Headbox of a paper machine

Claim 1

In a headbox of a paper machine having a stock distribution header part; a distribution pipe assembly following and communicating with said stock distribution header part in the direction of the stock flow; and a stock suspension flow passage downstream of and following said distribution pipe assembly having upper and lower wall means and including means defining an equalizing passage communicating with and following said distribution pipe assembly in the flow path of the stock suspension with an air tank in direct communication with said equalizing passage for damping pressure pulsations occurring in the stock flow, a turbulence section downstream of and communicating with said equalizing passage, and a converging slice part communicating with and following said equalizing passage in the direction of stock flow, said converging slice part having a lower lip wall and an upper lip wall, and wherein at least said turbulence section is constituted by at least one exchangeable grating cassette component removably attached to the headbox, the improvement comprising: said turbulence section includes two grating plates situated against each other extending transverse to the direction of stock flow, the first of the two plates having a plurality of first bores formed therethrough and the second of the two plates having a corresponding plurality of second bores formed therethrough, each of said second bores being coaxial with a respective one of said first bores and having a larger diameter than that of said respective first bore to form a step therebetween, and wherein said grating plates constitute mechanical supporting and load-bearing means between said upper and lower wall means of said stock suspension flow passage for taking up forces acting on said upper and lower wall means of said stock suspension flow passage.