Molds heating

Mold Coolers for Plastic Injection Molding. Heat pipes are used for local temperature control in the injection molding of plastics (see Polymerprocessing). A heat pipe is often used to force local cooling within a mold to speed operation, control viscosity, retention of material in a difficult mold area, or to reduce thermal stresses on cooling. 

A press, a homemade toggle job, or a hot-stamping machine can be used to perform the cold working operation. When heat is required (usual requirement) the male forming die should be about 132 to 138°C (270 to 290°F). Pressure should be maintained for about 10 seconds. This time can be reduced if the product still retains residual molding heat or is preheated. The recommended preheating temperature is from 80 to 110 C (175 to 230°F). 

Number of times molded (Heat history effects performances)... 

Productivity is directly related to cycle time. There usually is considerable common knowledge about a geometry and process conditions that will provide a minimum cycle time. Practices such as using thinner wall sections, cold or hot runners for TPs or hot or cold ones for TSs narrow sprues and runners, the optimal size and location of coolant (or heat) channels, and lower melt or mold heat, will decrease the solidification time reducing the cycle time. 

Mold Heating Cooling Part Conveyors Robotics... 

A hot metal mold will feel much hotter than a hot polyurethane or epoxy mold. This is because of the thermal conductivity of the mold material. For light metal molds, heat-resistant gloves must be worn. For larger molds, suitable mechanical handling must be employed. The handling equipment must be of suitable size and in good condition. 

Open Molding. Plastisol is poured into an open mold, heated to gel and fuse, cooled to solidify, and stripped out from the mold. Typical products are auto air filters, oil filters, truck flaps, and place mats. 

The necessary preheating and mold heating temperatures and mold pressure may vary considerably depending upon the thermal and rheological (refers to the deformation and flow properties of the plastic) properties of the plastic (Chapter 1). For a typical compression molding... 

Postcuring heat is usually below the actual molding heat. It is usually performed in a multistage heat cycle. The reinforcement system of the compound will dictate heating cycles. Products molded from compounds using organic reinforcements are postcured at lower heats than... 

Electrical heating, through the use of heater coils, strips, or cartridges, is the most popular method. Higher temperatures for faster cycles are easily obtained. Recognize that electric mold heating is only as fast as the wattage put into it. It is a cleaner system than steam that was used many decades ago. 

Close temperature control is required to obtain reproducible results, because the expansion of the polystyrene is a function of temperature. The polystyrene microspheres may be pre-expanded by steam or radiant heat and then added to the mold, heated in advance to a convenient temperature, such as 60°C. The mixed epoxy resin is then poured over the pre-expanded beads and allowed to cure. In this case, a limited amount of further expansion will occur as a result of exotherm or cure temperature to permit complete mold fill (10). A typical formulation is shown below ... 

The molds should have the ability to maintain constant temperature despite continual heat removal by the relatively cooler molding compounds this can be monitored by placing temperature sensors and heat cartridges to provide uniform temperature. Insulating blankets may prove beneficial in minimizing mold heat losses and variations caused by local air currents around the molds and presses. A cut out should be provided, which will cut off the power to the heat cartridges as and when it senses a few degree rise than the desired temperature. 

Fig. 4 (A) Stress relaxation curve of rotational molding grade ethylene copolymers. (B) Part density, which is indicative of the bubble content, measured after interrupting the rotational molding heating cycle at different heating times. (From Ref.. )...

Progress has also been made in part cooling. Portable and centralized chillers have been developed to cool the part in a minimum time. These closed loop systems use water or water-ethylene glycol combinations as the heat transfer medium. The application of heat transfer principles allows one to computer model the cooling process (35). For the new engineering resins such as polyamide-imide and polyphenylene sulfide, one must use mold heating. The use... 

Silica furnace containing integrally molded heating elements used for digestions and ashing... 

The ashing step is performed in a silica oven containing integrally molded heating elements, further minimizing the risk of contamination. 

Muffle furnace, silica lined, containing integrally molded heating elements and capable of maintaining a temperature of 525°C (model 51828 Moldatherm Furnace, Lindberg). 

FIGURE 4.3 Profiles of temperature either in the mold (extreme right) or in the rubber (right) and of state of cure (left) with a thickness of the rubber of 2 cm with the thickness of 1 cm for each slab of the mold, whereas the initial temperature is 20°C for the rubber and 180°C for the mold. Heating system on the external surface of each slab. Thermal and kinetic parameters in Table 4.1 with enthalpy of 14.3 J/g. Because of the symmetry, only half the thickness of the rubber-mold is shown, with the plane of syrtunetry at position 0. 

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