The relationship between the liquid and powder components in an investment slurry is quantified by the mixing ratio. This ratio is most commonly expressed as parts of liquid (water or a specialized binder solution) to parts of powder, typically measured by weight. For instance, a common specification might be “38 parts water to 100 parts powder” by weight, which is often translated to “38 ml water per 100 g powder,” leveraging the convenient approximation that 1 milliliter of water has a mass of approximately 1 gram.
Investment Slurry Calculator
Flask Parameters
Results
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Notes & Tips
- Water temperature should be between 21-24°C (70-75°F) for most investments
- Use deionized or distilled water for best results
- High-temperature alloys typically require lower water:powder ratios
- Vacuum mixing is recommended for removing air bubbles
- Always follow manufacturer’s specific recommendations
Manufacturer-Recommended Mixing Ratios for Investment Powders
Gypsum-Bonded Investment Powders for General Jewelry Casting
Gypsum-bonded investments are widely used for casting non-ferrous alloys such as gold, silver, and brass, which have relatively lower melting points. For these types of powders, the water-to-powder ratio typically falls within a narrow range, generally between 38 to 40 parts water per 100 parts powder by weight.
| Brand | Product Name | Water:Powder Ratio (ml:100g or Parts:100 parts by weight) | Recommended Application/Casting Type | Water Temperature (°C/°F) | Notes |
|---|---|---|---|---|---|
| Rio Grande | PlasticCast | 38:100 | General, high expansion for plastic/wax-plastic patterns | 24-26°C (75-80°F) | Deionized water recommended. |
| Kerr/Ransom & Randolph | Satin Cast 20 / SC20 | 38:100 | Heavy Castings (men’s rings, school rings) | 21-24°C (70-75°F) | Formerly Kerr, now R&R SC20, same formula. Deionized/distilled water recommended. |
| Kerr/Ransom & Randolph | Satin Cast 20 / SC20 | 40:100 | Regular Castings (ladies’ rings, pendants, filigree) | 21-24°C (70-75°F) | Formerly Kerr, now R&R SC20, same formula. Deionized/distilled water recommended. |
| SRS Powders | SRS Classic (example) | 38-40:100 | General jewelry casting | 22°C (approx.) | shows 100:40 and 100:38 based on mixing protocol. |
| Waymil | Prestige Oro | 38-40 ml water to 100g powder | Premium Blend for jewelry | Not specified | |
| Goldstar Powders | Omega+ | 38:100 (Machine Vacuum Mix) | General jewelry casting | Slurry temp 21°C advised | |
| Goldstar Powders | Omega+ | 40:100 (Hand Mix then Vacuum) | General jewelry casting | Slurry temp 21°C advised | |
| Goldstar Powders | XL | 38:100 (Machine Vacuum Mix) | General jewelry casting | Slurry temp 21°C advised | |
| Goldstar Powders | XL | 40:100 (Hand Mix then Vacuum) | General jewelry casting | Slurry temp 21°C advised | |
| Goldstar Powders | XXX | 38:100 (Machine Vacuum Mix) | General jewelry casting | Slurry temp 21°C advised | De-ionised water. |
| Goldstar Powders | XXX | 40:100 (Hand Mix then Vacuum) | General jewelry casting | Slurry temp 21°C advised | De-ionised water. |
| Ransom & Randolph | Liberty Vest | 38:100 | Low-temp alloy casting | Not specified |
Specialized Investment Powders
Beyond general jewelry applications, a range of specialized investment powders exists, formulated for more demanding conditions such as casting high-temperature alloys (e.g., platinum, steel), accommodating high-expansion pattern materials (like certain 3D-printed resins), or for specific techniques like stone-in-place casting.
| Brand | Product Name | Liquid Type | Liquid:Powder Ratio (ml:100g or parts:100 parts by weight) | Recommended Application | Special Considerations |
|---|---|---|---|---|---|
| Certus/Waymil/PMC Supplies | Prestige Optima | Water | 38-40 ml water to 100g powder | High-expansion resins, palladium, white gold, alloys requiring higher temperatures | Described as a “new generation, gypsum-bonded investment” with enhanced properties. |
| Goldstar Powders | Gemset | Water | 38:100 (Machine Vacuum Mix) | Stone-in-place casting | De-ionised water. |
| Goldstar Powders | Gemset | Water | 40:100 (Hand Mix then Vacuum) | Stone-in-place casting | De-ionised water. |
| Goldstar Powders | Pro-HT Platinum | Water | 33-35 parts water to 100 parts powder | High-temperature alloys, specifically platinum | Water must be below 7°C. |
| Goldstar Powders | Pro-HT Steel | Water | 32 parts water to 100 parts powder | High-temperature steel casting | Water must be below 7°C. |
| Ihor (Manufacturer not specified) | Platinum Investment | Binder Working Solution | 30 parts binder solution (by weight) to 100 parts powder. Alt: 39 ml binder to 100g powder. | Platinum casting | Binder concentrate diluted with distilled water (8 fl oz concentrate + 120 fl oz distilled water to make 1 gallon working solution). Powder added to binder. Mix 10-20 mins. |
| Doc’s Casting Plaster | Doc’s Casting Plaster | Binder | Approx. 25.7 ml binder to 100g powder (derived from 92-93ml binder for 360g powder) | Platinum, photopolymer resins. Phosphate-based dental investment. | Stated as a variation on a 25/100 (binder ml to powder g) recommendation. |
Calculating Required Investment Casting Powder Mix Ratio
In flask-based investment casting, a flask (a cylindrical or rectangular container, typically made of metal) is placed around the wax pattern assembly (tree), and the investment slurry is poured to completely fill the flask, thus encasing the pattern.
1.Calculating Flask Volume
- For a Round (Cylindrical) Flask: Vflask=π*(Diameter/2)^2Height=0.7854Diameter^2*Height
- For a Square or Rectangular Flask: Vflask=WidthLengthHeight
2.Accounting for Wax Pattern Volume and Utilizing Slurry Density
The calculated flask volume represents the total space to be filled. The volume of the wax assembly (Vwax) should ideally be subtracted from the total flask volume (Vflask) to get the net volume of slurry needed (Vslurry=Vflask−Vwax).
Once the required volume of slurry (Vslurry) is known (either total flask volume as an approximation or net volume), the weights of powder and water can be calculated if the specific density of the mixed slurry (ρslurry) is known:
- Determine Slurry Density (ρslurry): It can be found in manufacturer’s data, or determined empirically by mixing a known total weight of powder (Wp) and water (Ww) and carefully measuring the volume (Vmix) the resulting slurry occupies: ρslurry=Vmix(Wp+Ww).
- Calculate Total Weight of Slurry Needed (Wslurry): Wslurry=Vslurry×ρslurry.
- Calculate Powder Weight (Wp): If the water-to-powder ratio (R) is expressed as R=WpWw (e.g., for a 40:100 ratio, R = 0.40), then Wp=(1+R)Wslurry. For a 40:100 ratio, this would be Wp=1.40Wslurry.
- Calculate Water Weight (Ww): Ww=Wp×R.
| Parameter | Calculation / Value (Example) |
|---|---|
| Flask Diameter (D) | 3 inches |
| Flask Height (H) | 4 inches |
| 1. Total Flask Volume (V_{flask}) | 0.7854 \times D^2 \times H = 0.7854 \times (3~in)^2 \times 4~in = 28.27~in^3 |
| 2. Estimated Wax Tree Volume (V_{wax}) | 3.0~in^3 (approx. 49.2~cm^3) |
| 3. Net Slurry Volume Needed (V_{slurry}) | V_{flask} – V_{wax} = 28.27~in^3 – 3.0~in^3 = 25.27~in^3 (approx. 414.0~cm^3) |
| 4. Assumed Slurry Density (\rho_{slurry}) | 1.73~g/cm^3 |
| 5. Total Slurry Weight Needed (W_{slurry}) | V_{slurry} \times \rho_{slurry} = 414.0~cm^3 \times 1.73~g/cm^3 = 716.22~g |
| 6. Calculation for 38:100 Water:Powder Ratio | |
| Powder Weight (W_p) | W_{slurry} / (1 + 0.38) = 716.22~g / 1.38 \approx 519.0~g |
| Water Volume/Weight (V_w/W_w) | W_p \times 0.38 = 519.0~g \times 0.38 \approx 197.2~g \approx 197.2~mL |
| 7. Calculation for 40:100 Water:Powder Ratio | |
| Powder Weight (W_p) | W_{slurry} / (1 + 0.40) = 716.22~g / 1.40 \approx 511.6~g |
| Water Volume/Weight (V_w/W_w) | W_p \times 0.40 = 511.6~g \times 0.40 \approx 204.6~g \approx 204.6~mL |
