Part 1 (1/2)

Oxy-Acetylene Welding and Cutting.

by Harold P. Manly.

PREFACE

In the preparation of this work, the object has been to cover not only the several processes of welding, but also those other processes which are so closely allied in method and results as to make them a part of the whole subject of joining metal to metal with the aid of heat.

The workman who wishes to handle his trade from start to finish finds that it is necessary to become familiar with certain other operations which precede or follow the actual joining of the metal parts, the purpose of these operations being to add or retain certain desirable qualities in the materials being handled. For this reason the following subjects have been included: Annealing, tempering, hardening, heat treatment and the restoration of steel.

In order that the user may understand the underlying principles and the materials employed in this work, much practical information is given on the uses and characteristics of the various metals; on the production, handling and use of the gases and other materials which are a part of the equipment; and on the tools and accessories for the production and handling of these materials.

An examination will show that the greatest usefulness of this book lies in the fact that all necessary information and data has been included in one volume, making it possible for the workman to use one source for securing a knowledge of both principle and practice, preparation and finis.h.i.+ng of the work, and both large and small repair work as well as manufacturing methods used in metal working.

An effort has been made to eliminate all matter which is not of direct usefulness in practical work, while including all that those engaged in this trade find necessary. To this end, the descriptions have been limited to those methods and accessories which are found in actual use today. For the same reason, the work includes the application of the rules laid down by the insurance underwriters which govern this work as well as instructions for the proper care and handling of the generators, torches and materials found in the shop.

Special attention has been given to definite directions for handling the different metals and alloys which must be handled. The instructions have been arranged to form rules which are placed in the order of their use during the work described and the work has been subdivided in such a way that it will be found possible to secure information on any one point desired without the necessity of spending time in other fields.

The facts which the expert welder and metalworker finds it most necessary to have readily available have been secured, and prepared especially for this work, and those of most general use have been combined with the chapter on welding practice to which they apply.

The size of this volume has been kept as small as possible, but an examination of the alphabetical index will show that the range of subjects and details covered is complete in all respects. This has been accomplished through careful cla.s.sification of the contents and the elimination of all repet.i.tion and all theoretical, historical and similar matter that is not absolutely necessary.

Free use has been made of the information given by those manufacturers who are recognized as the leaders in their respective fields, thus insuring that the work is thoroughly practical and that it represents present day methods and practice.

THE AUTHOR.

CHAPTER I

METALS AND THEIR ALLOYS--HEAT TREATMENT

THE METALS

_Iron._--Iron, in its pure state, is a soft, white, easily worked metal. It is the most important of all the metallic elements, and is, next to aluminum, the commonest metal found in the earth.

Mechanically speaking, we have three kinds of iron: wrought iron, cast iron and steel. Wrought iron is very nearly pure iron; cast iron contains carbon and silicon, also chemical impurities; and steel contains a definite proportion of carbon, but in smaller quant.i.ties than cast iron.

Pure iron is never obtained commercially, the metal always being mixed with various proportions of carbon, silicon, sulphur, phosphorus, and other elements, making it more or less suitable for different purposes. Iron is magnetic to the extent that it is attracted by magnets, but it does not retain magnetism itself, as does steel. Iron forms, with other elements, many important combinations, such as its alloys, oxides, and sulphates.

[Ill.u.s.tration: Figure 1.--Section Through a Blast Furnace]

_Cast Iron._--Metallic iron is separated from iron ore in the blast furnace (Figure 1), and when allowed to run into moulds is called cast iron. This form is used for engine cylinders and pistons, for brackets, covers, housings and at any point where its brittleness is not objectionable. Good cast iron breaks with a gray fracture, is free from blowholes or roughness, and is easily machined, drilled, etc. Cast iron is slightly lighter than steel, melts at about 2,400 degrees in practice, is about one-eighth as good an electrical conductor as copper and has a tensile strength of 13,000 to 30,000 pounds per square inch. Its compressive strength, or resistance to crus.h.i.+ng, is very great. It has excellent wearing qualities and is not easily warped and deformed by heat.

Chilled iron is cast into a metal mould so that the outside is cooled quickly, making the surface very hard and difficult to cut and giving great resistance to wear. It is used for making cheap gear wheels and parts that must withstand surface friction.

_Malleable Cast Iron._--This is often called simply malleable iron. It is a form of cast iron obtained by removing much of the carbon from cast iron, making it softer and less brittle. It has a tensile strength of 25,000 to 45,000 pounds per square inch, is easily machined, will stand a small amount of bending at a low red heat and is used chiefly in making brackets, fittings and supports where low cost is of considerable importance. It is often used in cheap constructions in place of steel forgings. The greatest strength of a malleable casting, like a steel forging, is in the surface, therefore but little machining should be done.

_Wrought Iron._--This grade is made by treating the cast iron to remove almost all of the carbon, silicon, phosphorus, sulphur, manganese and other impurities. This process leaves a small amount of the slag from the ore mixed with the wrought iron.

Wrought iron is used for making bars to be machined into various parts. If drawn through the rolls at the mill once, while being made, it is called ”muck bar;” if rolled twice, it is called ”merchant bar” (the commonest kind), and a still better grade is made by rolling a third time. Wrought iron is being gradually replaced in use by mild rolled steels.

Wrought iron is slightly heavier than cast iron, is a much better electrical conductor than either cast iron or steel, has a tensile strength of 40,000 to 60,000 pounds per square inch and costs slightly more than steel. Unlike either steel or cast iron, wrought iron does not harden when cooled suddenly from a red heat.