Preferences in Frame Design
Page 35
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(-IF the, three main methods of L./chassis-frame construction at present adopted, that in which the various components were built up either by the use of bolts or rivets presented the fewer problems, and made for easier repair.
This was a point made by Mr. C. F. Cunningham, technical manager of the Projectile and Engineering Co., Ltd., when he read his paper, "Chassis Frame Construction and Repair," before the Institute of Road Transport Engineers, in London, last night.
The other methods were by arcwelding and by resistance or spotwelding. Whereas in the bolted or riveted frame there was practically no distortion, it was impossible to prevent this with welded frames, although it was far more serious when arc-welding was employed than when the frame structure was spot-welded.
Mr. Cunningham dealt at length with the painting operation which followed the final checking for dimensional accuracy and alignment. Painting, he said, was a purely protective covering and was not to be regarded as a finishing process. The paint, which had a bitumastic base, was applied by dipping, followed by a stoving period of up to two hours at a temperature of about 400 degrees F. With the box type of frame, the painting process had become more complex because of difficulties of draining the paint from the cavities, and the effective drying of the interior surfaces was a problem that had not been easy to solve.
Failure of a chassis frame,he said, was extremely rare, and could be brought about only by gross misuse. A welded frame that had suffered damage in a collision must be replaced, but a crack along the flange and vertical wall of a side member could effectively be repaired by fitting a fish plate.
This plate should be at least equal in thickness to that of the original sidemember, and in length should be at least equal to 2i to 3 times the depth of the side member.
The method of securing the fish plate was by the use of bolts in reamed holes. On no account should the crack be welded, or the fish plate attached by this means. This warning applied more particularly to frame members made of a steel having a high carbon content.
A frame that had become out of square could be corrected by the application of chains and turnbuckles. Following such corrective treatment, it was necessary to examine all bolts and nuts for slackness.