Difference between Blow Molding and Injection Molding

The products made by blow molding and injection molding process can be seen everywhere in our life. The common blow molding products are?beverage bottles, laundry detergent bottles, etc., and the common injection molding products include?plastic stools, stroller accessories, etc.

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What is injection molding?

The so-called injection molding heats the plastic to a certain temperature and melts it into a liquid nature. It?injects the molten liquid into the closed mold cavity with high pressure, cools and sets the mold, and then opens it?to get the desired injection product by ejecting.

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Injection molding is mainly divided into six?stages, which are:

1.?Mold closing

2.?Injection

3.?Pressure-holding

4.?Cooling

5.?Opening the mold

6.?Product removal

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Injection molding machine

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The injection?molding machine can be divided into two kinds of devices: mold closing device and injection device respectively.

1.?A mold?closing device is mainly used?to realize mold opening and closing and ejecting products.

2.?An injection?device is used?to melt the?resin material and then inject it into the mold.

3.?The mold injects the resin material into the model to get the product.

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Molded products

The molded product is composed of the main flow channel used for the molten resin to enter. It serves as the manifold to guide the molten resin into the mold cavity,?and the product.

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Molding conditions

The injection molding conditions refer to the barrel temperature, injection speed,?and mold temperature of the molding machine.

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What is Blow Molding?

Blow molding is one of the important processing methods of plastics processing, which can be used to process hollow products such as films and bottles and barrels, etc. Here we focus on the blow molding hollow product process.

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Blow molding equipment is simple, and the barrels or bottles produced can be rounded or flattened. It is suitable for pe, pp, PVC, pc, pet, and other thermoplastics molding processes.

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The list of Blow molding equipment used for the process includes?extrusion blow molding equipment, hollow blow molding machine equipment, injection blow molding machine, etc.

The main process of the blow molding process

According to the different processes, blow molding can be divided into extrusion blow molding and injection blow molding.

The extrusion?blow molding process uses the?extruder to melt resin plasticization and extrusion tubular blanks, followed by the blanks placed in the blow molding mold. It then blows it?with compressed air expansion, cooling,?and shaping to get the same shape as the mold barrel or bottle.

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The process of injection blow molding is to inject the molten material into the mold to form a tubular billet. It then opens the mold to make the billet stay on the core mold while blowing compressed air to make the billet blow?into the shape of the mold cavity. Finally, the product is created by cooling off the mold.

The Extrusion blow molding is suitable for a variety of plastics?and can produce large products, mainly barrels.?

Injection blow molding creates products with uniform wall thickness, which?are?suitable for the production of large quantities, small fine products, mainly bottles.

Blow molding is the main method of making hollow products, and is another most commonly used method in the processing of plastic products in addition to extrusion, injection molding,?and molding. It?is developing rapidly and belongs to the range of secondary molding technology.

Firstly, thermoplastic resin is extruded or injected to obtain a semi-molten tubular blank. After that, it gets?heated to a soft state, and the blank is placed in various shapes of molds. Now,?compressed air is introduced into the blank immediately after the mold is closed so that the rubber-like blank closed in the mold cavity is inflated by the gas pressure, which makes it stick to the inner wall of the cavity to form hollow products.

Injection molding equipment is used to melt hot and thermosetting plastics, and then it applies?a certain pressure to fill the mold.

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A.?the advantages of the injection molding process

1.?The injection mold can be used to accurately control the wall thickness distribution of the billet, so that the wall thickness of the resulting container is more uniform, avoiding the thinning of the corner part of the general blow molding products. The weight of the product can be controlled at +0.1g?and the accuracy of the thread can be controlled in the range of 100μM. The mouth size is accurate, and the precision of the thin-necked product molding is high.

2.?The products obtained do not need to be processed for E times, and there is no seam, which saves the time of trimming the products.

3.?All the blanks made by the injection molding process can be blown into the blow molding mold, so there is no waste during the process, thus reducing?the waste of molding materials.

4.?Smooth surface products can be obtained, with no scratches, clear surface text and patterns;

5.?It can be economically produced in small quantities.

6.?Wide range of applications?for plastic varieties

7.?The high?degree of automation, multi-mode production, and high production efficiency.

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Disadvantages of the injection molding process

1.?Product molding uses?two sets of injection molding and blow molding molds and a hollow core mold with a valve. Injection molding molds should be able to withstand high pressure, which is why their?molding equipment costs are high.

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2.?The temperature of the injection mold is high, and it needs a long cooling time after blowing in the injection mold, which prolongs the whole molding cycle of the product and affects the production efficiency.

3.?Injection molding produces?internal stress, coupled with uneven cooling in the process of mold conversion. Owing to this, the production of complex shapes and sizes of products is?prone to stress cracking. It is?only suitable for the production of cosmetics, daily necessities, pharmaceutical packaging, food packaging and other areas of small products.

4.?The operator?requires high operating?skills to carry out the process.?

Advantages and Disadvantages of the blow molding process

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Advantages

●?Products can be created without seams

●?It offers high strength at the bottom, accurate size of the mouth, clear surface text and patterns.

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Technical advantages.

●?The wall thickness distribution of the billet can be precisely controlled by the injection mold, thus making the wall thickness of the resulting container more uniform and avoiding the thinning of the corner part of the general blow molding products.

●?The blanks made by injection can all enter the blow molding mold, reducing the waste of molding materials and saving the trimming time of the products.

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Disadvantages

●?Product molding must use two sets of injection and blow molding molds and a hollow core mold with felling, thus the?cost of the injection mold and core mold is?relatively high.

●?The temperature of the injection mold is high, and the high-temperature mold requires a long cooling time after blowing in the injection mold, which prolongs the whole molding cycle and reduces the production efficiency.

●?The higher internal stress of the injection molded blanks, coupled with the vulnerability to uneven cooling during mold conversion, increases the risk of stress cracking in polyolefin plastic blow molded containers.

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In general, the biggest difference between the injection molding process and the blow molding process?lies in their process, raw materials, and applications.

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Blow molding uses gas pressure to make the hot blanks, close?in the mold blowing into hollow products, or tube blanks without mold blowing into tube film.?Injection molding, on the other hand, melts the plastic material and then injects?it into the film cavity after molding.

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Speaking of raw materials, Blow molding uses raw materials like polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate, and polyacetal resin. Among these, polyethylene is the most used.

Injection molding uses raw materials like thermoplastic or thermosetting materials.

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Blow molding is widely used in bottles, jars, baby products, sporting goods,?and other industries.?Injection molding is widely used in cell phones, portable computers, many kinds of plastic housings, communications, micro motors, computers, electrical appliances, electronics, toys, clocks and watches, lighting, locomotives,?and other industries.