Stripper plate mold

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. 

Once the molded part has cooled sufficiently in the cavity, it has to be ejected. This is done mechanically by KO pins, KO sleeves, stripper plates, stripper rings or compressed air, used either singly or in combination. The most frequent problem in new molds is with ejection. Because there is no mathematical way of predicting the amount of ejection force needed, it is entirely a matter of experience. 

The two-part blow mold opens, and the core pin carries the complete blown container to the third stage, which ejects the part. Ejection can be done by using a stripper plate, air, a combination of stripper plate and air, robots, and so forth. 

When molding BDS the hotter the part the easier it is to eject the component fi om mold therefore, the ejection system should be designed so that wherever possible a stripper plate or sleeve/ring assembly is used. If ejector pins are used then the maximum diameter possible should be used, so as to ensure that the molding does not distort upon ejection. 

Stripper plate In molding, a plate that strips a molded piece from core pins or a force plug. The plate is actuated by opening the mold. 

Triple-daylight mold n. A mold having four plates feed plate, floating cavity plate, stripper plate, and moving mold plate. When the mold opens, all the plates move apart making three openings among them. 

There is another method for producing internal threads which are too rigid to be stripped off a mold. That involves a core mechanism which collapses. Such collapsing cores are patented and there is an added cost for this mechanism. Molds utilizing these cores cycle nearly as fast as stripper plate molds and the mechanisms require a moderate amount of additional space. However, these molds are reported to have higher maintenance costs than the other types of molds and are generally thought of as a solution for applications with lower production quantities. 

Ejector locations. Ejection devices for plastic parts can range from screwdrivers used to pry parts out of a hand mold to mechanized stripper plates and elaborate mechanisms which also retract collapsible cores. All of them share one common characteristic they exert pressure on a newly formed part. That pressure can distort the part to the point of disturbing its function or appearance if it occurs while the part is still too soft to withstand it. Therefore, the processor must delay ejection until the moldment can endure it. The more ejectors there are, the more ejection surface there is to distribute that pressure and the sooner the part can be removed from the mold, thereby shortening the molding cycle. However, ejectors cost money and leave marks on the surface of the moldment. Therefore, there is a mold cost associated with a faster molding cycle. (Differences between bidders on a project are often based on variations in cooling and ejection systems.) Additional ejectors leave more marks on the surface and their number and location may be limited by functional and appearance concerns. 

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 primary purpose of a stripper plate is to eject the part from the mold without distorting it or without the presence of objectionable ejector pin maiks. The stripper plate is usually used for parts with thin wall sections (0.010-0.040 in.) when the part... 

Figure S.9 Diagram showing construction used for a stripper plate mold. The stripper plated is pushed down by auxiliary press equipment causing molded parts to be stripped from the plunger. (Ref Buckleitner, E.V., ed., Basic Mold Types and Features , Plastics Mold Engineering Handbook, 5 ed..

Handling systems are not able to pick out parts which shrink on the mold cores at high-shrinking forces. Stripper plates are used more and more for this job. During the drop-out process, the handling clutch takes the piece out of the mold. Core-trains and racketeers require special attention in respect to mold construction. 

If a stripper plate is used to operate several pins simultaneously, it must be hard enough to prevent cold flow. During molding, the area of the stripper pin can reach pressures of 2500 psi. The... 

Ejection may be by means of pins or a stripper plate, or a combination of both. The stripper plate acts on the entire peripheral wall thickness of the part and so distributes the ejection force. This is the preferred method for thin-walled parts, but the method is difficult to apply to anything other than a circular periphery. A variant on this theme is the stripper bar which works on part of the periphery. Most ejection is performed by pins, usually cylindrical in form. Rectangular pins may be used in constricted areas these are often referred to as blade ejectors. Hollow ejector pins known as sleeve ejectors are commonly used to push the molding off small core pins. Ejection of deep-drawn or thin-walled parts is often assisted by an air valve that breaks the vaeuum between the molding and the mold core. 

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