The waxes used are rarely pure substances; they are precisely formulated blends designed to meet specific requirements. They can be broadly categorized as follows:
- Pattern Wax (The Primary Model Material)
This is the wax used to create the initial replica (pattern) of the final metal part. It is the most critical category and has several sub-types:
Paraffin Wax: A petroleum-based wax, inexpensive and with excellent replication of fine detail. However, it is relatively soft, has high shrinkage, and can be brittle at room temperature. It is almost always blended with other waxes to improve performance.
Microcrystalline Wax: Also petroleum-based, but with finer crystals, higher flexibility, toughness, and better surface finish than paraffin. It is a key component in blends to reduce brittleness and improve shape retention.
Polymer-Modified Waxes (e.g., Ethylene-Vinyl Acetate – EVA): Adding polymers like EVA significantly increases toughness, flexibility, and resistance to deformation at higher ambient temperatures. This is crucial for large, thin-walled, or complex patterns that must support their own weight.
Filled Waxes: These waxes contain fine, dispersed fillers (such as thermoplastic resins or organic materials). The filler reduces total solidification shrinkage, improves dimensional stability and rigidity, and minimizes warpage. This is essential for producing dimensionally accurate patterns for engineering components.
Water-Soluble Wax: Typically based on polyethylene glycol (PEG), this wax is used to create internal cores or support structures that are later dissolved in water, leaving complex internal passages in the ceramic shell. It does not mix with regular pattern wax.
**2. Runner and Gating Wax
Used to form the channels (sprues, runners, gates) that deliver molten metal to the pattern. It is generally cheaper, harder, and has higher viscosity to build up thick sections without sagging. Its properties are optimized for easy removal and good metal flow rather than ultra-fine surface finish.
**3. Repair and Welding Wax
A softer, more pliable wax with excellent adhesion, used to fix surface defects (like bubbles or nicks) on patterns, attach gates, or join pattern segments seamlessly.
**4. Investment (Shell) Wax
A low-ash content wax sometimes added to the primary ceramic slurry or stucco to improve the bonding of ceramic layers and control shell permeability.
