# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/Dd4Dqa7ghAm
- **Gondola URL:** https://gondola.cc/posts/71131439-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/7e9e708bd8.jpg
- **Posted:** 2026-09-29T15:17:02.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Every iron casting starts long before the metal hits the mold. The gating system, the network of channels that carries molten iron from the ladle into the cavity, decides whether you get a sound part or scrap full of slag, sand, and gas.

Anatomy of a gating system:
- Pouring basin: absorbs the ladle stream’s turbulence and keeps the sprue full
- Sprue: the vertical channel, tapered narrower toward the bottom
- Sprue well: a cushion at the base that reduces splash and erosion
- Runner: the horizontal channel that distributes metal and traps slag
- Ingates: the final openings into the casting cavity
- Risers: reservoirs that feed shrinkage as the metal solidifies

Why the sprue tapers:
Falling metal accelerates, roughly v = sqrt(2gh). By continuity (A1v1 = A2v2), a faster stream needs a smaller cross section. A straight sprue lets the stream pull away from the walls, which creates low pressure that pulls air and sand into the metal. The taper keeps the channel full.

Pressurized vs unpressurized:
- Gray iron often uses a pressurized ratio such as sprue:runner:gate = 1:0.75:0.5
- The gate area controls the flow, which keeps the system full and helps stop slag
- Unpressurized systems, common for aluminum, lower velocity to reduce oxide film damage

Pouring iron:
- Gray iron is typically poured around 1350 to 1450 C
- Pour too cold and you get misruns and cold shuts
- Pour too hot and you increase sand burn-in and gas pickup
- Pour time is often estimated empirically from casting weight and section thickness

Iron has one big advantage. Graphite precipitates during solidification and expands, which partially offsets shrinkage. That is why well-designed gray iron castings can need smaller risers than steel.

A good gating system is fluid mechanics, heat transfer, and metallurgy working together in a few inches of sand.

#stemantics #metalcasting #castiron #materialsscience #engineering

## Stats

- **Views:** 10,674
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## Tags

metalcasting, engineering, materialsscience, castiron, stemantics

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