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f+h Intralogistics 3/2014

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f+h Intralogistics 3/2014

From Research Faster

From Research Faster conveyance with quiet chains Klaus Nendel, Jens Sumpf, Sebastian Weise, Markus Grünert, Peter Bloss, Kathrin Klamt The recent development of a plastic chain conveyor system has led to a significant reduction of noise levels in production and storage buildings. This lowering of the sound pressure level allows greater conveying speed, without the generation of additional noise. The main functional element of the chain conveyor system is a hybrid component made from polyamide (PA) and thermoplastic elastomer (TPE), with which joint play is reduced to a minimum and wear compensated for during operation. 01 Whisper chain design Prof. Dr.-Ing. Klaus Nendel is Head of the Institute of Materials Handling, Conveying and Plastics Engineering at the Chemnitz University of Technology. Dr.-Ing. Jens Sumpf is Group Leader of Traction Mechanisms and Tribology, Markus Grünert and Sebastian Weise are members of research staff at the same institute. Dr. Peter Bloss is Managing Director of the Kunststoff-Zentrum in Leipzig gGmbH. Kathrin Klamt is a research associate in the area of Processing Technology at the same institute. The automation of cargo transport is essential for the flexible organization of material flow processes in production and service companies. In addition to the established workpiece carrier systems, sliding chain conveyors have become a popular choice in recent years for handling and chain processes, used for the internal transport of smaller, lighter cargo, whereby the chain glides along guide rails as a drag and carry mechanism. Plastic chains that require no lubrication are an increasingly popular choice here. When compared to the equally popular steel chains, this specific material boasts a number of advantages, e. g. low weight and favorable sliding properties, as well as high corrosion and media resistance. However, in the knuckle or cardan joints of the chains, tribological effects and a relatively large joint play that increases during continuous operation due to wear, lead to strong noise emissions that involve squeaking, creaking and rattling. In view of this, a joint project involving the Institute of Materials Handling, Conveying and Plastics Engineering at the Chemnitz University of Technology, the Kunststoff- Zentrum in Leipzig GmbH (Germany), tool manufacturer pro forma GmbH from Radeburg (Germany), plastics processor Hugo Stiehl GmbH in Crottendorf (Germany), and the conveyor manufacturer Beyer Maschinenbau GmbH in Rosswein (Germany), saw the development of a lownoise conveyor chain with cushioning elastomer components, also known as the “whisper chain”. Chain development The problem with current systems, as described above, primarily lies with the type of joint used. All chains used in materials handling, both steel and plastic versions, are connected by knuckle or cardan joints with clearance. The way in which these connections move involves the contact surfaces sliding against each other, which leads to heavy wear in these areas and the negative effects described. The aim of the research project was to eliminate the 02 Hybrid spring joint made from hard and flexible plastic 18 f+h Intralogistics 3/2014

From Research 03 Deformation of the elastomer spring in the swivel process (FEM Ansys Workbench) 04 Stress-strain curves compared to standard reference chains use of joints with clearance within the chain while retaining mechanical properties such as stability and stiffness, and facilitating the use of the chain in current frame and guidance systems as much as possible. The approach thus taken involved a hybrid construction of mechanically and tribiologically suitable plastics, as well as a thermoplastic elastomer material (TPE). The first step was to come up with a suitable chain construction, as the tractive forces of the chain are not transferred by the elastomer. Based on the standard geometry of a multi-flex chain with cardan joints, a multipart solution was developed (Image 01) whose primary multi-functional element comprises a hybrid component (Image 02). The basic chain body, together with the joint pin, transfers the tractive force, while the supporting plate carries the material and transports its load into the rack via chain guide rails. The chain geometry is based on current chains and thus fits into standard guide profiles. The polyamide (PA) joint pin involves a spring element made from thermoplastic elastomer. While the pin transfers the tractive forces and brings about the horizontal and vertical swinging movements, the elastomer spring has three functions: n A light preloading is used to press the pin in the direction of tension, against the joint bore of the basic chain body. Even with an increase of joint wear, the joint tolerance and thus the associated rattling noises are entirely prevented. n The rear part of the wings reduces the side clearance to the next chain link. Furthermore, the PA spacers on the inside of the wings, which come into contact with the polyacetal material (POM) of the basic body, exhibit excellent tribiological properties. The otherwise “characteristic pairing” of the chain links that rub against each other, together with strong wear and any squeaking noise, are avoided completely. n The elastomer material has three excellent damping characteristics and thus also reduces any noise appearing in other areas. In terms of geometry and materials, the elastomer spring and remaining chain components have been designed using FEM in such a way that the horizontal swiveling movement of the chain is hindered as little as possible, and service life is not reduced through excessive stress on the components, e. g. critical notch stress areas (Image 03). About IFK The Institute of Materials Handling, Conveying and Plastics Engineering is engaged in the development of continuous conveyors for in-house logistics and their basic components. In doing so, it is working closely together with leading industrial enterprises. The scientific work has a main focus on calculation and dimensioning of chain conveyor systems as well as on fundamental research regarding friction and wear of non-lubricated plastic slide pairings. This results for instance in the development of plastic conveyor chains with improved mechanical and tribological properties. 05 Test stand for noise measurement in low-reflection half-space f+h Intralogistics 3/2014 19


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