Laboratory

Practice technologist  >  Viscosity  > Teaching aids > Laboratory  

What is the dependence of the

quality indicators

     This term is called here to see prices  group of qualitative characteristics of motor oils, to which the mass fraction of active elements, base number and sulphate ash. "Relationship" is based on their chemical-based - content in the oil very specific chemical elements. Among these qualitative characteristics of the mass fraction of active elements can be considered "basic" indicator and base number and sulphate ash - "derivatives", as the latter is formed on the basis of active elements introduced into the oil with additives in the composition of various chemical compounds.

Base number of lubricants determined by the presence of active elements in the oil alkaline character, sulfate ash - sulfatoobrazuyuschih elements.

  Between the content in the oil schёlocheobrazuyuschih / sulfatoobrazuyuschih elements and the value of the base number / sulphated ash, there is a specific quantitative ratio, simply set based on the stoichiometry of the chemical reactions that take place during the analysis. These ratios (ratios) allow recalculation of the values ​​under s.

Knowledge of quantitative relationships between adjacent levels of quality allows a certain degree of "predict" the expected quality of the product during its manufacture.

On the other hand, the results of laboratory determination of related indicators provide an excellent opportunity to assess the reliability of the data, not just when the set of relevant indicators regulated by normative document interval 'of its values, but objectively "lights up" the very possibility of the existence of such a result.

Evaluation of the reliability of the analysis related indicators

     Stoichiometric relationship between base and derived measures so certain and unequivocal, that in fact they are alternative. For example, by ELF Lubrifiants each indicator couple "calcium - base number" is recognized as quite self-sufficient to characterize the properties of detergent oils, and to confirm the quality of oil firms may be determined in any of them.

Obtained by analyzing the values ​​of stoichiometric related quality indicators, expressed in the same units, should ideally be equal. Discrepancies between their values ​​objectively caused only within the error analysis methods.

But in practice this provision is often not observed even in the case of conformity of quality regulatory requirements for products. These facts can be called a "prima facie", in which the results of analysis do not reflect objectively existing stoichiometric relationships between adjacent levels of quality.

Such cases are a signal to the fact that there are certain

non-compliance with the methods of analysis or problem called "human factor". Should not be discarded and such a time as the applicability of the method of analysis of the existing design to the study of specific samples of the products in any case when there are significant differences in the results of the analysis of related indicators should assess these differences and find out the causes of these differences.

For an objective evaluation of the results of laboratory analysis of related indicators of the quality of oils the technique, which uses regulatory uncertainty analysis methods.

        Assess the validity of the essence

         analysis results related indicators

Evaluation of the reliability of the analysis is to compare the difference between the values ​​obtained in the analysis of related indicators, expressed in units of one of the indicators to measure the reliability of F, as the sum of the standard error indicators. As standard error of the proposed indicators coincidence of results of the analysis.

The assessment includes:

• Calculation of the criterion (factor) reliability of F, as the amount of regulatory methods for the determination of errors related indicators:

F = dC1 + DC2 (4.1) Here dC1 and dC2 - error methods for determining the first and second indicators respectively.

• Calculation of K - the difference values ​​of the first and second parameters obtained

analysis:

R = C1-C2 (4.2) Here, C1 and C2 - values ​​of the first and second indicators.

And determining the error values ​​calculated indices should be expressed in terms of one of the adjacent indicators.

Comparison of values of F and K

Reliability condition is the fulfillment of inequalities F> F = K. The values of K are boundary. For comparison, the K value using the absolute value. Inverse ratio of F and K, then F <K, indicative of the unreliability of the analysis results.

Examples assess the validity of the results of the definition of related indicators:

TBN    and    calcium 

We adopted for regulatory convergence error detection results of calcium and base number in the documentation.

Example 1. The analysis oil contains 0.4% calcium and has a base number of 10.5 mg KOH.

We expect reliability criterion F. According to Table 2 - dC1 = 0,02%

From Table 4 - dC2 = 1,0 mg KOH or based on calcium

dC2 = 1,0: 27,5 = 0.036% F = 0.02 + 0,036 = 0,056% difference in the actual

K = 0.4 - 10.5: 27.5 = 0.038%, which is less than the calculated value F. The results of the analysis is correct.

Example 2  Sample oil contains 1.2% calcium and has a base number of 29.36 mg KOH (calcium content in the oil is regulated within 1.02 - 1.27%, and TBN in the range 28.7 - 33.0 mg KOH). The calculation for the above-mentioned method, we find that the reliability criterion F: F = 0,06 + 2,0: 27,5 = 0,133%; the actual difference in the K = 1,2-29,36: 27.5 = 1,2-1,068 = 0.132%. F = K. The calculation for the base number we obtain F = 0,06 x 27.5 + 2.0 = 3.65 mg KOH, K = 1.2 x 27.5 - 29.36 = 3.64 mg KOH, hence F = K. The results can be considered reliable.

Example 3   Sample oil contains 1.03% calcium and has a base number of 32.37 mg KOH / g of oil 1 (calcium content in the oil is regulated within 1.02 - 1.27% and a base number in the range 28.7 - 33 0 mg KOH). Calculations on the base number is set: F = 2,0 + 0,06 x 27.5 = 3.65 mg KOH K = (1.03 x 27.5) - 32.37 = 4.05 mg KOH; F <K. Oil formally comply with the requirements of normative documents, but the result of the analysis of the adjacent pair of indicators objectively unreliable.

     This example is a case of apparent reliability of the results of this type of analysis when quality indicators are normalized specific intervals of their values. Obtained by analyzing the values ​​of indicators fit into intervals established normative document, and the products formally comply with regulations but the analysis results, however, are objectively unreliable, since their values ​​do not reflect the existing connection between indicators of stoichiometric. Oil can not have a real base number of 42.7 mg KOH at a content of 1.03% calcium as the base number of 42.7 mg KOH equivalent to the calcium content of the order of 1.55%. 

Example 4 Oil motor performance has: base number - 6.79 mg KOH per 1 g of an oil, the calcium content - 0.31%. When such data have: dCi = 0,5 mg KOH

dC2 = 0,02x27,5 = 0,55 mg KOH,

F = 0,5 + 0.55 = 1,05

K = 0,31 x27,5 - 6,79 = 1,735

Thus, F < K - indicators comply with the requirements of the normative document but objectively unreliable.

    This case is an example of the apparent validity of the results of this type, when the indicators are normalized on the basis of "no less than the value N», and any excess of N value of the index (excluding the stoichiometric ratio) can be counted as true. Objectively, the oil may not have the base number of 6.78 mg KOH at a content of 0.31% calcium, the calcium content because this is equivalent to about base number of 8.5 mg KOH / 1 g of an oil.

Example 5   The oil has a base number of 4.53 mg KOH and contains 0.19% calcium.

F = 0,1 + 0,02 x 28 = 0.1 + 0.56 = 0.57 K = 0,19x28 -4,53 = 5,32-4,53 = 0,79; F <K. Calculations on the base number we obtain F = 0,0236, K = 0.031, ie, inequality F <K is maintained.

Oil formally corresponds to the requirements of ND, but the result of the analysis of a given pair of indicators objectively unreliable.

Pair of adjacent indicators "calcium - base number in terms of the reliability of the analysis is the most problematic. At the same time, experience has shown that the calcium content in the cooking process more predictable than the base number. As a rule, obtained in the analysis of the results for  calcium content in the finished oil quite match the expected values, calculated according to the formula preparation. Therefore, the calcium content in the oil can serve as a completely objective determinant of a preliminary assessment of the analysis of the expected base number.

Sulphated ash content and

of its constituent elements

According to the analysis of oil contains 0.19% calcium and 0.12% zinc sulphate ash oil is 0.71%.

Error (reproducibility) of the definition of sulphated ash content and the metal is in the standard documentation. We expect F: dC, = 0,05

dC2 = 0,02x3,4 + 0,02x1,25 = 0,093

 F = 0.05+ 0,093 = 0,143

We hope sulfate ash content of metals and find the difference in.

Sulphate Ash = 0,19x3,4 + 0,12x1,25 = 0,796

The actual difference in the K = 0.796 - 0.71 = 0.086

As you can see, F> K. The analysis of the oil content of metals and sulphate ash should be considered correct. 

Allowable differences

between 

dependence of the

quality indicators

As noted above, ideally, the values ​​related quality indicators expressed, in units of any one of them should be the same. Valid [discrepancies between specific values ​​of parameters we consider the sum of: convergence analysis results in accordance with the regulations on the test methods, ie factor (criterion) the reliability of the analysis results related indicators.

     Below are the values ​​of allowable discrepancies between pairs of "calcium - base number", calculated according to regulatory documents:

 - Table 1 - to the calcium content of 0.036 to 1.0%;

 - In the attached figure - to the calcium content of more than 1.0 to 6.0%.

  Table 1

    UP   

Practice technologist  >  Viscosity  > Teaching aids > Laboratory