Propane Gas Forge

08/30/2020

Project Overview

The ability to heat treat various alloys of steel is advantageous in the manufacture of components for high wear, high stress, and fatigue applications. Examples of such components include: cutting tools, shafts, arbors, punches, and dies. In industry, heat treatment is achieved through a variety of processes including induction hardening, flame hardening, molten salt baths, fluidized bed furnaces, electric furnaces, and even cryogenic hardening. For the home shop, the most cost effective approach is to utilize propane in a gas fired furnace. Propane is readily available, inexpensive, boasts a higher energy density than natural gas, and its inherent stability makes it a safer choice over acetylene.

The objective of this project was to design, build, and test a propane fired gas forge with the intent of producing a suitable environment for the heat treatment, and forge welding of various alloys of steel for less than $500.

Discussion

The forge consists of a chamber measuring 457 mm x 168 mm x 114mm constructed from 64 mm thick alumina refractory brick encased in a 3 mm thick mild steel shell. Thermal energy sufficient for the forge welding of steel is supplied by two naturally aspirated venturi burners located in the ceiling of the forge chamber. The forge chamber is open to atmosphere on two sides to allow for selective heating of components longer than 457 mm which is often the case when manufacturing damascus steel billets.

Lessons learned

It was found through the testing phase of the project that sodium borate (a commonly used flux to prevent the formation of iron oxides during forge welding) will readily react with the alumina and calcium in the refractory brick during operation of the forge and form a glass-like liquid, causing the floor of the forge to dissolve. Alternative refractory materials are being investigated for future designs to mitigate this issue.

Future work

Future work will include finding alternate, preferably castable, refractory material that is resistant to liquification upon the introduction of sodium borate. The venturi burners will also be replaced with forced air burners to reduce propane consumption and improve the control over the temperature inside the forge chamber. Lastly, a PID temperature control system will be designed, built, and tested for more complicated heat treatment procedures.