Heat Treating

Click on the thumbnails for a larger view.

Though our Express aircraft are largely composite construction there are several critical parts that are made of heat treated 4130 steel. After the parts are machined to size, welded to assemble parts and ground for surface finish, they come to Pacific Metallurgical in Kent Washington to be hardened for strength. Depending on the part, they spend several hours in the heat treat ovens above.

The oven is about 15 feet deep. The back part of the oven is where the parts are heated to about 1,600° F, which changes the structure of the metal crystals into a harder configuration.

The normal atmosphere inside the heat treat ovens is replaced with endothermic gas, a mixture of 40% nitrogen, 40% Hydrogen and 20% carbon monoxide. The "endo gas" is generated by the big green machine above and even this gadget has flames coming out of the top of it. Steel cannot be heat treated in the normal atmosphere with oxygen in it or the steel would literally rust away in a few hours. The endo gas also controls the amount of carbon in the surface of the steel, which controls the hardness and brittleness of the metal.

The parts are quenched in an oil bath then tempered in these ovens at about 400° F to remove the stresses induced by the heat treating and quenching.

The temperature of the ovens is controlled and recorded in this room. Records are kept of the temperature profile of each batch of parts.

Every part is tested for hardness by this machine and a certificate of test results issued for each batch of parts.

Here are the wing pins for the Express after heat treating but before surface polish. Two of these one inch diameter pins are used to attach each wing spar to the spar carry through box.

We at Express do not use the vacuum heat treat oven but I couldn't resist adding a picture of it. The customers of Pacific Metallurgical are almost all aerospace companies and chances are if you ride a commercial airliner or executive jet you are riding on parts heated treated by PacMet, just like the parts in your Express.

If you are considering buying an aircraft kit from one of our competitors, the parts probably were made in a third world country. Were those parts heated treated with the above controlled and certified process or did someone take a torch to the part until it looked hot and dropped it in a bucket of water and called it heat treated?

Link to Pacific Metallurgical Inc. Web site