FIELD OF THE INVENTION
The present invention relates to testing of materials in particular hardness testing of
materials at elevated temperatures. More particularly, in particular, the invention
relates to an improved universal testing machine (UTM), capable of performing
tension and compression test at high temperature to provide an accurate hot-
hardness values of a test specimen. The invention relates to a method to perform
and evaluate Brinell hardness testing of a specimen at elevated temperature.
BACKGROUND OF THE INVENTION
Hardness testing is one of the important testing to assess the quality of material,
heat treatment, to determine wear and tear properties. Hot hardness testing is very
useful to assess the usability of products exposed to high temperature applications.
Hot hardness values are very important for products to be used in high temperature
service to study their strength at high temperature, hot-erosion, galling, abrasive
wear, and sliding wear.
Hot working process is extensively used in the fabrication of power plant
components. To establish the operating temperature for hot working process for a
particular material, hot hardness value is required to be taken into consideration,
since it provides information regarding the degree of hardening at the operating
temperature. Also Hardfacing weld overlay are used in components subjected to
high abrasion at high temperature for example, valves seat ring, and coal mill
nozzle. To determine the upper limit of usability of the components, the hot
hardness values are used. It is also used to evaluate the consumable used for weld
overlay applications.

Universal testing machine is capable of performing tension and compression testing
of materials. The prior art Universal testing machine systems use feedback control
closed loop load cell and a displacement transducer coupled with a computer
apparatus to monitor and apply highly accurate tensile and compressive force on the
sample to be tested.
U.S.Pat. No. 4435976 describes use of a load cell which has a feedback loop to apply
forces accurately to test specimens
U.S.Pat. No. 8132447 B2 describes use of a tension and compression machine to
carry out plurality of tests including various hardness testing.
U.S. Pat. No. 4275966 describes method and apparatus for measuring magnitude of
hardness test indentations separately using a light source.
Brinell hardness testing at room temperature is a well established standard for
hardness testing procedure both at national and international level (IS 1500/ISO
6506). However, national/international standard test procedure is not available to
determine the Brinell hardness of a material at elevated temperature, because of
which a standard hot-hardness tester is not available in the prior art. And, even if it
would be available, it must be highly expensive.
The current invention redresses the above difficulty by suitably increasing the
functionality of UTM to carry out plurality of tests both at room and high
temperature.
OBJECTS OF THE PRESENT INVENTION
Accordingly, it is an object of this invention to propose an improved universal testing
machine (UTM), capable of performing tension and compression test at high
temperature to provid an accurate hot-hardness values of a test specimen.

Another object of this invention is to propose an improved universal testing machine
(UTM), capable of performing tension and compression test at high temperature and
to provid an accurate hot-hardness values of a test specimen which uses advanced
electronics and sensing devices to monitor and control the rate of loading, force, test
temperature, soaking time and dwell time of the specimen during testing.
A still another object of this invention is to propose a method to perform and
evaluate Brinell hardness testing of a specimen at elevated temperatures in the
improved universal testing machine.
A further object of this invention is to propose an improved universal testing
machine (UTM), capable of performing tension and compression test at high
temperature to provid an accurate hot-hardness values of a test specimen., in which
a force device applies high accurate compressive forces across a range starting from
0.4% of the maximum capacity of a load cell corresponding to accurate force values
of Brinell hardness testing.
A still further object of this invention is to propose an improved universal testing
machine (UTM), capable of performing tension and compression test at high
temperature to provide an accurate hot-hardness values of a test specimen., which
uses an atmosphere controlled furnace to prevent oxidation of samples at high
temperature during testing.
Yet further object of this invention is to propose a method to perform and evaluate
Brinell hardness testing of a specimen at elevated temperatures in the improved
universal testing machine, in which nitrogen gas is continuously purged into the
furnace at atmospheric pressure during testing to displace and prevent ingress of
oxygen at high temperature.

SUMMARY OF THE INVENTION
The present invention provides a method of high temperature testing a test
specimen in a testing machine, comprising the steps of:
- fixing a device to an UTM along with sample to be tested and raising the
temperature using a split furnace.
- controlling a force applied on the test specimen via a control system; and
- measuring indentation diameter using a Brinell microscope or using an
automated indentation measuring system having auto focus and measuring
systems.
The present invention further provides an improved universal testing machine
(UTM), capable of performing tension and compression test at high
temperature to provide an accurate hot-hardness values of a test specimen,
the universal testing machine (UTM) comprising a split furnace to raise
temperature of a specimen under hot harness test; an indentor holder
attached to pull rods of the UTM through a first threaded coupling; a
specimen anvil attached to bottom of said pull rods via a second threaded
coupling; a cross head assembly having a cooling circuit to restrict heat
transfer to a load cell disposed on said cross head assembly; and at least one
tungsten carbide ball attached to said pull rods for Brinell hardness testing of
the specimen at high temperature;
The improvement is characterized in that the specimen anvil, and the indentor
holder constituting a holding device is modified to be a separately mountable
device on the UTM to allow conducting a plurality of testing of specimen, in
that the specimen anvil is made from tool steel and machined flat
corresponding to the dimension of the pull rods, in that the stem of the
indentor holder is machined to a dimension to allow attachment with the pull
rods including an accurate alignment of the anvil and the indentor holder, and

in that means for continuous purging of nitrogen gas into the split furnace to restrict
oxidation of the specimen under high temperature, is provided.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS:
Figure 1 View of a compression-tension Universal testing machine(UTM) according to
the preferred embodiment of present invention.
Figure 2 Flowchart for performing hot-hardness testing in an improved Universal
testing machine.
Figure 3 View of a Brinell testing using a standard ball according to prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:
Fig. 1 shows a known high accurate tension compression Universal testing machine
(UTM) (1) having a split furnace (8) to raise the temperature of a testing sample (4)
meant for hot-hardness testing. An indenter holder (6) and a standard tungsten
carbide ball 5 is used for Brinell hardness testing at high temperature is attached to
pull rods 2 of the UTM (1) through threaded couplings (9). An anvil (3) is attached
to bottom pull rods (2) of the machine (1), through threaded couplings (9). A water
cooling circuit (7) is provided at the upper and lower cross heads (10) of the UTM
(1) to avoid heat transfer to a load cell, which is placed either at the top/bottom
cross head.
If the split furnace (8) does not have provisions to maintain a controlled atmosphere
to contain oxidation at high temperature, then a comprising provisions must be
made at the top and bottom of the furnace (8) to allow for continuous nitrogen gas
purging through external an gas supply to avoid oxidation of the samples by
displacing oxygen during testing.

The high accurate load cell (not shown in the diagram) is located in the crosshead
assembly 10 to measure the forces applied on the sample. The upper and lower
crosshead 10 is driven by a servo electric motor(not shown in the diagram) through
a spindle attached to an UTM frame assembly (11) of the UTM machine, that
enables precise control of the displacement of upper and lower crosshead (10). The
displacement of the grips are accurately measured by an optical encoder system
(not shown in the diagram) and the feedback signal of the load cell and the optical
encoder system are fed to an electronics system coupled to the computer apparatus.
Since the above mentioned load cell, displacement measuring system, servo electric
motor, electronics and computer are all part of a known Universal testing machine,
the details of those, are not given in the present invention.
Since the device for hot-hardness testing machine is of demountable type, a plurality
of tests can be done within a single machine without affecting the regular tensile
compression testing. Flowchart for performing the hot-hardness in known UTM 1 is
shown in Figure 2. The Specimen anvil (3) made from a tool steel should be
machined flat to the dimensions required to fit inside the split furnace (8). After
mounting of the specimen anvil (3) in the pull rods (2) of the UTM 1, the flatness of
the anvil (3) is checked by using a known spirit level. The stem of the indenter
holder 6 has to be machined suitable enough to fit in the pull rods 2. Once the
alignment of the indenter holder (6) and flatness of specimen anvil (3) is
established, the sample (5) to be tested can be loaded on to the specimen anvil (3)
and the split furnace (8) can be closed. In case of non availability of the atmospher
controlled furnace (8), a continuous flow of Nitrogen gas can be purged inside the
split furnace (8) before switching on the furnace (8). The volume of nitrogen gas to
purge inside the furnace (8) depends on the volume of furnace (8) chosen for
testing. After the temperature in the split furnace (8) reaches the desired value and
after soaking the sample (5) for 10-15 minutes, depending upon the diameter of
send tungsten carbide ball indenter (5), the compressive load of F=30d2
Eqn(l)for steel samples should be applied to the sample (5) kept on the
specimen anvil (3) inside the split furnace (8) and hold for 10-15 sec. For Brinell

hardness testing at room temperature, depending on the accuracy of the load cell,
diameter of the tungsten carbide ball (5) can be chosen between 1mm to 10 mm
and the corresponding force of F=30d2, where d=diameter of the tungsten carbide
ball.
After load removal, the sample (5) should be allowed to cool to room temperature
and the diameter of the impression can be measured using the automatic
indentation measuring system, where Brinell hardness number is given by,

Where D is the indenter ball diameter, d is the indentation diameter and F is the
applied load in kg.

WE CLAIM :
1. An improved universal testing machine (UTM), capable of performing tension
and compression test at high temperature to provide an accurate hot-
hardness values of a test specimen., the universal testing machine (UTM) (1)
comprising a split furnace (8) to raise temperature of a specimen (4) under
hot harness test; an indentor holder (6) attached to pull rods (2) of the UTM
through a first threaded coupling (9); a specimen anvil (3) attached to bottom
of said pull rods (2) via a second threaded coupling (9); a cross head
assembly (10) having a cooling circuit (7) to restrict heat transfer to a load
cell disposed on said cross head assembly (10); and at least one tungster
carbide ball (5) attached to said pull rods (2) for Brinell hardness testing of
the specimen at high temperature;
The improvement is characterized in that the specimen anvil (3), and the
indentor holder (6) constituting a holding device is modified to be a
separately mountable device on the UTM (1) to allow conducting a plurality of
testing of specimen, in that the specimen anvil (3) is made from tool steel
and machined flat corresponding to the dimension of the pull rods (2), in that
the stem of the indentor holder (6) is machined to a dimension to allow
attachment with the pull rods (2) including an accurate alignment of the anvil
(3) and the indentor holder (6), and in that means for continuous purging of
nitrogen gas into the split furnace (8) to restrict oxidation of the specimen
under high temperature, is provided.
2. The improved machine as claimed in claim 1, wherein the cross head
assembly (10) consisting of an upper and lower cross head, is controllably
driven by a servo electric motor through a spindle attached to a frame
assembly (11) of the UTM (1), wherein the load cell is enabled to measure
the forces applied to the specimen (4) during testing, wherein displacement
of the anvil grips on the specimen (4) is measured by an optical encoder

system, and wherein the feedback signals from the load cell and the optical
encoder system are fed to an electronic circuit coupled to a display device.
3. A method to perform and evaluate Brinell hardness testing of a specimen at
elevated temperatures in the improved universal testing machine, the method
comprising the step of :-
- fixing a device to an UTM along with sample to be tested and raising the
temperature using a split furnace.
- controlling a force applied on the test specimen via a control system; and
- measuring indentation diameter using a Brinell microscope or using an
automated indentation measuring system having auto focus and measuring
systems.

4. The method as claimed in claim 3, wherein the diameter of the tungsten
carbide ball (5) can be selected between 1 mm to 10 mm, wherein a
compressive force of F=30d2 is applied on the specimen inside the split
furnace (8), and wherein xd' is the diameter of the tungsten carbide ball.
5. The method as claimed in claim 3, wherein the specimen after removal of
load, is allowed to cool to room temperature and the diameter of the
impression is measured in Indentation measuring system, where the Brinell
hardness number is determined by in which 'D' is the
indentor ball diameter 'd' is the indention diameter, and 'F' is the applied load
in KG.

ABSTRACT

The invention relates to an improved universal testing machine (UTM),
capable of performing tension and compression test at high temperature to
provide an accurate hot-hardness values of a test specimen, the universal
testing machine (UTM) (1) comprising a split furnace (8) to raise temperature
of a specimen (4) under hot harness test; an indentor holder (6) attached to
pull rods (2) of the UTM through a first threaded coupling (9); a specimen
anvil (3) attached to bottom of said pull rods (2) via a second threaded
coupling (9); a cross head assembly (10) having a cooling circuit (7) to
restrict heat transfer to a load cell disposed on said cross head assembly (10);
and at least one tungster carbide ball (5) attached to said pull rods (2) for
Brinell hardness testing of the specimen at high temperature; The
improvement is characterized in that the specimen anvil (3), and the indentor
holder (6) constituting a holding device is modified to be a separately
mountable device on the UTM (1) to allow conducting a plurality of testing of
specimen, in that the specimen anvil (3) is made from tool steel and
machined flat corresponding to the dimension of the pull rods (2), in that the
stem of the indentor holder (6) is machined to a dimension to allow
attachment with the pull rods (2) including an accurate alignment of the anvil
(3) and the indentor holder (6), and in that means for continuous purging of
nitrogen gas into the split furnace (8) to restrict oxidation of the specimen
under high temperature, is provided.