DE2255473B2 - PROCESS AND DEVICE FOR CONTINUOUS COATING OF A CORE WITH RUBBER OR PLASTIC - Google Patents

Description

50

The invention relates to a method for continuously sheathing a core with rubber or Plastic, in particular for the production of electrical cables, with a vulcanizable material around the core Kuatschuk mixture or a crosslinkable plastic, is extruded with degassing by means of a vacuum and the sheathed core for vulcanizing the rubber mixture or for crosslinking the plastic t> o fes is guided essentially in a straight line through a heated medium.

A crosslinking process is already known in which objects are placed at atmospheric Pressure immersed in a bath of high temperature t, which - compared to the well-known high-pressure steam vulcanization process - has the advantage has that the required equipment and the

Work steps are relatively simple.

It is known such a low-pressure hardening process for the production of rubber or plastic to apply existing objects, e.g. B. for a window frame pack. However, it is not yet has been used for the manufacture of multi-layered objects, such as electrical cables that use networked materials or a scarf with a multilayer structure are sheathed.

Such cross-linked layers are necessary in order to achieve higher quality electrical or mechanical properties to obtain. For this purpose, however, the low pressure process has been chosen for the following reasons not proven: 1) Air or moisture trapped in rubber or plastic cannot completely removed so that the rubber or plastic remains porous. 2) moisture and other volatile Components air present in the core or in the space between the core and the cladding is heated and expands while being crosslinked, causing the clad to separate from the core.

In order to avoid the formation of pores in the jacket during the low-pressure process, a Process known in which calcium oxide is added to rubber or plastic in order to increase moisture absoriberen, which otherwise forms vesicles. However, since the connection besides moisture is different The known method prevents volatile components that calcium oxide cannot absorb not the formation of pores in the cross-linked shell, which can be traced back to the volatile constituents will. Another method to avoid pores is to have a ventilated one, just a snail to use having extruder, which has a drum with an air hole (cf. O. W. Baumgarten, Kautschuk und Gummi, 19 [8], page 494 1966). But it has been shown that this procedure is completely inadequate for removal from moisture and volatiles which ir Rubber or plastic are present, and that e; furthermore, it is difficult to produce multilayer molded products afterwards to produce se with sufficiently large freedom from pores.

Vulcanization processes are also known in which elongated tubular cores are included be sheathed by wires with a polymer, the extruded product subsequently different exposed to heat treatment stages, steam and water. But this is not the point Special pressure ratios must be observed between two extruders (US-PS 34 97 913).

A vulcanization device with an extruder stage is also known to produce multilayered products how to vulcanize electrical cables at low atmospheric pressure, with the core before de Extrusion subjected to a heat treatment wire However, this is not about taking voi into account low pressure in the area of the extruder itself, for which the material is cut up like granules (US-P! 19 99 751).

A device for vulcanizing: elongated body made of rubber is also known, al Vulcanizing fluid can serve heavy salt solutions, since a cross-head is used The product is heated to different degrees and the vulcanizing fluid of the compressed air or a Pressurized gas is exposed. However, this is not just about the treatment of granular material (DT-P:

α of the magazine "Kautschuk und Gummi, Kunstff" 19th year, 1966, issue 8, pages 494 to 497, it is known to influence the extrusion of profiles and sheathing by pressureless continuous vulcanization,! "^ materials. Screw press is a degarification item in Λ screw press, in which vacuum is used. The vacuum is applied before Hp? Vulcanization. However, this involves the fabrication of blanks for pressed parts or synthetic profiles, the surface of which should be formed pore-free If wires and cables are also to be sheathed, it is not intended to use a special, cut-up granulate-like material as the wiping material, so that the special conditions that arise are not taken into account

^ble _De ^e _r "'The invention is based on the object of specifying a method which, when sheathing

η in particular keeps electrical cables away from harmful components such as moisture better than before, so λ β produces the relatively thin sheathing with increased freedom from pores and thus the quality of the insulation is improved.

According to the invention it is proposed for this purpose that the rubber mixture or the plastic, for degassing by means of vacuum, extruded into strands, which -e cut under vacuum to granulate-like goods as well is fed to a downstream extrusion point while maintaining a vacuum and that with this good the extrusion is done around the core. This means that the Coating reached.

The invention also relates to a device according to Hem generic term of the preceding claim 5, as it is known from the prior art. This device is used to carry out the Method according to the invention by the features listed in the characterizing part of claim 5

One embodiment of the invention is in Drawing shown and will be explained in more detail below. It shows

1 schematically shows an apparatus for manufacturing a coated cable with a cross-linked rubber or plastic sheath,

Fig. 2 shows a longitudinal section of an extruder according to Fi £ 1

Fig. 3 is a longitudinal section of a transverse extrusion head with an elongated tool and a Nozzle attachment is provided,

FIG. 4 shows a section along line II of F1 g. 3.

It can be seen from FIG. 1 that a core W fed from a drum A is passed through a drying preheating device B before it is fed to an extrusion head D of an extruder E in which the core VV is completely dried, preferably at a temperature of over 90 C. Then, the dried core conducted W by an additional preheating apparatus C, in which the core surface is heated periodically at a temperature not more than 90 ⁰ C under:.. ''"-" hpheizte ,, r Korrt Πργ core Vv

VUIKanisailuliaitnipv. · «'" · --- Β- ""', Ί-. · R-u

is immediately introduced into the cross extrusion head D and treated in a heating bath h. This method is effectively used for coating any core material. Examples of core material that is coated in series with plastic or rubber are electrical conductors, e.g. B. stranded bare conductors, a with a cross-linked layer of a rubber or plastic covered Leitar, such as stranded or spun strands or cables made of a plurality of insulated conductors, with or without jute filling. This also includes hose cores, such as tubular bodies made of cross-linked! Rubber, plastic or multilayered bodies that can contain a spring element between the layers.

The preheating or drying time in the dry preheating device B depends essentially on various parameters, e.g. B. the composition, the size of the core W or the preheating temperature. For example, in cores Wmit Jutefüllung containing plenty of moisture or oil, the Vorwärmzeil is unusual, that is, two to twenty-four hours at 90 ⁰ C or forty minutes to two hours at 105 ° C or five to ten minutes at 100 ⁰ C. If the circuit but with rubber or plastic insulated, the preheating time is one to three hours at 90 ⁰ C twenty minutes to an hour at 105 ⁰ C and from one to five minutes at 180 ⁰ C. the higher the preheating temperature of the core W is, the shorter the preheating time. However, since too high a preheating temperature causes the core W to disintegrate, the preheating temperature should preferably not be more than 200 ° C. However, this value differs depending on the composition of the core W.

If the preheating time exceeds one hour, it is advisable to heat the core batchwise instead of continuously as shown in FIG. The core W can be pre-heated at a temperature below 90 ⁰ C temperature, and this leads to a shortening of the pre-heating in the drying-preheating B.

If the surface temperature of the core W entering the cross extrusion head is low, air trapped between the core surface and the rubber or plastic layer may expand during crosslinking, creating a risk that the layer may become detached from the core W . Preferably, therefore, to W, to be heated at least on its surface, by the additional pre-heater C to a temperature of the core which is not lower is the temperature, 90 ° C, preferably urn 6O ⁰ C, is below the crosslinking temperature.

When the preheating of the core ßbei high temperature is W in the drying-preheating when W of the core is thus completely dried and the surface of the core Won increases a temperature which is greater than that temperature which is lower by 90 ⁰ C as the crosslinking temperature is, the additional preheating of the core W by the preheating device C is not required.

The core W dried and heated to a high temperature is then introduced into the extrusion head D when there is moisture absorption or a temperature drop in the core W before it reaches the extrusion head D, and a member is preferably used to absorb the moisture and the temperature drop at the core t "~ · avoid, e.g. a hot air tunnel between

■ ti

and there is a treatment in a heating bath l ·, avoid, l, d. cm ■ · <. ■ ».» _

optionally a washing in a washing area G preheating device C and the cross-strand press - ■■ - '"koDf D.

and winding on a reel H.

From Figure 2 it can be seen how the crosslinkable material is extruded while moisture and other gaseous components are removed. The material is extruded into a rectangular vacuum chamber 3 in the form of thin strands with the aid of a first extruder 1. The extruder 1 is provided with a screw 13 and a nozzle head 12, the front surface 11 of which faces the vacuum chamber 3. The extruded strands are immediately cut by a rotating cutting tool 2 present in the vacuum chamber 3 into granular material which lies opposite the surface 11 of the nozzle head 12. The cutting tool 2 is attached to a rotating shaft 21 which extends through the wall 24 of the vacuum chamber 3 and is driven by a motor M via a belt 29 and a pulley 26. The shaft 21 is supported by a bearing 23 which is held on the wall 24 of the vacuum chamber 3 by bolts. The bearing 23 is supported by an arm 27 which is attached to a base part (not shown) of the first extruder 1. There is a seal 35. The distance between the cutting tool 2 and the nozzle head 12 can be changed by turning an adjusting screw 25 screwed into the rear end of the bearing 23 to move a projection 22 provided on the shaft 21 or around the screw to withdraw from the projection 22. The vacuum chamber 3 is evacuated by a pump (not shown). The pump is in communication with an outlet opening 31. The pressure drop in the vacuum chamber 3 during work is indicated by a measuring device 33. The extruded strands are cut into granulate-like material by the knife-like cutting tool 2, and this falls onto a feed roller 42 at the bottom of the vacuum chamber 3. The feed roller 42 conveys the material into a second extruder 4, which has a screw 43, a nozzle head 45 and the Cross strand press head D is provided. The feed roller 42 in a feed section 41 of the second extruder 4 is used to transport particularly material into the second extruder 4 which tends to form lumps or stick in the feed section 41.

The material can adhere to the inner wall of the vacuum chamber 3. A sheet 34 made of polytetrafluoroethylene attached on the inner surface of the vacuum chamber 3, therefore, serves to prevent such adhesion. Instead of Sheet 34, other means can be used to avoid the adhesion of rubber or plastic, z. B. a sheet that is coated with silicone rubber, or you use a silicone oil layer instead of the polytetrafluoroethylene sheet.

During its stay in the vacuum chamber 3, the material is dried and under low pressure degassed. The drying and degassing is faster and more complete if the thickness of the granulate is small, the ratio of the surface to the volume is large. However, the thickness of the granules is preferably no more than forty, especially no more than twenty micrometers. The size of the vacuum in the Vacuum chamber 3 is preferably as high as possible in order to ensure good drying and degassing guarantee. Usually, in the vacuum chamber 3, a pressure of preferably about 65 to about 13.5 mbar or less is used.

For most materials, which are usually in an extrusion process around the core H ' are used, the waiting time in the vacuum chamber 3 is selected to be between 0.5 and 20 Seconds. Regularly it will be around 2 to 10 seconds. For the skilled person it is evident that the value of these quantities can fluctuate greatly, especially upwards, and that various parameters z. B. the size of the granulate grains, the level of vacuum and the size of the surface changed to carry out the treatment in the vacuum chamber 3 with different times.

Furthermore, in order to effectively degas and dry the material within a short period of time, it is important to use the material to mix vigorously in the first extruder 1. For this purpose it is preferably provided that the first Extruder 1 has an L / D ratio (L / D = the ratio Length of the screw 13 to its outer diameter) of at least 8, in particular in the range 10 to 12 and a compression ratio (the ratio of the channel volume of the feed section of the screw 13 to the front end part of the screw 13) has from 1, 2 to 3.

On the other hand, the second extruder 4 only has the

Function to extrude the granulate-like material that has been dried and degassed beforehand. To that Avoid scorching the material in the heat by mixing the material through the screw 43 arises in the second extruder 4, the second extruder 4 is preferably as small as possible L / D ratio, e.g. B. 4 to 10.

In the extruder E , the material is subject to frictional heating because the cutting tool 2 slits at high speed, in addition to the heat generated in the first extruder 1 and in the second extruder 4. Therefore, in order to avoid scorching of the material, it is necessary that the heat generated inside the extruder 4 is reduced during the extrusion. To achieve this, it is important that the sum of the L / D ratios of the first extruder and the second extruder 4 is not greater than 24, preferably not more than 20.

A nipple extension can be used in the cross-strand extrusion head D of the second extruder 4.

It is not always necessary to evacuate within the nipple neck during the extrusion of rubber or plastic onto the core W, because the ingress of air between the core and the jacket is to be avoided. Evacuation is preferred because an extrusion material is produced which results in a better connection between the core W and its jacket W ₂ .

example 1

The machine for the production of electrical winding wire has a preheating cylinder with hot air circulation over 20 m, the internal temperature is 1 TC and the electrically heated cylinder has a length of 2 m, the internal temperature of which is 180 C. The cross-strand extrusion head D was heated to a temperature of 90 ^° C .; the heating bath F of 20 π length was melted by a eutectic

with a mixture of 53% KNO ₃ , 7% NaNO ₁ , 40 ^ o NaNO. (Percent by weight) filled and kept at 200 ° C. This eutectic melts at 140 ^° C.

Three electrical wires, each one single Insulating layer of 1.2 mm made of natural rubber skin

i> '· were twisted together with the help of jute and di < Cotton tape was wrapped around the outer surface of the twisted material to form a core VV which had an outer diameter of 10.3 mm. Dam

the core W was sent through the device at a speed of 1 m / min. Natural rubber was extruded around the core W until its outer diameter was 13.1 mm, using an extruder ί according to FIG. 2, which contained a first extruder 1, the screw 13 of which had an L / D ratio of 12 and a compression ratio of 1.5, with a cylinder whose inner diameter was 90 mm, while a second extruder 4 had a screw 43 whose L / D ratio was 8, whose compression ratio was 1.5, and a cylinder having an inner diameter of 70 mm was used. The vacuum chamber 3 had a rotating cutting tool 2 with 4 cutting edges. The sleeves of the first and second extruder respectively t 4 were adjusted to temperatures of 60 or 70 ⁰ C.

The cutting tool 2 ran at a speed of 1700 rpm. The good was in 30 microns slashed thick flakes. The interior of the vacuum chamber 3 was kept at 80 mbar.

The core W provided with natural rubber after extrusion was put into the vulcanizing trough without bending inserted and withdrawn from it with the help of a guide wire.

The temperature prevailing at the core VV before entry into the transverse extrusion head D was determined to be 178 ° C. with the aid of a copper constantan thermocouple.

After the vulcanization, the fuel remaining on the surface of the layer was removed see. The electrical wire obtained, completely encased in pore-free natural rubber, could be five Can be continuously produced for hours without difficulty.

Here / u 2 sheets of drawings

Claims (5)

Patent claims: 1. A method for continuously sheathing a core with rubber or plastic, in particular for the manufacture of electrical cables, in which a vulcanizable rubber mixture around the core or a crosslinkable plastic, with degassing by means of vacuum, is extruded and the coated Core for vulcanizing the rubber mixture or essentially for crosslinking the plastic is guided in a straight line through a heated medium, characterized in that the Rubber mixture or the plastic, for degassing by means of the vacuum, into strands extruded, these cut under vacuum to granulate-like goods and maintained a vacuum is fed to a downstream extrusion point and that with this good the extrusion occurs around the core. 2t> 2. The method according to claim 1, characterized in that the core is heated to at least 90 ° C before sheathing and that its surface is heated to no more than 90 ° C, preferably no more than 60 ⁰ C, under the vulcanization or Crosslinking temperature lying temperature is maintained. 3. The method according to claims 1 or 2, characterized in that the cutting of the Strands to a thickness of at most 40 μίτι takes place. 4. The method according to any one of claims 1 to 3, characterized in that the degassing means a vacuum of at most 0.135 bar takes place. 5. Device for performing the method according to one of claims 1 to 4, with one with J5 A vacuum can be applied to the extruder, which has a cross-head for sheathing the core, which is a heatable liquid bath for continuous vulcanization or crosslinking of the casing is arranged downstream, characterized in that the extruder (4) has a gas-tight vacuum chamber (3) is arranged upstream, in which the nozzle head (12) of a further gas-tight upstream extruder (1) opens, with a rotating drivable at the outlet of the nozzle head (12) in the vacuum chamber (3) Cutting tool (2) for granulating the strands of material emerging from the nozzle head (12) is arranged.