FIELD OF INVENTION
This invention relates to a device for machining the weld notch of pellini
drop weight test specimen using an abrasive jet machining process.
BACKGROUND OF THE INVENTION
The pellini drop weight test specimen is used for determining the NDTT
(Nil ductility transition temperature) of ferritic steels by using ASTM
standard. This specimen is a rectangular block of test material over
which a weld bead deposited by a hard facing electrode is provided and a
notch is required to be machined exactly at the centre of the weld and
perpendicular to its longitudinal axis. The method of machining of the
notch is normally tedious by following those general but not exhaustive
methods prescribed in the ASTM standard. Adopting the abrasive jet
machining technique for machining the weld notch is a comparatively
easier solution. Hence, the present invention is directed to a device and a
method for machining the notch in pellini drop weight test specimen
using an abrasive jet machining process.
Reference may be made to the following known arts:
US patent 5824880 described an automated drop weight testing machine
consisting of a test fixture and a computer automated pneumatically
powered lift mechanism wherein the desired drop height is attained so as
to enable the drop weight testing.
The present invention is different in a way that, a device has been
fabricated with a nozzle locator using which the weld notch of a pellini
drop weight test specimen can be machined using an abrasive jet
process.
US patent 5861608 discloses a method of making precision notches in
tubular specimen according to API specification using an electrical
discharge machining process, whereas the present invention relates to a
fabricated device having a nozzle locator used for machining of weld
notch in pellini drop weight test specimen as per ASTM standard with
the help of an abrasive jet cutting process.
US 4948933 is directed to a portable electrode arc cutting tool for cutting
internal and external precision notches in a work surface using the
concept of electrical discharges between the electrode and the work
surface, whereas the present invention relates to a fabricated device for
machining a weld notch in pellini drop weight test specimen using an
abrasive jet cutting technique.
US patent 4806216 pertains to an apparatus and method for the
selective electrochemical polishing of a lateral tip of a deep longitudinal
notch in a work piece used to test crack initiation properties of materials.
The present invention is different in a way that a device is fabricated for
machining the weld notch of pellini drop weight test specimen in an
abrasive jet cutting process.
US patent 5042338 relates to a method and apparatus for cutting a slit
notch in a pattern piece during the cutting of the pattern piece from work
material consisting of a single sheet or a lay-up of sheets material. The
present invention is different in the sense that a fabricated device is
provided for machining the weld notch in pellini drop weight test
specimen using an abrasive jet machining process.
US patent 6806435 is related to a small hole electric discharge machine
drill which is provided with a depth-specific processor and a tillable unit
operable in fluid. On the other hand, the instant invention deals with a
device for machining the weld notch of a pellini drop weight test using an
abrasive jet cutting process.
OBJECTS OF THE INVENTION
The primary object of the present invention is to provide a device for
machining the weld notch of pellini drop weight test specimen.
Another object of the present invention is to provide a device for
machining the weld notch of pellini drop weight test specimen which is
simple in construction.
Still another object of the present invention is to provide a device for
machining the weld notch of pellini drop weight test specimen which is
efficient.
SUMMARY OF THE INVENTION
The instant invention provides a device comprising of two parts used for
holding the pellini drop weight test specimen so as to further carry out
the machining of the weld notch using an abrasive jet machining
process.
The first part comprises of a horizontal base which is a plate resting on
four support pins placed below each of the corners of the plate. This
horizontal base plate has a centrally machined hole for the purpose of
the abrasive jet to escape when it machines the weld bead deposited on
the specimen.
The second part comprises of a milled side support block having two
coaxially drilled holes on the two side walls of the side support block and
through these holes two tightening screws are inserted for securely
clamping the test specimen. There is a nozzle locator which is small strip
with a slot in its top. This nozzle locator is tack welded to the centre of
the length of side support block. The side support block is tack welded to
the horizontalf base plate at select locations to ensure rigidity of the
unit.
The pellini drop weight test specimen is taken and an adhesive mould is
cast on the surface of the specimen containing the weld bead in such a
way that, the weld is entirely immersed in the mould and the mould
should cover the entire length and width of the test specimen. The
proposed device is placed on the work table of the abrasive jet machine.
The test specimen is placed in a proposed device so that the specimen
surface parallel to the other surface containing the weld is butted against
the side support block and the tightening screws are used for firmly
securing the test specimen in such a way that the centre of the weld
bead deposited in the specimen coincides with the nozzle locator strip in
the side support block. Then the cutting nozzle is brought to the nozzle
locator and is moved away from it without changing the height of nozzle
from the work table of the abrasive jet machine and in the same plane
containing the nozzle locator. The abrasive jet is turned on with the
nozzle at this place and the nozzle is slowly moved till the notch of
required depth is machined. The control of depth of machining of the
notch can be achieved by visually looking for the disappearance of the
mark that is initially made on the cast adhesive mould based on the
depth of the notch required.
STATEMENT OF INVENTION
According to this invention, there is provided a device for machining the
weld notch of pellini drop weight test specimen comprising of a base
plate with a plurality of supporting pins and a hole supporting a side
support block accommodating pellini drop weight test specimen.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent
from the ensuing description when read in conjunction with the
accompanying drawings and wherein:
Fig. 1 shows : the horizontal base plate of the device
Fig. 2 shows: the side support block of the device.
Fig. 3 shows: complete set up of the device.
Fig. 4 shows: the pellini drop weight test specimen.
DETAIL DESCRIPTION OF THE INVENTION WITH REFERENCE TO
THE ACCOMPANYING DRAWINGS:
The present invention discloses a device for machining the weld notch of
pellini drop weight test specimen. The device comprising of two parts.
The first part of the proposed device comprises of a horizontal base plate
(1) to which are attached four supporting pins (2) in its bottom, one each
for the four corners of the base plate. Further, there is a hole (3) which is
bored in the centre of the base plate. Over the top surface of the base
plate (4), the side surface (12) of the pellini drop weight test specimen
rests.
The second part comprises of milled side support block (5). In the two
side walls (6) of the side support block (5), two coaxial holes are provided.
Two tightening bolts (7) are inserted through these two coaxially drilled
holes in the side walls (6). Again, there is a nozzle locator (8) which is a
small strip with a slot in its top. This nozzle locator is tack welded to the
top surface of the side support block in such a way that it lies in the
centre of the length of the side support block (5). The specimen surface
(10) is butted against the inner surface of the side support block (9). The
two tightening bolts (7) come into firm contact with the two side surfaces
(11) of the test specimen. The side support block (5) is placed on the
horizontal base plate (1) and tack welds are placed at the four corners of
the side support blocks that comes into contact with the horizontal base
plate (1).
The pellini drop weight test specimen is taken and an adhesive mould is
cast over the surface of the test specimen containing the weld bead. The
adhesive mould should fully immerse the weld bead (13) of the specimen
and the length and width of the adhesive mould should cover the entire
length and width of the specimen surface containing the weld bead (13).
The test specimen after proper moulding is then placed in the device in
such a way that the specimen surface (10) rests against the inner surface
(9) of the side support block (5) and is firmly secured by the two
tightening bolts (7). The specimen surface (12) is to be seated against the
top surface (4) of the horizontal base plate. The centre of the weld bead
(13) should be in-line with the nozzle locator (8) of the side support block
(5). The cutting nozzle of the abrasive jet machine is brought onto the
nozzle locator (8) of the side support block. Thereafter, the cutting nozzle
of the abrasive jet machine is moved away from the nozzle locator but in
the same vertical plane containing the nozzle locator and perpendicular
to the longitudinal axis of the weld bead (13) of the test specimen,
without altering the height of the cutting nozzle from the work table of
the machine. Then, the abrasive jet is turned on and is slowly moved
towards the nozzle locator (8) in the same vertical plane in which it was
moved earlier and the nozzle is stopped well before reaching the nozzle
locator so as to maintain the required depth of the notch in the weld
bead of the specimen. During machining of the notch by the abrasive jet,
the spent jet after machining will be expended through the bored hole (3)
of the horizontal base plate (1). Based on the depth of the notch that is to
be machined in the test specimen, a paint mark is made on the thickness
surface of the cast adhesive mould and it shall be in centre of the entire
length of the cast adhesive mould. The abrasive jet can then be slowly
moved towards the nozzle locator (8) and can be stopped when the paint
mark is reached by the abrasive jet. Thereafter, the abrasive jet is
stopped and the weld notch machining will be completed to the required
depth.
It is to be noted that the present invention is susceptible to
modifications, adaptations and changes by those skilled in the art. Such
variant embodiments employing the concepts and features of this
invention are intended to be within the scope of the present invention,
which is further set forth under the following claims:-
WE CLAIM:
1. A device for machining the weld notch of pellini drop weight test
specimen comprising of a base plate with a plurality of supporting
pins and a hole supporting a side support block accommodating
pellini drop weight test specimen.
2. A device as claimed in claim 1, wherein said side support block
comprising of atleast two side walls with atleast two coaxial holes
inserted with two tightening bolts.
3. A device as claimed in claim 1 or 2, wherein the side support block
is connected to a nozzle locator on its top surface in which the
specimen surface is butted against the inner surface of the side
support block.
4. A device for machining the weld notch of pellini drop weight test
specimen substantially as herein described with reference to the
accompanying drawings.

This invention relates to a device for machining the weld notch of pellini
drop weight test specimen comprising of a base plate with a plurality of
supporting pins and a hole supporting a side support block
accommodating pellini drop weight test specimen.