Shot weight

Injection molded styrenics span the width of the car in the form of instrument panels and crash pad retainers. Shot weights approach 10 lbs in some cases. 

Once the process has been optimized, plastic conditions should be recorded such as fill time, peak pressure at fill, cavity pressure,184 melt temperature, mold temperature, melt flow rates, and gate seal time. Record all basic machines setpoints on the setup sheet such as the transfer time (fill time) and weight, overall cycle time, and total shot weight, part weight, % runner, etc. 

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. 

The injection molding screw diameter chosen should be matched to the part s shot volume, which - as a general rule - should be not more than about 70% of the screw s theoretical swept volume. If the screw (diameter) chosen is too small, the swept volume will tend towards the shot volume, leaving insufficient leeway for correcting process fluctuations. On the other hand, if the injection unit is too large, only a small part of the swept volume will be employed per shot and the remainder of the melt in the barrel will possibly be exposed to too much heat. Furthermore, even small variations in the screw stroke would cause considerable variation in the shot weight. 

Samples filled on the production line and shot weight through use data generated... 

Standard sizes of the "RHP" series cover machines with flow rates from 43 to 300 lbs/min and for maximum shot weights from 2 to 20 lbs. (See table Figure 5). 

Metered-dose inhalations and nasal aerosols should be evaluated for appearance (including content, container, and the valve and its components), color, taste, assay, degradation products, assay for cosolvent (if applicable), dose content uniformity, labeled number of medication actuations per container meeting dose content uniformity, aerodynamic particle size distribution, microscopic evaluation, water content, leak rate, microbial limits, valve delivery (shot weight), and extractables and leachables from plastic and elastomeric components. Samples should be stored in upright and inverted/on-the-side orientations. 

Solution The machine output or plasticizing capacity, Q, is the ratio of the shot weight W to the cycle time t(,. 

The type of polymer used for the preceding job. If the compounds are similar, then purging will require three to four shot weights of rubber. If there is a change of polymer, and the machine is not modern, then considerably more will be required. Work with coloured stock has shown that vestiges of the previous rubber are evident after as many as 40 shots For this reason it is better to restrict machines to specific polymer types and colour. 

Consider the example where of a machine which is producing 6 components at a cycle time of 24 seconds (24s). The weight of each component and the feed system is 14 grams (14g) and 12g respectively, therefore the total shot weight is (6 x 14) + 12 = 96g. Given the following formula, the material consumption (Q) in kilos per hour (kg/h) can be calculated as follows ... 

As a general practice, the residence time for a material should be calculated, particularly when using small shot weights on large machines, as the material can suffer degradation which is not always visually detectable. Because of the importance of resi-... 

Should be kept as low as possible usually a nominal value of 5 bar (0.5MNm-2, 72.5psi) is used so as to achieve consistent shot weights. May need to be increased, to assist dispersion, when using colorant but keep as low as possible. Up to 150bar 15MNm-2 2175psi should however, be available. 

The above value does not include the cycle time at which the mold is to be run at. It must be noted the coolant flow rate in c.c. s or gallons per minute is determined by the total shot weight of the mold and the cycle time needed to produce moldings to the specified standard of quality. 

Shot shat n. (1) One complete cycle of a molding machine. (2) In woven pile floor coverings, the number of filling yarns per row of tufts. (3) Imprecise. Syn shot weight. 

Shot weight (shot) n. In injection and transfer molding, the entire mass of plastic delivered in one complete filling of the mold, including the molded parts, sprue, runners, cull, and flash. 

To obtain a homogeneous melt the shot weight should not exceed 40% of the machine rated styrene capacity. Screw speeds should be in the region of 40-100 rpm and the use of back pressure when plasticizing can be an advantage. Mould temperatures are often about 20°C, though sometimes higher temperatures may be necessary to achieve particular types of surface finish. 

Preheating provides more uniform melt temperature, reduces the possibility of localized overheating or hot spots in the cylinder, and frequently permits faster molding cycles. Preheating is especially advantageous in those cases where the molded shot weight exceeds 70 percent of the rated machine capacity. 

Shutoff valve provides exact and repeatable material displacement every shot with less than . 1% variation in shot weight from injection to injection. 

The resins should be dried before use at 75-90°C (100-105°C for ASA/PC blends) for 2-4 hours to moisture concentration below 0.04% (especially essential for ASA/PC blends which mechanical properties are sensitive to hydrolysis). Geloy resins can be injection molded in standard injection molding machines. Optimum results are obtained when total shot weight is equal to 30-80% of the machine capacity. It should be considered that some blends containing PVC may degrade on exposure to high temperature (200°C should never be exceeded for... 

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