Ejector pin

An alloy of molybdenum containing 1.2% hafnium with carbon at the level of 0.08—0.10% has a slight advantage over TZM. This alloy has been produced in small quantities for special extmsion dies and ejector pins in the isothermal forging of superalloys. 

When the mold is opened, the part should be easily removable. Cavities are made with a slight taper to reduce frictional drag of the part on the mold. The half of the mold attached to the movable platen is equipped with ejector pins, which push the part out of the cavity while the mold is being opened. When the mold is closed, the pins are flush with the cavity surface. Release agents or lubricants facilitate ejection and shorten the mol ding cycle. Some complex parts require that the mold open in several directions in addition to the direction of the platen movement. For a threaded part, eg, a bottle cap, part of the mold must be rotated to remove the article from the mold. 

A further source of stress may arise from incorrect mould design. For example, if the ejector pins are designed in such a way to cause distortion of the mouldings, internal stresses may develop. This will happen if the mould is distorted while the centre is still molten, but cooling, since some molecules will freeze in the distorted position. On recovery by the moulding of its natural shape these molecules will be under stress. 

Receptacle into which ejector pins are assembled. 

Ejector pin Pin or dowel used to eject molded articles from a mold. 

Ejector-pin-retainer plate Receptacle into which ejector pins are as-... 

Return ejector pins to retraced position as mold closes for next cycle... 

Force (Male Cavity) Guide Pin Bushing Rear Cav. Retainer PI. Push-back Pin Support Plete Ejector Pin Sprue Lock Pin Support Pillar Ejector RetBiner PI. Ejector Plate Clamp Slot Ejector Housing... 

Once the polymer has cooled to its solid state, the molding is ejected. This is accomplished with the aid of ejector pins that protrude from the mold walls as it opens. Small items typically drop directly into a catch pan or onto a conveyor belt below the mold. Larger items are removed manually. 

Rotational molding creates a wide variety of plastic products that cannot be made effectively, efficiently, or economically by other means. What sets this method apart from others is that it can create thin-walled, hollow parts that exhibit no weld lines or scarring from ejector pins and from the process itself. It also has the advantage of having little scrap and minimal molded-in stresses, due to the low pressure and low shear rate characteristics of the process. Finally, it can be used to make parts that are very large which would be impossible to manufacture by other methods. 

Ejector pins help to separate the finished molding from the mold cavity. These are driven mechanically during the mold-opening stage of the cycle. 

Different actions in molds occur such as using ejector pins to remove molded parts from their cavities. Side actions of molds may be required to remove parts that have undercuts. Other actions may be required such as unscrewing threaded parts, including inserts, and so on (Chapter 17). 

Ejector Pin Sprue Lock Pin Support Pillar Ejector Retainer PI. Ejector Plata Clamp Slot... 

Cartridge case such as Cl is extracted vrocn the breech 22 of barrel 13 by an extractor designated for example in FIG. 7 by the numeral 48. As the cartridge case such as Cl moves toward the left in unison with the bolt 21, ejector pin 49 strikes the cartridge case Cl and drives the case downwardly and outwardly through the ejector opening 50 formed in frame I. This action is depicted in FIG. 8. Of course the ejec-... 

The ejector pins should have an adequate cross-sectional area to minimize the possibility of distorting or puncturing the molded plastic at the time of ejection from cavities, as most of the thermoset compounds are slightly soft during that time. 

Figure 2.3 shows the molding cycle of pot-type transfer molding, and Figure 2.4 shows plunger-type transfer molding (sometime called auxiliary raw transfer molding). The taper of the sprue is pot-type transfer is such that, when the mold is opened, the sprue remains attached to the disc of material left in the pot, known as cull, and is thus pulled away from the molded part, whereas the latter is lifted out of the cavity by the ejector pins (Figure 2.3c). In plunger-type transfer molding, on the other hand, the cull and the sprue remains with the molded piece when the mold is opened (Figure 2.4c).

FIGURE 2.3 Molding cycle of a pot-type transfer mold, (a) Molding compound is placed in the transfer pot and then (b) forced under pressure when hot through an orifice and into a closed mold, (c) When the mold opens, the sprue remains with the cull in the pot, and the molded part is lifted out of the cavity by ejector pins. (After Frados, J. ed. 1976. Plastics Engineering Handbook, 4th Ed., Van Nostrand Reinhold, New York.)... 

Ejection of a molded plastic article from a mold can be achieved by using ejector pins, sleeves, or stripper plates. Ejector pins are the most commonly used method because they can be easily fitted and replaced. The ejector pins must be located in position where they will eject the article efficiently without causing distortion of the part. They are worked by a common ejector plate or a bar located under the mold, and operated by a central hydraulic ejector ram. The ejector pins are fitted either to the bottom force or to the top force depending on whether it is necessary for the molding to remain in the bottom half of the female part or on the top half of the male part of the tool. The pins are usually constructed of a hardened steel to avoid wear. 

In joining with solvents or adhesives, it is very important that the surfaces of the joint be clean and well matched since poor contact of mating surfaces can cause many troubles. The problem of getting proper contact is aggravated by shrinkage, warpage, flash, marks from ejector pins, and nonflat surfaces. 

These tend to be curved panels, or shallow containers. They have a variable thickness, since only the convex side contacts a metal die. They can be as thin as 0.1 mm, since a sheet of melt is stretched before contact with the cold mould, or as thick as 10 mm. There will be no signs of any injection point or ejector pins. Typical examples are disposable coffee cups (Fig. 1.16a), margarine containers, baths and shower trays. 

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