Abrading – Machine – Sandblast
Reexamination Certificate
1999-09-10
2001-11-20
Eley, Timothy V. (Department: 3723)
Abrading
Machine
Sandblast
C451S096000, C451S098000
Reexamination Certificate
active
06319101
ABSTRACT:
The present invention relates to a shot-blasting machine for cleaning a linear metal element, such as a metal rod, a metal wire and the like.
It is known that metal rods (bars) are obtained from metal billets via rolling at high temperatures. Afterwards, in order to form metal wires having a preselected diameter, the rods are submitted to drawing. Drawing consists in a reduction of the cross-section of the rod in a drawing machine performed by means of successive passages through dies provided with holes having decreasing dimension, called die plates or draw plates. In order to make easier the passage through the die plates, the surface of the rod is preferably coated with suitable lubricants.
It is also known that, during the rolling step and the subsequent cooling process, a layer of oxides is formed on the surface of the rods that prevents a good lubrication of the rod in the subsequent drawing step. Therefore, the surface of the rod has first to be cleaned in order to remove completely the layer of oxides before performing the drawing step.
Several methods are known for cleaning the rods. One of them is the shot-blasting method.
Shot-blasting is an acid-free method and has the advantage that it is applicable to a wide range of materials and products of different diameters.
Shot-blasting is a process wherein the external surface of a metal rod is exposed to vigorous jets of shots, preferably metallic, so as to obtain a clean surface.
Generally, shot-blasting is performed by passing longitudinally one rod having a diameter of from about 1 mm to about 40 mm, usually of from about 5 mm to about 18 mm, through a machine called shot-blasting machine. In the shot-blasting machine, metal shots are projected against the surface of the rod by means of rotors provided with radial vanes that are supplied axially from the center and that, owing to the centrifugal force, project the shots in a radial direction at a very high speed. Usually, a shot-blasting machine is provided with three rotors arranged at 120°, or with four rotors arranged at 90° one to the other, so that the surface of said rod is exposed to the jet of shots. The rotors are mounted with their axis of rotation orthogonal to the longitudinal axis of the rod, preferably staggered with respect to the direction of advancement of the rod.
The shots are continuously recycled to the rotor or the rotors, after they have been reconditioned.
Generally, the shot-blasting machine is arranged in line with a drawing machine so that a continuous process is provided. The shot-blasting machine is enclosed in a cabin provided with a suction system for sucking the dust, and with inlet and outlet prechambers, provided with labyrinths and curtains, that allow the passage of the rod and meanwhile prevent the outflow of shots.
These shot-blasting machines have several drawbacks.
The jet of shots leaving the rotor has, in a direction transversal to the direction of advancement of the rod, a width equal to the width of the vanes. Such width usually is of from about 40 mm to about 100 mm, while the diameter of the rod usually is of from about 5 mm to about 18 mm. In order to reduce the dispersion of the flow of shots in a direction transversal to the direction of advancement of the rod and to bring it to a dimension closer to that of the rod diameter, each rotor is generally provided with a pair of convergent plates (also known as concentrating plates) that convey the jet of shots projected by the rotor towards the rod. However, since the plates must be kept at some distance one from the other in order to ensure the immediate outflow of the shots, the width of the jet of shots is in any case substantially greater than the diameter of the rod to be hit. Therefore, a major portion of the shots projected by the rotor does not hit the rod and is ineffective for the cleaning process. In addition, the jet of shots undergoes a loss of kinetic energy due to the interference with said concentrating plates.
Owing to the low overall efficiency of the process, in order to obtain the desired level of cleaning it is necessary to use high powers motors and that increases the overall production costs. This results in high maintenance costs, high wear of the parts of the machine and high shots consumption.
Machines of this type are also used for cleaning the surface of metal wires.
FR-A-2 386 390 discloses a continuous, multiple passage shot-blasting machine comprising a chamber wherein there is mounted a rotor or another means capable of projecting shots against a wire. The wire to be shot-blasted passes through said chamber winding itself around two drums. Thus, inside the chamber there is formed a plurality of considerably close, crossed strands resulting in a layer having a width at least equal to that of the jet of shots. In this way, an upper surface and a lower surface of wire portions are alternately submitted to the jet of shots. In this machine, said wire portions move alternately along two planes inclined one respect to the other, i.e. crisscrossed planes.
The Applicant has found that this inclined arrangement has the drawback of hindering a good cleaning of the wire (Tables II and III, tests 04, 05 and 06).
CH-A-351 929 discloses a device for mechanical descaling an unfinished product, particularly a metal strip. In said device separate jet means are provided for each of two working steps. During each working step upper and lower surfaces of said unfinished product are hit by said jet means with the same angle of impact. Particularly, in
FIG. 8
of said document, it is shown an embodiment of the device wherein two strip portions move alternately along two planes inclined one respect to the other. Thus, a part of the upper surface and a part of the lower surface of said strip portions are simultaneously hit by a jet of shots.
This arrangement shows the same drawback as mentioned in relation to FR-A-2 386 390.
It has now been found that these drawbacks can be overcome by means of a shot-blasting machine for cleaning a surface of a linear metal element comprising guiding means for said linear metal element and at least a rotor provided with vanes, said rotor being capable of projecting a jet of shots against said linear metal element, said guiding means being capable of directing said linear metal element in the field of action of said jet of shots at least a first and a second time, exposing in said field of action simultaneously at least a first and a second part, respectively, of said surface, characterized in that said at least a first and a second part of said surface are kept by said guiding means under said jet of shots substantially on a same plane, side by side and at a prefixed close distance (dv) at least for the whole path travelled by said linear metal element in said field of action of said jet of shots.
According to a preferred embodiment, said linear metal element has a prefixed diameter and said distance (dv) is equal or lower than about 3 times the diameter of said linear metal element. Preferably, said distance (dv) is of from about 0.1 to about 2 times the diameter of said linear metal element. More preferably, said distance (dv) is of from about 0.5 to about 1.5 times the diameter of said linear metal element.
According to another preferred embodiment, said guiding means are capable of directing a first portion of said linear metal element in a first direction of movement and a second portion of said linear metal element in a second direction of movement substantially opposite with respect to said jet of shots.
According to a further preferred embodiment, said first portion of said linear metal element turns said first part of said surface towards said jet of shots and said second portion of said linear metal element turns said second part of said surface towards said jet of shots.
Advantageously, said guiding means comprise a first snub pulley capable of directing said first portion of said linear metal element, coming from a direction of advancement, towards said first direction of movement and a second snub pulley capable of di
Berry Jr. Willie
Eley Timothy V.
Nixon & Vanderhye P.C.
Pan Chemicals S.p.A.
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