SRS - Technical Centre: Helpful Hints

Sprueing

1.Good sprueing techniques are essential to obtain good castings. Metal should be able to enter the mould cavity quickly and easily without restriction.

2. Sprue size should be proportionate to the casting. Round sprues flared at the casting are the most effective.

SPRUES

3. Attach sprue to the heaviest area of the casting as the heaviest areas will solidify last. This allows the heavy area to draw molten metal from the sprue as it solidifies. Much of the shrinkage and related shrink porosity may be prevented in this way.

SPRUE / CAST ATTACHMENT

4. Multiple sprues may be needed on the more complex castings to obtain the best results.

5. Avoid choke sprues and sharp bends in sprues. Any restriction in the sprue can create turbulence in the metal flow causing mould erosion and porosity from entrapped mould gasses.

6. The main sprue in a cast tree acts as a reservoir of heat and metal to feed the castings as they solidify. Skimping on the main sprue will result in shrinkage defects in the castings.

7. Use manifold or fork shaped multiple sprues on long thin designs like bracelets. This will assist with the form filling and help avoid solidification problems.

8. For the main sprue always use a wax with a lower melting temperature than the wax patterns. This will allow the wax to flow out of the mould cavity without boiling inside the mould thus reducing mould erosion.

9. Avoid mixing light and heavy wax patterns on the same tree if at all possible. Light detailed castings require higher flask temperatures than heavy castings. Mixed trees can be an expensive compromise.

10. The wax patterns should be angled to the main sprue; this allows the wax to flow out and the molten metal to flow in without restriction. An angle of 45 degrees is recommended. If the wax patterns are attached flat there is a greater risk of shrinkage porosity on heavy pieces and a greater risk of flashing on filigree pieces.

FLAT	ANGLED

11. Care should be taken attaching the wax patterns to the main sprue. Avoid leaving any depressions or cavities as they cause protrusions of investment that could break off during casting and cause inclusions in the metal.

BAD	GOOD

12. Allow enough space between the flask wall and the wax patterns for the investment to fill around (1/2" min). This will reduce the risk of flashing. Leave enough room for a 1"thick layer of investment at the top of the flask, this will eliminate blow outs.

TOO CLOSE	GOOD

13. Leave 1" space between the button and the first row of patterns. This area takes up the largest amount of shrinkage during solidification. Castings placed in this area usually exhibit gross shrinkage porosity.

TOO CLOSE	GOOD

14. Check the metal flasks periodically, if they are rusty or scaly have them sandblasted or shotblasted.

RUSTY	CLEAN

15. The main sprue, feed sprues and the button will normally weigh as much as the castings.

View other helpful hints online or download (Acrobat Reader PDF) versions by selecting relevant links below:

HELPFUL HINTS

	Casting		Download PDF (92k)
	Dewax/Firing - Firing Cycles		Download PDF (148k)
	Investing		Download PDF (112k)
	Modelmaking		Download PDF (56k)
	Proportioning Charts		Download PDF (204k)
	Sprueing		Download PDF (204k)
	Wax Patterns		Download PDF (124k)