Analysis of gate freeze‐off time in injection molding

Abstract

Gate solidification time is an important topic in injection molding technology, as it determines cycle time, which itself is an important issue in the balance of the production process. In this work, a study of the effect of both gate and cavity geometries on gate solidification time was conducted, using a commercial polymer, injection molded with constant holding pressure into a rectangular cavity. Three cavity lengths were used, and for each, two cavity thicknesses were adopted. Special dies containing different gates were assembled in the mold. Gate thickness was found to be the most important factor determining gate sealing time. However the cavity geometry is also quite important. A clear indication on gate solidification could be drawn by analyzing time evolution of pressure distribution inside the mold. The solidification phenomenon leading to gate sealing was analyzed by a simple model, which also takes into account the effect of cavity geometry, by comparing the heat flow through the gate walls and the energy required to solidify the packing flow rate. Model results satisfactorily describe the main features of the experimental data.

Study on the replication quality of micro-structures in the injection molding process with dynamical tool tempering systems

“…If the fluid centre in the gate is completely frozen, no more melt is moved to the cavity. In this case, the pressure in the cavity changes to atmospheric pressure (Pantani et al 2004). …”

Monitoring of injection molding of thermoplastics: Average solidification pressure as a key parameter for quality control

“…A general decrease has also been found when increasing the holding time, until to the achievement of a plateau value at about 7 sec. This time at which a plateau in shrinkage is reached is often taken as equal to the gate sealing time 8 and is in fairly good agreement with the value found by analyzing the pressure curves.…”

“…18 A characteristic time for cooling can be defined as (6) in which α T is the thermal diffusivity of the polymer and H is the slab half-thickness. At each time, the time which is solidifying can be described by the following equation (7) in which (8) and (9) is a solution valid at short times (t < t c ) whereas (10) is a solution valid at times longer than t c . In eq.…”

Effects of gate design and cavity thickness on filling, morphology and mechanical properties of microinjection mouldings

“…Gate solidification only takes place when the heat lost though the gate walls by conduction overcomes the energy entering the gate from the runner because of convection. As described by Pantani et al [24], the conductive heat lost by transverse conduction in the gate, here denoted as Q cond , is of the order of…”

“…However, detailed design of a micro gate is still rare. In conventional injection molding, Pantani et al [24] found that both gate thickness and cavity thickness affected the freeze-off time and they related gate solidification time to cavity pressure-time curves. Their analytical model was used successfully to estimate gate solidification time.…”