राइस कुकर इनर पॉट्स के लिए हॉट-रोल्ड और कोल्ड-रोल्ड एल्यूमीनियम डिस्क के बीच इयरिंग अनुपात अंतर: दीवार की मोटाई एकरूपता पर प्रभाव, इन्सुलेशन आसंजन, और थर्मल प्रदर्शन

HW-ए. परिचय: Application Background of Aluminum Inner Pots and Process-Related Requirements

Aluminum inner pots are widely used in kitchen appliances such as rice cookers, इलेक्ट्रिक प्रेशर कुकर, and vacuum thermos flasks. Their popularity stems from “हल्के, uniform heat conduction, and good formability” characteristics.

Among these applications, rice cooker inner pots account for over 60% of the market. विशेष रूप से, में 2024, the global market size of aluminum discs for rice cooker inner pots reached 5.2 billion yuan (source: China Nonferrous Metals Industry Association), reflecting the critical role of these raw materials in the industry.

Most rice cooker inner pots are manufactured from aluminum discs for rice cooker inner pots through a four-step process: “blanking → stretch forming → annealing → shaping”. विशेष रूप से, this process chain directly determines the final quality of the inner pot.

Their core quality indicators include two key aspects: ① Wall thickness uniformity (tolerance ≤5%, in line with QB/T 4099 Aluminum and Aluminum Alloy Inner Pots for Household and Similar Electric Heating Appliances); ② Outer wall flatness (roughness Ra ≤0.8μm). These two indicators are non-negotiable for ensuring performance.

विशेष रूप से, these two indicators directly determine the adhesion of the insulation layer—usually polyurethane foam or modified phenolic resin. They further affect the thermal insulation performance of rice cookers, which strictly requires “temperature drop ≤5℃ after 12h insulation at 60℃”.

Industry research shows that approximately 23% of rice cooker inner pot manufacturers have experienced excessive wall thickness deviation (>8%). Crucially, this issue arises from using aluminum discs for rice cooker inner pots produced by different rolling processes, highlighting the link between raw material 工艺 and product quality.

Excessive wall thickness deviation leads to local gaps of 0.1-0.3mm in the insulation layer. It also causes a 15%-25% decrease in thermal insulation performance, directly impacting user experience.

The core issue lies in earing ratio differences. Aluminum discs for rice cooker inner pots produced by hot-rolling and cold-rolling processes have different earing ratios due to variations in rolling temperature, deformation amount, and grain orientation.

This parameter directly dominates the uniformity of plastic flow during stretch forming. Ultimately, it causes wall thickness deviation and insulation layer adhesion issues. An in-depth analysis from the cross-perspective of material processing and thermal engineering principles is therefore necessary to address this challenge.

HW-बी. Core Differences Between Hot-Rolling and Cold-Rolling Processes for Aluminum Discs for Rice Cooker Inner Pots and the Mechanism of Earing Ratio Formation

The earing ratio is a key indicator for evaluating the anisotropy of एल्यूमीनियम डिस्क for rice cooker inner pots during stretch forming. It serves as a critical benchmark for raw material suitability.

It is defined as “the ratio of the height of the ears on the stretched part to the average height of the bottom”. The industry typically requires an earing ratio of ≤3% for aluminum discs for rice cooker inner pots, as higher ratios lead to forming defects.

Earing ratio differences arise from the different regulatory effects of hot-rolling and cold-rolling processes. विशेष रूप से, these processes impact the microstructure (grain orientation, texture type) का aluminum discs for rice cooker inner pots in distinct ways, leading to varying performance.

(ए) Comparison of Key Parameters Between Hot-Rolling and Cold-Rolling Processes (Taking Common Aluminum Alloys 1060 तथा 3003 for Rice Cooker Inner Pots as Examples)

(बी) Microscopic Mechanism of Earing Ratio Differences

1. Grain Orientation Differences:

• • पहले तो, during the hot-rolling process, dynamic recrystallization of aluminum discs for rice cooker inner pots occurs at high temperatures. This results in relatively random grain orientations along the rolling direction (RD) and transverse direction (TD), lacking directional uniformity.

• • Consequently, only weak {111}<110> texture is formed. This structure leads to significant differences in plastic flow resistance in different directions during stretch forming. उदाहरण के लिए, the elongation in the RD direction is 8%-12% higher than that in the TD direction.

• • This uneven flow easily forms obvious “ears” (height difference 0.2-0.5mm) in the 45° or 0° direction. Such ears fail to meet the forming accuracy requirements of rice cooker inner pots, increasing defect risks.

• • In contrast, the cold-rolling process involves multi-pass low-temperature rolling (आमतौर पर 3-5 passes). This forced deformation forces the grains of these aluminum discs to align in specific directions, creating ordered microstructures.

• • Two strong textures are formed: “cube texture” ({100}<011>) तथा “brass texture” ({112}<110>). The synergistic effect of these two textures reduces the difference in elongation between different directions to 3%-5%, a significant improvement over hot-rolled discs.

• • This significant reduction in elongation difference lowers the earing ratio, making cold-rolled discs suitable for the uniform stretch forming of rice cooker inner pots, especially for high-precision products.

2. Dislocation Density and Residual Stress:

The dislocation density of these aluminum discs during cold-rolling (10¹⁴-10¹⁵ m⁻²) is much higher than that during hot-rolling (10¹²-10¹³ m⁻²). This higher density contributes to better mechanical stability.

इसके अतिरिक्त, cold-rolled discs have a more uniform residual stress distribution, which minimizes deformation inconsistencies during subsequent stretch forming.

हालाँकि, अगर aluminum discs for rice cooker inner pots undergo insufficient annealing during hot-rolling (जैसे, holding time <2एच), local stress concentration will occur at grain boundaries. This is a key hidden danger for subsequent processing.

This stress concentration further exacerbates uneven deformation during stretch forming. It increases the earing ratio and raises the risk of forming defects in rice cooker inner pots, such as cracking or uneven walls.

HW-सी. Forming Mechanism and Quantitative Analysis of Wall Thickness Unevenness in Rice Cooker Inner Pots Caused by Earing Ratio Differences

The stretch forming of rice cooker inner pots from aluminum discs for rice cooker inner pots is essentially a plastic deformation process. It involves “radial stretching + axial thinning”, with earing ratio being a decisive factor in deformation uniformity.

Earing ratio differences directly cause wall thickness unevenness through “anisotropy of plastic flow”. विशेष रूप से, the following manifestations and quantitative data illustrate this relationship clearly:

(ए) Wall Thickness Distribution of Rice Cooker Inner Pots Under Different Earing Ratios

(बी) Law of Wall Thickness Evolution During Stretch Forming

Taking a mainstream rice cooker inner pot as an example—with a diameter of 220mm and initial thickness of these aluminum discs at 1.5mm—finite element analysis (ABAQUS) and experimental verification were used to obtain wall thickness distribution. This case study provides concrete insights into real-world performance.

1. Cold-Rolled Aluminum Discs for Rice Cooker Inner Pots (Earing Ratio 2.0%):

• • After stretch forming, the wall thickness of the inner pot bottom (area with minimum stress) ranges from 1.45-1.50mm, showing minimal variation.

• • The side wall (main deformation area) has a thickness of 1.20-1.30mm, maintaining good uniformity.

• • The ears (45° direction) measure 1.15-1.20mm in thickness, with only slight thinning.

• • The maximum wall thickness deviation is ≤8% (1.50mm vs 1.15mm). This meets the requirement of “wall thickness deviation of rice cooker inner pots ≤10%” in QB/T 4099, ensuring compliance with industry standards.

2. Hot-Rolled Aluminum Discs for Rice Cooker Inner Pots (Earing Ratio 4.5%):

• • The bottom wall thickness ranges from 1.48-1.52mm, relatively stable due to low stress.

• • The side wall thickness is 1.10-1.25mm, with greater variation compared to cold-rolled discs.

• • The ears (0°/90° direction) are significantly thinner, at 0.95-1.05mm, a result of uneven plastic flow.

• • The maximum wall thickness deviation reaches 37% (1.52mm vs 0.95mm), far exceeding the standard limit. This deviation is unacceptable for functional rice cookers.

• • इसके अतिरिक्त, the ear area is prone to cracking during subsequent shaping. The defect rate of rice cooker inner pots reaches 12%, leading to substantial production losses.

(सी) Core Cause of Wall Thickness Unevenness: “Local Thinning Effect” Dominated by Earing Ratio

According to the “Hill anisotropic yield criterion” in material mechanics, the relationship between wall thickness variation Δt and elongation ε of these aluminum discs during stretch forming is: Δt = t₀×(1-ε) (where t₀ is the initial thickness). This formula quantifies the link between elongation and thickness change.

मूलरूप में, a high earing ratio indicates a large difference in elongation ε between different directions. This directional inconsistency directly translates to uneven thickness.

के लिए हॉट-रोल्ड एल्यूमीनियम डिस्क, the ε_max (ear direction) is 15%-20% higher than ε_min (non-ear direction). This large difference results in greater Δt and thinner wall thickness in the ear area, creating a “local thinning effect”.

For cold-rolled aluminum discs, the difference between ε_max and ε_min is only 5%-8%. This small variation leads to uniform Δt distribution and small wall thickness deviation, aligning with the functional needs of rice cookers.

This uniform thickness is more suitable for the uniform heat conduction requirement of rice cooker inner pots, as uneven walls can cause hot spots during cooking.

इसके अतिरिक्त, the coarse grains (50-80सुक्ष्ममापी) of hot-rolled aluminum discs are prone to “intergranular slip” during stretch forming. This microscopic phenomenon exacerbates macroscopic unevenness.

This slip causes “wavy undulations” in local wall thickness (deviation 0.05-0.10mm). It further exacerbates unevenness and affects the adhesion accuracy between the rice cooker inner pot and the heating plate, potentially reducing heating efficiency.

HW-D. Impacts of Wall Thickness Unevenness on Insulation Layer Adhesion and Thermal Insulation Performance of Rice Cookers

“Gap-free adhesion” between the rice cooker inner pot and the insulation layer is crucial for ensuring thermal insulation performance. Without proper adhesion, heat loss increases dramatically, undermining the product’s core function.

Wall thickness unevenness impairs thermal insulation performance through a dual mechanism: “gap generation → change in heat conduction path”. The following analysis breaks down this mechanism in detail:

(ए) Thermal Insulation Performance Comparison of Rice Cookers Under Different Wall Thickness Deviations

(बी) Damage to Insulation Layer Adhesion

The common insulation layer for rice cookers is “polyurethane foam” (density 35kg/m³, thermal conductivity λ=0.022 W/(एम·के)). Its low thermal conductivity makes it ideal for insulation, but this advantage is lost if adhesion is poor.

Its adhesion depends on the flatness and wall thickness uniformity of the inner pot’s outer wall. This is directly determined by the earing ratio of aluminum discs for rice cooker inner pots, creating a clear chain of cause and effect.

1. Inner Pots Made of Cold-Rolled Aluminum Discs (Wall Thickness Deviation 8%):

• • The outer wall roughness Ra is 0.5-0.6μm, with no obvious protrusions or depressions, providing a smooth surface for adhesion.

• • After foaming, the gap between the insulation layer and the inner pot is ≤0.05mm. The adhesion rate is ≥98%, ensuring nearly complete contact.

• • The thickness of the air layer in the gap is negligible, meeting the long-term thermal insulation requirement of rice cookers and maintaining consistent performance over time.

2. Inner Pots Made of Hot-Rolled Aluminum Discs (Wall Thickness Deviation 37%):

• • Due to excessively thin wall thickness in the ear area, “local depressions” form after shaping. These depressions have a depth of 0.15-0.30mm, creating physical barriers to adhesion.

• • The outer wall roughness Ra increases to 1.2-1.5μm, further reducing the contact area between the insulation layer and the inner pot.

• • During foaming, polyurethane cannot fill the depressions. This forms air layer gaps of 0.10-0.25mm, which act as heat transfer channels.

• • The adhesion rate is only 82%. Gaps are concentrated in the ear area—an active heat exchange area of the rice cooker inner pot—directly affecting thermal insulation performance and leading to rapid heat loss.

3. Impact of Air Layer Gaps on Thermal Loss:

The air layer in gaps has a thermal conductivity λ_air=0.026 W/(एम·के), slightly higher than that of polyurethane. While this difference is small, its impact is amplified by convection.

और गणनाओं को शामिल किया गया है जो शक्ति के विनियोग को भी जोड़ते हैं, the air in the gap generates natural convection due to temperature differences (flow velocity 0.1-0.3m/s). This convection significantly enhances heat transfer, far beyond static conduction.

This convection increases the convective heat transfer coefficient h from 0.5 डब्ल्यू/(m²·K) (no gap) प्रति 2.5 डब्ल्यू/(m²·K), a fivefold increase.

It leads to a 3-4 fold increase in heat loss, significantly weakening the rice cooker’s thermal insulation effect and failing to meet user expectations for long-term heat retention.

HW-ई. Process Optimization Solutions: Earing Ratio Control and Quality Improvement for Aluminum Discs for Rice Cooker Inner Pots

To address the earing ratio defect of hot-rolled aluminum discs for rice cooker inner pots, targeted optimization is needed. A one-size-fits-all approach is ineffective; instead, solutions must be tailored to the specific causes of high earing ratios.

Solutions should combine the forming requirements of rice cooker inner pots and focus on three aspects: “process parameter adjustment”, “pretreatment optimization”, तथा “forming process improvement”. The following specific solutions are proven to be effective in industrial practice:

(ए) Key Indicators of Aluminum Discs Before and After Process Optimization

(बी) Rolling Process Optimization for Raw Aluminum Discs

1. Hot-Rolling Process Improvement:

• • के लिए aluminum discs for rice cooker inner pots, adopt “multi-pass low-temperature hot-rolling”. The initial temperature is 450℃, decreasing to 350℃ in successive passes. This gradual temperature reduction controls recrystallization rate and grain growth.

• • This approach reduces grain coarsening caused by dynamic recrystallization. The grain size is controlled to 30-40μm, a range that balances strength and formability.

• • Add “intermediate annealing” (380℃×3h) to eliminate residual stress. This step is critical for reducing stress concentration at grain boundaries.

• • Consequently, the earing ratio of these aluminum discs is reduced from 4.5% to below 3.0%, making them suitable for basic rice cooker inner pot production.

2. Cold-Rolling Process Enhancement:

• • For medium-thin rice cooker inner pots (0.8-1.5मिमी), adopt “5-pass cold-rolling” with a total deformation rate of 70%. Multi-pass rolling ensures uniform deformation without overworking the material.

• • Control the deformation rate of each pass to 15%-20%. This moderate deformation enhances the cube texture strength of these aluminum discs, which is key to reducing anisotropy.

• • Adjust the final annealing temperature to 320℃×2h to homogenize the dislocation density. This step stabilizes the microstructure and prevents post-forming deformation.

• • नतीजतन, the earing ratio of these aluminum discs is stabilized at 1.5%-2.0%, suitable for the production of high-precision rice cooker inner pots that require strict thickness uniformity.

3. Pretreatment and Forming Process Optimization:

• • For hot-rolled aluminum discs for rice cooker inner pots, add a “10% pre-stretching” step. This pre-deformation adjusts grain orientation and reduces anisotropy, preparing the material for subsequent forming.

• • Change the traditional single-pass stretch forming to “2-pass stretch forming + intermediate annealing”. This dispersed deformation approach reduces local stress and minimizes thinning in the ear area.

HW-एफ. Industry Application Case: Process Optimization Practice of Raw Aluminum Discs in a Rice Cooker Enterprise

A leading domestic rice cooker enterprise—with an annual output of 5 million units—faced significant issues in 2023. These problems not only affected product quality but also led to substantial financial losses.

The enterprise used hot-rolled aluminum discs for rice cooker inner pots to produce inner pots. Two main problems emerged:

① Uneven wall thickness led to poor insulation layer adhesion. विशेष रूप से, users reported that “the thermal insulation time of the rice cooker was reduced from 12h to 8h”, a clear indication of performance failure.

② The cracking defect rate in the ear area reached 12%, resulting in an annual loss of over 8 million yuan. This defect rate was unsustainable for mass production.

To solve these issues, the enterprise implemented three targeted optimization measures, each addressing a specific root cause:

1. Raw Material Process Switch: Replace hot-rolled aluminum discs for rice cooker inner pots (earing ratio 4.2%) with cold-rolled ones (earing ratio 2.1%). Add a 10% pre-stretching treatment to further reduce anisotropy.

2. Forming Process Adjustment: In line with the characteristics of these aluminum discs, adopt “2-pass stretch forming + intermediate annealing” to reduce local thinning and cracking risks.

3. Inspection System Improvement: Introduce laser thickness measurement and ultrasonic flaw detection. Conduct 100% inspection on inner pots made from each batch of these aluminum discs to catch defects early.

The optimization achieved significant results, validating the effectiveness of the measures:

• विशेष रूप से, the wall thickness deviation of the rice cooker inner pot was controlled within 8%, meeting industry standards.

• The insulation layer adhesion rate reached ≥97%, restoring the product’s thermal insulation performance.

• The water temperature after 12h insulation increased from 63℃ to 74℃, exceeding user expectations.

• User complaints decreased by 90%, improving brand reputation and customer satisfaction.

• Annual cost savings reached 6.5 million yuan, directly boosting profitability.

• Meanwhile, the raw material utilization rate of these aluminum discs increased by 5%, reducing waste and environmental impact.

HW-G. Conclusions and Outlook

(ए) Core Conclusions

Overall, during the stretch forming of rice cooker inner pots from aluminum discs for rice cooker inner pots, earing ratio differences between hot-rolling and cold-rolling processes are the root cause of significant wall thickness unevenness. This conclusion is supported by both experimental data and industrial practice.

Hot-rolled discs have an earing ratio of 3.0%-5.5%, while cold-rolled discs range from 1.5%-3.0%. This difference is substantial enough to cause functional defects.

This variation leads to anisotropy of plastic flow. विशेष रूप से, inner pots made from hot-rolled aluminum discs have a maximum wall thickness deviation of up to 37%, far exceeding industry standards and rendering the product non-functional.

In contrast, inner pots made from cold-rolled aluminum discs have a deviation of ≤8%, meeting requirements and ensuring consistent performance.

Wall thickness unevenness further impairs insulation layer adhesion: the adhesion rate is 82% for hot-rolled discs and 98% for cold-rolled ones. This difference directly translates to thermal insulation performance gaps.

It also exacerbates heat loss through convection in air layer gaps, leading to a 23% or more decrease in the thermal insulation performance of rice cookers. This performance loss is unacceptable for consumer products.

(बी) भविष्य के अनुसंधान निर्देश

In the future, in-depth research on these aluminum discs should focus on three aspects to drive continuous improvement:

① Develop a “हॉट रोलिंग + cold-rolling composite process”. Use hot-rolling for rough rolling (to reduce cost) and cold-rolling for finish rolling (to control earing ratio). This hybrid approach balances cost and performance.

② Adopt AI-driven rolling parameter optimization. Predict the earing ratio of these aluminum discs based on machine learning algorithms to realize real-time adaptive process adjustment, reducing human error and improving consistency.

③ Develop new insulation materials, such as aerogel composite foam. This advanced material has ultra-low thermal conductivity, which can reduce the dependence of rice cooker inner pots on the wall thickness uniformity of these aluminum discs, expanding design flexibility.

(सी) Core Principle

Ultimately, NS “process selection” का aluminum discs for rice cooker inner pots should aim for the synergy of three factors: “wall thickness uniformity of rice cooker inner pots – insulation layer adhesion – thermal insulation performance”. No single factor can be prioritized at the expense of the others.

The cold-rolling process has significant advantages in medium-thin rice cooker inner pots (<2.0मिमी), where precision is critical.

Hot-rolled aluminum discs, after parameter optimization, can be applied to thick-walled rice cooker inner pots (≥2.0mm), where cost sensitivity is higher and thickness tolerance is more lenient.

Rational matching based on the product positioning and performance requirements of rice cookers is essential. It achieves a balance between “raw material quality – finished product performance – production cost”, ensuring sustainable and competitive manufacturing.