Heating and cooling arrangement particularly for an extrusion cylinder

The heating and cooling arrangement (3, 4) for an extrusion cylinder comprises a copper strip (4) bent aside at right angles at its ends (6, 7) and twisted by 45.degree., the middle portion (8) of which rests upon the extrusion cylinder (1) as well as a band-shaped flexible heating element (3) disposed over the middle portion (8). The cooling elements (4) are disposed on a cylinder section (b 5) at regular intervals over the whole periphery thereof. Two copper wires led through the end regions (9, 10) of the middle portions (8) of the cooling elements (4) fasten the same to the surface of the extrusion cylinder (1). The heating element has two outer metal sheets (15, 16), an insulating layer (17) lying therebetween, as well as heating wires (18). This heating and cooling arrangement can be disposed on as many sections of the extrusion cylinder (1) as desired and makes possible an individual cooling or heating of each section of the cylinder, which fact is important for very rapid extrusion processes. An optimum adaptation of the temperature profile along the extrusion cylinder to any extrusion process individually is made possible.

This invention relates to a heating and cooling arrangement for an 
extrusion cylinder, as well as to an extrusion cylinder with at least one 
heating and cooling arrangement. 
In plastic-extrusion machines, it is important for the extrusion process 
that the whole extrusion cylinder can be heated or cooled. It is known, 
for heating an extrusion cylinder, to provide for a casting with 
integrally cast heating at the periphery thereof. This arrangement has the 
disadvantage that it has a great time lag as regards heating and cooling 
and does not make possible any individual heating and cooling of a 
cylinder section. 
The heating and cooling unit according to U.S. Pat. No. 3,730,262 has the 
disadvantage that it comprises a rigid pipe which cannot well be adapted 
with optimum heat trasnfer to an extrusion cylinder. The result is poor 
heat distribution since air for cooling is conducted over a pipe around 
the extrusion cylinder. The heat distribution is not homogenous over the 
surface of the cylinder. 
The device for increasing the heat exchange according to U.S. Pat. No. 
4,236,578 has no heating elements. The heating elements would have to be 
disposed next to the cooling elements. Thus, at a specific location of the 
pipe, merely heating or cooling can take place. The arrangement according 
to this disclosure is likewise not flexible and cannot be optimally 
adpated to a given cylinder. With the rigid design according to this 
patent and the one mentioned above, a small space is possibly produced 
between jacket and tube, and this makes the heat transfer much poorer. 
Very precise machining of the jacket is necessary in order to ensure good 
heat transfer. The conduction of heat would not be ensured, for instance, 
if the heating elements were disposed under the cooling elements since the 
heating wires must be insulated. 
The air-cooled extruder according to U.S. Pat. No. 3,743,252 likewise has 
the disadvantage that the cooling arrangement is not flexible. The cooling 
plates must be very precisely machined. 
The heating and cooling unit for extruders according to U.S. Pat. No. 
3,285,329 yields the same problems as the device according to U.S. Pat. 
No. 3,730,262. The device is likewise rigid, which makes optimum 
adaptation to the extruder pipe impossible. Good heat transfer is not 
ensured. The air cooling with pipes also results in poor heat distribution 
on the surface of the cylinder. 
It is a task of the present invention to provide a heating and cooling 
arrangement by means of which individual cylinder sections can be both 
cooled and heated. The heating and cooling arrangement should be able to 
be adapted in a simple manner to any desired diameter of the extrusion 
cylinder. 
This is achieved, according to the invention, by means of at least one 
cooling element and at least one heating element, the arrangement being 
formed flexible. 
Furthermore, it should be possible to bring about an optimum adaptation of 
the temperature profile along the extrusion cylinder to each extrusion 
process individually. 
This is achieved in an extrusion cylinder with a heating-cooling 
arrangement according to the invention in that in each case on one section 
of the extrusion cylinder, at least on a great part of its periphery, 
cooling elements are fastened, and at least one heating element is 
provided over the cooling elements on the surface of the extrusion 
cylinder. By means of the arrangement according to the invention, the 
temperature profile can be adapted to the respective process speed. A 
dynamic heating and cooling system is provided, which is also suitable for 
very rapid extrusion processes. The heating-up and cooling processes take 
place much more quickly than with the rigid arrangements of the prior art.

In FIG. 1, the extrusion cylinder 1 with a hopper 2 is depicted 
schematically. On the periphery of the extrusion cylinder 1, heating and 
cooling arrangements 3 and 4 are provided at regular, preferably small 
intervals. On a single section 5 of the extrusion cylinder 1, in each case 
several cooling elements distributed at regular, preferably small 
intervals over the whole periphery of the cylinder, as well as a 
band-shaped heating element, are provided. 
In FIG. 2, a cooling element 4 is depicted in section (FIG. 2A) and in top 
plan view (FIG. 2B). The cooling element 4 is made from one piece, the 
ends being bent aside at right angles to the middle portion 8 as legs 6 
and 7 and also twisted by 45.degree. in the direction of their 
longitudinal axis for mechanical stabilization. In the transition regions 
9 and 10 from the middle portion 8 to the legs 6 and 7, the cooling 
element 4 has one bent section 11 and 12 each. The cooling element is 
preferably made of copper, a metal having good heat conductivity. The 
cooling element likewise has low heat-retention, which fact is important 
in the case of a rapid succession of heating and cooling operations of the 
extrusion cylinder. 
FIG. 3 shows a section through a heating and cooling arrangement provided 
on the extrusion cylinder 1, wherein, of the cooling elements disposed on 
a section 5 of the extrusion cylinder, radially on the whole periphery 
thereof, two elements offset by 180.degree. relative to one another, as 
well as the band-shaped heating element 3, are visible. The heating 
element is a good heat insulator and has low heat-retention. 
In FIG. 4, the heating and cooling arrangement 3, 4 is depicted in 
perspective. The cooling elements 4, consisting of copper strips forming 
an angle at their ends, are held by two copper wires 13 and 14 on the 
surface of the extrusion cylinder 1. The copper wires 13 and 14 are led 
through the bent sections 11 and 12 formed in the end regions 9 and 10 of 
the middle portion 8 of the cooling element. All of the cooling elements 4 
disposed over the whole periphery of a section 5 of the extrusion cylinder 
are fastened by the copper wires 13 and 14. The heating element 3 laid 
over the individual cooling elements 4 is formed in the shape of a band. 
It comprises two outer metal sheets 15 and 16, between which an insulating 
material 17 is provided. Disposed within the high-temperature-resistant 
insulating material 17 are heating wires 18. The heating element 3 can be 
fastened to the extrusion cylinder 1 by screws, which also makes possible 
easy exchanging thereof since the heating element is exposed to greater 
wear and tear than the cooling element. The heating element is so formed 
and mounted on the extrusion cylinder that as few flow losses as possible 
occur during cooling. 
FIG. 5 shows a view of the extrusion cylinder 1 with cooling elements 4 
disposed over the whole periphery thereof, forming a band, as well as the 
band-shaped heating element 3. Two connection wires 19 and 20 for the 
heating element 3 are led from the surface of the extrusion cylinder 1 
outward. The cooling air is blown radially onto the extrusion cylinder and 
flows axially away. 
The number of cooling and/or heating zones can be varied as need be. 
Through the ranging side by side of single, identical cooling elements, 
the arrangement can be adapted to any desired diameter of the extrusion 
cylinder. 
Instead of the cooling elements joined in the shape of a band, several 
extruded cooling elements might also be used. 
The described arrangement has proved to be an effective means of ensuring 
the adaptation of an extrusion cylinder in operation to any desired 
temperature profile. Each heating and cooling arrangement formed of a 
number of cooling elements and a heating element provides for the 
maintenance of a predetermined temperature at the location where it is 
affixed around the cylinder. Both the cooling elements and the heating 
elements have a low heat-retaining value. The heating elements, which act 
toward the outside as heat insulators, lie over the copper strips of the 
cooling elements and thus cause the heat to penetrate directly into the 
cylinder as a result of the direct contact between the heating elements, 
the copper strips, and the cylinder. If cooling is to be brought about, 
the respective heating element is switched off. The heat of the cylinder 
is then transferred to the outside air by the legs 6 and 7 of the cooling 
elements through radiation and convection. 
As in the customary installations, an axially acting fan is set up at the 
end of the cylinder, which provides for the air circulation.