Patent GB-866519-A (GB)
Title: Glass articles and method of and apparatus for fabricating them
IPC: C03B23/07
Filed: 1958-11-26
Abstract: 866,519. Glass manufacture. MORRILL, V. Nov. 26, 1958, No. 38152/58. Class 56. In conforming the bore of a glass tube to the surface configuration of a mandrel enclosed therein by progressively heating the tube from one end to the other by moving the tube and a heat source relative to each other and simultaneously withdrawing air from the space between the tube and mandrel, the air from this space is withdrawn from behind the heat source so that the flow of air takes place in a direction opposite to the direction of movement of the heat source relative to the tube, the mandrel being cooled so that after the tube has been collapsed on to it, it contracts slightly to provide a small space between its surface and the bore of the tube through which space air continues to be withdrawn as the heat source moves along the tube. The apparatus comprises a pair of opposed spindles 3, 53 with central bores 6, 47 in which the mandrel 40 is supported, the glass tube 100 being held on the spindles by chucks or the like. The hollow mandrel 40, for making a pipette, is composed of two tapered sections 42, 44 of different section giving a shoulder 43 against which a shell 90 is held by a magnet 80 or by gravity. The shell 90 is preferably of steel in two halves 92 and encloses a glass bead 91 of larger diameter than either mandrel section, the shell 90 forming the mixing section of the pipette. The shell 90 is sand blasted to prevent sticking and to give a frosted surface to the inside of the bulb of the pipette. The spindles 3, 53 are mounted in stocks 2, 54 for rotation by a motor 4. The spindle 3 has the bore 6 enlarged at 7 to form a shoulder 8 against which the end 35 of the mandrel 40 is seated and the counterbore 7 is connected by passages to a pressure gland 24 and thence to a compressor 26, the conduit 28 having a pressure gauge 29 so that the cooling fluid through the mandrel 40 can be regulated. The space between the tube 100 and mandrel 40 is connected to a vacuum pump 20 through conduit 22, vacuum gland 16 with an annular channel 18 communicating with radial passages. 14 and passages 12 in the spindle 3 and similarly at the other end to a vacuum pump 62. The open end of the mandrel 40 is connected by a gland 64 through a flowmeter 65 to the atmosphere. The tailstock 54 is mounted for movement towards and away from the headstock 2 by a screw 68 driven from motor 69 for regulating the thickness of the tube as it collapses on the mandrel. The tube is heated by a fixed burner 70 and a burner 72, or pair of burners, travelling along a screw 74 driven by motor 75, the burner 72 moving from the narrow end and the tube collapsed by the pump 62, the burner 72 then being turned off as it passes the shell 90 and relit to heat the tube over mandrel section 42, when the tube is collapsed by pump 20. The burner 70 is then lit to heat the area round the shell 90 and the tube is finally evacuated by pump 20. After cooling, the pipettes are trimmed and annealed and the shell 90 is then dissolved by acid and the salts rinsed out. In a modification, the air forced through the mandrel is used to cause the evacuation of the space between the tube and mandrel at the thin end; this end of the mandrel lying in an enlarged bore in the spindle which connects with the space. In this embodiment, the other end of the mandrel is mounted in a vibrator outside the spindle, the counterbore is closed by spring pressed washers and the compressed air passes into the mandrel through a node with radial passages. The mandrel is wiped each time before use with colloidal carbon to prevent sticking. Specification 866,529 and U.S.A. Specification, 2,735,230 are referred to.