Resource Library

Is it possible to braze leaded brasses such as CW614N (CZ121Pb3)? Are there any problems to look out for?

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.

Why are copper and copper alloys used in coinage?

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.

What is temper as applied to copper and copper alloys?

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.

What is the British Standard for the design and installation of domestic sprinkler systems?

BS 9251.

Why are installations earthed?

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.

Why is copper so efficient in heat exchanger applications?

Because the thermal conductivity is so high – it is 23 times better than stainless steel or titanium and 1.6 times better than aluminum.

What is the current standard for copper fittings?

EN 1254 Parts 1 to 5.

What is the difference between a voltage regulator and a Dynamic Voltage Restorer (DVR)?

Both are used to mitigate the effects of voltage dips. Dips are characterised by the depth – the retained voltage – and the duration. Short and deep dips are best served by a DVR while long and shallow dips are the province of the voltage regulator.

A voltage regulator has no energy store. It has a transformer secondary winding in series with the supply. When the input voltage moves outside the tolerance band the primary of that transformer is driven to boost, or in anti-phase to reduce, the voltage appropriately. Because the load voltage is kept constant, the power to the load is constant so, when the input voltage falls, the input current increases. The current capability of the supply and the device itself limits the working range to about +/-30% of nominal voltage.

A DVR has an energy store, so requires no additional input power (in the short term) to boost the voltage during a dip. A DVR can correct a dip to 0% retained voltage. But the DVR has a limited energy store and so is suitable for short-term effects only – it cannot correct for long term under voltage, for example. Also, the store has to be recharged between events so it is not suitable multiple dips are expected frequently. Typically, DVRs use super capacitors, large secondary batteries or high-speed flywheels as energy stores.

Unsurprisingly, DVRs are more expensive than voltage regulators.

In long strip roofing what is the maximum length of a bay?

This depends on the pitch of the roof. For 3-4 degrees 14.6m, for 4-10 degrees 11.0m, for 10-30 degrees 9.7m and for over 30 degrees 8.1m.

Why is copper the preferred material for busbars?

There are several reasons. Firstly, the bars are more compact because copper has a higher conductivity than aluminium. Secondly, it is much easier to joint copper. A hard, highly insulating oxide grows very rapidly on the surface of aluminium, making it very difficult to make good reliable joints in the field. On the other hand, the thin oxide layer that forms, more slowly, on copper is not an insulator so jointing is simple. Finally, copper is much stronger than aluminium, less susceptible to creep and better at withstanding short circuit current forces.

What is the history of copper tubes with aluminium fins?

Condenser coils with round copper tubes and aluminium fins have been a winning combination for ACR coils for many years. Manufacturers enjoy the assembly advantages provided by these components while technicians find it easy to join and repair copper tubing in the field. More importantly, this well established technology has a proven record of durability in the field resulting in a high level of customer satisfaction.

What is the main advantage of small diameter tubes for the design of air conditioner coils?

Smaller diameter tubes allow for more effective heat transfer.