Method and apparatus of uniform induction heating of an elongated workpiece

Claim 3

The method as defined in claim 1 further including the step of controlling the time interval during which the said inductor is moved in said workpiece feed direction.

Claim 4

The method as defined in claim 1 wherein said step of moving said inductor in said feed direction comprises substantially eliminating relative movement between said inductor and workpiece for a predetermined time interval.

Claim 5

The method as defined in claim 1 further including the steps of moving said inductor in said feed direction along with said workpiece for a predetermined time interval while the workpiece is inductively coupled with the energized inductor, and thereafter returning said inductor to said first position.

Claim 6

The method as defined in claim 4 wherein said step of returning said inductor to said first position is performed at a different speed than that at which said inductor is moved in said feed direction.

Claim 9

The method as defined in claim 6 wherein the said steps of feeding the workpiece, energizing the inductor, and moving and returning said inductor are performed for each of a plurality of substantially identical workpieces.

Claim 10

The method as defined in claim 6 wherein the said feeding of said workpiece and moving of said inductor are performed at generally the same rate of travel.

Claim 11

The method as defined in claim 8 further including the step of sensing said minor workpiece portion prior to the feeding thereof into said inductor, and initiating said step of moving said inductor following a predetermined time delay after sensing.

Claim 12

The method as defined in claim 6 wherein the said returning of the inductor to said first position is performed at a different rate of travel than that at which said inductor is moved in said feed direction.

Claim 13

The method as defined in claim 6 wherein said elongated workpiece includes a first minor portion adjacent one end of the workpiece and a second minor portion adjacent the other end, and said steps of moving and returning said inductor are performed for each of said first and second minor portions.

Claim 14

The method as defined in claim 11 wherein said step of returning said inductor to said first position, after heating the workpiece minor portion last fed to said inductor during the said feeding of the workpiece through the inductor, is performed at a faster rate of travel than the step of returning the inductor after heating the other said minor portion.

Claim 15

Apparatus for inductively heating an elongated workpiece with a multi-turn induction heating coil having an entrance end, and exit end, and an elongated workpiece receiving passageway, said workpiece having at least one enlarged portion and an elongated body portion having a generally uniform cross-section wherein uniform heating of said workpiece by said coil requires heating of said enlarged portion for a longer effective heating time with a predetermined power level of said coil at a given constant feed rate than said body portion with said predetermined power level at said feed rate, said apparatus comprising: a power supply connected to said coil and having a power output at said predetermined power level for energizing said coil, means for continuously conveying said workpiece longitudinally through said passageway at said constant feed rate along a feed path extending in a direction from said entrance end of the coil to said exit end and while said coil is continuously energized by said power supply; sensing means for creating a signal when said workpiece enlarged portion reaches a known position on said feed path adjacent said entrance end; and, means responsive to said signal and operative after a predetermined first time interval following creation of said signal for shifting said coil along said feed path and along with said workpiece at least when said workpiece enlarged portion is in said coil, said coil being shifted from a first normal position along said feed path at a given advance travel rate for a predetermined second time interval.

Claim 16

Apparatus for inductively heating an elongated workpiece with a multi-turn induction heating coil having an entrance end, and exit end, and an elongated workpiece receiving passageway, said workpiece having at least one enlarged portion and an elongated body portion having a generally uniform cross-section wherein uniform heating of said workpiece by said coil requires heating of said enlarged portion for a longer effective heating time with a predetermined power level of said coil at a given constant feed rate than said body portion with said predetermined power level at said feed rate, said apparatus comprising: a power supply connected to said coil and having a power output at said predetermined power level for energizing said coil, means for continuously conveying said workpiece longitudinally through said passageway at said constant feed rate along a feed path extending in a direction from said entrance end of the coil to said exit end and while said coil is continuously energized by said power supply; sensing means for creating a signal when said workpiece enlarged portion reaches a known position on said feed path adjacent said entrance end; and, means responsive to said signal and operative after a predetermined first time interval following creation of said signal for shifting said coil along said feed path and along with said workpiece at least when said workpiece enlarged portion is in said coil, said coil being shifted from a first normal position along said feed path at a given advance travel rate for a predetermined second time interval.

Claim 17

The apparatus as defined in claim 13 wherein said shifting means moves said coil back to said first normal position at a return rate of travel following said second time interval, said workpiece feed rate and coil advance travel rate being generally the same.

Claim 18

The apparatus as defined in claim 14 wherein said shifting means is operative to cause said coil advance travel rate and said coil return travel rate to be different from each other.

Claim 19

The apparatus as defined in claim 14 wherein said elongated workpiece has two enlarged end portions separated by said body portion, with one end portion comprising a leading end and the other end portion comprising a trailing end, said sensing means creating a signal when each of said leading and trailing ends reaches a known position along said feed path so that said shifting means will shift said coil at said advance travel rate after said first time interval in response to the signal created by said sensing means on actuation by each of said leading and trailing workpiece ends, said coil return rate being greater following coil shifting in response to said trailing end than following coil shifting in response to said leading end.