Mold water channel

Mold cooling is typically provided by water channels in the mold, when metal molds are used. A system of fans blowing air over the top of the mold can aid in cooling, and this can be used alone for wood or plastic molds, which do not generally contain internal cooling. 

The mold must be vented to allow for gas escape such vents must be placed near weld lines and also near the last areas to be filled. Typical vents are slots 6 to 13mm (0.236 to 0.512in) wide and 0.01 to 0.03mm (0.0004 to O.OOlin) deep such slots are located on the mating surface of one of the mold halves. If a negative pressure device is available it may be possible to vent the mold into the water channels. This can speed up mold filling, reduce component burning and, reduce the cycle times. 

Water channels Control temperature of mold surfaces, to chill plastic to rigid state... 

Large-core molds require water channels at various levels spaced about 1.5 in. on center. It is wise to provide the maximum amount of cooling possible when designing a mold, even if this additional cooling is not fully used. 

For moldings that possess both thick and thin sections, the distance of the water channel should be closer for the thicker sections (i.e. 1.0 to I.ID) than for the thinner sections. To achieve better cooling, particularly when molding thick sectioned components, certain areas of the mold should be made from beryllium copper in order to dissipate the heat more rapidly. 

Water-assisted injection molding experiments were carried out on newly developed equipment in our lab. The effects of four processing parameters, short-shot size, melt temperature, water injection delay time, and water pressure, on the water penetration length and residual wall thickness of water-assisted injeetion molded polypropylene curved pipe were investigated. The crystallization behavior difference between the beginning and the end of the water channel of the eurved pipe was analyzed using differential scanning calorimetry. 

Differential scanning calorimetry (DSC) (NETZSCH DSC 204) was used to investigate the erystallization behavior of the samples taken from the part molded at 68.5% short-shot size, 230 °C melt temperature, 8 s water injeetion delay time, and 6 MPa water pressure. Two positions, PI and P9 as shown in Figure 2, that is, near the beginning and the end of the water channel, respectively, were ehosen. Three samples, from the outer layer, middle, and the inner layer across the residual wall, respectively, were taken for each position. The DSC scans were performed in a nitrogen environment The samples were heated from room temperature (25 °C) to 200 °C at a heating rate of 10°C/min. 

The effects of four processing parameters on the residual wall thickness in molded parts are illustrated by the thicknesses measured at five positions (PI, P3, P5, P7, and P9) in Figure 4. On the whole, the residual wall thickness at position P5 is smaller than those at positions PI and P3. Furthermore, the thickness obviously decreases from positions P7 to P9. Position P9, that is, the position near the end of the water channel, exhibits the minimum wall thickness. This can be explained as follows. At 68.5% short-shot size used in this work, the injected polymer melt can only reach near position P7 in the mold cavity. The cavity downstream is filled with the melt pushed by the water. The time for the pushed melt to contact the cavity is short due to high filling rate of water. Moreover, the cavity warms up because of the contact with the hot melt during the water injection delay. So the water easily pushes the melt against the mold cavity. 

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