Molding methods

Along with the simple open-mold casting method, there are several other methods of casting polyurethanes. They include  

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Coppers and high copper aEoys can be successhEly cast using the centrifugal, continuous, investment, permanent, plaster, and sand molding methods. 

Properties of red brass alloys are given in Table 9. The members of this group are cast using the centrifugal, continuous, investment, and sand molding methods. General tensile strengths vary from 170 to 210 MPa (25,000—30,000 psi) minimum as cast in sand molds. 

Properties of copper—nickel alloys are Hsted in Table 14. The alloys in the copper—nickel group have been successfully cast using the centrifugal, investment, permanent, and sand molding methods. The minimum tensile strengths on test bars cast in sand molds are 207—310 MPa (30,000—45,000 psi). 

Processing PC resins by extmsion or injection-molding methods requires melt temperatures of 290—320°C. High melt viscosity at low shear rates prevents mold flash and drool. At injection shear rates, apparent viscosities decrease, and easy melt flow allows manufacture of large, complex parts. 

Table 18. Effect of molding method on mechanical properties of mica-filled thermoplastics (Vf = 0.5) [375]...

For several basic reasons, the extrusion process does not have the large number of possible process product interactions that the preceding molding methods presented. Due to this situation it can not fabricate the complex shapes and tighter tolerances obtained from molding. The process is a steady-state continuous production operation that can be brought to a condition of control. However it has its share of potential problems (Chapter 8, EXTRUSION). 

Optical properties of the material are less critical for microchips hyphenated with MS than for devices with on-chip optical detection where low background absorption or fluorescence is mandatory. Thus, completely opaque polymers like glassy carbon or polyimide " can be used as microfabrication substrates. Furthermore, polymer microchips are of great interest because their potentially low manufacturing costs may allow them to be disposable. Methods used for the fabrication of plastic chips include laser ablation and molding methods. 

Fig. 6. Scanning electron photomicrograph of a PLGA 50 50 scaffold in the shape of a half-cylinder prepared by a melt molding method [35] using 35 wt% gelatin microspheres with diameters in the size range 300-500 pm. (Reproduced with permission from [35])...

Molded products can be obtained without employing melt molding methods, such as injection molding, extrusion molding, and... 

There are several techniques for producing polymer mixtures for further processing into articles by the reactive (chemical) molding methods simultaneous formation of two polymeric systems with mutual entanglement of their chains and the appearance of so-called interpenetrating networks synthesis of the second polymer within an expanded network of the initial polymer incorporation of oligomers into a polymer matrix as a temporary plasticizer followed by polymerization. 

The device was fabricated using standard lithographic and replica molding methods [162]. 

Polymeric chips have been fabricated with various methods, as developed from the plastics industry. These processes include casting, injection molding, laser ablation, imprinting, and compression molding. The physiochemical properties of various polymeric materials and their molding methods have been summarized in a recent review article [7],... 

Compression molding method called coining is used for parts that are too complicated to be produced by machining. In coining, a sintered molding is heated to the melting point, then it is quickly pressed into a mold cavity and held under pressure until it solidifies.4... 

Structural-web molding is a low pressure foam molding method. It is the phrase usually used to identify the gap between structural foam (SF) molding and injection molding. Its surface does not have the usual SF characteristic swirl pattern. It can produce very large, lightweight parts with smooth surfaces like conventional injection molded parts. 

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