Author Topic: A few words about gating and risering  (Read 1542 times)

PatJ

  • Guest
A few words about gating and risering
« on: November 27, 2013, 05:04:18 PM »
There are volumns that have been written on gating and risering, and the methods used is as varied as automobile types.

I don't pretend to know the best method, but his is one layout I have used with some success.

The metal is poured into the pour basin, which is located at the top of the sprue (the vertical part).
The sprue terminates into a basin at the base of the sprue which is suppose to reduce turbulence.

The sprue is tapered so that it will fill completely and choke the flow to prevent air aspiration.

The runner extends from the lower basin to some location adjacent to the mold cavity (the mold is the open impression made in the sand, the sand being in the flask which is the two-part box what holds the sand in place).
Generally you want to extend the runner slightly past the last gate so that lose sand can be washed into a dead-end in the runner and trapped.

The gates are the parts that connect the runner to the mold cavity, and they are designed to fill the mold with molten metal slowly and evenly.
Often gates are wedge shaped to trap slag.

I often see runners with a v-section, and the gates are generally at the top of the runner to allow the metal to be self skimming as it enters the mold cavity.

Runners are generally suppose to be stepped so that they get smaller as you travel further from the pour basin, but I use a straight runner with no apparent problems.

And don't be surprised if you see a layout totally different than this that works perfectly.
There are many many foundry methods.
It is not a matter of right or wrong, but finding a method what works consistently, is easy to create, and gives you the desired final product  (no gas bubbles, inclusions, nice surface finish, minimal shrinkage, etc.)

This is just one arrangenent of many.
You may have one or more runners, one or more gates, and one or more risers (a riser is a vertical setion that feeds molten metal into the mold as the metal shrinks, and is often optional).