IEC 60426 pdf download – Electrical insulating materials – Determination of electrolytic corrosion caused by insulating materials – Test methods

IEC 60426 pdf download – Electrical insulating materials – Determination of electrolytic corrosion caused by insulating materials – Test methods
5.2Cut surfaces of rigid materials (blocks,plates, sheets or semi-finished materials)The test specimens shall be cut out or machined from the tested material to a thickness of4 mm, by means of a dry method without the use of cutting oils or lubricants and withoutoverheating or damaging them. lt is recommended to take several test specimens fromvarious layers of the product.
lt is permissible to use the test specimens of thickness smaller than 4 mm, but not smallerthan 2 mm.
The contact surface of the test specimen shall be smoothed using abrasive paper. Careshould be taken to keep parallelism of the opposite surfaces of the test specimen, in order toassure a good contact of the test specimen to the metal strips.The surface of contact shouldnot show any flaws, cracks, inclusions or bubbles.
The abrasive paper shall not contain any contaminations causing a bad corrosion index, forexample halogen components.
5.3Cast, moulding, injection and pressed materials
From insulating materials delivered in the form of liquid resin，moulding powder or granules,the test specimens shall be made in shapes and dimensions as shown in Figure 1. Thespecimens shall be made by casting or pressing in a special mould，following exactly thetechnological instruction recommended by the manufacturer of the tested material.
The test specimen and surface of contact shall be prepared as given in 5.2.
5.4Cut surfaces of flexible films, foils and thin sheets
Test specimens of these products shall be made up in layers to form small packs placedbetween suitable holding plates of insulating material not causing electrolytic corrosion itself,for example polymethylmethacrylate (PlexiglasR2).The preferred thickness of holding platesis 1 mm ± 0,2 mm.
The thickness of a pack should be approximately of 4 mm or 2 mm,depending on thethickness of the tested foils. The value of 4 mm is recommended in the case of the single foilthickness being less than 2 mm and more than 0,5 mm，whereas that one of 2 mm isrecommended if the single foil thickness is less than 0,5 mm.
These test blocks shall be compressed with screws made of the same material as holdingplates and then machined to the appropriate shape as shown in Figure 2.The material to betested should protrude 0,2 mm to 0,5 mm beyond the holding plates.
Apart from this, the particulars given in 5.2 apply.5.5Adhesive tapes
For adhesive tapes the method of Clause 7 of lEC 60454-2 is recommended.5.6 Flexible sleeving and tubing
Sleeving and tubing (both varnished fabric and extruded) are slit open， so as to make flatsheets, which can then be prepared as for films (see 5.4).
5.7Lacquers and insulating varnishes
The lacquer or insulating varnish to be tested shall be applied in the manner recommended bythe manufacturer to the surface of a test specimen of shape as shown in Figure 1 anddescribed in 5.2.The base material of the test specimen shall be a corrosion free plastic suchas polymethylmethacrylate.
In case of solvent incompatibility or a baking temperature being too high for the base material,another suitable base material such as cast, hot cured corrosion free epoxy resin or glassshall be used. lf the lacquer or insulating varnish is designed to contribute freedom fromcorrosion to another material, a test specimen of that material shall be used.
The tested lacquer or varnish shall be sprayed， dipped or otherwise coated to the desiredthickness and baked，if necessary, as specified or according to the directions of themanufacturer.
lf the thickness of coating is not determined by specification or direction of the manufacturer,it shall be of (30± 10) um.
5.8Cleanliness of contact surfaces
When preparing and handling the test specimens,any soiling of the test surfaces, for exampleby perspiration from the hands, shall be avoided.The specimens shall be touched only with apair of tweezers or with protecting gloves made of materials free from corrosion (e.g.polyethylene).After the test specimens have been machined or cut,their surfaces shall becleaned with a soft brush.Before cleaning， the brush shall be rinsed in ethanol (96 %) andthen dried.