IL27625A

IL27625A - Abrasion resistant surfaces

Info

Publication number: IL27625A
Application number: IL2762567A
Authority: IL
Original assignee: K & F Treatments Ltd
Priority date: 1966-03-25
Filing date: 1967-03-16
Publication date: 1970-09-17
Also published as: CH477565A; BE695926A; AT279192B; DE1646145A1; GB1184561A; ES338458A1; NL6704157A

Description

Patents Form No. 3 PATENTS AND DESIGNS ORDINANCE.

SPECIFICATION. "iHmQVEMRSS IN OR BEIATI 20 ABHASIQH HSSIS¾OT? SUHPACES" do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described aud ascertained in and by the following statement : - . 5 This invention relates to methods of coating surfaoes and articles to make them abrasion resistant.

It has become well known to apply to the surfaces, and particularly the internal surfaces of domestic utettsila^ a layer of polymeric materials such as fluorocarbon or silioone polymer such as polytetrafluoroethylene (PTPE)* known as "FLUON" (Registered Trade Mark), or tetrafluoroethylene-hexafluoropropylene (TEE/HEP) copolymer. These materials are well known for their exceptional lubricity and anti-adhesive and parting properties. They provide a surfaoe coating, having what will herein be called "non-stick" properties.

Previous methods have sought to obtain good bonding of the above substances to foundation metals by suoh methods as mechanical abrasion or etohing or both, but in each case although the coating will adhere satisfactorily for some purposes it is nevertheless of a relatively soft nature and can easily be damaged by sharp or hard tools, such as kitchen utensils and by abrasive materials. Also the use of certain etching fluids used in existing coating processes could be unacceptable in some instances, for example where food containers are involved.

The present invention aims at providing an improved method of producing a non-stick coating on various types of materials which can have molten metal applied thereto, particularly metals, for use in such things as cooking utensils, including pans and food containers, and food machinery, chutes, hoppers, and all surfaces where minimum friction and non-stick surfaces are required. It is intended to produce a surface that can withstand abrasion byrelatively hard scraping tools and kitchen utensils, abrasive cleaners and the like, but retain the desirable parting and non-stick properties of the polymer.

The invention includes a method of coating metal or other foundation material surfaces, but generally any surface that can be prepared by spraying a coating of molten ductile hard metal thereon to produce a continuous and impervious micro-crenellated coating to which a non-stick coating can be mechanically keyed.

The invention includes a method of producing an abrasion resistant surface with non-stick characteristics on a base material, consisting in submitting the material to be treated to a surface pitting or roughening process, spraying said base material surface with molten ductile hard metal to provide it with a hard abrasion resistant surface including a multiplicity of substantially microscopic prominences and interstices, abrading the latter surface, and coating said surface and filling said interstices with a non-stick coating. In describing the sprayed-on metal as being ductile and hard we imply that it is resistant to wear by abrasion while being at the same time sufficiently ductile to withstand without cracking the distortion which may occur in spinning or pressing or like conventional metal-forming operations.

The invention includes a method of coating surfaces which comprises producing a substantially finely pitted surface, flame spraying said surface with molten ductile stainless steel having a required minimum hardness characteristic when cold in the order of 115 Brinell ( or equivalent hardness test reading) , c ontrolling the spraying to produce a coating which leaves a multiplicity of substantially microscopic prominences, then applying a non-stick coating to the hard metal abrasi on resistant surface and sintering thi s coating.

The method includes the step of grit blasting the metal coated surface to prepare it t o receive the non-stick coating* The method includes treating the work surface initially to remove any p ossibility of grease and f oreign particles being present and then blasting it with grit .

The method may include the u se of fillers which have the effect of providing c oatings of varied opacity and shade or pigmentation and ductility.

The method includes sintering the non-stick coating in known manner and this coating method may be applied to the surface of a f ormed or partly f ormed article or t o material before it is f ormed into a desired shape .

Basically the invention includes preparing the surface of metallic or other material, or an article , by first of all ensuring there is no grease or f oreign particles present and then roughening this surface such as by submitting it to a grit, say sand, blasting or other abrasion operation . The prepared surface is then sprayed with molten metal, such as stainless steel or molybdenum, having a required hardness and ductility characteristics. A further grit blasting operati on can then take place t o remove oxides and a n on-stick coating is applied. This last coating is sintered in known manner.

The invention provides for the flame spraying of at least one harrier layer of a metal or alloy to obtain the required bond and c ondition of the surface t o accept the non-stick coating. It will be understood the metal or alloy is required to be chosen f or varying duties, f or instance , it requires t o be abrasion resi stant and t o prevent corrosi on. It is accepted that ΡΤΙΈ is not continu ous when used as a thin coating so that its p orosity can lead to eventual damage of the substrate t o which it is adhering. However, the polymer itself is resistant to most substances with few exceptions but not to abrasion and the barrier layer provides abrasi on resistance and a greatly improved laminated c oating with the non-stick layer.

It is important that the metal chosen for the c onditioning of the main surface t o take the coating is itself re sistant t o the substances that will be used in connecti on with it . Thus in cases where acids or alkalis, to which stainless steel is resistant , will be in contact with the finished coating, and would otherwise be likely to attack the substrate, a stainless steel metal is sprayed on to an aluminium substrate surface . Similarly aluminium or aluminium alloy could be used on an iron or steel surface if it is to be subjected to ru st producing liquids with a subsequent layer of stainless steel or molybdenum t o give abrasion resistance . The degree of resistance required to abrasi on , mechanical damage or manipulation after coating will determine the choice of metal or alloy sprayed, and ψ this should have a hardness characteristic when cold of at least 115 Brinell, or its equivalent reading.

The inventi on will now be more particularly described with reference to the acc ompanying drawing, in whichs- Fig. 1 is an enlarged fragmentary sectional view of a foundation material With a barrier metal coating applied to a prepared surface ? Fig. 2 is a sectional view, similar to Pig. 1, with a non-stick c oating applied to the metal coating; and Fig. 3 is an enlarged fragmentary secti onal view of a modified laminated coating, The invention basically includes a method of c oating surfaces by spraying metal on t o the surface 1 of a material 2 after suitable preparation, which produces a continuous and impervi ous micro-crenellated coating 3 in which the prominences 4 and interstices 5 are substantially microscopic, t o support a coating 6 of PTFE or TFE/HFP polymer which may be applied as an aqueous su spensi on or in p owder form, and sintered into the c oating 3 by heating to, say 750°F, for a period of , say, two to three minutes.

By way of example s- The substrate surface 1 t o be coated is first thoroughly cleaned and degreased, such as by the use of trichlorethyle e to carry away any greases on the surface, and then by heating t o, say, 400°F f or a peri od of time, say for two minutes, t o remove any f oreign particles that may be embedded in the material from a sheet rolling or pressing operation. Care should then be taken in handling, to prevent contamination from hands; for example the use of clean protective gloves is desirable. The prepared surface when cold or cool is then mechanically scoured and abraded, either by grit blasting, using, say, a grit size of 24 mesh at 40 lbs/sq. inch through a 5/16" nozzle, or by some other mechanical action so as to produce a pitted or roughened surface capable of accepting sprayed molten metal. The metal may be stainless steel or molybdenum. Stainless steel may be chosen for holloware for its abrasion resistance and which can be 18 per cent chrome, and 8 per cent nickel, which is sprayed in conventionally known manner using oxygen at 55 lbs per square inch, propane at 25 lbs per square inch, or acetylene at 15 lbs per square inch, and compressed air at 100 lbs per square inch. The thickness of the coating may be in the order of 0.001" - 0.006". The next operation comprises mechanically abrading the coating 3 to remove harmful oxides, say, by grit blasting with aluminium oxide using a 180 mesh grit, or by some other mechanical abrasive means. The surface so prepared now has the PTFE or TFE/HPP polymer applied as an aqueous suspension by spraying or brushing or other method to fill the surface interstices of the sprayed metal coating and to lie above the highest metal peaks. "FLUON" GP1, a chromate free ΡΤΙΈ dispersion, can be used for this purpose. The surface is then dried at 180°P until all moisture is removed.

Alternatively, a prepared polymer may be applied in sheet form with heat and pressure assistance.

Following the drying, the next operation is sintering the polymer fluoroearbon by heating the surface to 750°P in two to three minutes, the time taken depending upon the thickness of the coated material. Some non-stick materials do not require sintering at such high temperatures as PTFE itself, and for coating foundation materials such as thermosetting plastics material, wood or hardboard a non-stick material such as "FLUON5' MM1 (which is cured at 200°F) may be used* The invention also includes an improvement in preparing the PTHE or like polymer, by the addition of a ductile and sraearable filler medium. For example, a suitable medium comprises aluminium or stainless steel powders in micro-particle form in the order of, say, li per cent by volume, or with additional pigment for colouring only, to a total maximum amount of, say, 3 per cent by volume.

Alternative mediums are graphite, molybdenum di sulphide, glass or asbestos fibres or the like in fine flake or powder form. Such filler mediums act as pigmenting or opacifying agents for the surface coating and also give such coating an improved ductility characteristic, and are herein generally termed pigment/filler mediums. The prepared polymer, when applied to the metal coating, fills the interstices and covers the prominences of the sprayed metal surface and enhances the characteristics of the coating when manipulation such as spinning and pressing are carried out on a flat disc or sheet or partly formed shape after coating. It also improves the appearance of the final c oating f or articles such as pans and f ood containers.

Pig. 3 indicates a f oundati on material 2 which has been cleaned, abraded by, say, grit blasting, and a metal coating 7 ( of , say, aluminium or other n on-corrosive metal ) sprayed thereonto. This first coating is then abraded and a stainless steel or molybdenum c oating 3 sprayed there onto. This sec ond c oating is abraded as af oresaid and a non-stick coating is applied.

As stated the invention includes a method of coating not only finished articles, but also discs, sheets, partly finished articles or other parts or surfaces of metal which are afterwards formed int o a desired shape such as a frying pan or other pan or oven sheet or panel or other element. Experiments and producti on have shown that the abrasi on resistant barrier layer of duotile metal and superp osed non-stick coating (particularly when the latter includes micro-particle metal or other filler medium) in c ombination allow sheet metal to be spun or pressed to a required shape with all the required metal elongation, say, in the order of 20 per cent , v/ithout damage t o the c oated surface, although for this purpose it is considered the barrier layer should not be more than 0.003 inch thick.

If material or an article coated in the manner described herein , is abraded on the finished non-stick surface , tiny areas of the non-stick agent will be removed, but microscopic abrasi on resistant peaks of the barrier layer metal will be revealed surrounded by non-stick areas. Thu s the surface will remain virtually the same as before abrasion and the latter work hardens the said peaks in view of the type of ductile metal employed. A surface prepared according to the invention when submitted to a hardness test should produce a minimum reading of 115 Brinell, or equivalent hardness test reading. Moreover, the laminated coating is chrornate free and ductile and can be reinforced with a pigment/filler medium as stated.

Although it is usual to coat articles individually, the invention may be applied in a continuous or "flow-line" operation on strip or long sheet material. The material, if metal, can be fed through a degreasing plant, dried and heated for the removal of foreign particles, say, by a high frequency method, abraded, coated with hard ductile metal, abraded and then provided with the non-stick coating.

The term "article" is used in a general sense in the following claims to include solid sheet base or foundation material (which may be of disc or other formation), so-called holloware or other shaped or partly shaped pieces or elements.

Claims

BkVm i par icularly the nature of our said invention a d in what manner the same, is to ©e performed* we declare that what we elaim is t 1· A laminated article comprising a base (foundation) layer, a thin impervious layer of ductile hard metal (as herein defined) permanently bonded to the base layer to form 5. a continuous and impervious micro-crenellated intermediate surface and a coating of non-stick material (as herein defined) pplied over and sintered to said intermediate surface to form an abrasion resistant non-stick surface.
2. An article as claimed in claim 1 Wherein the

10. base layer is a metal Or alloy·
3. An article as claimed in claim 1, wherein the base layer is a thermosetting plastics raaterialf wood, hardboard or the like non-metallic material.
4. An article as claimed in claim 2, consisting of 15, coated metallic sheet.
5. Holloware produced by forming a shaped piece of coated metallic sheet according to claim 4·
6. A method of coating surfaces of articles which includes the steps of preparing the surface in conventional

20. manner to receive a sprayed coating of molten metal, spraying over said surface a coating of an abrasion resistant ductile hard metal (as herein defined) to provide a continuous and impervious micro-crenellated intermediate surface, abrading said intermediate surface to remove any surface film such as 25, oxide and finally applying a coating of a non-stick agent to the abraded surface so as to provide a firmly bonded complete covering to the sprayed hard metal coating thus producing an abrasion resistant and non-stick outer surface.
7. A method of producing an abrasion resistant surface with non-stick characteristics on a metallic base material, which includes the steps of cleaning the surface of the base material, heating the cleaned surface , abrading the cleaned 5. surface , spraying said abraded surface with molten ductile^ hard metal to superimpose a layer of abrasi on resistant material having a continuous and impervi ou s micro-crenellated outer surface, abrading said outer surface , and coating said outer surface with a non-stidk coating agent *

10.
8. A method according t o claim 7 , in which the molten ductile hard metal is applied by flame spraying t o produce a c oating of a thickness in the order of 0.001" to 0.006" , and in which the n on-stick coating agent is sintered t o the ductile hard metal abrasion resistant surface . 15 # 9· A method according to claim 7 , including the step of grit bla sting the surface of the sprayed hard metal layer to prepare it t o receive the non-stick c oating.

10. A method according to claim 7 , wherein at least one filler medium is included with the non-stick coating agent

20. produce a coating of a desired c olour, shade or opacity.

11. A method according t o claim 10, wherein a ductile and smearable filler medium is added to the non-stick c oating agent bef ore spraying so as t o facilitate any subsequent shaping operation of the c oated material as well as t o

25. achieve a colour, shade or opacity.

12. Method acc ording to claims 10 and 11, including adding metallic powders, such as aluminium or stainle ss steel, in micro-particle f orm to the non-stick coating agent.

13. Holloware article formed by a forming or a spinning operation on a metallic sheet or disc coated on at least one face, by the method of any of the preceding claims.

14. Method according to claim Ί, wherein the laminated

5. abrasion resistant non-stick coating is applied to the surface of a formed article.

15. Sheet-like material coated by the process claimed in any of the preceding claims 6 to 13.

16. Formed articles which have been coated by the

10. process claimed in any of the preceding claims.

17. A method of coating articles substantially as herein described. B ed this Sixteenth day of tlapch 1 Agent op Applicants*