Creasing-unit Transmission Study Part II

Abstract

The aim of the thesis was to help Tetra Pak with problems that have occurred with the creasing-unit. This unit is one of great importance in the production line for a final package with good quality. The unit is built up in modules, where each module performs the wanted operation. The motion between and in the modules is transferred by a gear transmission.
The quality of the packages is decided by the precision in the transmission and therefore the backlash in the transmission must be kept within the right values to get the accuracy wanted.
This project consisted of three parts. The first part was to make a structural analysis of the currently used gear transmission in the creasing-unit. Secondly a completely new type of transmission or solution to transfer motion between the unit cylinders is searched for. Finally a new drive of the creasing-unit that gives a quicker connection between the creasing-unit and the motor is searched for.
The structural analysis show that the gears easily can break with the now used 10° pressure angle. Gears with 20° angle handle the stresses better. The reason for breakage is that the gears are often out of tolerances and the inaccuracy in mounting/adjustment gives that sometimes negative backlash occurs. Problems also exist with interference this is studied in the other thesis.
Alterations to the used solution with change in some parameter like an increase of the amount of teeth, a reduction of the root-radius and rounded edges in the plane between the two parts of the divided gear could change the performance.
The theoretical values show that an increase in the amount of teeth should reduce the stresses. On the other hand will a reduction of the root-radius increase the bending stress but reduce or completely eliminate the effects of interference. Cracks usually initiates from sharp edges and when divided gear is loaded during negative backlash breakage easily can occur. It is shown from the FE-analysis that rounded edges reduces the stresses to about half in the regions were cracks have initiated in the broken gears sent back to Tetra Pak.
How these solutions are best combined will have to be studied further if they should be implemented in the creasing-unit.
A new type of transmission could replace the one now used. By using conical gears that are loaded by a spring in the axial direction backlash could be completely eliminated. This solution needs no adjustment between orders. One of the main advantages is that it is probably quite easy to adapt this solution to the existing creasing-units and the older units already in production.
The drive between the motor and creasing-unit is now by a belt. To mount/dismount the belt takes time and better safety is wanted in case of an emergency stop. This could all be solved with a specially designed safety clutch. This clutch consists of a safety against emergency stop and an elastic element for a quick connection that also can handle misalignments that can occur in the system. When the creasing-unit is moved
iv
into position this connection automatically connects engine with the unit. No supervision or adjustments after insertion is needed.

• author: Karlsson, Emanuel
• supervisor: Giorgos Nikoleris
• organization: Innovation
• course: MMK820
• year: 2008
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Creasing-unit, Divided gear, Gear calculations, Conical gear, Backlash, Elastic connection, Intermediate gear, Safety clutch
• language: English
• id: 1497261
• date added to LUP: 2009-11-09 10:20:17
• date last changed: 2010-02-01 14:40:04