Sequential molding

Especially cavity temperature sensors are increasingly used to control the injection molding process. Here, the arrival of the melt front on the sensor is detected in real time and used for switch over operations in real time. In contrast to the cavity pressure measurement, the position of the melt is always known this way and can he optimized with the help of programmable delay times. This allows moving weld lines in a certain direction, and the meeting of the melt (e.g., in sequential molding) can he optimized [8]. 

Figure 5.23 shows a door sill from the automotive sector that is produced in the sequential molding process. After opening the first nozzle (1), the melt reaches the first cavity temperature sensor, which automatically initializes the opening of the second nozzle (2). Following the same principle, the following nozzles (3 and 4) are automatically opened and the melt flow can be optimized with the help of programmable delay times. 

In classical sequential molding, the opening and closing of various nozzles is usually path- or time-controlled. In this method, the position of the melt is unknown, which is why an optimization of weld lines or the melt flow is practically impossible. 

Other methods based on the cavity pressure are also not suitable for optimizing sequential molding processes, since a pressure threshold, which could be used to open a nozzle, can only be set when a pressure rise has occurred. However, the location of the melt at this moment is unknown because the position depends on the viscosity of the melt. An optimization of weld lines or a targeted manipulation of the melt flow is a function of pressure and is therefore not possible either. 

To enhance water-vapor- or gas-barrier properties, layers of different plastics may be injected together or sequentially. Multilayer injection-molded pieces may be prepared as packaging or for blowing into bottle or jar shapes. 

Injection stretch-blow molding may be performed on a single one-stage machine in sequence or on two independent sequential two-stage machines. PET carbonated beverage botties are usually produced by injection stretch blow molding. 

Cold curing permits the formation of dual density foam products. We either sequentially inject different formulations or we mold the first foam then mold the second around or on top of it. When making dual density foams, it is important that the first component develop a continuous skin prior to the injection of the second reactive mixture. 

The effect of mutation is different in case of stopped samples, but the phenomenon cannot be completely avoided. Here, the experimental time period At is determined by the poison diffusion. The catalyst poison solution is sprayed on top of a reacting sample and then diffuses into the core of the sample where it stops the reaction sequentially layer by layer. This leads to small inhomogeneity in the sample, since the reaction near the upper surface is stopped earlier than the reaction near the bottom of the mold. 

Control cine propagation in thick parts by curing from inside to outside (hollow parts), or cure sequentially along part, which can be done by partial heating of the mold... 

According to Challenger (127), arsenate is transformed to trimethyl-arsine by the mold Scopulariopsis brevicaulis, by sequential reduction and oxidative methylation of the arsenic species (Fig. 7). The proposed intermediates in the pathway were MMA, DMA, and TMAO. Although Challenger could not detect these compounds, when they were added to a culture of S. brevicaulis trimethylarsine was formed. Challenger (129) considered that the likely source of methyl groups was S-adeno-sylmethionine (AdoMet), which had previously been identified as an... 

Two-component injection machines, using separate injection units for each of the two components perform the standard sandwich molding process. This process is characterized by a sequential injection of the two components using the same gating system. After filling the mold partially with the skin material with one injection unit the core component will be injected by the second injection unit. In order to avoid flow marks on the part surface a simultaneous phase is inserted between the injection of skin and core components. The final packing phase may be performed either with the core or the skin component. 

Figure 6.1 2 Examples of different shaped sequential extrusion blow molding products...

Thielen, M., Blow Molding, Sequential Coextrusion Advanced Technology Opens Door into a New World of Tailored Parts, Modem Plastics Encyclopaedia, 1999. 

Large parts with long flow paths require many gates. Here cascading gates (sequential injection molding) will exclude weld lines. 

Female gametes of the water mold Allomyces prefer to use the sesquiterpene sirenin 29 as an attractant for the opposite sex cells. The sea weed Achlia bisexualis mutually coordinates and controls the processes of the formation and growth of both male and female gametes by a sequential release of a set of exohormones into water. One of the most important participants during this interlude to mating is the steroid anteridiol 30. ... 

Two basic methods are used in this process to deliver material to the processing units. These are extrusion and injection. In the next step, the preformed material is expanded to form parison. There are many commercial variations on this basic technique some of which include continuous-extrusion-blow-molding, coextrusion-and-sequential-blow-molding, and injection-stretch-blow-molding. Both extrusion and injection molding are the subjects of later discussions below, we will concentrate here on the parison formation, its processing, and the related effects. 

In contrast to the thermoset IPNs, thermoplastic IPNs can be processed in standard extrusion and molding equipment. They are made either by mechanical blending or chemically by sequential polymerization. 

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