Our industry trained operators use the latest CNC mandrel bending machines to fashion highly accurate bends to customer specifications.
Tube bending can vary from the simple tube bends seen on furniture and equipment handles to the complex form of a helical coils of an amusement park. Often the appearance of the bend is most important, especially if the item is to be seen as well as enhance the product or equipment. Other times the quality and precision of the bend is of greater importance. This is true for demanding application in the oil, gas and chemical production industries. A tube or pipe bend has to stand up to the rigours of its application. Many of our products must withstand extreme temperatures and pressures, this is particularly true for reformer tubes, which are used in process plants, and boiler tubing, used in thermal power stations. Uneek Bending produce countless bends for a wide variety of application. All bends are quality checked to ensure manufacture is to applicable standards. For example AS1228 for water tube boilers and AS4458 for pressure equipment manufacture. We also meet the requirements of ASME-I for power boilers and TEMA for heat exchanger U-bends.
Some of the most difficult bends are found on platen superheater elements. These bends, often referred to as squeezed bends, require a two stage process, first a critical cold bend and a second hot squeezed operation to achieve the tight outside radius/diameter ratios.
Mandrel bending is an often misused term. The term mandrel bend is often used to emphasize that the customer wants a good quality bend. The word mandrel technically only refers to the part of the tooling that is inserted inside the tube to prevent collapsing of the tube and minimize ovality. However, this is only part of the story. Technically speaking this type of bending is called rotary draw bending. In order to pull a good bend, the whole set of tools needs to be considered: the former, the clamp, the backformer (or follower) and the wiper die. All these, along with the mandrel (which may be of a plug, spoon, single ball or multiple ball type), need to be precision made from tool steel and hardened. Once completed, the tool alignment, as well as the clamping parameters need to be considered. We now have the setup up test.
All that is now needed to complete the bend is an experimental operation to check everything is set up correctly and a craftsman to man the electric hydraulic bending machine. As you can see it is not as simple as pressing a button to manufacture a quality bend.
Once the bend is completed it often needs further work done on it. For visual products it may need to be polished both mechanically or electro-chemically to achieve the desired finish. For bends that face high temperatures and pressures heat treatment to either enhance or restore their properties may be required. Typical boiler tube bends, for example, may undergo stress relief heat treatment. Or in the case of chrome moly tube bends, a normalizing heat treatment cycle followed by a tempering heat treatment cycle.
Stainless steel bends normally do not require any heat treatment, but if stress corrosion cracking (SCC) resistance is required the bends may need a solution heat treatment cycle. Or if the stainless material grade contains stabilizing elements a further stabilizing heat treatment cycle may be required. Uneek Bending offer all these processes complete with heat treatment charts and calibration records.
In demanding applications ovality (or deviation from perfect roundness), of the bend needs to be kept to a minimum. By careful selection of tooling and operating parameters (hydraulic pressures) ovality can be minimized. Where required Uneek Bending check and record the ovality of its bends. These records make up part of the MDR (Manufacturers Data Report) accompanying the final product.
The outside wall of the tube bend is stretched during bending, resulting in a reduction of wall thickness along the outside (bend extrados) of the part. This thinning needs to be kept to a minimum to ensure a high quality bend. This is achieved with the right combination of tooling, the right type of mandrel and correct pressures. Uneek Bending measure wall thickness of the pipe using ultrasonic thickness gauges. Again results are recorded and these records are included with the ovality documentation in the products MDR.
Uneek Bending can carry out destructive testing on sample bends by sectioning the bend in three places and measuring its flow area. This value can then be compared to the unrestricted flow area of the straight tube. This is an often overlooked part of QA for tube bends but can be very important in some applications. For example, changes in flow area can significantly impact the pressure drop in a system.