally 20,000 cycles. After testing the door’s lifespan, it was found that insufficient opening force can lead to performance degradation. Currently, there are few manufacturers in China capable of producing this type of hinge. Adjusting the hinge’s opening force is achieved by modifying the spring tension and the shape of the hinge plate. The improvement process involves repeatedly fine-tuning the trigger force curve to find the most suitable range of force values and opening feel. After the manufacturer finalizes the plan, samples will be sent for testing the opening and closing lifespan. During the testing process, several anomalies were encountered, such as severe trigger wear, significant force degradation, and unusual noises from the hinge. Through perseverance in overcoming these challenges and repeated testing and verification, the opening force was ultimately confirmed to be in the range of (45-60) N. The hardness of the sealing ring is also a critical factor affecting sealing effectiveness and opening force. If the hardness is too high, it will affect the sealing deformation, leading to poor sealing effectiveness; if the hardness is too low, the sealing ring may lack sufficient strength and exhibit irreversible plastic deformation after prolonged stress. Through extensive testing, verification, and analysis, the final matching opening force determined the sealing ring hardness to be (40±5) degrees.
3.5 Control of Sealing Ring Dimension Stability
The issues of air and water leakage from the door are closely related to the dimensional control of various components. How to control the dimensions of the sealing ring is a challenging task. Due to the irregular structure of the sealing ring, measuring its dimensions is difficult. Incoming material inspection generally only verifies the appearance of a component and checks if the sealing ring exhibits severe anomalies during trial assembly. The detailed dimensions are not properly controlled. Therefore, it is required to increase the measurement of cross-sectional dimensions of the components, while also creating inspection tools to check the main dimensions of the sealing ring, such as the height of the sealing edge, and providing a reasonable tolerance range. It is also required that each batch undergoes random inspection. Once the inspection tools are completed, the supplier also provides a set for double-checking, ensuring the stability of each critical dimension of the sealing ring.
The core issues of air and water leakage from the steam oven door are related to many factors, and the associated components, dimensions, and parameters all need to be reasonably controlled. By optimizing the opening force of the door hinge within a reasonable range, compensatory reinforcements were added to the corners of the sealing ring, the middle was designed with a gradient of adhesive to increase thickness and enhance strength, preventing collapse and deformation after long-term aging, and selecting appropriate sealing ring hardness values.