Ketchup - The Tomato Slurry

We all struggled with getting ketchup out of the bottle. Today, you are no longer with the squeeze bottles but with good old glass bottles. You tried to get the ketchup out. You clapped on it and tried to shake it, but nothing happened. You continued and tried harder. Suddenly, the whole plate was full of ketchup.

But why has ketchup behave like that? And what does the favourite dipping sauce for French fries have to do with Rheocasting?

At the core of Rheocasting lies a metal slurry, a solid and liquid aluminium mix that behaves very differently than the fully liquid melt used in HPDC. And the secret to that difference is the solid fraction. Once you exceed 35% solid content in your slurry, everything changes. Flow can become laminar with the right tool design. The melt front doesn’t splash; it slides. Air isn’t trapped; it’s pushed aside. This shift in behaviour means you can fill parts with tall, thin ribs and long flow paths while avoiding shrinkage porosity and cold shuts with lower pressures.

Thixotropy is the basis of all of this, and it’s the defining characteristic of Rheocasting slurries and ketchup. When shear force is applied, the viscosity drops, allowing the semi-solid slurry to flow smoothly. Gravity and shaking are used for the ketchup. The plunger, combined with a narrow cavity, is the perfect shear force generator in casting.

A Slurry is a Pocket Warmer

In Rheocasting, another effect boosts the flow length even further besides the good flow characteristics of the thixotropic behaviour. The globular solids in the slurry act like miniature pocket warmers. The surface area of these globulites is much larger than the surface area of the part, so most solidification occurs on these globulites. The latent heat is released, not into the cooling system; it goes back into the surrounding melt. This internal redistribution of heat keeps the melt hot and flowable for longer.

The result? Melt fronts remain hot enough to fuse and feed properly, even at the furthest corners of the cavity. This self-sustaining thermal property means longer flow lengths and evenly distributed high mechanical properties.

Expand into new Applications

These thixotropic slurry properties, in combination with the pocket warmer effect, expand the possibilities of casting. Classical HPDC keeps its relevance, but with Rheocasting, you gain a tool for new applications beyond what we already cast. The slurry, and precisely the solid fraction, is your gateway to better casting quality, improved performance, and access to new markets that demand more than HPDC can offer.

Ready to learn more? Schedule your free consultation today and take the first step toward success with Rheocasting.