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With China Plastic Machinery
With China Plastic Machinery
Bakelite powder, also known as bakelite, has good electrical insulation and high temperature resistance. It is used to manufacture electronic appliances, daily industrial products, and automotive parts. It is a phenolic plastic with wood powder as filler, which is formed into products through molding (injection molding, die casting, transfer molding).
Bakelite powder is a thermosetting plastic made by the polymerization reaction of phenol and formaldehyde to produce resin, adding a certain proportion of fillers, hardeners, additives, and mixing and crushing.
Bakelite powder is also known as phenolic plastic powder or bakelite powder. It is a compression molding powder with phenolic resin as the basic raw material. The relative density is below 1.4, the water absorption is not more than 0.3% in 24 hours, and the oil resistance is not more than 0.03% in 24 hours. It has high heat resistance, acid resistance and water resistance, good dielectric properties, changes with temperature and frequency, and low arc resistance. It is mainly made of phenolic resin and fillers, etc., which are mixed and crushed. There are many types of fillers used, including wood flour, rags, asbestos, mica, hexamethylenetetramine, slaked lime, pigments, etc. It is often used to make electrical insulation products (such as electrical switches, etc.), so it is also called bakelite powder; it is also used to make industrial products, such as pumps, chemical equipment, pipes, etc., as well as daily necessities and cultural and educational supplies. The color of the general products is darker.
When the formaldehyde/phenol (molar ratio) is less than 1, a thermoplastic product can be obtained, called thermoplastic phenolic resin, that is, linear phenolic resin, which does not contain further condensation groups and can only be cured by adding a curing agent and heating. For example, if hexamethylenetetramine is used as a curing agent, the curing temperature is 150¡ãC, and the molding powder mixed with fillers is commonly known as bakelite powder. When the formaldehyde/phenol (molar ratio) is greater than 1, the first phase resin is obtained under alkali catalysis, that is, the thermosetting phenolic resin, which is soluble in organic solvents. The phase resin contains hydroxymethyl groups that can be further polycondensed, so it can be cured without adding a curing agent: the reaction under heating obtains the phase resin B, also known as the semi-soluble phenolic resin, which is insoluble and infusible but can swell and soften. Further reaction obtains the insoluble and infusible body structure phase C resin, also known as the insoluble phenolic resin. The phase resin A can also cure itself after long-term storage.
The curing forms of thermosetting phenolic resin are divided into room temperature curing and heat curing. Room temperature curing can use non-toxic room temperature curing agent NL, or benzenesulfonyl chloride or petroleum sulfonic acid, but the latter two materials are more toxic and irritating.
Phenolic resin
The polycondensation product of phenols and aldehydes is generally called phenolic resin, which generally refers to the synthetic resin obtained by the polycondensation reaction of phenol and formaldehyde. It is the earliest synthesized type of thermosetting resin.
Although phenolic resin is the oldest type of thermosetting resin, it is still widely used in the manufacture of glass fiber reinforced plastics, carbon fiber reinforced plastics and other composite materials because of its easy availability of raw materials, convenient synthesis, good mechanical strength and heat resistance, especially outstanding instantaneous high temperature ablation resistance, and the resin itself has extensive room for modification. Phenolic resin composite materials are particularly important in the aerospace industry (space vehicles, rockets, missiles, etc.) as structural materials that are resistant to instantaneous high temperatures and ablation.
The synthesis and curing process of phenolic resin completely follows the law of bulk polycondensation reaction. By controlling different synthesis conditions (such as the ratio of phenol and aldehyde, the type of catalyst used, etc.), two different types of phenolic resins can be obtained: one is called thermosetting phenolic resin, which is a resin containing hydroxymethyl active groups that can further react. If the synthesis is not controlled, the polycondensation reaction will continue until an infusible, insoluble, three-dimensional network structure is formed. Therefore, this type of resin is also called a first-order resin; the other is called thermoplastic phenolic resin, which is a linear resin that will not form a three-dimensional network structure during the synthesis process. A curing agent must be added during the further curing process. This type of resin is also called a second-order resin. These two types of bakelite powder are thermosetting materials that are different from general thermoplastic materials. They have excellent properties that are different from thermoplastics.
a. Composition: phenolic resin, wood powder, hardener and additives, where the additives include curing agent, plasticizer, colorant, lubricant, and curing accelerator.
b. Phenolic resin: The resin obtained by the polycondensation of phenolic compounds and aldehyde compounds (mainly the condensation product of phenol and acetaldehyde) is called phenolic resin.
c. Bakelite: Phenolic resin has high mechanical strength, stable performance, hardness, wear resistance, heat resistance, flame resistance, resistance to most chemical reagents, low hygroscopicity, and excellent electrical insulation performance. It is an ideal insulating material, commonly known as Bakelite.
d. Bakelite powder plasticizes at 70~90¡æ, has the lowest viscosity and the best fluidity at 90~120¡æ, and suddenly hardens at around 160¡æ to form an infusible solid, which becomes a hardening reaction.
e. T385J is best for injection molding, while T373J has good electrical properties, heat resistance, and flame retardancy.
f. The maximum temperature that Bakelite powder can withstand is 275¡æ.
g. The average shrinkage rate of Bakelite powder is 0.8%, and the expansion coefficient after molding and curing is 0.14%.
h. Bakelite powder will not burn, but will only char.
i. T385J, T373J, and T355J Bakelite powders are all soft materials.
(1) Heat: the heating system of the thermosetting injection molding machine barrel and the bakelite mold;
(2) Pressure: the hydraulic control system and mechanical transmission system of the bakelite machine;
(3) Time: the electronic control system of the bakelite machine.
Bakelite powder, bakelite machine, and bakelite mold.
Plasticization stage, injection cavity stage, and curing stage.
Thermosetting plastic (Bakelite powder) is added into the barrel, and the Bakelite powder is heated by external heating of the barrel and friction heat of the raw material when the screw rotates, so that it melts and generates fluidity. Under the pressure of the screw, the thick molten material passes through the nozzle of the barrel and is injected into the gate and runner of the mold to fill the cavity. A chemical reaction is carried out under high temperature and high pressure, and after a period of pressure maintenance, it is solidified and formed.
Generally, it consists of a mold opening and closing system, an injection molding system, a heating and cooling system, a lubrication system, a hydraulic transmission system, an electrical control system, a safety insurance system, and a detection system.
1. Definition: Bakelite mold is a type of injection mold, which is mainly used to mold thermosetting plastic products.
2. Structure: a. The cavity and core parts are used to form the structure and shape of the product, ensuring the positioning and dimensional accuracy of the product; b. The ejection system ensures that the product can be ejected after the mold is opened; c. The pouring system is the channel for the injection machine to eject the molten material to flow to the mold cavity. It is mainly used to transport the molten material and transfer pressure during the injection and pressure holding process to ensure the normal molding of the product; d. The dynamic and fixed mold guide positioning system, as well as the coordination of the guide column and the guide sleeve, ensure the accuracy of each movement of the mold; e. The core pulling system is set according to the structure and requirements of the product; f. The heating system is generally composed of electric heating pipe holes and electric heating pipes.
3. Features: a. Higher surface hardness, wear resistance and toughness; b. Good heat resistance and corrosion resistance; c. The mold surface is polished and electroplated; d. The mold has a heating system.
Main manufacturers include: Japan Sumitomo Bakelite, Japan Panasonic, Japan Hitachi, Taiwan Changchun, Shanghai Eurasia, Shanghai Shuangshu, Changshu Southeast, Japan Otalite, Germany Bakelite, etc. Mainly used in: electronic industry (frames, relays, switches, etc.), kitchen supplies (pot handles, insulation rings, etc.), automotive industry (commutators, impellers, etc.), grinding wheels, aviation supplies and many other fields. The synthesis and curing principles of resins are not the same, and the molecular structure of resins is also different.
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