Effects of process conditions on the heat transfer coefficient at the polymer-mold interface and tensile strength of thin-wall injection molding parts

2019 ◽  
Vol 39 (5) ◽  
pp. 493-500
Author(s):  
Laiyu Zhu ◽  
Liping Min ◽  
Xianglin Li ◽  
Zhanyu Zhai ◽  
Dietmar Drummer ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Tensile Strength ◽  
Weld Line ◽  
Polymer Melt ◽  
Mold Cavity ◽  
Cavity Surface ◽  
Thin Wall ◽  
Wall Injection ◽  
The Heat Transfer Coefficient

Abstract Generally, the strength at the weld line of the injection molded part is very weak. The heat transfer coefficient (HTC) between the polymer melt and the mold cavity surface was analyzed to solve this problem. The surface roughness of the mold cavity and the material of the mold insert were changed to adjust the interface environment between the polymer melt and the mold cavity surface. HTC was obtained by combing the experimental measurement with the theoretical calculation. In the current study, the influence of HTC on the tensile strength of the weld line of the molded specimen was investigated. The results show that the weld line strength of the molded specimen increases with the decrease in HTC between the polymer and the mold cavity surface. Meanwhile, the decrease in the surface roughness of the mold cavity or replacing the mold material with lower thermal conductivity can reduce the value of the HTC between the polymer and the mold effectively and can delay the cooling rate of the hot polymer melt. This provides a new idea to solve thin-wall injection molding weld line defects.

Theory Study and Numerical Analysis of Ultra-Thin Wall Injection Molding

2012 ◽  
Vol 538-541 ◽  
pp. 1145-1153 ◽  
Author(s):  
Su Feng Yin ◽  
Feng Ruan ◽  
Jian Yu Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Injection Molding ◽  
Transfer Coefficient ◽  
Wall Slip ◽  
Viscosity Model ◽  
Thin Wall ◽  
Wall Injection ◽  
Relationship Of ◽  
The Heat Transfer Coefficient

The article focuses on the discussion of size relationship of melt viscosity of ultra-thin wall injection molding, revising the viscosity model of traditional stimulant Cross-WLF. It takes the theory of Uhland wall-slip, trying to analyze the influence which the wall-slip of the molding makes on injection molding. It also points out the limitation of constant heat transfer coefficient in the molding. The change rules of the heat transfer coefficient is among the study. Using the method of numerical simulation and experience, the article verifies the consistency of experience result and the change of the factors, such as using ultra-thin viscosity model, wall-slip and the change of heat transfer coefficient while doing the simulation.

scholarly journals Heat Transfer and Flow on the Squealer Tip of a Gas Turbine Blade

2000 ◽  
Author(s):  
Gm S. Azad ◽  
Je-Chin Han ◽  
Robert J. Boyle
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Rotor Blade ◽  
Static Pressure ◽  
Cavity Surface ◽  
Edge Region ◽  
Blade Tip ◽  
The Heat Transfer Coefficient

Experimental investigations are performed to measure the detailed heat transfer coefficient and static pressure distributions on the squealer tip of a gas turbine blade in a five-bladed stationary linear cascade. The blade is a 2-dimensional model of a modern first stage gas turbine rotor blade with a blade tip profile of a GE-E3 aircraft gas turbine engine rotor blade. A squealer (recessed) tip with a 3.77% recess is considered here. The data on the squealer tip are also compared with a flat tip case. All measurements are made at three different tip gap clearances of about 1%, 1.5%, and 2.5% of the blade span. Two different turbulence intensities of 6.1% and 9.7% at the cascade inlet are also considered for heat transfer measurements. Static pressure measurements are made in the mid-span and near-tip regions, as well as on the shroud surface opposite to the blade tip surface. The flow condition in the test cascade corresponds to an overall pressure ratio of 1.32 and an exit Reynolds number based on the axial chord of 1.1×106. A transient liquid crystal technique is used to measure the heat transfer coefficients. Results show that the heat transfer coefficient on the cavity surface and rim increases with an increase in tip clearance. The heat transfer coefficient on the rim is higher than the cavity surface. The cavity surface has a higher heat transfer coefficient near the leading edge region than the trailing edge region. The heat transfer coefficient on the pressure side rim and trailing edge region is higher at a higher turbulence intensity level of 9.7% over 6.1% case. However, no significant difference in local heat transfer coefficient is observed inside the cavity and the suction side rim for the two turbulence intensities. The squealer tip blade provides a lower overall heat transfer coefficient when compared to the flat tip blade.

scholarly journals The Feasibility of an Internal Gas-Assisted Heating Method for Improving the Melt Filling Ability of Polyamide 6 Thermoplastic Composites in a Thin Wall Injection Molding Process

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1004 ◽  
Author(s):  
Thanh Trung Do ◽  
Tran Minh The Uyen ◽  
Pham Son Minh
Keyword(s):  
Injection Molding ◽  
Heating Rate ◽  
Temperature Control ◽  
Cavity Surface ◽  
Heating Process ◽  
Injection Molding Process ◽  
Thin Wall ◽  
Molding Process ◽  
Filling Ability ◽  
Wall Injection

In thin wall injection molding, the filling of plastic material into the cavity will be restricted by the frozen layer due to the quick cooling of the hot melt when it contacts with the lower temperature surface of the cavity. This problem is heightened in composite material, which has a higher viscosity than pure plastic. In this paper, to reduce the frozen layer as well as improve the filling ability of polyamide 6 reinforced with 30 wt.% glass fiber (PA6/GF30%) in the thin wall injection molding process, a preheating step with the internal gas heating method was applied to heat the cavity surface to a high temperature, and then, the filling step was commenced. In this study, the filling ability of PA6/GF30% was studied with a melt flow thickness varying from 0.1 to 0.5 mm. To improve the filling ability, the mold temperature control technique was applied. In this study, an internal gas-assisted mold temperature control (In-GMTC) using different levels of mold insert thickness and gas temperatures to achieve rapid mold surface temperature control was established. The heating process was observed using an infrared camera and estimated by the temperature distribution and the heating rate. Then, the In-GMTC was employed to produce a thin product by an injection molding process with the In-GMTC system. The simulation results show that with agas temperature of 300 °C, the cavity surface could be heated under a heating rate that varied from 23.5 to 24.5 °C/s in the first 2 s. Then, the heating rate decreased. After the heating process was completed, the cavity temperature was varied from 83.8 to about 164.5 °C. In-GMTC was also used for the injection molding process with a part thickness that varied from 0.1 to 0.5 mm. The results show that with In-GMTC, the filling ability of composite material clearly increased from 2.8 to 18.6 mm with a flow thickness of 0.1 mm.

scholarly journals Polymer Flow Influenced by Mold Cavity Surface Roughness

2019 ◽  
Vol 19 (2) ◽  
pp. 327-331 ◽  
Author(s):  
Michal Stanek ◽  
Miroslav Manas ◽  
Martin Ovsik ◽  
Martin Reznicek ◽  
Vojtech Senkerik ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Mold Cavity ◽  
Cavity Surface ◽  
Polymer Flow

Heat Transfer During Evaporation on Capillary-Grooved Structures of Heat Pipes

1995 ◽  
Vol 117 (3) ◽  
pp. 740-747 ◽  
Author(s):  
D. Khrustalev ◽  
A. Faghri
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Surface Roughness ◽  
Thermal Resistance ◽  
Heat Pipes ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Interfacial Thermal Resistance ◽  
Interfacial Resistance ◽  
The Heat Transfer Coefficient

A detailed mathematical model is developed that describes heat transfer through thin liquid films in the evaporator of heat pipes with capillary grooves. The model accounts for the effects of interfacial thermal resistance, disjoining pressure, and surface roughness for a given meniscus contact angle. The free surface temperature of the liquid film is determined using the extended Kelvin equation and the expression for interfacial resistance given by the kinetic theory. The numerical results obtained are compared to existing experimental data. The importance of the surface roughness and interfacial thermal resistance in predicting the heat transfer coefficient in the grooved evaporator is demonstrated.

scholarly journals The feasibility of external gas-assisted mold-temperature control for thin-wall injection molding

2018 ◽  
Vol 10 (10) ◽  
pp. 168781401880610 ◽  
Author(s):  
Pham Son Minh ◽  
Thanh Trung Do ◽  
Tran Minh The Uyen
Keyword(s):  
Temperature Distribution ◽  
Injection Molding ◽  
Heating Rate ◽  
Temperature Control ◽  
Mold Temperature ◽  
Cavity Surface ◽  
Thin Wall ◽  
Mold Surface ◽  
Hot Gas ◽  
Wall Injection

Simulation and experimental testing were conducted on an external gas-assisted mold-temperature control combined with a pulsed cooling system used for thin-wall injection molding to determine its effect on the heating rate and temperature distribution of a mold surface. For mold heating via external gas-assisted mold-temperature control, a hot gas was directly discharged on the cavity surface. Based on the heat convection between the hot gas and the cavity surface, the cavity temperature rose to the target value. Practically, the gap between the heating surface and the gas gate is an important parameter as it strongly influences the heating process. Therefore, this parameter was analyzed under different values of plate-insert thickness herein. Heating was elucidated by the temperature distribution and heating-rate data detected by the infrared camera and sensors. Then, external gas-assisted mold-temperature control was applied for the thin-wall injection-molding part of 0.5 mm thickness with the local-gate-temperature control. The results show that with 300°C gas temperature, the heating rate could reach 9°C/s with a 0.5-mm stamp thickness and a 4-mm gas gap. The results show that with local heating at the melt-entrance area of the mold plate, the cavity was filled with a 20-s heating cycle.

Investigations on the Weldline Tensile Strength of Thin-wall Injection Molded Parts

2004 ◽  
Vol 23 (6) ◽  
pp. 575-588 ◽  
Author(s):  
Rean Der Chien ◽  
Shia-Chung Chen ◽  
Hsin-Shu Peng ◽  
Pao-Lin Su ◽  
Chun-Sheng Chen
Keyword(s):  
Tensile Strength ◽  
Thin Wall ◽  
Molded Parts ◽  
Injection Molded ◽  
Wall Injection

scholarly journals The Influence of Surface Roughness on Nucleate Pool Boiling Heat Transfer

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Benjamin J. Jones ◽  
John P. McHale ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Polished Surface ◽  
Transfer Coefficients ◽  
Two Fluids ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

The effect of surface roughness on pool boiling heat transfer is experimentally explored over a wide range of roughness values in water and Fluorinert™ FC-77, two fluids with different thermal properties and wetting characteristics. The test surfaces ranged from a polished surface (Ra between 0.027 μm and 0.038 μm) to electrical discharge machined (EDM) surfaces with a roughness (Ra) ranging from 1.08 μm to 10.0 μm. Different trends were observed in the heat transfer coefficient with respect to the surface roughness between the two fluids on the same set of surfaces. For FC-77, the heat transfer coefficient was found to continually increase with increasing roughness. For water, on the other hand, EDM surfaces of intermediate roughness displayed similar heat transfer coefficients that were higher than for the polished surface, while the roughest surface showed the highest heat transfer coefficients. The heat transfer coefficients were more strongly influenced by surface roughness with FC-77 than with water. For FC-77, the roughest surface produced 210% higher heat transfer coefficients than the polished surface while for water, a more modest 100% enhancement was measured between the same set of surfaces. Although the results highlight the inadequacy of characterizing nucleate pool boiling data using Ra, the observed effect of roughness was correlated using h∝Ram as has been done in several prior studies. The experimental results were compared with predictions from several widely used correlations in the literature.

Effects of Surface Roughness on the Pool Boiling of Water

2007 ◽  
Author(s):  
Benjamin J. Jones ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Electrical Discharge Machining ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Polished Surface ◽  
Aluminum Surfaces ◽  
The Heat Transfer Coefficient

The effect of surface roughness on the pool boiling of water is studied. Five aluminum surfaces of varying roughness were prepared: one polished (0.062 μm RMS) and four roughened by electrical discharge machining (EDM) with surface roughness of 1.37, 2.81, 7.37, and 12.53 μm RMS. All experiments were performed in water at atmospheric pressure and saturation temperature. The roughest EDM surface showed up to a 100% improvement in the heat transfer coefficient compared to the polished surface. The other EDM surfaces (1.37, 2.81, and 7.37 μm) showed up to a 60% enhancement in the heat transfer coefficient compared to the polished surface. Constants are proposed for prediction of pool boiling in water from the polished and rough aluminum surfaces studied using the Rohsenow pool boiling correlation.

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