Method and device for obtaining shaped test-pieces of steel as required in tensile under corrosion fatigue tests

Abstract

A method is described to prepare shaped steal test-pieces ( 1 ) for tensile under corrosion fatigue tests, which provides for contacting a test-piece ( 1 ) subject to rotation about its longitudinal axis and, each time, a disk ( 10 ) of sand paper, also rotating, the contact being ensured by the own weight of the test-pieces itself. A device for carrying out this method is also described, which comprises a swinging arm ( 2 ) at an end of which the test-piece ( 1 ) is rotatably mounted, being driven by a motor ( 5 ), all these being mounted on a support central table ( 6 ), substantially stationary, around which a support ( 7 ) can rotate, having an annular shape on which a number of abrasive disks ( 10 ) are mounted, each on a rotatable shaft ( 9 ), to be successively positioned at the processing station in front of said supporting arm ( 2 ).

1 . A method to obtain shaped steel specimens, as required in tests of tensile under corrosion tests to subject the same to the final surface finishing steps to bring them to the lowest values of roughness required, characterized by comprising the step of keeping in rotation about its longitudinal axis the steel specimen ( 1 ) already machined at its central portion ( 1   a ), to reach slightly larger sizes than the prescribed final size, by bringing the same to contact with a rotating sandpaper disk ( 10 ) in a plane tangent to the outer surface of the central length ( 1   a ) of said specimen ( 1 ), the contact being ensured by the specimen own weight.  
     
     
         2 . A method according to  claim 1 , characterized in that the abrasive disk ( 10 ) used is centrally registered with respect to the cylindrical median length ( 1   a ), of smaller diameter, of the specimen ( 1 ), with its profile contacting the end zones at which said central length ( 1   a ) merges with the cylindrical end zones ( 1   b ) of larger diameter of the specimen itself.  
     
     
         3 . A method according to  claim 1  or  2 , comprising successively further steps of surface finishing with abrasive disks ( 10 ) having finer and finer grain size.  
     
     
         4 . A method according to anyone of the preceding claims, wherein the first step of surface finishing is carried out with a sandpaper disk having grain size from 80 to 250 GRIT, while for the subsequent working steps sandpaper disks are used having grain size from 250 to 1000 GRIT until reaching roughness values of less than 0.81 μm, preferably down to 0.1 μm.  
     
     
         5 . A device for the surface finishing of steel specimens to be used in tests of tensile strength combined with corrosion, characterized by comprising a swinging arm support ( 2 ) of a specimen ( 1 ) rotatably held at the ends to rotate about is own longitudinal axis, there been provided a motor ( 5 ) for driving such a rotation, being mounted on the same support of a hinge fulcrum ( 3 ) of said swinging arm ( 2 ), the specimen ( 1 ) carrier end of which extends itself, with lowered arm, until a contact zone within an annular support ( 7 ) with the center on said fulcrum ( 3 ), substantially parallel to the longitudinal axis of rotation of specimen ( 1 ), said contact zone or working station being located between the inner periphery of said annular support ( 7 ) and an intermediate circumference (C) comprised between said inner periphery and the outer one, said circumference (C) having thereon, equally spaced apart from each other, a number of vertical seats ( 14 ), each of which is capable to house a shaft ( 9 ) for carrying an abrasive disk ( 10 ), whereby there is interference between the profile of disk ( 10 ) at the working station and said specimen ( 1 ) on its support ( 2 ) when the latter is lowered due to the own gravity force of said specimen.  
     
     
         6 . A device according to  claim 5 , characterized by the fact of comprising driving means ( 12 ) for rotating, about a vertical central axis passing through the center of said circumference (C) of said annular support ( 7 ) with respect to said fulcrum ( 3 ) fixed on a support ( 4 ) mounted on a central support table ( 6 ) with respect to said outer annular support ( 7 ), also said motor ( 5 ) being mounted on that table ( 6 ).  
     
     
         7 . A device according to  claim 5  or  6 , characterized by further comprising rotation driving means ( 11 ) mounted at a fixed position in correspondence with the said working station coincident with one of said seats ( 14 ) when brought, through the rotation of said support ( 7 ), in front of a specimen ( 1 ) on its swinging arm support ( 2 ).  
     
     
         8 . A device according to  claim 7 , characterized in that means ( 22 ,  25 ) are provided to be driven by an actuating means ( 21 ) to transmit the rotation from said driving means ( 11 ) to a shaft ( 9 ) supporting an abrasive disk ( 10 ) and fitted in said seat ( 14 ) at the working station.  
     
     
         9 . A device according to  claim 8 , characterized in that said actuating means ( 21 ) is made as a cylinder, the rod of which drives the end of a lever ( 22 ) the opposite end of which is capable of thrusting an idle pin ( 25 ) driven into rotation by said actuating means ( 11 ) to mesh the same with the said shaft ( 9 ) and drive the latter into rotation about its axis.  
     
     
         10 . A device according to  claim 9 , characterized by further comprising on said lever ( 22 ) stop means ( 23 ) for blocking said annular support ( 7 ) with said shaft ( 9 ) at the exact position of working station at the same time of said shaft ( 9 ) being driven by said actuating means ( 21 ).  
     
     
         11 . A device according to any of claims  6 - 10  characterized by comprising means ( 15 ,  15 ′) for adjusting the position, in its plane, of said support table ( 6 ) by means of small angle rotations in opposite directions about said central vertical axis.  
     
     
         12 . A device according to any of claims  6 - 11 , characterized in that said support table ( 6 ) is in turn mounted on base plates ( 17 ,  18 ) overlapping with an intermediate gap ( 26 ), one of which ( 17 ) can swing around a horizontal median axis coincident with the diameter of said circumference (C) passing through said working station, there being provided jack means ( 13 ) to cause such a swinging movement and a hinge means ( 19 ) between said two plates ( 17 ,  18 ), there being further provided springs ( 16 ,  16 ′) housed within said plate ( 17 ) in contact with the said support table ( 6 ) to automatically register the positioning of the latter on the base plates.  
     
     
         13 . A device according to  claim 5 , characterized in that an adjustable counterweight ( 20 ) is provided at the end of the swinging arm support ( 2 ) which is opposite to the end on which the specimen ( 1 ) is rotatably mounted.