DE2525561C2 - Process for the continuous production of heat-insulated line pipes - Google Patents

Description

In the main patent is a process for continuous Manufacture of heat-insulated pipes described in which initially a foamable plastic is extruded onto a metal tube and then foamed, initially a crosslinking of the Thermoplastic material introduced and carried out during the crosslinking of the foaming will.

The present invention relates to an improvement of the above-mentioned method, with the help of which it is possible is. to apply crosslinked foam layers on metal pipes in a particularly simple manner. this will achieved according to the invention in that the mixed with a crosslinking agent and a blowing agent Plastic mixture in a plasticizing unit from the inlet to the outlet increasingly and immediately before the outlet is heated by means of shear above the reaction temperature of the crosslinking agent and the blowing agent will. The mixture mixed with the crosslinking agent and the blowing agent is within a maximum of six seconds to the reaction temperature of the mixed crosslinking agent or blowing agent brought. Since the decomposition temperature of the blowing agent has already been reached in the extruder head, the Mold from an expanding melt that is cross-linked and when expanding outside of the extruder still further crosslinked It is essential that the decomposition temperatures for the crosslinking agent and the propellant can be reached and exceeded within a very short time. Immediately after crossing The shaping and the melt must take place at the reaction temperature of the crosslinking agent leave the extruder head. The warming of the children

to substance mixture can go up to just below the decomposition temperature the crosslinking agent can be carried out in the extruder. In the extruder head it still has to be required temperature increase of the melt take place. This heating occurs through shear. This can can be achieved, for example, in that a rotating mandrel is arranged in the extruder head The rotational speed is adjustable. The rotational speed influences the shear speed and thus the heating of the plastic mixture, so that the temperature of the plastic mixture by the speed of the mandrel can be adjusted exactly.

The crosslinking agent should be added in such an amount that a degree of crosslinking of at least 10% is achieved on exit from the plasticizing unit and of at least 50% in the foamed state. The degree of crosslinking is determined according to the Sol-Gcl-Melhode. If the degree of fusion is too low, the viscosity of the melt is too low, ie the melt flows off the pipe and the cell walls of the foam burst due to the gas pressure in the pores. If the degree of crosslinking is too high, the melt is too tough. The propellant does not cause optimal foaming.
The propellant should be added in such an amount that the foam produced has a density between 50 and 300 kg / m ³ . The decomposition temperature of the crosslinking agent should be chosen below the decomposition temperature of the blowing agent. As a result, crosslinking begins earlier than foaming. It is also useful to smooth and compact the outer surface of the heat insulating layer. This can be done, for example, by sending the expanded insulating layer through a heated die or, which is particularly favorable.

that the mouthpiece of the extruder is designed and tempered so that the heat insulating layer is smooth and less is strongly foamed. In this way you get a wümicisolicrics conduit pipe, which is optimal Has thermal insulation properties and an optical Leaves a good impression, as the insulating layer has a firm maniel-like rind.

D'.e invention is based on one in the figure schematically illustrated embodiment explained in more detail.

The figure shows a plan view of a device with the aid of which the method according to the invention is preferred can be carried out.

Premixed polyethylene granulate, blowing agents, crosslinking agents and anti-aging agent is already introduced into the feed opening of an extruder 1 and 2 is intimately mixed by means of a screw 3 in the mixer 2 and heated to a temperature of about 13O ⁰ C. The screw 3 of the extruder 2 transports the plastic mixture into the extruder head 4, in which a

b5 mandrel 5 is rotatably mounted. The plastic mixture is pressed by the screw 3 into the annular space between the mandrel 5 and the extruder head housing and occurs from the mouthpiece 6 in the form of a hose 7.

The mandrel 5 has a continuous axial bore 8 through which the metal pipe 9 to be insulated can be passed is on which the plastic tube 7 is shrunk

The plastic mixture to be extruded consists preferably of 100 parts of polyethylene, hard or Soft polyethylene - or a mixture of both types, 0.3 to 2% of a peroxide, for example dicumyl peroxide as a crosslinking agent, preferably 0.7%, 2 to 7%, preferably 4% of a blowing agent, for example Azodicarbonamide and approx. 0.5% of various anti-aging agents, which the foam against UV radiation. Copper. Keep oxygen etc. stable.

The plastic mixture emerging from the extruder 2 is ^{heated to about IJO 1-} C when it is introduced into the extruder head and is now up to its; Auslriii from the mouthpiece 6 increasingly heated is exiting the mouthpiece 6 the mixture to a temperature brought, which is above the decomposition temperature of the peroxide and the blowing agent, the decomposition of the peroxide starts at dicumyl peroxide at about 150 ⁰ C, the blowing agent at about 180 ⁰ C. the exit temperature should be in the region of the mouthpiece 6 approximately be 190 ° to 200 ⁰ C. This means that an expanding melt emerges from the mouthpiece 6, which is partially crosslinked and is further crosslinked during expansion.

With the aid of the method according to the invention, it has been possible to use Mclallrohrc 9 in a continuous manner to provide a heat insulating sleeve 10, which can be produced in an economical manner and compared to the Uncrimped foam layers customary up to now a much better one due to the lower density Thermal insulation and has a significantly higher temperature resistance due to the crosslinking

1 sheet of drawings

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Claims (6)

Patent claims: 1. Process for the continuous production of heat-insulated line pipes, with your first one foamable plastic is extruded onto a metal tube and then foamed, wherein Initially a crosslinking of the thermoplastic material is initiated and during the crosslinking the foaming is carried out, according to Patent 24 11 949, characterized in that, that the mixed with a crosslinking agent and a propellant plastic mixture in one Plasticizing unit increasing from the inlet to the outlet and means immediately before the outlet Shear is heated above the reaction temperature of the crosslinking agent and the blowing agent. 2. The method according to claim 1 ,. characterized that a polyolefin, preferably polyethylene, is used as the thermoplastic. 3. The method according to claim 1 or 2, characterized in that the crosslinking agent in one such an amount is added that on exit from the plasticizing unit a degree of crosslinking of at least 10% and in the foamed state of at least 50% is achieved. 4. The method according to one or more of claims 1 to 3, characterized in that the blowing agent is added in such an amount that the foam produced has a density between 50 to 300 g / m ^J 5. The method according to one or more of claims 1 to 4, characterized in that the The decomposition temperature of the crosslinking agent is slightly below the decomposition temperature of the blowing agent is chosen. 6. The method according to one or more of claims 1 to 5, characterized in that the outer Surface of the heat insulating layer is smoothed.