Plastic article or earthenware shaping or treating: apparatus – With means applying coating material to work or work contact... – Separate means applying material directly to shaping means,...
Patent
1992-06-04
1993-10-12
Woo, Jay H.
Plastic article or earthenware shaping or treating: apparatus
With means applying coating material to work or work contact...
Separate means applying material directly to shaping means,...
425380, B29C 4702, B29C 4794
Patent
active
052520498
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lubricating arrangement for a plastic extruder for the production of cylindrical plastic tubes with a smooth inner wall, said plastic extruder comprising a mandrel, consisting of a form core which is a cylindrical coaxial extension of the extruder screw and rotates with the latter, and a stationary external die means with the lubricating arrangement being provided on the external die means for lubricating its forming surface.
2. Prior Art
From NO-PS No. 158 087 such a lubricating arrangement is known which comprises slots between members of the external die means, said members being movable relative to each other in the axial direction of the die for adjustment of the width of slots. The slot or slots are connected with a source of lubricant, supplying lubricant under pressure. In the embodiment preferred in practice the movable members consist of annular disks. This lubricating arrangement does indeed function as intended, and adjustment of the amount of lubricant is very readily achieved by adjusting the slot width. A disadvantage of this lubricating arrangement, however, is that the slots supplying the die wall with lubricant extend radially into the die wall and normally to the centre line of the external die means in the die wall, whereas the supplied plastic mass describes a helical line due to axial forward squeezing of the mass from the extruder and the influence of the rotating mandrel on the plastic mass. The lubricator slots will, thus, form an acute angle to the helical path of the plastic mass, and this will cause non-uniform lubrication, especially at the inlet to the stationary external die means where shaping of the tube profile begins. This will be especially disadvantageous in connection with production of tubes with a smooth inner surface and with ribs following a helical line on their outside. Such extrusion is very sensitive to non-uniform lubrication, and there will easily be a hazard of uneven extrusion on even a hazard of tearing the tube being moulded. It is an object of the present invention to provide an improved lubricating system, in which the above disadvantage is avoided and by means of which lubricating arrangement uniform lubrication is achieved, especially when tubes with a smooth internal surface and a ribbed external surface are manufactured.
OBJECTIVES AND SUMMARY OF THE INVENTION
According to the invention this is achieved by the means of a lubricating arrangement of the above mentioned kind, which is characterized in that a plurality of radially extending plugs are provided with each plug in its bore in the external die means, with an inner end of the plug lying in the surface of the die, that lubricating ducts are provided to said bores said ducts are connected with a source of lubricant supplying lubricant under pressure.
A preferred embodiment is characterized by the fact that plugs are provided in groups, that said groups are arranged about the periphery, and that the plugs of each group are arranged along the helical line followed by the flowing plastic mass being squeezed axially onwards by the extruder screw and due to the influence of the rotating mandrel on the mass. A lubricating arrangement according to the invention which is especially designed for a plastic extruder for production of cylindrical plastic tubes with a smooth inner wall and an external wall provided with helical ribs, is characterized in that the ends of the plugs are shaped to form part of the moulding surface of the external die means, adapted to the ribbed profile of the extruded tube.
In a preferred embodiment the plugs are circular cylindrical and have a conical portion cooperating with a conical portion of the bore, intended to adjust the volume of lubricant by more or less hard tightening of the conical plug portion against the conical bore portion.
By means of the invention more selective lubrication is achieved, and with a sufficient number of lubricating points the entire helical flow will
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Goncharov, Abstract no. 88-328468146, Derwent Publications Ltd., 1988.
Leyson Joseph
Sonnichsen A.S.
Woo Jay H.
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