plastic mould, injection mould

Plastic molding and the main processing methods

 Plastic molding process is a construction technology, involving the contents of the plastic into the various processes of plastic products. Central Standing Committee in the process of change one or more of the following circumstances occur, such as polymer rheology and the physical and chemical properties change. Many methods of plastic molding

Plastic molding method

Pressing: Compression molded laminated low-pressure molding cold molding transfer molding casting centrifugal casting embedded static casting spin casting plastic rotational casting slush cast sculpture

Extrusion molding hand lay

Extrusion molding fiber pull-winding

Exhaust injection molding of mobile non-runner injection molding injection molding injection molding thermoset reaction injection molding injection molding calendering

Blow Molding Injection Blow Molding Extrusion Blow Molding Stretch Blow film coating melt stream of spray deposited by flame spraying, plasma spraying electrostatic spraying 

Physical foaming foaming foaming molding machine foam molding Thermoforming second solid phase forming biaxial tensile 

    1. Compression molding. Also known as compression molding molding is molding with pressure in the closed mold cavity (generally yet to heating) of the molding method. Typically, compression molding applied to thermosetting plastics, such as phenolic, amino plastic, unsaturated polyester plastics. 

Compression molded by the pre-press, preheating and molding the composition of three processes: 

Preloading to improve product quality and increase efficiency, molding, molding the powder or fibrous pre-pressure to shape the operation. 

Preheat molding processing to improve performance and shorten the molding cycle, the molding compound before the first heat in the molding operation. 

Molded in the mold to add the required amount of plastic, closed mold, exhaust, temperature and pressure in the molding to maintain a period of time, then stripping clean mold operation.

Compression molding press with the main equipment, and modeling. Press with the most is self-contained hydraulic machine, tonnage from several tons to several hundred tonnes. Are under pressure type press and the pressure type press. The mold for compression molding as to suppress mold is divided into three categories; flash-type mold, semi-flash-type mold is not overflow-type mold. 

The main advantages of compression molding can be molded products and a larger plane to mass production, the drawback is long production cycle and low efficiency. 

    2. Laminate molding. With or without adhesive, by heat, pressure to the same or a different combination of two or more layers of materials for the holistic approach.

Laminating machines commonly used laminate molding operation, the dynamic of this press fitted between the plate and fixed plate may be floating multi-layer hot plate. 

Laminated reinforced material forming a common cotton cloth, glass cloth, paper, stone and cotton cloth, phenolic resin, epoxy, unsaturated polyester and certain thermoplastic resins. 

    3. Cold molding. Cold molding is also called cold sintering, and the general compression molding of the difference is in the room temperature compression molding of materials. After stripping the molded product can be re-heating or using chemical reaction to cure. The method is mainly used PTFE molding, also used in some high-temperature plastic (such as polyimide, etc.). General process for the system blank - sintering - the cooling of three steps. 

    4. Transfer molding. Thermoset transfer molding is a molding method, molding plastic mold when the first heat in the heating chamber to soften, and then pressed into the cavity had been heated Curing. Transfer molding equipment according to different types of forms are: (1) live plate; (2) tank; (3) plunger.

Transfer molding of plastic demand is: does not meet the pre-curing temperature, plastic should have greater mobility, to curing temperature, it should have a faster cure rate. Meet this requirement are phenolic, melamine formaldehyde and epoxy resins.

Transfer molding has the following advantages: (1) edge less waste products, can reduce the amount of post processing; (2)can with a fine or brittle molded insert and perforated products, and can maintain the insert and the correct hole location; (3) product performance uniform, accurate size, high quality; (4) wear a smaller mold. Drawback is: (5) mold manufacturing costs higher than the compression mold; (6) plastic deplete; (7) fiber reinforced plastics produced by fiber orientation and anisotropy; (8) around the plastic around the inserts, sometimes due to fusion products by not strong Er Shi the intensity decreases. 

    5. Low pressure molding. Using the molding pressure equal to or less than 1.4 MPa pressure or laminated touch method.

Low pressure molding method for the manufacture of reinforced plastic products. Reinforced materials such as glass fiber, textiles, asbestos, paper, carbon fiber. Most commonly used are thermosetting resins, such as phenolic, epoxy, amino, unsaturated polyester, silicone and other resins.

Low pressure molding, including bags, spray method. 

(1) bag molding. With flexible bag (or other flexible diaphragm) received fluid pressure and elastic modulus Er Shi bags between rigid reinforced plastic between the uniform compression and a workpiece, a method. Fluid pressure caused by different methods, generally can be divided into bags of molding pressure, vacuum bag molding and autoclave molding hot.

(2) injection molding. Reinforced plastic molded products, the use of spray gun to short fiber and resin spray while laminated mold and curing methods for the products. 

    6. Extrusion. Extrusion molding or extrusion, also known as extrusion, it is the extruder by heating, pressure Ershi material to flow through the port state continuous casting method. 

Extrusion method is mainly used for molding thermoplastics, thermosetting plastics can also be used for some. Extrusion products are continuous profiles, such as tubes, rods, wire, sheet, film, wire and cable coating layer. In addition, the mixture can be used for plastics, plastics granulation, color, blending and so on.

Extruder from the extrusion device, transmission, and heating and cooling systems and other major components. Extruder with screw-type (single screw and multiple screw) and plunger types. The former is a continuous extrusion process, which is intermittent.

Single screw extruder, including the basic structure of the main transmission device, feeding device, cylinder, screw, die and die and some other.

Auxiliary equipment extruder before the material handling equipment (such as material handling and drying), extrusion material handling equipment (shape, cooling, traction, or roll material cut paper) and the production condition control equipment three categories.

    7. Crowded drawing forming. Crowded drawing forming a thermoset fiber reinforced plastic molding methods. Fixed for the production cross section shape, length, unlimited profiles. Molding process is a continuous fiber impregnated with resin glue pulled out by the heating mode, and then through the heating chamber, further solidifying the resin prepared with a one-way continuous high strength reinforced plastic profiles. 

Commonly used in extrusion molding of the resin pull unsaturated polyester, epoxy and silicone are three. Unsaturated polyester resin used most. 

Squeeze pulling machine is usually arranged by the fiber device, resin tank, pre-forming device, die, and heating devices, traction devices and cutting equipment and other components. 

    8. Injection molding. Injection molding (injection) is to make the first thermoplastic or thermosetting molding plastics in uniformly heated barrel, then pushing the plunger or screw to move the die cavity in closed molding methods. 

Injection molding is suitable for almost all thermoplastics. In recent years, injection molding is also successfully used in forming some of the thermosetting plastic. Injection molding cycle is short (seconds to minutes), the quality of molding products can be several tens of grams to kilograms, can form a complex shape, size precision, with a metal or non-metallic insert molded products. Therefore, the method has strong adaptability and high productivity. 

Injection Molding injection machine into plunger injection machine and injection machine screw two major categories, from the injection system, clamping system and the mold has three major components; the molding methods can be divided into: 

(1) exhaust injection molding. Exhaust vent type injection molding applications, injection machine, the barrel with the central exhaust port, connected with the vacuum system, when the plastics plastic, plastic vacuum pump can be combined and some water vapor, single, volatile material and air by the exhaust suck out; materials without pre-drying, thereby increasing productivity, improving product quality. Particularly suitable for polycarbonate, nylon, glass, cellulose materials such as molding moisture easily. 

(2) injection molding. Injection molding can be used ordinary mobile screw injection machine. Plastics and plastic that is constantly squeeze through a certain temperature, the mold cavity, the cavity filled with plastic, the screw stops turning, through the thrust screw to mold material under pressure to maintain an appropriate time, then cooling setting. Flow injection molding have overcome restrictions on the production of large products, equipment, part quality can exceed the maximum injection volume of injection machine. It features an object is not stored in plasticizing the barrel, but continued to squeeze into the mold, so it is the combination of extrusion and injection method.

(3) of injection molding. Coinjection molding is used with two or more injection units of the injection machine, different species or different color of plastic, simultaneously or successively injected into the mold method. This method can produce a variety of colors and (or) a variety of plastic composite products, representative of a total of two-color injection molding is the injection and multi-color injection.

(4) No runner injection molding. Mold does not set the shunt, but by the injection machine nozzle extension points directly to the molten material to each mold cavity injection molding method. In the injection process, the flow of plastic to maintain melt flow within the state, the ejection time and the products together emerge, so there is no flow workpiece residue. This molding method not only saves raw materials, lower costs, and reduce the process to achieve fully automatic production.

(5) reaction injection molding. Reaction injection molding materials will reflect the principle is measured by the measuring device after the pump into the mixing head, mixed in the mixing head in the collision, and then injected into the closed mold high speed, the fast curing, stripping, removal products. It is suitable for processing polyurethane, epoxy and unsaturated polyester resins, silicone resins, alkyd resins such as some of thermosetting plastics and elastomers. Now mainly used in polyurethane processing. 

(6) thermosetting plastic injection molding. Granular or agglomerate thermosetting plastics, in the strict control of temperature of the barrel, the role of the screw, stick plastics into plastic state, in the high injection pressure, the materials into the mold within a certain temperature range, crosslinking. Thermosetting plastic injection molding except for changes in physical state, there are chemical changes. Therefore, compared with thermoplastic injection molding, molding equipment and processing technology in the existence of significant differences. The following table compares the thermoset and thermoplastic injection molding difference.

Thermosetting and thermoplastic injection molding conditions for comparison

Thermoset thermoplastic processing conditions

Barrel temperature, low temperature, plastics, barrel temperature below 95 , temperature control, demanding high temperature plastics, barrel temperature above 150 , temperature control is not strict

In the barrel in a short time longer

Barrel heating mode liquid medium (water, oil) heating

Mold temperature of 150 1 200 100 the following

Injection pressure 100-200MPa 35-140MPa 

Injection volume of injection was smaller, front barrel more than a small injection of large amount of material, front barrel more than expected

Thermosetting plastic injection molding is the most widely used Bakelite. 

    9. Blow molding. Closed by gas pressure in the heat in the mold of parison inflation become hollow products, or possession of non-parison into a tubular film die Inflation a way. The method is mainly used for a variety of packaging containers and the manufacture of tubular membrane. Where melt index of 0.04 to 1.12 is rather good Blow Molding materials such as polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyesters, polycarbonates, polyamides, cellulose acetate and poly acetal resin, of which polyethylene applications most.

(1) injection blow molding. Department of Law with the first plastic injection molding parison with bottom, then move the parison then blow blow mold made of hollow products. 

(2) extrusion blow molding. Line with the extrusion parison with bottom plastic first, then move the parison then blow blow mold made of hollow products. 

Injection blow molding and extrusion blow molding of the difference is that different methods of manufacturing blanks, blow molding process is basically the same. 

In addition to injection blow molding machines and extrusion equipment, machines, the main blow molding mold. Blow mold usually 2 synthesis, which has coolant channels, a small hole into the surface type of pressurized gas blowpipe. 

(3) stretch blow molding. Biaxial oriented stretch blow molding is a stretch blow molding, which is also first-type longitudinal stretching, and then blown with compressed air to transverse tensile expansion. Stretch blow molding products can transparency, impact strength, surface hardness and rigidity is greatly improved for polypropylene, polyethylene terephthalate (PETP) of the blow molding.

Stretch blow molding include: injection stretch blow molding parison orientation, extrusion stretch blow molding parison directional, multi-directional stretch blow molding, compression molding and other directional stretch blow molding.

(4) blown film method. A method of forming thermoplastic films. Line with the extrusion of plastic extruded tube first, and then blown through the air to the tube so that a continuous expansion to a certain size tubular membrane, cool, double layer winding folded flat film.

Manufacture of plastic film can be used many ways, such as blow molding, extrusion, casting, rolling, casting and so on, but blowing the most widely used method.

This method is suitable for polyethylene, polyvinyl chloride, polyamide films such as manufacturing.

    10. Casting. Without pressure or under slight pressure, the liquid monomer, resin or their mixture into the mold and make it a method of solid-state products. Casting method into a static casting, inlay casting, centrifugal casting, slush, rotational molded plastic, rotational molding and casting plastic and so on tape. 

(1) static casting. Static casting is the casting forming the more simple and more extensive use of two methods. This method commonly used in liquid monomer, part of the polymerization or condensation of the slurry material, polymer and monomer solution, blended with additives (such as initiator, curing agent, promoting etc), or thermoplastic resin melt into the mold cast cavity shape.

(2) embedded cast. Insert molding casting, also known as enclosure is to the samples, spare parts and other entrapment to the middle of a plastic molding technology. Embedded object will be placed in the mold, into the monomer, prepolymer or polymer such as liquid, and then to polymerization or curing (or hardening), ejection. This technique has been widely used in electronic industry. Plastic molding process for these species have gills formaldehyde, unsaturated polyester, acrylic and epoxy resins.

(3) centrifugal casting. Centrifugal casting is the use of centrifugal force, forming tubular or hollow tubular products approach. Through the extruder hopper or dedicated to quantitative liquid resin or resin dispersion into the rotation and heating of the container (ie, mold), by its rapid rotation around the axis (tens of per minute to 2000 rpm), then put Jibei centrifugal force into the material distributed in the mold area near the wall. In the rotation, while the material into the curing occurs, and then as needed through the cooling or post-processing that is able to obtain products. When the molding reinforced plastic products can also added to enhance the filling of.

Centrifugal casting melt viscosity are usually smaller, better thermal stability of thermoplastics such as polyamide, polyethylene, etc..

(4) slush. Slush is a method of molding hollow articles. When the plastic molding paste down and start the hollow mold until the required capacity. Mold in the loading should be carried out before or after the heat loading in order to make the material into a gel in the mold wall. When the gel when the intended thickness, pour excess liquid materials, and re-heated to make it melt, after cooling can be stripped out of products from the mold. Slush is mainly used in PVC plastic.

(5) spin-cast plastic. The law is the liquid material into a closed mold in which it at a lower speed (several to tens of change per minute) around a single or multi-axis spin, so that materials that can be distributed by gravity and the inner wall of the mold on, and then cured by heating or cooling or hardening up, you can get products from the mold. Around the axis of rotation for the production of cylinder-shaped product, or by vibration around the axis movement is used to produce closed products.

(6) rotational (rotational molding). A similar spin casting plastic molding methods, and different is its use of the materials are not liquid, but sintering of powder materials. The process is the powder into the mold and make it around the two vertical axis rotation, heat and even melt in the mold wall on bedrock, and then after cooling can be obtained from the mold hollow articles.

Rotational use of a polyethylene, modified polystyrene, polyamide, polycarbonate and cellulose plastics.

(7) cast sculpture. Preparation of thin film methods. Manufacturing, the first dispersion liquid resin or resin is dispersed in the running of the carrier (usually metal band), the subsequent use of appropriate methods to cure (or harden), and finally stripping can be obtained from the carrier film.

Casting for the production of plastic film are: the three cellulose acetate, polyvinyl alcohol, vinyl chloride and vinyl acetate copolymers, etc., in addition to some of the engineering plastics such as polycarbonate, etc. can also be used to produce cast film.

11. Hand lay-up. Hand lay-hand wall paper, also known as forming, molding, manufacturing reinforced plastic products is one way. In this method, the mold release agent coating on the reinforcing material laid by hand while brushing aside until the resin until the desired thickness, and then obtained by curing and stripping products. Hand lay in the synthetic resin is mainly used in epoxy resins and unsaturated polyester resin. Reinforcement with glass cloth, rovings Plaid, glass blankets.

    12. Filament Winding. Scheduled in control of tension and linear conditions in order to dip a resin glue to the core of continuous filament winding up mold or mold forming reinforced plastic products. This method is only suitable for manufacturing such a cylindrical and spherical rotating body. Commonly used resin is phenolic resin, epoxy resin, unsaturated polyester resin. Glass fiber reinforced materials commonly used winding, it has two: a twist fiber and untwisted fiber.

    13. Rolling. Will be through a series of heated thermoplastic roller, but its role in the compression and extension under the link to become a film or sheet molding method. Ting-pressure product film, sheet, leather and other coated products. Calendering the main raw material used is PVC, cellulose, modified polystyrene.

Rolling equipment, including rolling machine and other auxiliary equipment. Calendar roll is usually the number and arrangement of classification. According to the number of different roller, rolling machine with double rollers, three rollers, four rollers, five rolls, and even six-roll, with three or four roll calendar roll used most.

    14. Coating. For anti-corrosion, insulation, decoration and other purposes, in liquid or powder form in the fabric, paper, metal foil or board surface on the coated plastic thin (for example .0.3 mm or less) of the method.

The most common plastic coating method is generally thermoplastic, such as polyethylene, polyvinyl chloride, polyamide, polyvinyl alcohol, PCTFE, etc..

Hot melt coating process has deposited, fluid spraying, flame spraying, electrostatic spraying and plasma spraying.

(1) hot melt deposition. After the plastic powder with compressed air spray gun, spray off the surface to warm, plastic melting, cooling form a covering layer.

(2) fluid spray. Preheat the workpiece immersed in a container suspended in a resin powder resin powder melt and adhere to the surface.

(3) flame spraying. The fluidized resin through the mouth of the cone-shaped flame spray gun to make it melt and to achieve a method of spraying.

(4) electrostatic spraying. Electrostatic field caused by high voltage static electricity, that is a positive level ground parts, plastic powder emitted when a negative charge, the electrostatic spray plastic to the workpiece.

(5) plasma spraying. Plasma spray gun used to flow through areas such as ions of inert gas (such as argon, nitrogen, helium gas mixture) into a high-speed 5500 ~ 6300 high energy plasma flow, volume, high-speed spray resin powder lead to surface melting Results into the coating.

    15. Foam molding. Plastic foam molding is to produce porous structure of the process. Almost all of thermosetting and thermoplastic plastics can be made of foam, commonly used resin is polystyrene, polyurethane, polyvinyl chloride, polyethylene, urea formaldehyde, phenol and so on.

In accordance with the foam cell structure can be divided into two categories, if the majority of pores connected to each other, then known as the hole foam; if the majority of stomata are separated from each other, then known as closed-cell foam. Opening or closed cell foam structure is determined by the manufacturing method.

(1) chemical foam. Specifically added by the chemical foaming agent, thermal decomposition or chemical reaction between components of raw materials caused by the gas, so full of foam plastic melt. Chemical blowing agent released in the heating gas are carbon dioxide, nitrogen, ammonia and so on. Chemical foam used in the production of polyurethane foam.

(2) physical foaming. Physical foaming plastics dissolve in the gas or liquid, and then to expand or gasification foaming method. Physical foaming plastic varieties more suitable.

(3) Mechanical foam. By mechanical stirring method to gas mixed with the liquid mixture, then shape the process through the formation of foam in the foam. This method is commonly used in the urea-formaldehyde resin sleep, others such as polyvinyl formal, poly vinyl acetate, polyvinyl chloride sol, also apply.

    16. Secondary molding. Secondary molding is one of the methods of plastic molding. Parison of plastic material or as raw materials to make it through the heating and the external force into the shape of the products required for a method.

(1) hot molding. Thermoforming thermoplastic sheet is heated to soften, the gas pressure, liquid pressure or mechanical pressure, the use of appropriate molds or fixtures and products to become a molding method. Plastic thermoforming many ways, and can be divided into:

Molding using single-mode (mode or yin yang mode) or mode, using external mechanical pressure or weight, will be a variety of products made from sheet molding method, which is different from a process of compression molding. This law applies to all thermoplastics.

Differential pressure molding using single-mode (mode or yin yang mode) or to die, you can not die, under the effect of differential pressure in the gas, so that heat to the soft plastic sheet close to mold surface, made of a variety of products, after cooling The molding method. Pressure forming can be divided into vacuum forming and pressure forming.

Especially suitable for hot forming thin wall, the manufacture of large surface area. Varieties of common types of polystyrene plastics, glass, PVC, ABS, polyethylene, polypropylene, polyamide, polycarbonate and polyethylene terephthalate, etc..

Thermoforming equipment, including clamping system, heating system, vacuum and compressed air systems and forming tooling.

(2) biaxial tension. To thermoplastic film or sheet such as molecular reorientation, especially above the glass transition temperature of the process of two-way stretch. Tensile direction in the polymer glass transition temperature and melting point between, after orientation stretch and quickly cooled to room temperature after the film or the single wire, the tensile direction on the mechanical performance has greatly improved. 

For the polymer stretching direction are: PVC, polyethylene terephthalate, polyvinylidene chloride, polymethylmethacrylate, polyethylene, polypropylene, polystyrene, and some styrene.

(3) solid phase forming. Solid phase formation is a thermoplastic material or blank in the mold under pressure to use the method of forming the products. Melting in the plastic molding process (as softening) temperature of the following (at least below the melting point of 10-20 ). Are solid phase forming. One class of non-crystalline plastic in the glass transition temperature above the melting point below the processing of high-elastic region often referred to as hot forming, the glass transition temperature in the following processing is known as cold forming or molding at room temperature, often referred to as plastic cold plastic processing method or at room temperature. 

The method has the following advantages: short production cycle; improve the toughness and strength of products; equipment is simple, can produce large and very large products; cost reduction. Disadvantage: difficult to produce complex shapes, precision products; production process difficult to control, products, deformation, cracking. 

Solid phase forming, including: sheet rolling, deep drawing or sheet punching, hydraulic molding, extrusion, cold stamping, roll forming and so on.

    17. Secondary processing. After molding of plastic products, or profiles, according to the need for re-processing, such as mechanical processing, connection, modification, etc.. The following table lists the methods of secondary processing of plastics.

Plastics secondary processing methods

Classification processing method

Machining sawing, shearing, punching, car, plane, scraping, milling, drilling, grinding, polishing, sand blasting, kneading dough, thread processing

Laser processing finding, drilling, carving, etc.

Connect hot air welding, heating tools, lasers, rotating friction, vibration, friction, high-frequency, ultrasonic, induction, etc. 

    Bonding solvent, solution, melt, etc.

    Machine screw, spring, spring bolt, rivet, hinges, etc.

Decorative paint surface coating, solvent brightening, coating, printing, painting, hot stamping, vacuum coating, plating, electroplating, etc.

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