Temperature Control Channels

Proper temperature control channels to maintain correct balance between heated plastic and cooling via metal mould. 

The necessary molds for this application are basically mono-block molds with integrated steam and temperature control channels, as well as a steam- and wear-resistant coating developed specially for this process. 

The temperature control channel is the simplest and most commonly used temperature control element. It can be applied in many shapes, arrangements, and modifications. The cheapest way is to drill round channels. Physically, however, non-round geometries, due to the larger contact surfaces, are more effective. However, round temperature control channels impact the stiffness of the mold plate to a lesser extent. 

In general, temperature control channels should be located relatively close to the mold surface, the distance between channels should be as small as possible, and the channel diameter should be as large as possible. However, this is only achievable with restrictions because the stability of the mold plate must not be compromised. 

Since each molded part must be tempered individually, only rough ideas on the arrangement of temperature control channels can be given at this point ... 

The temperature control channels in the mold can be flown through in three basic ways discussed below. 

Figures 2.84 and 2.85 show two examples for flat temperature control. 0-rings are provided as sealing elements in two-layered mold plates with milled-in temperature control channels.

The temperature of molded part corners should particularly he taken into account, as the well-known corner warpage can be avoided. In the arrangement of the temperature control channels, heat dissipation is inevitably better in the counter sunk area than in the core area. This can be explained by the smaller contact area in the core. This leads to a displacement of the plastic polymer core in the direction of the core (Figure 2.86), wherein the contraction of the shifted residual melt causes a distortion of the corner geometry. 

The heat pipe (the operating principle is shown in Figure 2.92) is a self-contained system that uses the evaporation of a volatile liquid to transport heat. In this case, heat can be transported only by the evaporation/condensation process over the length of the pipe. Heat is only dissipated if the cold end of the pipe is cooled by a temperature control channel. The heat pipe is ideal for all the other places where temperature control channels cannot be directly accessed. Using the compact heat pipes, heat can be removed locally and can then be transferred to a geometrically favorable position. The heat pipe is therefore also suitable for tempering of slender cores and other inaccessible areas. 

However, it should be noted that the heat is only derived not dissipated for example, the copper elements have to be able to supply heat to a temperature control channel in other areas. The higher thermal conductivity of copper alloys in comparison to steel is limited and not comparable to liquid temperature control. 

For contour-dependent temperature control, the disassembly of the mold insert into single-layer elements is required (Figure 2.97) and into which the temperature control channel is milled in. Later, these layer elements are connected together in a vacuum brazing technology and then result in a uniform temperature control system. Figure 2.98 shows the comparison between a conventional and a contour-dependent temperature control. 

Before storing the molds, they should cool down, so that no condensation occurs on the mold surface and corrosion is thus inhibited. The temperature control channels are to be kept closed in order to prevent exposure to oxygen. Another possibility is that the temperature control bore holes are completely removed from water before the deposition. Corrosion is not only a problem for the temperature control channels. Oil, as a temperature control medium, forms decomposition products that usually accumulate in the tank of the temperature control system. At some point, it gets into the mold and can clogg riser holes in the mold cores. It is therefore not only essential to replace the temperature control medium, but also to clean the heater tank. 

A measurement point position like this is not suitable for regulating the mould temperature, because of the temperature variations referred to. The temperature gauge should therefore be sufficiently far away from the mould wall, so that at the measuring point the temperature variations have already been sufficiently dampened. But it should also be an adequate distance away from the temperature control channels, so as to exclude reverse effects from this side. A middle position between the mould wall and the temperature control channels is recommended. Because the temperature falls towards the clamping surface, the measuring point should naturally not he too close to this. It is in any case advisable to insulate the mould halves from the clamping surface, so as to reduce the interference factors. For high mould temperatures, economic considerations also require this. 

A microreactor was also applied to this reaction. The slit interdigital micromixer was purchased from IMM (Mainz, Germany). The width of the interdigital channels is 25 pm. HPLC pumps were used to feed the two reaction solutions. One is a mixture of Boc-AMP and 1.2 molar equivalents of r-BocaO. The other is a 50% aqueous KOH solution. The microreactor was immersed in a temperature controlled cooling bath at 15 °C. The product was quenched with an acid, and samples were taken for HPLC analysis. 

Investigations with the modular multi-channel [28,98] and silicon chip [19, 56-62] micro reactors demonstrate that by exact temperature control the oxidation of ammonia can be run with increased and deliberately steered selectivity. A major application is provided by carrying out former high-temperature reactions in the low-temperature regime. In the case of ammonia oxidation in the chip micro reactor, the yield of the value product NO was actually lower in that regime. In the case of the multi-plate-stack micro reactor, higher yields of the value product NO2 were achieved. 

A flow assay system (Fig. 3) enables ligand binding and functional activity measurements in glass channels with dimensions approximately 20 x 15 pm. It has a temperature-controlled stage to hold the chip. 

Temperature control is accomplished in one of three general ways. One method is by controlling the temperature of the platen, usually by means of an integral channel in the platen through which temperature-controlled heat transfer fluid flows. Second, the temperature of the slurry itself can be regulated prior to being dispensed onto the platen. Finally, a means of heating the backside of the wafer can be built into the carrier [42,43]. 

The surface trough was made of Lucite, 45 X 15 X 1.5 cm. and was divided into two compartments of equal size by a septum of Lucite, 1.5 cm. high. Cooling channels for temperature control were milled into the bottom of the trough. The monolayer was spread inside a paraffined mica frame which floated on the water and was firmly positioned by external mounts. The surface tension was measured with a double-hook torsion balance and a sand-blasted platinum Wilhemy plate. A Beckman model G pH meter with standard glass and KC1 electrodes was used to measure pH. 

---