BACKGROUND

Manufacturing heat exchangers for heating, ventilating and air conditioning (HVAC) systems often includes expanding the diameter of a tube by applying a pressurized fluid to the interior of the tube, thereby causing the exterior surface of the tube to expand into contact with the fins of a heat exchanger coil. Such processes can be performed hydraulically or pneumatically.

Challenges in such processes can include identifying and providing an optimal pressure at which the internal pressure of the tube is above the yield point or yield threshold of the tube material—thereby causing the material to become plastic and change shape (e.g., expand)—but below the failure point or failure threshold that would result in the tube bursting or otherwise failing. Further, it is necessary to accomplish this while also ensuring the tube sufficiently expands to provide a tight fit (i.e., frictionally attached) with the internal diameter of holes in the fins.

SUMMARY

These and other problems are be addressed by the technologies described herein. Examples of the present disclosure relate generally to methods for heat exchanger manufacturing and, more specifically, to methods for pressure expanding a tube to fit a heat exchanger fin.

The disclosed technology includes a method for expanding a tube for manufacturing a heat exchanger that includes fluidly connecting a pressurizing device to the tube and providing, by the pressurizing device, pulses of positive pressure to an interior of the tube. each of the pulses can have a duration that is less than or approximately equal to 200 milliseconds, and at least one of the pulses can provide a pressure that is greater than or approximately equal to a maximum pressure threshold of the tube. The pulses can cause a diameter of a wall of the tube to increase.

The method can be simultaneously performed on multiple tubes.

At least some of the pulses can have a duration that is less than or approximately equal to 100 milliseconds.

The maximum pressure threshold can be associated with failure of the tube.

The maximum pressure threshold can be less than or equal to approximately 3000 psig.

The method can include creating a temperature differential between straight sections of the tube and a bend section of the tube such that the bend section has a temperature that is less than a temperature of the straight sections.

Creating the temperature differential between the straight sections and the bend section can include heating the straight sections.

Creating the temperature differential between the straight sections and the bend section can include cooling the bend section.

The method can include creating an external pressure differential between straight sections of the tube and a bend section of the tube such that the bend section experiences an external pressure that is greater than an external pressure experienced by the straight sections.

Creating the external pressure differential between the straight sections and the bend section can include (i) substantially enveloping the bend section with a pressurizing device such that at least part of the bend section is located in a cavity of the pressurizing device and (ii) pressurizing the cavity of the pressurizing device, thereby increasing the external pressure experienced by the at least part of the bend section.

Creating the external pressure differential between the straight sections and the bend section can include (i) substantially enveloping the straight sections with a depressurizing device such that at least part of each of the straight sections is located in a cavity of the pressurizing device and (ii) creating a negative pressure in the cavity of the depressurizing device, thereby decreasing the external pressure experienced by the at least part of each of the straight sections.

The disclosed technology includes a method for expanding a tube for manufacturing a heat exchanger that includes creating an external pressure differential between straight sections of the tube and a bend section of the tube such that the bend section experiences an external pressure that is greater than an external pressure experienced by the straight sections. The method can include fluidly connecting a pressurizing device to the tube and providing, by the pressurizing device, a positive pressure to an interior of the tube, thereby causing a diameter of a wall of the tube to increase.

Creating the external pressure differential between the straight sections and the bend section can include (i) substantially enveloping the bend section with a pressurizing device such that at least part of the bend section is located in a cavity of the pressurizing device and (ii) pressurizing the cavity of the pressurizing device thereby increasing the external pressure experienced by the at least part of the bend section.

Creating the external pressure differential between the straight sections and the bend section can include (i) substantially enveloping the straight sections with a depressurizing device such that at least part of each of the straight sections is located in a cavity of the pressurizing device and (ii) creating a negative pressure in the cavity of the depressurizing device thereby decreasing the external pressure experienced by the at least part of each of the straight sections.

Providing the positive pressure to the interior of the tube can include providing pulses of positive pressure to an interior of the tube. Each of the pulses can have a duration that is less than or approximately equal to 200 milliseconds, and at least one of the pulses providing a pressure that is greater than or approximately equal to a maximum pressure threshold of the tube.

The method can include creating a temperature differential between the straight sections and the bend section such that the bend section has a temperature that is less than a temperature of the straight sections.

Creating the temperature differential between the straight sections and the bend section can include heating the straight sections.

Creating the temperature differential between the straight sections and the bend section can include cooling the bend section.

The disclosed technology includes a method for expanding a tube for manufacturing a heat exchanger that includes creating a temperature differential between straight sections of the tube and a bend section of the tube such that the bend section has a temperature that is less than a temperature of the straight sections. The method can include fluidly connecting a pressurizing device to the tube and providing, by the pressurizing device, a positive pressure to an interior of the tube, thereby causing a diameter of a wall of the tube to increase.

Further features of the disclosed design, and the advantages offered thereby, are explained in greater detail hereinafter with reference to specific examples illustrated in the accompanying drawings, wherein like elements are indicated be like reference designators.

