What is the shrinkage of molding and how to calculate the shrinkage of injection molds

Molding shrinkage is the percentage of the reduced value of the room temperature size to the original uncooled size after the plastic part is taken out of the mold and cooled to room temperature. Since shrinkage is not only the thermal expansion and cold contraction of the resin itself, but also related to various molding factors, the shrinkage rate of the plastic part after molding should be called the molding shrinkage.

The shrinkage rate is calculated as (r-r-r) before r*100%. Shrinkage percentage.

The shrinkage is expressed by: s = 100% (1) where: s - shrinkage; d-Mold size; m-Part size.

Below is the shrinkage rate of plastics, in (%)

pp(；pmma(；

pc(；pa6(；

pa6-gf(；

pa66(；

pa66-gf(；

ps(；abs(；

abs-gf(；

pom(；pbt(；

pet(。The above is the shrinkage ratio of commonly used plastics, there is a range, and the general manufacturer does not specify, so take the median value!

Summary. Hello dear! Thermoplastics are characterized by expanding when heated, shrinking when cooling, and of course shrinking when pressurized.

In the injection molding process, molten plastic is first injected into the mold cavity, and after filling, the melt cools and solidifies, and shrinkage occurs when the plastic part is removed from the mold, which is called molding shrinkage. During the period of time between the removal of the mold and the stabilization of the part, there will still be small changes in size, and one change is that it will continue to shrink, and this shrinkage is called post-shrinkage. Another variation is that some hygroscopic plastics swell due to moisture absorption.

For example, when the water content of nylon 610 is 3%, the size increase is 2%; The water content of glass fiber reinforced nylon 66 is 40%, and the size increase is. But the main role played by this is the shrinkage of the molding.

Hello dear! Thermoplastics are characterized by expanding when heated, shrinking when cooling, and of course shrinking when pressurized. In the injection molding process, the first solution is the trapped molten plastic injected into the mold cavity, after the filling is completed, the melt cools and solidifies, and the shrinkage occurs when the plastic part is taken out of the mold.

During the period of time between the removal of the mold and the stabilization of the part, there will still be small changes in size, and one change is that it will continue to shrink, and this shrinkage is called post-shrinkage. Another variation is the expansion of some hygroscopic plastic grips due to moisture absorption. For example, when the water content of nylon 610 is 3%, the size increase is 2%; The water content of glass fiber reinforced nylon 66 is 40%, and the size increase is.

But the main role played by this is the shrinkage of the molding.

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Summary. The shrinkage of an object after heat treatment depends on several factors, such as the type of material, heating temperature, time, cooling rate, and so on. As a result, the shrinkage of different materials after heat treatment will also vary.

For example, in the case of ordinary steel, the shrinkage rate is approximately in between, after annealing heat. However, if heat treatment such as quenching and aging is carried out, the shrinkage may be greater. In short, the shrinkage after heat treatment needs to be analyzed and calculated according to the specific situation, and it is recommended to adjust it according to the experimental data in actual operation.

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The shrinkage of the object after heat treatment depends on a number of factors, such as the type of material, heating temperature, time, cooling rate, etc. As a result, the shrinkage of different materials after heat treatment will also be different. For example, in the case of ordinary steel, the shrinkage rate is approximately in between, after annealing heat.

However, if heat treatment such as quenching and aging is carried out, the shrinkage may be greater. In short, the shrinkage after heat treatment needs to be analyzed and calculated according to the specific situation, and it is recommended to adjust it according to the experimental data in actual operation.

Molding shrinkage refers to the percentage of the shrinkage of the size at room temperature to the original uncooled size of the plastic part after it is taken out of the mold and cooled to room temperature. Since the shrinkage is not only the thermal expansion and cold contraction of the resin itself, but also related to various forming factors, I guess that the shrinkage rate of the plastic part after molding should be called the molding shrinkage. This concept is commonly used in polymers.

Serial number Plastic name Code shrinkage.

1 Acrylonitrile, butadidimine, styrene ABS

2 Amino resin AF

3 Chlorinated polyether CP

4 epoxy EP

5 Polychlorotrifluoroethylene F3

6 Teflon F4

7 PTFE reinforced F4+20%GF

8 Polyperfluoroethylene propylene F46

9 HDPE (HDPE) HDPE 2 10 High Impact Polystyrene (Non-Brittle Glue) HIPS11 Rigid PVC HPVC

12 Liquid crystal polymer LCP

13 LDPE LDPE

14 Modified polyphenylene ether MPPO

15 polyamide 6 pa6

16 Polyamide 6 reinforced PA6 + 30% GF

17 Polyamide 66 PA66

18 Polyamide 66 reinforced PA66 + 30% GF19 polyaryl sulfone PASF

20 Polybutylene terephthalate PBT

21 Polybutylene terephthalate reinforced PBT+30%GF22 polycarbonate (bulletproof adhesive) PC

23 Polycarbonate Reinforced PC+30%GF

25 PEEK

26 PEK

27 PEKK

28 Polyethersulfone PES

29 Polyethylene terephthalate PET

30 (Polyester (really cool)) PET+30%GF31 phenolic plastic (bakelite powder) PF

32 Polyimide Pi

33 Polymethacrylate (Acrylic) PMMA34 Polyoxymethylene Copolymer (Saigang) Copolymer POM

35 Polyoxymethylene Copolymer Reinforced Copolymer POM + 25% GF36 Polyoxymethylene Homopolymer Homopolymer POM

37 Polypropylene (100 fold rubber) pp 1

38 Polypropylene reinforced PP+30%GF

39 Polyphenylene ether PPO

40 Polyphenylene Sulfide Reinforced PPS+40%GF <41 Polystyrene (Hard) PS

42 Polysulfone PSF

43 Polyurethane PU

44 Flexible PVC SPVC

45 UHMWPE 2 3

There is a detailed record in the folder [Molding Conditions Table], which was provided by Intertek in April last year.

If not, you can ask the ** merchant to get it!

The shrinkage rate generally refers to the difference between the size of the mold cavity at room temperature (22) and the size of the product after 24 hours of molding. Taking HDPE bottles as an example, 80% to 90% of the shrinkage rate occurs within 24 hours after molding.

Influence blow molding. There are many factors for the shrinkage rate of products, and the product shrinkage rate of crystalline plastics is greater than that of amorphous plastics; For crystalline plastics (e.g., PE), shrinkage increases with part wall thickness because a smaller cooling rate leads to more ordered crystal growth; Although increasing the melt temperature of the parison will not obviously affect the external size of the product, it will cause more shrinkage to appear in the wall thickness, because the higher melt temperature can reduce the strain recovery and blowing stress. Blow flatulence.

Higher or lower mold temperature can reduce the shrinkage rate of the hood; The added filler will also affect the shrinkage rate of the product; Blow.

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