European 'CEN' Standard Designations
- Designation Requirements
- CEN Numbering System For Copper and Copper Alloys
- Temper Designations
The CEN standards being produced for European materials are being adopted without modification by all European countries. They are being dual numbered and published in each country by the relevant national standards organization. Conflicting national standards must be withdrawn within six months. The standards include all materials already in common use in Europe and have a new designation system to give a common terminology in all countries.
Describing materials by a recognised designation system is very important in order that orders can be placed with a clear understanding that correct materials will be procured. Such systems are an essential part of material standardisation common to all countries. There are, however, many different systems in use throughout the world. There are three basic types of designations based either on terms, symbols or numbers. For European CEN standards, a numbering system has been developed that can be easily understood by personnel with or without computers and that has a common meaning across all countries and all languages. This systems does not conflict with any others in use elsewhere in the world.
There are many numbering systems in existence of recognised significance throughout the world. Many of these are the subject of extensive trade references and have been based on carefully conceived concepts. Many other designations are also well established and, by virtue of their long history of usage, have become very well known to the individuals and areas of commerce in which they are employed. Some confusion can be caused when they are used outside the usual sphere of influence.
One of the biggest, most well-known, systems is the Unified Numbering System developed by the National Institute of Standards and Technology (formerly National Bureau of Standards) in the USA. This predominates throughout most ASTM (American Society for Testing and Materials) Standards used extensively through North America and significantly in other parts of the world by organisations with North American connections. The administration of this system is based in North America. It has proved impossible to adopt it to a system suitable for other national and international preferences. Similar considerations apply to other national systems.
A common designation system used within International Standards Organisation (ISO) is a compositional system described in ISO 1190 Pt 1, based on the element symbols and the descending order of magnitude of alloying elements. For example, a leaded brass containing 60% copper and 2% lead is designated CuZn38Pb2. This system is easy to use by humans but can be unwieldy when used to describe complex alloys with many alloying elements. It can be difficult to sort and index using computer programs. It has, however, been widely adopted throughout Europe during the last 20 years or so as many countries have been adapting ISO Standards with modifications for use as national standards. It is also now common practice in European technical meetings for materials to be referred to by this compositional designation. The use of common names or trade names causes confusion to those unfamiliar with them.
Some time ago the International Standards Organisation (ISO) published Technical Report No TR 7003 "International Numbering System for Metals". This gave a very logical system by which designations could be established with an alpha-numerical series of numbers easily understood by computers. For ISO purposes, there was not much impetus towards its adoption. With the onset of the mandatory nature of the European CEN standards, this attitude has changed. This has resulted in discussions to formulate a European Numbering System.
During discussions in working groups and committees preparing the standards, it became obvious that agreement on a computer-friendly numbering system was essential. It was agreed that there was a need to keep a designation simple, and to be able to define the material as closely as possible including, if achievable, composition, form (type of wrought product or casting) and main mandatory properties (such as tensile strength, hardness or proof stress). The possibility of using a simple numbering system was considered but proved impractical because of the limited number of variations possible. It was agreed, therefore, that an alpha-numerical system would be used. In a six digit system there is a possibility of only one million variations in an all-numerical system, whereas in an alpha-numerical system of three letters and three digits, not only can the letters appear to be more meaningful but over 12 million combinations are possible.
CEN Numbering System For Copper and Copper Alloys
Having agreed to use a basic six-digit system, CEN/TC 132 agreed to use C as the first letter to indicate a copper alloy. A second letter was introduced to indicate the material state (i.e. W for a wrought material, B for ingots, C for castings and M for master alloys). Three numbers are then used to identify the material and a final third letter is used to identify the classification of individual copper material groups and to enlarge the capacity. This also prevents confusion with the existing BSI designations and the old C/three-digit CDA numbers administered by Copper Development Association, New York.
This system will cater for both CEN materials and other non-standardised materials, but initial allocations have been made for the numbers to ensure a minimum of confusion within CEN preferred materials. This means that not every material sub-group starts at number '1'. As an example, while coppers do commence at 001, miscellaneous copper alloys start at 100, copper aluminium alloys start at 300, copper zinc alloys at 500 and so on, as shown in Table 1, below.
|Material Groups||Number ranges available for positions 3, 4 and 5||Final letter, designating material group||Number range allocated to materials preferred by CEN|
|* Letter as appropriate for the Material Group|
|Miscellaneous Copper alloys (max 5% alloy elements)||001-999||C||100-149 C|
|Miscellaneous Copper Alloys (over 5% alloying elements)||001-999||E||200-249 E|
|Copper nickel Alloys||001-999||H||350-399H|
|Copper-Zinc Alloys, complex||001-999||R||700-749R|
|Copper material not standardised by CEN/TC 133||800-999||A - S*||800-999*|
The lack of overlap in preferred number series ensures that common materials in differently lettered material groups will not normally share the same number. There will, however, be many spare numbers available in reserve.
|ISO Symbols||CEN Numbers|
|Wrought Brasses||CuZn37||CW 508L|
|Other Wrought Alloys||CuNi2Si||CW 111C|
|Cast Alloys||CuZn33Pb2-GB||CB 750S|
|Master Alloys||CuAl50 (A)-M||CM 344G|
For temper designations CEN TC 133 covering copper and copper alloys has agreed to use a system similar to that already established by DIN indicating the minimum value of specified properties. For example, tensile strength R 250 indicates the minimum of 250 N/mm² while a hardness of H090 indicates a value of 90 (Vickers for wrought materials and Brinell for cast) and Y140 indicates a minimum 0.2% proof stress of 140 N/mm². This meets the requirements of the wide variety of customers who have individual needs for special properties to ensure fitness for purpose but do not need to know the way in which a temper was originally produced.
|B||Spring bending limit|
|H||Hardness (Brinell for castings, Vickers for wrought products)|
|M||(as) Manufactured, i.e. without specified mechanical properties|
|R||Tensile strength Y 0.2% proof stress|