Thermoplastic injection molding is the process of melting a plastic material and then injecting it into the membrane cavity. Once the molten plastic enters the mold, it is shaped into a shape by the cold cavity. The resulting shape is often the final product and no further processing is required prior to installation or use as a final product. Many details, such as bosses, ribs, threads, can be formed in one injection molding operation.
Injection molding machines have two basic components: an injection device and a clamping device for melting and feeding plastic into the mold. The function of the mold device is: 1. The mold is closed while receiving the injection pressure; 2. The product is taken out of the injection device and melted before the plastic is injected into the mold, and then the pressure and speed are controlled to inject the melt into the mold. There are two types of injection devices currently in use: a screw pre-plasticizer or a two-stage device, and a reciprocating screw. The screw pre-plasticizer uses a pre-plasticized screw (first stage) to inject molten plastic into the injection rod (second stage).
The advantages of the screw pre-plasticizer 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 strengths 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 common reciprocating screw injection device does not require the plunger to melt and inject the plastic.
First, extrusion blow molding
Extrusion blow molding is a method of making hollow thermoplastic parts. Widely populated objects are bottles, barrels, cans, boxes and all containers for food, beverages, cosmetics, pharmaceuticals and daily necessities. Large blow molded containers are commonly used in the packaging of chemical products, lubricants and bulk materials. Other blow molded products include balls, bellows and toys. For the automotive industry, fuel tanks, car shock absorbers, seat backs, center brackets, and armrest and headrest covers are blow molded. For machinery and furniture manufacturing, blow molded parts have outer casings, door frames, frames, pots or boxes that have an open side.
polymer
The most common blown plastic extruded material is high density polyethylene, and most of the milk is usually made of this polymer. Other polyolefins are also often processed by blow molding. Depending on the application, styrenic polymers, polyvinyl chloride, polyester, polyurethane, polycarbonate and other thermoplastics can also be used for blow molding.
Recently, engineering plastics are widely accepted in the automotive industry. Material selection is based on mechanical strength, weatherability, electrical properties, optical properties, and other properties.
Process
3/4 of the blow molded articles are manufactured by extrusion blow molding. The extrusion process forces the material through a hole or die to make the product.
The extrusion blow molding process consists of 5 steps: 1. Plastic type embryo (extrusion of hollow plastic tube); 2. Close the flap mold on the parison, clamp the mold and cut the parison; 3. To the mold cavity Cold wall inflation type, adjust the opening and maintain a certain pressure during cooling, open the mold, write down the blown parts; 5. Trim the flash to get the finished product.
Extrusion
Polymer blending is defined as a process of increasing the grade of a polymer or polymer system by melt mixing. The compounding process ranges from the addition of a single additive to a variety of additive treatments, polymer alloys and reactive blending. It is estimated that one-third of the US polymer production will be mixed. The compounding can be tailored to the performance requirements of the final application. The compounded product has miscellaneous properties such as high gloss and excellent impact strength, or precision moldability and good stiffness.
The blended polymer is typically pelletized for further processing. However, there is an increasing interest in the industry to combine compounding with the next step, such as profile extrusion, which avoids heating the polymer again.
mixing
Various types of melt mixing equipment are used, from roll mills and batch mixers to single and twin screw extruders. Continuous compounding (extrusion) is the most common equipment because it provides consistent quality and reduces operating costs. There are two types of blending:
Distributed mixed material remarriage ingredients can be evenly distributed without the use of high shear stress. Such mixtures are known as extended or laminar mixing.
Dispersive mixing, also known as intensive mixing, in which high shear stress is applied to break up the solidified solids. For example, when the additive mass is broken, the actual particle size becomes smaller.
Compounding operations often require two types of mixing in one process.
Second, rotomolding
Rotational molding, also known as rotational molding, is a processing method for making hollow seamless products of various sizes and shapes. Traditionally, it has been mainly used in thermoplastic materials. In recent years, rotomolding of thermosetting materials such as cross-linked polyethylene has also developed rapidly. Since rotomolding does not require high injection pressures, higher shear rates or precise compound gauges. Therefore, the molding and the machine are relatively inexpensive, and the service life is also long. The main advantages are: the performance / price of the machine is relatively high; the molding of complex parts does not require post-assembly; multiple products and multiple colors can be molded at the same time; the cost of the mold is low; the color and material are easy to change;
The basic process is simple. The powdered or liquid polymer is placed in a mold, heated while rotating around two vertical axes, and then cooled. At the beginning of the heating phase, if a powdery material is used, the surface of the mold is formed into a porous layer and then gradually melted as the cycle progresses to form a uniform layer of uniform thickness. If a liquid material is used, it is first flowed and coated. The surface of the mold stops flowing completely when the gel point is reached. The mold is then transferred to the cooling station, cooled by forced air or water spray, and then placed in the work area where the mold is opened, the finished part is removed, and the next cycle is performed.
Third, casting
Cast nylon 6 has high strength, abrasion resistance, scratch resistance and resilience. Casting reactions are mostly carried out at atmospheric pressure or at very low pressures, so casting nylons have a distinct advantage over extruded or molded nylon. Compared with jade extruded nylon, cast nylon has higher crystallinity and molecular weight, better dimensional stability, easy machinability, higher modulus and heat distortion temperature.
Because the size and shape of the cast nylon is not limited, it has greater flexibility. Casting nylon with a simple shape can be produced with low-cost tools, and the production cycle is short; complex parts need to be produced in complex tools. Try not to use a high-priced casting machine in the social club. The lactam monomer undergoes an anionic polymerization in a mold and is finally converted into a polymer. Therefore, the reaction of the anhydrous acid catalyzed process is poor, and the conversion efficiency is low. Therefore, many kinds of catalytic reactions are selected to obtain better results. The catalyst has been developed since the 1950s, and the development of more efficient production machinery in the late 1960s accelerated the commercialization of cast nylon.
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