TOOL WEAR FOR VAPOR BORON-TREATED COMPOSITES

Transcription

1 IRG/WP THE INTERNATIONAL RESEARCH GROUP ON WOOD PRESERVATION Section 4 Processes and Properties TOOL WEAR FOR VAPOR BORON-TREATED COMPOSITES W. A. Jones 1, H. M. Barnes 1, H. A. Stewart 1, and R. J. Murphy 2 1 Forest Products Laboratory, Mississippi State University, USA 2 Department of Biology, Imperial College of Science, Technology & Medicine, UK Paper prepared for the 32 nd Annual Meeting Nara, JAPAN May th, 2000 IRG Secretariat SE Stockholm Sweden

2 TOOL WEAR FOR VAPOR BORON-TREATED COMPOSITES 1 W. A. Jones, H. M. Barnes, H. A. Stewart, and R. J. Murphy Abstract A series of composites, including oriented strandboard and medium density fiberboard, were treated via vapor boron technology. Treated samples were compared to untreated composites using a tool force measuring technique. Tool forces measured with a dynamometer indicated a positive effect of boron addition. Visual and SEM examination indicated a wider wear zone on the rake face of the tool for the untreated material. Boron transfer to the tool material was confirmed by SEM. Introduction Numerous investigators have reported on the properties of composites treated with boron compounds (Barnes, et al. 1989, Bergervoet et al. 1992, Burton et al. 1990, Hashim, et al. 1992, 1994, Laks and Palardy 1993, Murphy et al. 1993). The negative effects of vapor boron treatment (VBT) have generally been limited to high retentions (Hashim et al. 1994). In an earlier paper we reported on some ancillary properties of VBT composites (Jones et al. 2001). The objective of this work was to ascertain the tool wear experienced when cutting nontreated composites vs. VBT composites. One way to measure tool wear is to monitor the cutting forces associated with the cutting tool. When the normal forces exceed the parallel force, this indicates that the knife is very dull (Stewart 1985). Greater cutting forces indicate more tool wear. The results from this test indicate the effect the wood composite may have in the dulling and wearing of tools and tool forces related to tool edge recession indicating dulling. The treatment of tool material with boron in a process known as boriding has been shown to increase tool life (Stewart 1987). It is hypothesized that boron treatment of wood may have the same result on tools used to cut and shape it. Methods and Materials Materials & Treatment--Oriented strandboard (OSB) from southern (SO) and northeastern (NE) US manufacturers and medium density fiberboard (MDF) intended for the siding market from southern (SO) or northern (NO) mills were included in the study. They have been described in a previous paper (Jones et al. 2001). The vapor boron treatment regime utilized (Hashim, et al. 1992, 1994) is described in the same paper. One additional treatment level (LOW) was utilized for some of the boards in this study. For these samples, the vapor boron contact time was 40 minutes. Testing Methods--The tool wear test monitors cutting forces for a long continuous cut with a single knife-edge on a lathe to compare cutting parameters (Stewart 1985). Samples tested were rounded into roughly 11-inch circles and placed onto a lathe. The lathe tool for turning the disks had a single knife-edge (standard C2 tungsten carbide) with a 15-degree rake and 10-degree clearance angle. This tool was held in a force transducer that measured the parallel and the normal forces simultaneously. The total length of cut was dependant on the number 1 Approved as Journal Article FP-209, Forest & Wildlife Research Center, Mississippi State University, USA. 1

3 of disks (usually 3) for each combination of composite and treatment level. The total length of cut was 18,000 inches/disk at a constant cross feed (depth of cut) of inches per revolution. Turning speed was 550 rpm. After completion of the machining operations, the knife edges were examined for wear and boron transfer using scanning electron microscopy (SEM). Results and Discussion Data for parallel and normal forces for the NE-OSB samples are shown in Figure 1 for the parallel and normal forces. For this group, the control showed more severe tool dulling compared to that associated with VBT-treated samples. All treated samples had less negative effect on tool forces than the untreated controls. The reduced tool forces in the NE board indicated that the addition of boron to wood reduces tool wear. Parallel force (lbf) CONTROL LOW MEDIUM HIGH Length of cut (in x 10 3 ) Normal force (lbf) CONTROL LOW MEDIUM HIGH Length of cut (in x 10 3 ) FIGURE 1. Effect of boron addition on the parallel (left) and normal (right) tool force components for OSB from a northeastern US mill. For the untreated control OSB-SO samples the tool forces indicated that the tool was almost dull after cutting the first disk. Dulling continued during cutting of the next two disks. The low VBT treatment level had the worst effect on tool forces indicating more rapid dulling of the tool after the first disk. The medium treatment level proved to be the optimum level for tool forces, although none of the medium or high treatment level specimens appeared to dull the tool. Data for OSB is shown in Table 1. 2

4 Table 1. Parallel and normal tool forces for cutting OSB disks. BAE Force (lbf) Treatment Level Disk Number (% w/w) Parallel Normal NORTHEASTERN MILL LOCATION (Initial) 3 (Initial) Control (Initial) 4 (Initial) Low (Initial) 3.5 (Initial) Medium (Initial) 4 (Initial) High SOUTHERN MILL LOCATION (Initial) 5 (Initial) Control (Initial) 5 (Initial) Low (Initial) 4 (Initial) Medium (Initial) 3 (Initial) High The addition of boron to OSB from both mill locations was associated with less tool wear than untreated OSB, but the NE boards had better results than the SO boards. The SO boards had a slightly higher density than those from the NE and this could have affected the results. Tool wear data are shown in Table 2 for medium density fiberboard and typical force curves for MDF are shown in Figure 2. 3

5 Table 2. Parallel and normal tool forces for cutting MDF disks. Treatment BAE Force (lbf) Disk Number Level (% w/w) Parallel Normal NORTHEASTERN MILL LOCATION Control (Initial) 3.5 (Initial) Control Control Control Control Control Control Low (Initial) 4 (Initial) Low Low Low Low Medium (Initial) 11 (Initial) Medium Medium Medium Medium High (Initial) 3 (Initial) High SOUTHERN MILL LOCATION Control (Initial) 22 (Initial) Control Control Medium (Initial) 4 (Initial) Medium Medium Medium Medium Medium Medium High (Initial) 4 (Initial) High High High High High High

6 Parallel force (lbf) CONTROL MEDIUM HIGH Normal force (lbf) CONTROL MEDIUM HIGH Length of cut (in x 10 3 ) Length of cut (in x 10 3 ) FIGURE 2. Effect of boron addition on the parallel (left) and normal (right) tool force components for medium density fiberboard from a southern US mill. None of the VBT specimens appeared to completely dull the knife according to force assessment. For the SO mill location, the medium retention indicated an optimum treatment level for tool forces appears to exist at the medium retention. Six medium level disks were tested and did not dull the knife. Note the lower parallel and normal forces for the medium level in Figure 2. The high level VBT samples did not completely dull the knife according to force assessment, but did have a less positive effect. The control samples for the NO mill location had a greater negative effect on tool forces than the treated samples. Six control samples were tested, and after four disks were cut, the normal force was greater than the parallel force indicating severe dulling (See Table 2). The low retention specimens had slightly lower forces than the control. As with the SO samples, the medium treatment level proved to be the optimum level for tool wear. In both types of MDF, the untreated control specimens were associated with greater tool wear than the treated samples. The extent of tool wear appears to decrease to a minimum with increasing treatment to the medium level and then increase for subsequent boron addition. This suggests that there is a finite amount of boron which is beneficial to reducing tool wear. These tests show that moderate vapor phase boron treatment actually improves the machinability of medium density fiberboard. The reduction of tool wear can be seen in the SEM micrographs shown in Figure 3 for treated and untreated medium density fiberboard. 5

7 FIGURE 3. SEM micrograph of knife edge wear zones for untreated control (left) and boron-treated (right) MDF. Note the much wider wear zone on the control knife edge on the left compared with that for VBT MDF on the right. Not only is the wear zone wider, but also less of the cobalt binder has been removed from around the tungsten carbide grains at the knife edge after machining the treated MDF. This can better be seen in Figure 4. The boron appears to have bonded to, and perhaps diffused into, the cobalt and formed cobalt borides. As previously indicated, the cobalt borides are chemically stable. Consequently, tool wear from machining vapor boron treated composites is reduced. FIGURE 4. High magnification of the wear zone of knife edges used to machine untreated (left) and VBT-treated (right) MDF. In Figure 4 note the tungsten carbide grains with missing cobalt binder between them. In the micrograph on the right, the grains are less evident with cobalt filling the interstices. Conclusions This study has shown that treating composites with VBT reduces the tool wear associated with machining them. Analysis of cutting tool forces coupled with visual observations of the knife edges confirmed this positive effect. 6

8 Literature Cited Barnes, H. M., T. L. Amburgey, L. H. Williams, and J. J. Morrell Borates as wood preserving compounds: the status of research in the United States. International Research Group on Wood Preservation, Document No. IGR/WP/3543, 16 pp. Bergervoet, A., R. Burton, K. Nasheri, D. Page, and P. Vinden Gaseous boron treatments of wood and wood products. International Research Group on Wood Preservation, Document No. IGR/WP/ Burton, R., T. Bergervoet, K. Nasheri, P. Vinden, and D. Page Gaseous preservative treatment of wood. International Research Group on Wood Preservation, Document No. IGR/WP/3631. Hashim, R., D. Dickinson, R. Murphy, and J. Dinwoodie Effect of vapor boron treatment on mechanical properties of wood based board materials. International Research Group on Wood Preservation, Document No. IGR/WP/ Hashim, R., D. Dickinson, R. Murphy, and J. Dinwoodie The mechanical properties of boards treated with vapor boron. Forest Prod. J. 44(10): Laks, P. E. and R. D. Palardy Properties and process considerations for preservativecontaining waferboards. In: Protection of wood-based composites (A. F. Preston, ed.), IUFRO Symposium, Orlando, FL, May 1993, Forest Products Society, Madison, WI. Murphy, R. J., D. J. Dickinson, P. Turner, P. J. Wickens, and R. Hashim Vapor boron treatment of wood composites. In: Protection of wood-based composites (A. F. Preston, ed.), IUFRO Symposium, Orlando, FL, May 1993, Forest Products Society, Madison, WI. Stewart, H A turning method for monitoring tool wear when machining reconstituted wood products. Forest Prod. J. 35(11/12): Stewart, H Borided tungsten carbide reduces tool wear during machining of MDF. Forest Prod. J. 37(7/8):