Electric heating – Inductive heating – With power supply system
Reexamination Certificate
2004-01-02
2004-11-09
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
With power supply system
C219S668000, C377S015000, C377S016000
Reexamination Certificate
active
06815650
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a counting sensor for use in conjunction with an induction heat treating process. More particularly, the present invention relates to a system for counting the cycles of an individual inductor coil and maintaining and transmitting this data to a remote unit location or self contained unit within the counting sensor.
BACKGROUND OF THE INVENTION
The induction heat treating process is used in various applications for hardening, and annealing of metals. The process includes applying energy directly to metals and other conductive materials via an alternating electric current passing through an induction heating coil positioned in close proximity to a workpiece. A common use for induction heating is case hardening of carbon steel, or alloy parts for use in the formation of automobiles, farm equipment, airplanes and other production apparatuses. Induction heating rapidly heats the workpiece in a short period of time. The workpiece is then quenched and a hardened surface, or through hardened part is formed. The depth of the hardened surface is regulated by the frequency of current, temperature of the part surface, and quenching of the part.
Much of the prior art is directed to systems for measuring and maintaining the temper and surface hardness to insure proper performance and quality control of the heated parts. The concept of monitoring an induction heating cycle is disclosed in U.S. Pat. Nos. 4,897,518 and 4,816,633 to Mucha et al. and for monitoring the current in an induction heating coil is disclosed in U.S. Pat. No. 5,434,389 to Griebel. These prior patents are incorporated by reference herein for general background information as they relate to the conventional induction heating treating processes. Similarly, U.S. Pat. Nos. 3,746,825 and 5,250,776 to Pfaffmann disclose a method for measuring input energy and temperature and heating rate of a workpiece, respectively. U.S. Pat. No. 6,455,825 to Bentley et al. discloses the use of miniature magnetic sensors strategically placed about the workpiece to monitor changes in the magnetic properties of the workpiece as it heats up during induction heating and cools down during quenching. These patents are also incorporated by reference for the further purpose of illustrating the state of the art of induction monitoring systems.
The conventional induction heat treating process is detrimental to the perishable heat treating tool. The tool, or inductor coil, is designed and shaped specifically to the workpiece undergoing the heat treatment. An induction heating machine may include a specifically designed coil, or multiple identical coils mounted to the machine, or various coil designs mounted to a single machine in series, all used for hardening various workpieces during production. Each coil may be formed of multiple copper parts and flux concentrators that are brazed or attached to form an inductor assembly. The joints have a limited life cycle and are prone to failure or leakage and must be repaired. Further, arcing often occurs where there are small air gaps between the tool and the workpiece causing stress cracks and damage to the coil. These examples only exacerbate the already short tooling life of a coil and lead to costly repairs. Each time tooling is changed, the induction heating machine and the heat treated parts must be validated to ensure that the new coil is performing per required specifications. Tooling and production shutdown are costly and time-consuming. Employing multiple coils with each machine, without knowing the cycle history of each individual coil increases the opportunity for production interruption.
Currently, an end user/purchaser of induction heating equipment will contract an induction equipment supplier (OEM) to design an optimal coil configuration for the part requiring induction heating. Based on the quality of material used and quality of workmanship, the coil will need repairing after an unknown amount of cycles. More often than not, the end user will choose to send the coil to an after market company for the repair based mainly on the cost of the repair. A costly inventory of inductor coils is maintained at the production site for immediate replacement when a coil fails during production. Occasionally a replacement coil is removed from inventory without ordering new replacements, thus creating an immediate need for a new replacement coil.
A blind count is recorded of how many times the induction heating machine is cycled for purposes of determining the amount of parts that have been heat treated. However, no record is kept of how many times each individual inductor coil is energized, or cycled. Nor is a record kept of how many different inductor coils are used in a multiple coil machine. Therefore, no hard record is created to determine the cycle life of each inductor coil, i.e. how many cumulative cycles in the life of an average inductor coil. Best estimates are that a perishable coil must be replaced approximately every 5,000 to 100,000 cycles based on each individual application. These tool costs are incorporated into the overall cost of each manufactured part.
When an inductor coil fails, production stops. The coil must be changed and the machine and subsequently heat treated parts must be validated. This requires the transportation and quarantine of the parts to a separate storage area for analysis of quality control. If the parts do not meet the specified criteria, they are scrapped, resulting in an expensive waste of material and labor. The alternative option is to wait until the metallurgical results are verified before running production, this may take hours.
SUMMARY OF THE INVENTION
The present invention provides an induction heat treating process with a sensor for counting the amount of cycles attributable to an individual inductor coil. The sensor is preferably a counting mechanism attached to or embedded within the induction coil or bus bar and is triggered by and responds to the change in voltage generated as the coil is energized. Alternative designs may measure current, magnetic field, frequency and/or temperature differentials on each individual coil. Additionally, the sensor may be an identifier or tag attached to or embedded within the induction coil or bus bar assembly that signals an indicator to an external data maintenance source, such as a control cabinet or personal computer for example, to register a consecutive count of cycles for the identified coil. The data culled from the sensor or other data maintenance and retrieval sources provides useful information for determining the lifespan of an induction coil. Predicting the lifespan of a coil optimizes production by anticipating failure and replacement of a coil during a predetermined down time, limiting on-site inventory, and revolutionizing the repair billing cycle based on a per cycle cost while decreasing overall production costs.
Initially, the sensor is used to measure the amount of cycles sustained by each individual coil until failure of the coil to establish a base line life span of a typical industrial application. To do this, a sensor may be provided as an attachment to a pre-existing production coil. In a preferred embodiment, the sensor is embedded in a bolt typically used to secure the coil bus bar together. When the machine is activated, the sensor responds to the voltage change across the bus bar and signals a single cycle. Each activation, or cycle, of the induction heat treating coil registers a consecutive cycle. The sensor tallies and stores the amount for reading. The sensor may also transmit to an external device such as a bar code reader, hand held personal computer, cellular telephone, or any other device capable of receiving such transmitted information.
Once an average baseline lifespan for each coil design is established, the monitoring system of the present invention can provide useful information to optimize the operation of each induction heating machine and overall production. The monitoring system includes providing an induction coil w
Dobrusin & Thennisch PC
Leung Philip H.
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