Publication: Glass and Ceramics
New York, NY, United States
PRODUCTION OF TELEGRAPH INSULATORS ON AUTOMATIC LINES.
V. K. Gegelashvili andV. V. Zhukovskii
At the Ordzhonikidze Glassware and Insulator Plant, the mass production of insulators of low-alkaline glass on automatic lines has been successfully carried out for the first time in the USSR. A group of workers from the Glass Institute under the leadership of the Candidate of Technical Sciences, L. I. Buneeva, has taken an active part in this accomplishment.
The production of the insulators was organized in a new shop with a designed capacity of 24.5 million insulators annually. The first section of the shop with three automatic lines was put into operation in August 1965 and the second one with four lines, in December 1966.
The insulators are intended for the electrical insulation of the wires of low-voltage aerial lines of electric networks and telegraph communication lines and are mounted on pins or hooks. The insulators should fulfill the following requirements: to have a high volume and surface electrical resistance, be chemically stable under various external influences and resistant to mechanical and thermal effects. Based on this, the Glass Institute recommended for the production of the insulators a low-alkaline glass grade 13c with the following chemical composition (in weight %): 63.6 silicon dioxide; 15.5 aluminum oxide; 13.0 calcium oxide; 4.0 magnesium oxide; 2.0 sodium oxide; 2.0 fluoride; and a permissible iron (III) oxide content of not more than 1%.
The following charge is used to make a glass of this composition (in kg of dry substance for 100 kg glass): quartz sand 59.84; alumina 12.56; dolomite 24.68; fluorspar10.34; and nepheline concentrate 10.05. The charge components are processed by the usual glass-making methods.
Before storage in the bins, all the raw materials were passed through a No. 08 screen (81 mesines per cm²).
The melting of the glass was carried out in two regenerative continuous furnaces with transverse flame. The area of the glass surface in the melting section was 142 m² and in the working section 12 m². The depth of the tank of the melting section of the furnace was 800 mm and that of the working section 700 mm.
The following refractories were used for the lining of the furnace: the bottom of the tank was lined with chamotte brick Sh-1, the walls of the tank in the melting section with quartz brick, the walls of the tank of the working section with dinas brick, and the neck with quartz brick; the breast-walls and crown of the furnace with dinas brick. On the basis of the results of operation of one furnace during a period of 20 months (which was shut down owing to damage to the bottom at the bubbling section of the glass) it can be inferred that a furnace lined with the above-mentioned refractories can give more than two years of continuous service when used for making the glass 13c.
These furnaces have five pairs of burners and are fired with natural gas from the Stavropol field which has a caloric value of 8.5 kcal / Nm3. The following temperatures were established along the length of the furnace: between the first and second pair of burners 1520 ºC, between the second and third 1540º, between the third and fourth 1540º, at the shield 1540º, and in the working section of the furnace 1410º. The average daily output of glass per m³ of the melting section was 350 kg.
The molding of the insulators was carried out on seven automatic presses of the type API-12A designed by the Orlov State Special Planning and Design Office. Three machines were installed as one and four at the other furnace. The glass is supplied to the automatic machines by the automatic feeder PM-312 with a window diameter of 75 mm.
Because of the high viscosity of the glass 13c, the process of making the insulators was modified by taking away the rotating bushing and letting the plunger rotate at 8 rpm. The temperature of the lump for making the insulators was maintained at 1195ºC.
Instead of 12 lumps per minute according to the design, an optimum speed of 14.8 lumps per minute according to the design, an optimum speed of 14.8 lumps per minute was chosen. This increase in speed made it possible to exploit the design capacity of the shop. The pressure of the compressed air for driving the automatic tables was 3.5 atm and for the pressing mechanism 1.2 atm.
The pressing of the insulators is carried out in the following sequence. After the lump arrives in the mold in the first position, the turntable moves the mold to the second or pressing position, the piston of the press cylinder descends and the dismountable threaded core carries out the fashioning of the insulator and its threaded apperture with a force of 1200 kg. Then the piston of the pressing cylinder with the main core is lifted off the mold, leaving in the pressed part the threaded core which is to be removed in the sixth position. The molded insulator is, by means of a removing device, transferred to a band conveyor of the type EKP-130. Additional gas burners are installed on the conveyor to maintain the prescribed temperature of the insulator. From the conveyor, the insulators are transferred by means of an automatic loading device of the type PA-1800 to the moving grid of the annealing furnace. The annealing of the moldings is carried out in an electric convection annealing furnace PKE-1800 at a maximum temperature of 680ºC. The residence time of the insulators in the annealing furnace is four hours.
When the insulators emerge from the annealing furnace, they are sorted, tested, and packed into wooden transport boxes. The average yield of serviceable insulators is 55 - 60 %.
During the development of the production method for insulators of the type TS, of low-alkaline glass, there was a long period during which the glass was inhomogeneous which was caused primarily by the installation of bubbling jets in the charging area and by retaining the bubbling in this section after shutting off the jets in the section of the fourth pair of burners. Moreover, the furnace at the Ordzhonikidze Plant had initially a large working tank (29 m²) with a fifth pair of burners for the heating of the glass. During the re-heating of the low alkaline glass, thermal cords were formed on its surface, so that it arrived in the working section with a large number of thermal cords.
Cutting out the bubbling in the charging section improved the quality of the glass with regard to inhomogeneity, but this still amounted to 3 - 4º.
To improve the quality of the glass, barrier devices were installed at the feeders which made it possible to take the glass from a depth of 100 - 150 mm.
During the second building-up period of the shop, the furnace was rebuilt on the basis of a heat engineering study, carried out by the laboratory of the Glass Institute and the practical experience gained from the first furnace. The furnace was provided with a working tank of 12 m² and as a result of this measure the homogeneity of the glass in the rebuilt furnace was 1.5 - 2º.
During the development of the production process, the design of the insulators was modified to conform to the technical conditions of molding; different rounding radii on the insulator were tried and its internal petticoat was shortened. The design change did not have any adverse effect on the electromechanical properties of the parts.
Furthermore, the plant together with the laboratory of the Glass Institute and the Orlov State Special Planning and Construction Office carried out much work on the adaptation and on the modification of individual details and units of the glass-molding automatic machines API-12A.
Translated from Steklo i Keramika, No. 5, pp. 39 - 40, May 1968.