Lecture №14.
Auxiliary materials.
1. Pressurizing and sealing materials.
2 . Electroinsulating materials.
3 . Materials for drawing coverings.
4 . Glues and sealants.
Pressurizing and sealing materials.
For density and tightness giving to connections of cars details (pipe, various
connections, etc.) and elimination of possible infiltration of liquid and break of
gases, we use pro-masonry and sealing materials.
Paronite - is a sheet material from asbestos, rubber and fillers. It is applied to
consolidation of water and steam highways, and also to consolidation of
pipelines and fittings for oil products: gasoline, kerosene, oils.
The felt-sheet porous material made of fibers of wool. Air time in it makes not
less than 75% of volume. It possesses high warm and soundproofing, and also
shock-absorbing properties. Felt use for stuffing of omental consolidations and
production of laying.
Important problem of modern mechanical engineering is reliable sealing and
consolidation of connections of details and assembly units working in severe
constraints. The material of usually used sealing laying (paronite, cardboard,
etc.) not always provides reliable and long tightness of connections. Under the
influence of temperature and vibration, layings over time undergo a number of
changes, lose the condensing properties, there are gaps and cracks in them. In
use it leads to leakage of oil, fuel, etc. To elimination of such malfunctions, we
apply various sealants.
Condensing liquid laying of GIPK-244 is intended for sealing of motionless
connections of details and assembly units working in water, steam-and-water,
acid-base and oil gasoline environments.
Condensing putty U-20A is intended for sealing of connections in air and
water environments.
Sealant Elastoil 137-83 pressurizes motionless connections in water, steam-
and-water, acid-base and oil environments.
Anaerobic DN-1 glue provides sealing of connections with gaps to 0,15mm.
Mineral cotton wool - is a product of processing of metallurgical or furnace
slags. It serves for isolation of surfaces with low and high temperatures of
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heating. Application of mineral-cotton plates glued by phenolic pitch or
bituminous emulsion is possible as well.
Electroinsulating materials.
As electroinsulating materials only such materials which don't carry out an
electric current or carry out it very poorly can be applied. They have to possess
also necessary mechanical durability, warm and moisture resistance. Such
materials are wood materials already considered by us, plastic, and also rubbers,
electroinsulating varnishes, asbestos, fiber, layered plasticity.
Paper - is the sheet material made of vegetable fibers and cellulose. Cellulose -
is the vegetable fibers cleared of pitches and other components. Cardboard - is a
specially processed thick paper (thickness 0,25-3 mm). Depending on a way of
processing, cardboard gets oil - and benzine resistance, electro - and thermal
insulating. Paper and cardboard are applied as electroinsulating, pro-masonry
and sealing material.
Fiber - is a version of paper material, it is produced from paper impregnated
with solution of chloride zinc. Differs high durability and well machinable, oil -
and petrolrack. Lack of a fiber - considerable hygroscopicity therefore when
moistening it is deformed. Fibers are applied to production of washers, laying
and plugs.
The press-spahn - is produced in the form of firm cardboard sheets. It is
produced from paper stock impregnated with linseed oil. It is applied to isolation
in electric cars.
Mica - represents the refractory layered mineral which is easily splitting on
thin transparent leaflets. Mica possesses high electroinsulating properties and is
applied as dielectric in condensers, collectors, electric generators and starters, in
electric heaters.
The leaflets of mica which have been stuck together by glyptal pitch under hot
pressing, is called micanite.
Insulating varnishes (№ 458, 460, 447, 13, 1154, etc.) represent a mix of
asphalt or bitumen, vegetable oil, organic solvent and desiccant. They are
applied to isolation of polar coils windings of generators and starters, and also to
protection of electrodetails against moisture and oil products.
The insulating rubberized tape represents the severe fine cotton fabric (muslin)
impregnated from one or two parties with a sticky crude rubber mix.
The sticky insulating tape is the film plastic covered with a layer of
perchlorovinyl glue. Insulating tapes are produced of various sizes and colors.
Materials for drawing coverings.
Coverings from metals and alloys.
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In mechanical engineering providing the set characteristics of materials not in
all volume of a product, and only in its blanket with preservation in a core of a
product of properties of an initial material is often required. It belongs to such
important characteristics of materials in operation of products as durability, wear
resistance, resistance to electrochemical corrosion and oxidation.
Except methods superficial thermal and chemical heat treatment, change of
properties of products surface can be achieved by drawing of coverings on the
main material - rather thin layers of other material with demanded properties.
Coverings from metals and alloys are used mainly for increase of corrosion
resistance and wear resistance of metal products. For this purpose most often we
apply coverings from aluminum, cadmium, nickel, tin, lead, chrome, zinc and
their alloys. For increase of reliability of electric contacts work they are covered
with precious metals and alloys.
For drawing of anticorrosive coverings we use:
-galvanic sedimentation,
- metallization by dispersion,
- immersion in fusions.
In mechanical engineering, the greatest distribution was gained by coverings:
- zinc (galvanizing),
- nickel (nickel plating),
- cadmium (cadmium plating),
- chrome (chromium plating).
Galvanizing is applied to protection against corrosion of steel and cast iron
details at influence of water and damp air on them. The covering is most
efficient up to the temperature plus 70ºС.
Nickel plating is used for receiving protective and decorative and wearproof
coverings on surfaces of details of the cars working in the atmosphere at
temperatures to 60ºС. When processing steel details, nickel plating is made on a
copper underlayer to eliminate influence of covering porosity.
Cadmium plating is applied to protection against atmospheric corrosion of
products from staly, cast iron and copper alloys.
Chromium plating of details is carried out for their protection against
corrosion in the atmosphere of gases, in the damp environment, alkalis and
acids. Thicker coverings (5-100 mkm) are applied to increase wear resistance of
the details working in severe constraints.
Coverings from inorganic materials.
Coverings from inorganic materials are put on surfaces of metal products for
the purpose of their protection from corrosion, decrease in coefficient of friction,
increase heat- and wear resistances.
Such coverings as oxides, carbides, nitrides and phosphates of metals, enamels
and firm greasings belong to the main materials.
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Methods of formation of coverings:
- heat and chemical treatment,
- surfacing from powders,
- chemical sedimentation from a gas phase,
- cathodic dispersion in vacuum.
Protective oxidic coverings are formed on a product surface as a result of
oxidation of their blanket under chemical influence. Widespread methods of
processing steel are:
- thermal oxygenating (burnishing),
- chemical oxygenating in boiling caustic rub,
- phosphate coating (formation of a phosphatic film).
High-strength and wearproof coverings from oxide of aluminum are put on
products from metals, firm alloys and ceramics with methods of a plasma
dusting.
Carbide, nitride and carbonitride coverings are put on products from steel and
firm alloys for increase of their wear resistance and corrosion resistance with
methods of plasma dusting and chemical sedimentation from a gas phase.
Materials for coverings are carbide, nitride and titanium carbonitride, and also
chrome and molybdenum carbides.
Silicate coverings (enamels) combine strength properties of metals with
corrosion, thermal and abrasive resistance of silicates. They are put in the form
of powders on products from steel and cast irons and then subject to annealing at
the temperature 1000ºС. To products from aluminum alloys, coverings from
fusible enamels with the high content of lead are applied.
Coverings from polymers and rubber.
In recent years, independent value was gained by the coverings received from
firm powdery polymers. They are widely used not only as protective and
decorative, but also as wearproof and antifrictional coverings, and also as facing
of products and components of composite coverings of a universal purpose.
Originally for drawing coverings, generally thermoplastics - polyamides,
polyolefins were used, and then more considerable application was received by
thermosets.
In most cases polymers when drawing coverings are combined with various
ingredients - softeners, stabilizers, hardeners, fillers.
Glues.
Glues are intended for creation from various materials of one-piece
connections of the demanded durability.
Process of pasting is based on coupling of glue with a surface of materials.
The way of pasting simplifies and accelerates technological process of a product
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production. Glue connections in certain cases are the unique types of
connections among themselves diverse materials.
Modern glues stick together various plastics, silicate and organic glasses,
natural and artificial skin, rubbers, ceramics, products from paper and cardboard,
various breeds of tree, cotton and woolen fabrics, products from synthetic fibers,
and also metals and alloys, nonmetallic materials and their combinations.
Indicator of mechanical durability of glue compounds of metals is strength at
shift. High durability of glue connection can be provided only at application of
glue of the relevant structure and observance of technological process of
pasting:
- cleaning and roughening of connected surfaces,
- their degreasing,
- putting glue by a thin layer and its drying,
- pressing of stuck together details,
- heating for heat treatment of glue connection.
Common fault of glue connections is low temperature firmness.
At car repairs, glue has found application for connection of frictional slips
with brake shoes and coupling disks. VS-10T glue is used for this purpose
represents solution of synthetic pitches in organic solvents. It is uniform
transparent liquid of dark red color without foreign impurity. VS-10T glue can
be applied to pasting of steel details, dural, plastic and other materials. It
possesses high heat resistance, oil - and benzine resistance, protective ability
against corrosion, is ecologically harmless.
The pasted worn-out frictional slips are removed by cutting, location in hot
alkaline solution or the warmed-up formic acid or, most often, heating to
temperature of a slips carbonization (300-320ºС).
Pasting of frictional slips with brake shoes and coupling disks instead of their
connection on rivets provides considerable economic efficiency mainly at the
expense of increase in the used thickness of slips and, therefore, increase in term
their service. VS-10T glue is applied also at repair of plastic details.
Details from thermoreactive plastic stick together with the VIAM B-3 pitch
glues, BF-2, BF-4, K-17 on the basis of phenolformaldehyde, epoxy and other
pitches. Pasting of details is provided with swelling of stuck together surfaces
and emergence of glutinosity.
The dichloroethane or the glue representing solution of sawdust of organic
glass in formic acid or in a dichloroethane is applied to pasting of organic glass.
The glue widely applied at production and repair of wooden details can be of
two types:
- casein (proteinaceous) for the details protected from moisture,
-synthetic (pitch) for the details which are exposed to influence of moisture,
demanding the increased durability of connection and protection them from
destruction by fungus.
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The casein glues - represents water solution of casein powder (product of milk
processing).
Synthetic glues consist of pitch (thicket phenolformaldehyde, epoxy) or
difficult vinyl air (PVA, PVB) and solvent (acetone, ethyl alcohol) and hardener.
Pasting by casein and synthetic glue is possible at the room temperature. The
prepared glue needs to be used within 3 hours. Humidity of stuck together wood
shouldn't exceed 18%.
Connection of gaps, imposing of patches at repair of bodies is made by means
of synthetic BF-6 glue. PVB is also widely used for preparation of films,
varnishes and sheetings. PVA-polyvinyl acetate represents a product of
polymerization of vinyl-acetic ester. Possesses good film-forming properties,
can be dissolved in many solvents, therefore the main application of PVA-
pasting of paper, fabrics, skin, glasses, ceramics, tree. A number of paints on the
basis of water dispersions of PVA is developed.
The repaired place after putting synthetic glue is pressed through a damp rag
by the iron heated to 130ºС during 12-15 with short breaks. Upholstery gluing to
wooden details is made by AK-20 nitroglue and to cardboard – glue № 4010. To
gluing of rubber details to the metal, we apply glue №88, №88Н, №66.
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