The invention relates to a method to furnish the edge portion of a sheet with a strip, as a strip of plastic material using a device comprising a die space. The invention relates especially to anode and cathode sheets used in the processing industry, the edges of which must by means of a plastic strip be kept electrically non-conductive.
Previously known is an injection moulding method of plastic material, where on using a die, of the material an object similar to the die is produced. Also known are die applications, where before injection moulding into the die ready-made objects are placed, for instance metal objects wholly or partly fitted in the die. The plastic strip meant for the sheet edge could be accomplished with such a die-casting die in length of the sheet edge, where the sheet edge would have been taken into the die, cast and die of the strip could be opened and the sheet with its strips removed. As example of this patent specification U.S. Pat. No. 5,928,482 can be mentioned.
A production process of this kind requires a long and expensive die. The compactness on the die would be complicated and perhaps impossible on using high injection moulding pressures. One edge of the sheet could be done at a time and even slight variations of thickness cause immediate compaction problems in the die. It can also be considered to fit a ready-made profile strip in some way on the sheet edge, which is however a difficult method and by means of it a sufficient fuse of strip on the sheet surface is not reached so that the oxygen of the electrolytic bath could not get in between strip and sheet.
Further known from publications EP 028284, EP 707937 and U.S. Pat. No. 5,336,349 is a method to produce an edge portion of plastic material using an extrusion device comprising the die space. In these ones the edge is placed into the die space of the extrusion device and the sheet is moved in regard to the die space. The adhesiveness of the strip cannot be secured in the above presented applications, because the strip gets cool at first in the portions, where it is contact against the cold sheet edge.
In order to solve the above presented disadvantages and problems a new method is developed characterized in that the die space of the device is heated during the process and the sheet is heated in its edge portion at least 10-200° C. higher than the temperature of the plastic mass steered into the die.
The advantage of the invention is that furnishing the sheet edge with a plastic strip can be easily automated, when it is a process taking place on a moving track. The opposite edges of the sheet can be furnished with a strip at the same time. In the method a quite short extrusion die is sufficient, at which the feed of plastic material to the sheet edge takes place. Due to the short extrusion die the variations of sheet thickness can be compensated by packing lips. Due to proper temperature arranged for the material no high pressure is needed either in the die or the extruder and by means of sheet edge preheating in the strip a strong and it in the sheet keeping compression is achieved and by cooling the produced strip it is secured that shrinking takes place lastly in the internal part of the strip.
In the following the invention is disclosed with reference to the enclosed drawing, where
a and b show some edge shapes of the sheet,
The opening of the die space 7 one end is completely stopped up by sheet 1 and removing strip 2. The inlet opening of the die space of sheet 1 is in this embodiment stopped up only by sheet 1. When through tube 6 plastic material is fed by pressure to die space 7 it fills the die space, sticks to the moving sheet and gets out together with the sheet as a ready-made list. Feed pressure and feed quantity into die space 7 is so regulated that the plastic material does not extrude faster than sheet 1 gets out through the output opening of die space 7. Also material is not allowed to extrude out of the inlet opening of the die space 7.
a shows groove 9 improving the adhesiveness of sheet 1 to the edge, and
In order to avoid the peeling phenomenon of strip described above it is necessary that sheet 1 is warmer than the plastic mass in extrusion die 3. This means that according to
Number | Date | Country | Kind |
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20031822 | Dec 2003 | FI | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FI04/00756 | 12/13/2004 | WO | 6/9/2006 |