What's the difference between blow molding and injection molding

1. Injection molding and blow molding process is different, blow molding is injection and blow; Injection molding is injection pressure; Blow molding must have the head left by the blow pipe, injection molding must have a gate section

2. Generally speaking, injection molding is solid core body, blow molding is empty core body, blow molding surface is not smooth. Blow molded with a blow port.

3. Injection molding, also known as thermoplastic injection molding, this method is to melt the plastic material and then inject it into the membrane cavity. Once the molten plastic is in the mold, it is cooled and molded into a certain shape according to the mold cavity. The resulting shape is often the final product and no further work is required before installation or use as the final product. Many details, such as bumps, ribs and threads, can be molded in one step. An injection molding machine has two basic components: an injection device for melting and feeding plastic into the mold, and a clamping device. The function of the summing device is to:

1) Make the mold close under the pressure of injection;

2) Take the product out The injection device melts the plastic before it is injected into the mold, and then controls the pressure and speed to inject the melt into the mold. Two designs of injection devices are currently in use: screw preplasticizer or two-stage device, and reciprocating screw. The screw preplasticizer uses a preplasticized screw (stage 1) to inject molten plastic into the feed rod (stage 2). The advantages of screw preplasticizers are constant melt mass, high pressure and high speed, and precise injection volume control (using mechanical thrust devices at both ends of the piston stroke).

These advantages are required for transparent, thin-walled products and high production rates. Disadvantages include uneven residence time (resulting in material degradation), higher equipment costs, and maintenance costs. The most commonly used reciprocating screw injection devices do not require a plunger to melt the plastic together

4. Blow molding: also known as hollow blow molding, a rapidly developing plastic processing method. Thermoplastic resin extrusion or injection molding of the tubular plastic billet, while hot (or heated to soften the state), placed in the split mold, closed immediately after the billet into the compressed air, the plastic billet blowing and close to the inner wall of the mold, after cooling stripping, that is, a variety of hollow products. Blow molding film manufacturing process in principle and hollow products blow molding is very similar, but it does not use a mold, from the perspective of plastic processing technology classification, blow molding film molding process is usually included in the extrusion.

The blow molding process began to be used to produce low density polyethylene vials during the Second World War. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology was widely used. The volume of hollow vessels can reach thousands of liters, and some production has been computerized. Suitable for blow molding plastic PE, PVC, PP, PET, HDPE, EVOH,PEGT etc., the resulting empty container is widely used as industrial packaging containers.

Development Information:

Blow molding will follow the market demand for its products in materials, machinery, auxiliary equipment, control systems, software and other aspects of the following development trend.

(1) Raw materials to meet the function and performance requirements of blow molded products (medicine, food packaging), blow molded grade raw materials will be more abundant, better processing performance. Such as PEN materials, not only high strength, good heat resistance, strong gas barrier, transparent, uv resistance, can be used for blowing all kinds of plastic bottles, and high filling temperature, good barrier performance of carbon dioxide gas, oxygen, and chemical resistance.

(2) Product packaging containers, industrial products will have a greater growth, and injection blow molding, multi-layer blow molding will have a rapid development.

(3) Precision and high efficiency of blow molding machinery and equipment; Assist in the automation of production equipment. Precise and efficient "not only refers to the mechanical equipment in the production of molding process with high speed and high pressure, and the production of products in terms of appearance size fluctuations and a heavy all can achieve higher stability, that is to say, the size and shape of each place production products high geometric accuracy, deformation and narrow, Product appearance and internal quality and production efficiency and other indicators to achieve a higher level. Auxiliary operations include flanging, cutting, weighing, drilling, leak detection, etc., and the process automation is one of the trends of development.

(4) The research of blow molding simulation blow molding mechanism is more in-depth. Reasonable construction of mathematical model of blow molding simulation and fast and accurate numerical algorithm are the key points of simulation. Blow molding simulation will play a more and more important role in product quality prediction and control.

Injection molding:

Generally speaking, there are three main aspects of the evaluation of the performance of plastic products:

First, appearance quality, including integrity, color, luster;

Second, accuracy between size and relative position, that is, dimensional accuracy and positional accuracy;

Third, and the corresponding use of mechanical properties, chemical properties, electrical properties, that is, functional

Therefore, if any of the above three aspects of the problem, it will lead to the production of defects and expansion.

Classification of common defects in injection molding products

Appearance defect: silver discoloration, weld mark

Process problems: flapping, shrinkage, lack of glue

Performance problems: warping, embrittlement