DE1941592A1 - Process and device for external and internal coating of skeleton pipes - Google Patents

Description

DipL-Ing. W. iabbuscli

Patent attorney ■ 1 Q A 1

29 Oldenburg ' ^{Ό H} '

F-bsahetlxsixaBe 6

5158 / bu

Patent and, Grebrauehsmuster aid application

Josef-Helmut Danzer, 56 Wuppertal-Elberfeld, Annenstr. 9

Processes and devices for external and internal coating of skeleton tubes - - - '

The invention relates to a method and devices for carrying out the process for the continuous external and internal coating of skeleton pipes and / or others Hollow profiles with plastic, in which the plastic is applied in powder form to the hollow profile and then melted or is burned in "

Various processes are known for external coating and in some cases for internal coating of pipes and hollow profiles in which powdered plastics are either melted directly (fluidized bed sintering process), or in which the powder is electrostatically coated and the powder coating is then melted or burned in. These known methods have the disadvantage that very high voltages are required for electrostatic applications in order to guarantee sufficient powder adhesion until the melting or baking process, in particular despite the Faraday effect occurring with small hollow profiles. A high voltage iet also necessary in these processes because

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the amount of powder required for application only in a few Individual particles touch the electrode surface and are therefore not positively charged at all or only indirectly. The ideal Condition would be that every single particle with the electrode comes into contact before the coating and thereby its charge directly and not indirectly via other particles learns. If this could be achieved even approximately, it would be even a low voltage is required.

Further, as opening for the beka nn th process also occurs for bridging the distance between the central and the powder of drilling or hollow-interior surface and thus required for attraction of the powder particles have a relatively high charge. The ideal condition here would be that the particles cover this distance by mechanical impulses and that the charge would only be so great that the particles are sufficiently held on the surface to be coated. In this case, the increased charging would be superfluous, which would otherwise have to bring about the transport of the powder particles to the coating surface. An additional acceleration of the powder particles by increased air pressure, which is used to transport the particles from the nozzle outlet to the inner wall, is not very suitable because the increased amount of air generates a strong vortex formation and rebound.

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From the above considerations it follows that appropriate measures should be achieved with a low voltage to avoid the emergence of the To counteract the effect of a Faraday cage. This should be supported by this essentially »« let him Structure of the inner field does not have its full effect and this field in a pulsed manner or through repetitive interruptions is forced to collapse.

The invention is based on the object of creating a method that is more economical than the known method is superior, especially for the production of coated pipe profiles with a small inner diameter suitable is.

This object has been achieved according to the invention in that the tubular hollow profile is electrostatically charged and guided over a coaxially arranged powder feed tube, that the plastic powder in the powder feed tube is pushed through an electrostatically charged contact spiral with opposite polarity and is charged and set in rotation, that the plastic powder radially deflected upon exit from the powder feed tube and in cooperation with. χ Centrifugal force and acceleration and electrostatic attraction is thrown and held against the inner wall of the hollow profile, and that the powder layer is subsequently, preferably by heating

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in an induction heating, melted or burned in will.

In this training, the application of the plastic powder in particular significantly improved as a result of extensive static charging. The contact of each Eörnehen with the positive electrode is achieved by * that the electrode is arranged within the transport flow of the particles and is spiraled several times, that is is designed as an Eontaktspirale. The snail formation creates a large contact surface, with the result of simultaneous swirling of the particles Due to the swirl, the particles are forced into contact alternately and inevitably by changes in direction have to come. Finally, the transported powder material is transported in by the screw design offset in rotation in the axial direction. When leaving the powder feed tube eventually becomes the coating material radially deflected, and due to the intrinsic rotation and the resulting centrifugal force, the individual powder particles are directed through the ring nozzle onto the one to be coated Surface spun in a directionally stable manner. The single ones So you need to go through the electrostatic effect to be held only on the surface of the hollow profile, for which "" or a relatively small voltage is required is. The powder particles are subsequently obtained by heating

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melted or burned in. The amount of powder per unit of time (Speed m / ") is determined by appropriate air pressure (conveying speed of the powder) and through Adjustment of the ring slot nozzle regulated.

The Eontaktspirale gets its tension over a Electrically conductive rod electrode, while the skeleton tube is directly connected to the negative pole (earth).

According to the invention, the direct voltage supplied to generate the electrostatic effect is preferably periodically interrupted (pulsating direct current), the pulse sequence being controllable in such a way that the opposing field is largely prevented from building up. This improves the possibility of electrostatically coating small dimensions of pipe and hollow profiles with powder. By warming up to approximately before the softening point of the powder material and the pipe or hollow profile to be coated, a much thicker powder adhesion and coating can be achieved. B ¹ The same principle applies to the external coating.

There are possible applications that are far require thicker and surface-improving coating than is economical with powder coating is portable or technically possible. In this case, the inner and / or outer coating of the described method made relatively thin

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and preferably then in the continuous process the top layer is heated to the melting point and an optionally thick layer is additionally coated by extrusion with internal and / or external coating heads. Here, a homogeneous connection (fusion-welding) achieved with the subsequent top coat if a weldable material is used finds. In this further process step, however, can also a different color or even a material with whole other properties are used, e.g. the pre-coated material can have the property of a special Have good adhesion to the support tube or hollow profile, while the outer material (final coating) has a good one Welded connection with this enters into, but even in the material price is significantly cheaper and has better properties in terms of light resistance, weather resistance or the like having*

It is within the scope of the invention, the individual process steps to be exchanged with regard to the inner and outer surface of the hollow profile · As plastic powder or liquid can be thermoplastic or thermosetting material with or without a two-component reaction can be used, especially with additional recoating Different materials are used that are different in their Distinguish properties and colors.

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Embodiments of the invention from which Further inventive features are shown in the drawing shown. Show it:

Fig. 1 and 2 shown in continuation and schematically a possible embodiment of the method according to the invention,

3 shows a longitudinal section through a schematic and enlarged extrusion end coating head and

4 shows the mutual assignment of an extrusion precoating head and the extrusion end coating head according to Fig. 3

In the method according to FIGS. 1 and 2, a from the left Tubular skeleton largely pre-formed from a sheet metal strip and fed via an axially arranged powder feed tube 2 led. Shortly behind the powder feed nozzle 8 of the powder feed pipe, the pipe skeleton becomes complete bent to form a tube and welded together with a welding electrode 10. At 11 is a scraper for removing the Weld diamond.

The powder feed tube 2 is made of heat-resistant, insulating material and is inside, preferably in Area of the contact spiral, electrically conductive. In the powder feed tube 2 iat a rod electrode 3 arranged coaxially

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net, which at the rear end with a contact spiral 4 · ■ is conductively and mechanically connected, which fills the diameter of the powder feed tube. With the end of the Eontaktspirale 4- is connected to a distributor head 5 located in front of the rear end of the powder feed tube, which has an insulating end cap 6. The front end of the Rod electrode 3 is held axially adjustable in powder feed tube 2 with the aid of an axial adjusting screw 7, see above that the nozzle slot formed by the distributor head 5 can be changed.

With 9 centering cams are referred to for centering the powder feed tube in the pipe skeleton moved past, 12, 13 and 14- are devices for sandblasting, degreasing and cleaning and coating the pipe skeleton. 16 is a hot air drying tunnel. With I7 is a powder application device for coating the outer surface of the pipe skeleton. 15-is an induction heater and 18 is one Cooling device. 19 with a hot air drying channel is designated j. and 20a, 20b are pipe guide centering rollers. 22nd is an optional extrusion finish coating head for post-coating which has an annular surface on it Melting device 21 is provided.

The coating process is carried out with the system described carried out as follows: From left to right continuous behind the powder feed nozzle 8

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The welded pipe frame 1 is first coated on the inside. The plastic powder passes under pressure through the Pulverzuführstutzen 8 in the Pulverzufü hr ungsrohr 2 and the powder delivery tube of the clock spring and the inner wall of the tube is electrostatically charged, and set into rotation here before exiting from the rear end. The electrostatic charge is brought about by connecting the rod electrode and contact spiral to a positive direct current high voltage pole, preferably pulsating in that the individual powder parts are thrown against the bare metal and are positively charged by touch. The powder can be fed into the powder feed tube by a screw conveyor or with air pressure. be pressed. If air is used, it is diverted through the pipe skeleton to be coated, with any free-floating, disruptive powder particles being conveyed out. In order to ensure a smooth, eddy-free discharge, the insulating end cap 6 is designed in a streamlined, torpedo-shaped manner. The transport air can also optionally be heated in such a way that it heats the powder parts to be conveyed in order to enable thicker layers of coating.

When exiting the powder feed pipe, the rotating powder particles experience a through the distributor head 5 radial deflection so that it is directionally stable against the inner wall of the pipe skeleton by centrifugal force and air pressure

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be transported. At the pipe skeleton is a negative one Voltage applied so that the positively charged powder particles adhere well to the wall. To prepare the external coating of the pipe skeleton 1, the pipe skeleton is successively in the degreasing device 12 with solvents degreased, roughened in the sandblasting device 13 and in the coating device 14- with an adhesion promoter or / and glue prepared. In the hot air duct 16 with the hot air inlet 16a and the hot air outlet 16b the pipe skeleton is dried after this external pretreatment and also on the outside in the powder application device 17 coated with plastic powder. The external powder application device 17 works in a manner known per se in such a way that that the positively charged plastic powder is whirled up by means of compressed air so that it is placed on the pipe skeleton is brought. The pipe skeleton coated on the inside and outside then gets into the induction heater I5 with the electrical Connections 15a / and 15b, in which the powder layers are melted or baked and thus finished the coatings will. In the cooling device 18, the pipe skeleton is cooled, for example, in a water bath, and in the Hot air duct 19 with inlet 19a and outlet 19b, the moisture remaining on the pipe skeleton is dried. The extrusion device head 22 is used to apply another thick outer coating 24 to the tubular skeleton,

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For the purpose of producing better adhesion, the pipe skeleton is removed from an extrusion head 22 before it enters the extrusion device heated annular surface melting device 21;

The I ¹ Ig. 3 and 4 show a variant of the production of the outer coating 24 on a precoated, smooth and / or surface-perforated and / or perforated skeleton tube JO, as can also be used in the production according to FIGS. 1 and 2. The. The skeleton pipe 30 is precoated in an extrusion precoating head and the final coating is preferably carried out continuously in an extrusion final coating head 34 arranged at a distance behind it, as FIG. 4 illustrates. Both coating heads receive the plastic material from an extruder 36. A branch pipe 3.7 *, for example, runs from the extruder to the final extrusion coating head 34

stole
Chrome-nickel, and a gradient with low voltage and high amperage is applied to the extruder and to the extrusion end coating head, whereby the branch pipe is heated in a thermally controllable manner as a result of the resistance effect. 38 is a cooling channel with inlet 38a and outlet 38b, which freezes the precoat. 35a and 35b are centering rollers for guiding the pipe skeleton ο

As shown in Fig. 3, the extrusion finish coater head 34 an inner guide nozzle 34a. for applying the plastic and an enlarged one in front of the inner guide nozzle

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Cavity 34-b with an annular surface remover disposed therein 39 for melting the Yorbesehichtung 32 to effect a fusion with on-, finally applied final coating compound. Due to the surface coating, the perforations are inevitable resulting sink marks 40 compensated.

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Claims (1)

5158 / bu - 15 - Expectations; MV) Process for the continuous outer and / or inner coating of skeleton tubes or other hollow profiles with plastic, in which the plastic is applied to the hollow profile in liquid or powder form and subsequently melted or burned in, characterized in that the hollow profile (1) is electrostatically charged and over a coaxially arranged powder feed tube (2) is guided so that the plastic powder in the powder feed tube is pushed through an electrostatically oppositely charged contact spiral (4) and is charged and set in rotation so that the plastic powder is radially deflected and through when it exits the powder feed tube "Centrifugal force" and acceleration and electrostatic attraction is transported against the inner wall of the hollow profile, and that the powder layer is subsequently melted or burned in, preferably by heating in an induction heater. 2 ·. Method according to claim 1, characterized in that the coating is carried out with a liquid medium. Method according to claim 1, characterized in that that the hollow profile ale sheet metal strips brought up and behind 109808/17 & 4 5158 / bu - 14 - the powder feed nozzle (8) of the powder feed tube (2) a skeleton tube or skeleton hollow profile (1) is bent together and welded. 4 »The method according to claim 1, characterized in that the outer surface of the hollow profile is subsequently coated with powder in a powder application device (17) known per se, and the powder is preferably melted or burned in by heating in an induction heater. 5. Method according to one of the preceding claims, characterized in that the hollow profile is subsequently coated on the inside and / or outside with a second plastic layer (24), and this is preferably closely connected to the pre-coating by means of adhesive, adhesion promoter or welding. 6. The method according to claim 1, characterized in that the electrostatic field generated in the hollow profile (1) is interrupted periodically in a continuously controllable manner. [_j_ device for carrying out the method according to Claim 1, characterized in that the powder feed tube (2) as inside with an electrically conductive layer provided insulating tube is formed, and that the PuI- 109808/1784 5158 / bu. - 15 - supply tube lying contact spiral (A) with a lying outside in front of the end of the powder supply tube Distributor head (5) is connected and axially displaceable. 8 ^ device according to claim 7 »characterized in that that the distributor head (5) has a teardrop-shaped insulating end cap (6). 2a extrusion coating head for carrying out the method according to claim 5 »in particular for recoating a perforated skeleton tube or skeleton hollow profile, characterized in that an enlarged cavity (3 ² ^ b) is arranged in an inner guide nozzle (34-a) ^ s * the skeleton tube which supplies the plastic in which there is an annular surface fuser (39). 10. Apparatus for carrying out the method according to claim 5 »characterized in that an extrusion precoating head (31) and an extrusion end coating head (3 ^ -) are arranged one behind the other and the extrusion end coating head is connected to the material supply of the extrusion precoating head through a branch pipe (37), and that the branch pipe (37) from high-impedance resistant material, preferably stainless steel, is, to which an adjustable circuit is connected to the heating of the tube by resistance heating. 1 η α ο η ο / 1 1 c /.