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Metallic Fusion: Putting it Together in 1632

Written by Kevin H. Evans

The construction of machines and devices requires that sections of material be attached to each other. This can be accomplished by friction, adhesives, mechanical connections, and welding.

Down-time fastening methods were mostly mechanical. That is the methods depended on adhesion (stuff sticking together) created by means of a device compressing the parts together. Screws, rivets, nuts and bolts, trunnels (tree nails), pegs, lashings, glues, and gravity were all used to hold stuff together. All of the fastening methods described are composed of layers, and so have some inherent weaknesses. While suitable for most construction, the methods described do not provide the strength needed for many things our up-timers want to make.

Of all of the fastening methods described, rivets and glues come closest to being able to provide the strength to weight connections needed.

Rivets involve making a hole through the two (or more) parts to be joined and putting a pin through the holes. Then the ends of the pin are hammered down to form a mushroom shaped head on each side of the parts. This compresses the parts together and holds them firmly in place. Well done riveting can make seams that will hold pressure (as in a boiler), or stand up to great stress. Rivets have problems where the demands of the connection do not allow room for the mechanical process of riveting or space for the rivet heads in the finished application. Countersunk rivets (cone shaped depressions in the plates to be riveted) allow rivets that are flush to the surface, but reduce the strength of the join, thus increasing the number of rivets in the seam or requiring the increase in thickness of the parts.

Glues can form very strong joints, but require that the material glued be porous. Often this limits the utility of the method. Soldering and brazing are a form of gluing, and were known before the ROF, but due to limitations in heating methods were used mostly in smaller applications. Brazing and soldering also need pores in the material connected and can shear under stress or heat.

Welding is the connection of two parts by actually mixing the metal of the two parts so that they form one continuous piece. Welding is also normally done to ferric (iron based) metals. Non ferrous welding is possible but requires care due to the tendency of the metals to oxidize before the parts can be joined into one piece. Welding also allows the rapid fabrication of devices in a fraction of the time needed to make the devices by other methods.

Welding can be accomplished in a number of ways. Down-time welding was most often forge or percussion welding. This weld is made by heating the two pieces until they are soft and plastic, placing flux on them, putting them one on the other and applying force, hammer blows or pressure, causing the metal to fuse into one piece. This is also called hammer welding and can be done manually or by a forging machine like a drop hammer. The flux is usually sand or borax and serves to exclude oxygen and oxides from the join. Hammer welding is most effective with low carbon steels and iron. High carbon steel requires much higher temperatures and this makes the exclusion of oxides harder. Hammer welding is a skill well known by the smithing community of the 1600s and even high carbon steels are with in the ability of a master smith. The greatest limitation of hammer welding is the amount of heat that needs to be applied. Normally the heating time possible with a forge fire means that larger pieces have to be heated over larger areas than are required for just the weld. This slow heating increases the fuel consumed and also increases the difficulty in handling the work.

New to the down-time world are gas, electrical, and chemical welding. Gas welding is accomplished with a torch burning a fuel and an oxidizer, normally acetylene and oxygen. The torch is used to apply heat directly to the point to be welded and cause the material to liquefy and flow together. Often a rod of the same metal is used to control the heat and provide additional material for joining the gap between the two pieces to be fused. Gas welding markedly decreases the amount of time needed to heat a join to welding temperature. Also a weld created with the gas method does not need percussion applied to fuse the metals. However welds heated by a gas torch can run into the same problem, heat traveling, and requiring the heat of large areas before welding heat is available to the join in large pieces.

While at first glance a new gas welding set would seem to be outside of the industrial base available down-time, careful consideration brings to light workarounds that will allow the technology to spread. Hoses can be made from leather tubes wrapped in latex-impregnated cloth with an outside leather case protecting the cloth. The latex is locally available as milkweed sap or dandelion sap and while it is not as pure as rubber tree sap, it was used during WWII as a substitute until the synthetic rubber industry came on line. Gas regulating valves also looked very difficult, but I "bit the bullet" and tore one of my old regulator sets down to see how they were made. To my surprise they are not complicated, and the hardest parts to make will be a large spring that holds the diaphragm against the valve that controls the pressure released from the storage device. The valve bodies are made of brass and the spring and diaphragm can both be made by any smith that can make a knife that will hold an edge. Storage is a little harder as down-time produced tanks are likely to be more cumbersome, probably riveted and seal welded on the seams. All in all, a down-time set will be larger, not as long lasting, but will be possible. That leaves the gas. Welding gasses, normally acetylene and oxygen, need to be produced in quantity. Both will need electric current, oxygen produced by electrolysis, and the acetylene produced by adding water to calcium carbide. The calcium carbide is also produced by applying an electric arc to coke (refined coal not the drink) and limestone. While not explicitly canon, production of calcium carbide is implied in the operation of the mines in Grantville as "carbide lamps" were the industry standard prior to long duration batteries, and I am sure that as the high tech bulbs burn out, that old lamp of dad or grandpa's will come out of storage.

Electric welding uses a high current electric spark to create the heat needed to fuse the metal and form the joint. Of note, is that the electrode is normally sacrificial and is used to add metal to the joint created. This current may be AC or DC and can be provided by batteries or by a generator set. Variations on "stick" welding include wire-fed inert gas shielded welding where the electrode is a wire fed through the welding handle and is shielded from oxidization by an inert gas fed to the weld site from a tank connected to the "stinger". Also of note, is that electric welding is an immediate heat in a small area and can be used to weld large sections of material with minimal heat.

The major problems with electrical welding are the need for insulating the cables used and providing ...