Tooth on tooth

Screws with external toothing have a double function, and both drive and sort.

Thanks to existing knowledge from various different sectors, Manfred Dilling was able to draw upon various ideas for different PET bottle transportation methods. The company was founded in the year 2000 in Germany, and now employs 20 employees. In 2002, a second plant was founded in Slovakia. Before starting up his own business, Manfred Dilling was a mechanic for a major packaging machine company. In this role, he gathered extensive knowledge of designing, assembling, and servicing packaging machines. Manfred Dilling Metallbearbeitung & Maschinenbau specializes in the manufacturing of machines, the overhauling of old machines, the design of form sets for packaging machines, and special customer-specific machinery. In addition, the Baden-Württemberg company also acts as a subcontractor for companies in the packaging sector, automotive industry, aviation branch, and shop fittings construction industry.

Dilling was able to use this expert knowledge in order to develop a solution whereby feed screws are installed on both sides of the system in the feed zone just in front of the first capping carousel. These screws gently and smoothly ensure the trouble-free transportation of the bottles out of the tailback. The sticking points: A drive is only available on one side of the feed area; thus, only one screw can be driven.

In addition, Manfred Dilling had to consider the extremely complex contours of the bottles. The solution: Both screws were given external toothing, allowing the first screw to drive the second.

Manfred Dilling Metallbearbeitung & Maschinenbau is based in Schrozberg, Baden-Württemberg, Germany and was confronted with this filling issue in summer 2010 as the result of a customer inquiry. The customer in question required a filling solution with low material consumption and thus a reduction in costs for a new product - a glass cleaner. At the same time, the separation process was required to be as trouble-free as possible, with the bottles of glass cleaner being conveyed to the downstream capping carousel without jams.

The system used by the customer was a machine that conveys PET bottles standing in cartons as described above. The bottle-filled cartons were separated using a plastic screw.

Around 800 million PET bottles are in circulation each year in Germany. This is a huge quantity - and it's sure to rise further in the future. PET bottles are now indispensable in today's drinks, cleaning agents, and cosmetics industries, since they have irrefutable advantages in comparison with glass bottles: They are light, not prone to breakages, and have a low transport energy requirement.

However, some problems do arise when filling PET bottles. For example, a PET bottle quickly deforms as a result of dynamic pressure; this often results in the undesirable leakage of liquid products. To prevent this, stable product cartons and bases generally space out the PET bottles and safely convey them onwards. However, this solution increases costs since the product cartons have to be produced especially for filling transportation processes.

Results: These screws have been used since October 2010 and run in three-shift operation with no disturbances. The Murtfeldt screws have enjoyed full acceptance by the customer; however, it has been possible to improve the performance per minute of the machine by around 15% by means of making various fine adjustments to the machine as a whole. In addition, a further improvement in throughput is possible thanks to the trouble-free feed system and great separation method.

The customer is also impressed with the fact that only one drive is needed for the screws and by the material savings, since cartons/bases are no longer required in order to transport the PET bottles. The clean, jam-free method of transportation to the downstream capping carousel has also gone down extremely well. "Thanks to the fact that the system is practically malfunction-free, it was also possible to cut down on production personnel and use these people more effectively elsewhere" says Manfred Dilling, pointing out a further advantage. He's certain of one thing: "Thanks to our positive experiences during this project, we are keen to work with Murtfeldt again in the future."

Murtfeldt Kunststoffe was provided with the design data for the screws - including the diameter, overall length, separation distance, and end machining data - and used it to determine missing parameters such as the toothing size of the module, the gradient of the separation gap, and the recesses. Moreover, Murtfeldt had to make sure that the screws can be inserted and removed by means of a quick-change mechanism.

The screws and their external toothing are manufactured in four steps. In the first step, the inner and outer contours are turned from the blanks. In the second step, the long-standing Dortmund-based company manufactures the tool for the external toothing; this is used to incorporate the product helix in step three. In the last step, the front ends are cut to make the product the correct length.

Murtfeldt uses Murytal C Black for both feed screws. The first screw, which is mounted on the drive side, has a diameter of 160 mm and a length of 1000 mm; the second screw, which is driven by the first, has the same diameter but is 750 mm long.

Manfred Dilling requested the collaboration of the Dortmund-based plastics manufacturer and processor Murtfeldt Kunststoffe for the final construction and realization of the screws. Murtfeldt Kunststoffe has been a supplier of Manfred Dilling Metallbearbeitung & Maschinenbau for several years already - and always delivers goods punctually and to the company's full satisfaction. "In addition, when I phoned Murtfeldt to make my inquiry, it turned out that Murtfeldt has just installed a new machine for manufacturing screws and had seen extremely good results already," explains Manfred Dilling, as he reflects upon other reasons for strengthening the company's ties with Murtfeldt. Although his company did make inquiries of other screw manufacturers, no other firm was able to reassure him that it could satisfactorily carry out the task at hand.

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