(1) Plastics for manufacturing containers, outer casings, covers, and conduits.
Such products generally do not require a large load, but require good or even excellent impact strength and hardness, good or moderate tensile strength and dimensional stability, as well as good appearance and environmental resistance, and the price of the material is required. Moderate. Special consideration should be given to other special performance requirements. If made of metal, steel, steel, cast aluminum or die-cut aluminum, light alloy or die-cast metal are generally used. These materials have high strength and hardness. However, the use of plastic is more appropriate when the following conditions and requirements are encountered.
a. Resonance must be prevented and the sound transmission must be small;
b. Requires some elastic deformation to prevent dents caused by accidental collisions;
c. The shape of the product is complicated, and it is difficult to produce it by metal processing;
d. The product does not wish to be processed later;
e. requires the product to be electrically insulated (or partially insulated) and insulated, or integrally colored or required to be transparent and translucent;
f. Requires corrosion resistance and moisture resistance, no rust;
Considering the above characteristics, the more suitable materials are shown in the table (to be added). Sometimes, a material that does not meet the requirements often requires plastics and other materials to be compounded. For example, when it is necessary to control creep or flexural deformation or special wear resistance, a threaded metal insert can be embedded in a plastic part if a structural shell is required. When the physical energy is subjected to collision and rough use, it is conceivable to use a composite plate of metal and plastic or a composite plastic on a metal surface.
(2) Plastics for low-friction applications require materials with low friction coefficient, low friction coefficient even when not lubricated, good abrasion resistance, moderate to good shape stability, heat resistance and Corrosion resistance. In the past, copper-tin-tin alloy, bronze, cast iron, pre-lubricated wood, graphite, and the like were used. However, the use of plastic is more appropriate when the following conditions and requirements are encountered.
a. Corrosive or abrasive;
b. Lubricants can contaminate the product during processing;
c. The component must be operated at a temperature above or below the normal lubricant;
d. No maintenance required;
e. Plastics can avoid complicated lubrication systems;
f. When it is urgent to ask for weight loss;
g. requires electrical insulation;
h. Require weakening of noise and noise;
I. Requirements to minimize scratches and nicks;
j. High-load, low-speed operation of the system will extrude ordinary lubricants;
k. When the slip viscosity is not suitable.
According to the above requirements, suitable plastics for bearing antifriction parts are shown in the table (to be added). However, when the operating temperature exceeds 260 ° C for a long time or there is a large radial load, thrust load, or continuous high-speed operation, and the long-term time required to minimize the deflection of the shaft or require the wear of the shaft before the bearing Other materials should be considered when wearing. Sometimes (especially in the following cases) consider a combination of plastic and other materials, such as: a. Need to dissipate heat as soon as possible, b. Requires minimal creep; c. Only plastic can not withstand too high loads, and so on.
(3) Materials used as heavy stress mechanical parts (such as gears, cams, racks, couplings, rollers, etc.)
Such applications require high mechanical strength, especially high bending, tensile and impact strength, good fatigue resistance and stability at elevated temperatures, good machinability, dimensional stability, and moldability. Forming precision tolerance products. Cast iron, steel, brass, etc. have been used in the past, but it is more appropriate to consider plastic when encountering the following conditions and requirements.
a. Urgent demand for weight loss;
b. The use of the environment is dusty, abrasive and corrosive;
c. Minimize sound or vibration;
d. I hope to have comprehensive performance.
According to the above requirements, the more suitable plastics are shown in the table (to be added). However, if it is required to withstand heavy loads, high operating temperatures, and the urgent need to reduce material costs. Other materials should be considered. If high impact resistance, bending resistance, and low cost are required, structural composites made of plastic and other materials such as metals may be considered.
(4) Applications such as plastics and heat-resistant plastics used in chemical equipment require chemical corrosion resistance and low hygroscopicity. They also require high and low temperature resistance, and generally have good mechanical strength. In the past, stainless steel, chrysanthemum, enamel, and other precious metals were used. However, plastics may be considered more suitable when encountering the following conditions and requirements.
a. Specially required to resist corrosion, and stainless steel can not meet the requirements;
b. requires corrosion resistance and wear resistance;
c. Urgently demanding to reduce costs or extend the service life of chemical equipment;
d. Requires reduced maintenance and easy maintenance;
e. Requires thermal insulation, heat insulation and resistance to transient high temperatures or ablation (for the convenience of material selection, heat-resistant plastics can also be divided into one category)
According to the above requirements, a more suitable plastic is shown in the table (to be added). In addition, unsaturated polyester FRP is used for large hand lay-up products; phenolic or modified phenolic plastics are used for products that are resistant to high temperatures, ablation, or both heat and require high strength. However, if the required mechanical strength is not high, the operating temperature exceeds 290 ° C for a long time, and when dimensional stability is required in the case where the range of high and low temperature varies widely, new composite materials or other materials should be considered. If the working conditions require high strength and excellent corrosion resistance, or require extreme corrosion resistance at elevated temperatures, or if plastics need to be slowly ablated at high temperatures to protect the metal from damage, consider Composite materials made of plastics and other materials (such as graphite, heat-resistant resin and filler or composite materials composed of asbestos, carbon fiber, SiO 2 fiber, etc.).
(5) Plastics used as electrical structural parts These applications require excellent electrical insulation at low to medium frequency, high strength and impact resistance, good fatigue resistance and heat resistance at elevated temperatures. , dimensional stability is good. In the past, ceramics, glass or mica were used, but it is more appropriate to consider plastics when encountering the following conditions and requirements.
a. Impact load;
b. Urgent demand for weight loss;
c. The dimensional accuracy requirements are stricter, and the processing of inorganic insulating materials such as ceramics and glass does not meet the requirements;
d. It is required to manufacture a conductor or insulator of complex shape into a unitary article or part (such as a printed circuit, a collector ring assembly, a potting or an insert, etc.).
According to the above requirements, the more suitable plastics are shown in the table (to be supplemented). In addition, there are polyester (PETP, PBTP), fluoroplastics, polyphenylene ether, polysulfone, polyimide, polyamideimide, phenol ether. Resin (xylok-new phenol ether resin. Parylene is also a good insulating material. As a general insulating material, polyethylene, polypropylene, polystyrene, and polyvinyl chloride can be used to manufacture general wire and cable insulation. Carbonate is used for transparent parts requiring high impact strength; cast epoxy or molding compound can enclose electronic and electrical components. It is suitable for applications requiring maximum resistance to the environment. Encapsulation of combined electrical components can be made of silicone rubber. Combined with epoxy for better performance; molded epoxy for dimensionally stable parts over a wide temperature range; melamine formaldehyde plastic for parts requiring greater hardness; silicone polymer for Where high temperature resistance is required; aminoplasts are used for low cost applications; phenolic laminates are used for die cutting and stamping parts, etc. However, if the operating temperature is extremely high, or pressure When the load is high, consider use of other materials.
(6) Transparent or colored translucent materials such as plastics used as light-transmitting parts, transparent plates and models require good light transmission, good to excellent secondary formability and molding processability, and are not brittle (impact resistant) ), and generally have a good tensile strength. Most of the past used glass, but glass has some shortcomings, especially the following requirements:
a. The product is required to withstand impact, vibration and breakage;
b. requires a certain bendability;
c. requires a higher specific strength;
d. The material must be naturally translucent and should not be translucent by surface treatment;
e. It is required to easily form an article having a complicated shape; and the like.
According to the above requirements, a more suitable plastic is shown in the table (to be supplemented). Among them, acrylate plastics are recommended for general applications, especially for optical, decorative and outdoor applications. Cast acrylic cheeseboard sheet with high strength and transparency, can produce medium and low precision lenses, acrylate plastic for extrusion molding is cheaper (especially for making thin products), and has better two Sub-formability; polycarbonate has the highest strength in transparent plastics, making transparent masks, safety glasses or shields. Cellulose acetate butyrate has excellent impact resistance and can be formed by deep molding; transparent polyvinyl chloride has excellent secondary formability and printing adaptability; cellulose acetate plastic can be used as flexible transparent plate and protective sheet Medium-impact polystyrene and rigid PVC plastics are inexpensive transparent and translucent materials; polystyrene produces the lowest-priced molded transparent parts. Allyl diglycol ester resin (CR-39) is currently the main thermosetting plastic used in optics. It has good transparency, abrasion resistance, impact resistance and chemical resistance. It is coated with surface coating or coated with silicone. The film is used to improve the surface hardness and wear resistance, and can continuously withstand 100 ° C and withstand 150 ° C in a short period of time. However, there are still problems such as high hygroscopicity, which is currently mainly used for making lenses. However, if the product is required to have excellent chemical resistance or to adapt to high operating temperatures, or to wear under operating conditions, and to require excellent dimensional stability over a wide temperature range, consideration should be given to the surface of the plastic. Handle or use other materials. With the continuous emergence of new materials, the selection of materials should be constantly revised and modified to improve product quality and reduce costs. For example, low-friction materials such as bearings and bushings have been used in the past, but in recent years, nylon and polyoxymethylene are used, which requires a smaller friction coefficient and a polyacetal containing a plastic powder or fiber at full heat resistance. Or polyimide.
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