# Determination of evenness of mechanical strength for graphite electrodes Ⅱ

The constant *B*=*mX-Y** *; the constant *t*_{0}=exp*B** *;

After the above deformation, the corresponding data of the 2015 product is converted (see Table 2), get the graphite electrode products here. According to formula (6) into the converted value in Table 2, the product in 2015 corresponds to the Weibull modulus:

*m*=14.3183; *B*=38.1340; *t*_{0}=3.6424x10^{16},

So the specific form of the Weibull model is:

The same process, the 2016 product corresponds to the Weibull modulus:

*m*=9.9548; *B*=27.3338; *t*_{0}=7.4288x10^{11},

So the specific form of the Weibull model is

When it is only used to determine the uniformity of the mechanical strength of graphite products, it is enough to calculate the *m* value, and the *B* value and *t*_{0} value do not need to be calculated.

From the comparison of the m-values of the 6FG7 high-powered graphite electrodes of the same specification produced in 2015 and 2016, it can be seen that *m*=14.3183 in 2015 and *m*=9.9548 in 2016. In 2016, the uniformity of the mechanical strength of the product deteriorated year-on-year.

Using the above formula, when the cumulative strength failure probability *F*(*t*) is specified, it is also easy to calculate the corresponding strength value *t*_{0}. In 2015, when the products were used in steel plants, 3% of the products were cracked, chipped, and broken at the bottom of the hole, etc. accident, that is, the cumulative strength failure probability *F*(*t*)=3%, then the corresponding flexural strength* t *is:

Similarly, for the 2016 product, when the designated cumulative strength failure probability *F*(*t*)=3%, the corresponding flexural strength* t *is:

It can be seen from the above comparison that although the average flexural strength of the product in 2016 is 14.9 MPa higher than the average of 13.9 MPa in 2015, when the cumulative strength failure probability of the product is 3%, the corresponding flexural strength of the product in 2016 is 10.9690 MPa. The annual rate is 11.2399MPa. That is to say, when the products are used in steel plants in 2016, the probability of accidents such as cracking, falling blocks, and hole bottom breaking is expected to be greater than that of the products in 2015. Comparing the minimum flexural strength values of 12.4 MPa and 11.8 MPa in 2015 and 2016 with the corresponding calculated values of 11.2399 MPa and 10.9690 MPa for the strength failure probability of 3%, the calculated values have exceeded the measured data range, but this is the advantage of the probability analysis method, and you can compare the data that has not been tested.

For graphite electrodes with higher quality requirements and electrodes for special users, calculate the corresponding flexural strength* t* when the cumulative strength failure probability of the graphite electrode is *F*(*t*)=2%～3%. For the corresponding strength Electrodes with too small values should be processed at a lower level or selected by ultrasound to eliminate products with too low sound velocity. Graphite electrode used in steel-making experiment, can also be *F* (*t*) as the electrode crack, metal shed and broken at the bottom of the bore, damages the ratio, the number of accident intensity so that you can get graphite electrode accidents, the corresponding relationship between flexural strength of the electrode of accidents in use, can calculate the corresponding to the flexural strength; In turn, the accident rate in the use of graphite electrode can be predicted based on the flexural strength.

**Judgment criteria for the uniformity of mechanical strength of graphite electrode products**

The author conducted a large number of data calculations based on the flexural strength data, and obtained the criterion for the uniformity of the mechanical strength of graphite electrodes (Table 3): The greater the *m* value, the better the uniformity of the mechanical strength of the product; the smaller the *m* value, the worse the uniformity of the mechanical strength of the product. Generally speaking, when the value of *m* ≥ 10, the uniformity of the mechanical strength of the product is better; when the value of *m* < 10, the uniformity of the mechanical strength of the product is worse. In essence, the uniformity of mechanical strength reflects the uniformity of the internal structure of graphite electrode products. However, it should be noted that the uniformity of mechanical strength is not the same thing as the size of mechanical strength. It discusses the degree of dispersion of mechanical strength data from the perspective of probability.

The *m* value and the flexural strength value corresponding to the strength failure probability can be managed as the internal control strength index of the carbon production enterprise's product to facilitate the improvement of production technology and the stability and improvement of product quality, talk with us for more technical guidance.

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