Caf Digital Imaging
page 24
MF36
Four pieces of each wire type are required, the samples are prepared as follows:
Cut a piece of wire 30mm in length.
Using a pair of pin nose pliers, form one end of the wire into a coil so that when standing on a
flat surface it supports a 12mm vertical column of wire. See fig 19.
The samples are positioned on the sample tiles, which are placed on the sample carrier as shown
in fig 20.
5.4.3. Test Procedure.
The calibration test is based on BS 1016:Part 113:1995 ISO 540:1995, Methods for Analysis and
testing of Coal and Coke. Conduct the test as follows:
5.4.3.1 Turn the furnace on, adjust the control instrument set point to 815
°
C (1499
°
F) and allow the
furnace to stabilise.
As the furnace warms up prepare the sample carrier and samples (see section 5.4.2.) and load
into the work tube (see section 4.4.). Close the door and clamp securely to seal the work tube.
5.4.3.2 When the furnace has stabilised at 815
°
C (1499
°
F) run a CAF test on a ramp rate of 7
°
C/min
(12.6
°
F/min) to reach a maximum temperature of 1600
°
C (2912
°
F). During the test maintain an
‘oxidising’ atmosphere in the work tube (see section 4.5.).
5.4.3.3 A digital image sequence of the samples is required as they pass through their melt temperatures
to enable the melting sequence to be assessed after completion of the test. Set the digital image
software to record at 1
°
C (2
°
F) temperature intervals, starting at 20
°
C (35
°
F) below the expected
Gold melt point and finishing at 1600
°
C (2912
°
F) (see section 4.5.).
5.4.4. Interpretation Of Results.
5.4.4.1.Definitions:
The “
individual melt temperature
” of a wire sample is the temperature at which the wire
sample, having fallen over onto the sample tile, melts and forms one or more stable “balls” of
molten material.
The “
mid melt temperature
” of a set of four wires is the average of the lowest and highest of
the four individual measured melt temperatures.
The “
spread
” of melt temperature is the difference between the highest and lowest of the four
individual melt temperatures.
The “
actual
” melt temperature is a fixed value for each wire sample type.
5.4.4.2.Documentation of results.
Record the individual melt temperature of each wire sample using the CAF Test Software (see
section 4.5.) and print out the results using the report sheet. See fig 18.
For each wire type work out the mid melt temperature and the spread.
5.4.4.3.Temperature Limits.
The following limits apply with respect to the melt (ball) temperatures of the wire samples.
Furnace in °C
Furnace in °F
Actual Gold melt (ball) temp.
1063
°
C
1945
°
F
Min. permissible Gold melt (ball) temp.
1057.5
°
C
1935
°
F
Max. permissible Gold melt (ball) temp.
1068.5
°
C
1955
°
F
Actual Palladium melt (ball) temp.
1554
°
C
2829
°
F
Min. permissible Palladium melt (ball) temp.
1548.5
°
C
2819
°
F
Max. permissible Palladium melt (ball) temp.
1559.5
°
C
2839
°
F
Max. permissible spread (both wire types)
11
°
C
20
°
F
