Properties of molded products

Molded products have excellent electrical properties (especially anti-leakage properties), mechanical properties, heat resistance, fire resistance, chemical corrosion resistance and dimensional stability, and can be adjusted according to the needs of each component type and dosage to obtain products with special performance requirements. The main performance is as follows：

1.Electrical property

Molded plastics are widely used in high voltage electrical applications due to their arc resistance, acer performance, flame resistance, dimensional stability, moulding and low cost. The ability of arc suppression is mainly due to the presence of inert inorganic fillers such as hydrated alumina, silica and ceramic. Add a small amount of polyethylene powder (5% by weight) and use nylon fiber to improve arc resistance. In order to obtain better arc resistance, the resin and glass fiber content should be reduced to the minimum, however, such results reduce the mechanical properties.

2. Mechanical property

The mechanical properties of molding materials vary with the types and proportions of reinforced fibers and resin substrates used. In DMC, when the fiber length exceeds 6.35mm, the modification of product properties is very small.

Most SMC products are made from short-cut felt, and there is no published data on the effect of fiber length changes. Although the length of the general fiber is 50mm, this length is not necessarily suitable for all applications.

Increasing the content of reinforcing materials can improve the mechanical properties, but too much fiber content will bring inconvenience to molding. For example, when the fiber content in DMC exceeds 20%, it has little influence on its mechanical properties.

3. Heat resistance or fire resistance

Heat resistance refers to the ability of products to withstand thermal decomposition for long periods of time below the flammable temperature. "Short-term thermal strength" or "thermal strength" is related to the thermal deformation temperature of the resin. Although some fillers can improve the heat resistance of products, the heat resistance and thermal strength mainly depend on the properties of the resin. Flammability is a measure of apparent combustion, divided into "non-ignition", "self-extinguishing" and "flame-retardant" according to the ability and speed with which a material is able to extinguish easily or when the ignition source is removed. Polyester resins achieve flame resistance by adding halogen and phosphorous compounds and by using alumina hydrate as the main filler in the components.

Phenolic resins are inherently fire-resistant. Halogen compounds and phosphorous compounds, as well as HET anhydride used as hardener, can make epoxy resins flame resistant.

4.Dimensional stability

General molding materials have good dimensional stability, water absorption rate: small, thermal expansion coefficient and aluminum is very similar, when continuous exposure to high temperature, size is almost no change.

5. Corrosion resistance

The chemical resistance or corrosion resistance of molding material mainly depends on the selected resin matrix. The suitable resin and filler can be used to prepare the moulded material which can meet the requirement of resisting special bristle dew

DMC can be made of acid-resistant and alkali-resistant ligulates and acid-resistant epoxy resins. The choice of a resin for SMC is currently limited because the resin must also have a chemical structure that thickens easily. In common fillers, clay and silica have better corrosion resistance and other properties.

6.Contractility

 The shrinkage of moulded material is very low after release, the typical maximum shrinkage rate is 0.004, and the shrinkage rate of many moulded materials is close to 0.001, which is mainly due to the small thermal shrinkage of glass fiber and inorganic filler. However, the combination of low-shrinkage, high-strength fibers with the resin systems commonly used for rapid curing and high thermal shrinkage results in greater stress on the resin matrix between the fibers. The collateral effects of this stress cause surface ripples, cracks, warping, and internal voids. These defects can be reduced by the use of organic fiber reinforced materials compatible with resin shrinkage or by the use of short or filamentous glass fibers.

 

 

 

 

 

Raw material for molding

The commonly used molding materials are mainly composed of resin matrix, reinforcing materials, fillers, pigments, etc., and according to the process and performance requirements, the resin matrix is also added with curing agent, thickener, internal release agent, solvent and other additives. Reinforcement material is the skeleton material of die pressing material, which mainly endows die pressing material with excellent mechanical properties and prevents the propagation of micro-cracks. The main varieties of reinforcement materials are various glass fiber felt, no twist roving, no twist coarse gauze, chopped fiber, ground fiber, glass yarn and fabric and other varieties of fiber. The main function of resin matrix in molding material is to bond the reinforcing material and filler together, which not only protects the reinforcing material, but also makes it uniform force under external load. Theoretically, most types of thermoplastic and thermosetting resins can be used as resin matrix materials. There are polyester resin, epoxy resin, amino resin and phenolic resin. A large number of various types of fillers are used in the molding material, the main function of which is to reduce the material cost, improve the process, improve the molding material some physical properties, appearance and give some characteristics. Fillers are mostly in powder form, such as clay, calcium carbonate, talcum powder and some fillers with special performance requirements.

 

The basic requirements of resin in molding are as follows: good infiltration performance of reinforcing materials and fillers to improve the bonding strength between resin and glass fiber; Resin to have the appropriate: viscosity, good fluidity, so that in the molding process of resin and glass fiber at the same time full of all corners of the cavity, to obtain a balanced strength of the molding products; Resin curing temperature is low, less volatile in the curing process, good technology (such as viscosity easy to adjust, good solubility with various solvents, easy to release mold, etc.), and can meet the mold products specific performance requirements. In addition, from the point of view of application or other point of view, the resin should also meet some other special performance requirements, such as corrosion resistance, heat resistance and so on. From the perspective of production efficiency, fast curing speed of resin is required, but for some large products with complex structure and higher requirements, the curing speed should be properly controlled. Resin curing after high mechanical strength, good toughness, avoid from the mold when taken out, in the case of bending cracking or breaking. Therefore, the selection of resin, will become a very important factor affecting the whole process.

 

Molding products are commonly used in thermosetting resin, thermoplastic resin in the molding process of the application of less. The main thermosetting resins are phenolic resin, epoxy resin, epoxy phenolic resin, polyvinyl butanal resin, unsaturated polyester resin, etc.

 

 

 

 

 

The molding process of the press automatic Moulding Machine

Is moulded plastic processing and molding the application in the city one of the oldest technology. It has a mature production technology, equipment and mold is simple, easy to forming large products, can use multiple modes to improve the production of small parts, etc, in machinery, electronics, transportation and daily life, and many other fields has been widely used.

 The market will often see a lot of kinds of Press Moulding Machine, for example: Polymer/PTFE Push press Automatic Moulding Machine, Polymer/PTFE Flange press Automatic Moulding Machine, Polymer/PTFE gasket automatic Moulding Machine, Semi-automatic Molding Machine and so on.

 Molding is widely used in the following fields:

Electrical: insulator, switch box, electrical equipment housing, insulation tools, wiring board, etc.

Automobile: lamp shade, front and rear bumper, battery bracket, engine soundproof board, etc.

Railway: window frame of vehicle, toilet components, seats, table tops, siding and roof of carriage, etc.

Construction: water tank, bath products, door panels, purification tank, building template, etc.

Bathroom: bathtub, integral bathroom equipment, integrated wash basin, etc.

And other areas of industry and agriculture.

 Molding technology is a method of putting quantitative molding materials (powder, granular or fibrous plastic) into the metal mold and forming products under the action of temperature and pressure. During the molding process, heat and pressure are required to melt (or plasticize) the molding material, fill the mold cavity with flow, and make the resin solidify. The principle is that the process of pressurizing, shaping and heating depends on the closure of the heated mold.

 Moulding Machine technology is the oldest molding method in plastic processing technology. Because of its long history, the molding technology has been quite mature, at present in thermosetting plastics and some thermoplastic plastics (fluoroplastics, uhmwpe, polyimide, etc.) processing is still the most widely used and the main position of the molding method. Moulded thermosetting plastic, placed in the cavity of the thermosetting plastic under the action of heat, first changed from solid to melt, melt flow under pressure with the shape of the cavity and cavity has given, as the crosslinking reaction, resin molecular weight increased, the curing degree rise, moulding material viscosity increase gradually and becomes solid, finally becomes demoulding products. Thermoplastic plastic mold pressure, in the previous stage of the situation and thermosetting Plastic the same, but because there is no cross-linking reaction, so in the flow of full cavity, the mold must be cooled to make its molten plastic into a solid with a constant strength can be demodulated into products. Because thermoplastic plastic mold pressing mold needs to alternately heating and cooling, production cycle is long, so thermoplastic products generally choose injection molding method more economic, only in the mold larger plane of Plastic products or because of the flow of thermoplastic plastic injection molding method is difficult to use molding.

 In the mold press material filled with the mold cavity flow process, not only the resin flow, the reinforcement material also to flow, so the mold press molding process molding pressure is higher than other process methods, belongs to the high pressure molding. Therefore, it needs not only the hydraulic press which can control the pressure, but also the high strength, high precision and high temperature resistant metal die.

 

Types of Plastic Blow and Injection Molding

Each plastic part requires a specific manufacturing process which can be significantly different from one product to another. Injection molding is used to manufacture solid components while blow molding is used to make plastic products with hollow areas, such as bottles and containers

Injection stretch blow molding combines the injection molding and blow molding processes.The plastic is first molded into a solid preform, to create a threaded bottle neck. Once the preform cools it is fed into a stretch blow mold machine. The preform is then reheated using an infrared heater and blown into a plastic bottle with forced compressed air.

The Injection Molding Process

Injection molding is used to manufacture higher volume quantities of plastic products ranging in size from large components to small components requiring micro-precision accuracy.

There are many types of manufacturing  methods categorized under injection molding, such as thermoplastic injection molding, over molding, insert molding, cold runner molding and hot runner molding.

Thermoplastic Injection Molding

Thermoplastic injection molding uses thermoplastic polymer, meaning it changes to a liquid state when heated. Unlike thermoset plastics that cool into permanent solid, thermoplastics can be remitted into a liquid after cooling into a solid.

Overmolding

Overmolding, or two shot molding, is a process that covers an injection mold over another substance, such as metal, to improve the performance or durability of a product. A rubber-like compound, called thermoplastic elastomer (TPE), is a commonly used overmold material. An example of a TPE overmold application is the handle grips on a toothbrush.  Overmolds can also be used to seal products with parts made from several injection molds.

Insert Molding

Like overmolding, insert molding is an injection moldingprocess that combines two or more components into a single finished product. Insert injection molding inserts a component into the injection mold cavity and plastic material is filled around the insert. Inserts can add strength to a product and eliminate the need for additional parts to reduce the product weight.

Cold Runner Injection Molding

Cold runner molds use a sprue to fill the runners that inject plastic resin into the mold cavity.  In 2 plate molds, the runner system and parts are attached, and an ejection system may be used to separate the pair from the mold.The cold runner can reduce waste by recycling and regrinding the material, but this can also increase the total cycle time. Cold runner systems can be used for a wide variety of polymers and can allow for easy color changes.

Hot Runner Molds

Hot runner molds use a manifold to heat melted plastic resin and then send the material through a gate to fill the mold cavity. The two main types of hot runner molds are externally heated and internally heated.  The externally heated molds can be used with polymer that is less sensitive to thermal variations while internally heated hot runner molds allow for better control of material flow.

Because  hot runner molding  does not require the use of runners, potential waste material is reduced and  the recycling and regrind and process of virgin plastic does not impact the total run cycle time.

The Blow Molding Process

During the blow molding process, the raw plastic material is shaped into a hollow tube with one open end called a parison. The parison is pressed into a cooled metal mold and compressed air is forced into the parison. When the formed plastic cools and hardens, the metal mold opens and expels the product.

Source:https://www.sukoptfe.com/types-of-plastic-blow-and-injection-molding

PTFE Plastic Molding Machine

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Since PTFE will not flow above its melting point, it cannot be injection molded and requires special processing techniques. Molded PTFE is processed by first compression molding the powder into preforms, and then sintering the preforms in a process analogous to sintered metal processing. This process creates geometric shapes that can then be machined, fused, and/or welded.

Product Description for Automatic Molding:

Automatic molding, a semi-automated form of compression molding, is the process Sunkoo uses for the manufacture of medium-volume to large-volume net molded and near net molded PTFE components. The automatic molding process requires dedicated tooling, typically requires minimal operator intervention and plastic parts can be fabricated relatively rapidly.

With the use of precise tooling and processing, parts manufactured using the automatic molding process can be produced to relatively close tolerances, but not to the accuracy of a fully machined part. Components are economically molded by utilizing a process of automated filling of the die cavity, applying pressure, and part ejection.

Other advantages of the Automatic molding process include:

·         Little or no scrap material as compared to the "typical" PTFE machining process from stock shapes (rod or tube)

·         Lower part cost, with minimal or sometimes no machining steps required

·         Components that are molded and sintered into final forms and shapes have reduced stress defects compared to machined parts (from cutting, milling, etc.)