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 form is often the final product and no additional processing is required prior to installation or use as the final product. Many details, such as protrusions, ribs, and 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 die device is:
1. The mold is closed while receiving the injection pressure;
2. Remove the product from the injection device and melt it before it is injected into the mold, then control the pressure and speed 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 shot bar (second stage).
The advantages of the screw pre-plasticizer are constant melt mass, high pressure and high speed, and precise injection volume control (two mechanical thrusters with piston stroke). These advantages are required for transparent, thin walled articles and high production rates. Disadvantages include uneven residence time (resulting in material degradation), high equipment availability and maintenance.
The most common reciprocating screw injection device does not require the plunger to melt and inject the plastic.
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.
The most common blown plastic extruded material for polymers is high density polyethylene, and most of the milk is usually made from 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.
Extruded polymer blending is defined as a process that progressively grades 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. Blends can be tailored to the performance requirements of the ultimate 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, the industry is increasingly interested in combining compounding with the next step, such as profile extrusion, which avoids heating the polymer again.
Mixers use various types of melt mixing equipment, from roll mills and batch mixers to single and twin screw extruders. Continuous compounding (extrusion) is the most common equipment, because it provides a consistent quality product and reduces maneuverability. 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 destroy the cohesive 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.
Rotational molding, also known as rotational molding, is a process for the manufacture of 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. Its 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 easily changed; the loss of scrap is small.
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 moved and coated. The surface of the mold, when it reaches the gel point, completely stops moving. The mold is then transferred to the cooling zone, 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.
Cast nylon 6 has high strength, abrasion resistance, scratch resistance and resilience. Casting reactions are mostly carried out at atmospheric pressure or very low pressure, so cast nylon produced has a very significant advantage over extruded or molded nylon. Compared with nylon extrusion, cast nylon has higher crystallinity and molecular weight, better dimensional stability, easy machinability, higher modulus and heat distortion temperature.
Since the size and shape of the cast nylon are not limited, it has greater flexibility. Low-cost tools can be used to produce cast nylon with a simple shape, 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. Since the 1950s, catalysts have been developed. In the late 1960s, more efficient production machinery was developed to accelerate the trade of cast nylon.
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