Cavity molding

Main portion of the mold containing the molding cavity, mold pins, guide pins, etc. 

An alternative approach for injection molding is the use of a rotary table injection machine. This type of machine uses the multistation concept, each station having a single cavity mold generally using a point gating/ injection point as previously mentioned. Consider a rotary table machine with eight stations, station one would be the injection station and station seven would be the unload and load metal insert station. This type of process has been successfully used for different types of lip type rotary shaft seals where more expensive elastomers are used and waste needs to be kept to a minimum. 

The use of small injection molding machines with a single cavity mold. This approach removes the need for a runner system and, when using a dia-... 

The use of multinozzle injection machines. In general, this type of machine has a horizontal reciprocating screw that feeds four injection nozzles each connected to a single cavity mold thus minimizing waste. However, one concern with this approach is the need to have the mold accurately lined up (the top and bottom surfaces of the mold will be in the vertical plane) to eliminate compound leakage at the nozzle/mold interface. 

Figure 24 Seal/flash cap/runner system configuration from four cavity mold.

Figure 7.75 Schematic diagram of eight-cavity mold for injection molding operations. The molded parts of interest are indicated by the shaded regions.

Weighed amounts of PVC and metallic powders were mixed thoroughly for one-half hour in a rotary blender at room temperature. The mixture was compacted in a cavity mold for 10 minutes at 120°-130°C under a pressure of 10,000 psig. The mold was then allowed to cool under pressure to room temperature, and the cylindrical compact was removed. The dimensions are length 3.5 cm diameter 2 cm. Density measurements indicated that this procedure provided samples of porosity <1.5%. 

Schematic diagram of an eight cavity mold system with various runner lengths and...

Figure 9.34 Photograph of optical lens parts molded by a four-cavity mold [10] (courtesy of 3M Precision Lens).

Reservoir wall a cylindrical cavity molded from a synthetic elastomer, which is easily deformable by gentle squeeze. The fexible reservoir wall is impermeable to water molecules. 

Rate (4 cavity mold, Spark plug production ... 

The process is used for high volume BM of very small containers such as pharmaceutical vials and whiskey bottles. A multi-cavity mold is used with an extruded parison whose circumference approaches twice the total width of the closely spaced cavities. Before the mold closes, the parison is stretched and semi-flattened laterally so that it extends across the full width of the cavities. The process is usually combined with blow/fill/seal techniques. 

Blow mold usually consists of two halves, each containing cavities which, when the mold is closed, define the exterior shape of the BM (Chapter 17). Multiple cavity molds are used. Because the process produces a hollow article, there are no cores to define the inner shape. Mold details and actions will vary considerably according to the geometry of the product and the BM process in use. Even though the following review concentrates on EBM, the information can also be applied to IBM. The two halves that meet on a plane are known as the parting line. The plane is chosen so that neither cavity half presents an... 

As with other mold operation process mold release agents are usually required because the plastic melt can adhere to the surface of the mold cavity. Molds with very little or no draft usually require a release agent. Like other molding operations, a textured cavity can provide a textured product surface. Most texturing of cavities is by chemical etching so it is important to use the appropriate mold material to create a particular texture. An effective release is needed at the parting line to aid in demolding. 

When compared with compression molding, transfer molding provides better product consistency, shorter cycle times, and better bonding of rubber to metal [55]. However, considerable amount of material is lost as scrap in the transfer pad, sprues, and flash. The basic three-plate multiple cavity mold is more complex and expensive than a comparable compression mold but is suited better for intricate parts or securing inserts [56]. 

The molten plastic is extruded into a cavity mold at high pressure. The material cools in the cavity and solidifies. The mold is then opened and the article is removed. Very intricate configurations can be obtained by this technique (e.g., to provide intricate and strong components for the electronic, telecommunications, and clock-making industries). 

Mold-release agents create a barrier between the resin and the metal mold, preventing adhesion to the mold. The same additives that promote mold release are sometimes used to reduce viscosity and ease flow, thereby improving surface detail and ensuring more complete filling of small complex cavities. Mold-release agents may also have an antistatic function (43). 

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