Mold Structure encyclopaedias

Mold structure encyclopaedias

Sositar mould have more than 15 years in mold manufacture field,and accumulate lots of experience in mold design and mold making process, to help the new entrants and our customers to understand mold better,we list some mold animation as below:

  1. three plates mold

This is a a popular design for mold,the advantage is :we can make more than one gate for molding,and can place the point gate in the center of product.

2)  insert mold

Ussaully we can molding steel pieces, copper nut, screws in plastic for some special use

3) mold with lifters

Lifter is use to release the undercut in product

4)mold with submarine gate

Submarine gate mark is very small,so we can place the gate on product surface and the mold can full automotively.

5)submarine on ejectors

when we can not find a good position for gate,we make cut the ejectors and put the gate there

6) hot runner mold

Hot runner can save the material for runner,reduce the cycle time and improve the production quality

7) thread release mold

the core will retote itself and release the thread

8)mold with sliders

slides for the under release

9,mold for hubs

10)sleeve ejectors

Sleeve ejector is a good solution for long bosses which have a hole in the center

if you would like to find a professional plastic mold manufacturer in China,please contact us,I am sure our service will satisfy you


Cracks issue in plastic injection molding process

Cracks refer to the narrow crevices or crazes that occur on molded plastic part surface, of which the causes might lie in the injection molding machine, the mold, the process or the raw materials.

(1) Injection Molding Machine
Mainly because of the insufficient plasticizing capacity, i.e. the plasticizing capacity is too low, leading to inadequate plasticization. Need to change for an injection molding machine that has a larger plasticizing capacity.

(2) Mold
① Poor venting tends to cause flow marks, which decreases part strength;
② Gate size is too large, making the plastic injection molded part over-pressured; gate size should be reduced;
③ Water leakage occurs in the cavity or core – check whether there are any fine cracks;

④The plastic part is designed to be too thin – reinforcing ribs are needed;

⑤ Check the mold cavity, to see whether the mold core enjoys a sufficient draft angle;

⑥ Ejector pin oil spreads to the surface of mold cavity – the mold needs to be maintained and repaired;

⑦ Increase ejector pin diameter, and lower ejection speed;

(3)Injection Molding Process
① Adjust the temperature of material barrel. If the temperature is too high, the material will be decomposed; if too low, sufficient welding strength cannot be guaranteed;

② Adjust injection pressure. Raise temperature to ensure smooth mold filling and reduce viscosity; if the pressure is too high, cracks will be caused by internal stress, so the pressure needs to be reduced;

③ Reduce pre-molding back pressure and screw speed, to avoid material decomposition;

④Appropriately increase injection speed;

⑤ Increase cooling time. If the cooling time is too short, sufficient solidification cannot be guaranteed, thus causing ejection cracks or ejection marks;

(4)Raw materials
① Ensure raw materials are completely dried;

② Raw materials are contaminated; find out the cause and take control measures;

③ Excessive recycled materials are added – identify the proper proportion of recycled materials through test results.

Discoloration issue in plastic injection molding

Discoloration means the surface color of a molded part is not consistent with the required color. Discoloration may be caused by a variety of reasons, which may cover the several aspects of injection molding machine, mold, process and raw materials, etc.

(1) Injection Molding Machine
① Equipment is not clean and needs to be cleansed. Dusts or powders are deposited in the barrel, which contaminates and discolors the materials;

② Temperature control failure caused by malfunction of thermal couple, temperature controller or the heating system;

③ Obstacles exist in the barrel, causing the plastic material to decompose; foreign metal objects are stuck in the barrel or the screw channel, which keep grinding, causing plastic material discoloration;


① Poor mold venting, causing plastic to be compressed in a heat-insulated environment, so the material tends to be burnt when reacting with oxygen under high-temperature and high pressure conditions;

② Mold gate is too small;

③ Too much lubricants/mold releasing agents exist in the barrel. Clean the material barrel, to remove the additives which possess poorer heat resistant properties than the plastic, such as antistatic agents;

④ Nozzle, sprue and runner sizes are too small;


(3)Injection Molding Process

① Screw speed/pre-molding back pressure is too high;

② Barrel/nozzle temperature is too high;

③ Injection pressure is too high/injection time is too long/injection speed is too fast, causing product discoloration.


(4) Raw Materials
① Material is contaminated;

② Too much moisture/VOC content contained in the material;

③ Coloring agents/additives are decomposed.

The Cooling System(water line) for plastic injection mold


The Purpose of The Cooling

The design purpose of the cooling system is to ensure uniform cooling, as well as the shortest possible ejection time of the molded products, so as to complete the production process. Cooling design has a direct influence on product quality and molding cycle.


Cooling Location

  1. For materials that shrink a lot, such as PP, PE and PVC, it is better that the cooling system is deployed along the shrinkage direction of products.
  2. On condition that the strength of mold material is guaranteed, the cooling should be close to the mold cavity or mold core surface as much as possible and evenly deployed around the molded product, of which the dimensional requirements are shown in the following diagram:


  1. When the mold adopts the inserting structure while the insert is big enough, it should be cooled separately. Ring-like cooling channels are often designed for circular mold inserts, such as the gear inserts. Large sliders need to be separately cooled, too. D = d + (1 – 2) (d refers to channel diameter)


  1. Each part of the mold has to be cooled in a uniform way. The BeCu alloy is often employed in cooling the structures that does not allow the design of a cooling system.
  2. When two cooling channels form an overhead crossing or on the same level, the minimum space between them should be 3mm if the channel width is smaller than 150, and 5mm if the width is greater than 150. See the diagram.


  1. Cooling design should try to avoid ejector pin, ejector sleeve, ejector guide pin, lifter, ejector, screws, etc. and the smallest clearance around them should be at least 3mm. When the mold is designed with an early ejector return, the water inlet/outlet location should be able to avoid interference with it.
  2. If there are more than 2 sets of cooling systems in a plastic injection mold, the water inlet/outlet location should be marked with “IN” and “OUT”, which refers to Water Inlet and Water Outlet respectively. At the same time, they should be numbered to indicate connection sequence.

Cooling channel Dimensions

  1. Try to use the largest possible cooling channel, with the minimum being ø1/4’’. Accept the ø3/16” option when there are no other choices, but the largest cannot be larger than ø1/2”. The commonly used channels are sized ø1/4”, ø5/16” and ø3/8”. Try to keep the diameter of pipes in a cooling channel as consistent as possible, so as to ensure a uniform flow rate. In a mold, there cannot be too many joints in a single set of cooling channel, so as not to affect the cooling effect.


Positional Relationship between Cooling Channel & Mold Base

  1. It is preferred that water inlet/outlet are deployed along the width direction of the mold base, or 4 corner columns are needed to be added along the length direction of the mold base.
  2. In principle, cooling water gets in the mold from mold base, instead of connected to mold interior directly. When cooling water has to get in mold interior directly or be used to cool the sliders, a 20 – 40 clearance should be kept between mold base and hose nipple.
  3. For vertical molds, it should be avoided that the water pipes go through the clamp slots which should be at least 5mm from the cooling drilling.

See the diagram:


  1. When the cooling systems of the core and cavity get in and out from the same direction, the outlets should be at least 35mm from each other.


  1. When mold plate is not thick enough but cooling is needed, it should be guaranteed that the cooling center is 15mm from the top of the plate. When plate thickness measures 20mm, the distance should be kept at 13mm.


Cooling Tower

For products designed with deep cavities, to ensure thorough cooling of product, a cooling tower should be designed. When an angle hole is needed to join 2 cooling towers, the biggest angle should be no larger than 45°, and A should be no less than 3.0mm (see the diagram). Cooling tower adopts the bronze spacer, of which the dimensions are shown below:

1) 1/8″x1″x1200mm

2) 1/8″x1-1/4″x1200mm

3) 1/8″x1-1/2″x1200mm


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