During the fragrant rice packaging process, the thermal stress distribution in the sealing area directly affects the sealing strength and particle integrity. The traditional constant temperature heat sealing process cannot adapt to the hot melting characteristics of polyethylene materials and the heat resistance limit of rice grains, which easily leads to carbonization of the sealing layer or charring of rice grains. The introduction of gradient temperature field control technology provides a scientific path to solve this contradiction.
This technology constructs a dynamic temperature field through a segmented heating module to form a linear temperature gradient from 120¡æ to 85¡æ in the sealing cross section. The high temperature zone (near the inner layer of the bag) ensures that the polyethylene material is fully melted and bonded, the medium temperature zone (transition layer) maintains the ductility of the material, and the low temperature zone (contact layer) controls the surface temperature of the rice grains below the critical point of starch gelatinization (82¡æ). Experimental data show that the gradient temperature field can reduce the standard deviation of the thermal stress distribution in the sealing area from 18.3¡æ in the traditional process to 4.7¡æ, effectively avoiding material degradation caused by local overheating.
The system uses an infrared temperature sensor array to monitor the surface temperature distribution of the heating plate in real time, and dynamically adjusts the power output of 6 independent heating units through a PID control algorithm. When the thickness of the rice bag changes, the system automatically calculates the temperature field compensation scheme based on the heat transfer model: for every 1mm thickening of the bag mouth, the temperature of the high temperature zone increases by 2°C, and the temperature gradient expansion slope increases by 15%. This adaptive mechanism enables the equipment to adapt to a variety of composite packaging materials of 40-120g/m².
In the packaging test, the gradient temperature field technology showed a dual advantage: the sealing peel strength was increased to 23.5N/15mm (41% higher than the constant temperature process), and the carbonization rate of the surface rice grains was controlled within 0.02%. More importantly, the technology reduces the energy loss in the heat sealing process to 62% of the traditional process. Through thermal imaging analysis, it can be seen that the temperature fluctuation range of the rice grain accumulation area is narrowed from ±14°C to ±2.3°C, significantly reducing the damage of thermal shock to the microstructure of the rice grains.
Current research is exploring the linkage between the gradient temperature field and the pressure feedback system, and realizing the real-time optimization of the sealing parameters by establishing a three-dimensional control model of temperature-pressure-deformation. Preliminary tests show that when the system detects changes in the distribution density of rice grains, it can automatically adjust the temperature field gradient slope and the pressing time, so that the sealing pass rate of the special-shaped bag mouth is increased to 99.8%. This progress provides a new technical paradigm for the intelligent packaging of long-grain agricultural products.
