How Does Techno-Weld Work?
As far as the application of the Techno-Weld System is concerned, there are two separate categories of alloy that have to be treated in two entirely different manners:
- Alloys that have a melting point greater than 770 degrees F.
- Alloys that have a melting point similar to Techno-Weld material.
It is not easy to identify between the two categories of alloy, and care needs to be taken in checking before a job is started.
Most Aluminum alloys found in sheet, tubing and extruded form, tend to fall into the first category, including many of the cast materials used in main engine casings, cast material that will be subject to high stress etc. It must be noted however, that many of the ancillary alloy castings attached to main casings can be an alloy of the lower melting point variety.
The low melt alloys are generally made up of a high proportion of zinc with Aluminum, and with other odd and variable alloys thrown in for good measure - this is commonly called "Pot Metal". Usually the casting appearance tends to be a darker grey in color, and proportionally heavier than alloys of mainly Aluminum.
Other low melt alloys can have various concentrations of Magnesium in the mix, and are often used for gearbox casings, and other very light weight castings. These castings tend to be lighter in weight than mainly Aluminum alloys.
The only simple way to test the alloy to find out to which group it belongs, is to use a "belt-and-braces" method outlined in the Techno-Weld instructions - i.e. take a chipping of both the cast material and Techno-Weld of equal size, and place adjacent to each other on top of a steel sheet. Gently warm up the sheet from underneath with a soft flame, and as the heat builds, check the state of each "chipping" by tapping it with a suitable implement, until the first "chipping" melts. If both melt simultaneously, then the alloy is of a Low Melt variety.
If there is an appreciably different melting time, then the alloy can be treated as follows:HIGHER MELT ALLOYS - A large area of the workpiece can be heated with a broad flame to 720°F(380°C).
- The TECHNO-WELD filler rod melts in contact with the heated Aluminum surface of the job, rather like a high temperature solder stick, and forms a molten bead sealing the Aluminum oxide layer (always present on Aluminum alloys) between the two metals.
- The oxide layer is ruptured by passing the Stainless-steel Abrader through the molten bead a few times (or using ultra-sonic etc.), which allows the TECHNO-WELD material to creep through the tear and lift off the remainder of the Aluminum oxide which floats to the surface (It can be seen as fine grey particles on top of the molten surface).
- Once the TECHNO-WELD material makes direct contact with the Aluminum, fusion takes place between the metals. Molecules of TECHNO-WELD material interchange with the Aluminum alloy surface to form a new alloy made up from TECHNO-WELD and the Aluminum alloy it is working upon. This "Alloying " process will continue until either the heat of the job falls below 720°F (380°C) or the original pool of TECHNO-WELD material becomes too diluted by the new alloy.
- The result is a multiple layered but contiguous "weld " area starting with TECHNO-WELD at the top, the newly created TECHNO-WELD/Aluminum Alloy in the middle, phasing to Aluminum Alloy underneath.
LOW MELT ALLOYS are treated in an entirely different manner, using a technique more akin to traditional gas welding, but nonetheless it is relatively easy compared with gas welding steel or Aluminum.
- The workpiece is gently heated to around 400°F through the use of a domestic oven, or by smearing one side of the workpiece with a little oil to act as an indicator, and using a broad, soft gas flame until the oil begins to smoke.
- The next process requires a fine or pin-point flame which is directed on to the area to be welded, and the stainless-steel abrader used to "pick" at the surface under the flame until the metal becomes soft or molten. The TECHNO-WELD rod is then fed directly through the flame path into the molten pool.
JOINING COPPER OR BRASS TO ALUMINUM - TECHNO-WELD forms a strong bond with copper or brass rather like a hard solder, although it does not form a "fusion weld" as with Aluminum Alloys.
- The brass or copper is "tinned" with TECHNO-WELD, and "keyed" by brushing the molten "TECHNO-WELD" into the surface with a Stainless-Steel brush.
- The Aluminum Alloy is prepared in the normal way, and the "tinned" brass or copper can then be "sweat" together, and a good fillet of TECHNO-WELD added for extra strength..