Automatically Separated Runner

Hollow plastic tube from which a part is blow molded. A machine or system used to automatically separate parts from the runner system after molding. Separated parts go to their next station and the runner moves to a granulator for reuse if permitted. The system may use blades, rigid pins, or a degating station with parts placed by a robot for separation. 

A stripper plate mold is a two-plate mold in which the core and ejector plates are combined into a stripper plate. It is used for thin wall parts and parts with symmetry and no undercuts. A three-plate mold has two parting Unes, thereby providing automatic separation of the parts and runner system. This does not work with all materials brittle materials tend to fracture on ejection. It also limits the selection of gate locations and does not eliminate scrap. A stack mold is used to mold two layers of parts without increasing clamp force. Because stack molds are not as precise as two-plate molds, they are used for low-tolerance parts such as polystyrene drinking cups. 

The machine must be capable of consistent repetitive action. All molded parts, gates, and runners must be ejected automatically. There is usually some method of separating runners and gates from molded parts when runnerless molding is not used (i.e., wiper mechanisms, air blast, etc.). Some systems weigh the part after ejection and stop the machine or sound an alarm on off-weight parts. 

Simplified production. After sprues and runners are eliminated, automatic separators or manual sorting to separate them from the mouldings are no longer required, which makes the automation of work easier. 

If the effort for hotrunner systems are not justifiable, then a tunnel gate (Figure 1.36) which is the most common gate type, is being used. Advantageous is that the automatic separation of the runner from the molded part occurs inside the mold without any additional mechanism. 

This type of mould, also often referred to as a three plate mould, is used when it is desired to have the runner system in a different plane from the parting line of the moulding. This would be the case in a multi-cavity mould where it was desirable to have a central feed to each cavity (see Fig. 4.38). In this type of mould there is automatic degating and the runner system and sprue are ejected separately from the moulding. 

Degating equipment n. Equipment used to separate the molded part, automatically or manually, from an injection molded sohd runner system. 

Multi-plate moulds are usually more expensive than two-plate moulds and can be slower in production if an operator has to remove the sprue and runner system when the mould is open. This can usually be avoided by providing automatic ejection of sprue and runner. The distance travelled by the plates is governed by the length of the chain or the length of the bolts used to separate them. 

Point gates for simple or multiple sprues are frequently foimd in the mould parting line. The runners are guided up to just before the mould cavities with a somewhat larger cross-section, in order to flow into the narrow, short gate runner. The sprue can thus be separated easily from the form part, although not automatically. 

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