Process for production of glass tubes having at least one tube end section of reduced stress

A process of producing a glass tube having at least one tube end section with a reduced stress, said process comprising the steps of:

• a) drawing a glass tube line from a glass tube production plant;
• b) cutting a glass tube from the glass tube line to form a still heated glass tube, said glass tube extending in a longitudinal direction;
• and
• c) transporting the still heated glass tube, after being cut from the glass tube line, in a predetermined direction that is different from a tube drawing direction and passing the still heated glass tube through a heating region with a predetermined temperature profile in which the still heated glass tube is subjected to a local heat treatment at said at least one tube end section prior to cooling down completely, so that in said heating region a respective temperature of the glass tube is selectively and locally increased depending on a corresponding distance from a tube end of said at least one tube end section, said heating region extending in the longitudinal direction of the glass tube;
• d) distributing heating devices along said predetermined direction in the heating region, wherein the heating devices are arranged at predetermined positions along a curve or straight line, wherein a distance between the curve or the straight line and the tube end of the at least one tube end section decreases continuously along the predetermined direction and wherein the curve or the straight line intersects the predetermined direction at an acute angle in one location, so that stresses in said at least one tube end section are reduced;
• e) measuring said stresses within said at least one tube end section;
• and
• f) varying said local heat treatment as a function of the stresses measured during the measuring of step e) so as to obtain a predetermined stress profile.

A process of producing a glass tube having at least one tube end section with a reduced stress, said process comprising the steps of:

• a) drawing a glass tube line from a glass tube production plant;
• b) cutting a glass tube from the glass tube line to form a still heated glass tube, said glass tube extending in a longitudinal direction;
• c) transporting the still heated glass tube, after being cut from the glass tube line, in a predetermined direction that is different from a tube drawing direction and passing the still heated glass tube through a heating region with a predetermined temperature profile in which the still heated glass tube is subjected to a local heat treatment at said at least one tube end section prior to cooling down completely, so that respective temperatures of the glass tube in said heating region at corresponding distances from a tube end of said at least one tube end section are selectively and locally increased depending on said corresponding distances from said tube end of said at least one tube end section, said heating region extending in the longitudinal direction of the glass tube;
• and
• d) distributing heating devices along said predetermined direction in the heating region so that the heating devices apply heat to the moving glass tube and said respective temperatures increase in a direction towards the tube end of the at least one tube end section when said glass tube approaches an end of said heating region during the transporting in the predetermined direction;
• whereby stresses in said at least one tube end section are reduced.

A process of producing a glass tube having at least one tube end section with a reduced stress, said process comprising the steps of:

• a) drawing a glass tube line from a glass tube production plant;
• b) cutting a glass tube from the glass tube line to form a still heated glass tube, said glass tube extending in a longitudinal direction;
• c) transporting the still heated glass tube, after being cut from the glass tube line, in a predetermined direction that is different from a tube drawing direction and passing the still heated glass tube through a heating region with a predetermined temperature profile in which the still heated glass tube is subjected to a local heat treatment at said at least one tube end section prior to cooling down completely, so that respective temperatures of the glass tube in said heating region at corresponding distances from a tube end of said at least one tube end section are selectively and locally increased depending on said corresponding distances from said tube end of said at least one tube end section, said heating region extending in the longitudinal direction of the glass tube;
• d) distributing heating devices along said predetermined direction in the heating region so that the heating devices apply heat to the moving glass tube and said respective temperatures increase in a direction towards the tube end of the at least one tube end section when said glass tube approaches an end of said heating region during the transporting in the predetermined direction;
• e) measuring said stresses within said at least one tube end section;
• and
• f) varying said local heat treatment as a function of the stresses measured during the measuring of step d) so as to obtain a predetermined stress profile.

A process of producing a glass tube having at least one tube end section with a reduced stress, said process comprising the steps of:

• a) drawing a glass tube line from a glass tube production plant;
• b) cutting a glass tube from the glass tube line to form a still heated glass tube, said glass tube extending in a longitudinal direction;
• c) transporting the still heated glass tube, after being cut from the glass tube line, in a predetermined direction that is different from a tube drawing direction and passing the still heated glass tube through a heating region with a predetermined temperature profile in which the still heated glass tube is subjected to a local heat treatment at said at least one tube end section prior to cooling down completely, so that respective temperatures of the glass tube in said heating region at corresponding distances from a tube end of said at least one tube end section are selectively and locally increased depending on said corresponding distances from said tube end of said at least one tube end section, said heating region extending in the longitudinal direction of the glass tube;
• d) distributing heating devices along said predetermined direction in the heating region so that the heating devices apply heat to the moving glass tube and said respective temperatures increase in a direction towards the tube end of the at least one tube end section when said glass tube approaches an end of said heating region during the transporting in the predetermined direction;
• so that said predetermined temperature profile varies locally and/or with respect to time in the longitudinal direction of the glass tube, so that stresses in said at least one tube end section are reduced to less than 6.0 MPa when said local heat treatment lasts less than 2 minutes.