Gräbener Maschinentechnik GmbH & Co. KG

Netphen. A leading global manufacturer of longitudinally welded large-diameter pipes relies on the special machine manufacturer from the Siegerland region. With the new Graebener® Pipe Bending Press, the global player optimizes its production processes and is able to manufacture an enormous range of the most diverse special pipes with a wide range of dimensions and extreme diameter-to-wall thickness ratios.

The machine manufacturer Graebener® Maschinentechnik has been building customized machines for use in pipe mills for decades. The recently developed pipe bending press is used for bending open seam pipes and half-shells in a step bending process. The special feature of this custom-built machine is its enormous flexibility, as it can be used to produce tubes of the most varied dimensions: with outside diameters from 12" to 48" (up to 100" for half-shells), wall thicknesses from 12 to 75 mm, and lengths between 6 and 13.2 m. Above all, the unique feature of the bending press is that it can also be used to produce tubes with very small diameters and high wall thicknesses. Materials with high yield strengths, such as X80, X90 and X100, are processed without any problems. For such an enormous production spectrum, large-diameter pipe manufacturer normally need several lines.

Another economic plus point common to all Graebener® Pipe Bending Presses is the enlarged stroke of the bending sword as well as its stable lateral guidance. The enlarged stroke ensures that the sword can be completely pulled out of the tube after completion of the bending process. This means that the remaining gap in the tube can be closed directly in the machine with the aid of the sword itself. The stable lateral guidance makes this process possible even for small, thick-walled tubes. An additional pipe closing press, as would be regularly used, is thus no longer necessary.

With the Graebener® Pipe Bending Press, investment volumes can be reduced and production cycles shortened - the basis for a long-term economical production process.

Technically superior

The bending press has a press force of 70,000 kN, which is achieved by six controlled hydraulic cylinders on the bending sword. Thanks to a special force distribution and control system, even the small, thick-walled tubes can be produced. For six-meter-long tubes, for example, the press achieves a press force of an exceptional 52,000 kN.

If tube diameters of up to 100" are to be produced, the press can be used to bend half-shells which are later assembled into a tube. A specially developed handling system ensures the automated removal of the half-shells after the bending process. Simultaneously, all process parameters are stored with help of the Graebener® BendPro automation system, so that the settings and travel range for recurring products can be recalled at any time.

Faster production of different batches

On the one hand, large pipe producers have to ensure high throughput with consistent quality. On the other hand, they are expected to respond flexibly and quickly to customer requirements, even for special dimensions and small batches. Frequent tool changes, however, especially for small batches, cost time and money. All Graebener® bending presses are therefore designed in such a way that the various tube sizes in the standard dimension range can be produced flexibly and without changeover using only a single tool set. The changeover time for dimension-dependent tools is eliminated and thus contributes to increasing the efficiency of the bending process.

Limited heavy-duty route requires design rethinking

It was not only the customer's requirements that demanded special design solutions. The new pipe bending press was also a challenge for the special machine builder from a logistical point of view. Due to the required output and the resulting design, the press weighed around 1,100 tons and was not only the largest and heaviest pipe bending press in the history of Graebener®, it also required a special design of the cross beams. Since these far exceeded the maximum weight of the heavy-duty route, Graebener® carried out the construction in such a way that the individual cross beams were manufactured in two parts and welded together on site.

Kreuztal/Netphen. The company Eisenbau Krämer GmbH (EBK), an internationally renowned specialist for the production of large steel pipes once more banks on an innovation by the special machine builder Graebener®. Graebener® delivered a 2-Side Pre-Bending Press for the production of thick-walled pipes which raised the pre-bending technology to a new level.

Up until now, the company EBK, internationally renowned for high quality pipes, has been using conventional roller pre-bending machines for the pre-bending process. During the roller pre-bending process, top and bottom rollers move along the plate in parallel which creates the corresponding radius at the longitudinal plate edge. This standard procedure has proven and established itself over decades and is the most widespread pre-bending method worldwide. In the meantime, however, this process is being looked at more and more critically. The problem of the process is the creation of thinning in the material which in turn requires extensive reworking efforts to achieve a high pipe quality. Ever increasing requirements for pipe tolerances and weld seams are becoming more and more challenging for pipe manufacturers – especially when it comes to high quality special pipes for the gas and oil industry. For this reason, EBK was looking for a solution and turned to the German company Graebener®.

The Graebener® 2-Side Pre-Bending Press, in contrast to the roller pre-bending machine, is suitable for the simultaneous pre-bending of both longitudinal plate edges in a step-by-step process. While the plate is moved through the machine step-by-step, the longitudinal plate edges are pre-bent to the respective radius by means of the upper and lower pre-bending tools. This way, crushed edges and thinning out of the plate ends can be avoided.

This process is not an entirely new one on the market, but up until now has been causing a plate waviness throughout the entire length of the pre-bent edges. As the goal is to produce a perfect open seam pipe, a faultless weld seam and thus achieving a zero gap without edge offset are very important. Otherwise, excessive reworking efforts such as multiple calibration steps are necessary to compensate and remedy the waviness. Thus, avoiding a plate waviness during the economic production of open seam pipes with proper zero gap is indispensable.

Graebener® has taken up this issue and developed the machine in such a way that today various international customers rely on the Graebener® 2-Side Pre-Bending Presses. Together with EBK, the process has been further perfected during the last year. The key to success: perfectly designed tools.

The tool contour was optimized so that now plate waviness in the pre-bent edges is a thing of the past. Today, the Graebener® 2-Side Pre-Bending Press can achieve a result which is unrivaled worldwide: 100% forming of the pipe, i.e. an open seam pipe with zero gap, no edge offset and with a perfect weld seam preparation. "Our Graebener® pre-bending press is operating with such precision that we can significantly reduce  additional process time on the Graebener® calibration press," says Dr. Scott McCann, Managing Director at EBK.

The Graebener® 2-Side Pre-Bending Press can be used independent of the material (suitable for all kinds of common steels in pipe production, especially Clad material) and can process plates with increased wall thickness and of high steel qualities and special grades.

The forming tools necessary for the pre-bending are designed for cost efficiency. To reduce the number of tools necessary, they are designed in a way that they can be used for wide diameter range with a variety of plate thicknesses.

Hubertus Valpertz, Authorized Officer and Technical Manager Sales at Graebener®, lists yet another cost advantage: "Our process creates a constant pre-bending over the entire plate length, i.e. even at the beginning and at the end of the pipe to be produced. Due to this constant form, in contrast to the conventional roller pre-bending method, the entire plate length can be processed further which eliminates the previously required cutting of the two pipe ends. This, in turn, leads to a significant cost reduction."

EBK has been trusting in Graebener® and the company's know-how in the sector of material forming for decades. Dieter Kapp, Managing Partner at Graebener®, has high hopes for the sophisticated technology: "The pre-bending results with our press for wall thicknesses larger than 50 mm are unparalleled. No matter how accurately the works were carried out in the past, with the technologies available to date it simply was not feasible physically to eliminate waviness over the entire pipe length for this wall thickness range. This chapter is closed now. I am absolutely sure that our solution with conquer the market very soon."

Netphen. To this day in large pipe manufacturing, the production large-diameter pipes in a step-by-step process is set up and monitored manually using templates. This is time-consuming and requires well-trained machine operators. fabforce®, in cooperation with Graebener®, has now developed a radius measurement system that allows the radius to be checked conveniently, safely and precisely via a monitor. In addition to this, the system offers insights into the material behavior of the pipe. An important milestone on the way to a fully automated bending process.

Since the beginning of large-diameter pipe production, it has been common practice to check the individual steps in the bending process using a template. In other words, the operator interrupts the bending process at regular intervals and measures the result using an analog template which he places on the partially bent pipe. For this purpose, the machine must be switched to safe mode and the operator has to leave his operator desk. During all this time, the machine is not working productively. Therefore, the time exposure and the costs of manual measuring are quite significant. The industry has long been striving for an uncomplicated and cost-effective solution. fabforce®, a company specializing in Industry 4.0 applications, has taken up the issue and, in cooperation with Graebener®, a special machine manufacturer with a 100-year tradition, has developed a digital template that paves the way to a fully automated pipe bending process in the medium term.

The RadiiPro® radius measurement system uses a laser system that transfers the contour in the bending process to the operator's screen in real time. The trick: the measurement system is located in the lower tool and can therefore measure live during the entire bending process, even under load. At the same time, the software compares the bending of the contour with the desired target radius and calculates the contour deviations. This way, the forming differences without load and under load can be seen. The result is displayed precisely and objectively within milliseconds on a screen in the operating panel. For this reason, non-productive times of manual measuring as well as possible misinterpretations when placing the template are avoided. In addition to this, the information obtained can be saved for each pipe, enabling transparent quality management right up to the final product.

But the RadiiPro® application has even more to offer: the calculation of the local curvature of the contour. A characteristic value with considerable potential. This value offers the advantage that the degree of current deformation can be displayed with high precision even on very small measuring sections. This way it can be seen in minute detail which areas are actually formed and in what way. The operator gains information about the optimum bending step width, the correct tolerance values and the evenness of the pipe.

Incidentally, the data of the curvature also allow a multitude of further conclusions, e. g: Does the steel mill supply the correct quality? How can the workpiece properties be ideally reacted to in subsequent processes? Does the quality vary within the component or batch and, if so, within which tolerances?

Fabian Kapp, Managing Partner at fabforce®, sums up the advantages in a nutshell: "No matter how qualified an individual operator may be, a human being cannot in fact keep up with the precision and speed of our measurement system. Added to this is the safety advantage and the immense additional gain in information. Our application offers our customers the opportunity to clearly set themselves apart from the competition and to lay an important foundation for the digitalization of their pipe mills".

In the medium term, fabforce® and Graebener® are even aiming at full automation of the entire pipe bending process. "This would then allow the forming of any common material quickly and in highest quality - without any operator training, without corrections and without non-productive time," says Hubertus Valpertz, Authorized Officer and Technical Sales Manager at Graebener®.

fabforce® has also specialized in the backup and evaluation of machine data. In connection with the RadiiPro® data, there is huge potential for process optimization: from tracking the pipe quality through the entire production process up to the monitoring and maintaining of the machine quality over the entire life cycle.