Morning journal and courier., 1888-02-03
Different Types of Car wheel.
From the Boston Herald.l

From the Boston Herald
 The different types of wheels in use in. clude those made entirely of cast-iron l east-iron bodies with steel tires, the so. ! called paper wheels made of iron or stee | disks and hubs with steel tires, the interior I space between the disks being occupied by | the hub and tires, and wheels made from coil of ribbon comparatively thin strips l of metal and then welded. By far the l largest number of car wheels in this ooun. try are cast-iron, while abroad wheels with
 tires are almost exclusively used. To give durability to the wheels as regards wearing qualities and avoid rolling down on account of it's seftness, when steel tires are used 6 comparatively hard metal is employed, and east-iron wheels without tires are made with chilled faces. There is a liability in the processes of manufacture that the metal may be left more or less brittle, and therefore in condition to finally end in unexpected failure.
 Just how and why brittleness is brought about at times is not positively known. h. vestigators have not been able to reproduce at all times the conditions which will cause results identical with those met when they are not wanted. It is pretty certain, how ever that some of the causes of brittleness, ] which are only identified after their effects are produced are the initial strains in the l metal, which tend to warp it in various directions. Initial strains may exist to such
 an extent, and beyond our ability to ascer- tain without destroying the metal, that a slight additional load is sufficient to cause complete rupture, and the processes of manu- facture, particularly with cast-iron, are known to introduce these initial strains and dangerous conditions. To avoid as far as possible severe strains from cooling, curved surfaces in the webs are employed, which allow them to spring instead of fracture These strains may be released by anrealiag, but that softens the metal and removes the effects of the chill; in steel, the metal would still retain degrse of hardness com mensurate with it's chemical competition, which is point in favor of the latter metal. When once crack is started in homogsn- eous mass it will, when strained, extend readily, and it probably doesn't matter whether the straining is from external sources or within the metal itself This rather dry discussion is necessary to explain,
 in o measure, an intricate feature of these metals, which feature no doubt has played
 an important part in many a serious *dis-
 aster.
 The fact that the wheel was a compare
 lively new one which fractured at 6 recent
 accident would give weight to the suppo-
 sition that it's initial condition may have
 contributed largely to it's destruction, unless
 conclusive evidence of another kind is shown.
 In some places initial strains are not objeo-
 tionable, they ara even valuable, but they
 must be regular in their action and under
 control, and not scattered here and there
 threughout the mass. Where ear wheels
 are slid, by excessive brake pressure stopping
 their revolutions, intense heat is developed,
 as shown by the display of sparks, and, as