Note: Descriptions are shown in the official language in which they were submitted.
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A Tubular Die for Extrusion, more partirularly a Blow Head.
The invention relates to a tubular die for extru~ion and
more particularly to a blow head for the production of tubular film
of thermoplastic resin, con~i~ting of an inner ring or core and an
outer ring, between which an annular die pa~sage is defined.
Such tubular die~ have been disclosed for instance in the
German patent publication 2,140,194 ~3 and the German patents
2,947,293 and 2,950,003.
In order to extrude tube~ or to blo~ mold tubular film with
a constant wall or film thickness along the entire periphery, it is
nece~ary to be able to adjust the mass temperature of the fused
resin in the annular die gap of the extrusion die by suitable
modification of the vi~co~ity in order to regulate the flow of the
emersing fused resin.
In the prior art tub~llar dies the temperature control
segments or temperature control sectors are provided with ducts or
holes through which a cooling or heating fluid may be passed in
order by a suitable a increase or lowering of the temperature of
the re~pective temperature control sector to change the temperature
pattern around the periphery of the tubular die in the desired
manner. In the case of known tubular die~ the cooling or heating
fluid is air, oil or some other liquid or gaseous material, which
is able to supply or abstract heat to or from the temperature
control sectors.
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The heating of the temperature control sectors of a tubular
die by flowing fluids is a complicated method in view of the
connections for supply and return lines and owing to the necessity
of keeping fluid on standby at the requisite temperature~
Furthermore, plant failure may be caused by leaks in the
connections .
Accordingly one object of the invention is to provide a
tubular die of the ini~ially specified type whose temperature
control sectors may be heated and, if required, cooled in a simpler
10 manner than hitherto.
In order to achieve this object a tubular die of the type
specified with an inner and an outer ring is so designed that at
least one of said rings is divided in a plurality of temperature
control sectors, in which electrical heating cartridges are placed
15 in holes or recesses.
In the tubular die in accordance with the invention the
electrical heating cartridges or heating elements may be readily
accommodated in suitable holes or other recesseq. The electrical
leads needed for the supply of electrical energy may be arranged in
20 a simple manner and call for very little maintenance.
In order to heat the temperature control segments it is
only necessary to supply the respectively associated heating
cartridges with electrical power. If a cooling effect is required
no current is then supplied to the respective heating cartridge so
25 that the respective temperature control segment will cool down to
the temperature of the mass of fused resin emerging from the
tubular die.
The tubular die in accordance with the invention iR more
particularly suitable in connection with a film blowing extruder as
30 described in the German patents 2,947,293 and 2,950,003.
One working example of the invention will now be deRcribed
in detail with reference to the drawing.
Figure 1 is a longitudinal section through a
tubular die.
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Figure 2 is a cross section taken through the
tubular die taken on the line I-I of
figure 1.
The main parts of the tubular die shown in the drawing are
5 a central core 1 and an outer ring 2 able to be centered relative
to the same. Between the core 1 and the outer ring 2 the annular
die gap 3 is formed.
The outer ring 2 i~ provided with holes 4 evenly spaced out
along its circumference in order to receive heating cartridges.
10 The holes 4 are set obliquely and after the insertion of the
heating cartridges 5 their upper end may be sealed by a plug 6,
which is welded in place. The electrical leads 7 are connected
through a radial hole with the respective hole 4.
