Aperture requirements of hydraulic tube expander

Aperture Requirements for Hydraulic Tube Expanders

1. Ensure a sufficient number of hole bridges to ensure secure and reliable expansion.

2. The hole diameter after drilling or reaming should be 0.007 (0.18mm) to 0.010 (0.25mm), larger than the outer diameter of the pipe being used.

3. If conditions permit, it is recommended to fine-machine or calender the inside of the plate hole to achieve a higher surface finish. This also improves the tensile strength of the hole bridge.

4. Grooving the plate hole can increase the mechanical strength of the expansion opening.

5. When replacing discarded slotted plate hole tubes, remove any metal residue and other debris from the hole. Regarding the processing of copper tube-aluminum fin convection radiators, what are mechanical expansion, hydraulic expansion, and interference fit? To ensure close contact between the copper tube and the aluminum fin, the copper tube and aluminum fin must be tightly connected during radiator production. Furthermore, the copper tube must be threaded with aluminum, and the diameter of the copper tube must be smaller than the inner diameter of the aluminum fin's circular hole. After dressing, the following two methods can be used for expansion and tightening. (1) Hydraulic expander: When the aluminum sheets in the copper tube are connected in series and the elbows of the connecting box are all welded, high-pressure liquid (such as water) is passed through. When the water pressure rises to 1200-200kg/cm2, the copper tube is hydraulically expanded to make it in close contact with the aluminum sheet. The disadvantage is that the uneven wall thickness of the copper tube and the uneven state of the copper material cause a large expansion, which makes it difficult to ensure the expansion of the copper tube. In addition, interference is also difficult. (2) Mechanical expander: Because the copper tube is soft and the aluminum sheet is hard, a mechanical expander is used. The mechanical force forces the expansion head of the alloy steel to the inner diameter of the copper tube, causing the copper tube to expand by 30-40 mm. The positive deviation of the outer diameter of the copper tube, the negative deviation of the inner diameter of the aluminum sheet hole, and the pipe spacing are calculated to ensure that the copper tube is tightly connected and the corresponding expansion coefficient is increased again. This increased expansion is called interference. The interference fit must ensure both the self-shrinkage rate of the copper tube after mechanical expansion and a tight fit between the tube and the fins under the action of hot and cold water, reducing thermal resistance and ensuring heat transfer. Mechanical tube expanders precisely control tube expansion, resulting in highly consistent and effective products. They are currently a commonly used advanced process internationally. However, their drawbacks are stringent equipment requirements and high costs.