CA1039592A - Wire enamelling method and apparatus - Google Patents
Wire enamelling method and apparatusInfo
- Publication number
- CA1039592A CA1039592A CA231,747A CA231747A CA1039592A CA 1039592 A CA1039592 A CA 1039592A CA 231747 A CA231747 A CA 231747A CA 1039592 A CA1039592 A CA 1039592A
- Authority
- CA
- Canada
- Prior art keywords
- wire
- coating
- fluidised bed
- hot
- particles
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
- B05D7/20—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to wires
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
- B05D3/0218—Pretreatment, e.g. heating the substrate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
- B05D3/0254—After-treatment
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Processes Specially Adapted For Manufacturing Cables (AREA)
Abstract
A B S T R A C T
Wire to be enamelled is pre-heated to an elevated temperature and, whilst it is hot, at least one coating of liquid resinous material is applied to it; the heat content of the wire is sufficient to eliminate any volatile solvent by flash evaporation and to cure the enamel coating to a non-tacky condition. Thereafter the coating is fully cured by immersion in a fluid-ised bed of hot inert particles.
Wire to be enamelled is pre-heated to an elevated temperature and, whilst it is hot, at least one coating of liquid resinous material is applied to it; the heat content of the wire is sufficient to eliminate any volatile solvent by flash evaporation and to cure the enamel coating to a non-tacky condition. Thereafter the coating is fully cured by immersion in a fluid-ised bed of hot inert particles.
Description
~039S~Z
This inven~ion relates to a method of and apparatus for enamelling wire; by 'wire' is meant any elongate electrical conductor especially round wires and ~lat strips of copper and aluminium up to about 10 mm2 but including also electric resist-ance wires; and by "enamelling" is meant the application of an adherent electrically insu~$ing thin film of curing synthetic resin to the wire surface.
In all conventional wire enamelling techniques, the resin is applied to the wire in solution in a volatile solvent, and the wire with the solution thereon is passed into an oven (usually gas fired, but sometimes electrically heated) to evaporate the solvent and cure the resinous coating remaining.
Recently the development of 'solventless' or at least 'semi-solventless' enamels has become a serious possibility, but use of ovens for curing has not hitherto been questioned. (For the pur-pose of this specification, an enamel is considered 'solventless' if it contains no appreciable quantity of vQlatile solvent (and the inclusion of solvents which polymerise as part o~ the curing process is not excluded) and 'semi-solventless' i~ it contains 20 volatile solvent in an amounk insufficient to render it liquid -~
at 25C).
Such ovens have heat transfer characteristics that are not as good as those that can be obtained with some other heat trans-fer techniques, and it is an object of the invention to provide a wire enamelling process utilising more efficient heat transfer equipment, and apparatus ~or use in the method.
~ he method of the invention is applicable especially to enamelling with solventless and semi-solventless enamels, but can also be used with some conventional solvent-based enamels.
~0 In the method of the invention, the wire (which may be bare or may be already coated with enamel or covered with another insulating material) is pre-heated to an elevated temperature
This inven~ion relates to a method of and apparatus for enamelling wire; by 'wire' is meant any elongate electrical conductor especially round wires and ~lat strips of copper and aluminium up to about 10 mm2 but including also electric resist-ance wires; and by "enamelling" is meant the application of an adherent electrically insu~$ing thin film of curing synthetic resin to the wire surface.
In all conventional wire enamelling techniques, the resin is applied to the wire in solution in a volatile solvent, and the wire with the solution thereon is passed into an oven (usually gas fired, but sometimes electrically heated) to evaporate the solvent and cure the resinous coating remaining.
Recently the development of 'solventless' or at least 'semi-solventless' enamels has become a serious possibility, but use of ovens for curing has not hitherto been questioned. (For the pur-pose of this specification, an enamel is considered 'solventless' if it contains no appreciable quantity of vQlatile solvent (and the inclusion of solvents which polymerise as part o~ the curing process is not excluded) and 'semi-solventless' i~ it contains 20 volatile solvent in an amounk insufficient to render it liquid -~
at 25C).
Such ovens have heat transfer characteristics that are not as good as those that can be obtained with some other heat trans-fer techniques, and it is an object of the invention to provide a wire enamelling process utilising more efficient heat transfer equipment, and apparatus ~or use in the method.
~ he method of the invention is applicable especially to enamelling with solventless and semi-solventless enamels, but can also be used with some conventional solvent-based enamels.
~0 In the method of the invention, the wire (which may be bare or may be already coated with enamel or covered with another insulating material) is pre-heated to an elevated temperature
-2- ~ ~
: - - . - - - ..................... . . . .
- . .. .. .
- - ' .: ' : `'' -'' ~ 0395~2 and, whilst it is hot, at least one coating o~ liquid resinous material is applied to it. The heat content of the wire is s~cient to eliminate any volatile solvent by flash evaporation and to cure the enamel coating to a non-tacky condition, and the coating is thereafter fully cured by immersion in a ~luidised bed of hot inert particles.
Any pre-existing enamel coating may have been applied by the method of the invention or by a conventional method.
Preferably the pre-heating of the wire is carried out also by use of a fluidised bed of hot inert particles, but other methods can be used, for example in the case of bare wire direct application of a flame or direct electrical resistance heating or induction heating.
When, as is usualJ more than one coating of enamel is requiredJ it is preferable to apply all the coatings in a single pass through the apparatus. Ideally all the coatings would be applied in succession without intermediate heating, a single fluidised-bed heating step serving to complete the cure of all the layers, but this will not always be possible: in some cases the pre-heating temperature required would be too high (for instance because the wire would melt or otherwise lose strength or because the first coating of enamel would be pyrolysed), and in other cases volatile by-products of the curing reaction might be prevented from escaping. When such problems are encount-ered or an~icipatedJ they may be overcome by using two or more pre-heating steps for individual coatings or for groups of consecutive coatings. In this case the fluidised bed effecting cure of one coating or groups of coatings preferably serves also as the pre-heating means for the next coating or group. Where an enamel coating passes ~hrough more than one fluidised heating bed it should normally emerge from the first and any intermediate bed less than fully cured, so as to avoid risk of degradation
: - - . - - - ..................... . . . .
- . .. .. .
- - ' .: ' : `'' -'' ~ 0395~2 and, whilst it is hot, at least one coating o~ liquid resinous material is applied to it. The heat content of the wire is s~cient to eliminate any volatile solvent by flash evaporation and to cure the enamel coating to a non-tacky condition, and the coating is thereafter fully cured by immersion in a ~luidised bed of hot inert particles.
Any pre-existing enamel coating may have been applied by the method of the invention or by a conventional method.
Preferably the pre-heating of the wire is carried out also by use of a fluidised bed of hot inert particles, but other methods can be used, for example in the case of bare wire direct application of a flame or direct electrical resistance heating or induction heating.
When, as is usualJ more than one coating of enamel is requiredJ it is preferable to apply all the coatings in a single pass through the apparatus. Ideally all the coatings would be applied in succession without intermediate heating, a single fluidised-bed heating step serving to complete the cure of all the layers, but this will not always be possible: in some cases the pre-heating temperature required would be too high (for instance because the wire would melt or otherwise lose strength or because the first coating of enamel would be pyrolysed), and in other cases volatile by-products of the curing reaction might be prevented from escaping. When such problems are encount-ered or an~icipatedJ they may be overcome by using two or more pre-heating steps for individual coatings or for groups of consecutive coatings. In this case the fluidised bed effecting cure of one coating or groups of coatings preferably serves also as the pre-heating means for the next coating or group. Where an enamel coating passes ~hrough more than one fluidised heating bed it should normally emerge from the first and any intermediate bed less than fully cured, so as to avoid risk of degradation
3-during curing of subsequent coatings.
Although in the preceding paragraph reference has been made to two or more fludised beds, it will be understood that equivalent results can be achieved by using a single ~luidised bed suitably par~itioned or with sui~ably designed enamel applica~ors immersed in it, an essential requirement being that particles from the bed are not allowed to contact enamel that is in a liquid or tacky condition.
The particles of the or each fluidised bed are preferably mineral particles of high thermal capacity ; either solid particles or hollow ones can be used. An example of a suitabl e solid material is silica, for example in the form of fine sandJ
and an example of suitable hollow particles is the material known as 'ballotini', consisting of small hollow glass beads.
They may be blown withair, or with a protective gas (nitro-gen or steam for example): the air or other gas is preferably recycled to conserve heat.
In the case of solventless enamels, it may sometimes be possible by the method of the invention to obtain a solid film ~ -in contact with the hot wire whilst still immersed in liquid enamel, and so to obtain a thicker, and yet more uniform, coating than can be obtained by conventional techniques.
The apparatus in accordance with the invention comprises a pre-heater, at least one enamel applicator, and at least one fluidised-bed curing chamber arranged for operation as described.
The invention will be further described, by wa~v of exampleJ
with reference to the accompanying drawings in which each of Figures 1 - 3 illustrates a different way of carrying out the invention.
In the apparatus shown in Figure 1, wire 1 taken from a conventional pay-off stand or (in accordance wi~h our patent no. 944313) direct from a low speed wire drawing machine (neither - - . - ..
1~395g2 of which is sho~n) is first pre-heated by passage through a heated fluidised bed 2. The hot w~re passes through a suitable fluid-ti~ht seal ~ into a trough~o~liquid enamel 5, which is continuously circulated from a heated reservoir 6 using a pump 7 in conjunction with a constricted return pipe 8 to maintain a controlled level in the ~rough.
Immersed in the enamel in the trough are a series of wiping dies 9 o~ increasing diameter which produce an effective wiping action despite being immersed because the wire is hot enough to ensure that the enamel film that enters a die wet reaches a set condition before it emerges from the die. The wire passes from the trough through a further seal 10 into a second heated fluid-ised bed 11; a short length of wire downstream of the seal is protected by a screen 12 to avoid contact of wet enamel film with the fluidised bed particles.
The coated wire emerges from the fluidised bed a~ 13 and passes to any conventional take-up mechanism (not shown).
The form of apparatus shown in Figure 2 is similar~ except that the enamel is pumped via manifold 14 to a series of individ-20 ual applica~ors 15 and the trough 4 serves simply to collectexcess enamel and return it to the reservoir. In this case it is only necessary for the enamel of each coat to be set before it reaches the next applicator (or, in the case of the last appli-cator~ before it enters the fluidised bed 11).
In the arrangement shown in Figure 3, a series of heated fluidised beds 16, 17 ... 17, is used: fluidised bed 16 is used to pre-heat the wire, which is passed to an applicator 18, and each of the fluidised beds 17 serves to re-heat the coated wire before it enters a respective one of the further enamel applica-tors 19 ... 19, 20. The temperatures of the beds 17 are chosento avoid complete curing of the coatings therein, and all the coatings are cured together in the fluidised bed 11 as in the l03ssa2 other examples. For simplicity, the applicators 18, 19 ... 19,20 have been shown as metering applicators fed through ducts 21, but ot~er types of applicator can be used and provision made for returning excess enamel if required.
If the temperatures of the fluidised beds 17 are chosen to obtain a considerable degree of cure therein, it may be desir-able, or even necessary, to cool the wire somewhat between the hot fluidised beds 17 and the subsequent applicators; this can be done (for example) by use of a cool fluidised bed, an air ~et, or by spacing the applicators sufficiently from the outlets of the fludised beds.
~.
Although in the preceding paragraph reference has been made to two or more fludised beds, it will be understood that equivalent results can be achieved by using a single ~luidised bed suitably par~itioned or with sui~ably designed enamel applica~ors immersed in it, an essential requirement being that particles from the bed are not allowed to contact enamel that is in a liquid or tacky condition.
The particles of the or each fluidised bed are preferably mineral particles of high thermal capacity ; either solid particles or hollow ones can be used. An example of a suitabl e solid material is silica, for example in the form of fine sandJ
and an example of suitable hollow particles is the material known as 'ballotini', consisting of small hollow glass beads.
They may be blown withair, or with a protective gas (nitro-gen or steam for example): the air or other gas is preferably recycled to conserve heat.
In the case of solventless enamels, it may sometimes be possible by the method of the invention to obtain a solid film ~ -in contact with the hot wire whilst still immersed in liquid enamel, and so to obtain a thicker, and yet more uniform, coating than can be obtained by conventional techniques.
The apparatus in accordance with the invention comprises a pre-heater, at least one enamel applicator, and at least one fluidised-bed curing chamber arranged for operation as described.
The invention will be further described, by wa~v of exampleJ
with reference to the accompanying drawings in which each of Figures 1 - 3 illustrates a different way of carrying out the invention.
In the apparatus shown in Figure 1, wire 1 taken from a conventional pay-off stand or (in accordance wi~h our patent no. 944313) direct from a low speed wire drawing machine (neither - - . - ..
1~395g2 of which is sho~n) is first pre-heated by passage through a heated fluidised bed 2. The hot w~re passes through a suitable fluid-ti~ht seal ~ into a trough~o~liquid enamel 5, which is continuously circulated from a heated reservoir 6 using a pump 7 in conjunction with a constricted return pipe 8 to maintain a controlled level in the ~rough.
Immersed in the enamel in the trough are a series of wiping dies 9 o~ increasing diameter which produce an effective wiping action despite being immersed because the wire is hot enough to ensure that the enamel film that enters a die wet reaches a set condition before it emerges from the die. The wire passes from the trough through a further seal 10 into a second heated fluid-ised bed 11; a short length of wire downstream of the seal is protected by a screen 12 to avoid contact of wet enamel film with the fluidised bed particles.
The coated wire emerges from the fluidised bed a~ 13 and passes to any conventional take-up mechanism (not shown).
The form of apparatus shown in Figure 2 is similar~ except that the enamel is pumped via manifold 14 to a series of individ-20 ual applica~ors 15 and the trough 4 serves simply to collectexcess enamel and return it to the reservoir. In this case it is only necessary for the enamel of each coat to be set before it reaches the next applicator (or, in the case of the last appli-cator~ before it enters the fluidised bed 11).
In the arrangement shown in Figure 3, a series of heated fluidised beds 16, 17 ... 17, is used: fluidised bed 16 is used to pre-heat the wire, which is passed to an applicator 18, and each of the fluidised beds 17 serves to re-heat the coated wire before it enters a respective one of the further enamel applica-tors 19 ... 19, 20. The temperatures of the beds 17 are chosento avoid complete curing of the coatings therein, and all the coatings are cured together in the fluidised bed 11 as in the l03ssa2 other examples. For simplicity, the applicators 18, 19 ... 19,20 have been shown as metering applicators fed through ducts 21, but ot~er types of applicator can be used and provision made for returning excess enamel if required.
If the temperatures of the fluidised beds 17 are chosen to obtain a considerable degree of cure therein, it may be desir-able, or even necessary, to cool the wire somewhat between the hot fluidised beds 17 and the subsequent applicators; this can be done (for example) by use of a cool fluidised bed, an air ~et, or by spacing the applicators sufficiently from the outlets of the fludised beds.
~.
Claims (12)
1. A method of enamelling wire comprising pre-heating the wire to an elevated temperature and, whilst it is hot, applying to it at least one coating of liquid resinous material, the heat content of the wire being sufficient to eliminate any volatile solvent by flash evaporation and to cure the enamel coating to a non-tacky condition, and thereafter fully curing the coating by immersion in a fluidised bed of hot inert particles.
2. A method of enamelling wire comprising pre-heating the wire to an elevated temperature by immersion in a fluidised bed of hot inert particles and, whilst it is hot, applying to it at least one coating of liquid resinous material, the heat content of the wire being sufficient to eliminate any volatile solvent by flash evaporation and to cure the enamel coating to a non-tacky condition, and thereafter fully curing the coating by immersion in a fluidised bed of hot inert particles.
3. A method of enamelling wire comprising pre-heating the wire to an elevated temperature and, whilst it is hot, applying to it at least one coating of liquid resinous material, the heat content of the wire being sufficient to eliminate any volatile solvent by flash evaporation and to cure the enamel coating to a non-tacky condition, reheating the wire by immersion in a fluid-ised bed of hot inert particles and, whilst it is hot, applying to it at least one further coating of liquid resinous material, the heat content of the re-heated wire being sufficient to cure to a non-tacky condition the further coating or coatings, and thereafter fully curing both of all the coatings by immersion in a fluidised bed of hot inert particles.
4. A method as claimed in Claim 3 in which the steps of reheat-ing the wire and applying at least one further coating are repeated at least once more before the final curing step.
5. A method as claimed in Claim 1 or Claim 3 or Claim 4 in which the wire is initially bare and it is pre-heated by direct application of a flame, by direct resistance heating, or by induction heating.
6. A method as claimed in Claim 3 or Claim 4 in which the wire is pre-heated by immersion in a fluidised bed of hot inert particles.
7. A method as claimed in Claim 2 or Claim 3 or Claim 4 com-prising using a single fluidised bed for at least two heating steps.
8. A method as claimed in Claim 1 or Claim 2 or Claim 3 in which the particles of the or each fluidised bed are mineral particles of high thermal capacity.
9. A method as claimed in Claim 1 or Claim 3 or Claim 3 in which the particles are of silica.
10. A method as claimed in Claim 1 or Claim 2 or Claim 3 in which the particles are "ballotini".
11. A method as claimed in Claim 1 or Claim 2 or Claim 3 in which the or each fluidised bed is blown with air.
12. A method as claimed in Claim 1 or Claim 2 or Claim 3 in which the or each fluidised bed is blown with nitrogen, steam, or another protective gas.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB3314374A GB1462286A (en) | 1974-07-26 | 1974-07-26 | Wire enamelling method and apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1039592A true CA1039592A (en) | 1978-10-03 |
Family
ID=10349112
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA231,747A Expired CA1039592A (en) | 1974-07-26 | 1975-07-18 | Wire enamelling method and apparatus |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU8341275A (en) |
| CA (1) | CA1039592A (en) |
| GB (1) | GB1462286A (en) |
| IN (1) | IN144903B (en) |
-
1974
- 1974-07-26 GB GB3314374A patent/GB1462286A/en not_active Expired
-
1975
- 1975-07-18 CA CA231,747A patent/CA1039592A/en not_active Expired
- 1975-07-22 IN IN143/CAL/75A patent/IN144903B/en unknown
- 1975-07-25 AU AU83412/75A patent/AU8341275A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| IN144903B (en) | 1978-07-22 |
| GB1462286A (en) | 1977-01-19 |
| AU8341275A (en) | 1977-01-27 |
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