Abstract: A tube forming apparatus performs a forwardly rotating step in which a main roll is rotated forwardly with a pair of subsidiary rolls in a forming position during a move of a contact position between the main roll and a work from a first end of the work to a central portion of the work, a feeding step in which the main roll is rotated forwardly with the pair of subsidiary rolls in a retracted position during a move of the contact position between the main roll and the work from the central portion of the work to a second end of the work, and a reversely rotating step in which the main roll is rotated reversely during a move of the contact position between the main roll and the work from the second end of the work to the central portion of the work.

Abstract: A tube forming apparatus sequentially performs a forwardly rotating step in which a main roll (2) is rotated forwardly with a pair of subsidiary rolls (3) in a forming position during a move of a contact position between the main roll (3) and a work (W) from a first end (W1) of the work (W) to a central portion (W3) of the work (W), a feeding step in which the main roll (2) is rotated forwardly with the pair of subsidiary rolls (3) in a retracted position during a move of the contact position between the main roll (2) and the work (W) from the central portion (W3) of the work (W) to a second end (W2) of the work (W), and a reversely rotating step in which the main roll (2) is rotated reversely during a move of the contact position between the main roll (2) and the work (W) from the second end (W2) of the work (W) to the central portion (W3) of the work (W), while rotating the pair of subsidiary rolls (3) in a direction opposite to the direction of rotation of the main roll (2) in each of the steps.