Comparison of four basic approaches in machine strength grading

Transcription

1 Comparison of four basic approaches in machine strength grading Alpo Ranta-Maunus, VTT, Finland Topic of presentation Comparison of four methods of determination of settings in machine strength grading: 1. Yield and strength (5 percentile, and 0.5 percentile) are compared. Methods are applied to GE 706 grading data at a sawmill with added simulated strength values 1

2 Sawmill strength grading data MiCROTEC GoldenEye 706 results at a Finnish sawmill Oct March 009 Average properties of boards with different widths, n = specimens. Numbers in parenthesis are mean values of numbers shown for all widths. width n E dyn,mean COV ρ mean COV f m,mod,mean COV in mm in N/mm² in % in kg/m³ in % in N/mm² in % all (1 300) (17) (443) (10) (41.) () 3 Moving average of predicted bending strength of 500 consecutive specimens fm,mod [N/mm] h = 75 mm h = 175 mm h = 5 mm Number of specimen 4

3 Simulation of strength values of sawmill data f m,sim = f m,mod + ε σ [ f m ] σ [ f ] + σ [ ε ] = m,mod fm,sim [N/mm ] f m,mod [N/mm ] 5 Methods to be compared 1. European machine control method (EN and -4). "Input control method", settings of EN adjusted to IP of 100 previous boards on order to achieve required 5 percentile of strength 3. "Absolute method" based on confidence/prediction intervals, a zero-bandwidth method 4. Absolute method adjusted to 10 N/mm bandwidth 6 3

4 Methods to be compared: Input controlled method EN-settings are used with modified IP f ( f f ) mod, adj = f mod 0, 8 mod, mean, ref mod, mean Difference of f m,sim,k [N/mm ] 5 C7 0 C Linear (C7) -5 y = 0,805x + 3, Difference of fm,mod,mean [N/mm ] 7 Methods to be compared: Absolute method: f mod,th = f s f m,sim = f m,mod + ε ; ε = N(0;s) fm [N/mm ] y = 0,9913x + 0,5687 R = 0,615 s = 6 N/mm MOR sim IP-1,65s IP-s Linear (IP-1,65s) Linear (MOR sim) IP = f m,mod [N/mm ] 8 4

5 Methods to be compared: Adjusted absolute method f mod,th = f 05 + s for 10 N/mm bandwidth f f=f mod f=f mod -1,65s ½ f mod f mean f 05 45º f mod,th f mod,th + f mod f mod 9 Settings used in examples for IP-MOR (f m,mod ) Grade Settings EN f f C C C

6 Results Dataset Grade f m,05 [N/mm ] f m,005 [N/mm ] Yield [%] EN EN f f EN EN f f EN EN f f adj adj adj 5 all C low C density C all C normal C density C CONCLUSIONS 1. EN settings gave acceptable 5 percentiles of strength for normal quality material sample, as expected, but too low values when low quality material was graded: 0.4 N/mm for C7 and 18.1 N/mm for C4. 0,5 percentiles were only half of the requirement for 5 percentiles of these grades.. When using adjusted indicating property based on previous 100 boards, 5 percentile values were improved to nearly acceptable level: 4.0 N/mm for C7 and 1.4 N/mm for C4 and 0,5 percentiles improved by 15 to 30 percent. For normal quality sample the adjusted ENsettings give practically same strength values and yields as EN-settings, exept that for yield to C40 raises from 7 to 31 percent when using adjusted values. 1 6

7 CONCLUSIONS 3. Absolute grading method gives conservative strength values also when low qualiy material is graded and 0,5 percentiles are less than 10 % lower than nominal strength value given in C-class title. 4. When absolute method is adjusted to 10 MPa bandwidth, strength values are conservative for normal quality sample, but not in all cases for low density material, and yield to C40 raises from 3 to 40% for normal material, which is higher yield than given by adjusted EN-method (31%). The same time, yield to C4 is so much lower that we obtain 5% rejects, whereas EN-methods give 0% rejects. 13 SUMMARY TABLE OF CONCLUSIONS Material quality Settings Yield [%] to C40&4 5- percentile 0,5- percentile C7,C4 Normal EN OK 0.70 EN adjust 100 OK 0.70 Absolute 88 High 1.0 Abs adjust 95 OK Low EN Low 0.45 EN adjust 89 OK 0.58 Absolute 57 High 0.93 Abs adjust 93 OK