Page 22 - ST Sept

WELDING WELDING

mm) and small parts (balls and rollers parallel to the surface of the object have been developed to control flat welded joints and joints
of bearings, hardware, etc.). At the with a small surface curvature. Crack detector EDM-65 is used to detect surface defects in
same time, the inspection productivity cleaned welded seams of aluminum alloys.
can reach 50 m / s (for wire) or several Scanning crack detectors with a relatively large diameter head are difficult to use for
thousand small parts per hour. The inspection of welded joints of complex configuration. In these cases, portable and small-sized
performance of inspection of pipes crack detectors with small-diameter converters operating in static mode are usually used. The
and rods is limited by the inertia of most common crack detectors of the DNM and VD20NST series. Crack detectors DNM series
transportation and sorting devices and (DNM-15, -500, -2000) are designed to control the surface
rarely exceeds 3 m / s. quality of welded joints made of aluminum and heat-
The sensitivity threshold, the resistant alloys, and VD-20NST allows detecting surface
crack detector parameter, determines defects in ferromagnetic and non-ferromagnetic materials.
the minimum dimensions of a defect For inspection of small parts (mainly bearing parts), crack
of a given shape, at which the signal- detectors SK-27-MDSh5, -31, -39, MDR-1, -2 and -3
to-noise ratio is two. The sensitivity have been developed for industry purposes. From foreign
threshold is usually set using a crack detectors of this type, various modifications of the
calibrated sample with artificial defects Tsirkograf and Crack detector series developed at the
of various shapes, for example, Ferster Institute are widespread. Crack detectors of the
in the form of holes of different "Tsirkograf" series with rotating attachment converters
diameters and depths in pipes and are equipped with replaceable scanning heads, which
rods, longitudinal marks on the wire, make it possible to control the quality of objects with
etc. The actual sensitivity threshold Fig. 4. Diagrams of the external checkpoint (a), internal checkpoint (b) a diameter of 2 ... 120 mm. To control short parts and
of the flaw detector depends on the and energy field systems (c) of electromagnetic control (arrows show the assemblies having a complex surface of revolution, a
level of interference associated with directions of propagation of electromagnetic waves): 1 - welded joint; L - comb with floating converters, fixed in special holders,
inductor; H - vector of magnetic field strength
variation of parameters object (for is connected to them. Crack detectors of the "Tsirkograf"
example, from surface roughness). series, intended for inspection of the inner surface of
The sensitivity threshold of a flaw detector with a bore transducer is usually determined by pipes, have internal rotating converters that can be
the depth of a narrow long longitudinal defect, expressed as a percentage of the transverse installed in a stationary or portable (in the form of a
dimension (diameter) of the object. hand drill) device.
Crack detectors differ from each other mainly in design: the presence or absence of sorting
units, presentation and registration of information, marking of defective areas, magnetization,
etc. Currently, domestic crack detectors of the IPP-1M, TNM1M, IDP-1, ASK- models are widely
used 12, EZTM, DKV-2, VD-20P and -30P.
The IPP-1M crack detector is designed to detect surface defects in rods with round and
hexagonal profiles with a diameter of 4 ... 47 mm, made of ferromagnetic and non-ferromagnetic
metals and alloys, in the conditions of in-line production. The depth of
the threshold defect for it is 1 ... 2% of the diameter, but not less than
0.1 mm, and the length is 2 mm. Crack detector IDP-1 is used to
detect surface defects in rods 1 ... 5 mm in diameter made of non-
ferromagnetic and ferromagnetic metals and alloys: cracks, hair
lines, cavities, etc. The depth of the threshold defect for it is 0.05
mm. The quality of ferromagnetic welded pipes with a diameter
of up to 60 mm is controlled using an EZTM crack detector. The
leading-through converter, made in the form of a three-turn
transformer system, ensures reliable operation of such a crack
detector at high temperatures, even in the presence of scale and
oils. With its help, lack of penetration in the weld is detected, and its use
makes it possible to exclude hydrotesting. To control the quality of extended
welded structures with a wide range of standard sizes and types of materials, the
VD-30P universal crack detector has been developed.
Comparing the foreign models of this type, the most effective are the crack detectors
developed at the Foerster Institute (Germany). In our country, they are used to control pipes,
rods and wires, mainly from ferromagnetic and non-ferromagnetic materials.
Crack detectors with surface-mounted converters. To control linearly extended objects extxe.com
with a circular cross-section (rods, pipes), scanning crack detectors with surface-mounted
converters rotating around the object are used: VD-40N, -41N and -43N. These crack detectors
are designed to detect surface defects in welded joints made of ferromagnetic and weakly
magnetic steels, as well as non-ferrous metals and alloys.
A number of portable small-sized crack detectors with converters rotating in a plane

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