Sleeper dowels are usually plastic or wooden pegs, the purpose of which is to fill the old sleeper screw holes. This should guarantee that the sleeper can be used again and prevent the penetration of moisture into the sleeper.
Octagonal interior pegs:
The wooden pegs are 110 to 130 mm long and have an octagonal cross section. They are made of hard or soft wood and are impregnated and protected against moisture. The pegs should fill in the old sleeper screw holes which occur in old wooden sleepers. As well as filling in the holes they should protect them from moisture.
Hollow dowels (material: compressed wood) are also impregnated and are made of beech or poplar wood. The beech dowels are required when reconditioning soft wooden sleepers, while dowels made of poplar wood are used with hard wooden sleepers.
Hollow dowels Hdü 2 / Hdü 3 (made of plastic material):
For use in rework of wooden sleepers in tracks and turnouts
Screwed inserts Sdü9 / Sdü9a:
Plastic threaded inserts are used to fix the coach screws in the concrete sleeper track.
Corrugated dowels Wdü 2 (made of plastic):
These are used for the replacement of hard wood corrugated dowels on concrete sleepers. Plastic corrugated inserts are used to secure the coach screws in concrete sleeper track. When inserting them in refurbished screw holes, care should be taken that the new dowels fit exactly in the hole as the shape of the hole is specified. The reconditioned concrete sleepers are then suitable for all the technical requirements of the insulation resistance.
Spiral dowels Spdü 1,2,3 - 4:
These are used for the reclamation and reconditioning of sleeper screw holes in wooden sleepers on track and turnout sleepers. They come in different colours, since different spiral dowels have to be used with different coach screws.
Reconditioning of concrete sleepers in the track:
Concrete sleepers must be renewed regularly to renew the tensioning between the screws and the sleeper and to correct the distance between the pair of rails.
Wooden sleepers tend to be damaged earlier and the tensioning is manipulated by the damage more often. Regular corrugated dowels have mostly been replaced by corrugated dowels Wdü 2.
You can find suitable specialist literature to the topic here:
The Basic Principles of Mechanised Track Maintenance
This book is dedicated to the many people involved in the day to day planning and performance of track maintenance activities. Providing a practical approach to everyday challenges in mechanised track maintenance, it is not just intended as a theoretical approach to the track system.
Railways aim at transporting people and freight safely, rapidly, regularly, comfortably and on time from one place to another. This book is directed to track infrastructure departments contributing to the above objective by ensuring the track infrastructure’s reliability, availability, maintainability and safety – denoted by the acronym RAMS. Regular, effective and affordable track maintenance enable RAMS to be achieved.
Best Practice in Track Maintenance, Vol 1 - Infrastructure Management
Infrastructure Management Volume 1 looks at aspects of infrastructure management with particular reference to the single European railway area. Based on best-practice examples from Central Europe, measures for the targeted retrofitting and improvement of the infrastructure maintenance of the existing network are presented. In many cases, infrastructure operators are faced with a generational change, which accelerates the process. Modern information and communication technology can simplify the comprehension and presentation of complex contexts. Modified approaches to asset management and life-cycle management enable implementation of the "transparent permanent way" or the "railway 4.0".