In fact, the terms "medium-temperature wax" and "low-temperature wax" are names used in the early stages to refer to mold materials. Although many people still use these terms, strictly speaking, they should be referred to as medium-temperature mold materials and low-temperature mold materials.
With the rapid development of science, technology, and industrial production, the application range of the investment casting process continues to expand. However, wax materials have struggled to keep up with the rapidly evolving investment casting industry in terms of performance and quantity. As a result, various organic substances, plastics, and inorganic salts have been successively adopted. Some are added as fillers to wax materials, while others directly replace wax materials for mold making. Therefore, the terms "wax molds" and "wax materials" have gradually been replaced by "mold materials" and "investment mold." However, in conventional usage, people still habitually refer to them as "wax molds." It's just that the term "wax mold" now refers to something different.
Due to the wide variety of mold materials and their different compositions, classification can be complex.
There are two recognized classification methods:
The first classification method is based on the thermal stability of the mold material. Thermal stability is an important property of mold materials and is closely related to their melting point. Generally, the higher the melting point, the higher the thermal stability. Conversely, lower melting points indicate lower thermal stability. Therefore, based on the melting point of the mold material, it can be classified as high melting point mold material, medium melting point mold material, or low melting point mold material. From the perspective of thermal stability, they can also be categorized as high-temperature mold materials, medium-temperature mold materials, and low-temperature mold materials.
Hence, when we talk about "low-temperature wax" and "high-temperature wax," it is evident that we are distinguishing them based on the thermal stability of the mold material. This is the first point.
The second classification method is based on the composition of the matrix material of the mold material. Based on modern developments in mold materials, they can be divided into wax-based mold materials, rosin-based mold materials, plastic mold materials, water-soluble mold materials, and filler mold materials.
Now let's further explain the first type of mold material classification.
1. Low-temperature mold materials: These typically have a melting point below 70°C, low strength, poor thermal stability (30°C), significant shrinkage, and varying dimensions with changes in room temperature. The commonly used typical mold material in China is composed of 50% paraffin wax and 50% stearic acid. However, these materials have a simple production process, high mold recovery rate, reusability, and lower cost. They are generally produced through paste pressing, and manual operation, and can be dewaxed with hot water. These mold materials are usually used together with sodium silicate binders.
2. Medium-temperature mold materials: Mainly include rosin-wax-based mold materials and filler mold materials, with a melting point between 70-100°C. They exhibit higher strength, good thermal stability (35°C), less shrinkage, excellent dimensional stability, smoother surface roughness when produced through liquid pressing, and good replication performance. They can be reused but require more complex production processes and have higher costs. Dewaxing can be done using water, steam, or microwaves. These mold materials are generally used together with silica sol binders. They are often produced using wax injection machines.
3. High-temperature mold materials: These include rosin-plastic-based, plastic, and salt-based mold materials, with a melting point above 100°C. These mold materials have high strength, good thermal stability, and minimal shrinkage but require complex production processes and cannot be reused. They are usually removed through flash burn, water, or organic solvent methods. They are costlier. It is evident that water-soluble mold materials and 3D printing mold materials belong to this category. In the book "Investment Casting Technology," high-temperature mold materials are described as having a significant thermal expansion, which often causes the shell to crack due to insufficient strength during demolding.
