Flange facing in a sentence
The process of flange facing (or flange refacing) involves the machining of flange mating surfaces so that they they produce a tight, leak-proof seal when assembled.
Industry standards for flange facing
The American Society of Mechanical Engineers (ASME) are the go-to organisation for many standards for mechanical engineering around the world. They have the set the standards to which many engineers work to for flange facing surface finishes.
ASME set the standards for flange face surface finish types through the ANSI accredited ASME Standard B 16.5 ensuring all gasket and flange fittings are consistent and fit for purpose allowing a high quality seal.
Flange facing vs milling
Milling is the process of machining a surface using a multi-point cutting tool. While a milling machine is capable of getting a smooth surface finishes and cutting in a circular stroke (such as our range of orbital milling machines), they are not capable of getting the required surface finish needed to meet the ASME B 16.5 standard.
In order to reach some of the finishes required to meet ASME B 16.5, the flange should be machined using a single point cutting tool. The single point tool enables on-site machinists to achieve the grooves required to created surface finishes suitable of creating a strong leak-proof seal for gasket flanges, such as the serrated surface (see image). As such, single point cutting tools will be used with a flange facing machine.
For users that are happy simply to produce a flat finish on the flange (with no defined machine profile), machines can be supplied with milling heads rather than single-point cutters. This dramatically reduces the machining time which has made flange facing machines an ideal tool for use in wind turbine production.
Internal diameter or outside diameter mounting
There are typically two methods of mounting a flange facing machine to a flange in need of recovery; internally or externally. Internally mounted machines sit inside the flange with stabalising legs extending out and clamping in place. Externally mounted machines side around the outside of the flange with clamping legs that push inwards. You may see internally mounted machines referred to as ID flange facing machines and externally mounted machines referred to as OD flange facing machines.
At Mirage Machines we have manufactured the first internal/external mounting machine which can be used for either mounting position. This is unique within the industry and provides on-site machining service companies with an asset capable of multiple machining applications.
Servicing or production
The flange facing is a process often associated with flange recovery as part of routine plant maintenance processes. The process is not limited to maintenance though as many machines are used are part of manufacturing production processes,particularly in the production of wind turbines.
“Whether our flange-facing machines are being used in a maintenance or a production setting, there is invariably pressure to get the work done as quickly as possible. On top of that, there is a huge demand for machines that can be easily operated by less highly trained individuals.” Mirage managing director Richard Silk
“The makers of wind turbines are under immense pressure to increase productivity,” says Silk. “Their order books are filling rapidly as more and more wind farm developments get the go-ahead in many countries around the world. Flange facing is a significant part of the manufacturing process: the composite blades are each finished with a part-steel flange to connect them to the turbine generator, which itself sits on a steel flange on top of the tower. Getting the tower flange very flat is particularly important, as this has been found to heavily influence the life of the bearings in the turbine. Here, we are seeking to achieve 0.1-mm flatness around a flange that can easily be 2–3 m in diameter.”