Lubrication-free testing

Two industrial clerks, four cutting machine operators, one technical drawer and one industrial technician formed a team. As part of their training at Munsch Kunststoff-Schweißtechnik GmbH based in Ransbach-Baumbach, this team was tasked with designing a bend testing device that is able to test the quality of a plastic welded seam according to the pertinent regulation, DVS 2203-5. This involves a destructive test where the measurement results have to be recorded or documented.
 
The main criteria for the actual measuring process are, firstly, positioning accuracy and, secondly, zero clearance of the testing device. Furthermore, special importance was placed on the following factors: freedom from lubrication and maintenance, robustness and long service life for the entire machine as it will be mainly deployed on construction sites.

The format of the bending punch is adjusted by a lead screw linear system from the drylin® SHT range from igus®. This involves a lubrication-free linear axis that is driven by a trapezoidal thread or high helix thread or toothed belt. From lightweight solid plastic units up to heavy-duty stainless steel solutions: the extensive range of modular products provides every user with a solution customised to their needs. The stroke length is freely selectable and the drive given either by hand-wheel or motor. "We rely fully on a standard solution with trapezoidal thread and motor", reports Marcel Keßler, industrial clerk at Munsch. He has completed his training in the meantime and now works in the company's sales and distribution department. The further technical data of the linear unit in the testing device are as follows: The shaft has a diameter of 12 millimetres. Hard-anodised aluminium is used as the material for the shaft.

The three support distances specified by the DVS are implemented by means of a linear guide. The drylin® W is a cost-effective harnessed system. The design allows flexibility during build and assembly thanks to the use of individual or double rails. Hard-anodised aluminium is likewise used as material for the rails; it provides the best friction and wear results for profile guides. The absence of lubrication makes the profile guide system extremely dirt-resistant. In the bend testing device, a round double rail with pillow block proves its robustness in locking and absorbing the forces from the respective plastic test specimen.

"As the measurement results are recorded, the aspects of positioning accuracy and zero clearance are of special importance," says Georg Krebs. This is ensured by an additional pre-loaded lead screw nut from SHT linear modules. The gliding material used here is iglidur® J. It provides the best results in terms of coefficient of friction and wear with a rail made of hard-anodised aluminium as counter partner. "As a construction site does not always offer optimum conditions, freedom from the need for lubrication and maintenance were also an important aspect," says Lars Braunisch looking back at the project. He has completed his training as technical drawer in the meantime. "The device has got to work even under difficult conditions. “

After a simple assembly procedure, only the motor has to be adapted to render the device fully functional. Thanks to the materials used, aluminium and plastic, the system concerned is not only robust but also light-weight; factors that contribute to its reliability in day-to-day operations. "Furthermore, it is economical", explains the designer. Dipl.-Ing. (FH) Bernd J. Wirtgen. "Polymer plain bearings are virtually unbeatable in terms of performance and price. This is the reason why they have been used in a large number of our products for many years now. "Alongside the two linear guides, an energy chain made of plastic, the second major Business Unit besides lubrication-free plain bearings of the motion plastics® specialist igus®, is used in the testing device for measuring the pressure of the testing stamp.
 
Consideration is being given to an extension in order to be also able to test thicker materials. The plan is to continue the collaboration with polymer specialist igus® when this idea reaches implementation stage.