At the heart of each plastic extrusion machine is the extrusion screw which is carefully designed to transport the raw material, heat it in a pre-defined manner and deliver it to the die. With machines often having to manage changes in in-feed material the extrusion screw is liable to jam and so has to be protected by a torque limiting device; the ideal solution from an operating cost point of view, is to fit an adjustable torque limiter that can protect the machine effectively while being fast and easy to re-set.
Plastic extrusion equipment is used across a wide range of industries for creating a huge variety of profiles and products, both flexible and rigid. In many cases the extrusion screw is specifically designed for a particular application and is the most costly aspect of the design. It is therefore crucial that this essential component is properly protected during operation so that it remains undamaged in the event of a blockage. Furthermore, it should be possible to clear any obstruction, reset the local protection devices and continue with normal production at the earliest opportunity.
Due to the versatility of extrusion machines, a variety of raw materials can be used but this has a significant impact on the design of the extrusion screw. In effect each one is crafted to suit the properties of the raw material and temperature at which the material needs to be delivered to the die. Needless to say, incorporating a safety mechanism that will prevent damage to the screw that may be caused by overloading would be a sensible precaution.
When designing a torque limiter into the machine to provide the best possible overload protection, it should ideally be placed as close as possible to the source of the jam. This will allow the system inertia and torque to be quickly and effectively disconnected from the jammed section. The system can then be allowed to coast to a stop without causing further damage to the machine.
Designers of plastic extrusion machines are required to concentrate on matching the screw design to the application and the materials involved as well as ensuring there is sufficient power for the process. The inclusion of a protection device between these two elements is essential for preserving the more costly components in the event of a blockage or overload.
The Ultimate Extruder Protection device or UEP range of modular torque limiters from Bibby Turboflex, part of Altra Industrial Motion, has been developed to provide optimum protection against overloads and deliver maximum safeguarding against expensive failures and prolonged downtime on machinery. It offers users the key benefits of simplified installation; very accurate release torque repeatability, achieved with minimal variation between static and dynamic release; simple fast manual re-engagement; and low cost maintenance.
The design of the UEP torque limiters has been based on 30 years’ experience in arduous applications and refined over time, culminating in the current range of products. This proven track record has led to the UEP range becoming the industry standard for twin screw extruders.
The UEP range of modular torque limiters was designed specifically to offer an alternative to shear-pin protection for high torque drives where its accurate release torque repeatability coupled with the fast reset feature offers a significant reduction in downtime. Also, being relatively tamper-proof, it prevents unauthorized personnel from changing the release torque setting, which can range from 450 Nm to 15,000 Nm, depending on the application.
The optimised design of the UEP torque limiters also means that installation is highly flexible, enabling the centre section of the torque limiter to be removed without the need to move the motor or gearbox. Similar design versatility ensures that any maintenance of the modules is a straightforward operation and that recalibration is a simple removal operation achieved without having to replace the complete torque limiter unit.
As part of Altra Industrial Motion, the Bibby Turboflex product line is supported by the extensive, worldwide network of sales and service facilities that can provide in-depth knowledge and support to designers, OEMs and end users.