SHOT SIZE

Foamed plastic articles may be produced with good results using normal screw-type injection moulding machines (see Fig. 4.43(a)). However, the limitations on shot size, injection speed and platen area imposed by conventional... 

To ensure consistency, the two critical areas for control specific to injection molding are shot size control and temperature control on the injection system, i.e., screw portion for the reciprocating screw machines, and both the screw and ram sections for the screw/ram machines. As mentioned previously, for temperature and cure control, the use of microprocessor controls has significantly improved the performance of injection molding machines, including control of the shot size. 

Shot Size Distance Pull Back Distance... 

Most of the compounds were extrusion compounded in a conical, partially intermeshing, counter rotating twin screw extruder (Haake Reomix TW-lOO). The extruder speed was set at 50 rpm and the barrel temperature profile was set to produce a melt temperature of 260°C at the die. Samples were injection molded in a 31.8 MT Battenfeld press with a 59 cc shot size. Where noted, samples were compounded in a 60 cc Brabender internal mixer and compression molded. 

The old US convention uses MANUFACTURER T/V where T is the clamping force in British tons and V the shot size in ounces of polystyrene. 

In shotgun shootings, the wads can provide useful information. They can be chemically examined to provide some information about the primer and propellant types, and physical examination can sometimes reveal the caliber and give an indication of shot size. Wads from different manufactures can vary in composition, color, thickness, and design, and physical examination may reveal the identity of the cartridge. (Wads are also found in some rifle, revolver, and pistol ammunition. There is never more than one wad and such ammunition is rare. Sometimes the wad is made of nitrocellulose but more commonly of glazed or waxed cardboard. Such wads are placed between the propellant and the bullet.)... 

Figure 4. Effect of shot size on thiophene conversion...

The effect of temperature on the curves of break-through rate vs. shot size was fairly small compared to the effect of sample size (Figure 10). On the other hand, a catalyst cleaned by heating to 400° C. in hydrogen and then cooled to 250° was found to adsorb about 1.5 cc. of H2S per gram of catalyst completely before allowing any additional amounts injected to desorb, so that there appeared to be a change in equilibrium sulfur content with temperature. 

Very few of the installed IMMs run shot sizes anywhere near the full shot size capacity of the injection unit (Chapter 4). Typical usage is from 25 to 60%. Most suppliers of injection machines offer several sizes of injection plasticating units for any given press tonnage. The problem of having too much shot capacity can render some IMM unusable for certain plastics and applications. An example is excessive residence time for the plastic particularly the engineering materials. Any plastic that... 

To increase shot size upsizing the plasticator can be made. A number of items have to be considered for the upsizing process, such as barrel wall thickness, resultant screw L/D, injection speed reduction, screw drive torque, and injection pressure drop. Before considering the upsizing process, one has to determine whether the output can be met properly using the decreased pressure and speeds that occur. The pressure and speeds will decrease directly proportional to the difference in the barrel ID projected areas. If this poses no problems, the L/D and structural integrity of the barrel have to be considered before proceeding. 

After observing each cycle, the shot size and transfer point will be adjusted frequently to set the process so that the first stage accomplishes 95 to 98% of the fill as measured by shot weight. Once the first stage shot size, transfer, velocity and pressure are set, we can set 2nd stage packing pressure. Adjust pack pressure as needed, but do not... 

To mold micron-scale precision parts with shot weights of only 0.0022 g, electrical operating IMMs are being used. Those who desire precise shot size (dosing) can buy electric injection machines with servomotors capable of very accurate screw positioning. With hydraulic IMMs, molders can install a valve gate that shuts when the correct amount of plastic has been injected into the mold. 

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