Development of journal design and joining method in a tissue machine press roll

Sammanfattning

The pulp and paper industry is a major industrial sector worldwide, with an annual production of more than 400 million tonnes. Manufacturing processes are highly energy dependent, making up 52% of total energy consumption for all Swedish industries during 2023. As such,efforts to improve energy efficiency and reduce environmental impact are crucial with increasing global warming. Efforts from companies producing paper machines introduces flexible loading elements for press rolls in the dryer section, which increases mechanical dewatering prior to thermal drying. This master’s thesis analysed possible improvements of a press roll in the dryer section of a modern tissue machine developed at a Swedish site. Improvements would allow increased nip loads which can yield a dryer paper prior to the dryer section and improving energy efficiency. The goal of the thesis was to investigate how alternative journal designs and joining methods could improve rigidity to support higher mechanical loads without compromising structural integrity. Work involved a literature study, concept generation using brainstorming and brainwriting, screening via Pugh matrices, and validation through analytical calculations and finite element simulations in Abaqus. Development followed an iterative process, improving designs following calculations and simulations of prior concepts. Relevant loading conditionssuch as current and future running conditions and draping methods were considered to ensure the validity of both current and proposed designs. Initial calculations showed that the current design remains well below material yield limits following an increased load but is limited by approaching maximum allowed deflection and insufficient stiffness. Eighteen design concepts were generated and screened, resulting in six which were selected for further development and analysis. Of these, a combined concept with increased wall thickness at the cylindrical section of the journal and a chamfered interface plate with increased thickness showed the best improvements for deflection (18,6% improvement) and interface surface separation (44,3% improvement). Simulations show that replacing the current material, cast iron, with a cast steel alloy with higher Young’s modulus would further improve rigidity. A change to a weldable material would also allow a welded design which showed good improvements for the deflection (18,0% improvement). The study concludes that significant improvements of beam deflection and reduced bolt stress are achievable through relatively minor design changes. These findings provide insight for future development of press rolls, supporting higher nip loads with possibility for increased energy efficiency and reduced environmental impacts.