R. J. N. Helmer, G. H. Covey, W. D. Raverty and N. Vanderhoek; Appita 1991
The production of paper in the laboratory where controlled forming conditions result in an anisotropic sheet of predictable properties, which match those of papers made on a commercial paper machines, is a long desired instrument for many researchers. A laboratory sheet former based on a novel interpretation of the flow in the forming region is being developed to meet this challenge. The key sheet characteristics for a given fibre stock were identified to be formation and fibre orientation. The ability of the laboratory former developed to simulate commercial paper was assessed by a number of standard tests. The sheets formed on the initial proto-type (MkI) confirmed that the conceptual design was worth pursuing, and that improvements to the control and operation were required. The design improvements made to the former resulted in a second device (Mk II) which produced oriented laboratory sheets in a repeatable manner with sheet characteristics comparable to commercially made paper. The practical difficulties encountered in the development of this device are discussed along with the solutions which were found.
This paper addresses the preliminary developments of a laboratory paper former and highlights the approach taken to produce paper sheets with controlled anisotropy. The laboratory production of paper sheets which simulate paper made on a commercial machine in a way which is usefully predictive has been a long desired goal for both researchers and development engineers alike. The ability to predict the papermaking potential of particular fibre sources with a degree of precision which approximates the achievements of pilot paper machines, but without the expense and logistical complexity of a pilot scale trial has been a worthwhile but elusive goal. To date the devices available to form sheets in the laboratory are quite varied in their design and operation (1-15). The fine structure of sheets produced on many of these laboratory formers differs quite markedly from paper which has been made on a commercial paper machine (10-12). Further problems with grammage profiles and fibre fractionation have also been reported (6-8, 16). The devices which have produced paper similar to a commercial machine have been reported to be bulky, difficult to operate and hard to control (9). None of these devices has been deemed to be a truly satisfactory predictor of what may be expected on a commercial machine from a given fibre stock. At the outset of this research a number of practical constraints and targets were imposed on the design in order to overcome the deficiencies of earlier laboratory formers. The specifications included:
- To occupy a space of less than 3 x 3 x 3 m3.
- Capable of producing paper sheets of at least A4 size repeatably.
- Use minimal amounts of pulp, (1-2kg).
- Require a single operator.
- Relatively inexpensive to construct.
- Form at speeds of 0.01 – 1m/s.
- Sheet to have a controlled basis weight range of ~20-200 gsm.
- Simulate properties of a commercially made sheet in a usefully predictive manner.
- A simple relation between laboratory operating parameters and measurable commercial operating parameters.
- Device to facilitate an investigation of the forming phenomena.
The approach taken in the development of this former was to conceptually model the forming process and then to build a device which would allow test sheets to be formed, which could be used subsequently to validate the modelling perspective. Once this was achieved, further refinement of the device to improve the operability was envisaged.