Heat conducting pipes for tempering die casting dies

Newly designed heat conducting pipes for Installation in pressure die casting dies enable effective tempering an account of their high heat transmission capacities. They also require little space in dies and cores. The components have proved to be successful in practical use.

Heat conducting pipes have proved to be suitable for the solution of problems in the introduction and removal of heat in pressure and injection moulding. The SP pipes manufactured by Gerhard Speckenheuer GmbH have a range of use from 20 to 320 C, based an their own surface and up to 500 C based an the surface of the die casting dies.

Advantages of the heat conducting pipes. There are already advantages in the construction of pressure die casting tools. If heat conducting pipes are incorporated this simplifies the cooling circuits in the die, thereby saving time and costs. Their Installation also simplifies the assembly of the die and enables reduction of maintenance times an account of fewer cooling connections. This increases the die service life and thus contributes to reduction of die making costs. The advantages of the new system also manifest themselves in production.

Figure 1. Arrangement and functioning of heat conducting pipe

The optimized tempering enables improvement in the casting quality, especially the microstructure and dimensional accuracy. lt also facilitates removal of the casting and enables reduction in the amounts of release agents. Contingent on the design, in the extreme case it is possible to even re-use cracked dies.

Construction and functioning Figure 1 shows the construction and functioning of a heat conducting pipe. The main component consists of a closed tube produced in a highly conductive copper alloy, with an inner lining with a capillary action that incorporates a specific amount of liquid. The "cold" back end of the pipe can be additionally water cooled. Heat conducting pipes can transport large amounts of heat. Heat transport within the tube occurs through vaporization and condensation. The liquid vaporizes in the side facing the hot die contour, the vapour expanding to the cooler back end of the tube, where it condenses. The condensate returns into the vaporization zone by capillary and gravitational forces.

Figure 2. Location of heat conducting pipes in cores with different geometries

Installation in the pressure die The tube should be installed as near as possible to the die contour. For optimal tempering it is recommendable to use pipes with the largest possible diameter, the best being around half of the core diameter. Figure 2 shows proposals for the favourable location of the pipes in cores with a different cross-section. The following should be taken into consideration for the Installation depth and length of the pipe. Effective tempering is achieved when the 3 zones of the pipe - heat absorption, transport and heat removal - in each case make up a third of its total length. Figure 3 illustrates a favourable arrangement that fulfils these conditions. Because the thermal expansion of the pipe is greater than that of the tool steels it is recommended to provide an axial plag of around 0.3% of the pipe length. It should also be ensured that the core diameter is approx. 0.05 to 0.1 mm greater than the corresponding heat conducting pipe, thereby easing Installation. Contact with the die material is improved by thermally conductive pastes. The heat conducting pipes have a point angle of 120. Removal is simply effected through the incorporated extraction thread.

Tempering with heat conducting pipes. The pipes can not only be used for cooling but also for the introduction of heat into the contact area during the heating up phase. Because the pipe can be installed considerably nearer to the die contour than cooling cores the heat transfer is correspondingly higher. The Standard range of heat conducting pipes and pins available exstock have lengths between 50 and 250 mm and diameters between 2 and 16 mm.

figure 3. correct selection of length

Result: The new Super-Pipe SP heat conducting pipes provide a medium for the effective tempering of pressure die casting dies that, an account of the new manufacturing process, have favourable price/performance ratio. These components offer advantages in the design and manufacture of pressure dies and, through the transportation of large amounts of heat, improve the quality of the castings.