Abstract An article is hardened or tempered in a localized zone. Where the article is a thread-forming device the zone is that part of its thread that does the thread-forming in the workpiece. The hardness of the remainder of the body of the article is left unchanged. The localized hardening is carried out by a method that includes high frequency induction heating only of the zone followed by quenching of the zone whereby the hardened zone is a skin of predetermined depth. A machine for making articles in accordance with the method comprises means for delivering the articles in succession to an induction heating element, a mechanism for advancing the articles through the heating element for progressive heating of the surface of the article in the localized zone to a predetermined depth, a quenching manifold for applying a spray of quenching liquid to the heated article, and means for removing the heated articles from the heating element and conveying them to the quenching manifold.
A method according to claim 1 wherein the heating process is carried out in an atmosphere that leaves the composition of the hardened part substantially unchanged.
Claim 2
Dependent Claim
122 words
In a method of making a thread-forming screw having a peripheral thread, an axial portion which is less than the total axial length of the thread and which portion constitutes a swaging sectiOn for entering an opening in a workpiece and swaging a thread therein, the steps of locally inductively heating said swaging section by passing it between opposed bars of an induction heater such the bars are entirely radially outwardly of the swaging section and with the axis of the screw being between said bars, and then quenching said section to harden the thread at said section while leaving substantially unchanged the hardness of a core of the screw surrounded by said section and the screw axially remote from said section.
Claim 3
Dependent Claim
33 words
A method according to claim 3 in which the axis of said screw is disposed generally perpendicular to a general plane defined by said opposed bars as the screw passes between said bars.
Claim 4
Dependent Claim
29 words
A method according to claim 3, in which a plurality of screws are disposed between said bars at one time and the screws are advanced along said bars progressively.
Claim 5
Dependent Claim
122 words
In a method of making articles each having a section which is less than the total axial length of the article, the steps of feeding articles in succession to an inductor for heating said articles only in the region of said section and in an atmosphere that does not substantially change the composition of said articles, passing said articles progressively and substantially non-rotatably through said inductor and with a plurality of said articles being in said inductor at one time for inductive coupling and peripheral heating, thereby to cause progressive heating of the section of each article from the periphery thereof to a predetermined depth and at least to a tempering temperature, and then discharging said heated articles successively from said inductor.
Claim 6
Dependent Claim
133 words
In the making of discrete articles each having a peripherally threaded shank with a localized zone of the thread on the shank being of a type for producing a thread in a workpiece, a method that comprises providing an induction heating device that produces a region with a high frequency alternating current field, passing said discrete articles through said field for inductive heating and by said inductive heating locally heating the articles in their respective zones circumferentially therearound, and then quenching each article at its zone to leave a hardened part of a depth that includes at least a portion of the thread thereat while leaving a core of the shank that is surrounded by said hardened part and a portion of the shank remote from said zone substantially unchanged as to hardness.