Apparatus and method for shaping glass tubes with molds

A mold for shaping the end region and the opening at a selected end of a hollow cylindrical glass tube used in the manufacture of optic fibers, when the end region of the tube is rendered malleable, comprising:

• two complementary elongated side pieces having inner surfaces for application to the periphery and along the length of the end region at the selected end of the tube;
• an end cap with a cylindrical stub for insertion within the opening of the tube at the selected end;
• said side pieces and said cylindrical stub for shaping the tube when the tube is rendered malleable;
• the inner surfaces of the two elongated side pieces, when joined together, defining an arcuately shaped space for encircling and tapering the end region of the tube from a first point to a second point from the end of the tube, where the first point is a distance L1 plus L2 from the end of the tube and the second point is a distance L2 from the end of the tube;
• whereby the inner diameter of the tube is narrowed gradually in going from the first point, farthest from the end, to the second point nearest to the end of the tube;
• said side pieces leaving an opening aligned with the tube opening for the insertion of the end cap stub through the opening between the two side pieces and into the tube opening;
• and
• the end cap stub extending from the end of the tube for a distance at least equal to L2 and being shaped such that, when inserted into the opening of the tube, the stub causes the inner diameter of the tube to have no less than a second value (do1) for a first distance from the edge of the tube and it prevents the narrowing of the inner diameter of the tube at the second point from being less than a first value (d1);
• where the second value is larger than the first value.

A multi-piece mold for shaping the end region and the opening at a selected end of a first, hollow, generally cylindrical, glass tube to mate with a second tube, of smaller diameter than the first tube, and to enable the second tube to be inserted a first distance within the opening of the first tube at its selected end, comprising:

• two elongated sleeve-like pieces of the mold having inner surfaces which, when joined, encircle the outer periphery of the end region of the first tube for gradually reducing the inner and outer diameters of the first tube along the end region proximal to the mating end;
• and
• a third piece of the mold comprising an end plug having an inner face with a cylindrical stub extending from the inner face of the plug, the stub for insertion into the opening of the first tube at its selected end, the stub having first and second sections, the first section of the stub, extending directly from the inner face of the plug, having a diameter of first value for a first distance, and the second section of the stub extending from the first section having a diameter of second value;
• and, when the tube is rendered malleable, the two sleeve-like pieces and the plug cooperating to squeeze the rim of the tube between the two side pieces and the first section of the stub along said first distance such that the inner diameter of the first tube, for a first distance from the edge of the first tube, has a second value which is slightly greater than the outer diameter of the second tube and, the three pieces of the mold causing a narrowing of the inner diameter of the first tube at the first distance from the edge, for preventing the second tube from being inserted deeper into the first tube than said first distance.

A mold for shaping the end region and the opening at a selected end of a hollow cylindrical tube when the selected end region of the tube is rendered malleable, comprising:

• two complementary elongated side pieces having inner surfaces for application to the exterior and along the length of the end region of the tube at, and near, the selected end;
• an end cap with a cylindrical stub extending from the end cap for insertion within the opening of the tube at the selected end;
• the inner surfaces of the two elongated side pieces, when joined together, defining an arcuately shaped space for encircling and tapering the end region of the selected end for causing it to assume a conic shape, while leaving an opening, between the two elongated side pieces aligned with the tube opening for the insertion of the end cap stub through the opening between the two side pieces and into the tube opening;
• and
• the cylindrical stub having first and second sections;
• the first section, extending directly from the end cap, having a diameter d1 and length L2, and the second section, extending beyond the first section, having a diameter d2, with d2 being smaller than d1;
• whereby when the stub is inserted into the opening of the tube, it causes:
• a) the inner diameter of the tube to be no less than d1 for a first distance, L2, from the edge of the tube;
• and b)after the first distance, it allows a narrowing of the inner diameter of the tube, but it simultaneously prevents the inner diameter of the tube at L1 from being less than d2.

A multi-piece mold for shaping a selected end region of a cylindrical tube and concurrently shaping the opening at the selected end region of the tube, when the selected end of the tube is heated to the point that it is malleable, comprising:

• first and second components of the mold having inner surfaces for tapering a length of the tube extending from the edge of the selected end of the tube;
• said first and second components, when joined, encircling the selected end region of the tube while leaving an opening between the two components in line with the opening of the tube at the selected end region;
• and
• a third piece of the mold comprising an end plug including a cylindrical stub for insertion through the opening between the first and second components and into the opening of the selected tube end for shaping the rim and opening of the selected end of the tube.

Apparatus for shaping a selected end region of a first cylindrical tube used in the manufacture of optic fibers, when the selected end region of the tube is heated to the point that it is malleable, comprising:

• a mold having first and second side pieces for tapering a length of the tube extending from the edge of the selected end region of the first tube and having a third end piece for shaping the rim and the opening of the selected end of the first tube;
• and the first and second pieces of the mold for being applied around the outer periphery of the first tube and extending from the one end of the first tube a predetermined distance along the length of the first tube;
• said first and second side pieces imparting a smooth reducing curve to the first tube with the end face of the first tube having a smaller diameter than the portion of the first tube distal from the end;
• said first and second side pieces leaving an opening at their end corresponding to the end of the first tube;
• and the third, end, piece of the mold including a cylindrical stub for being applied within the opening of the first tube for enlarging the inner diameter of the first tube along a first distance from the end of the tube and for creating a lip functioning as a stop in the rim region of the first tube at a distance corresponding to said first distance, between the inner and outer walls of the first tube, said enlarging of the inner diameter and said lip for enabling a second tube to be fitted within the first tube and to be easily located on the same centerline as the first tube and for preventing said second tube from going beyond said first distance.