What Is Slush Casting And What Products Can I Use To Do This?

What is Slush Casting?

Casting material is manually “slushed around” in the mould, creating a thin layer. This results in a hollow, lightweight casting.

What is the difference between Slush and Rotational Casting?

The difference between slush casting and rotational casting is that rotational casting is done by a rotational casting/moulding machine. The rotational casting machine allows the walls of the castings to be fine-tuned for thickness and consistency. Slush casting is more common for quick prototypes or samples and is not typically used for production casting.

Which resins are suitable for Slush Casting?

Not all casting resins are ideal for slush casting. Generally, this process is not good for for resins with working times longer than five minutes. A product with a longer working time of 22 minutes, would require a lengthy period of manual rotation. It can be done, but is unrealistic.

EasyFlo 120 Casting Resin (a polyurethane plastic) is a product we most often recommend for this process. It has a mix ratio of 1A:1B, a working time of 2 – 2.5 minutes, and a demould time of 15 – 30 minutes.

EasyFlo 120 is designed to gradually solidify over its working time, as opposed to “snap-set” (like the curing characteristics of EasyFlo 60). This gradual thickening over the last 30 – 45 seconds of the working time helps to provide an even coat.

This resin typically requires 5 – 10 minutes of manual rotation. If multiple coats are being applied, allow approximately 10 minutes before applying the next coat. This would provide enough time for the resin to gel and not pull away from the mould. When the final coat has been applied, allow 20 – 30 minutes before removing the casting from the mould.

How to Slush Cast?

Slush casting can be done in an open or closed mould. A small amount of resin is poured into the mould. The mould is manually rotated in all directions until a thin layer of resin coats the mould, creating a hollow part.

We suggest using enough resin to create a 1/4″ thick casting, which can require 2 to 3 coatings. To determine how much resin needs to be used, estimate the surface area of the mould and multiply by the thickness of the layer you intend to cast. Take this number and divide by the specific volume of the casting resin. This will result in the number of pounds needed for the casting.

Example:

8.0″ L x 8.0″ W x 0.125″ (thickness of the first layer of resin)= 8.0 in³.

8.0 in³ ÷ 26.9 in³/lb (the specific volume of EasyFlo 120 liquid plastic) = approximately 0.29 lb

TIP: Hollow slush-cast parts are often backed with lighter weight or less expensive materials, such as foam. Both rigid and flexible foams are frequently used.

Original Source: Polytek Development Corp.