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.pdf-ЕХ-ТАЗЗЛ7 ШБТИШ FOR METALLURGICAL STUD ESS
0 Foundry Department )
Dr* Bastrakov V.
Casting Defects and Measures of
Their Prevention
( Methodical Supplement to the Course *' Technological Fundamentals of
Foundry Production” )
production,# The purpose |
of |
this text-hook is to provide |
a functional perspective |
for |
the technician and engineers |
whose dob requires correct decisions, related to the det
ermination of a kind |
of |
a casting |
defect and to its succ |
||
essful elimination from |
castii |
-"i |
future, |
и£ |
|
modern notions about |
a character |
of |
physical, |
ckesdcai. |
|
thermal, hydrodinamical, and mechanical interactions of metal and mould it gives a realistic understanding of rea sons of main casting defects which are observed in the fo undry practice.
Although the book is intended for students of meta llurgical specialities, especially for foundrymen, it can be successfully used by technicians, engineers, research men, and investigators whose .job is connected, with the foundry production,
3.V.
1* Classification of Casting Defects
Following different principles of various kinds of
defects classification |
may be used at the |
quality control |
of castings* Each type |
of a defect can be |
subdivided acc |
ording to a shape, size, position or other special features
and can be brought to one or to another group of defects.
On the other hand, an origin of defects may be associated
with molten metal, mould, core, |
or castinjg process chara |
||
cteristics, |
Each of them can be |
the base of |
the cla ssifi |
cation too. |
|
|
|
Another classification may be founded |
on the base of |
||
defects division in accordance with a technological opera tions of a casting manufacture during which some defect may arise (during melting of the metal, pouring, s o lid ifi cation or cooling a casting). But such the classification is not available as in this case real reasons of some def ect origin are overshaded by other unessential, but raised into a classification principle, signs typical for the def inite stage of forming a casting.
Well-known classification of casting defects accor
ding to external indications and to special |
characteristics |
|
is generally |
accepted. Following this a ll |
defects in ca- |
sting can be |
divided ihto four main groups |
s |
complex of different newest devices allowing foundrymen to control needed properties very quickly and to reoieve the detail information in a suitable form j
unsatisfactory nochunical properties of a casting metal, or alloy, such ,.s a low strength or plasticity, a small shock resistance, ^tc. c.eterminati'on of mochanxcal properties is carried out with the help of special st andard machines and equipment using standard methods of tests and quality control of specially made and machir.ec1 samples.
Sometimes |
a ll kinds of |
defects |
are divided |
into |
only |
three groups, |
In this case |
two last |
groups are |
united |
tog |
ether г.ь mechanical properties of a casting metal are sup
posed to depend on its composition and structure. Is |
our |
opinion it is not so in general cane beceuse composition |
|
standards establish the basic chemical indehtity of |
an a ll— |
oy and,. It is oovious, that a wide row of structures |
and, |
hence, different properties, can be obtained in castings mad? of the ailoy of the samp composition.- Especially it
is true for cast iron as different mechanical properties of this meta , at a constant chemical composition^ can be obt ained ar different rates of a metal coolingr
Or. the other hand, an alley with a proper c.nomical composition and structure may possess different properties as they oan be affected by microscopic cavities- .inclusi ons or by small additions of elements not normally .-.cte-i-:.
These castings are allowed to be used in different devices and machines only with a permission of main specialists of industrial enterprises ;
- remediable or partial rejects. This is castings having such defects after the repairing of which the cas tings can be allowed to be machined and to be used in d if ferent devices ;
— irremediable or final rejects. That is castings having such defects the repairing of which is technically impossible or economically unprofitable.
However it ought to mean that the decision about m admissibility or inadmissibility of some defect is in a great degree, determined by technical conditions or by spe cia l requirements of technical documents. Therefore the notion "quality of castings" is relative and depends on technical conditions or requirements to castings.
