Into water glass investment casting: process, alloy and application knowledge

Water glass investment casting is also known as “lost wax casting”. It is a method of obtaining castings by coating several layers of refractory materials on the surface of the wax mold. After it hardens and dries, the wax mold is melted away to make a shell, which is then roasted and poured to obtain a casting. Since the obtained casting has high dimensional accuracy and surface finish, it is also called “investment precision casting”.

The types of alloys that can be produced by investment casting include carbon steel, alloy steel, heat-resistant alloy, stainless steel, precision alloy, permanent magnetic alloy, bearing alloy, copper alloy, aluminum alloy, titanium alloy and ductile iron. The shape of investment castings is generally more complex. The minimum diameter of the hole that can be cast on the casting can reach 0.5mm, and the minimum wall thickness of the casting is 0.3mm.

In production, some parts that were originally composed of several parts can be designed as integral parts by changing the structure of the parts and directly cast by investment casting to save processing time and metal material consumption, making the part structure more reasonable. The weight of investment castings is mostly a few tenths of a Newton (i.e., tens of grams to several kilograms). It is more troublesome to produce too heavy castings by investment casting, but the weight of large investment castings produced so far has reached about 800 Newtons. Solution casting is to make a model with fusible materials, and then coat the model with refractory materials. After hardening, the model is melted and discharged from the mold, thereby obtaining a casting without a parting surface. After the casting is roasted, it is poured.

Water glass investment casting process:

1) Wax mold making and pressing:

• Special molds for wax molds, steel, copper, aluminum, cut and made
• Wax mold pressing: paraffin, beeswax, stearic acid, rosin, etc., press the melted wax into the pressing mold, take it out after condensation, and remove the burrs to get the wax mold
• Wax mold assembly: several wax molds are welded on a direct casting rod. Shelling: wax mold is coated with paint, hardened, dried, etc.

2）Subsequent process flow

• Dip paint (quartz powder + adhesive paste) to make the surface smooth;
• Sanding (coarse quartz sand) purpose: thicken the shell
• Hardening (water glass + NH4CL SIO2) Chemical hardening
• Dewaxing: hot water or steam
• Roasting: heating to improve the shell strength
• Dewaxing and roasting
• Sand filling: pouring
• Sand filling: put the shell into the iron box, and fill it with dry sand around
• Pouring: pour while hot
• Sand removal and cleaning After cooling, destroy the shell, take out the casting, remove the gate, burrs, anneal or normalize to obtain the required mechanical properties

Steel casting processes applicable to water glass investment casting:

Cast carbon steel
Cast steel with carbon as the main alloying element and a small amount of other elements. Cast low carbon steel contains less than 0.2 carbon, cast medium carbon steel contains 0.2~0.5 carbon, and cast high carbon steel contains more than 0.5 carbon. With the increase of carbon content, the strength of cast carbon steel increases and the hardness increases. Cast carbon steel has high strength, plasticity and toughness, and low cost. It is used in heavy machinery to manufacture parts that bear heavy loads, such as rolling mill frames, hydraulic press bases, etc.; it is used on railway vehicles to manufacture parts that bear large forces and impacts, such as bolsters, side frames, wheels and hooks.

Cast low alloy

Cast steel containing alloying elements such as manganese, chromium, and copper. The total amount of alloying elements is generally less than 5, with greater impact toughness, and can obtain better mechanical properties through heat treatment. Cast low alloy steel has better performance than carbon steel, can reduce the weight of parts and increase service life.

Cast special steel
There are many varieties of alloy cast steels refined to meet special needs, usually containing one or more high-amount alloying elements to obtain certain special properties. For example, high manganese steel containing 11 14 manganese can resist impact wear and is mostly used for wear-resistant parts of mining machinery and engineering machinery; various stainless steels with chromium or chromium-nickel as the main alloying elements are used for parts working under corrosive or high temperature conditions above 650, such as valve bodies, pumps, containers for chemical industry or turbine housings of large-capacity power stations.