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 Graphite for Manufacturing Shaped Parts


Examples of Graphites Application

Piping and Screens
Pipes of graphite grades , -1, , , find extensive application in various branches of industry due to their anticorrosive and thermostable properties. They are recommended as heaters and screens in resistance furnaces operating in vacuum or protective medium, for caking hard alloys, melting quartz as well as in the production of semiconductors and other materials. Since the material is easily machined, it can be employed for production of pipes up to 500 mm in diameter and 1500 mm long. The pipes can be made sectional, consisting of two to four parts and glued together by special cement. Electric resistivity of graphite pipes is 10-25 W mm2/m. The electric resistance of pipes drops gradually with the temperature rise to 700 C and rises with further rise of temperature. Graphitized pipes are made of three types: heating petticoat pipe with a boat for caking hard alloys in Tamman furnaces sectional threaded pipes and sectional socket pipes, each section being 400-1500 mm long. The screens made of graphite grades , -1 andcome in two types: cylindrical and shaped. Service life of screens in vacuum furnaces -9 intended for quartz block building-up is 150-200 cycles (cycle duration 5 h). Working zone temperature is 2000 C, vacuum down to 5x10-2 mm Hg. The graphite of these grades is used for the production of supports on which the screens in the vacuum furnaces are mounted. Maximum dimensions of supports are limited by the blank size.

Heaters
Heaters made of graphite grades , -1, , -0, are used instead of tungsten and molybdenum ones for melting rare and semiconductor metals in vacuum and other closed electric furnaces. They can operate at temperatures up to 2000-2200 C. Heaters made of the graphite grade operate in vacuum down to 1x10-2 mm at 2000 C, current intensity 1500-2000 A, voltage 12-24 V and withstand on the average 20 meltings of 5 h duration each. The heaters come in three basic types: cylindrical, slotted and spiral. Basic heater dimensions are limited by the maximum blank sizes. Heaters made of graphite grade have outside diameters up to 300 mm, of graphite grade sectional with total length up to 2000 mm and tubular slotted with maximum diameter up to 500 mm and up to 1500 mm long.

Boats
Boats made of graphite grades , , -1, , are used for caking hard alloys, melting rare and semiconductor materials in electric furnaces in protective atmosphere. The boats can be rectangular, round and closed with a cover made to Customers drawings.

Crucibles
The crucibles are made from blanks of graphite grades , -1, , .
They find their application mainly in vacuum and high-frequency electric furnaces or in furnaces with protective atmosphere at temperatures up to 2000 C which permits speeded-up metal melting, service life of these crucibles being considerably longer as compared to the rammed ones.
The crucibles can be used repeatedly by boring them out or grinding after each working cycle.
The crucibles can be made cylindrical, tapered or shaped to customers drawings depending on the maximum blank sizes.
Machining accuracy is limited by the following tolerances, mm:
  Crucible diameter   up to 200 200-400
  tolerance in diameter   2 4
  tolerance in height   3 7

Protective Casings and Blocks for Thermocouples and Thermometers
Protective blocks and casings for thermocouples and thermometers are made of graphite grades , to protect the thermometers against damage and corrosive effect of acids and alkails.
Protective casings can be employed in gaseous reducing and neutral media at temperatures up to 2300 C, in oxidizing medium up to 400-450 C.
The graphite is a perfect material for protective tips in thermocouples designed for brief measurements (1-3 min) of liquid cast iron and slag temperature since it is non-wettable by metals and slags and is practically insoluble in them, whereas quartz casings (tips) are readily wettable by cast iron and or slag, and casings of SiC and other materials have low mechanical strength at high temperatures and cannot withstand the force of the flow. The total time spent in the slag of a graphite tip having 10 mm thick wall is 6-7 h while the thermocouple itself serves under these conditions only 2-3 h and has to be replaced. In case of complete submersion of the graphite casing (block) into liquid cast iron or slag the operating time runs up to 30 h. In the event of complete submersion into slag the graphite is washed off and burnt (1mm/h).
Thermal inertia of a graphite block having 30 mm thick wall is about 8 min which at an average time of slag discharge can be considered quite satisfactory. Average service life of a block for measuring temperature of liquid metal in the baths of open-hearth and electric steel-melting furnaces and in pouring ladles 40 measurements. The application of graphite casings under these conditions makes it possible to measure temperature by the contact method which ensures obtaining data closely approximating the true temperature values.
The protective casings are made 400-800 mm long and up to 90 mm in diameter. With the length of casings being 1000-2000 mm they are made sectional consisting of two to four parts connected by threading or cementing.

Graphite Casting Moulds
Casting moulds are made of graphite grades , -1, , , .
Graphite casting moulds find their application in mass and large-scale production of manganese steel castings, sprockets, pistons and covers, flanges and parts of pumps, railway wheels, casting moulds for centrifugal casting of bronze bushings and many other articles of not very intricate shapes.
The graphite mould casting is distinguished by higher technical and economic factors as compared to the expendable sand and metal moulds.
As compares to the ceramic moulds the graphite ones have higher thermal, chemical and corrosion resistance and are time- and labor-saving in their machining. The graphite moulds do not require any heat treatment. Their application does away with the burning-in of the filled metal to the body of the mould and ensures its non-wettability by slags as well as permits obtaining higher density and improved mechanical properties of castings, attaining higher ultimate accuracy and surface finish of castings, and, consequently, reducing the machining allowances.
The graphite moulds are three times higher with unchanged dimensions.
To produce graphite moulds used in the continuous or centrifugal casting of cylindrical blanks, pipes of graphite grade up to 400 mm in diameter, up to 1500 mm long are employed.
The pipe dimensions can be as follows: inner diameter 1-450 mm, length 10-1500 mm, wall thickness 3-20 mm.
The graphite moulds can be protected by metal enclosures needed both to increase their service life and to facilitate their use. High mechanical strength of the graphite makes it possible to use the graphite moulds without internal metal reinforcement and other accessories increasing their strength.
In the production of steel and cast iron castings the graphite moulds withstand 300 to 500 castings depending on their mass and shape.
Taking into account the possibility of mould regrinding (it can be done up to 20 times), the number of castings can be raised up to 6000 to 8000 in steel and cast iron casting and even more for casting non-ferrous metals and especially aluminum alloys.

Moulds for Ceramic Casting and Press Moulds for Powder Metallurgy
Moulds and inserts made of graphitized materials find wide application in casting glassware: tubes, rings, batchers, shaped glass vessels, protective glass screens for radio-electronic industry.
For production of special moulds in which glass can be alloyed with Kovar alloy or moulds for alloyung semiconductor contacts utilized in radio engineering and other industry branches dense fine-grained materials are used. Moulds for refractory articles made of graphitized material grade also find extensive application.
Graphitized moulds can also be employed for caking metal powders and various hard alloys used for the production of tungsten-molybdenum rings, inserts, draw dies, matrices and other hard-metal products.
Press moulds for powder metallurgy matrices, punches and casings are usually made of graphitized material grades -1, , .
The dimensions of the manufactured products depend on blank dimensions.

Lining Plates and Blocks
Plates and blocks are made of graphitized blanks grade and used for lining chemical devices, cast-iron and slag runners as thermostable anticorrosive protection. The lining plates are made to Customers drawings. Maximum block dimensions are 380x380x1450 mm.

Articles for Gasometry Devices
Heaters, screens, internal and external electrodes, crucibles and funnels made of fine-grained graphite grades-6 and >-1are used in devices determining the gas content in metals by the vacuum-melting method. The durability of graphitezed heaters and screens is sufficient for the conduction of 20 to 30 analyses; that of electrodes one-month operation. The crucibles and funnels are fit for one work shift. Articles for the gasometry devices are made to Customers drawings.

Raschig and Palley Rings
Raschig rings for absorbers are made of graphite grade 20 to 400 mm dia. Graphite Palley rings are the most inexpensive and effective types of capping for large installations. As compared to the Raschig rings (of identical dimensions and wall thickness), they enhance the absorption efficiency by 50 to 100% and reduce resistance per one theoretical plate* by 50 to 70%.

* Definite area of capping used in calculation.

Palley Rings Data
  Ring size
  (outer dia.),
  mm
Wall
thickness,
mm
Number
of rings per 1m3
of capping
volume, pcs
Contact
surface
m2/m3
Free
volume
in 1 m3
of capping
volume, %
  60 6 5900 120 79
  35 4,5 18200 170 76
  25 4 50000 230 73

Expanders (Plungers)
Expanders made of graphite grade are used for shaping parabolic surfaces of kinescopes on automatic multi-spindle machines. Contacting the molten glass, the graphitized tool renders the kinescope surface the required shape. The chief advantage of the graphite in this process is its complete non-wettability by glass and high heat conductivity.
Various shaped articles can be manufactured to Customers drawings, e.g., small rings, pouring gates, laboratory crucibles, all sorts of gaskets and covers, bushings, articles for vacuum engineering devices and other components.

Graphite for Spark Machining
The graphite -6 is utilized in the manufacture of electrodes-instruments for spark machining of various press moulds and dies which is to a considerable extent labor-and-cost-saving in the production of these articles.
The graphite grade -6 has fine-grained structure and good erosion resistance and durability.
The graphite grade -6 can be successfully employed in other industries for the production of mercury rectifier anodes, crucibles, electrodes for electron tubes and other articles.

High-Pure Graphite
Graphite grades , , , , -1, purity class -7-2, -7-3are used for production of various structural elements and technological equipment in semiconductor and electronic engineering. Boats and crucibles of the graphite are employed for germanium dioxide reduction, synthesis of intermetallic compounds, zonal cleaning and monocrystal pulling.
Graphite heaters, pedestals, screens and other parts operate in installations producing silicon monocrystals, epitaxial structures, silicon carbide, etc.
The structure of pure graphite can be coarse-grained (grades , , ) and fine-grained (grades, -1).
Total content of impurities in graphite of purity class -7-2 does not exceed 5x10-3 (by weight) and of purity class >-7-3 does not exceed 6.2x10-4 (by weight).
Various types of articles are manufactures to Customers drawings, their sizes are determined by blanks dimensions.
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