Water glass investment casting (also known as sodium silicate casting) is a form of lost-wax casting that uses a water-soluble sodium silicate binder in the ceramic shell.
As one of two main investment casting methods (the other being silica sol), it provides a balance of precision and cost-effectiveness.
Originating from traditional lost-wax techniques in Asia and Europe, water-glass casting gained industrial traction in the 20th century as foundries sought a lower-cost alternative to colloidal-silica processes.
By using common materials (quartz or silica sand with alkali silicate binders), this process is well suited for medium-precision, high-complexity parts where budgets are tighter.
Typical water-glass castings range from a few hundred grams to 150 kg, with maximum dimensions around 1m, making it ideal for larger, cost-sensitive components.
What Is Water Glass Investment Casting?
Water glass casting is a variant of precision investment (izgubljeni vosak) casting in which sodium silicate (“water glass”) serves as the ceramic binder.
U praksi, wax (or plastic) patterns are made and assembled into a tree.
The patterns are repeatedly coated in a slurry of fine refractory particles bound in sodium silicate solution, then covered with progressively coarser stucco layers to build up the shell.
Once the shell cures, the wax is melted or boiled out, leaving a hollow mold cavity. Molten metal (typically steel or iron alloys) is poured into this ceramic shell.
After solidification, the shell is broken away to reveal the cast part. Ukratko, water-glass investment casting “invests” a wax master in a sodium-silicate-based ceramic to form the mold.
Compared to silica-sol investment casting (which uses colloidal silica and zircon-based sands), the water-glass method trades some surface quality for lower material cost and simpler processing.
Why Use Water Glass?
Water glass casting is popular because it reduces cost and processing relative to other precision methods.
The sodium silicate binder and conventional silica sands are inexpensive and easy to handle, so tooling and materials cost much less than for colloidal-silica shells.
Na primjer, water-glass systems avoid the high expense of silica sol and specialty sands, yielding lower per-part investment cost.
The process also eliminates many secondary operations: parts come out near-net-shape (often requiring little welding or machining).
U praksi, water-glass castings can capture very complex geometries (with undercuts and thin webs) without cores, simplifying design.
According to industry sources, water-glass casting offers “complex design without draft angles” i “higher accuracy compared with sand casting”,
while avoiding the expensive cores, kalupi, or weldments that many large sand-cast parts need.
This flexibility makes it attractive for small-to-medium production runs where tooling costs must be minimized.
Istovremeno, water-glass parts are generally more accurate than sand casting.
Typical dimensional tolerances are in the range of ISO CT6-CT9, roughly matching fine sand-cast tolerance classes or lower-end investment casting classes.
Surface finishes are correspondingly moderate: on the order of Ra ~6–12 μm (Ra 250–500 μin),
better than green sand casting but rougher than silica-sol investment castings.
Ukratko, water-glass casting is chosen when one needs the complex shapes and reduced secondary work of lost-wax casting,
but tighter budget or larger size make the higher cost silica-sol process impractical.
Pregled procesa
Water-glass investment casting follows the general lost-wax procedure with a few differences in mold materials:
Wax Pattern and Tree Assembly.
A master pattern is produced (by injection molding, 3D Štampanje, or hand sculpting) and a pattern die/mold made if needed.
Wax replicas of the part are created from this master. Multiple wax patterns are then assembled onto a common sprue (forming a “tree”) using wax gates and feeders.
This wax cluster will form many castings in one pour. The wax surfaces are “dressed” to remove seams or defects, yielding an as-needled finish on each pattern.
Zgrada školjke (Ceramic Coating).
The wax assembly is repeatedly dipped into a refractory slurry of very fine sand or zircon flour suspended in a diluted sodium silicate solution.
Each dip coats the wax in a thin ceramic layer (often 0.5–1 mm) before stuccoing with coarser sand.
After draining excess slurry, a stucco layer (larger silica sand granules) is applied by pouring or fluidized bed to bond to the sticky slurry.
The cluster is then allowed to harden (often air-dried or low-heat cured). This coat-dry cycle is typically repeated 4–7 times to reach the necessary shell thickness (usually 5–15 mm total).
During this sequence, later coats use coarser and sometimes different refractories (e.g. fine silica first coats for detail, coarse quartz sand in backing layers) to maximize strength and permeability.
In water-glass processes, quartz/fused-silica sands and alumino-silicates are common refractories. The entire shell is finally dried thoroughly (sometimes in humidity-controlled ovens) to remove moisture.
Dewaxing i pucanje.
The hardened ceramic shell is dewaxed by melting the wax out of the mold.
Unlike silica-sol shells (which typically burn out wax in a burnout furnace or with flame), water-glass shells are often dipped into hot water or exposed to steam to melt the wax.
The purpose is to quickly clear the wax while minimizing shell stress (sodium silicate shells are stiffer when cold).
After dewaxing, the shell is fired (sintered) at high temperature (often 800–1000 °C) to strengthen the ceramic and to burn out any remaining organics.
This also causes the sodium silicate binder to sinter and partially vitrify, forming a rigid, gas-permeable mold.
Metal Pouring.
Molten metal is poured into the pre-heated shell in the usual manner. Because water-glass shells use conventional silica sands, their heat capacity and thermal conductivity are similar to sand molds.
The shell supports the metal until solidification (with minimal shrinkage cavities if risers are used).
Shell Removal and Finishing.
Once solid, the ceramic shell is removed by mechanical means (e.g. shot-blasting, vibration or hammering) to reveal the cast parts.
Residual quartz sand is cleaned off. The casting tree is cut apart, and gates and risers are trimmed.
Final završna obrada may include grinding, CNC obrada, i površinski tretmani as needed.
Because the initial shell finish is moderate, water-glass castings often require some surface grinding or machining, but less so than green-sand castings.
Crucially, the water glass process differs from a silica-sol process mainly in binder and dewax method.
In water-glass casting, sodium silicate (alkali silicate) sets by drying and curing, whereas silica-sol (colloidal silica) shells harden primarily by gelation.
Dewaxing is performed with hot water (a wet dewax) instead of flame. These differences affect cycle time and quality.
Na primjer, wet-dewax is gentler on brittle shells, but it requires waste-water handling. Also, water-glass shells generally have lower thermal stability than zircon-containing silica-sol shells, as discussed below.
Binder System
The binder in water-glass casting is sodium silicate solution (commonly Na₂O·nSiO₂). Chemically, water glass is highly alkaline (pH ~11–13) and made with a certain silica-to-soda ratio.
Typical formulations range from a 2:1 do 3.3:1 SiO₂:Na₂O weight ratio (often expressed by module, e.g. M=2.0 means about 2.3 parts SiO₂ per Na₂O).
The ratio and solids content control key properties. Lower ratios (more Na₂O) give a more fluid slurry and faster set-on-drying, but also a more hygroscopic and lower-refractoriness binder.
Higher ratios (more SiO₂) increase heat resistance and lower pH.
Water glass is water-thin (viscosity similar to water) and cures by evaporation and mild heat. As it dries, it forms a rigid amorphous silicate glass network.
The binder is hygroscopic, so shells must be thoroughly dried before firing or exposure to humid air or water, or they can re-soften and degrade.
In service, residual moisture can lead to steam pockets or porosity if metal is poured too hot. The curing stage typically includes baking at 100–200 °C to harden the shell fully and drive off moisture.
Advantages of sodium silicate binders include their low cost, unlimited “shelf life”, and ease of use (no toxic solvents or acid catalysts).
They set by simple drying (or with a salt cure) and yield very stiff shells.
Međutim, limitations exist: their high alkalinity can attack refractory grains or metal (especially aluminum, causing gas pickup), and their glassy nature gives lower high-temperature strength than silica-sol shells.
Općenito, water glass shells soften if heated above ~800–900 °C, so they suit steel/iron alloys but are marginal for very hot-casting alloys.
Despite this, sodium silicate remains a proven binder in the industry. It is one of three conventional binders (along with ethyl silicate and colloidal silica) commonly cited for investment mold making.
Shell Materials and Construction Techniques
The shell for water-glass casting is built almost entirely from silica-based refractories. U praksi, the primary materials are silica or quartz sand (fused or crystalline), possibly mixed with alumino-silicates.
Typical particle sizes for prime (fine) coats might be 100–200 mesh (75–150 μm) to capture detail, while backup coats use coarser sand (e.g. 30–60 mesh).
Zircon is rarely used in water-glass shells (unlike silica-sol shells) due to cost – instead, cheaper silica sands are employed.
Finer alumina or titania flour can be added to improve thermal shock resistance, but the base is silica.
pH control is crucial in the slurry. The sodium silicate binder is very alkaline, so often a small amount of buffer or salt (like sodium bicarbonate) is added to adjust gel time and prevent immediate cure.
Manufacturers monitor the slurry pH (often around 11–12) and viscosity to ensure consistent coating thickness. Overly high alkalinity can cause the first coat to gel prematurely on the wax.
U praksi, water-glass shells use 4 do 7 coating layers (prime coat plus several stucco-backed coats).
Na primjer, an initial dip in a fine silica slurry is followed by stuccoing with fine quartz sand (this “prime coat” locks in pattern detail).
Subsequent coats use progressively coarser sands to build strength. Each coating must dry (often 1–2 hours at room temperature or faster in a low-heat oven) before the next coat.
The final shell thickness is usually on the order of 5–15 mm total.
During drying, temperature and humidity are carefully controlled – too rapid drying can crack the shell, while too slow drying can cause running or distortion.
Compared to silica-sol shells, water-glass shells tend to be strong but less refractory.
Fused silica layers give decent hot strength up to ~900 °C, but beyond that the sodium silicate glass network can begin to soften.
By contrast, silica-sol shells often use zircon and alumina layers that remain stable above 1200 ° C.
In other words, silica-sol moulds can better withstand the higher pouring temperatures of superalloys, whereas water-glass shells are typically limited to steels and irons.
Casting Metals and Compatibility
Water-glass casting excels with common ferrous alloys. Typical steels include Carbon čelik, nisko- and medium-alloy steels, heat-resistant Nerđajući čelici, and manganese steels.
Cast irons (grey and ductile) are also commonly cast. These alloys can be poured in the 1400–1600 °C range without catastrophically damaging the silica shell (with proper heat schedules).
In fact, water-glass is especially popular for wear parts and heavy components made of steel, where the extra shell strength (compared to sand cast) and complexity pay off.
Water glass is less suited to reactive or light metals. Aluminum and magnesium alloys, na primjer, require very dry, clean shells.
Any moisture or soda in the shell can generate hydrogen porosity in aluminum or cause oxidation.
Titanium and other reactive alloys usually demand silica-sol or ceramic shell systems (or vacuum melting) because water glass shells do not have the required inertness or purity.
(Practically, lost-wax casting of titanium is done almost exclusively with refractory zircon/alumina-shell systems, not water glass.)
Thus, metallurgical compatibility is a key consideration: water glass is chosen when the cast metal is compatible with silica (ferrous systems) and the process economy is needed.
In terms of metallurgy, water glass shells can influence casting quality.
Na primjer, carbon steels may undergo slight carburization at the shell interface if dewaxed with acidified water, so neutral water is used.
Gas permeability of the ceramic helps vent hydrogen and gas; međutim, any inadequate dewax or moisture can produce gas porosity.
Shrinkage porosity is managed via risers and vents as usual.
Općenito, water-glass castings behave metallurgically like other precision castings of the same metal – the shell chemistry has minimal alloying effect but can slightly alter surface decarburization.
Proper process controls (like vacuum or inert-atmosphere pouring for certain steels) may be applied as needed, but are independent of the binder type.
Dimensional Accuracy and Surface Finish
Water glass investment castings achieve moderate precision. Dimensional Tolerancije are typically ISO CT7-CT9 for general dimensions. (For fine walls, tolerance may relax to CT9 or CT10.)
To put this in perspective, ISO CT7 on a 50 mm feature allows about ±0.10 mm deviation, whereas CT6 would be ±0.06 mm.
U praksi, small parts and well-controlled processes can approach CT6-CT7,
but larger or more complex castings often are in the CT8-CT9 range.
This is comparable to fine sand casting tolerances.
By contrast, high-end silica-sol castings can reach CT4-CT6 on small dimensions, so water glass is less accurate by about one tolerance grade.
Quality-conscious shops will specify the tolerances based on ISO 8062, often noting “CT8” as a baseline for water-glass processes.
Surface finish is likewise coarser than silica-sol but smoother than sand cast. Tipičan surface roughness for water-glass castings is on the order of RA 6-12 μm (250–500 μin).
One foundry reported that water-glass castings reached roughly Ra = 12.5 μm in comparison tests. U kontrastu, silica-sol parts may achieve Ra 3–6 μm.
The higher roughness of water glass is due to the larger grain sizes in the shell and the nature of the sodium-silicate binder.
Factors that affect the finish include slurry solids content, stucco grain size, shell thickness, and pattern quality.
Na primjer, finer prime-coats and additional prime layers can improve surface quality.
Nonetheless, designers should expect a rougher initial surface: typical castings often need light grinding or machining to reach smoothness around Ra 3–6 μm for critical surfaces.
To manage accuracy, most shops use dimensional inspection (calipers, Cmm, mjerači) on first-parts and production samples.
Since the wax pattern and tree introduce some variability, careful layout and shrink compensation are needed.
The coefficients of thermal contraction for steel (about 1.6 mm/m·100 °C) are used to scale patterns. Process documentation defines shrink factors and tolerances per ISO.
Kontrola i inspekcija kvaliteta
Quality control in water-glass casting mirrors other foundry disciplines. Critical steps are inspected at multiple stages:
- Shell inspection: Before pouring, shells are examined for cracks, blisters, or incomplete coating.
Contractors often measure shell thickness with ultrasonic gauges and verify that each layer is uniform. Any delamination or pinholes can cause casting defects.
Containers of wet slurry are monitored for pH and solids; variations can produce weak shells. Dryer ovens are checked for even heat distribution. - Dimensional checks: After shakeout and finish-machining, castings are measured against design dimensions.
First-article parts typically undergo CMM inspection to verify critical dimensions to within the specified tolerance class (e.g. ISO CT8).
Simple gauge blocks or plug gauges are used for hole diameters. Because the tree pitch and wax shrinkage add small errors, it’s common to adjust pattern master dimensions if runout occurs. - Defect detection: Water-glass castings may suffer defects like gas porosity, uključivanja, or shell fusion defects.
Common inspection methods include X-ray/radiography (to find internal cavities or inclusions), fluorescent penetrant (for surface cracks and porosity), and magnetic-particle testing (for ferrous parts).
Where appropriate, pressure testing or flow tests are applied. Metallurgical analysis (macro etch, micrographs) can be used during process development.
All testing should reference standards (e.g. ASTM E165 for penetrant, ASTM E446 for radiography) to define acceptance. - Process documentation: Strict traceability is maintained on water-glass casts. Records include slurry mix ratios, cure schedules, and furnace times.
Many foundries use in-process checklists (temperature logs for dewax ovens, humidity logs for drying rooms, and binder usage logs).
For high-reliability parts (e.g. Aerospace komponente), a full heat code and chemical/physical certification accompany the part.
ISO 9001 or Nadcap standards may govern documentation in critical industries.
Overall, the control philosophy is to standardize every step so that any casting failure can be tracked back to its root cause (e.g. an unstable slurry or a missed drying cycle).
Economic Considerations
Water-glass lost-wax casting is valued for ekonomičnost in suitable applications. Key economic factors include material cost, labor, cycle time, and yield:
- Materijali: Sodium silicate binder and quartz sand are inexpensive compared to colloidal silica and zircon.
Na primjer, sodium silicate solution may cost a few cents per kilogram, whereas colloidal silica binders cost an order of magnitude more.
The salts or accelerators used are minimal. Wax patterns (especially if 3D-printed) add cost, but yield is high.
There is some scrap ceramic waste (broken shell) but it can often be recycled as sand. Overall, consumables are low-cost. - Labor and processing time: Building a water-glass shell is labor-intensive, requiring multiple dips and drying cycles.
Cycle times of 24–72 hours from wax tree to pour are typical (faster than high-temp silica-sol which can take longer cures).
The wet dewax step is longer (immersion vs open flame burn), but this is usually an overnight soak. Labor is needed for pattern prep, coating/stucco operations, and shakeout.
Despite this, the lower tooling costs and reduced machining often offset higher labor.
In a cost model, water glass can be competitive when part volumes exceed a few hundred per year, especially for heavy or complex parts that would be very expensive in sand or die casting. - Throughput: Single-purpose water-glass lines can run continuously, but each build (shell loading, dewax, fire, pour, knock-out) handles only the parts on that tree.
Throughput is moderate; few hundreds of kilograms of castings per batch might be normal. Međutim, automation exists for wax injection and shell spraying.
The limiting step is often dewaxed and firing, which can be batch ovens with defined loads. Effective scheduling (stacking trees) can improve utilization. - Yield and scrap: Because the process is precise, scrap rates can be low if controlled. Međutim, any shell crack or metal leak-through yields a total loss of that casting.
Failures due to shell defects (e.g. post-dewax cracking) are minimized by tight process control.
Compared to sand casting, water-glass generally has higher yield since parts are easier to clean and nearly net-shape.
Compared to silica sol, yield is similar or slightly lower (silica-sol shells can be more forgiving of dewax issues).
A rough cost comparison might show that water-glass casting can be 50–70% cheaper per part than silica-sol casting for medium-precision steel parts,
due to lower material and tooling cost, albeit with modest loss of surface quality.
It is more expensive than cheap sand casting per unit, but because final parts need much less machining, The total finished-part cost can be competitive.
Ukratko, water-glass casting allows companies to shift cost from machine hours to process time,
which is often advantageous for parts that are complex or low-volume enough that dedicated tooling is not justified.
Industrijske aplikacije
Water-glass investment casting finds its niche in heavy-duty and complex components across several industries. Notable applications include:
- Machinery and heavy equipment: Components for mining, ulja & plin, and construction machinery often use water-glass casting.
Na primjer, zupčanici, Kućišta pumpe, ventili, and impellers in these sectors benefit from the strength of steel and the geometric freedom of investment casting.
Water Glass Casting Stainless Steel Valve Pipe Fitting - Agricultural parts: Parts like tractor housings, plow components, and heavy farm equipment linkages are made this way.
The ability to cast ductile iron or low-alloy steel shapes (e.g. tiller parts, seed drilling plates) with intricate profiles is a key advantage. - Automobilski: While not common for mass-produced car parts, water glass casting is used in low-volume automotive or truck components (e.g. small batches of steering knuckles, heavy suspension arms, brake components for specialty vehicles).
Its precision surpasses sand casting for critical fit parts, yet remains cost-effective for moderate runs. - Industrial valves and pumps: Cast iron and steel valves, pump bodies, and flanges often come from water-glass investment molds.
These parts need complex internal passageways and a good surface finish (to avoid leakage) – water-glass casting yields valves ready for machining without cores. - Construction and architectural castings: Povremeno, decorative or structural iron/steel elements (like flanges, hardver, or ornate supports) are cast via water-glass.
The process can capture fine artistic details while using affordable sand, making it suitable for specialty castings (e.g. bronze replacement in architectural elements). - Offshore and maritime components: As mentioned by industry sources, parts for trailers, cranes, and marine rigs utilize this method for durability in harsh environments.
Overall, water-glass casting is chosen in industries that demand robust ferrous castings with moderate detail at reasonable cost.
It competes with sand casting when higher accuracy or net-shape detail is required, and it competes with silica-sol investment casting when large size or budget constraints make the latter too costly.
Comparative Analysis
Compared to other casting methods, water-glass investment casting occupies a middle ground:
Water Glass vs Silica-Sol Investment Casting:
Silica-sol (colloidal-silica binder with zircon flour) produces the finest detail, best surface finish (Ra as low as 3–6 μm), and tighter tolerances (ISO CT4-CT6).
Međutim, it is more expensive: silica sol solutions and zircon sands cost significantly more, and the process requires flame burnout and higher firing temperatures.
Water-glass casting, Suprotno tome, has a coarser finish (~Ra 6–12 μm) and wider tolerances (CT6-CT9), but uses cheap materials and a simpler dewax.
Water glass shells also tend to be stronger in handling before pouring (they are very rigid after drying) and can be thicker, which benefits heavy pours.
In summary, silica-sol is chosen for high-precision, small parts; water-glass is chosen for larger, tough components where surface finish can be sacrificed.
Water Glass Investment Casting vs Pijesak Livenje:
Livenje pijeska (green sand or chemically bonded) is the lowest-cost, most flexible mold-making for large parts.
Međutim, sand castings have very rough surfaces (Ra > 25 μm, often 50–100 μm) and loose tolerances (ISO CT11 or worse).
Water-glass casting gives significantly better surface and accuracy (as noted above) at higher cost.
If a sand-cast part requires extensive machining or repair (like welding in cores), it may be cheaper to use water glass.
Also, certain complex shapes (tanki zidovi, internal voids) are hard or impossible in sand without cores; water glass easily produces such shapes.
The trade-off is that sand casting scales better for extremely high volume (die molds or molds that can be used many times),
whereas water-glass is limited to around 150 kg per mold and requires multi-day cycles.
Shell Strength and Thermal Behavior:
Water glass shells are composed of fused-silica layers, which are slightly less refractory than the zircon or alumina layers often used in silica-sol shells.
This means water-glass shells typically have a lower maximum service temperature and may allow more metal–shell reaction in very hot pours.
U praksi, though, both methods produce shells that easily withstand steel/iron pour temperatures.
In terms of strength, both silica-sol and water-glass shells are rigid after firing, but silica-sol can maintain structural integrity at higher temperatures.
Best Use Cases:
Summarizing best uses, water-glass casting is ideal for medium to large steel/iron parts where high precision is not critical,
such as pump housings, gear blanks, heavy machinery parts, and any component where cast-on features save welding.
Silica-sol is best for small-to-medium high-precision parts (Aerospace komponente, nakit, Medicinski implantati, small stainless parts).
Green-sand casting wins for massive heavy parts or extremely large volumes where tight detail isn’t needed (e.g. large housings, blokovi motora, pump casings in bulk).
The table below highlights a few comparative metrics:
- Hrapavost površine (typical Ra): Silica-sol ~3–6 μm; water-glass ~6–12 μm; zeleni pijesak >25 μm.
- Dimensional Tolerance: Silica-sol ISO CT4–CT6; water-glass ~CT6–CT9; green sand CT11–CT12 (very loose).
- Material Cost: Low for sand, moderate for water-glass, high for silica-sol. Sodium silicate binder is very cheap, whereas colloidal silica binder is expensive.
- Shell Strength: Good for silica-sol at high T, moderate for water glass. Zircon/alumina shells (silica-sol) have higher refractoriness.
- Production Scale: Water glass suits small-to-medium volumes (dozens to thousands per year), especially when parts are heavy. Silica-sol suits small/precision runs; sand suits large volumes.
Overall, water-glass casting bridges a gap: it offers better control and finish than sand casting, ali lower cost than silica-sol.
When design demands are moderate and budgets are constrained, it is often the most economical precision technique.
Zaključak
Water glass (sodium silicate) investment casting is a isplativ precision casting process optimized for ferrous, complex components.
By using inexpensive binders and sands, it enables manufacturers to achieve near-net-shape steel and iron parts with reasonable tolerances (ISO CT7-CT9) and finishes (Ra ≈6–12 μm) at a fraction of the cost of silica-sol casting.
The process’s strengths are its material economy, strong shell rigidity, and ability to produce complex geometries without core collapse.
Its main limitations are a rougher surface finish and lower high-temperature stability, which restrict it to medium-precision, heavy-duty applications.
Veseliti se, water-glass casting remains relevant for applications like machinery, automotive subassemblies,
agricultural and construction equipment, and any parts that benefit from a good compromise of detail and cost.
Ongoing improvements (such as optimized silicate formulations and automated shell coating) may push its accuracy slightly higher.
Ipak, engineers should carefully match parts to process: use water glass when steel/iron complexity and economy dominate requirements,
silica-sol when ultra-fine detail or special alloys are needed, and sand when sheer volume or size overrule precision.
Overall, water-glass investment casting is a mature, well-understood technique.
Its continued use is driven by global demand for robust, intricately shaped metal parts at moderate tolerances and competitive costs.
Proper application of its chemistry and process controls – and thorough inspection – yields consistent, high-quality castings for a wide range of industrial needs.
Ovo je savršen izbor za vaše potrebe za proizvodnjom ako vam je potreban visokokvalitetni water glass investment casting services.
