GB2196879A - Apparatus for powder coating cables - Google Patents

Description

1

SPECIFICATION

Method of and apparatus for bringing a coating material particularly a powder onto a moving surface The invention relates to a method of -and an apparatus for bringing a coating material, parti cularly a powder onto a moving surface of an object. According to the state of the art the method includes the known steps of forming a material stream consisting of the coating material and bringing it into contact with the surface to be coated of a moving object. The known elements of the apparatus include a vessel comprising. the material to be applied for coating, means for maintaining the flow of the material stream and transporting means for movi - ng an object with at least one surface to be coated.

The process and the apparatus according to the invention are intended for primary use in the cable and rubber industries for coating ob jects forwarded continuously with a powdered material, and by means of the invention it is possible to apply technologies resulting in high quality coatings bound to the surfaces of the objects by adhesive forces.

In several technical fields it is a common requirement to bring a coating material, parti cularly a powder, onto a surface of a continu ously moving object. Among the many oper ations of this kind coatings made of paints or lacquers and anticorrosive layers are to be noted. Application of powders, and especially of talc, is of high importance in the cable in dustry and in producing rubber elements be cause of the necessity of hindering adhesion, sticking the different products during the tech nological process can be noted. This relates also to other processes applying synthetic ele ments where the danger exists that they may stick together.

In the cable industry the powder for hinder ing the sticking of different rubber or synthetic parts is applied in a stream flowing onto the surface to be coated. Under a covering plate the powder state coating material is spread onto the cable elements. This process is char acterized by high loss of the material and causes scattering the powder particles around the machine. The scattered powder is danger ous for the health of the workers, it deterior ates the electric contacts and the quality of surfaces contacted with one another during movement.

Some examples of the powdered materials applied in the different technologies are chalk (calcium carbonate, CaCO,), talc (3 MgSiO,.H 2S'O,) as inorganic compounds and calcium stearate (C16H,0O,Ca) or zinc stearate as or ganic substances.

The present invention proposes a method - and an apparatus primarly applicable with powdered materials; however, the proposed 130 GB2196879A 1 solutions are suitable also in the case of coating materials present in other forms as aerosols, drops or particles of small size. The invention will be described with reference to powdered coating materials, but this is no limitation of the scope of its application in connection with other materials.

The powdered materials to be bound by means of adhesive forces on the surface of a moving object are generally characterized by stable chemical composition. Their. physical behaviour depends, however, on the conditions of the given technological process and it is difficult to predict what changes occur in conditions differing from the nominal ones.

The changes result generally in difficulties in the course of the technologies applying pow der, e.g. in very high material losses, in low efficiency and poor quality of coating.

Several attempts have been made for solv ing the problems involved by the technology mentioned above. A separate problem has been to find a solution for coating surfaces of objects forwarded continuously. The known solutions show, however, lots of disadvantages.

For eliminating the disadvantages of the different apparatuses based on mechanical principles electrostatic apparatuses have been created, wherein electrically charged powder is applied in a continuous stream in a tank. The powder is charged positively or negatively, and the object to be coated receives the opposite charge. The powder charged is main- tained in continuous flow in the tank. Under the effect of the electrostatic forces acting between the different charges the powder particles deposit on the surface of the object. The apparatus solves a lot of problems fol- lowing from the technology of applying powder, however, the reliability is relatively low and lots of problems are linked with supplementary supply of the coating material. The construction of the apparatus is sophisticated resulting in relatively high costs and lowering the reliability, as well.

Another solution of the problems mentioned has been sought by the application of fluidization methods. The simple and effective tech- nology of fluidization is very advantageous when the objects to be coated are immersed into the fluid bed. The disadvantages of this method is the difficulty of realising a method wherein the object to be coated can be for- warded in a continuous way through a tank. If openings are provided in the tank underneath the higher level of the fluid bed for forwarding the object to be coated, it is always to be feared that the coating material escapes from the tank and contaminates the environment. Fluidization is applied therefore in factories wherein the relatively small objects to be coated should be immersed into a fluidized bed, which is very difficult to realise in production lines for producing very long objects 2 GB2196879A 2 such as cables, rubber elements etc.

In the cable industry and in other industries producing elongated articles the coating material, particularly powder, is scattered onto the article in a discontinuous way, generally in a very simple way. The technology causes high losses of the coating material which is spread in the environment of the technological equipment. The powdered or fluid coating ma- terial may be dangerous for the staff, deteriorates the electric and mechanical contacts. When applying talc, serious danger of silicosis has to be taken into account.

The task of the present invention is to elimi- nate the above-mentioned disadvantages by developing a solution realisable essentially without moving parts ensuring the surface of moving objects continuously, with high efficiency. The method and apparatus should en- sure the conditions of avoiding the contamination of the environment, the application of sophisticated equipment, of fulfilling the requirements to be met in the cable industry.

The invention is based on the recognition that the acoustic vibrations can be applied for generating a current of a coating material in a closed space and this current is capable of effectively transporting the coating material along a closed line, and the objects crossing the closed line can be covered by the coating material with high efficiency.

Thus, the object of the invention is a method of and an apparatus for bringing a coating material, particularly a powder onto a moving surface based on the acoustic princi pie, making use of the acoustic vibrations of advantageously low frequency lying in the range from 20 to 40 Hz.

The method proposed by the invention in- cludes the steps of bringing an appropriate coating material, particularly a powder into a material current along a path remaining in a closed vessel, thereby, if necessary, comminuting the coating material, and connecting the coating material with a surface to be coated of an object moved advantageously in a continuous way, wherein the novel features are the steps of introducing the coating material into a vessel closed by an elastic top wall, generating acoustic vibrations of side walls of the vessel, acoustic vibrations having advantageously the frequency range from 20 to 40 Hz, creating the material current upwards from below, and recycling the coating material fall- ing down to the material current. The acoustic vibrations of the side walls are advantageously involved by vibrations of acoustic sources connected with the side walls of the vessel.

The invention proposes also an apparatus which is capable of realising the method outlined above and is equipped with a vessel for receiving a coating material, especially a powder, means for involving a material current bringing the coating material, transporting means for introducing an object with a surface 130 to be coated into the vesssel and carrying it away therefrom, wherein according the invention the vessel includes side walls arranged in a wedge form, connected to acoustic sources adjusted for generating the material current upwards from below, the acoustic sources forming a part of an acoustic generator, the vessel is closed from its top side by a covering element, especially synthetic foil capable of resiliently following the pressure changes occuring in the closed vessel, showing lower resistance against the material current in the inner space of the vessel than the resistance of the transporting means including the object with a surface to be coated.

It is especially advantageous to apply at least two pairs of acoustic sources, e.g. loudspeakers to the side walls of the vessel and connect them to regulating means. In the ves- sel there is a densitometer for measuring density of the coating material remaining in the material current, and the densitometer is coupled with the regulating means for giving a basic signal necessary in adjusting at least one selected parameter, as frequency or amplitude, of the acoustic vibrations.

The efficiency of bringing the coating material to the surface to be coated can be further improved by applying an inner sack for receiving the coating material, the sack made of elastic material and hung in the inner space of the vessel by fixing it above the level of the acoustic sources in a way ensuring a spacing between the sack and the acoustic sources.

Another way of further improving the efficiency of bringing the coating material to the surface to be coated is to apply-instead of the inner sack-covering plates arranged in the inner space of the vessel in front of the acoustic sources, the covering plates being made in the form of wave plates having openings in their parts lying farther from the acoustic sources, in their crests and made with homogeneous material in the crests. The crests and troughs of the waves lie advantageously along parallel lines. If applying a frequency range from 20 to 40 Hz likely to be the most advantagous in case of powders it is proposed to use wave plates with openings of 1 to 2 mm diameter, wherein the distance between the crests and troughs is between and 10 mm-i.e. there are 10 to 20 waves for each 100 mm of the longitudinal dimen- sions (diameter or length) of the acoustic source.

Under given conditions it is possible that the coating material agglomerates during the technological process in the lower regions of the vessel. For avoiding this it is proposed to apply limiting elements arranged underneath the transporting means in a way that they do not disturb the material current. The limiting elements cover the lower regions of the vessel.

3 GB2196879A 3 In the height of the transporting means it is advantageous to shape the side walls of the vessel in form of a curved, especially cylindri cal outer surface which is inclined backwardly in the direction of the transporting means.

The method and the apparatus proposed by the invention render it possible to hold the coating material in a closed current within a closed vessel, whereby the contamination of the environment is avoided and high effectivity of the coating process can be ensured.

The invention will be now described in more detail with reference to the accompanying drawings and on the basis of some advan tageous embodiments shown by example. In the attached drawings.

Figure 1 shows a vertical cross-section of the apparatus according to the invention, Figure 2 is a side view -of the apparatus shown in Fig. 1, Figure 3 outlines a block diagram of apply ing the apparatus according to the invention, Figure 4 shows a side view of wavy cover ing plates applied in the apparatus according to the invention before the acoustic sources, Figure 5 is a top view of the covering plate shown in Fig. 4, Figure 6 is a vertical cross-section of an embodiment of the apparatus according to the invention equipped with an elastic sack ar- 95 ranged. in the inner space of the vessel for receiving a coating material, and Figure 7 outlines a side view of the appara tus shown in Fig. 6.

The method of the invention will be de- 100 scribed in more detail with reference to an application in the cable industry. In the course of manufacturing the cables the insulating coatings of the single strands and their twists should be covered by talc or calcium stearate. 105 The powdered coating material is arranged in a closed vessel covered from the top side by a membrane member or an elastic foil. At the side walls of the vessel there are acoustic sources excited by an appropriate acoustic generator. Due to the acoustic sources, espe cially loud-speakers the coating material is formed to flow in a material current in practi cally vertical planes. In order to create the possibility of simply fixing the acoustic planes 115 it is proposed to arrange the vessel with side walls including to one another in wedge form.

The walls of this shape offer the simplicity of fixing the acoustic source, e.g. loud-speakers.

The acoustic waves generated in generally vertical planes create a material current of the coating material directed upwards from below and the increase of the inner pressure causes change in the top region of the vessel: the membrane member or the foil by its move ment or deformation gives increased volume of the vessel. This is the situation when the resistance of the element covering the top re gion of the vessel has lower resistance against the flow of the material current than 130 the openings of the vessel taking into account that the object to be coated is in some of these openings. That is, after generating the material current in the vessel a deformation of the foil or the translation of the membrane member should occur, but the coating material may not leave the inner space of the vessel through the openings of the latter during tran sporting the object to be coated.

The frequency of the acoustic vibrations should be selected according to the coating material applied and to the conditions of the technological process. Our investigations car ried out for powdered materials resulted in the discovery that for such materials the most advantageous frequency values are from 20 to 40 Hz. It is obvious that depending on the coating material another range of frequency values may also be advantageous.

The amplitude and the frequency of the acoustic vibrations should be determined in order to ensure a required amount of the coating material at the level of the object having the surface to be coated and the current of this material should be sufficiently intensive. The lower the amplitude the lower generally the amount of the coating material brought into the current and the lower the level reached by the material. That is, the low amplitude generally results in a low quantity of the coating material at the level of the object. A turbulent flow of the material in the current can be regarded as more advantageous than a laminar flow thereof.

The apparatus according to the invention (Fig. 1 to 7) is, as mentioned above, capable of realising the method described above. The apparatus includes a vessel 3 connected to transporting means 2 for introducing an object, e.g. a cable strand 1 in a continuous process into the inner space of the vessel 3 and taking it away therefrom. Before the transporting means 2 and after them-if it is necessary-there are directing means for damping vibrations of the object and keeping it in the middle line of the transporting means 2. The transporting means 2 advantageously comprise parts reaching the inner space of the vessel 3.

The inner space of the vessel 3 is closed from all sides. On the top side of the vessel 3 there is a closing element 5 made of an elastic foil or in the form of a membrane member movably supported in the vessel 3. The closing element 5 should constitute a member capable of resiliently following the changes of the pressure in the inner space of the vessel 3. That is, the resistance of the closing element against the pressure increase caused by the current of an appropriate coating material, e.g. a powder P, is lower than the resistance of the transporting means 2 taking into account the fact that the object to be coated is in the openings of these means. In this way powder P cannot leave the inner space of the 4 GB2196879A 4 vessel 3. The closing element 5 has to ensure hermetic sealing of the vessel. If it is made in form of a foil, a grid cover 10 is very advan tageous which, applied over the foil, allows it to move and protects it against dangerous ex ternal mechanical influences. Another possibil ity of realising the closing element 5 is to build in a lightly movable construction sup ported in an appropriate way. Such construc tion is e.g. a piston-like arrangement. The up per wall of the piston can be made also of elastic material, as a foil.

The vessel 3 comprises side walls arranged in a wedge form tapering to one another. The side walls can be connected in a straight line 80 at the bottom of the vessel 3 or can be linked with a bottom made of curved plates.

The vessel 3 by its side wall is connected with acoustic sources, preferably loudspeakers 6, 6' arranged oppositely to one another, advantageously symmetrically to the longitudinal axis of the vessel 3. In front of the acoustic sources there are covering element 7, e.g.

membrane plates in the side walls for transmitting the acoustic vibrations into the in- 90 ner part of the vessel 3. The loud-speakers 6, 6' are connected to an acoustic generator capable of generating acoustic vibrations of required frequency and/or amplitude or other value. The acoustic generator constitutes a part of regulating means V (Fig. 3) receiving signals from a clensitometer 8 arranged for detecting changes in the inner space of the vessel 3 that may occur in the density of the material current. The density measured by the densitometer 8 is the basis of the regulation during the continuous work of the apparatus.

In the inner space of the vessel 3 the cur rent of the coating material, e.g. of the pow der P can be generated in different ways. One of the possibilities lies in applying an inner lining or sack 4 made of an appropriate elastic material, e.g. rubber and intended to receive the coating material. The inner sack 4 is fixed in the vessel 3 over the level of the acoustic sources, advantageously at the level of the transporting means 2 and its lower part should be suspended in the vessel 3 with a spacing assured between the sack 4 and the acoustic sources (the inner walls), so that the sack hangs in the inner space of the vessel 3 without any contact with its walls (Fig. 6 and 7).

Another, perhaps more advantageous solu tion is to fix covering plates 9 before the covering elements 7 (Fig. 4 and 5). The covering plates 9 include parts lying farther from the covering element 7 and parts lying nearer to it, they are made advantageously in the form of wave plates. For fixing the cover ing plates 9 there are elastic supporting ele ments 11 e.g. made of rubber on the inner walls of the vessel 3.

The covering plates 9 consist of crests and troughs lying along parallel lines in their parts 130 arranged before the covering elements 7. Of course, the covering plates 9 can be made, of course, with higher and lower parts being neither parallel, nor curved. For example, it can be made with parts of rectangular cross-section. In the troughs 13 the covering plate 9 is built-up homogeneously, but in the crests 12 there is a series of openings 14, so that in the wave plates (covering plates 9) there are openings 14 allowing the coating material to flow and the openings 14 are prepared on the surfaces of the covering plates 9 lying farther from the acoustic sources (the loud-speakers 6, 6').

Test investigations of the apparatus shown in the present application during manufacturing have shown that the apparatus works especially advantageously when applying acoustic vibrations within the frequency range from 20 to 40 Hz to pulverulent coating materials, and in this case the parallel lying waves of the wave plates lie at a distance of about 10 mm. The openings 14 have a diameter in the range of 1 to 1.5 mm. These dimensions are only non-limiting examples based on one kind of industrial activity and they can show wide variety in dependence on the given coating technology being used, the coating materials applied and the objects to be coated, but it is important that the openings 14 are provided in the crests 12 of the covering plates 9.

When applying covering elements 9 it is especially advantageous to build in limiting members 15 between the acoustic sources into the vessel 3. The limiting members 15 cover the bottom part of the vessel 3 and by its shape ensures conditions of avoiding agglomeration of coating material during the coating technology. The limiting member 15 is generally of saddle form and may be arranged in parallel with the direction of transporting the object or stepwise when the object to be coated is transported along a non-horizontal line.

The cross-section of the vessel 3 with the covering plates 9 when seen in planes perpendicular to the direction of transport, cardioid shaped, i.e. it looks like a heart. This is possible by applying a transitional part 16 of curved cross-section, generally of cylindrical form. By applying such a cross-section of the vessel 3 the conditions of the flow of the coating material are especially advantageous for powders. The part 16 is inclined towards the transporting means 2.

The apparatus proposed by the invention operates in the following way:

The object with the surface to be coated, for example a cable strand with a synthetic covering is transported in a continuous manner to the interior of the vessel 3 by the transporting means 2. During transport, acoustic vibrations are generated with a predetermined frequency and/or amplitude by the acoustic sources, e.g. the loud-speakers 6, 6'.

GB2196879A 5 It is obvious that acoustic vibrations with a wide range of frequency and amplitude values can be applied, also simultaneously. The am plitude and the frequency of the acoustic vi brations should be selected in such a way that 70 the powder P forms a continuous current of material under the influence of the acoustic vibrations. A turbulent current of the powder P should reach the level of the object to be coated, possibly along a closed curved line. 75 The loud-speakers 6, 6' or other acoustic sources radiating upwards from below cause intensive oscillations of the material of the in ner sack 4 or intensive bidirectional flow of the coating material over the openings 14 of the covering plates 14. The coating material sucked in over the openings 14 leaves the region of the acoustic sources along the inner surface of the side walls, upwards from below to the part 16. The material current results in increasing pressure in the inner space of the vessel 3 and the increased pressure is taken over by the closing element 5-the foil an d/or the piston arranged on the top side of the vessel 3. In this way the escape of the coating material from the inner space of the vessel 3 to the environment can be avoided.

Both the inner sack 4 hanging in the vessel and the transitional part 16 serve for control ling the conditions of the flow for the material current. The conditions should ensure that the material current be directed upwards, form a turbulent flow and be able to reach the level of the object to be coated. The turbulent flow of the material can be utilised also for commi nuting the coating material.

A vessel 3 can be equipped with a higher number of transporting means 2, whereby it is possible to introduce more objects to be coated into the inner space of the vessel 3. In 105 this way a single material current applied to a higher number of objects ensures very high efficiency of the coating process.

As mentioned, the acoustic vibrations-act ing over the walls of the inner sack 4 or by means of the covering plates 9-result in a material current transporting the coating ma terial within the vessel 3 only. The material current flows around the objects with surfaces to be coated, for example the cable strands 115 and the particles of the coating material are bound on the surfaces by adhesive forces. The material current tears particles weakly bound from the surface of the objects, result- ing in a limited cleaning of the surface. This process can be applied also for regulating thickness of the coating on the objects. The acoustic vibrations generated in a continuous manner ensure recycling of the particles falling out from the material current back thereinto. 125 The method and the apparatus proposed by the invention can be 'inserted' into the exist ing technologies without disturbing them, without the necessity of cleaning or preparing the objects after coating.

The method and the apparatus as shown above render it possible to coat the surface of different objects according to the requirements of the continuous technologies, ensur high material savings, high efficiency, and avoiding the danger of damaging health. The method can form a basis of automation technological process of coating the surface of a moving object.

From the above description, it should be understood that methods and apparatuses equivalent to those outlined above will be within the scope of the claimed invention and such methods and apparatuses will depend on the field of the application and the given circumstances.

Claims (25)

1. A method of bringing a coating material, particularly a powder, onto a moving surface, comprising the steps of introducing a coating material into a closed space, covering the closed space on one side by a wall capable of resiliently following pressure changes occurring in the closed space, generating acoustic vibrations in the closed space for bringing the coating material into a material current remaining within the closed space, adjusting the parameters of the acoustic vibrations for creating the material current with a height reaching a predetermined level in the closed space, transporting an object having the moving surface to be coated through the closed space, the surface to be coated remaining in a region determined by the height of the material current and recyling the coating material failing down in the closed space into the material current.

2. A method according to claim 1, characterized in generating the acoustic vibrations by elastic side walls limiting the closed space.

3. A method according to claim 1 or 2, charaterized in comprising a further step of measuring density of the coating material remaining in the material current in the closed space and adjusting the frequency of the acoustic vibrations to a predetermined value, preferably to 20 to 40 Hz, and the amplitude thereof in dependence on the density measured.

4. A method according to any of claims 1 to 3, characterized in bringing the coating ma- terial into a turbulent current flowing along a closed path, following within the closed space the shape of the surface of the object to be coated as it is transported through the closed space.

5. An apparatus for bringing a coating material, particularly a powder onto a moving surface, comprising a vessel for receiving a coating material, means for forming the coating material into a current in the vessel, and transporting means for introducing an object 6 GB2196879A 6 having a moving surface to be coated into the vessel and for leading it away therefrom,including acoustic sources arranged at the vessel facing one another and connected to an acoustic generator for generating acoustic vibrations of the sources for bringing the coating material into the current, in a closing element arranged at the top of the vessel for resiliently following pressure changes occurring in use in the closed space of the vessel, a closing element exhibiting lower resistance against the current of the coating material than the resistance exhibited by the transporting means during introduction and guidance of the object.

6. An apparatus according to claims, characterized in that the acoustic sources are provided for generating acoustic vibrations of a frequency in the range of 20 to 40 Hz.

7. An apparatus acording to clain 5 or 6, characterized in arranging the acoustic sources in openings in the side walls of the vessels, the openings being covered by covering elements made of resilient material and rigidly fixed in the walls of the vessel.

8. An apparatus according to any of claims 5 to 7, characterized in comprising at least two pairs of acoustic sources connected to the acoustic generator, the acoustic sources being arranged symmetrically to a longitudinal axis of the vessel below the level of the transporting means.

9. An apparatus according to any of claims 5 to 8, characterized in comprising a densito- meter monitoring the current of the coating material, arranged in the closed inner space of the vessel.

10. An apparatus according to any of claims 5 to 9, characterized in comprising re- gulating means connected to the acoustic gen- 105 erator for adjusting at least one selected parameter of the acoustic vibrations.

11. An apparatus according to claim 10, characterized in that the selected parameters are the frequency and the amplitude of the acoustic vibrations.

12. An apparatus according to claim 10 or 11, characterized in that the regulating means are connected through one of its inputs to the densitometer applied in the inner space of the vessel.

13. An apparatus according to any of claims 5 to 12, characterized in further cornprising covering plates arranged in the inner space of the vessel before the acoustic sources, the covering plates made of rigid material and having a wavy surface with holes provided in the wave crests lying farther from the acoustic sources. 60

14. An apparatus according to claim 13, characterized in that the covering plates is built up with wave crests and roughs lying along parallel lines.

15. An apparatus according to claim 13 or 14, characterized in further comprising resilient supporting elements fixed on the side walls of the vessel for bearing the covering plates at a distance from the openings of the acoustic sources.

16. An apparatus according to any of claims 8 to 15, characterized in further corn prising a limiting member arranged underneath and between the acoustic sources in the inner space of the vessel for avoiding agglomeration or congestion of the coating material during the coating process

17. An apparatus according to any of claims 5 to 16, characterized in that the vessel comprises a curved part at the height of the transporting means between the closing element and the side walls, wherein the curved part is inclined backwardly towards the transporting means.

18. An apparatus according to claim 17, characterized in that the curved part of the vessel is cylindrical.

19. An apparatus according to any of claims 13 to 18, characterized in that the covering plates include 10 to 20 waves for each 100 mm of the longitudinal dimension of the acoustic source measured along the side walls of the vessel.

20. An apparatus according to any of claims 5 to 12, characterized in further corn- prising a sack made of elastic material, the sack being fixed over the level of the acoustic sources, wherein the sack is suspended so as to ensure a gap between the sack and the acoustic sources. 100

21. An apparatus according to claim 20, characterized in that the sack is made of rubber and the transporting means are equipped with parts reaching the inner space of the sack.

22. An apparatus according to any of claims 5 to 21, characterized in further cornprising directing elements arranged before the transporting means and after them, said directing elements being applied before and after the vessel for damping vibrations of the object and leading it along a straight line in the vessel.

23. An apparatus according to any of claims 5 to 22, characterized in applying loud- speakers as acoustic sources.

24. A method of powdering moving surfaces substantially as herein described with reference to and as shown in any of the embodiments shown in the drawings.

25. An apparatus substantially as herein described with reference to and as shown in any of the embodiments illustrated in the drawings.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR53 RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.