5 general plastic injection molding process details

Polypropylene (PP) injection mold processing technology

PP is a transparent, semi-crystalline thermosetting plastic with high toughness, good dielectric strength, low water absorption, high thermal deformation temperature, low relative density, and high grain size. Modified material fillers are generally glass fiber, mineral fillers, thermosetting vulcanized rubber, etc.

Not the same main use of PP its flowability varies greatly, the general application of PP flow rate is close to the middle of ABS and PC.

1. The solution of plastic

Pure PP is transparent color Hippopotamus white and can be dyed with various colors. the coloring of PP is only with masterbatch on the general plastic machine. On top of some equipment with separate melt components that enhance the efficacy of the blending rubber, you can also use pigments for coloring. For outdoor applications, UV thickeners and carbon black additives are generally applied. The application of recycled particles does not have to exceed 15% of the proportion, otherwise, it will cause a reduction in compressive strength and dissolution of color loss. PP injection mold processing before the general does not require a special dry solution.

2. Plastic machine

There is no special requirement for the adoption of plastic machines. Because PP has a high crystal shape. It is necessary to use the computerized plastic machine with high injection pressure and multi-stage operation. The clamping force is generally defined by 3800t/m2, and the injection volume is 20%-85%.

3. Mold shell and gate design scheme

The mold temperature is 50-90℃, and the high mold temperature is used for the high specification. The core temperature is 5℃ lower than the concave mold temperature, the runner diameter is 4-7mm, the length of the pin gate is 1-1.5mm, the diameter can be as small as 0.7mm, the length of the edge gate is as little as possible, about 0.7mm, the depth is half of the wall thickness, the total width is two times of the wall thickness, and the length of the melt flow in the core will be improved. The mold shell must have excellent exhaust pipe sex, discharge air hole deep 0.025mm-0.038mm, 1.5mm thick, to prevent the collection marks, it is necessary to use a large and round injection mouth and ring flow channel, the thin thickness of the tendon plate should be small (for example, it is 50-60% of the wall thickness). Homopolymer PP production and manufacturing goods, the thin thickness can not exceed 3 mm, or there will be vapor bubbles (thick-walled tube products only with copolymer PP).

4. Melting temperature

The melting point of PP is 160-175℃, and the dissolving temperature is 350℃, but the temperature setting should not exceed 275℃ during injection production and processing, and the melting section temperature is better at 240℃.

5. Injection rate

To reduce thermal stress and deformation, the injection rate should be selected, but some levels of PP and mold shells are not suitable (bubbles and air patterns). If the surface layer of the engraved pattern has a two-color pattern of light and dark junction line diffused from outside the gate, a lower injection speed and higher mold temperature should be used.

6. Melt glue condensation type

The molten glue condensation type can be used at 5 bar, and the condensation type of color granule material can be adjusted moderately higher.

7. Injection and pressure-holding

Choose a high injection working pressure (1500-1800bar) and holding pressure (about 80% of the injection working pressure). Turn pressure-holding at about 95% of the full stroke arrangement, and use a long pressure-holding time.

8. Post-treatment process of the product

To avoid the closing deformation caused by post-crystallization, the product must generally be solved by boiling water immersion.

High-pressure polyethylene (PE) injection molding process processing technology

PE is crystalline raw materials, water absorption is very small, not more than 0.01%, so in the production of processing before the dry solution, PE molecular structure of the chain of soft, small inter-bond interaction force, the low viscosity of the melt, good circulation, so the molding without too high working pressure can be formed out of thick-walled long step products. LDPE shrinkage rate is 1.22% or less, HDPE shrinkage rate is 1.5% or less. Therefore, it is very easy to deformation up and down, mold shell cooling standards on the shrinkage rate of the danger is very big, so should manipulate the temperature of the mold shell, maintain the cooling uniform, smooth.

PE crystallization workability is high, the temperature of the mold shell to the plastic crystal situation has a very great harm. Mold temperature is high, the melt cooling is slow, the plastic grain size is high, the compressive strength is also high.

PE's melting point is not high, but the specific heat is very large, so the melt must still consume more heat, so the provisions of the melting equipment to have a large heating output power, to facilitate the enhancement of productivity.

PE softening temperature range is small, and the melt is easy to air oxidation, so the forming production process should try to prevent the melt from touching with oxygen to prevent the reduction of plastic parts quality.

PE products are too soft and easy to get out of the mold, so when the plastic parts have shallow side grooves can be super strong out of the mold.

PE melt non-Newtonian is not significant, the change in shear rate is less harmful to the viscosity, PE melt viscosity by the temperature is also less harmful.

The cooling rate of PE melt is slow, so it must be sufficient cooling. The mold should have a good cooling system.

If the PE melt in the injection of the choice of the immediate inlet into the material, should expand the ground stress and cause the collection of disproportionate and specificity significantly expand deformation, and therefore should pay attention to the selection of the main parameters of the inlet.

PE forming temperature is wide, in the case of liquidity, a small amount of temperature fluctuations on the injection molding process is not harmful.

PE's heat resistance is good, generally below 300 degrees without significant dissolution conditions, there is no harm to the quality.

PE key molding standards

Barrel temperature: The barrel temperature is mainly related to the relative density of PE and the size of the melt flow rate, in addition to the type and characteristics of the plastic machine and the appearance of the first-level plastic parts. Because PE is a crystalline polymer, the crystal should absorb certain heat when melting, so the barrel temperature should be 10 degrees higher than its melting point. For LDPE, the barrel temperature is manipulated at 140-200℃, and the barrel temperature of HDPE is manipulated at 220℃, with the backside of the barrel taking a very small value and the front side developing the highest value.

Mold temperature: mold temperature has a great danger to the crystallization situation of plastic parts, mold temperature is high, melt grain size is high, compressive strength is high, but shrinkage will also expand. General LDPE mold temperature is manipulated at 30℃-45℃, while HDPE temperature is relatively high at 10-20℃.

Injection processing working pressure: Enhancing the injection processing working pressure is beneficial to the wear-resistant material mold filling because the circulation of PE is very good, so in addition to thick-walled long and thin products, should be superbly selected lower injection working pressure, the general injection working pressure of 50-100MPa. look easy. After the wall is very large plastic parts, injection working pressure can be lower, the opposite is high.

Polyethylene (PVC) injection molding

Typical application areas:

Water supply pipe, home installation line, house panel wall, commercial equipment cover, electronic equipment packaging, medical machinery, food packaging material, etc.

Organic chemical and physical properties:

PVC material is an amorphous raw material, which is often used in specific applications with the addition of thickeners, lubricants, auxiliary processing agents, dyes, impact agents, and other preservatives, and has non-flammability, high toughness, weather resistance, and high geometrical reliability.

PVC is highly resistant to reducing agents, oxidizing agents, and strong alkalis. It is not known that it can be leached by concentrated air oxidizing acids such as sulfuric acid and concentrated sulfuric acid and is also not suitable for places where it touches aliphatic hydrocarbons and isopropyl titanate hydrocarbons.

The melting temperature of PVC is a key parameter in the production and processing of PVC, if this parameter is not good, it will cause the problem of dissolving the raw material. The flow characteristics of PVC are very poor, and the scope of its processing process is narrow.

Especially the large content of PVC material is more difficult to produce and process (such raw materials generally need to add lubricating fluid to improve the flow characteristics), so the general application of all small content of PVC material. The shrinkage rate of PVC is very low, generally 0.2~0.6%.

Injection mold processing process standards. 1:

1. dry solution: generally no dry solution. 2.

2. Melting temperature: 185~205℃ Molding temperature: 20~50℃.

3. Injection working pressure: can be as large as 1500bar. 4.

4. Holding pressure: up to 1000bar. 5.

5. Injection rate: To prevent the dissolution of raw materials, the injection rate should be very high.

6. runners and gates: all basic gates can be used. If small parts are produced and processed, it is better to apply needle-type gates or submerged gates; for thick parts, it is better to apply fan-type gates. The minimum diameter of the needle gate or submerged gate should be mm; the thickness of the fan gate should not be less than mm.

7. Organic chemical and physical properties: Rigidity PVC is one of the most commonly used plastic materials.

Polyethylene (PS) injection molding

Typical application areas:

Packaging design, household products (kitchenware, mop trays, etc.), electrical equipment (fully transparent utensils, light transmitters, insulating layers of plastic film, etc.).

Organic chemical and physical properties:

Most of the PS used in commercial services are fully transparent, atomic crystalline raw materials. PS has excellent geometric reliability, heat resistance, electro-optical pass-through properties, insulation properties, and its tendency to absorb moisture very slightly.

It is resistant to strong oxidizing agents of water and diluent, but can be leached by strong air oxidizing acids such as sulfuric acid and can be deformed in some solvents. The typical shrinkage rate is in the middle of 0.4~0.7%.

Injection mold processing process standard:

1. dry solution: unless the storage is not good, generally do not need to dry solution. If it is necessary to dry a manicure, the proposed dry manicure standard is 80℃, 2~3 hours. 2.

2. Melting temperature: 180~280℃. For flame retardant raw materials, the limit is 250℃.

3. Mold temperature: 40~50℃. 4.

4. Injection working pressure: 200~600bar. 4.

4. Injection rate: proposed application of rapid injection rate. 5.

5. Cross runners and gates: All basic types of gates can be applied.

ABS injection molding

Typical application areas:

Car (car dashboard, special tool hatch, wheel cover, mirror box, etc.), home refrigerator, large compressive strength special tools (hair drying equipment, mixing device, food cooking machine, lawn machine, etc.), telephone cover, printer computer keyboard, game and entertainment car such as golf cart and its jet type sled car, etc.

Organic chemical and physical properties:

ABS is produced from three organic chemical singles: acrylonitrile, butadiene, and butadiene. Each individual has different characteristics: acrylonitrile has high toughness, heat resistance, and organic chemical reliability; butadiene has firmness and impact resistance; butadiene has easy production processing, high smoothness, and high toughness. In terms of shape, ABS is a non-amorphous raw material.

The key to the properties of ABS is the ratio of the three individual phases and the molecular formula in both. This allows for a very large degree of coordination in the design of products and has resulted in the sale of thousands of different quality ABS materials on the market. The different qualities of the raw materials show different characteristics, such as from this to high impact resistance, from low to high smoothness and high distortion characteristics.

ABS materials have strong processability, formability, low-stress relaxation excellent specification reliability, and high impact and compression strength. Response to "ABS", click to view

Injection molding process standard:

1. Dryness solution: ABS material has water absorption, so it is required to carry out dryness solution before production processing. The proposed standard of dry manure is at least 2 hours at 80~90℃. The raw material temperature should be ensured to be lower than 0.1%. 2.

2. Melting temperature: 210~280℃; proposed temperature: 245℃.

Mold temperature: 25~70℃. (The temperature of the mold shell will harm the smoothness of plastic parts, and the lower temperature will cause the lower smoothness). 3.

3. injection working pressure: 500~1000bar. 4.

4. Injection rate: medium to high-speed operation.