Burnout of Polymeric Binder in Sinter Metallurgy

Sinter products can be produced in many different ways. One of the most common methods is mixing a fine powder with an organic binder. From this mixture, a so-called green body with a specific geometry can be shaped, for example, by means of cold-isostatic pressing.

The first step of subsequent production process is the burnout of polymeric binder by thermal treatment (binder burn-out).

The speed of this binder burn-out must be controlled very well. If the speed is too high, then micro-cracks are produced in the green body, because the created gases do not have enough time to diffuse out from the inside. Otherwise, if the speed of the binder burn-out is too slow, then much time is consumed, leading to an increase in production effort.

The experience clearly demonstrates that the best temperature profile for the burnout of the binder shows a constant mass loss rate. Therefore, the aim of investigation of this binder burn-out is the determination of a set of temperature profiles for various levels of constant mass loss rate.

This problem can be solved experimentally by various measurements, executed under the condition of a constant mass loss rate. Much more universally and also much cheaper is the combination of a series of measurements, executed with constant but different heating rates, with the kinetic analysis. This way will be demonstrated in the following:


Measurements
InstrumentNETZSCH TG 209 C Iris
Temperature range/°CRT to 800
Heating rates/(K/min)0.01 to 10
AtmosphereN2, 20 ml/min
Samples mass/mg40 to 50

TGA measurements of their fit by a multiple step reaction
Using the presented model it is possible to approximate all measurements with a high quality. The higher the fit quality, the more confident the predictions are.

Fig.1. Kinetic model for measured TG data for decomposition of polymer binder.

Temperature profile for a mass loss rate of 0.5%/min, estimated on the basis of TGA measurements. It is very easy and fast to determine the temperature profile for another value of mass loss rate.

Fig.2. Calculated temperature program (red) for RSM (rate controlled mass loss) with constant mass loss of 0.5%/min

Temperature Program for a Mass Loss Rate of 0.5%/min

#Temperature iCScan rate (K/min)Total time min
150.00.00
2142.710.009.26
3152.59.7310.27
4156.22.0412.09
5165.83.0315.84
6172.73.6517.73
7179.73.6519.62
8186.11.8423.20
9187.20.3026.84
10188.80.3231.60
11204.90.5064.22
12211.10.6473.85
13218.60.7983.39
14226.70.8792.70
15237.41.13102.19
16249.91.39111.23
17265.51.62120.85
18289.72.48130.61
19329.44.08140.36
20369.64.28149.74
21381.91.40158.55
22389.20.77168.04
23402.31.35177.72
24426.22.37187.82
25454.95.36192.91
26490.69.89196.53
27600.310.00207.49

This temperature program can be exported as an ASCII file and transferred in any program.