Waar brute krachten zinvol aan het werk zijn

The steel support rollers produced by Artur Küpper in Bottrop for high-performance conveyor belt systems bear the full load on their flanks for 12 to 15 years. They handle mass flows that can be as much as 37,500 metric tons per hour for transporting brown coal (Figure 1). Depending on the belt width and transport capacity, the trough-shaped conveyor belt runs on a combination of two or three support rollers, which is called a ‘garland’.
For more than ten years now, the company has been successfully managed by Werner Christiansen, and during that time Küpper has become the European market leader in gravity rollers. It provides its customers, including all major conveyor system builders worldwide, with products that are developed, designed and manufactured to fulfil the needs of specific applications.

A robust machine design for massive machining

Production of support rollers at Küpper in Bottrop also reflects more than 30 years of experience. The production process involves the individual steps described below. Starting with 6-m lengths of C 45 steel rod stock, the first step is to cut the roller axles to length using automated saws. This is followed by longitudinal machining on a lathe. After this, the ends of the axles are milled to a concave profile, a key flat is machined, and a transverse hole is bored (Figure 2).
Here production manager Rolf Schwandtke (Figure 3) can point to rapid evolution in terms of manufacturing technology: ‘In the 1970s, our machines were still predominantly conventional. Final machining was performed using three separate machines in turn, and they had restrictions with regard to the machinable range of diameters. In the 1980s we followed the trend to CNC technology for turning and milling. The milling machine we purchased then had a single workspace with a machining length of 1.7 metre. Despite a multiple clamping fixture, we had considerable non-productive times during loading and unloading with a crane. Support rollers have also become longer and longer over time, so we have acquired a modern machining centre with shuttle-mode operation.’
Relatively small and light axles with diameters up to 50 mm are now milled on this machine. The drive power and torque of the spindle, as well as the robustness of the machine, were not sufficient to handle massive machining work, such as machining the ends of the increasingly heavy axles. The large key flats, with a cutting depth of 10 mm on each side, had to be produced using a time-consuming process involving several steps. In addition, the very nimble tool changer (2 seconds clamp-to-clamp time) proved to be a weak point in everyday operation. It was recently necessary to completely rework the curves in the motion controller. As the capacity of this machine ultimately became a bottleneck, a decision to make an additional investment was made one year ago.

A difficult requirements profile fulfilled in all respects

The technical requirements specification generated by company management and the employees proved to be extremely selective: ‘We wanted a solution without any compromises. Our first requirement was for a mature, robust machine design that would provide the basis for high availability and process reliability. We work six days a week with three shifts, and this makes reliability an absolute must. A second criterion was drive power, which had to be sufficient to generate the key flats with a single clamping. With the exception of tool changing and fitting new parts, there should not be any non-productive times, and in this regard we were convinced that a moving-column machine operating in shuttle mode was the right approach. As we produce axles with lengths up to 3 metres, the machining length had to be at least 6.5 metres. Finally, of course, the price/performance ratio should be suitable.’
Particularly with regard to the last criterion, Meppen-based HEDELIUS emerged from the selection process as the favourite.

The company specialises in vertical machining centres designed for high cutting capacity with torsionally stiff machine bodies built using welded box construction and carriages running on broad guideways. The choice fell on a BC 100 moving-column machining centre (Figure 4). The following properties of the machine are essential for fulfilling the requirements:

• a 50-kW servo spindle with a torque of 528 Nm

• a stiff SK 50 tool holder

• a travel distance of 6.5 m in the X axis for shuttle machining

• a supplementary, screened pick-up magazine on the machine table, mounted outside the machining area (Figure 5)

• an ergonomic workspace with good access thanks to angled doors

Following extensive information, the machine was delivered within three months

Another decisive factor was after-sales service, with which HEDELIUS strives to underpin long-term customer loyalty. Sales representative Peter Schnieder (Figure 3): ‘As far as I know, HEDELIUS is the only manufacturer that guarantees 95 percent availability of the machines and 24-hour local service for all of the machines in the standard configuration. Naturally, you can only venture this if the availability is actually higher. Other manufacturers are very reluctant to give such guarantees and do so only under pressure, so they take only isolated risks.
Investment decisions of this magnitude are prepared especially carefully in privately run companies such as Küpper, and the responsibility is distributed over as many people as possible. For instance, the machine operators were given an opportunity to look around for suitable solutions three years ago at the Metav trade fair in Düsseldorf. At the HEDELIUS stand they obtained a good initial impression of the machines on exhibit, after which Rolf Schwandtke contacted the machine builder. This was followed by visits to several existing customers and a visit to Meppen to inspect the machine production facilities. The mutual trust attained in this way ultimately led to a contract. Sales manager Dennis Hempelmann (Figure 3): ‘As far as we are concerned, the achieved delivery time of three months after confirmation of order was a tour de force considering the size of the machine. After all, this wasn’t an off-the-shelf machine – it had to be built first. This is where our tight organisation and the reliability of our suppliers pay off. Nevertheless, in the future we aim to have delivery times of less than 16 weeks for all machines. In order to achieve this, we will further expand our production area. This is the only way we can extend our product spectrum with additional innovative solutions. A new machine generation is already in the pipeline for next year.’
An entirely new approach to machine control was also taken with the Küpper machine. Machining expert Schneider recommended the TNC 430, ‘because in our view Heidenhain is the first choice due to the logical overall concept and the extensive package of functions.’ The controller of the Küpper machine is also advantageous because the company produces different versions and certain cycles are fixed components of the NC program. They can be modified directly at the machine for new parts and stored on a large hard-disk drive. In contrast to other controller manufacturers, these programs can also be used unchanged after switching to a new controller generation.
Due to these aspects, more than 90 percent of the customers, which are predominantly small or medium-sized companies, choose a Heidenhain controller when they buy a HEDELIUS machine.

No vibration at low speeds

For the machine builder, milling the key flats using the large Iscar slot milling cutters was the ‘key machining operation’(Figure 6).

According to Schneider, they ventured into uncharted territory with this because there was a lack of comparable machining parameters up to then. It was uncertain whether the massive machining operation, which occurs at low speeds due to the large diameter of the slot milling cutters (up to 250 mm), would cause vibrations that would be superimposed on the natural resonant-frequency behaviour of the machine.
However, all their concerns – including those of production manager Rolf Schwandtke – were put to rest in the tests. ‘There are lots of manufacturers of machining centres that boast non-engaged feed rates of 70 mm/min, fast tool changing, and wonderful cutting volumes in aluminium. HEDELIUS has shown that a balanced, robust overall concept can also master this difficult machining task. With the Iscar flute milling and slot milling cutters, we have invested in high-performance and durable tool technology, which we can now finally exploit fully on the machine performance side.’
The reliability of the machine in its first year of use has confirmed the investment decision. Although the ancillary times are somewhat longer because it does not have a tool changer, so the spindle has to travel to the magazine located in the middle instead and pick up tools there directly, this is relatively unimportant with a machining component of 97 percent. In addition, there is no possibility of problems arising from a tool changer – which is exactly what the user wants.

USER

In 1933, Artur Küpper founded a plant in Velbert-Tönisheide for producing special anti-friction bearings. These specially made bearings, which are used in the automotive, conveyor, machine building and transfer system sectors, are still one of the two principal products of the company. Support and conveyor-belt rollers for piece goods and bulk goods logistics systems were launched as a new product in 1950. The principal customers in the piece goods area are the beverage and packaging industry and package and container conveyor systems, and in the bulk goods area they are brown-coal and hard-coal mining operations and conveyor systems for sand, stone and soil. In 1971, this production area moved to a new site in Bottrop due to capacity shortages. The site was subsequently expanded in two stages in 1977 and 1993 to its present size of approximately 7000 m2 of roofed-over area. The company has around 200 employees, of which 120 are at the Bottrop site, who generate an annual turnover of 21 million euros under the leadership of Werner Christiansen.

Artur Küpper GmbH & Co. KG,
Plant 2
46209 Bottrop, Germany
Phone +49 (0) 20 41/1 77-0
Fax +49 (0) 20 41/1 77-1 00
www.akuepper.de

Helmut Damm
"Machines and systems"

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Figure 1: In leading roles: trough-shaped conveyor belts for transporting bulk goods, running on durable support rollers made by Küpper; Photo: Küpper, Bottrop