Ejection System: The ejection system in a mould should be: Positive in action, No ejection mark will be seen on the product, No defects on the product (I.e. distortion, flash, witness mark) the configuration of the product:
Ejector grid: The ejector grid is that part of the mould which supports the mould plate and provides a space into which the ejector plate assembly can be fitted and operated.
There are three alternatives deign:
1. In-line ejector grid
2. Frame type ejector grid
3. Circular support block grid
Ejector plate assembly: The ejector plate assembly is that part of the mould to which the ejector element is attached. The assembly consists of an ejector plate, a retaining plate and an ejector rod.
Ejector plate actuation: The mould is mounted on the moving platen of the injection machine. To the left of the moving platen is the machines actuating rod. This member can be adjusted to allow for various alternative strokes. When the moving platen is caused move to the left and mould opens, the moulds’ ejector rod at some point of the stroke strikes the actuating rod. The entire ejector plate assembly is arrested .The remainder of the moving half continue to move to the left until the opening stroke is complete.
Types of ejection: Pin ejection (Round Pin, D-Pin), Blade ejection, Stripper ejection (Stripper plate, Stripper Ring), Sleeve ejection, Air ejection (Valve ejection)
Sleeve ejection: this is one type of hollow circular ejection pin which is fitted at the rear end to the ejector assembly. The sleeve is sliding fit in the cavity insert and core pin. The core pins extends completely through sleeve and is attached to the back plate.
The sleeve moves relation to the core and cavity and hence moulding is ejected easily. In this method the moulding is ejected by me3ans of a hollow ejector pin, termed as a sleeve. It is used for the ejection of circular mouldings and for the ejection of circular bosses on a moulding of any shape.
Pin ejection: This is the most common type of ejection as it is simplest to fit in a mould. In this technique the moulding is ejected by the application of a force by a circular steel rod called ejector pin.
Blade ejection: The main purpose of the blade ejector is for the ejection of very slender parts, such as ribs and other projections.
Stripper bar ejection: This method is an extension of the parting surface ejector pin principle, in which the ejector element is caused to push against the bottom edge of the moulding. This method is particularly suitable for the thin-wall box-type mouldings.
Stripper plate ejection: - this ejection technique is primarily used for the ejection of circular or box type moulding. In this a steel plate is situated between the core and cavity for purpose of ejection, which is called stripper plate. The stripper plate is sliding fit on the core when the mould starts to open the stripper plate moves back along with core plate. Once the mould plate is clear with cavity, the movement of stripper plate is rear ward direct, and hence the moulding is eject easily.
This technique is used primarily for the ejection of circular box-type mouldings while the design is used for those which have thin wall sections.
Integer core and cavity plates: When the core and cavity is machined from a large plate or block of steel is termed as an integer cavity plate or integer core plate. This design is preferred for single impression moulds because of the strength and lower cost characteristics.
Valve ejection: This type of ejection is used for the ejection of large component. The valve ejector is a large diameter ejector
Pin, which applied the ejector force on the insert surface of the moulding. The ejection element forms a valve type head which is seated into the core to ensure a material leak face joint a small parallel portion of length 0.8 to 2.4mm is provided. The valve ejector element is basically a large diameter ejector pin. This method is normally used for the ejection of relatively large components. It is also alternative to stripper plate ejection in some circumstances.
Air ejection: in this ejection system, compressed air is used directly on to the moulding face via a small air valve. The effective ejector force is depending upon the pressure of the compressed air and area on its acts. With this ejector method the ejector force is provided by compressed air which is directly on to the moulding face via a small air ejector valve.
No comments:
Post a Comment