The sliders for plastic injection mold

Due to the special requirements of some products, the mold release of some part is not consistent with the mold opening direction of the injection machine, which needs the side parting core pulling mechanism to eject the product smoothly.
The side parting core pulling mechanism comes with two types: slider(also known as slide) and lifter.
1. Slider travel calculation:
To ensure smooth product release, the travel distance of the slider has to be sufficient. Usually, the shortest travel distance that can guarantee smooth product release is 2 – 3mm:
AB = AC + (2 – 3)
   sliders stroke
2. All core sliders adopt the press plate + guide pin + spring structure as shown in the diagram (sometimes, when the slider is wider than 100 and yet it is not convenient to adopt the structure, T-plate structure may be considered). However, when the slider is vertically placed and restricted by pin position/mold size, press plate will not be necessary – an integrated mold base may be the option.
 sliders press block
The press plate is a standard self-built part of the company, which shall be located with a locating pin.
3. No matter whether the slider sides are sealed, both of its sides need a gradient design. Usually, the angle of a single side is 3 – 5 °; but when two sliders which travel in vertical direction join with one another, the angle will be 45°. During the design process, if there are sliders joining with one another on the four sides of a product, the ear of one of the sliders may stick out to guarantee accurate location.
4. The ratio of slider height to its length should be no greater than 1, or slider movement will be affected by overturning moment, leading to movement failure. General requirement: L≧1.5H.
5. Usually, the angle of a slider guide pin is 15° – 25°, with the biggest no larger than 25°. The angle of a guide pin is usually 2° smaller than that of the slider. In general, try not to use small guide pins, so as to ensure smooth slider movement.
6. The hole of a guide pin is 1/64" larger than a single side of it, about 0.4. When a guide pin goes through a slider, enough clearance should be kept on the mold plate.
7. Identify the location of a guide pin in a slider: try to place the guide pin in the center of a slider. See the diagram for specific measurements:
guide pin hole for sliders
8. It is required that the wedge surface matched with the slider should be higher than 2/3 of slider height, and the screws used on wedges should as big as possible. The following diagrams show wedges of two different structures. Try to avoid the structure shown in diagram b.
the wedge for sliders in plastic injection mold
9. Identification of slider spring length: Guarantee a sufficient space for spring, so as to avoid spring failure.
Assume slider travel is M and total spring length is L; assume the spring is compressed by 40%, and after the slider quits completely, the spring still bears 10% of the pressure, then:
Space for spring is 0.6L.
When L is too small, to prevent spring failure, spring length is often to be increased.
10. To ensure smooth slider movement, there cannot be obstacles to movement around it, such as pointed angles. Generally, chamfers of R3 – R5 should be designed around it.
11. When a spring is needed to be mounted under a slider (see the diagram for dimensional requirements), to prevent screws from being seized by the spring, Table 4-1 should be referred to for selection of springs and screws.
sliders spring
Spring Matching Screws
ø3/8” M3/16”
ø1/2” M1/4”
ø5/8” M5/16”
ø3/4” M3/8”
ø1” M1/2”
ø1-1/4” M1/2”
12. Large sliders should be cooled separately, and wear blocks should be fitted on the slider or the wedge. At this point, there should be a 0.5 clearance between the slider and the wedge.
See the diagrams.
clearance between slider and wedge

What is guide pin for plastic injection mold?

Guide pins for plastic injection mold

  • Guide pin function:

1.Guide pin is for Accurately locate core and cavity side of plastic injection mold,make them match perfectly and move smoothly

2.Support the mold weight

3.Protect core or cavity inserts

  • Material of guide pin:

SUJ2  ,hardness:HRC 60+/-2 degree.(high-frequency quenching)

  • The types and application of guide pin

Guide pins type

  • How to design the length of guide pin?

guide pins length design



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What is the stop pin?

stop pins for plastic injection mold

The function of the stop pin

1.Reduce the contact surface betwwen ejector plates and clamping plates,it is easy to control the flatness of ejector plates by adjusting the thickness of stop pins.

2.Buffer against ejector plates

The material of stop pin

S45C,hardness HRC40°~45°

Position of stop pin

1.An STP must be installed under the RP to prevent deformation caused by large stress,see pic 1#

2. Avoid to interfere with other mold components,such as support,EGP,KO .etc. see pic 2#

The quantity of stop pins

The quantity of stop pin designing

Note:For a large size plastic injection mold, Stop pin is needed to increase the supporting points of the ejector backing plate, so as to prevent ejector plates from deformation


Injection mold cooling system design

Definition of injection mold cooling system:

Injection mold cooling system: AKA. injection mold temperature control system

Heat or cool the mold to keep its temperature within a reasonable range.

-Mold cooling medium: water, oil, beryllium copper (BeCu) and air, etc.;

-Mold heating methods: hot water, steam, hot oil and heating rod, etc.

injection mold cooling system

Influence of Mold Temperature on Different Plastics

  • For plastic materials with great fluidity (PE, PP, HIPS, and ABS, etc.), lowering the mold temperature helps reduce stress cracking (the mold temperature is usually around 60°C);
  • For plastic materials with poor fluidity (PC, PPO and PSF, etc.), raising the mold temperature helps reduce the internal stress of the plastic product (the mold temperature usually ranges between 80°C and 120°C).

Influence of mold temperature on quality of molded plastic products

  • Temperature too high: The plastic products deform greatly after mold release, and it is easy to cause flashing and sticking;
  • Temperature too low: Leading to poor melt fluidity, as well as such surface defects as silver streaks, flow lines, and underfilling;
  • Uneven temperature: The plastic products shrink unevenly, resulting in warping deformation.

Mold temperature directly affects the injection cycle  

  • Injection mold cooling time takes up about 80% of the injection cycle.

injection mold cooling line

Ways to improve mold temperature control

  • Appropriate size of cooling lines: diameter 5-13mm (3/16″-1/2″).
  • Select mold materials with high thermal conductivity.
  • Reasonable plastic product design.
  • Proper cooling circuit.
  • Enhance the cooling of the thick areas of a plastic product.
  • Fast and slow cooling.
  • Strictly control the temperature difference between the coolant outlet and inlet.

Key considerations for injection mold cooling channel design

1.Which is more important, cooling or ejection?

2.Try to keep the thermal balance of the mold, so that the temperature is uniform in each part of the mold.

cooling in plastic injection mold

3.A parallel cooling channel is not preferred

injection mold cooling in types of parallel and series

 Location of cooling lines:

1.Try to keep a consistent distance between the coolant and the filled plastic in the cavity, 10-15mm is preferred. The center distance of the coolant is about 5D.mold cooling location

2.The cooling lines should not be close to locations where the melt flows finally meet;

3.Prevent the cooling lines from interfering with other mechanisms in the mold, and maintain a steel part of 3mm in the middle;

4.The coolant for cavity insert should be as close as possible to the filled plastic, and that of the core insert should be set as far as possible to the outer edge. When the mold cavity / core is too big, the coolant must be in contact with it.

5.For the BeCu mold, coolant may go straightly between plate A and plate B.

Coolant channel length design 

The longer the coolant channel, the more difficult it is to process and the worse the cooling effect. The number of cooling line elbows should not exceed five.

The distance between the hoses should not be less than 30mm

injection mold cooling chanel location

O-ring design

1.When the cooling channel passes through two inserts, a O-ring is added in the middle;

2.Try to avoid wear and shear on O-rings during assembly.

injection mold cooling and o-ring

Empirical identification of injection mold cooling line diameter:

Mold width < 200mm: diameter 5-6mm (or φ3/16″-1/4″);

Mold width between 200 to 400mm: diameter 6-8mm (or 1/4″ – 5/16″);

Mold width between 400 to 500mm: diameter 8-10mm (or 5/16″-3/8″)

Mold width > 500mm: diameter 10-13mm (or 3/8″-1/2″)

injection mold cooling channel diameter

Mold core cooling

1.Core diameter ≤ 10MM: natural cooling;

2.Core diameter between 10 to 15mm: cooling with inlaid BeCu;

3.Core diameter between 15 to 25mm: jet cooling system;

4.Core diameter 25-40MM: cooling bladder + spacer

injection mold cooling special types

5.When mold core diameter is greater than 40mm and the height is less than 40mm, it is inconvenient to guide the coolant through to the center, so cooling from the lower surface is recommended.

6.When mold core diameter is greater than 25mm, cooling from the outer side can be adopted when it is inconvenient to guide the coolant through to the center.

injection mold cooling design