When it comes to gating style selection, Mold-Masters hot runner systems have processed virtually every available thermoplastic in the world, at times even before it had become commercially viable. We’ve translated that knowledge into the industry’s widest range of gating methods.
Most Common Types of Gating Style
The tip gate is the most commonly used gating method. Acceptable for crystalline and amorphous materials, this gating method relies on gate diameter, gate area cooling, and temperature control at the tip to optimize the part quality. Tip gating leaves a small mark on the molded part surface (gate vestige).
The size of this mark is directly related to the gate geometry and material properties. The less notch sensitive the thermoplastic, or the larger the gate diameter, the more the vestige will protrude. For this reason, the gate is often sunk into a spherical depression (referred to as a ‘technical gate’) so that the mark does not protrude above the part surface. Tip gating is generally not suitable for shear-sensitive and highly filled materials due to the high temperature/high shear effects of the relatively small gate.
Sprue gates use an “open” gate, characterized by a small cold sprue that remains on the surface of the molded part, where the cosmetic appearance of the gate is less critical. The sealing of the gate is accomplished by solidification during the cooling phase of the cycle, and is affected by gate diameter and gate cooling. The relatively large gates, although not suitable for very “stringy” materials, permit good packing with reduced part stresses. Applications include technical components where gate appearance is not critical and when gating onto cold sub runners.
With this gating method, the valve pin tip mechanically closes the gate on completion of the holding pressure time. Since pin closing occurs before the gate solidifies, valve gates frequently offer decreased cycle times when compared to open gating methods. Unlike the other gating methods, valve gating creates no gate vestige but leaves only a barely visible ring. For this reason, it is the best solution for all parts where surface quality is critical. Due to the unrestricted gate opening, reduced shear heat and pressure drop is realized with this gating method. As a result, valve gating imparts lower mold filling stresses and gives a wide processing window suitable for even the most difficult thermoplastics that contain sensitive additives. With all materials, valve gating results in better part characteristics, especially with higher shot sizes and injection speeds. For stringy materials, this gating method eliminates the possibility of drooling entirely. Although normally oriented perpendicular to the part surface, valve gates can also gate onto inclined or profiled surfaces.
Mold-Masters offers several types of valve gates to accommodate the varying solidification rates of different thermoplastics.