In investment casting waxes are widely used as a pattern material with few exceptions. As the ultimate quality of castings in this process depends primarily on quality of wax patterns, so it is necessary to understand how best performance of wax – blend can be achieved. For the purpose, we will understand basics of wax moulding process.
Process of pattern – making needs either gravity pouring of molten wax or injection moulding of wax under pressure.
Gravity pouring is practiced when it is not possible to exert pressure on the mould (or only nominal pressure is permitted). In this case pouring is at comparatively high temperature to ensure proper fluidity. Mould material must be specially formulated to achieve low shrinkage values and cavitation to account for this high temperature.
Injection moulding in general, is preferred with semi-liquid or paste form of wax. To replicate the die for wax pattern, it should be filled at as low a temperature as possible to contract minimum on solidification.
Although for special requirements, billet injection is carried out by pressurizing solid blocks in to die, practically, considering mechanical set-up requirement etc. semi-liquid or the paste form is the best choice.
Selection of a wax blend for pattern – making must consider below mentioned points,
- Should be suitable for injection and other processes in current plant set-up
- Quality requirement of castings should be fulfilled by pattern performance on injection
While understanding the waxes we should know how the wax will perform in the shop floor condition and what is required to achieve its optimum performance, so it is very important to understand the nature of formulation of pattern – waxes.
Straight, Resin-filled & Water Emulsified Waxes
Normal straight formulation of pattern – wax is prepared from constituents, each of them
melting and forming a homogeneous melt.
When molten wax solidifies, it sets with dimensional shrink and cavitation or dishing effect, to reduce shrinking effects, a component may be added which is called filler and it does not melt but remains in the fine particulate suspension in the wax melt. Filler reduces the tendency to shrink of liquid wax thereby reducing the shrinkage percentage.
For this application, several natural or synthetic chemical entities have been tried in past. But research have resulted in the choice of synthetic resins, often styrene based homo or copolymers till date.
Water emulsified waxes are prepared by making slightly changes in normal straight formulation of pattern waxes so that with suitable emulsifiers, water added in the molten wax forms emulsion in the melt and fine droplets remain dispersed throughout the wax volume.
Water reduces the proportion of liquid which solidifies, reducing the shrinkage by that ratio hence it act as filler also these waxes are also called resin-filled waxes.
Due to function of water as a fillers in water emulsified waxes we can eliminate high initial cost of resin filler and later filler replenishment cost in subsequent cycles for reuse of wax after dewaxing.
Concept of Wax Conditioning:
Homogeneity of wax melt is very important to get good patterns.
The process to achieve the thoroughly homogenized phase of wax is called as ‘conditioning’ Need of wax conditioning arises due to poor thermal conductivity of waxes.
Total wax mass must attain the same physical form viz. semi-liquid, paste etc. and throughout maintain the same temperature. Generally, it is attained by slowly cooling wax molten at higher temperature under continuous agitation. Care must be taken to prevent air entrapment in the process of conditioning.
Conditioning is a very slow process and should be carried out before feeding into injection machine.
For achieving pattern quality is depend on function of injection conditions, wax conditioning, die design considerations, dedicated shop floor practice and very important quality of waxes, We, Saffroshine Organics Pvt,Ltd. is a leading investment casting wax manufacturer our waxes are available in the world market like India, Taiwan, China, Turkey, Germany, USA and other leading countries.