US2572597A - Porosity tester for coating materials - Google Patents

Porosity tester for coating materials Download PDF

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Publication number
US2572597A
US2572597A US204013A US20401351A US2572597A US 2572597 A US2572597 A US 2572597A US 204013 A US204013 A US 204013A US 20401351 A US20401351 A US 20401351A US 2572597 A US2572597 A US 2572597A
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pad
plate
layer
porosity
solution
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US204013A
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Thomas J Connor
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General Electric Co
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General Electric Co
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/20—Investigating the presence of flaws
    • G01N27/205—Investigating the presence of flaws in insulating materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials

Definitions

  • This invention relates to apparatus for testing coating materials and more particularly to apparatus for determining porosity in non-conducting coating materials applied on metallic surfaces.
  • the common method of protecting exposed metallic surfaces is to cover them with a thin layer of a non-conducting coating material such as paint, lacquer or the like.
  • a metallic surface is to be exposed to the atmosphere, as for example are many transformer and circuit breaker tanks, it is especially important that the protecting layer be continuous over the entire surface. Even small holes or pores in the coating layer, imperceptible to the human eye, may lead to flaking of the layer and the forming of rust and corrosion on the metallic surface.
  • the metallic structure on whose surface lies the non-conducting coating layer for which a porosity test is desired, is connected in open series circuit with a source of electrical potential, a current indicating device, and a metallic member or plate.
  • the metallic plate is positioned to contact a pad of absorbent material saturated with .a water solution of a volatile salt, such as amonium carbonate.
  • the metallic plate, the absorbent pad, anda supply of the solution for continuously wetting the pad are ordinarily contained in a portable applicator member.
  • the pad is rubbed over the coating layer so that the solution contained in the pad permeates any pores in the coating layer.
  • the contact of the electrically conductive solution with any bare metal of the metallic surface completes the circuit through the indicating device.
  • the indicating device by its deflection provides an indication of the presence of the pores in the coating layer.
  • a metal sheet I has a layer 2 of non-conducting coating material, such as paint, applied over the greater portion of one of its surfaces.
  • An alligator clip 3 by gripping sheet I in an area which is not covered by layer 2 provides a good electrical connection to the sheet.
  • Clip 3 is connected by a wire 4 to an output terminal 5 of a portable battery and meter case 6.
  • terminal 5 is serially connected with two dry cell batteries 1 and la, an indicating device 8, such as a direct current ammeter, and an output lead 9.
  • Lead 9 is connected through wire it to a terminal ll mounted on the closed end of a portable applicator member l2.
  • Applicator member I2 is shown in the drawing as a tubular container having a closed end and an open end. The shape of member I2 is not essential to the operation of the device, but whatever shape is employed, it must form a container having at leastone opening to the space enclosed within it.
  • member I2 Positioned within member I2 is a member or plate l3 which is made of an electrically conducting metal such as silver.
  • plate [3 is movable within member l2.
  • plate l3 may be positioned permanently by screws or other means without appreciably affecting the functioning of the device, so long as the positioning means used do not seal off the space on one side of plate I3 from the space on the other side.
  • Pad I4 is held in place by friction with the inner wall of member It.
  • pad I4 is made slightly oversize with respect to the opening in member l2 and is forced into the opening.
  • Plate I3 is so positioned within member I! that, when pad It comes to firm contact with the plate, a portion of pad It still protrudes be- 55 yond extremity of member l2.
  • a spring I5 provides an electrical connection between terminal I I and plate I3, and, when plate I3 is movable, also serves to keep plate I3 in firm contact with pad I4.
  • the space surrounding spring I5 is filled with an electrically conducting water solution I6 of a volatile salt, such as ammonium carbonate. Since plate I3 does not seal off the space surrounding spring I5, pad I4 is continuously wetted by solution I6.
  • applicator member I2 In operation applicator member I2 is moved so that the exposed portion of pad I4 is rubbed on layer 2 over all the area to be tested for porosity. If any pores exist in layer 2, as pad I4 is rubbed over these pores, solution I6 penetrates them and contacts the metal surface of sheet I. Since salt solutions in water, such as the ammonium carbonate solution I6, are electrically conductive, the contact of the solution with the metal completes the electrical circuit through indicating device 8.
  • the wetted felt pad I4 between plate I3 and metal sheet I in efiect forms an electrolytic cell for the passage of current.
  • the current indicated by device 8 depends upon the area of metal contacted by solution I6, i. e. the number of holes in or the porosity of layer 2.
  • Solution I6 may be formed of almost any salt which does not leave a corrosive residue that will interfere with the durability of the coating layer. It has been found that a water solution of ammonium carbonate gives excellent results. Salt film deposited on the coating layer by a solution made of ammonium carbonate decomposes after a few hours into the vapors of carbon dioxide, ammonia and water. Examples of other salts which may be used to form solutions suitable for employment with this invention are ammonium carbamate, ammonium carbamate acid carbonate, ammonium formate, ammonium bicarbonate, ammonium cyanate, ammonium fluoroborate and ammonium thiocarbonate.
  • the salt used should be one possessing fairly high solubility as well as high ionization.
  • the purpose of the wetting agent is to aid in the solution in permeating very small holes or pores in the coating layer.
  • Plate I3 may be perforated to allow better flow of solution I6 into pad I4, particularly when the plate is permanently positioned.
  • the perforations The 4 not only aid the flow of solution but also help to eliminate polarization of the plate.
  • This invention possesses a major advantage in that, since it damages neither the metallic surface or the coating layer, the porosity test may be made on the actual surfaces which are to go into use rather than being made on a test sample. Moreover, the invention is not restricted to metallic surfaces small in area but may be used equally as well with large surfaces, such as for example the outside of power transformer tanks.
  • a device for determining porosity in a layer of non-conducting coating material applied to a metallic surface comprising a portable applicator member including a container having an open end; a metallic plate positioned within said container; a pad of absorbent material contacting said plate, filling said open end, and protruding beyond the extremity of said member; an electrically conductive water solution of a volatile salt filling said container and wetting said pad to establish electrical contact between said plate and said metallic surface through any pores in said coating material in response to movement of said pad across said coating material; and a circuit arranged to be completed by said contact including a source of voltage and a current indicating device, said contact to cause a deflection on said indicating device indicative of porosity in said layer of coating material in response to permeation of said solution into the pores in said coating material.

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  • Chemical & Material Sciences (AREA)
  • Biochemistry (AREA)
  • Physics & Mathematics (AREA)
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  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Testing Resistance To Weather, Investigating Materials By Mechanical Methods (AREA)

Description

Oct. 23, 1951 1'. J. CONNOR v 2,572,597
POROSITY TESTER FOR COATING MATERIALS Filed Jan. 2. 195] I Inventor: Thomas J. Connor,
-l is Attorney.
Patented Oct. 23, 1951 POROSITY TESTER FOR COATIhlG MATERIALS Thomas J. Connor, Lower Merlon, Pa., asslgnor to General Electric Company, a corporation of New York Application January 2, 1951, Serial No. 204,013
1 Claim. 1
This invention relates to apparatus for testing coating materials and more particularly to apparatus for determining porosity in non-conducting coating materials applied on metallic surfaces.
The common method of protecting exposed metallic surfaces is to cover them with a thin layer of a non-conducting coating material such as paint, lacquer or the like. Where a metallic surface is to be exposed to the atmosphere, as for example are many transformer and circuit breaker tanks, it is especially important that the protecting layer be continuous over the entire surface. Even small holes or pores in the coating layer, imperceptible to the human eye, may lead to flaking of the layer and the forming of rust and corrosion on the metallic surface.
In the past, the detection of these small pores in the layer of coating material has presented a serious problem. The means principally employed for determining the condition of the layer of coating material has been visual inspection, but unfortunately, visual inspection, no matter how carefully performed is often subject to serious error. Layers of coating material which appear to the eye to be continuous throughout may in fact contain a myriad number of extremely small holes or pores.
It is an object, therefore, of this invention to provide new and improved means for determining porosity in non-conducting coating material applied on metallic surfaces.
It is another object of this inventionto provide a new and improved portable device for determining porosity in non-conducting coating material applied on metallic surfaces, which harms neither the layer of coating material nor the metallic surface by its operation.
In this invention, the metallic structure, on whose surface lies the non-conducting coating layer for which a porosity test is desired, is connected in open series circuit with a source of electrical potential, a current indicating device, and a metallic member or plate. The metallic plate is positioned to contact a pad of absorbent material saturated with .a water solution of a volatile salt, such as amonium carbonate. The metallic plate, the absorbent pad, anda supply of the solution for continuously wetting the pad are ordinarily contained in a portable applicator member. To test for porosity in the coating layer, the pad is rubbed over the coating layer so that the solution contained in the pad permeates any pores in the coating layer. The contact of the electrically conductive solution with any bare metal of the metallic surface completes the circuit through the indicating device. The indicating device by its deflection provides an indication of the presence of the pores in the coating layer.
For a better and more complete understanding of my invention, together with additional ob jects and advantages thereof, reference should now be had to the following description and accompanying drawing which is a schematic diagram of a preferred embodiment of this invention.
Referring to the drawing, a metal sheet I has a layer 2 of non-conducting coating material, such as paint, applied over the greater portion of one of its surfaces. An alligator clip 3 by gripping sheet I in an area which is not covered by layer 2 provides a good electrical connection to the sheet. Clip 3 is connected by a wire 4 to an output terminal 5 of a portable battery and meter case 6.
In case 6, terminal 5 is serially connected with two dry cell batteries 1 and la, an indicating device 8, such as a direct current ammeter, and an output lead 9. Lead 9 is connected through wire it to a terminal ll mounted on the closed end of a portable applicator member l2. Applicator member I2 is shown in the drawing as a tubular container having a closed end and an open end. The shape of member I2 is not essential to the operation of the device, but whatever shape is employed, it must form a container having at leastone opening to the space enclosed within it.
Positioned within member I2 is a member or plate l3 which is made of an electrically conducting metal such as silver. In the preferred embodiment of this invention illustrated in the diagram, plate [3 is movable within member l2. However, plate l3 may be positioned permanently by screws or other means without appreciably affecting the functioning of the device, so long as the positioning means used do not seal off the space on one side of plate I3 from the space on the other side. Filling the open end of member [2 and contacting plate I3 is a pad I formed of absorbent material, such as felt. Pad I4 is held in place by friction with the inner wall of member It. In order that sumcient friction be provided to hold pad I securely, pad I4 is made slightly oversize with respect to the opening in member l2 and is forced into the opening. Plate I3 is so positioned within member I! that, when pad It comes to firm contact with the plate, a portion of pad It still protrudes be- 55 yond extremity of member l2.
A spring I5 provides an electrical connection between terminal I I and plate I3, and, when plate I3 is movable, also serves to keep plate I3 in firm contact with pad I4. The space surrounding spring I5 is filled with an electrically conducting water solution I6 of a volatile salt, such as ammonium carbonate. Since plate I3 does not seal off the space surrounding spring I5, pad I4 is continuously wetted by solution I6.
In operation applicator member I2 is moved so that the exposed portion of pad I4 is rubbed on layer 2 over all the area to be tested for porosity. If any pores exist in layer 2, as pad I4 is rubbed over these pores, solution I6 penetrates them and contacts the metal surface of sheet I. Since salt solutions in water, such as the ammonium carbonate solution I6, are electrically conductive, the contact of the solution with the metal completes the electrical circuit through indicating device 8. The wetted felt pad I4 between plate I3 and metal sheet I in efiect forms an electrolytic cell for the passage of current. The current indicated by device 8 depends upon the area of metal contacted by solution I6, i. e. the number of holes in or the porosity of layer 2. Thus this invention not only provides means for determining the presence of porosity in a layer of coating material, but also provides a relative measurement of the seriousness of the porosity.
Solution I6 may be formed of almost any salt which does not leave a corrosive residue that will interfere with the durability of the coating layer. It has been found that a water solution of ammonium carbonate gives excellent results. salt film deposited on the coating layer by a solution made of ammonium carbonate decomposes after a few hours into the vapors of carbon dioxide, ammonia and water. Examples of other salts which may be used to form solutions suitable for employment with this invention are ammonium carbamate, ammonium carbamate acid carbonate, ammonium formate, ammonium bicarbonate, ammonium cyanate, ammonium fluoroborate and ammonium thiocarbonate. Preferably, the salt used should be one possessing fairly high solubility as well as high ionization. In some cases it is desirable to add a small amount of wetting agent, such as aerosol, to the solution. The purpose of the wetting agent is to aid in the solution in permeating very small holes or pores in the coating layer.
Plate I3 may be perforated to allow better flow of solution I6 into pad I4, particularly when the plate is permanently positioned. The perforations The 4 not only aid the flow of solution but also help to eliminate polarization of the plate.
This invention possesses a major advantage in that, since it damages neither the metallic surface or the coating layer, the porosity test may be made on the actual surfaces which are to go into use rather than being made on a test sample. Moreover, the invention is not restricted to metallic surfaces small in area but may be used equally as well with large surfaces, such as for example the outside of power transformer tanks.
Although in accordance with the provisions of the patent statutes, this invention has been described as embodied in concrete form, it should be understood that the invention is not limited to the precise structure or exact connections shown in the drawing since these are merely illustrative and modifications and alterations willreadily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claim.
What I claim as new and desire to secure by Letters Patent of the United States is:
A device for determining porosity in a layer of non-conducting coating material applied to a metallic surface comprising a portable applicator member including a container having an open end; a metallic plate positioned within said container; a pad of absorbent material contacting said plate, filling said open end, and protruding beyond the extremity of said member; an electrically conductive water solution of a volatile salt filling said container and wetting said pad to establish electrical contact between said plate and said metallic surface through any pores in said coating material in response to movement of said pad across said coating material; and a circuit arranged to be completed by said contact including a source of voltage and a current indicating device, said contact to cause a deflection on said indicating device indicative of porosity in said layer of coating material in response to permeation of said solution into the pores in said coating material.
THOMAS J. CONNOR.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Wright May 2, 1950
US204013A 1951-01-02 1951-01-02 Porosity tester for coating materials Expired - Lifetime US2572597A (en)

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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2696589A (en) * 1952-04-18 1954-12-07 Continental Can Co Means for detecting scratches in lacquer coatings
US2717203A (en) * 1952-06-25 1955-09-06 Hartford Nat Bank & Trust Co Method of producing aperture in hollow article
US2812491A (en) * 1957-01-11 1957-11-05 American Cyanamid Co Electrical tester for non-metallic linings
US2824281A (en) * 1954-02-26 1958-02-18 Gen Electric Method and apparatus for measuring thickness
US3106677A (en) * 1960-07-21 1963-10-08 Tube Kote Company Apparatus for electrically detecting discontinuities in electrically nonconductive coatings on electrically conductive materials
US3147430A (en) * 1962-02-05 1964-09-01 Allis Chalmers Mfg Co Apparatus using liquid electrodes for measuring the electric breakdown strength of thin films
US3409825A (en) * 1966-01-04 1968-11-05 Esb Inc Multicell storage battery tester having sponge-like material in contact with each probe
US3719884A (en) * 1970-02-17 1973-03-06 Alusuisse Process and apparatus for determining the porosity of a dielectric layer coating a metallic surface
US3792458A (en) * 1971-01-08 1974-02-12 Coal Ind Method and apparatus for detecting pinholes in sheet material
US4359727A (en) * 1980-08-25 1982-11-16 Oliver Gene S Detector of defective coating
EP0529409A2 (en) * 1991-08-22 1993-03-03 Klaus Jörgens Method and device for testing the porosity of coated objects

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1953155A (en) * 1931-12-19 1934-04-03 Sorg Paper Company Device for testing paper
US2506478A (en) * 1945-10-12 1950-05-02 Kelvin Bottomley & Baird Ltd Instrument for testing paper

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1953155A (en) * 1931-12-19 1934-04-03 Sorg Paper Company Device for testing paper
US2506478A (en) * 1945-10-12 1950-05-02 Kelvin Bottomley & Baird Ltd Instrument for testing paper

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2696589A (en) * 1952-04-18 1954-12-07 Continental Can Co Means for detecting scratches in lacquer coatings
US2717203A (en) * 1952-06-25 1955-09-06 Hartford Nat Bank & Trust Co Method of producing aperture in hollow article
US2824281A (en) * 1954-02-26 1958-02-18 Gen Electric Method and apparatus for measuring thickness
US2812491A (en) * 1957-01-11 1957-11-05 American Cyanamid Co Electrical tester for non-metallic linings
US3106677A (en) * 1960-07-21 1963-10-08 Tube Kote Company Apparatus for electrically detecting discontinuities in electrically nonconductive coatings on electrically conductive materials
US3147430A (en) * 1962-02-05 1964-09-01 Allis Chalmers Mfg Co Apparatus using liquid electrodes for measuring the electric breakdown strength of thin films
US3409825A (en) * 1966-01-04 1968-11-05 Esb Inc Multicell storage battery tester having sponge-like material in contact with each probe
US3719884A (en) * 1970-02-17 1973-03-06 Alusuisse Process and apparatus for determining the porosity of a dielectric layer coating a metallic surface
US3792458A (en) * 1971-01-08 1974-02-12 Coal Ind Method and apparatus for detecting pinholes in sheet material
US4359727A (en) * 1980-08-25 1982-11-16 Oliver Gene S Detector of defective coating
EP0529409A2 (en) * 1991-08-22 1993-03-03 Klaus Jörgens Method and device for testing the porosity of coated objects
DE4127740A1 (en) * 1991-08-22 1993-03-04 Klaus Joergens METHOD AND DEVICE FOR CHECKING THE POROSITY OF COATED ITEMS
EP0529409A3 (en) * 1991-08-22 1994-09-28 Klaus Joergens Method and device for testing the porosity of coated objects

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