Isopipes

Cooling Core Pins Types

The Isopipe is used to cool (or heat) Core-Pins in mould tools by using its very high thermal conductivity to transport heat from one end of the Isopipe to the other. The liquid / vapour phase changes within the Isopipe and the vapour flow from one end allows large levels of thermal energy to be absorbed, transmitted and rejected with a maximum temperature difference of only 3 degrees C along the outer sheath

The ISOPIPE is inserted into the core-pin (drill size = Isopipe diameter) using thermal interface material to achieve a good thermal joint. Cooling water is passed over the exposed end (ideally 50% of the heated length, not total length).

Even when using engineering grade plastics, the Isopipe temperature will rarely exceed 1000C. The largest temperature gradients will occur through the molten / solidifying plastic and the steel wall of the core-pin. This situation gives the maximum heat transfer into the cooling water, which should preferably be of high velocity rather than high volumetric flow rate.

General features

Fast cycle times
More flexibility in product design
Easy to install
No sink marks
Reduced tooling and operation costs
Less waste and maintenance
Simplified tool construction
Lower water consumption
Suitable for use in cracked cores
Can be used to heat as well as cool core-pins
Uniform cooling

Use the largest diameter Isopipe possible to allow large surface areas to absorb and reject heat.

Isopipe Technical Notes

General Description

The ISOPIPE consists of an evacuated and sealed boiling-condensing system with capillary return (via an absorbent .Wick. structure) of the condensed working fluid from the condenser to the evaporator. By utilising the latent heat of vapourisation of the circulating working fluid, large quantities of thermal energy may be transferred considerable distances through relatively small diameters in an entirely passive manner.

Cooling Cores

The Isopipe method of cooling cores is illustrated in. Water circulation through cores means expensive tool costs and when in operation unforeseen troubles frequently occur. Any contaminants in the system soon begin to block passageways, particularly at bends, and scale deposition may even begin at low temperatures. When nucleate boiling within a core occurs it is usually at the tip and scale deposition is rapid, both restricting the water flow and reducing the cooling effect dramatically at the most vital region.

Chilled water may be used to overcome these problems but at this stage the remedy may be too late and the by-product is often, a tool that sweats. Apart from these problems, and including cracked cores, which will allow water seepage into the cavity, the downtime and maintenance cost often produce an average cycle time, and consequent expense, exceeding the anticipated production costs.

These problems can be eliminated by using the ISOPIPE to act as a thermal transformer, extracting high energy levels from the core and passively conducting the heat into the body of the tool, where adequate water cooling is readily available. Because no water enters the core no clogging or scaling can occur, even if the core is cracked no water can leak into the cavity. The necessity of chilled water is eliminated because of the high heat absorption and rejection rate of the Isopipe.

Indeed, in some applications this heat transfer system will work better with un-chilled water because the Isopipe power handling increases temperature. Consequently over cooling of some parts of the core, if chilled water is used, is eliminated and a product with much reduced stress and shrinkage marks may be produced. Thus the high heat fluxes encountered in the metal die casting and plastic moulding industries may be readily absorbed and transported. Even over considerable distances. Hot spots and associated temperature gradients may be similarly removed.

The Isopipe can replace mould fountains, cascades etc. It simplifies tool construction, no wear, no blocking of the waterways due to excessive scaling. These are some of the advantages Isopipe have over conventional water cooling systems.

Cores Converting into Isopipe

A Core may be turned directly into an Isopipe by capping or attaching an extension into the water cooled end. This process is usually undertaken if the diameter is small, or the cross section of the core is not circular. By using the hole in the core pin as the inner surface of the Isopipe a larger vapour space is provided, together with a slightly larger wicked area. This implied that a higher performance can be achieved. Inevitably, in a very small core pins this method of cooling may be the only practical method.