The French scientist Millardet – while seeking a cure for downy mildew-diseased vines in the Bordeaux district of France – chanced to notice that those vines bordering the highways, which had been daubed with a paste of copper sulphate and lime in water in order to make the grapes unattractive to passers-by, appeared freer of downy mildew. This chance observation led to experiments with mixtures of copper sulphate, lime and water, and in 1885 Millardet announced to the world that he had found a cure for the dreaded mildew. This became known as Bordeaux mixture and saw the commencement of protective crop spraying.
Specially degreased copper tubing, to BS EN 13348 is cleaned to the requirements of Hospital Technical Memorandum HTM02 (which replaces HTM2022). Such tubing, which is eminently suitable for use on medical gas (including breathable air) and oxygen lines, comprises half-hard temper, phosphorous de-oxidised, non-arsenical copper, complying with the chemical requirements of BS EN 1976, Cu-DHP, CR024A (supersedes BS6017 Cu-DHP).
When jointing tubing with brazing alloys, the temperatures involved in hard soldering convert the metal, in the heat-affected zone, from the half-hard to the soft condition. This effectively reduces the maximum safe working pressure by approximately one-third.
Precautions should also be taken during jointing operations to prevent the formation of oxide along the lines described in HTM02. Copper tubing is suitable for most gases with a few exceptions. Where there is any doubt regarding the type of material or internal finish required, the tube manufacturer should be consulted.
A Phosphorous deoxidised copper (C106)-this is CW 006A.
The same or better performance can be achieved with less tube and fin material. In other words, more heat can be dissipated with less material. Less tube, more heat! Technically speaking, a coil made with smaller diameter tubes can be designed with a higher ‘heat transfer coefficient’ compared to a coil made with larger diameter tubes.
Taps are die cast from a general composition of 60% copper, 40% zinc. This composition gives a fluid alloy with essential hot ductility. A typical die cast alloy is DCB3 (CuZn40Pb-CC754S).
Taps may be plated with successive layers of copper (3-4 microns), nickel (10-12 microns) followed by about one micron of chromium to give a hard shiny surface. Remember that when taps are replaced, they have value as a source of recycled copper alloy scrap.
Note that in order for copper alloys to retain their inherent hygienic properties, they should not be plated or coated.
The following brasses have sufficient strength, machinability and electrical conductivity: CW508L (CZ108), CW509L (CZ109) and CW614N (CZ121).
1 degree, using batten rolls.
The problem caused by lead is it becomes molten before brazing occurs and wetting of the joint is impaired. To counter this, use plenty of flux and agitate to break up the surface tension of the lead. Use a joint gap of 2 to 5 thousands of an inch and specify a low melting point silver brazing alloy from BSEN 1044: 1999 Brazing Filler Metals. Select alloy Ag103.
Since ancient times copper has been used in coins; the Romans used copper widely in this application. The reasons for using copper are its excellent corrosion resistance, ease of stamping, good electrical conductivity for vending machines and ease of recycling.
Strength and hardness increases with the percentage of cold reduction after hot working. Properties are defined in standards. See also CDA publications in the Resource Library.
In general an earthing system needs to satisfy three demands:
- It must conduct lightning and short-circuit currents without introducing intolerable step and touch-voltages .
- It must protect the occupants, equipment and fabric of the building against damage due to short-circuit currents and lightning strikes.
- It must provide a suitable environment for electronic equipment by providing a low impedance path to interconnect equipment.
Although requirements for these three aspects are very different and are often specified separately, the implementation of them requires an integrated systems approach.