Seamless tubes are not only our passion; they are also part of our foundation: Since the Mannesmann brothers invented the seamless tube in 1885, we have continuously developed and enhanced the seamless tube production process. We work closely with tube manufacturers and partners, who serve the OCTG, construction, and automotive industries, to ensure that our technology and solutions meet the demands of the tube and pipe market.
Advanced mandrel mill technology
The continuous rolling process – using mandrel mills – has been successfully used as a method of producing seamless steel tubes since the 1970s. The mandrel mill comprises several two-roll stands, which roll the hollow longitudinally to form a shell. SMS PQF® (Premium Quality Finishing) plants allow for operation at maximum efficiency, optimized operational costs, and reduced downtimes without compromising on productivity and high-quality results; while conventional seamless tube lines cannot viably compete with the high-precision PQF® quality, nor with its levels of productivity.
A PQF® mill consists of up to six stands, with three driven rolls each. The force is therefore applied more uniformly across the circumference of the rolls than it is with MPM (Multistand Pipe Mills) technology featuring a conventional two-roll arrangement.
Whether high-alloy steel tubes or particularly thin-walled precision tubes, our PQF® technology is designed to produce even the highest-grade products efficiently and reliably. By using less material, it achieves better output than conventional solutions. This ensures savings in tool and energy costs thanks to low reheating during the rolling process and thus a smaller CO2 footprint.
Push bench mill (CPE/TPE)
CPE (Cross-roll Piercing and Elongation) and TPE (Three-roll Piercing and Elongation) push bench process
SMS group has further developed the push bench process into CPE (Cross-roll Piercing and Elongation) and TPE (Three-roll Piercing and Elongation). This means thee product range is has thereby been extended compared to previous concepts and the processes offer substantial benefits in terms of both quality and cost efficiency. Both methods differ from the conventional push bench method in the first forming stage, the piercing process.
With the CPE method, the piercing press, elongator, and hollow billet reducing mill are replaced by a high-performance two2-roll piercing mill, which acts as a piercing and pre-stretching unit. The process therefore requires fewer forming stages, so plant owners can reduce conversion costs measurably. At the same time, they can use higher billet weights and achieve better wall thickness tolerances. The output on CPE mills is considerably higher than with the conventional push bench method. Modern CPE mills, therefore, are a highly efficient, flexible, and economic alternative in the production of tubes with medium to small diameters.
With TPE mills, SMS group uses a three3-roll instead of a two2-roll cross-roll piercer. As a result, the quality of the hollow before the stretching process on the push bench has increased even further.
for the production of seamless heavy-duty tubes
The assel mill is a three-roll cross-rolling mill used for producing medium and thick-walled tubes of high quality and dimensional accuracy. They are mainly used for ball bearing tubes and general mechanical engineering pipes and tubes, which need to be subsequently machined. SMS group has continuously further developed this technology and thereby managed to double the maximum producible tube diameter. Today, tubes with an outside diameter of up to 460 mm and wall thicknesses of up to 80 mm can be produced on assel mills.
As part of the rolling process, a mandrel bar is inserted into the hollow – with the conventional assel process it is free-running, and with high-performance assel mills it is moved in a controlled manner. SMS group has further developed this proven technology for such high-performance assel mills, meaning the technology has been improved and the dimensional range extended.
Hot pilger mill
For the production of seamless tubes up to 28 inches
The hot pilger rolling method is one of the oldest processes for elongating pierced billets into tube shells. Today, it is mainly tubes for the power generation, petrochemical, and construction industries that are produced on hot pilger mills. A key feature of SMS group’s hot pilger mills is the large dimensional range of rollable stock – even for high-alloy steel grades.
Rotary expanding mill
For the largest-diameter tubes
SMS group rotary expanding mills are used for producing seamless tubes with very large diameters, which cannot be produced on a ‘normal’ seamless tube plant. The tubes are first heated then rolled to larger dimensions – using this technology plant owners can produce a wide spectrum of finished tube diameters and wall thicknesses from just a narrow range of primary products.
The rotary expander is a special kind of cross-rolling mill with conical, axially adjustable rolls. The tubes are expanded by rolling them over a plug. The position of the rolls mandrel here determines the wall thickness of the tubes. This can also be adjusted hydraulically during the rolling process.
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Quality right from the start
The piercing process is at the top of the process chain, which starts with the solid steel billet and ends with the seamless tube. It is of crucial importance for the subsequent quality of the finished tube, as the billet must demonstrate excellent surface and tolerance characteristics straight after piercing. Only then is it possible to produce high-quality tubes with flawless surfaces and high dimensional accuracy. The high-performance cross-rolling mills from SMS group are perfectly designed to achieve this, enabling particularly cost-effective production at the same time.
Cross-roll piercing ranks as the leading piercing method for seamless tubes and offers considerable advantages compared to alternative methods such as piercing presses or press-piercing mills. Plant owners are able to process heavier billets as well as achieve measurably closer wall thickness tolerances.
As an alternative to the two-roll piercing mill, three-roll piercing mills are also used for the piercing process. This further improves the wall thickness quality of the hollow.
SMS group has continuously further developed the cross-roll piercing process with several inventions, such as hydraulic gap control. Today’s high-performance cone-type piercers produce particularly thin-walled hollow blooms with very tight tolerances and the highest levels of productivity. These innovations give advantages during the subsequent processing stages in the production of seamless tubes: the loads on the elongating and sizing units are reduced and the production range can be increased. This enables tube manufacturers to produce more cost-effectively – even in the case of large dimensional ranges, small batch sizes, and low capacities.
Billet centering machine
BCM for centered piercing
The Billet Centering Machine (BCM) ensures that the plug enters the billet exactly in the center to optimize the rolling process. For this purpose, the BCM makes recesses in one or both ends of the billets before the piercing process. As a result, the plug enters the billet precisely in the center.
Rolling solid billets over a piercer plug creates ‘hollows’. It’s crucial here that the piercing plug contacts the billets exactly in the center, otherwise faults known as ‘onion rings’ occur at the ends of the pipes. To avoid this, BCM makes recesses in one or both ends of the billets before the piercing process. As a result, the plug enters the billet precisely in the center, creating virtually no onion rings as it exits.
Moreover, the BCM ensures minimal wear on the plug and uniform wall thicknesses. Due to the optimized rolling process, the BCM also leads to increased productivity.
- Optimized rolling process dues to the exactly centered entering of the piercing plug into the billet
- Optimized product quality through uniform wall thickness
- Increased productivity thanks to minimal wear on the plug