US 3141270 A
Description (OCR text may contain errors)
July 21, 1964 M. FERRAND 3,141,270
ABRASIVE TOOL Filed April 18, 1962 L Fzg4.
r.-.J.--J '--I 5 4g 9 INVENTOR Fug 6 MHHCEL EERRHND United States Patent 3,141,270 ABRASIVE TOOL Marcel Fer-rand, 13 Les Routes, Toulon, Var, France Filed Apr. 18, 1962, Ser. No. 183,593 1 Claim. (Cl. 51-205) This is a continuation in part of my abandoned United States patent application No. 808,344 filed April 23, 1959.
The surfaces of electrical contacts, used in switches and the like, require to be kept clean and also of even shaping and free from pitting etc. To carry out this cleaning, it is necessary to remove a preferably very small thickness, of the order of 1 micron, of the contact material which may be a hard metal such as tungsten.
There are already in use various forms of scrapers and spatulas which are abrasive-surfaced so as to retain their cutting action and not to wear out on the hard metal contacts. Hitherto, to obtain the necessary strengthened rigidity whilst still being thin enough to introduce between contacts, such tools have necessarily been made entirely of metal and, being electrically conductive, they could not be used under current-flow conditions without possibly causing disturbance to the electrical circuits involved, and perhaps also at a risk to the user.
If such a contact-cleaning tool is made of a non-conductive material, so as to overcome this disadvantage, it is then found that the non-conductive materials do not have suflicient mechanical strength either to provide an adequately rigid tool or to form an efficient bond for the grains of abrasive.
It is accordingly the object of the present invention to provide a new and improved construction of tool, for the cleaning of electrical contacts, which combines the advantage of general rigidity and secure bonding for the diamond grains with the advantage of being generally insulating so as to permit application to live contacts.
An embodiment of the invention is hereinafter particularly described with reference to the figures of the accompanying drawing, wherein:
FIG. 1 is a plan view of a body portion of the tool;
FIG. 2 is a side elevation of the body portion of the tool;
FIG. 3 is a plan view of a diamond-surfaced metal plate forming one of a pair for mounting on the body as a sandwich assembly;
FIG. 4 is a side elevation of the complete tool, with the end having the diamond-bearing plates shown in longitudinal section;
FIG. 5 is a plan view of the complete tool;
FIG. 6 is a section of a detail on a larger scale.
The body of the tool is shown in FIG. 1, and comprises a sleeve or handle portion 1 one end of which is extended by a flattened, and widened stem 2 carrying at its end 3 a somewhat thinner wafer-like flexible blade portion 4. The portions 1, 2 and 4 are all integrally formed in a suitable insulating material such as a synthetic resinous plastic material. On each surface of the blade 4 are provided two sets of grooves 4a cut, e.g. by engraving, at an angle and intended to provide a keying formation for adhesive.
FIG. 3 shows an abrasive element consisting of a hard metal plate 5, one surface of which has grains of diamond embedded therein. This formation of a diamond-bearing surface may conveniently be carried out by electrodeposition of additional hard metal onto a base on which diamond dust has been scattered, thereby to 3,141,270 Patented July 21, 1964 entrap the grains of diamond on the plate and provide a secure mechanical fixation thereof on the plate. The plate 5 is of exactly the same shape as the blade portion 4 of the body.
Where the blade portion 4 of the body joins to the stem 2, there are formed two transverse shoulders 6, 7. When two of the plates 5 are positioned one on each of the two surfaces of the blade 4, the straight end surface 8 of each plate abuts against the respective shoulder 6 or 7. The two plates 5 and the blade 4 together form a rigid sandwich assembly. It will be appreciated that, when the plate 5 is anchored mechanically to the blade 4, the abutting of its end against the shoulder 6 or 7 of the stem 2 will provide a very strong reinforcement tending to prevent bending of the blade 4 about the line where it joins to the stem 2.
The plates 5 are secured onto the two surfaces of the blade 4 by a layer 9 of any suitable adhesive capable of gripping onto the metal of the plates and onto the plastic or other insulating material of the blade 4. The grooves 4a of the blade 4 provide a better keying of the adhesive on the metal. If required, the underside of the plates 5, that is to say the surface thereof which is not provided with diamond grains, could likewise be provided with grooves or any other convenient keying formation for the same purpose.
The enclosing of the blade 4, of insulating material, between two plates 5 of hard metal serves to make the sandwich assembly extremely rigid, particularly in view of the abutting of the linear ends of the two plates against the respective shoulders 6 and 7 of the stem 2. The reinforcement is so effective that the blade 4 may be made of a thickness of only a few thousandths of an inch, and of relatively soft plastic. Thus whilst retaining the advantages of being relatively extremely thin, the tool is nevertheless highly resistant to bending and permits quite high pressure to be applied on the diamond bearing sur faces by the user grasping the body, thereby to ensure rapid and efiicient cleaning and levelling of the contact surfaces of the switch being cleaned.
The presence of the two plates 5 also ensures that the blade 4, which would otherwise be relatively weak, will not twist under torsional stresses exerted during handling of the tool. The tensile strength of plastic insulating materials tends normally to be rather low, and the addition of the metal plates 5 ensures accordingly that any pulling forces exerted on a plate longitudinally thereof are distributed over the whole of the surface area of the blade and stretching of the blade 4 is avoided. Any longitudinal forces exerted on the plates 5 in the direction to urge the plates towards the shoulders 5, 6 are directly absorbed by the relatively sturdy shoulders themselves, thereby relieving the adhesive joint of those stresses. The tool gives substantially the same rigidity as would be obtained with an all-metal construction.
The two metal plates 5 and 6 remain always fully insulated one from the other, although the assembly of blade and plates is of very small thickness permitting introduction between very narrowly spaced contacts to be cleaned.
The mounting of the plates 5 onto the blade 4 permits the plates to be manufactured and handled separately from the remainder of the tool. Accordingly such other treatments as may be necessary, e.g. final shaping, heattreatment for hardening purposes etc. may be carried out in a convenient manner on the plates, whereafter a 41- they are secured onto the blade 4 in an already comside and each fixed on the side opposite said exposed pleted form. side by a layer of adhesive to each fiat side of said Obviously, other materials than diamond grains could blade and each having an edge abutted against each be included on the plates 6, e.g. carborunduin grains. shoulder of said stem and I claim: 5 (f) abrasive material on the exposed side of each of As an article of manufacture, a tool for cleaning and said metal plates. shaping electrical contacts comprising (a) a handle of flexible electrical insulating material, References Cited in the file Of this Patent (b) a stern connecting said handle to UNITED STATES PATENTS (c) a thin flat blade, said stern having a thickness 10 847,012 Korper Mar. 12 1907 greater thanthe thickness of said blade, said blade 2,137,329 Boyer 22 1938 havlng fiat 81d, 2,379,544 Scutt July 3, 1945 (d) two stepped shoulders formed in saidstem at the 2,503,299 Rodriquez APR 11 1950 line at which said'blade and'said' stem join together at each fiat sideof said blade, 15 FOREIGN PATENTS (e) two rigid metal plates each having one exposed 1,149,036 France July 1937