Shaping of plastics

Xem 1-16 trên 16 kết quả Shaping of plastics
  • Plastics have had a significant influence on industrial, domestic and cultural aspects of everyday life in the twentieth and twenty-first centuries. They represent advances in technology, illustrated by the dramatic growth in number and type of information storage media available since the 1970s, credit and payment cards, medical applications and food containers which can be taken directly from freezer to microwave oven to dinner table. The development of plastics reflects economic history.

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  • In today’s practical and cost-conscious world, sheet-metal parts have already replaced many expensive cast, forged, and machined products. The reason is obviously the relative cheapness of stamped, or otherwise mass-produced parts, as well as greater control of their technical and aesthetic parameters. That the world slowly turned away from heavy, ornate, and complicated shapes, and replaced them with functional, simple, and logical forms only enhanced this tendency. Remember old bathtubs? They used to be cast and had ornamental legs.

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  • There is a vast multitude of materials with strongly differing properties. A copper wire, for instance, can be bent easily into a new shape, whereas a rubber band will snap back to its initial form after deformation, while the attempt to bend a glass tube ends with fracture of the tube. The strongly differing properties are reflected in the application of engineering materials – you would neither want to build cars of glass nor rubber bridges. The multitude of materials enables the engineer to select the best-suited one for any particular component.

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  • The mold is probably the most important element of a molding machine. It is a arrangement, in one assembly, of one (or a number of) hollow cavity spaces built to the shape of the desired product, with the purpose of producing large numbers of plastic parts. Thus the primary purpose of the injection mold is to determine the final shape of the molded part (shaping function). In addition to give the final shape of the molding, the mold performs several other tasks.

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  • Traditionally its triangular and made of canvas, although most modern ones are made of nylon and come in a variety of shapes and sizes. It's made of plastic and iron. It's wide at one end and narrow at the other, with a plastic handle on top. Most of them are designed to spray water. The bottom part gets very hot.

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  • Basic Tasks of a Mold q Accomodation and Distribution of the Melt q Shaping of the Molded Part q Cooling/Heating and Solidification of the Melt q Ejection (Demolding) of the Molding q Mechanical Functions Accomodation of forces Transmission of motion Guidance of the mold components CORETECH SYSTEM The mold is probably the most important element of a molding machine. It is a arrangement, in one assembly, of one (or a number of) hollow cavity spaces built to the shape of the desired product, with the purpose of producing large numbers of plastic parts.

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  • Metal-forming processes use a remarkable property of metals—their ability to flow plastically in the solid state without concurrent deterioration of properties. Moreover, by simply moving the metal to the desired shape, there is little or no waste.

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  • Solid mechanics, which includes the theories of elasticity and plasticity, is a broad discipline, with experimental, theoretical, and computational aspects, and with a twofold aim: on the one hand, it seeks to describe the mechanical behavior of solids under conditions as general as possible, regardless of shape, interaction with other bodies, field of application, or the like; on the other hand, it attempts to provide solutions to specific problems involving stressed solid bodies that arise in civil and mechanical engineering, geophysics, physiology, and other applied disciplines.

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  • Common engineering materials reach in many engineering applications such as automotive or aerospace; their limits and new developments are required to fulfill increasing demands on performance and characteristics. The properties of mate- rials can be increased, for example, by combining different materials to achieve better properties than a single constituent or by shaping the material or constituents in a specific structure. Many of these new materials reveal a much more complex behavior than traditional engineering materials due to their advanced structure or composition.

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  • At a recent meeting of the American Academy of Esthetic Dentistry a survey questioned whether aesthetic treatment methods were ethical. The situation typical for that time was used as basis for the survey: "Let's assume that the patient is completely healthy and there are no biological or physical reasons for a therapeutic intervention.

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  • Most of the RP technologies are additive; that is, the model is made automatically by building up contoured laminations sequentially from materials such as photopolymers, extruded or beaded plastic, and even paper until they reach the desired height. These processes can be used to form internal cavities, overhangs, and complex convoluted geometries as well as simple planar or curved shapes.

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  • Several proposals have been submitted to ease the pain of RSS on webmasters. Many of these are described in detail in the RSS Feed State HOWTO [17]; exam- ples include avoiding transmission of the feed content if it hasn’t changed since the client’s last request, gzip compression of feed data, and clever ways to shape the timetable by which clients may poll the RSS feed. Unfortunately, because the schedule of micronews is essentially unpredictable, it is fundamentally impossible for clients to know when polling is necessary.

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  • 1. Rubber can be stretched and will then return to its original shape because it is… a. plastic b. elastic c. flexible d. light 2. Spaces… in the building include a lecture room, laborataries and a library. a. provide b. provided c. providing d. to provide 3. The… in the concrete block is 20N/ m2. a. illumination b. density c. stress d. mass 4. The … of a surface in the room is measured in square metres. a. area b. volume c. width d. length 5. The longitudinal section of a cone is … a. square b. rectangular c. cirular d. triangular...

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  • Choose the word or phrase that best completes the sentence. Circle A, B, C or D 1. People … to enter the house need protecting from the weather. a. wait b. waiting c. to wait d. waited 2. The post-and-lintel structure is… of straight members. a. composed b. included c. consisted d. used 3. Bitumen can be dented or scratched easily because it is… a. elastic b. plastic c. flexible d. soft 4. The… of the block material is 500kg/m3. a. density b. stress c. mass d. illumination 5. The cross-section of a cone is… in shape. a. circular b. triangular c.

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  • Process and Control Objectives Forming of metallic materials is the process of choice when complex net shapes with high levels of productivity are desired. Myriad processes, ranging from job-shop metal bending machines to very high speed stamping and forging presses are available. In all cases, the processes involve plastic deformation of the workpiece, and the resulting strong

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  • Fig. 18.12 Surface flaw shape parameter. (From Ref. 22. Adapted by permission of Prentice-Hall, Inc., Englewood Cliffs, New Jersey.) To approximate the effects of strain hardening, a flow stress cr0, taken to be an average of the yield and ultimate strengths, is often used when computing the plastic collapse stress. The plastic collapse stress ac is that applied stress which produces cr0 across the remaining uncracked ligament, and is the maximum applied stress that a perfectly plastic material can sustain. This stress may be determined using a limit load analysis.

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