Ejector and rocker mechanism are mainly used for inner concave and convex of molded plastic parts, and also have ejection function. This mechanism has a simple structure, but poor rigidity and small stroke. Typical structure commonly used is as follows:
(1) Structure 1 Ejector mechanism
Figure 7.7.1a is the most basic ejector mechanism. During ejection process, ejector 1 moves along oblique square hole of rear mold under action of ejection force to complete lateral molding. Root of ejector requires assembly structure shown in figure. Figure 7.7.1b is a schematic diagram of its assembly.

 

1-Ejector 2-Insert 3-Slider 4-Fixed block 5-Upper ejector plate 6-Lower ejector plate
In ejector mechanism, in order to ensure stable and reliable operation of ejector, following points should be noted:
(A) Rigidity of ejector. To enhance rigidity of lifter, generally:
1. If structure allows, increase lifter's cross-sectional dimensions as much as possible.
2. If lateral ejection is possible, minimize lifter's angle "A," generally no greater than 20°. Lifter's lateral load point should be shifted downward, such as by adding insert 2 (see Figure 7.7.1a). This insert also provides increased rigidity, extending mold life.
(B) Providing lateral movement space for lifter. As shown in Figure 7.7.1a, dimension "D" should be considered. To ensure that lifter does not interfere with other components on part during ejection, lifter's lateral mold separation distance and angle "A" should be carefully considered to ensure sufficient lateral movement space.
(C) Repositioning lifter in mold opening direction. To ensure that lifter returns to its intended position after mold closing, following structural configuration is generally employed. See Figures 7.7.2a and 7.7.2b.

 

(D) Bottom of Lifter should slide smoothly and stably on ejector plate.
(2) Structure 2: Rocker mechanism, as shown in Figure 7.7.3.
During ejection process, when head of rocker 1 (range shown by L1) exceeds rear mold core, rocker 1 swings upward under action of inclined surface A to complete parting.
When designing rocker mechanism, it should be ensured that: L2>L1; E2>E1.
Disadvantages: "B" point in figure is prone to wear and hardness of this point must be increased. It is generally required to design this point into an inlaid structure.

 

1- Rocker 2- Upper ejector plate 3- Lower ejector plate

 

Elevators can be categorized as cylindrical pin-type (Figure 3) and T-block-type (Figure 4).
Of these two types, cylindrical pin-type lifters are widely used in designs, primarily due to their ease of fabrication, installation, coordination, and maintenance. T-block lifters are primarily used for larger products requiring higher precision. They require a specialized T-shaped base (Figure 5) (Figure 6), which is more difficult to fabricate and integrate, increasing manufacturing costs.

 

As shown in left image, lifter is placed in an inclined hole in a fixed mold plate, mating with hole. A thrust is applied from below, pushing lifter upward for a certain distance. Forced by inclined hole and thrust, lifter not only moves upward but also moves a certain distance in direction of lifter's inclination (as shown in image).
During ejection process, since product moves vertically, lifter not only moves vertically but also moves in opposite direction of blind spot, thus facilitating removal of product.
Prerequisite: Dimensions of mold plate, mold core, and mold base have been determined, as shown in figure below.

 

1. Review drawings and carefully analyze them to determine size of dead angle, as shown in figure.
2. Determine starting point of 0" support surface and its length (see Figures AB). If a 0" support surface is not designed, select point A as starting point of elevator's bevel.
3. Using point B as reference, deviate by a certain distance, as shown in figure BC, where BC minus ejector stroke.
4. Using point C as reference, deviate by a certain distance in opposite direction of elevator's movement, as shown in figure CD. CD = Ejector stroke (rounded to an integer) = Dead angle size + a minimum safety margin greater than or equal to 3mm.
5. Connect DB to obtain angle DBC. This angle is usually a decimal. Let's take an integer, M". This angle is desired inclination angle of lifter.
6. Remaining design components can be completed based on previously described structure and requirements.

 

In fact, main purpose of complex instructions above is to teach us how to calculate inclination angle of lifter. We can simplify it as shown in following diagram:

Issues to note when using a bevel lift:
1) Slope of lift should generally be less than 15 degrees, and slope should be as small as possible.
2) Strength of lift should be balanced between lift's slope and lift distance.
3) Consider whether product will stick to lift and whether a positioning mechanism is in place to hold product in place. Generally, following diagram is used.

 

Check whether head of lifter is reverse-inclined (ejector will scrape glue), and pay attention to whether lifter will interfere with other parts (such as other lifters, ejector pins, and bone positions). Be sure to check.

 

Safety distance for lifter release is 2~3, and lifter surface shown should be made with an inclination of 2~3 degrees.

 

When product is very deep and has a bevel on the side, a step should be added to position bevel, as shown in figure below. Alternatively, bevel may be on the side of product (which has a certain depth) and have a deeper bone on one side.

 

When width of ejector body exceeds 50mm, it is called a large lifter.
Considering material cost, processing workload, and mold maintenance, large lifters are generally constructed as split pieces. Back of ejector body is sloped 1-2 degrees higher than angle of ejector guide rod to prevent friction between back of ejector body and punch. Both sides of ejector are also designed with a corresponding slope, typically 3 degrees.
In most cases, round guide rods are used for ease of processing and maintenance. In special cases, square guide rods or a one-piece structure may also be used.
For molds with lifter structures, ejection clearance should be kept within 180mm, angle of ejector should be kept within 15 degrees, and cross-sectional area of ejector guide rod should be as large as possible to ensure that ejector guide rod does not bend or deform during movement. When lift distance is greater than 120mm and lift movement angle is greater than 10 degrees, it is suitable for molds of equipment above 500 tons. Sliding block in lift base connection part shall preferably adopt a rotatable structure to ensure that lift guide rod will not bend or deform during movement.

A small lift refers to a core pulling area that is relatively small. Cooling is generally not designed, and a single rod guide drive is often used. A small lift is a very common core pulling mechanism and is frequently used. It is generally available in both integral and split configurations. A lift structure consists of following components. Split configurations generally use a round rod and sleeve, with variations in sliding block. Alternatively, similar components can be used as with an integral configuration, with square hole in guide block replaced by a round hole.
Recommended lifter core pulling angles are 4, 6, 8, 10, 12, and 15 degrees. Avoid using angles greater than 15 degrees whenever possible. In special circumstances where a core pulling angle greater than 15 is necessary, an auxiliary guide mechanism must be designed. Sometimes, direction of lifter core pulling motion is at an angle to parting surface, tilting upward or downward. Upper and lower wear plates of lifter are designed as a single piece, forming a guide seat for lifter. For molds with a lifter structure, ejection space should be controlled within 180MM as much as possible, degree of lifter should be controlled within 15 degrees as much as possible, and cross-sectional area of guide rod of lifter should be as large as possible to ensure that guide rod of lifter will not bend or deform during movement.

 

Note:
1. Above-mentioned lifters are all rear-mold lifters.
2. Design of an lifter is generally carried out in following order (for reference):
1. Determine angle of lifter based on actual stroke. Typical angles are: 3 degrees, 5 degrees, 8 degrees, 10 degrees, and 12 degrees.
2. Determine width of lifter based on width of hook.
3. Determine type of lifter seat (T-type or pin-type) based on width of lifter.
4. Determine length and width of wear block based on length and width of lifter. Thickness of wear block is generally 15 mm, as shown in figure above. Material is 2510.
5. When designing lifter, be sure to clearly calculate stroke and ejection travel to ensure sufficient ejection clearance. Generally, ejection clearance of lifter should be approximately 0.5 to 2 mm larger than actual ejection clearance.
6. Lifters are typically made of 8407 material and must be quenched to HRC 48-52. Standard lifters use 718H and must undergo surface ammoniating.

3. Because lifter and sloping lift seat are closely related, following are several commonly used lift seat types for reference during design.

 

 

Notes:
1. Sloping lifters are often designed with a T-slot, as shown in Figure 1 above. If lifter is very thin and a T-slot is not possible, consider designing a fixed seat, as shown in Figure 2.
2. All lifters are made of WY718 steel and must undergo a nitriding treatment.
3. Design lifter as large as possible, if mold allows.