Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
1995-06-01
2001-04-03
Crispino, Richard (Department: 1734)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S336000, C162S343000
Reexamination Certificate
active
06210535
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox.
In the prior art, systems for the operation of multi-layer headboxes are known in which there are separate fresh stocks for the surface layers of a pulp flow discharged from the headbox and for the middle layers thereof. Thus, in the prior art systems, there have been at least double fresh-stock systems for the formation of the different pulp layers. In the prior art equipment, the stocks introduced along at least two separate fresh-stock lines have been processed in vortex cleaning and in deaeration tanks, and feeds of fillers or starch complying with the required paper grade have been passed into the at least two fresh-stock lines.
With the prior art technology, a paper machine into whose headbox stock is fed at different consistencies requires a complete short circulation which comprises more than one stock systems. This is also the case when the stock in the different layers is in the other respects the same, but the consistencies are different.
Increased consistency of layers may be necessary, for example, in order that an improved purity of the layers can be achieved. When the middle layer is thicker than the surface layers, water of the middle layer is drained through the surface layers to a relatively limited extent. In such a case, particles of the middle layer are not carried along with the water into the surface layer, and the purity of the layers remains good.
A very thick middle layer is highly flocculated, in which case it has a high bulk. Then, the structure of the paper results in a bulky paper of good bending stiffness, in which the formation of the middle layer is poor but the formation of the surface layers is good, which secures good printing properties.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new and improved stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox in which each layer of a multi-layer pulp web discharged from the headbox can be diluted separately and/or simultaneously, in which case, e.g., the stocks passed into the inlet headers of a multi-layer headbox can be given the desired consistencies.
In order to achieve the object stated above, and others, in the present invention, the stock for one or several layers in the feed pipe systems for the inlet headers of the headbox are diluted. The diluting can take place before screens in the feed path through the feed pipe system if each layer has a screen of its own, or after the stock has been divided to be fed into the different layers.
In the present invention, in a paper machine that comprises a multi-layer headbox and therein at least two separate inlet headers or equivalent, for the inlet headers, separate stocks are prepared out of the same fresh stock, and they are passed into the inlet headers from the same stock tank. According to the invention, the fresh stock passed out of the stock tank is divided into two or more component flows. Into these component flows to be fed into the multi-layer headbox, chemicals and/or additives purposeful for the quality or the economy of production of different paper grades are passed.
Further, according to the invention, the system also includes dilution-water lines passing to the stock system of the headbox. Preferably, the dilution lines are arranged to pass from a dilution-water header through valves and to join the stock line connected with the inlet header for each stock layer. Thus, according to the invention, in the stock feed system, each layer can be diluted separately and/or simultaneously, in which case, e.g., the stocks passed into the inlet headers of a multi-layer headbox can be given the desired consistencies. When certain additives are added to the stock flow, it may be the case that the stock has a low dry solids content before mixing of the additive. Thus, before the additive is passed into the stock, the stock may be diluted to the desired dry solids content to add the additive concerned into the fresh stock in an optimal manner.
In the stock system in accordance with the present invention for a multi-layer headbox, into each inlet header of the multi-layer headbox, a stock concept is passed which has been produced out of the same fresh stock by adding the necessary chemicals and fillers to the fresh stock. The stock feed system in accordance with the present invention for a multi-layer headbox thus comprises at least one dilution-water line.
In the method in accordance with the invention, the stock for each inlet header is prepared out of a single fresh stock by adding the necessary chemicals and fillers to the fresh stock. Dilution water is passed into at least one stock line that passes into an inlet header of the multi-layer headbox. Thus, in one embodiment, the method is used in the operation of a multi-layer headbox having at least two inlet headers into which a respective stock concept is passed, the stock flowing from the inlet headers through a system of distributor pipes into a turbulence generator and further into a slice cone. A single flow of fresh stock is provided and then divided into a plurality of stock flows. Chemicals and/or fillers are independently added to each of the stock flows. Each of the stock flows is then passed after the chemicals and/or fillers have been added thereto into a respective one of the inlet headers, and a diluting-water flow is passed into at least one of the stock flows. Preferably, the diluting-water flow is passed into individual ones of the stock flows which form outer layers of a web discharged from the headbox.
The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings. However, the invention is not confined to the illustrated embodiments alone.
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Huovila Jyrki
Linsuri Ari
Crispino Richard
Steinberg & Raskin, P.C.
Valmet Corporation
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