Microwave heating control and calorimetric analysis

• US 4,434,342 A
• Filed: 01/11/1982
• Issued: 02/28/1984
• Est. Priority Date: 01/11/1982
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Schubring, Norman W.
• Primary Examiner(s): Envall, Jr., Roy N.
• Assistant Examiner(s): Leung, Philip H.
• Application Number:
  US06/338,636
• Time in Patent Office: 778 Days
• Field of Search: 219/10.55 M, 219/10.55 B, 219/10.55 R, 219/10.55 A, 219/497, 374/14, 374/31, 374/32, 374/142, 374/149, 324/58 B, 324/58 C, 324/58.5 B, 324/58.5 C, 264/25, 264/125, 264/26
• US Class Current: 219/710
• CPC Class Codes: H05B 6/645 using temperature sensors

Abstract

In accordance with a preferred embodiment microwave heating of a material is controlled by producing an electrical signal indicative of the rate of change of the net applied microwave power with the change of temperature of the material and using the signal in control of the energy input to the material.

Claims

1. A method of controlling the input of microwave energy in heat processing of a material that is heatable with microwaves to produce therein a desired temperature response with time, comprising

subjecting a load of such material to microwave energy at a power level sufficient to commence heating the material while the material is situated in a cavity receptive to microwave radiation,

monitoring the temperature of the material as it is heated by said energy and continually producing an electrical signal indicative of such temperature,

monitoring the microwave power applied to the load and the power reflected from the load and continually producing an electrical signal indicative of the net power absorbed by the load,

continually producing an electrical signal indicative of the rate of change of said net applied power with the change of said temperature by continually using said temperature indicative signal and said net power indicative signal, and

employing said rate of change indicative signal in control of the mircrowave energy input to said load so as to produce therein said temperature response with time.

2. A method of controlling the application of microwave energy to a material for the purpose of increasing the temperature of the material at a desired rate where such material to be heated has an apparent heat input requirement that varies over the temperature range to be traversed, comprising

subjecting a load of such material to microwave energy while the material is situated in a cavity receptive to the microwave energy and retentive of radiation from the heated body, said microwave energy being generated at a controllable power level at a location remote from said cavity and conducted to the cavity through a suitable microwave waveguide,

continually producing a voltage indicative of the temperature of the load in said cavity while it is being heated with said microwave energy,

monitoring the microwave power transmitted through the waveguide from said source to the cavity and the microwave power reflected from the cavity back through the waveguide toward the source and continually producing a voltage indicative of the net microwave power absorbed by said load,

continually producing a voltage indicative of the rate of change of said applied power with temperature using said temperature indicative voltage and said net power indicative voltage, and

continually using the rate of change indicative voltage to control the microwave power from said generator to the load so as to produce therein said temperature response with time.

3. A method of sintering alumina spark plug insulator bodies using microwave energy where said bodies are heated from ambient temperature to nearly 3000°

F. over which temperature range the apparent specific heat of the load varies markedly, comprising

subjecting a load of said alumina insulator bodies to microwave energy while the load is situated in a kiln receptive to microwave radiation and retentive of infrared radiation emanating from the heated bodies, the microwave energy being delivered at a controllable power level from a source through a waveguide to the load cavity,

continually monitoring the temperature of the load in the cavity and producing a voltage indicative of the instantaneous temperature,

monitoring the microwave power transmitted through the waveguide from said source to the cavity and the microwave power reflected from the cavity through the waveguide back toward the source and continually producing a voltage indicative of the net microwave power absorbed by said load,

continually producing a voltage indicative of the rate of change of said applied power with temperature using said temperature indicative voltage and said net power indicative voltage, and

continually using said rate of change indicative voltage to control the microwave power input to said cavity so as to produce a substantially straight-line increase in temperature of said load with time until the load reaches its sintering temperature.