Presentations

Presentations have proven to be very effective in the understanding of the different negative effects of vibration and its solutions. Their main purpose is not so much to advertise the company but strictly to give you a more in-depth description of the subjects they cover. A mobile engineer is available for your convenience.

Basis Weight Variability

The paper and accompanying presentation, titled The Struggle for Paper Uniformity, outline the machine direction basis weight variability at a specific paper mill. It shows the problems that resulted from the MD basis weight variation and the steps taken to solve the problems. The clearly identified problems were register variations and cockling. Other problems that would be associated with variations but not clearly identified were paper runnability on the machine, on the winder and in the pressroom. The problem solving process included spectral analysis, operating deflection shape analysis, modal analysis and finite element analysis. The presentation shows an animation of the headbox vibration, the key problem area.

Calender Barring

Calender barring is a self-excited vibration that typically occurs at frequencies of 75 Hz and above. Much work was done in this field 10 to 20 years ago; yielding a number of computer programs that attempted to model the vibration, and recommended offsets that would eliminate the barring. These models assume that the roll is a rigid mass -that there is no flexibility in the roll and each end of the roll follows the motion of the other end exactly. Subsequent work has shown that the rolls do flex and that one end of a roll does not necessarily move in phase with the other end.

A fresh look has been taken into the fundamentals of calender barring using theory that has been developed for self-excited vibration in fields such as machine tool dynamics. This presentation shows a new model developed for calender barring. The dynamics of the calender stack is shown without the caliper variations of the paper present, and with the caliper variations acting as the self-excited vibration force. The presentation goes on to outline a procedure to understand and eliminate calender barring.

Oxbow Effect and Surface Temperature Profiles of Calender Rolls

Oxbow Effect and Surface Temperature Profiles of Calender Rolls Calender rolls distort on the ends where the paper is not acting as a heat sink. This can cause soft edges and cracks on the reel due to ends that have expanded more than the rest of the roll. Alternatively, the rolls can have hard edges when the ends of the rolls have been over-insulated and are of smaller diameter.

This presentation will go through the calculation procedure using finite element analysis of the shape of the calender roll in use. It gives examples of the calculated temperature and distortion profile. It discusses the methods that can be used to reduce the amount of deformation. The discussion concludes with the measurement of a temperature profile through a calender stack.

Mill Application of Finite Element Analysis to Solve the Problem of the Oxbow Effect

The finite element technique is applied to a calender roll to predict its temperature profile and deformed shape. This is used to design the required insulation at the end of the calender roll to prevent undue distortion. The design procedure is outlined, and the results of the procedure noted.

Paper Machine Speed Increase

Paper machine speed increases can affect the vibration of the machine leading to problems in paper quality or in excessive vibration, shortening the life of the machine. This presentation shows the effect that it can have on paper quality and on the machine. It also covers the techniques used for predicting what the vibration will be when the machine speed is increased. Of particular concern is preventing unwanted resonances, to ensure that there will be no surprises at the higher operating speeds.