EP2475795A1

EP2475795A1 - Method for determining the machinability of a compacted graphite iron

Info

Publication number: EP2475795A1
Application number: EP10815695A
Authority: EP
Inventors: Kerstin Richnau; Fredrik Wilberfors; Johan ESBJÖRNER
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2009-09-08
Filing date: 2010-09-07
Publication date: 2012-07-18
Also published as: WO2011031211A8; CN102612568A; RU2509820C2; BR112012004790A2; IN2012DN01724A; SE1050470A1; CN102612568B; RU2012113744A; SE534626C2; WO2011031211A1

Abstract

Method for determining the cuttability of a compact graphite iron, characterised by the steps of: - arriving at a relationship between cuttability and contents of carbide-stabilising substances in compact graphite iron, which relationship is arrived at empirically from measured cuttability and measured contents of carbide-stabilising substances in a plurality of test pieces of compact graphite iron; - providing a compact graphite iron; - determining the contents of carbide-stabilising substances in the compact graphite iron provided; - determining a value for the cuttability of the compact graphite iron provided on the basis of the relationship and contents of carbide-stabilising substances in the compact graphite iron provided.

Description

Method for determining the machinability of a compacted graphite iron TECHNICAL FIELD

The present invention relates to a method for determining the cuttability of a compact graphite iron according to the preamble of claim 1.

BACKGROUND

The vehicle industry faces continually increasing demands for more efficient engines with less emissions. One way of achieving cleaner combustion is by using a higher combustion pressure in diesel engines, but this entails more exacting requirements for the material of cylinder blocks and cylinder heads. The strength characteristics of the traditionally dominant material, grey iron, are not sufficient to cope with the loads to which the material in future generations of diesel engines will be subject. Many operators within the vehicle industry are therefore changing to using compact graphite iron in diesel engines instead. Compact graphite iron, referred to as CGI for short, has at least 45% - 75% more rigidity than and double the fatigue strength of grey iron. Engine components made of CGI are currently already being produced by various vehicle manufacturers.

Making compact graphite iron involves the use of scrap material containing substances which result in carbides in the material, so-called carbide- stabilising substances. Examples of such substances in compact graphite iron are molybdenum (Mo), chrome (Cr) and manganese (Mn). The carbide- stabilising substances chrome and manganese occur naturally in the scrap material which is melted down and used in making compact graphite iron. Molybdenum is an alloy substance added to give CGI greater strength at high temperatures. A problem in using compact graphite iron in production is that the carbides formed by chrome, manganese and molybdenum reduce its cuttability. High contents of carbide-stabilising substances therefore entail low cuttability and result in slow production and high machining costs. Moreover, compact graphite iron with low contents of carbide-stabilising substances is expensive in that cleaner scrap has to be used, resulting in a high procurement cost for compact graphite iron.

A problem in using compact graphite iron in production is to provide CGI which has good cuttability at favourable cost.

An object of the invention is therefore to provide a method for easily and reliably determining the cuttability of compact graphite iron on the basis of its contents of carbide-stabilising substances.

A further object of the invention is also to provide a method for classifying CGIs for optimum cuttability at as low a cost as possible.

SUMMARY OF THE INVENTION

According to the invention this object is achieved by a method for

determining the cuttability of a compact graphite iron, characterised by the steps of:

- arriving at a relationship between cuttability and contents of

carbide-stabilising substances in compact graphite iron, which relationship is arrived at empirically from measured cuttability and measured contents of carbide-stabilising substances in a plurality of test pieces of compact graphite iron;

- providing a compact graphite iron;

- determining the contents of carbide-stabilising substances in the compact graphite iron provided;

- determining a value for the cuttability of the compact graphite iron provided on the basis of the relationship and contents of carbide- stabilising substances in the compact graphite iron provided;

The method makes it possible for the cuttability of an existing compact graphite iron to be determined quickly and reliably, with consequent great advantages in industrial production of parts made of compact graphite iron by cutting machining in that the method makes it easy to select compact graphite irons which are optimum for production purposes. The method therefore contributes to very cost-effective production in cutting machining of compact graphite iron.

The method may also comprise the steps of

- providing at least a first predetermined comparison value for cuttability of compact graphite iron;

- classifying the cuttability of the compact graphite iron provided by comparing the value for its cuttability with the predetermined comparison value.

According to an alternative, the cuttability of the compact graphite iron provided is classified as suitable for production if the value for the cuttability of the compact graphite iron provided is higher than the predetermined comparison value.

According to an alternative, the method comprises the step of:

- providing at least a second comparison value for cuttability of compact graphite iron, whereby the cuttability of the compact graphite iron provided is classified as very suitable for production if the value for its cuttability is greater than the second comparison value.

Cuttability is with advantage defined as tool life in chip-breaking machining of compact graphite iron, preferably milling.

Tool life is with advantage defined as maximum oblique wear of the tool. The relationship for cuttability is based with advantage on a model which comprises relationships between contents of carbide-stabilising substances in compact graphite iron. According to an alternative, the model is based on linear relationships, cross- relationships and quadratic relationships between contents of carbide- stabilising substances.

According to a first embodiment, the relationship arrived at is:

Tool life in minutes = 27 - 50^*Mo - 186*Cr + 127^*Mn - 146*Mn² +

146*Cr^*Mo + 151^*Cr^*Mn.

Cuttability expressed as tool life can thereby be determined very accurately through being based on a large number of relationships between carbide- stabilising substances.

According to an alternative, the model is based on linear relationships between contents of carbide-stabilising substances in compact graphite iron. According to a second embodiment, the relationship arrived at is:

Tool life in minutes = 57.20 - 18.46*Mn - 80.90^*Cr -38.98*Mo.

This relationship is easy to use through being based on a linear model. According to a third embodiment, the relationship arrived at is:

Tool life = 1 - (0.32 + 0.21 )^*Mn - (1.41 + 0.39)^*Cr - (0.68 + 0.31)* Mo, where tool life is standardised.

The fact that this relationship is standardised eliminates external sources of error, e.g. due to varying machining requirements or systematic measuring error. The carbide-stabilising substances preferably comprise at least manganese, molybdenum and chrome.

With advantage, the contents of carbide-stabilising substances in the compact graphite iron are:

Mn: 0.1 - 0.8 wt%, Cr 0 - 0.2 wt%, Mo 0 - 0.3 wt%.

Preferably, the contents of carbide-stabilising substances in the compact graphite iron are:

Mn: 0.4 - 0.8 wt%, Cr 0 - 0.2 wt%, Mo 0 - 0.3 wt%.

DESCRIPTION OF DRAWINGS

Figure 1 : Schematic illustration of the location for measurement of tool wear expressed as oblique wear.

Figure 2: Schematic illustration of a test piece used in the method according to the invention. Figure 3: Coefficient diagram illustrating relationships between carbide- stabilising substances and tool life by cross-relationships and quadratic relationships.

Figure 4: Coefficient diagram illustrating statistically relevant relationships between carbide-stabilising substances and tool life by cross-relationships and quadratic relationships.

Figure 5: Diagram illustrating R² and Q² values for relationships according to Figure 4. Figure 6: Diagram comparing tool life as calculated by the equation according to a first embodiment of the invention and measured average values for tool life for sample materials. Figure 7: Diagram comparing tool life as calculated by the equation according to a third embodiment of the invention and measured standardised average values for tool life for sample materials.

DEFINITIONS

The expression "cuttability" in this patent application means a measure of how easy or difficult a material is to machine with chip-breaking tools. The cuttability of a material is with advantage expressed as tool life, cutting force, surface uniformity or chip shape. According to a preferred alternative of the present invention, cuttability is expressed as tool life.

The expression "tool life" in this patent application means the amount of time for which a tool, e.g. a cutter made of sintered hard metal (TC) for drilling, milling or other cutting machining, can be used actively before it reaches a predetermined wear limit.

The nature of edge wear in cutting machining may differ depending on the various load factors to which the tool is subject. The types of wear most commonly occurring are abrasive wear, diffusion, oxidation, fatigue and adhesion (Berglund et al., 2006). Oblique wear is the wear mechanism most commonly measured (Stjernstoft, 2004).

Measurement of oblique wear of a tool edge in machining involves measuring the abrasive wear on the edge of the tool as v_B in mm according to Stjernstoft, 2004 and Berglund et al., 2006. Figure 1 depicts a tool for cutting machining as seen from in front and from the side. The broken line in the diagram on the right is a region which has undergone wear. The diagram on the left shows where measurement of oblique wear is performed. If tool wear is measured as oblique wear of the tool edge, the predetermined wear limit is represented by ¾ in mm.

DESCRIPTION OF THE INVENTION

Material samples were prepared from 17 compact graphite irons (CGI materials) with different levels of Mn, Cr and Mo.

The samples were cast to produce test pieces with dimensions of 350*120*49 mm, see Figure 2 schematically illustrating the test pieces. The casting skin was removed from the test pieces by planar milling of their bottom surface, top and sides. This was done to ensure the dimensions of the test piece after casting and to achieve a more homogeneous microstructure, since the microstructure of the casting skin differs from the remainder of the material.

Thereafter, the test pieces of the 17 different CGI materials were machined. To ensure sufficient statistical relevance, two extra sets of CGI material 17 were also machined. These samples were designated 18 and 19. Duplicate machining experiments were carried out for each material, making a total of 19*2 machining tests. The machining was performed by the test pieces being planar-milled, using a CoroMill 365 machine (R365-063Q22-S15H) provided with three cutters of grade K20W (R365-1505ZNE-KM K20W). The machining was performed in a multi-operation mill of Mazak make. The test pieces were fastened by means of a magnetic table.

The cutting data applied were cutting depth (a_p) 3 mm, feed rate (t_z) 0.2 mm/tooth and cutting rate (v_c) 200 m/min. After a number of machining cycles, the tool holder was taken out of the mill and the cutters' wear was measured as maximum oblique wear [v_B in mm] in a microscope. Machining and measurement of oblique wear were repeated until the average value of the maximum oblique wear of the three cutters reached 0.3 mm or when two of the three cutters reached maximum oblique wear of 0.3 mm, which was the predetermined wear limit for the cutters. When the oblique wear reached 0.3 mm, the cutters were deemed spent. Tool life, i.e. the total time for which machining proceeded before the cutters were spent, was measured and recorded for all the materials. Table 1 sets out the results of the machining.

Table 1 Tool life measurement results

The chemical composition of the 17 materials was measured by GD-OES (glow discharge optical emission spectrocopy). As samples 17, 18 and 19 had the same composition, the chemical analysis treated them as just one material, 17. Table 2 shows the chemical composition of the 17 test pieces.

Material

no. C Si Mn s P Cr Ni Mo Cu Ti Sn Mg Cek

1 3.63 1.82 0.38 0.007 0.018 0.02 <0.050 <0.010 0.63 <0 010 0.051 <0.010 4.09

2 3.68 1.81 0.38 0.007 0.018 0.03 <0.050 0.10 0.64 <0.010 0.051 <0.010 4.14

3 3.67 1.81 0.39 0.006 0.018 0.03 <0.050 0.2 0.64 <0.010 0.055 <0.010 4.13

4 3.68 1.83 0.38 0.007 0.018 0.03 <0.050 0.28 0.64 <0.010 0.05 <0.010 4.15

5 3.75 1.93 0.39 0.007 0.019 0.22 <0.050 <0.010 0.66 <0.010 0.062 <0.010 4.25

6 3.64 1.95 0.39 0.007 0.019 0.24 <0.050 0.12 0.65 <0.010 0.061 <0.010 4.14

7 3.71 1.92 0.38 0.008 0.018 0.22 <0.050 0.19 0.65 0.01 0.061 <0.010 4.19

8 3.78 1.94 0.39 0.008 0.019 0.23 <0.050 0.29 0.66 <0.010 0.058 <0.010 4.28

9 3.79 1.97 0.76 0.006 0.019 0.03 <0.050 <0.010 0.66 <0.010 0.061 <0.010 4.29 10 3.78 1.95 0.74 0.007 0.019 0.03 <0.050 0.1 0.66 <0.010 0.058 <0.010 4.27

11 3.65 1.84 0.76 0.007 0.02 0.03 <0.050 0.21 0.62 <0.010 0.053 <0.010 4.12

12 3.77 1.93 0.73 0.007 0.02 0.04 <0.050 0.28 0.66 0.01 0.058 <0.010 4.26

13 3.85 1.97 0.73 0.007 0.02 0.20 <0.050 <0.010 0.66 <0.010 0.052 <0.010 4.35

14 3.79 1.96 0.78 0.009 0.019 0.23 <0.050 0.1 1 0.65 <0.010 0.067 <0.010 4.29

15 3.82 1.97 0.75 0.008 0.019 0.21 <0.050 0.19 0.65 <0.010 0.06 <0.010 4.32

16 3.75 1.95 0.76 0.009 0.022 0.22 0.051 0.3 0.64 <0.010 0.052 <0.010 4.25

17 3.72 1.97 0.58 0.007 0.019 0.12 <0.050 <0.010 0.66 0.01 0.062 <0.010 4.23

Table 2 chemical composition of sample materials

The results of the machining experiments and the chemical compositions of the materials were used to arrive empirically at relationships between cuttability, expressed as tool life, and contents of carbide-stabilising substances in the material, by the following procedure:

The results from the machining experiments and the chemical compositions of the materials were analysed by full-factor analysis by the Modde programme from Umetrics (Umetrics version 7) to identify relationships between tool life and the carbide-stabilising substances Mo, Cr and Mn.

The programme started from a statistical model and compared the various levels of carbide-stabilising substances in the material with the results from the various measurements described above. The analysis was done by the programme doing repeated calculations and statistical analyses of the results from the machining experiments and the chemical compositions of the materials. The relationships found in the analysis results between cuttability and contents of carbide-stabilising substances made it possible for the coefficients in the model to be adapted so that the model described as well as possible the measured values.

According to a first alternative, the programme started from a first model, see equation 1 , which took linear relationships, cross-relationships and quadratic relationships into account: Tool life = constant + a*Mo +b*Cr +c^*Mn + d*Mo*Mn + e*Mo*Cr + f*Cr*Mn + g *Mo² + h*Cr* + i*Mn² [equation 1] According to a second alternative, the programme started from a second model, represented by equation 2 below, taking only linear relationships into account:

Tool life = constant + a*Mo +b*Cr +c^*Mn [equation 2]

The relationships analysed by the programme may be described in various ways. An easy and comprehensive way is in a form of a coefficient diagram, see for example Figure 3. A coefficient diagram makes it possible to read off which substance has the greatest effect, how great that effect is compared with that of the other substances, and whether the effect is positive or negative. It is also possible to read off the error stacks of the coefficient. If the error stack is greater than the effect, i.e. if an error stack crosses the zero point, the relationship is not statistically assured with the chosen significance level of 95%.

Figure 3 illustrates relationships between carbide-stabilising substances and tool life when the advanced model according to equation 1 is applied. The diagram provides a picture of the influence exerted by cross-relationships and quadratic relationships.

As may be seen from the error stacks in Figure 3, a majority of the coefficients have larger error margins than effects, i.e. their error stacks cross the zero axis, which means that the effect is not assured at the chosen level of significance. These coefficients were eliminated from the model and a new coefficient diagram was arrived at. Figure 4 illustrates a coefficient diagram for the reduced model. This model shows inter alia that Cr has the greatest adverse effect on tool life. There are various ways of evaluating how well the above model corresponds to reality (the measured values). The most usual and most important value is R². The R² value may range between 0 and 1 , where 1 means that the model corresponds perfectly to reality. Another important value is Q², which describes how robust the model is. The Q² value may range between 0 and 1 , where 1 is a robust model not sensitive to changes in data. Q² is always slightly lower than R², and for a good model the difference between R² and Q² is small. Figure 5 shows that the advanced model arrived at matches well with the measured values. It shows that the R² value is 0.94 and the Q² value is 0.87 for the model.

A first embodiment uses the results of the calculations and the statistical analysis set out above as a basis for arriving at a relationship in the form of an equation for how cuttability expressed as tool life in cutting machining depends on the carbide-stabilising substances Cr, Mo and Mn. The relationship is described by equation 3 and comprises a constant and the terms which are of statistical relevance and their coefficients: Tool life = 27 - 50*Mo - 186*Cr + 127*Mn - 146*Mn² + 146*Cr*Mo + 151 *Cr*Mn

[equation 3]

A second embodiment of the invention arrived at a further relationship empirically in the same way as described above. The relationship according to the second embodiment was based on the linear model according to equation 2 and is represented by equation 4 below:

Tool life = 57.20 - 18.46*Mn - 80.90*Cr -38.98*Mo [equation 4] A third embodiment arrived at a standardised equation. This was done by equation 4 being standardised and taking into account the minimum and maximum limits of the coefficients according to equation 5: Tool life = C1 + (min; max) ^* Mn + (min; max) *Cr+ (min; max)^*Mo [equation 5]

The standardisation resulted in equation 6:

Tool life = 1+ (-053; -0.12)*Mn + (-1.81 ; -1.02)^*Cr + (-0.99; -0.37)*Mo [equation 6]

The coefficients in equation 6 were recalculated to ranges according to equation 7:

Tool life = 1 - (0.32 + 0.21 )*Mn - (1.41 + 0.39)^*Cr - (0.68 + 0.31)* Mo [equation 7]

This standardised relationship makes it possible to exclude external error factors which might affect the result, e.g. systematic measuring error or machining variations due to the condition or settings of the machines used for the machining.

Classification of cuttabilitv

To make it possible to classify compact graphite iron with respect to cuttability, comparison values were arrived at for the suitability of various compact graphite irons for production machining.

According to an alternative, the predetermined comparison values were determined on the basis of equation 7:

Tool life = 1 - (0.32 + 0.21)*Mn - (1.41 + 0.39)^*Cr - (0.68 + 0.31)* Mo [equation 7]

All the coefficients in equation 7 were taken at their respective average values. Based on that assumption, comparison values were determined for the suitability of compact graphite irons for production machining with respect to carbide-stabilising substances (expressed as tool life) as follows:

Level 1 : tool life >0.81 Very suitable for production Level 2: tool life 0.68 - 0.80 Suitable for production

Level 3: tool life <0.67 Unsuitable for production

According to a further alternative it is also possible to determine comparison values for equations 3 and 4. These may be determined by actual tool life being measured during production machining of compact graphite irons containing different contents of carbide-stabilising substances. The measured tool lives are thereafter assessed at three levels: Level 1 : Very suitable for production

Level 2: Suitable for production

Level 3: Unsuitable for production

It should here be emphasised that the assessment of suitable tool life for production machining varies with factors such as cutting tool, cutting tool prices, cutting data or other types of machining machines. The above levels have therefore to be adapted by specialists to prevailing conditions. An example which may be cited is that in machining with grade K20W cutters in a multi-operation mill of Mazak make a tool life of more than 40 minutes is regarded as very suitable for production, a tool life between 40 and 20 minutes as suitable for production and a tool life of less than 20 minutes as unsuitable for production.

Calculation of comparison values may take various factors into account, e.g. material costs may be included. It is possible to apply various weighting values to tool life or material cost. It is also possible to arrive statistically at average values for tool life in machining of a plurality of materials with different contents of carbide-stabilising substances. Average values may similarly be arrived at for the material cost of further materials.

EXAMPLES The invention is described below with respect to two concrete tests carried out with the relationships arrived at and measurements on actual materials.

Test 1

A first test did a comparison between measured tool lives and calculated tool lives according to equation 3.

A tool life calculation for the respective samples 1 - 19 was done by putting their contents of the carbide-stabilising substances Mo, Cr and Mn into equation 3. The calculated tool life was then compared with tool life measured for the respective samples (see Table 1). Figure 6 shows a very good match between calculated and measured tool lives.

Test 2

A second test used two separate series of samples to do a comparison between measured tool lives and calculated tool lives according to equation

7.

The previously described group of sample materials 1-19 (see Table 1) was supplemented by a second series of four more sample materials designated 20-23.

Sample materials 20-23 were made (were cast) and analysed in the same way as materials 1-19 but were machined in a different machine from that used for materials 1-19. The machine was also used by a different operator. The machine used for materials 20-23 was a Huller Hille nb-h 150. Tool life measurement on the sample materials was done in the same way as for samples 1-19. Table 3 shows the chemical composition of sample materials 20-23: Material

no. C Si Mn S P Cr Ni Mo Cu Ti Sn Mg Cek

3.64 2.24 0.13 0.006 0.022 0.03 <0.050 <0.010 0.65 0.014

20 0.055 <0.010 4.21

3.63 2.27 0.34 0.007 0.022 0.05 <0.050 <0.010 0.69 0.014 0.067 <0.010 4.21

21

3.63 2.29 0.41 0.008 0.022 0.09 <0.050 0.03

22 0.69 0.014 0.062 <0.010 4.21

3.60 2.27 0.48 0.007 0.023 0.09

23 <0.050 <0.010 0.69 0.014 0.062 <0.010 4.18

Table 3: Chemical composition of sample materials 20-23

Table 4 shows measured tool lives in machining of sample materials 20-23:

Table 4: Tool life measurement results for sample materials 20-23 Table 5 below shows that measured tool lives in minutes for materials 20-23 differ from materials 1-19 which are of similar composition. This is due to systematic error factors caused by the use of different machines for material groups 1-19 and 20-23. The machine used for group 20-23 was set differently from that used for group 1-19.

To cater for this, tool lives for materials 1-23 were calculated with the standardised equation 7, taking all the coefficients in equation 7 at their average values, as follows: Tool life = 1 -0.32*Mn-1.41 *Cr-0.68*Mo.

Table 5 below sets out the results.

The measured tool lives for samples 1-23 were then standardised against reference materials 17^* and 23. As previously mentioned, the first group comprised 17 unique material samples and material 17 was also used twice more to ensure statistical relevance, with designations 18 and 19. Reference material 17* is therefore an average value of the measurements from materials 17, 18 and 19. Standardisation was done as described below.

The following assumption was made for reference materials 17* and 23:

Calculated tool life = Measured standardised tool life

The standardised measured tool life was then calculated for each material 1- 23 as follows:

Standardised (x) = Measured (x) ^* [Standardised (ref)/Measured (ref)]

Materials 1-19 were standardised against material 17^*, and materials 20-22 against material 23.

Table 5 sets out the results

mater a s -

The values for measured standardised tool life are plotted against the calculated tool lives in Figure 7, which also shows a continuous linear curve corresponding to Calculated tool life = Measured tool life. As may be seen in the diagram, there is little scatter of the measured standardised values relative to the continuous line, showing a good match between measured and calculated tool lives even for series of samples machined under different conditions. The above description in detail of specific embodiments of the invention is for illustrative purposes and is not intended to limit the invention. It is obvious that the embodiments described may be combined and that various changes and modifications to the invention may be made within the scope of protection of the attached claims.

Claims

A method for determining the cuttability of a compact graphite iron, characterised by the steps of:

- arriving at a relationship between cuttability and contents of

- providing a compact graphite iron;

- determining a value for the cuttability of the compact graphite iron provided on the basis of the relationship and contents of carbide- stabilising substances in the compact graphite iron provided.

The method according to claim 1 , comprising the steps of:

- classifying the cuttability of the compact graphite iron provided by comparing the value for its cuttability with the first predetermined comparison value.

The method according to claim 2, in which the cuttability of the compact graphite iron provided is classified as suitable for production if the value for the cuttability of the compact graphite iron provided is higher than the first predetermined comparison value.

The method according to claim 3, comprising the steps of:

5. The method according to any one of claims 1 - 4, in which cuttability is defined as tool life in chip-breaking machining of compact graphite iron.

6. The method according to claim 5, in which tool life is defined as

maximum oblique wear of the tool. 7. The method according to any one of claims 1 - 6, in which the

relationship for cuttability is based on a model which comprises relationships between contents of carbide-stabilising substances in compact graphite iron. 8. The method according to claim 7, whereby the model is based on linear relationships, cross-relationships and quadratic relationships between contents of carbide-stabilising substances.

9. The method according to any one of claims 5 - 8, in which the

relationship arrived at is:

Tool life in minutes = 27 - 50*Mo - 186^*Cr + 127*Mn - 146^*Mn² + 146^*Cr^*Mo + 151^*Cr^*Mn.

10. The method according to claim 7, in which the model is based on linear relationships between contents of carbide-stabilising substances in compact graphite iron.

11. The method according to any one of claims 5 - 7 and 10, in which the relationship arrived at is:

Tool life in minutes = 57.20 - 18.46*Mn - 80.90*Cr -38.98*Mo.

12. The method according to any one of claims 5 - 7 and 10, in which the relationship arrived at is:

Tool life = 1 - (0.32 + 0.21)*Mn - (1.41 + 0.39)*Cr - (0.68 + 0.31)* Mo, where tool life is standardised.

13. The method according to any one of claims 1 -12, in which the carbide- stabilising substances comprise at least manganese, molybdenum and chrome.