Sprue removal

These are usually self-adhesive, precut, printed patterns on a substrate that are simply adhered to the surface of a product. Decals generally use a transparent plastic film while labels are usually on an opaque plastic, metallic and multilayer sandwich base. Labels of sufficient thickness are useful for hiding unavoidable appearance problems such as gate and sprue removal areas, sink marks, blushes, splays, and weld lines. 

Structural foam Due to low pressures, significant design Good structural integrity Sprue removal Lower tooling cost Vibration welding, ultrasonic... 

Once the interlocks are satisfied, the mold closes. Then the injection unit occasionally moves slightly forward to coimter a motion called sprue breakaway. With cold runner systems, the injection rmit is moved slightly away from the sprue bushing to facilitate sprue removal and/or prevent nozzle freeze-off. Thus, injection unit must be moved forward to provide intimate contact between the nozzle and sprue bushing during injection. Sprue breakaway is not used with hot runner systems. 

Cast materials will usually need to have the gate or sprue removed by hand or machining methods. For appearance parts, additional... 

Before drilling the sprue, remove the plug insert from the top mold half. Then put the mold halves back together and mark the... 

Reduction of finishing work on mouldings (sprue removal) ... 

Gate closure and sprue removal. Gates may be thermally closed, i.e., self-freezing or mechanically closed using a pin. Sprues are removed by breaking them off, in the case of open and tip-type nozzles, or by shearing (for side gating nozzles). 

Figure 25 Schematic diagram of an injection/transfer molding machine [9]. (a) Hydraulic separation unit for upper mold plate, (b) Hydraulic separation unit for middle mold plate, (c) Shuttle system with automatic sprue nipple removal, (d) Brushing unit for cleaning middle mold plate, (e) Hydraulic ejector for automatic ejection.

Are secondary operations required except to remove sprue No No Yes, e.g., removing material where a window is required (often done within the molding cycle)... 

Rosato, D. V., Parts Removal With On-Robot Secondary Operations and Simple Sprue Pickers in chapter sections of Tool Manufacturing Engineers Handbook, Vol. 9, Materials Parts Handling, SME, 1998. 

Pour the liquid pewter into the sprue opening. Allow the pewter to cool. Remove the piece with pliers. 

Saw off the sprue with a jeweler s saw. If any metal has run beyond the mold, this too should be removed. 

The casting is kept in the oven long enough to develop sufficient strength to allow the part to be successfully demolded without any damage or distortion. Careful removal of risers and sprues may now be carried out. 

A variation of the compression molding technique is to use transfer molding. In this method the liquid polyurethane mix is placed in a pot and allowed to thicken. The polyurethane semi-gel is forced through sprues into the mold, and the air is allowed to escape through vent holes. The part is allowed to cure sufficiently so that it can be removed. Figure 5.2 shows the general layout of a compression and transfer mold. 

Any minor adjustments to the mold need to be made at this time, for example, the dimensions or any air pockets being removed by adding suitable sprues and or bleed holes. 

Even yet experts say that the best combs are saw-cut from flat uniform pieces of bone (and such combs remain on sale in more-expensive shops). Combs can be cut in the same way from plastic sheet, achieving comparable quality, but the stock must be prepared suitably and the work as a whole is more costly than the commercial method of making plastic combs in large numbers—injection moulding using materials such as nylon or polypropylene from the moulding process, after removal of the sprues, fully finished, saleable products (teeth included) can be obtained in a few seconds. 

The surface finish is important for resonance and any imperfections from machining or moulding (including sprue marks), should be avoided if necessary, they should be removed in a suitable finishing process (perhaps in a lathe fitted with cup holders of suitable size and diameter). A careful visual inspection of representative samples taken after the finishing may be advisable. 

Sprue. (1) The main feed channel that runs from the outer face of an injection mold to the gate in a single-cavity mold or to the runners of a multiple-cavity mold. The hquid polymer is forced through this orifice from a nozzle till the mold is filled to capacity. Some polymer remains in the sprue after the mold is closed, leaving a projecting piece that must be removed after the product is ejected. The viscosity of the polymer must be low enough to permit it to pass through the sprue readily. 

A three-plate mold design (Figure 2.10) features a third, movable, plate which contains the cavities, thereby permitting center or offset gating into each cavity for multicavity operation. When the mold is opened, it provides two openings, one for ejection of the molded part and the other for removal of the runner and sprue. 

One can see from Figure 2.10 that a three-plate mold operation necessitates removal of the ruimer and sprue system, which must be reground, and the material reused. It is possible, however, to eliminate the runner system completely by keeping the material in a fluid state. This mold is called a hot-ruimer mold. The material is kept fluid by the hot-runner manifold, which is heated with electric cartridges. 

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