# Casting Gating System Choke Area Calculator

> Source: https://netray.co/tools/casting-gating-system-choke-area-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Calculate choke area, sprue diameter, runner and ingate areas from poured weight, density, pour time, discharge coefficient and effective head.

## Category

industry-templates

## Industry

Foundry and Forging

## Audience

- Foundry engineer
- Pattern designer
- Methods engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Total poured weight

**Key:** pour_weight

**Type:** number

**Default:** 120

**Min:** 0.1

**Step:** 5

**Unit:** kg

**Help:** Casting plus gating plus risers filled through the system.

#### Liquid metal density

**Key:** density

**Type:** number

**Default:** 6.9

**Min:** 1

**Step:** 0.1

**Unit:** g/cm3

**Help:** Approximate values: liquid steel about 6.9 to 7.0, gray iron about 6.9 to 7.0, aluminum about 2.4.

#### Target pour time

**Key:** pour_time

**Type:** slider

**Default:** 20

**Min:** 3

**Max:** 120

**Step:** 1

**Unit:** s

#### Discharge coefficient

**Key:** cd

**Type:** number

**Default:** 0.8

**Min:** 0.3

**Max:** 1

**Step:** 0.05

**Help:** Typical 0.7 to 0.9 depending on sprue and choke shape.

#### Effective metallostatic head

**Key:** head

**Type:** number

**Default:** 30

**Min:** 1

**Step:** 1

**Unit:** cm

**Help:** Height from the pour basin level to the choke.

#### Runner area / choke area

**Key:** runner_ratio

**Type:** number

**Default:** 2

**Min:** 0.5

**Max:** 4

**Step:** 0.25

**Help:** Pressurized systems are about 0.75; unpressurized systems often use 2 or more.

#### Total ingate area / choke area

**Key:** gate_ratio

**Type:** number

**Default:** 1

**Min:** 0.25

**Max:** 4

**Step:** 0.25

**Help:** Pressurized about 0.5; unpressurized about 1 or more.

**Outputs:**

#### Mass flow rate

**Key:** flow_rate

**Expr:** pour_weight / pour_time

**Format:** decimal

**Description:** kg per second.

#### Choke velocity

**Key:** velocity

**Expr:** cd * sqrt(2 * 981 * head)

**Format:** integer

**Description:** cm per second, Bernoulli with a discharge coefficient.

#### Choke area

**Key:** choke_area

**Expr:** pour_weight * 1000 / density / pour_time / velocity

**Format:** decimal

**Primary:** true

**Description:** In cm2.

#### Round choke diameter

**Key:** choke_dia

**Expr:** sqrt(4 * choke_area / pi)

**Format:** decimal

**Description:** In cm.

#### Runner area

**Key:** runner_area

**Expr:** choke_area * runner_ratio

**Format:** decimal

**Description:** In cm2.

#### Total ingate area

**Key:** gate_area

**Expr:** choke_area * gate_ratio

**Format:** decimal

**Primary:** true

**Description:** In cm2; divide among the number of ingates.

**Chart:**

#### Choke area vs pour time

**Type:** line

**X:** pour_time

**From:** 5

**To:** 60

**Steps:** 28

**Series:**

- choke_area

**Disclaimer:** Uses the classic Bernoulli choke equation. It ignores friction losses, air entrainment limits and metal-specific maximum velocity limits; verify with simulation for critical castings.

## Content

**Intro:** The gating system controls how quickly and how calmly metal enters the mold. This calculator sizes the choke from the Bernoulli equation and then scales the runner and ingate areas by the gating ratio you choose.

**Sections:**

#### How to use the calculator

**Body:** Enter the total poured weight including gating and risers, the metal density, a pour time from your foundry practice, and the effective head. Then set the runner and ingate ratios. The tool shows the choke area, an equivalent round diameter, and the areas for the runner and the combined ingates.

**Bullets:**

- Divide the total ingate area by the number of ingates.
- Measure head from the basin liquid level, not the top of the flask.
- Round the choke to a standard sprue or ceramic filter size.

#### The method behind it

**Body:** Flow through the choke is volume per second equals area times velocity. Velocity is the discharge coefficient times the square root of 2 g H, with g = 981 cm/s2. Rearranged, area = volume / (time x velocity). A ratio such as 1 : 2 : 1 (sprue : runner : gate) is unpressurized and slows metal in the runner to reduce turbulence; 1 : 0.75 : 0.5 is pressurized and fills faster but with more velocity at the gates.

#### Reading the result and common mistakes

**Body:** The chart shows that doubling the pour time roughly halves the required choke area. Too short a pour time can cause erosion and cold shuts if it forces unrealistic velocity, while too long a pour time can let thin sections freeze before they fill. Stay within the pour time window your alloy and section thickness allow.

**Bullets:**

- Using casting weight alone and forgetting riser and gating weight.
- Mixing cm and mm units in the head.
- Applying a steel ratio to aluminum, which is sensitive to oxide entrainment.
- Not accounting for filters, which add flow resistance.

**Cta:** If gating practice and scrap causes sit in different systems, we can discuss connecting them for your engineers. This is optional and the calculator works on its own.

**Faq:**

#### What is the choke in a gating system?

**Answer:** The choke is the smallest cross-section in the gating system and controls the flow rate. In many designs it sits at the bottom of the sprue or at a filter. Sizing it correctly sets the pour time and prevents the mold from filling too fast or too slowly.

#### What is pressurized vs unpressurized gating?

**Answer:** In a pressurized system the choke is at the ingates, so the runner stays full and flow is fast. In an unpressurized system the choke is at the sprue base and runner and gate areas are larger, which slows metal and reduces turbulence, common for aluminum and some irons.

#### Why use 981 in the formula?

**Answer:** Gravity is 981 cm per second squared. Using centimeters for head and area gives velocity in cm per second and area in cm2, so the volume in cm3 divided by time matches. If you work in meters, convert consistently.

#### Can I use this for aluminum?

**Answer:** The equation applies to any liquid metal, but aluminum needs low velocity, often under about 0.5 m per second in the runner, to avoid oxide films. Use an unpressurized ratio and check velocities at the ingates, then confirm with simulation or a trial.

## Search terms

gating system design calculator, choke area calculation casting, sprue runner gate ratio, pouring time calculator foundry, gating ratio pressurized unpressurized, ingate area calculation, sand casting gating design, bernoulli gating calculator

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