Veneer Peeling With Fluid Injection

Abstract

This invention relates to improvements in the production of veneer. In accordance with the invention a heated fluid, preferably steam, is directed into the cutting region as the veneer is being cut. Improvements that can be obtained are decrease of the cutting force, surface roughness and severity of lathe checks for the resulting veneer. Preferably the heated fluid is channeled in contact with the cutting blade before being released to the cutting region, in order to raise the temperature of the blade.

Description

BACKGROUND OF THE INVENTION

This invention relates to improvements in the production of veneer and particularly to a method and apparatus for directing a heated conditioning fluid, such as steam, into the cutting region.

It is known to improve the cutting properties of wood by prior conditioning. Logs have been conditioned by heating of the wood with steam or hot water in chambers. Log conditioning chambers however, are expensive to construct and costly to operate. This method also represents a source of water pollution, since the heat removes some of the wood extractives which combine with the hot water or steam condensate. This fluid must be removed from the system periodically and disposed of.

It is known that the cutting properties of wood varies with temperatures and that the optimum temperatures differ for different species. The optimum cutting temperature of different wood species has been documented in the past. A list of wood species and their optimum veneer cutting temperature can be found in "Veneer Species that Grow in the United Stated," U.S.D.A. Forest Service Research Paper FPL 167, 1972 U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, Wis. For example, the cited optimum veneer cutting temperatures for those wood species referred to herein, for rotary cut and sliced veneer, respectively, are: White spruce (Picea glauca) 70.degree.-120.degree.F and 120.degree.-140.degree.F; Douglas-fir coast (Pseudotsuga menziesii) 60.degree.-140.degree.F and 140.degree.-180.degree.F; and Western red cedar (Thuja plicata) 140.degree.-160.degree.F and 160.degree.-180.degree.F.

It is known that stresses are developed in the veneer during cutting and that these stresses can induce ruptures or lathe checks in the veneer's loose side surface, i.e., veneer surface opposite back of blade.

Documentation states that the depth of the lathe checks has an adverse effect upon veneer strength, but perhaps most important they have a strong influence on the amount of face checking that will develop in the assembled plywood during use.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and apparatus which combines log conditioning and peeling into one operation.

It is another object to provide relatively smooth veneer.

It is another object to reduce the depth of lathe checks in veneer.

It is another object to reduce the forces required for cutting veneer.

It is another object to apply the invention to present conventional veneer lathes with a minimum of alteration.

In accordance with the present invention a heated pressurized fluid is directed into the cutting region of a veneer cutting apparatus.

In accordance with one aspect of the invention, the introduction of steam to the cutting area reduces the surface roughness of the veneer and also reduces the cutting forces. These advantages are obtained when the word being cut is below its optimum cutting temperature, as referred to above. It should be noted, however, that this invention is not to be limited by the accuracy of the optimum temperatures as cited in the publication referred to above.

Although the theory of the mechanism that causes reduced roughness and cutting forces is not clearly understood, it is believed that the heated fluid provides for efficient heat transfer to the wood at the cutting region by direct heating of the wood at the cutting region by fluid contact and also by heating the cutting blade. Experiments, which are detailed herein, were performed in an attempt to isolate the mechanism responsible for the improved results. It was found that a heated blade, per se, i.e., a blade heated directly without the introduction of steam to the cutting area, produced relatively small improvements in cutting properties. Measurements indicated that the temperature at the tip of the blade fell rapidly when the cutting operation began. It appears that inadequate heat can be transferred to the cutting area in this manner. It was also found that the introduction into the cutting area of a mixture of air and water at relatively low temperatures did not produce the desired results as is obtained by the introduction of steam.

According to another aspect of the invention lathe check depth is reduced particularly under conditions of high compression with a pressure bar. It has been found that when using high compression, that is higher than a certain value which differs for different wood species, the depth of checks can be significantly decreased with steam injection. It has also been found that heated wood, for example, wood that has been conditioned by other means, also benefits with regard to lathe checks with steam injection.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the drawings in which:

FIG. 1 is a cross-sectional elevational view of a typical rotary veneer lathe and including a blade backing member adapted for conveying a fluid in accordance with the present invention.

FIG. 2 is a partial view of the blade backing member as seen at a section taken on line II--II of FIG. 1.

FIGS. 3 and 4 show cross-sectional views of alternate embodiments of the invention.

FIG. 5 shows a portion of the bottom of the fluid introducing attachment as seen at a section taken on line V--V of FIG. 4.

FIGS. 6 and 7 are elevational views of other embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a typical industrial veneer lathe 10, comprising a cutting blade 1, a blade clamp 3, a pressure bar 4, and a blade backing member 2, which is a removable element that has been adapted in accordance with the present invention. With reference to both FIGS. 1 and 2 the knife backing member 2 is provided with means for conveying a heated conditioning fluid to the cutting region of the blade 1. Longitudinal recesses 5 in the member 2 substantially parallel with the cutting edge define a chamber 6 when placed against the blade 1. Using two intercommunicating chambers reduces pressure losses in the chamber and maintains more uniform pressure across the width of the blade and also minimizes thermal stresses by providing more uniform heating of the member 2. The conditioning fluid is supplied to the chamber 6 by means of a suitable conduit 8. Since the blade 1 forms one wall of the chamber 6, rapid heat transfer to the blade from the conditioning fluid is obtained. A plurality of spaced grooves 7 in the member 2 interconnected with recess 5, form orifices disposed such that the conditioning medium supplied to the chamber is directed generally toward the cutting edge of the blade 1. The member 2 is thermally isolated from the supporting structure 11 by insulating material 12.

FIG. 3 shows another embodiment having a pair of longitudinal chamber defining recesses 35 in the member 32. A plurality of spaced orifices 37 communicate with the chamber 35 by means of passageways 39 and suitable connecting conduits supply the chambers with a heated pressurized conditioning fluid. As shown the orifices 37 are drilled into replaceable plugs 38 that are removably positioned into the passageway 39.

The previous embodiments of FIGS. 1 to 3 are directed to conventional rotary lathes. However, the invention may be adapted for use in veneer slicers or other types of rotary lathes. In the embodiment of FIGS. 4 and 5 the conditioning fluid conveying means is in the form of an adapter member 41 which is fastened to the knife backing member 42. A recess 45 in the member 41 forms a chamber when placed against the knife and fastened to the knife backing member 42. A conduit supplies the conditioning fluid to the chamber 45. Orifice means are provided by a recess 47 which extends longitudinally substantially along the entire width of the knife and communicates with the chamber 45.

The invention is not to be limited by the apparatus described herein. It will be appreciated that a veneer cutting apparatus of different design may require other structural means for conveying the conditioning fluid. For example the fluid may be introduced to the cutting region on the opposite side of the blade as in FIG. 6 or at the blade tip as in FIG. 7. In FIG. 6 the conditioning fluid is directed through a passageway 69 in the blade 61 from a chamber 65 in the blade supporting member 62.

In FIG. 7 the conditioning fluid from the chamber 75 is directed through a passageway 70 in the blade 71 to the blade's sharpened tip 72.

At the present time industry does not have an accepted standard for measuring veneer roughness or lathe check depth.

The values of veneer roughness referred to herein are based on a system developed by P. L. Northcott and D. C. Walser and described in British Columbia Lumberman, July, 1965, in an article entitled "Veneer-Roughness Scale." The authors have assumed that at least two attributes of veneer roughness are of importance in plywood manufacture; firstly, the depth of the hollows and, secondly, the frequency of irregularities.

The definition of measured veneer roughness as used herein is defined in the aforesaid publication as follows:

"Measured veneer roughness is defined as the difference between the highest peak and the lowest trough measured along a randomly chosen 1-inch trace in the roughest portion of the "tight" face and perpendicular to the grain of the veneer. Frequency is defined as (N-1)/2 where N is the number of measurements which must be made to record the peaks and valleys in a 1-inch trace. For this purpose minor irregularities (.+-. 0.001 or 0.002-inch) observed between a peak and a valley should be ignored.

Measurements shall be to the nearest 0.001 inch using a veneer-roughness gauge which meets the following requirements:

1. the veneer shall be firmly held against a flat plate while measurements are taken.

2. the foot of the dial micrometer shall be replaced with the ballpoint of a ballpoint pen; to assist in measuring the bottoms of the hollows without penetrating into the wood and to assist in traversing across the rough surface of the veneer.

3. the rails on which the micrometer gauge base travels shall be parallel to the plate against which the tight face of the veneer is held . . .

Note 1: Avoid knots and the areas of wild grain surrounding them unless knots occupy more than 20 percent of the area of the veneer sub-sample area.

Note 2: Pick out any obviously loose splinters before measuring."

The values of veneer lathe check depth referred to herein are based on the method described in the "Department of Environment" information report VP-X-107 entitled "Methods and Techniques for Veneer Peeling Research" by J. R. T. Hailey and W. V. Hancock.

Lathe check depth is defined as the fractional thickness of the veneer to which the majority of the lathe checks penetrate, measured to one decimal point then multiplied by 100 and expressed as a percentage. (A value of 100 percent would imply that the veneer disintegrated into the many strips formed by the lathe checks). The severity of lathe checks shall be measured at a moisture content suitable for estimating the penetration of the lathe checks. The application of sufficient dye (of a type which readily penetrates lathe checks to their extremities) is to be applied to the loose face to make the lathe checks readily visible when the veneer is sawn.

It should be noted that all tests described herein, with the exception of Examples 4 and 5, were conducted on the experimental veneer lathe and fluid injection apparatus detailed in Example 1.

It should also be noted that in the Tables 1 to 9 inclusive the weighted total values were obtained by applying a weighting factor of two to heartwood and one to sap and core wood.

The values of "average depth of roughness" as given in the following examples are an average of a number of measurements of veneer roughness as defined above.

EXAMPLE 1

Forty Western Red Cedar (Thuja plicata) veneer blocks were peeled in the green condition in an experimental veneer lathe of the general type shown in FIG. 4, but having orifice (1/32 in. diameter) means similar to that shown in FIG. 2, spaced 2 inches apart. Steam at 54 psi was supplied to the chamber.

In operation the temperature of the knife edge was heated to 210.degree. .+-. 5.degree.F. Half of the blocks were peeled at a temperature of 35.degree.F and the remainder were peeled at 70.degree.F. For each temperature ten blocks were peeled using steam and 10 blocks without steam. The cutting speed was 150 ft. per minute.

TABLE 1 __________________________________________________________________________ VENEER ROUGHNESS MEASUREMENTS FOR DIFFERENT PEELED BLOCK TREATMENTS TENTH-INCH WESTERN RED CEDAR GREEN VENEER TEN BLOCKS SAMPLED PER TREATMENT Block treatments Block section Veneer roughness measure Percent Average veneer Average depth of Standard rougher block Use of roughness deviation than Temp. Steam .times. 1/1000 in. .times. 1/1000 in. 0.020 in. __________________________________________________________________________ Sapwood 14.9 4.9 6.7 Heart 15.6 4.6 5.8 No Core 17.5 5.3 9.6 Total block 16.0 4.9 7.4 35.degree.F Sapwood 15.9 3.8 1.7 Heart 15.8 3.9 0.8 Yes Core 16.1 3.4 0.8 Total block 15.9 3.7 1.1 Sapwood 17.1 6.3 17.5 Heart 18.2 5.6 24.6 No Core 21.2 8.0 41.7 Total block 18.8 6.6 27.9 70.degree.F Sapwood 15.7 3.7 2.1 Heart 15.6 3.5 1.3 Yes Core 15.8 3.6 3.8 Total block 15.7 3.6 2.4 __________________________________________________________________________

Veneer-samples were collected from the sapwood, inner heartwood (core) and outer heartwood zones of each veneer block. A 23.degree. blade was used and veneer lathe settings were held constant for the tests at: Horizontal gap- 0.090 in.; Vertical gap-- 0.090 in; Pitch angle-- 89.degree. 30'; for veneer of 0.105 in. nominal thickness

The results of these tests are summarized in Table 1. The effect of the steam is most clearly shown in the "Total Block" line of the table. In each test the steam knife performed better than the standard cutting apparatus.

Table 1 also includes the standard deviation showing a greater uniformity of veneer quality when using steam.

Table 1 also shows the amount of veneer rougher than 0.020 inc., considered to be too rough. The amount of degrade is substantially improved with the use of steam.

EXAMPLE 2

The results of tests for roughness on Western White Spruce (Picea glauca) are shown in Table 2 which compares roughness with and without steam injection.

A 25.degree. blade was used and veneer lathe settings were held constant for the test at: Horizontal gap-- 0.094 in. (10 percent Compression); Vertical gap-- 0.090 in; Pitch angle-- 89.degree.30'; for veneer of 0.105 in. nominal thickness. Cutting speed was 150 ft. per min.

For the tests using steam, saturated steam at 54 psi was supplied.

The degrade (roughness greater than 0.02 in.) for the standard apparatus was 14.1 percent while the degrade when using steam was 7.0 percent.

TABLE 2 ______________________________________ VENEER ROUGHNESS MEASUREMENTS FOR DIFFERENT PEELED BLOCK TREATMENTS TENTH-INCH WESTERN WHITE SPRUCE GREEN VENEER SIX BLOCKS SAMPLED PER TREATMENT Veneer roughness measure Average Percent Steam depth of Standard veneer Knife Pres- roughness deviation rougher Treat- sure Block .times.1/1000 .times.1/1000 than ment (psi) Section inch inch 0.020 in. ______________________________________ Sapwood 16.1 4.7 12.0 Stan- 0 Heart 17.1 5.0 17.6 dard Core 15.7 4.7 9.3 Wtd. 16.5 4.9 14.1 total Sapwood 15.1 5.7 8.3 54 Heart 14.9 5.4 5.6 Steam Core 13.8 5.7 8.3 * Wtd. total 14.7 5.5 7.0 ______________________________________ * Weighted total developed by applying a weighting factor of two to heartwood and one to sap and core wood.

EXAMPLE 3

The results of tests for roughness on Western Red Cedar (Thuja plicata) are shown in Table 3 which compares roughness with and without steam injection and also with steam at different pressure (temperature) values. Table 3 shows that increasing the steam pressure from 10 psi to 54 psi further improved the roughness characteristics.

TABLE 3 ______________________________________ VENEER ROUGHNESS MEASUREMENTS FOR DIFFERENT PEELED BLOCK TREATMENTS TENTH-INCH WESTERN RED CEDAR GREEN VENEER TEN BLOCKS SAMPLED PER TREATMENT Veneer roughness measure Average Percent Steam depth of Standard veneer Knife Pres- roughness deviation rougher Treat- sure Block 1/1000 1/1000 than ment (psi) Section inch inch 0.020 in. ______________________________________ Sapwood 17.1 6.3 17.5 Stan- 0 Heart 18.2 5.6 24.6 dard Core 21.2 8.0 41.7 * Wtd. Total 18.7 6.4 27.2 Sapwood 16.0 6.7 12.9 Steam 10 Heart 16.9 4.8 12.9 Core 18.5 6.5 23.5 * Wtd. Total 17.1 5.8 15.6 Sapwood 16.2 5.1 13.2 Steam 54 Heart 15.2 3.9 2.1 Core 14.9 5.0 5.6 * Wtd. Total 15.4 4.5 5.8 ______________________________________ * Weighted total developed by applying a weighting factor of two to heartwood and one to sap and core wood.

EXAMPLE 4

The results of tests for roughness on Douglas-fir (Pseudotsuga menziesii) are shown in Table 4. Roughness was measured for veneer cut without steam, with saturated steam at 100 psi and steam at 155 psi. Average roughness and percent degrade decreased with increased steam pressure. These tests were carried out on an industrial veneer lathe modified for fluid injection similar to that shown in FIG. 3. A 23.degree. blade was used. Cutting speed was 550 ft. per min.

TABLE 4 ______________________________________ VENEER ROUGHNESS MEASUREMENTS FOR DIFFERENT PEELED BLOCK TREATMENTS EIGHTH-INCH DOUGLAS-FIR VENEER Veneer roughness measure Average Percent Steam depth of Standard veneer Knife Pres- roughness deviation rougher Treat- sure Block 1/1000 1/1000 than ment (psi) Section inch inch 0.020 in. ______________________________________ Sapwood 17.0 5.3 15.2 Stan- 0 Heart 17.7 6.1 22.7 dard Core 24.3 7.7 57.6 * Wtd. 19.2 6.3 29.6 Total Sapwood 15.8 6.3 20.0 Steam 100 Heart 16.8 6.8 20.0 Core 18.3 6.9 25.0 * Wtd. 16.9 6.7 21.3 Total Sapwood 12.9 3.7 1.9 Steam 155 Heart 12.8 3.7 1.9 Core 20.5 6.9 37.0 * Wtd. 14.7 4.7 10.7 Total ______________________________________ * Weighted total developed by applying a weighting factor of two to heartwood and one to sap and core wood.

EXAMPLE 5

Table 5 compares the cutting forces for the following cutting modes:

1. standard slicer -- blade temperatures during cutting approximately 70.degree.F.

2. slicer with heated blade -- blade temperatures during cutting 200.degree.F .+-. 5.degree..

3. slicer with air-water aerosal injection -- blade temperatures during cutting 60.degree.-65.degree.F -- pressures 40 psi, applied to two 0.050 in. diameter orifices on 21/4in. blade.

4. slicer with steam injection -- blade temperatures during cutting 200.degree.F -- steam pressure 38-40 psi, applied to two 0.050 in. diameter orifices.

Western Red Cedar (Thuja plicata) was used in the following tests performed on a laboratory model veneer slicer in which the veneer sample size was 0.105 inch thick, 2 inches wide, 4 inches long and the cutting speed was 3 inches per minute.

From the above the average resultant forces using steam (average of samples 2 and 4) decreased by 36.1 percent from the standard apparatus, (samples 1 and 3). Similarly, the average resultant forces from the hot blade (6 and 8) decreased only 7.7 percent from the standard apparatus (5 and 7). The average resultant forces using an air-water aerosal (10 & 12) increased 7.6 percent from the standard apparatus (9 and 11).

TABLE 5 ______________________________________ Sam- Knife Roller Bar Combined ple Treat- Resultant Resultant Resultant Force No. ment Force Force Force* Angle ______________________________________ 1 Std. 72.76 82.24 139.91 54.degree.53' 2 Steam 41.19 70.91 90.49 52.degree.15' 3 Std. 63.45 60.72 113.92 54.degree.12' 4 Steam 33.94 65.39 71.77 49.degree.42' 5 Std. 59.4 52.74 97.94 49.degree. 1' 6 Hot 44.02 60.73 87.41 52.degree. 7' 7 Std. 64.99 72.27 120.99 51.degree.53' 8 Hot 55.44 78.81 114.67 53.degree.39' 9 Std. 64.11 106.39 145.61 54.degree.50' 10 Air- Water 66.38 125.77 156.55 55.degree.10' 11 Std. 96.2 105.18 183.65 54.degree.31' 12 Air- Water 100.1 116.61 197.89 54.degree.56' ______________________________________ * Resultant of the combined knife and roller bar forces

EXAMPLE 6

The results of tests for lathe check depth on Western White Spruce (Picea glauca) are shown in Table 6 which compares lathe check depth for heated blocks with and without steam injection.

The blade angle was 25.degree. and veneer lathe settings were held constant at; Horizontal gap-- 0.094 in. (10 percent Compression); Vertical gap-- 0.090 in; Pitch angle-- 89.degree.30'; for veneer of 0.105 in. nominal thickness. Cutting speed was 150 ft. per. min.

The blocks were heated in a conditioning chamber to 110.degree.F before veneering. Saturated steam at 54 psi was used for the fluid injection tests.

Table 6 shows that average lathe check depth for the standard apparatus was 34 percent of veneer thickness and that average lathe check depth decreased to 17 percent when using steam injection.

TABLE 6 ______________________________________ PEEL QUALITY OF 1/10" GREEN WHITE SPRUCE VENEER PRODUCED UNDER DIFFERENT BLOCK PRECONDITIONING TREATMENTS ______________________________________ Lathe Check Depth (Percent of thickness) Knife Steam Block Sta- Sap- Heart- Inner Wtd. Treat- Pressure Temp. tis- wood wood Heart Total ment (psi) (.degree.F) tic Area ______________________________________ Steam 54 110 Avg. 24 14 14 17 Std. 18 16 16 17 Std. 0 110 Avg. 43 32 29 34 Std. 21 20 23 21 ______________________________________ *Weighted total developed by applying a weighting factor of two to heartwood and one to sap and core wood.

EXAMPLE 7

The effect of blade angle, percent horizontal compression and knife treatment on lathe check depth for Western White Spruce (Picea glauca) is shown in Table 7. Cutting apparatus same as in Example 1.

The lathe check depth for veneer cut with 20.degree. and 25.degree. blades and 15 percent horizontal compression decreased when using steam injection.

TABLE 7 __________________________________________________________________________ PEEL QUALITY OF 1/10" WHITE SPRUCE GREEN VENEER PRODUCED UNDER DIFFERENT KNIFE ANGLES AND PERCENT HORIZONTAL COMPRESSIONS Lathe Check Depth (Percent of Thickness) Knife Knife Steam Horizontal Stat- Sap- Heart Inner *Wtd. Angle Treat- Pressure Compression istic wood wood Heart Total (.degree.) ment (psi) % Area __________________________________________________________________________ 20 Steam 54 15 Avg. 13 12 19 14 Std. 15 14 19 16 20 Std. 0 15 Avg. 33 32 37 33 Std. 13 14 21 16 25 Steam 54 15 Avg. 26 25 33 27 Std. 17 13 15 15 25 Std. 0 15 Avg. 48 44 45 45 Std. 18 15 17 17 __________________________________________________________________________ *Weighted total developed by applying a weighting factor of two to heartwood and one to sap and core wood.

EXAMPLE 8

The results of tests for lathe check depth on Western Red Cedar (Thuja plicata) preconditioned to 130.degree.F is shown in Table 8.

A 23.degree. blade was used and veneer lathes settings (similar to Example 1) were held constant for the tests.

Average veneer lathe check depth decreased 15.9 percent when using steam injection.

TABLE 8 ______________________________________ PEEL QUALITY OF 1/10" GREEN WESTERN RED CEDAR VENEER PRODUCED UNDER DIFFERENT TREATMENTS Lathe Check Depth (%) Steam Knife Pres- Block Sta- Sap- Heart- Inner *Wtd. Treat- sure Temp. tis- wood wood Heart Total ment (psi) (.degree.F) tic Area ______________________________________ Std. 0 130 Avg. 50.3 41.2 48.5 45.3 Std. 22.3 20.9 20.2 21.1 Steam 54 130 Avg. 21.9 27.6 40.5 29.4 Std. 17.4 20.2 21.5 19.9 ______________________________________ *Weighted total developed by applying a weighting factor of two to heartwood and one to sap and core wood.

It should be noted that the examples, while they demonstrate that improvements in the production of veneer can be obtained with steam injection, do not necessarily indicate the optimum conditions of steam injection for the respective wood species or cutting conditions. This is due in part to the limitations of the apparatus used. Example 4 has shown that increased steam pressure resulted in decreased roughness. No cut-off point was reached in the experiments conducted. Furthermore, the heat transferred from the steam to the wood will necessarily vary with different cutting speeds. Since veneer cutting speeds vary greatly in practice and since heat transfer data is very limited for this application it can only be suggested that steam pressure (temperature) and/or the volume injected, be increased until improvement in veneer quality diminishes, or it becomes impractical mechanically. It should also be noted that improvements in veneer roughness and lathe check depth do not necessarily occur simultaneously.

Claims

1. An apparatus for reducing surface roughness of veneer and the cutting forces in a veneer peeling apparatus having a cutting blade, means for supporting a wood piece and means for providing relative movement between the cutting blade and wood piece, the improvement comprising elongated chamber defining means extending substantially parallel with the cutting blade, inlet means for said chamber defining means and means for supplying pressurized steam thereto, and orifice means communicating with said chamber defining means disposed so as to direct steam generally towards

2. The apparatus of claim 1 wherein said chamber defining means comprises a recessed member adapted for placement against a surface portion of the

3. The apparatus of claim 2 wherein said veneer peeling apparatus comprises a knife backing member and wherein the chamber defining member is

4. The apparatus of claim 2 wherein said chamber defining member is separably attached to the veneer peeling apparatus.