Method of and apparatus for straightening and configuring a preform tube from which lightguide fiber is drawn

A method of making a preform tube from a glass substrate tube having a generally circular cross-section, said method comprising the steps of:

• supporting the substrate tube at its ends for rotation;
• exposing each successive increment of length of the outer surface of the substrate tube to a zone of heat having a temperature profile and a maximum temperature within a first range by causing relative motion between the zone of heat and the substrate tube;
• while
• turning the supported ends to cause the substrate tube to be turned about a rotary path of travel;
• and
• depositing doped reactants into the substrate tube to form a preform tube having a predetermined profile;
• then
• moving a contact device into engagement with the preform tube along a portion of the rotary path of travel;
• and
• exposing each successive increment of length of the outer surface of the preform tube to a torch which is disposed along the portion of the rotary path of travel and which provides a zone of heat having a temperature profile and a maximum temperature within a second range that is higher than the first range by causing relative motion between the torch and the preform tube;
• while
• causing the preform tube to have a central longitudinal axis which is a substantially straight line by causing relative motion between the contact device and successive increments of length of the preform tube during their exposure to the zone of heat of the second range with the contact device being spaced from the torch a distance as measured along the length of the tube to cause each successive increment to be engaged by the contact device along the portion of the rotary path of travel after it has been exposed to at least an initial portion of the zone of heat, the step of engaging being sufficient to cause each successive increment of the preform to be disposed substantially concentrically about an axis which extends between the supported ends of the tube.

An apparatus for causing an elongated glass substrate to have a predetermined configuration, said apparatus including:

• means for supporting each end of the substrate for rotation;
• heating means for producing a zone of heat having a temperature profile;
• means for causing relative motion between the substrate and said heating means along a longitudinal axis of the substrate to cause each successive increment of length of the outer surface of the substrate to be exposed to the zone of heat;
• means for causing rotation of the substrate by turning its ends;
• and
• contact means spaced from said heating means as measured along the axis of the substrate for causing the substrate to have a central longitudinal axis which is a substantially straight line and to have a predetermined configuration, said contact means applying forces in a reproducible manner to successive increments of length of the substrate during exposure to and in a fixed relation to the zone of heat after each successive increment has been exposed to at least an initial portion of the zone of heat.

An apparatus for making a preform tube having a generally circular cross-section from a glass substrate tube, said apparatus including:

• supporting means for holding ends of the substrate tube to allow the tube to be turned through a rotary path of travel;
• torch means for heating the substrate tube, said means including means for directing a flow of combustible gases toward the substrate tube to provide a zone of heat having a temperature profile, said torch means including means for providing a confinement of the heat to a portion of the length of the substrate tube and to a portion of the rotary path of travel to control the temperature along the portion of the length of the substrate tube;
• means for moving said torch means along the substrate tube in a direction along a longitudinal axis of the tube to cause successive increments of the length of the substrate tube to be heated and to cause the zone of heat to traverse the tube;
• means for rotating the substrate tube about its ends;
• means for depositing doped reactants into the substrate tube to form a preform tube having a predetermined profile;
• and
• contact means in tandem with said torch means and moved therewith relative to the tube for engaging along the portion of the rotary path of travel each successively heated increment of the preform tube after the doped reactants have been deposited to cause each successive increment to be disposed substantially concentrically about an axis which extends through said supporting means, said contact means engaging each successive increment of length after each successive increment has been passed by a centerline of said torch means.