Abstract: A modular type replaceable heating unit with a downwardly facing heating ring for use in an apparatus for sealing a flat lid with a lower layer of heat bondable material onto the upper, generally flat surface of a flange extending around the periphery of an access opening in a container. The apparatus moves the heating unit between first and second positions. The apparatus includes a generally fixed high frequency power supply for energizing the heating ring, connecting the high frequency power supply to the heating ring only while the heating unit is moving between the first and second positions. The ring is forced against the lid as the power supply is energized and is released from the lid after the power supply has been de-energized. Preferably the ring is an inductor. A plurality of these heating units is carried by a turret to define individual heating stations on the turret which stations rotate to selectively energize the individual heating units.

Abstract: A method and apparatus for sealing a flat lid with a lower layer of heat bondable material onto the upper, generally flat surface of a flange extending around the periphery of an access opening in a container of the type used to store a substance susceptible to deterioration when exposed to atmosphere for a prolonged time such as prepared foods, which method and apparatus moves a separate and distinct heating unit with a downwardly facing heating ring in a preselected path, preferably circular in shape, between first and second positions, includes a generally fixed high frequency power supply for energizing said heating ring, connects this fixed high frequency power supply to the individual heating rings of the moving heating unit only when the unit is moving between the first and second positions, and energizes the power supply only while the heating unit is moving between the first and second positions.

Abstract: A method and apparatus for sealing a flat lid with a lower layer of heat bondable material onto the upper, generally flat surface of a flange extending around the periphery of an access opening in a container of the type used to store a substance susceptible to deterioration when exposed to atmosphere for a prolonged time such as prepared foods, which method and apparatus moves a separate and distinct heating unit with a downwardly facing heating ring in a preselected path, preferably circular in shape, between first and second positions, includes a generally fixed high frequency power supply for energizing said heating ring, connects this fixed high frequency power supply to the individual heating rings of the moving heating unit only when the unit is moving between the first and second positions, and energizes the power supply only while the heating unit is moving between the first and second positions.

Abstract: A method and apparatus are provided for an improved power inverter circuit, including a separate starting inverter having an A.C. output applied across a load prior to energizing the main inverter, and driven by a series of repeating gating signals. On achieving a preselected load condition, the starting inverter is removed from the circuit and the main power inverter is energized.

Abstract: A method and apparatus for controlling the frequency of a power inverter for converting D.C. current into A.C. current having a frequency controlled by gating signals, which apparatus and method includes a load voltage detector for deriving a voltage wave; a load current detector for deriving a current wave; a phase shifter to shift the phase of one of the waves by 90.degree.; a multiplier to multiply the voltage and current waves; one with the other to produce a product; a reference signal for comparison with the product to create a control signal; and, a gating signal controller responding to the control signal.