Heat-sealing apparatus

Claim 2

A heat-sealing machine for sealing lids to preformed containers comprising a housing, an actuatable pressure head defining the heat-sealing position of said machine, an AC power source supported by said housing having a pair of terminals thereon, means for supporting and positioning at least one preformed container in operable relation to said pressure head, means for positioning a lid upon said container, at least one heater element attached to said supporting and positioning means and adapted to be connected to said AC terminals and means connected in the circuit path of said heater element for controlling the partial cycle conduction of current in said path to set a predetermined power per unit length of said heater element and a control circuit connected to said partial cycle conduction control means to control the portion of the half-cycle during which conduction occurs for setting said power; said control circuit having means selected according to the resistance of said heater element to set a specific fixed phase angle for said partial cycle conduction control means appropriate to deliver said predetermined level of power to bring said heater element to operating sealing temperature.

Claim 3

A heat-sealing machine according to claim 1 wherein said control circuit is adapted to be connected between said AC terminals and to said partial cycle conduction control means and includes impulse-forming means for affecting said predetermined partial cycle conduction and means for switching off the flow of current from said power terminals to said impulse-forming means; and temperature-sensing means are located in proximity to said heater element and adapted to pass a signal to said control cIrcuit when the temperature of said heater element rises to a predetermined level to switch off the flow of current to said impulse-forming means.

Claim 4

A heat-sealing machine according to claim 2 wherein said impulse-forming means includes resistance means selected to set said impulse timing, said resistance means and said temperature-sensing means being attached to and moveable with said supporting and positioning means into and out of said heat-sealing position and adapted to be connected to said control circuit when in said heat-sealing position, said control circuit and said partial cycle conduction control means being fixedly supported by said housing.

Claim 5

A heat-sealing machine according to claim 3 wherein said temperature-sensing means has a resistance means in series therewith for compensating for variation in the operating characteristics of the electrical elements in said control circuit, said resistance means being attached to and moveable with said supporting and positioning means.

Claim 6

A heat-sealing machine according to claim 1 wherein said control circuit includes impulse-forming means having a controllable time constant and power adjust means associated with said impulse-forming means selected to control the impulse timing to provide said predetermined heater power.

Claim 7

A heat-sealing machine according to claim 1 having means for switching off the power through said control circuit when said predetermined temperature is reached.

Claim 8

A heat-sealing machine according to claim 6 wherein said switching means is adapted to switch off only once per sealing operation.

Claim 9

A heat-sealing machine according to claim 2 wherein said current impeding means comprises relay means having a contact thereof in the current path of said impulse-forming means, and switching transistor means adapted for conduction in the energizing path of said relay means and adapted to receive said signal from said temperature-sensing means to switch its conduction state in said energizing path.

Claim 10

A heat-sealing machine according to claim 8 wherein said temperature sensing means has a resistance which decreases as the temperature which it senses increases, said temperature-sensing means being connected to vary the current at the terminal of said transistor means which controls said conduction state thereof and means provide DC current through said temperature sensing means to said conduction control terminal.

Claim 11

A heat-sealing machine according to claim 2 wherein said current-impeding means comprises bidirectional conductive means in the current path of said impulse-forming means having gate means to control the conduction state thereof, means connected to said gate means having a breakdown voltage characteristic which determines its conduction state and adapted to be switched from conduction to nonconduction by said signal from said temperature-sensing means.

Claim 12

A heat-sealing machine according to claim 1 in which said selected means comprises resistance means which resistance is selectively decreased as the total linear length of heater element is increased to provide a constant heating value of current.

Claim 13

A heat-sealing machine according to claim 9 wherein said control circuit comprises a bidirectional conductive means having gate means to control the conduction state thereof, means connected to said gate means having a breakdown voltage characteristic which determines its conduction state, a saturable pulse transformer having a primary winding connected to said bidirectional conductive means and a pair of secondary windings attached to said partial cycle conduction control means, means connected to said breakdown voltage means and chargeable over time to at least the level of said breakdown voltage and adapted to be precluded from charging to said breakdown voltage level by said signal from said temperature-sensing means.

Claim 14

A heat-sealing machine according to claim 12 wherein said temperature-sensing means is shunt arranged with said chargeable means and has a resistance which decreases as the temperature which it senses increases.

Claim 15

A heat-sealing machine for sealing lids to preformed containers comprising a housing, an actuable pressure head defining the heat-sealing position of said machine, an AC power source supported by said housing and having a pair of terminals thereon, a rigid backing member having means for positioning at least one preformed container in operable relation to said pressure head, a sheet of heater element material secured over said rigid backing member and rigidly arranged electrical circuit in said sheet of heater element material over the surface of said backing etched through to provide a unitary arrangement of heat-sealing elements and conducting leads interconnected in a continuous electrical path between said terminals, said heat-sealing elements comprising unconvoluted strips of heater element material substantially surrounding said container positioning means and of relatively substantial width and material selected to provide a heat seal thereabout in a single pass, the width of said heat-sealing elements being many times its thickness, said conducting leads being arranged entirely over said backing member and formed integrally with said heat-sealing elements, said heat-sealing elements and said conducting leads lying entirely in a single plane and having a uniform thickness and composition of material from one end of said circuit path to the other.

Claim 16

A heat-sealing machine for sealing lids to preformed containers comprising a housing, an actuable pressure head defining the heat-sealing position of said machine, an AC power source supported by said housing and having a pair of terminals thereon, a rigid backing member having means for positioning at least one preformed container in operable relation to said pressure head, a sheet of heater element material secured over said rigid backing member and rigidly arranged electrical circuit in said sheet of heater element material over the surface of said backing etched through to provide a unitary arrangement of heat-sealing elements and conducting leads interconnected in a continuous electrical path between said terminals, said heat-sealing elements comprising unconvoluted strips of heater element material substantially surrounding said container positioning means and of relatively substantial width and material selected to provide a heat seal thereabout in a single pass, the width of said heat-sealing elements being many times its thickness, said conducting leads being arranged entirely over said backing member and formed integrally with said heat-sealing elements, said heat-sealing elements and said conducting leads lying entirely in a single plane and having a uniform thickness and composition of material from one end of said circuit path to the other.

Claim 17

A heat-sealing machine according to claim 14 in which the connecting lead portions of said sheet between heat-sealing strips have sufficient cross section to operate at no appreciable sealing temperature.

Claim 18

A heat-sealing machine according to claim 18 in which said sheet is etched through to provide contact surfaces at each end of said continuous electrical circuit to connect with said AC terminals.

Claim 19

A heat-sealing machine according to claim 14 wherein said sheet is bonded to an insulating substrate positioned upon said backing member.

Claim 20

A heat-sealing machine according to claim 14 wherein said sheet has a nonstick coating.