# Study of Heat Transfer Strategy of Metal Heating/Conduction Plates for Energy Efficiency of Large-Sized Automotive Glass Molding Process

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Heat Transfer Model

#### 2.1. Heat Conduction Model and Its Initial Parameters

#### 2.2. Boundary Conditions

^{3}) of the mold; $k$, ${C}_{p}$ are the thermal conductivity (W/m °C) and the specific heat capacity (J/kg °C), respectively; ${T}_{1}$, ${T}_{2},$ and ${T}_{3}$ are the temperature (°C) of the mold, metal heat conductor, and metal heating plate, respectively. The contact thermal conductivity value of the conductor with the heating plate was 2500 W/m

^{2}°C, and the contact thermal conductivity value of the conductor with the mold was 2800 W/m

^{2}°C.

#### 2.3. Calculation of Production Energy Consumption

^{2}), respectively. Therefore, Equation (8) can be used to determine the energy produced by the heating device [22].

## 3. Results and Analysis

#### 3.1. Impact of Heating Rate on Energy Efficiency

^{2}·s), which effectively improved the forming effect of glass. Throughout the heating process, the value of heating rate strategy Ⅱ remained at 30 mJ/(mm

^{2}·s), the value of strategy Ⅲ remained at 40 mJ/(mm

^{2}·s), and finally, the value of strategy Ⅳ remained at 45 mJ/(mm

^{2}·s).

_{1}and A

_{2}as examples, the final temperatures of point A

_{1}under the conditions of increasing the heating rate from low to high were 695.2 °C, 698.4 °C, 702.8 °C, and 706.3 °C, with a maximum temperature difference of 8 °C (in Figure 8). The final temperatures of point A

_{2}at 160 s under the conditions of increasing the heating rate from low to high were 649.8 °C, 665.4 °C, 675.8 °C, and 677.2 °C, with a maximum temperature difference of 28 °C (in Figure 8). It is evident that the lower mold was more affected than the upper mold under the different heating rate strategies. This was due to the fact that the larger mold was heated, and the upper mold contained an additional heating tube than the lower mold, resulting in a more uniform finish.

^{2}·s)) can significantly shorten the processing time and effectively promote energy efficiency.

#### 3.2. Impact of Heat Flux Density on Energy Efficacy

_{1}-A

_{3}-B

_{3}-B

_{1}and K

_{1}-K

_{3}-J

_{3}-J

_{1}), and the lowest temperature appeared in the central area of the inner cavity (D

_{1}-D

_{3}-F

_{3}-F

_{1}), as shown in Figure 13b. The temperature distribution using heat flux density strategy III was similar to that of strategy II, and the maximum temperature difference of strategy III was smaller than that of strategy II. A large temperature difference can cause a decrease in the product processing performance (in Figure 13c). Therefore, the final molding performance was the best when using strategy III.

## 4. Discussion

_{2}emissions from the automotive glass molding process. In the whole process, direct CO

_{2}emissions account for about 92–97%, and indirect CO

_{2}emissions account for about 3–6%. In the heating process, heating the mold and manufacturing nitrogen are the main components of direct CO

_{2}emissions, accounting for 18–20% and 74–77%, respectively. In addition, the service life of graphite molds is significantly shortened in high-temperature environments; therefore, both graphite molds and glass raw materials are consumables, and the indirect emissions of CO

_{2}are mainly from the process of manufacturing graphite molds (1–3%) and glass raw materials (2–3%). It was found that the direct emissions of CO

_{2}are more significant than their indirect emissions.

_{2}emissions of heating rate strategy IV, heat flow density strategy III, and the original heat transfer strategy were 1.0374 kg, 1.0278 kg, and 1.0811 kg, respectively. This means that heat transfer strategy IV reduced carbon emissions by 4.04% compared to the original strategy, and heat transfer density strategy III reduced carbon emissions by 4.92%. Thereafter, the heat transfer model with heat flow density strategy III was the best strategy to reduce energy consumption and improve energy efficiency.

## 5. Conclusion and Future Work

- (1)
- After systematic theoretical analysis and experimental tests, a heat transfer model of a metal heating plate, a metal heat conductor, and a glass model was developed, which can accurately model the action of heat flow, and thus, predict the temperature changes in the glass mold for large-sized automotive instrument glass.
- (2)
- The analysis of the simulation results shows that different heating rate strategies had an impact on the energy efficiency of the GMP. Under heating rate strategy IV, the output energy of the heating device was lower than that under strategy I by 4.04%, and the heating time was reduced by 7.06%. Therefore, using heating rate strategy IV is the most ideal option.
- (3)
- The analysis of the numerical results shows that different heat flux strategies affected the energy consumption of the heating device. The results show that the heat flow density strategy III effect was the best. The output energy of the heating equipment was reduced by 4.92%, and the heating time was reduced by 6.06%.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Model of metal heat conduction plates for large-sized automotive instrument glass molding process; (

**a**) upper mold, (

**b**) lower mold, (

**c**) three-dimensional model and dimensions of the metal heating plate and heat-conducting plate (heating conductor).

**Figure 2.**Three-dimensional finite element (FEM) mesh model (using MSC Marc) and its cross-sectional view of GMP. (

**a**) 3D finite element mesh model of the glass molding process, (

**b**) the cross-sectional view of the model.

**Figure 7.**Simulation results of mold temperature under four different heating rate strategies. Upper and lower mold temperature measurement points: (

**a**) A

_{1}; (

**b**) A

_{2}; (

**c**) B

_{1}; (

**d**) B

_{2}; (

**e**) C

_{1}; (

**f**) C

_{2}; (

**g**) D

_{1}; (

**h**) D

_{2}.

**Figure 8.**Temperature distribution in the final stage of heating (t = 160 s) using four different heating rates of the heating devices and molds.

**Figure 9.**Comparison of output energy of heating tube and heating devices under four different heating rate strategies.

**Figure 10.**Schematic diagram of five different heat flux density strategies during the glass molding process; (

**a**) upper mold heat flux density distribution strategies, (

**b**) lower mold heat flux density distribution strategies.

**Figure 11.**Temperature distribution of heating device and mold under different strategies of heat flux density (t = 160 s).

**Figure 12.**Schematic diagram of the selection of observation points for the lower mold temperature (A1–K3 are the temperature detection points).

**Figure 13.**Temperature distribution on the inner surface of the mold under three different strategies of heat flux density; (

**a**) heat flux density strategy I, (

**b**) heat flux density strategy II, (

**c**) heat flux density strategy III.

**Figure 14.**Comparison of the output energy of the heating tubes and the heating device under three different heat flux density strategies.

**Figure 15.**CO

_{2}emission ratio of glass molding process for large-sized automotive instrument glass.

**Table 1.**Thermal and mechanical properties of SUS310S and WC materials [2].

Materials | SUS310S | WC |
---|---|---|

Young’s modulus $\mathrm{E}\left(\mathrm{GPa}\right)$ | 193 | 570 |

Poisson’s ratio $\upsilon $ | 0.3 | 0.22 |

Density $\rho ({\mathrm{g}/\mathrm{cm}}^{3})$ | 7.9 | 14.65 |

Heat conductivity $\mathrm{K}(\mathrm{W}/\mathrm{m}\xb0\mathrm{C})$ | 18.5 | 63 |

Specific heat capacity ${\mathrm{C}}_{\mathrm{P}}(\mathrm{J}/\mathrm{kg}\xb0\mathrm{C})$ | 500 | 314 |

Coefficient of heat expansion $(\xb0\mathrm{C})$ | 18.2 × 10^{−6} | 4.9 × 10^{−6} |

FEM Model | Constrained Displacement | Loading (MPa) | Initial Temperature (°C) |
---|---|---|---|

Upper heating plate | x/y | 0.3 | 780 |

Upper heat conduction plate | x/y | - | 780 |

Mold | x/y | - | 20 |

Lower heat conduction plate | x/y/z | - | 780 |

Lower heating plate | x/y/z | - | 780 |

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## Share and Cite

**MDPI and ACS Style**

Chen, Y.; Zhang, S.; Hu, S.; Zhao, Y.; Zhang, G.; Cao, Y.; Ming, W.
Study of Heat Transfer Strategy of Metal Heating/Conduction Plates for Energy Efficiency of Large-Sized Automotive Glass Molding Process. *Metals* **2023**, *13*, 1218.
https://doi.org/10.3390/met13071218

**AMA Style**

Chen Y, Zhang S, Hu S, Zhao Y, Zhang G, Cao Y, Ming W.
Study of Heat Transfer Strategy of Metal Heating/Conduction Plates for Energy Efficiency of Large-Sized Automotive Glass Molding Process. *Metals*. 2023; 13(7):1218.
https://doi.org/10.3390/met13071218

**Chicago/Turabian Style**

Chen, Yanyan, Shengfei Zhang, Shunchang Hu, Yangjing Zhao, Guojun Zhang, Yang Cao, and Wuyi Ming.
2023. "Study of Heat Transfer Strategy of Metal Heating/Conduction Plates for Energy Efficiency of Large-Sized Automotive Glass Molding Process" *Metals* 13, no. 7: 1218.
https://doi.org/10.3390/met13071218