Molding cold slug

Section provides opposite sprue opening of the injection mold, used for trapping cold slug. 

Cold slug First material to enter an injection mold. 

A problem had arisen with molded parts from a medical products company. Some injection-molded sheets were exhibiting small translucent areas (gels) within the opaque polymeric material, which had been designated as non-melt areas. One theory for the source of the non-melt was that a contaminant was present, while another postulate was that these areas represented a cold slug coming from the sprue. One sheet was chosen for analysis since the area of non-melt within it was largest. Both the non-melt area as well as a "normal" area were tested. 

Space provided directly opposite the sprue opening in an injection mold to trap the cold slug. 

In injection molding, a portion of the plastic composition held in the cold slug well by an undercut, used to puU the spme out of the bushing as the mold is opened. 

In order for the sprue assembly to be ejected cleanly from the mold use a 3 to 6 degree (inclusive) taper on the sprue and incorporate a T type, sprue puller pin in the cold slug well ensure that the pin is secured or keyed in the correct position so as to enable the feed system to fall away, under its own weight, from the undercut on the pin. 

Full round runners are preferred where typical diameters of 6 to 8mm (0.236 to 0.315in) (for component wall thicknesses of up to 4mm (0.157in)) and 8 to 12mm (0.315 to 0.472in) (for component wall thicknesses of greater than 4mm (0.157in)) are recommended. Z type, cold slug well pullers are preferred for cold runner molds. 

Cold slug n. The first material to enter an injection mold, so called because in passing through the sprue orifice it is cooled below the effective molding temperature. 

In some molds, a small well in the mold opposite the sprue catches the cold slug and thereby prevents it from entering the ruimer system. 

Although runners should deliver melt to each cavity at the same time, they may be naturally balanced or artificially balanced. In naturally balanced runners the distance from sprue to all gates is the same, whereas artificially balanced runners have the same pressure drop from sprue to all gates. Cold runner molds also incorporate cold slug wells at each turn in the melt flow. These collect the cold melt from the sprue plug (melt frozen at the nozzle), thereby preventing this melt from entering the cavities. 

The seating ring centers the sprue bushing on the injection platen of the machine directly in line with the nozzle of the injection cylinder. The sprue bushing should be as short as possible from the nozzle to the parting line of the mold and have a taper of at least 3 deg in order to maintain the heat of the melt. Cold slug wells should be used wherever possible to permit the leading cold resin to be trapped and to permit the hot resin to... 

Sprue Lock n In injection molding, a portion of the plastic composition that is held in the cold-slug well by an undercut, used to pull the sprue out of the sprue passage as the mold is opened. The sprue lock itself is pushed out of the mold by an ejector pin. When the undercut occurs on the cavity-block retainer plate, this pin is called the sprue-ejector pin. 

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