Mold-pressure transducer

In addition to the above formulation, they used two-noded elements to represent the runner system. Figure 9.29 presents the finite element mesh employed by Wang et al. [18] with the dimensions and location of the pressure transducers used to record pressure during mold filling. The fan gates were of variable thickness as pointed out in the figure, and the mold cavity was of constant thickness. 

A detailed study of mold filling was done by Krueger and Tadmor (6). The various stages of the injection process was followed by pressure gauges in the mold, as shown in Fig. 13.5. In this experiment polystyrene (PS) was injected into a shallow rectangular cavity with inserts as shown in the figure. Pressure transducers were placed in the nozzle, runner, and mold cavity their output was scanned every 0.02 s and retrieved by a computer. The nozzle pressure was set by machine controls to inject at a constant 10,000 psi and, upon mold filling, to hold the pressure at 5500 psi. 

During clamping and when applying pressure on the molds, the tie rods stretch. If everything is in balance, the platens and mold stretch evenly. The distance the rods stretch is directly proportional to the applied load. Sensors, such as electrical strain gauges, can be used to detect the stretch or load applied and if an unbalance situation occurs, an indicator can alert the operator or the process control system. Bar sensing can also be used as a means of signaling the switch from pack to hold pressures, a potential alternate or support to pressure transducer use. 

Examples of good preventive maintenance activities include (1) establish the frequency of lubrication and what types of oil or grease must be used (2) check for oil leaks and have a procedure to correct/eliminate them (3) check heaters, thermocouples, pressure transducers, and so on (4) set up schedules and procedure to clean machines and molds/dies (barrels, screws, sliding mechanisms, clamps, etc.) (5) check control circuits (electrical, hydraulic, mechanical, etc.) (6) schedule checks of conditions wherever questions of alignment, level, parallelism (mold parts, mold press, die system, etc.), and other similar situations exist (7) set up a schedule to check safety devices on all equipment and (8) schedule sessions to repeat instructions on safety equipment procedures to all personnel. Figure 11-8 shows where accidents usually occur (324, 325). 

K control must be exercised from anywhere, apart from screw penetration, then most molders will go for line pressure control as this is easier, simpler and the system is less prone to damage it is also virtually maintenance free. The use of mold parting, which occurs on injection, is now a commercial option. This is a very easy system to fit as, no machining is required as the sensor location is on the outside of the mold. However, it is probable that with the development of suitable nozzle pressure transducers that, control will be exercised in future from this part of the machine. 

Mold pressure n. The pressure measured inside a mold cavity, usually by a flush-mounted pressure transducer, at any time during a molding cycle, but in particular... 

It is a fact of life that many plastic components are designed without the benefit of simulation. For such a mold, how does one determine the optimal set of processing conditions so as to maximize part quality and minimize production time In general, the task falls to highly skilled machine setters who are, unfortunately, in short supply. What s more, there is only so much a machine setter can do without some level of instrumentation on the mold, for example, a pressure transducer. Use of in-mold sensors while providing some information brings some disadvantages ... 

Other pressure transducers use a piezoelectric element. A piezoelectric material has the ability to transform a very small mechanical deformation (input signal) into an electric output signal (voltage or current) without any external electric power supply. Quartz pressure transducers have been developed to measure large pressures in high temperature polymer melts. The absence of a membrane allows a very robust construction. This has led to widespread use in injection molding. 

Figure 23.20. Tensile test bar used for the moldings. Gates and the position of the pressure transducer are indicated in the figure by G and P, respectively...

New types of molds for SRIM have been developed for the study of polymer flow mechanisms in nonwoven fibrous structures and for the production of samples for the mechanical testing of composites. The molds proved useful during the development of new methods for the investigation of elastomer flow mechanisms in nonwoven mats. A combination of glass and rubber as construction materials for the molds enables visual observation of the polymer flow and easy installation of thermocouples and pressure transducers in the cavity of the mold. 

Melt temperature and fill rates have been demonstrated to be very important process variables for microcellular injection molding. Recent work has studied the use of fast response thermocouples along with traditional pressure transducers to determine their effectiveness in providing practical process monitoring tools for the microcellular molding process [7]. Behind the ejector pin, pressure transducers and fast... 

Figure 11.4 Cavity pressure plots (9) for the same part molded in solid PA6 with 30% glass fiber and also with microcellular (MuCell) process. Pressure transducer was located behind ejector pin near the gate.

It was determined in this case that both in-cavity (behind ejector pin) pressure transducers and temperature sensors can be utilized to monitor micro-cellular injection molding and should be able to be developed as a basis of a process control model. For the pressure transducer, the gate location appeared to track part weight and dimensions more closely than at the end of fill, across the range of process changes. 

Tooling. Tooling is relatively expensive for injection molds. Production molds are normally machined and burned (electro-discharge machined) from tool steels (P20) and must be sfructured to withstand high pressures. Precision is required to incorporate cooling lines, ejector pins, and cavity pressure transducers or temperature monitoring sensors. The use of hot runner manifolds adds further complexity and cost, but may be justified because cold runners and their associated costs are eliminated in manufacturing. 

Cavity thennocouples 2.Cawty pressure transducers S.Mold... 

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