Heat Treating, what is it all about?

I’ve often heard the term of “Heat Treating.” Apparently this is an important step in manufacturing bicycles. Without it, the material used for the frames wouldn’t be as as strong. So I asked our buddy Vince Rodarte of KHS Bicycles if he knew anything about it. The fella did, and check out what he wrote:

In one of my many ‘past lives’ I was production manager for Allied Manufacturers in La Habra (they’ve since relocated to Corona).

I WAS the bike division. I learned A LOT about bicycle production during my time there.

When a metal (chromo, aluminum) frame is welded, the heat associated with the welding process softens the material and makes the molecules scatter and move around.

Aluminum is a soft material in a un-heat treated state. You could grab the rear stays of a frame and crush them in or spread them out with ease.

If you were to leave a freshly welded frame on a shelf for an extended period of time, the molecules of the material would eventually align themselves and the frame would stiffen up (this is usually the normal process for 7000 series alloy, but not for 6000 series). But, in order for the frame to stiffen up enough to ride, it would take a LOOONNNGGGG time. This is where heat treating comes in. Basically, it speeds up the molecule alignment process. And you can monitor the alignment of the frame at the same time.

Welded frames are usually outfitted with spacers (basically false axles set at 130 or 135 wheel spacing to keep the rear end form spreading or collapsing). After that, the frame is aligned on an alignment table. This will check to make sure the frame is straight and the head tube is true in relation to the rest of the frame. (picture an imaginary line, starting at the head tube, cutting through the frame and intersecting the rear axle. The angle of the imaginary line and rear axle intersection should be 90 degrees; or perpendicular to each other. Once that is set, the frame is off to heat treating.

Photo courtesy of Co-Motion

Imagine a HUGE oven or boiling vat of some sort of liquid. Racks of frames are loaded into this oven or vat and heated to a certain temp (= Frickin’ HOT!). The heat allows all of the molecules to relax and spread out, not just the molecules near the weld area. Then the frame is allowed to cool. the molecules align themselves to each other as the material contracts. There is one more session of alignment just to make sure. Then the frames are aged by putting them in varying degrees of heat (above and below the initial heat treatment temp) to get to the proper strength or hardness (this is where the T-# comes from, ie: 6061 T6).

This allows the material to expand and contract. Due to this contraction, the frame becomes stiffer and VOILA. the frame is ready to ride!

It’s actually more complex than this. This is basically what I can remember. I once had my VP at Allied heat treat a prototype swing arm for ROTEC Cycles in his home oven, just to get a sample to ROTEC one time!

Here are a few contacts to get more info:
Alumatherm Heat Treating Co.
15535 Texaco Ave
Paramount, CA 90723-3921
Primary phone
(562) 531-1331

Newton Heat Treating
19235 East Walnut Drive
City of Industry, CA 91748
(626) 964-6528

I hope you all learned something today. I know I did! I do remember hearing about how people stole some GT bikes that were used for Interbike. They (GT) wanted to let the thieves know that the frames were NOT heat treated and that who ever rides those bikes runs the risk of breaking the frames…