Abstract:
A method of determining face paper properties of wallboard including providing a core strength value of the wallboard, determining a required nail pull value based the wallboard specifications and calculating a face paper stiffness value based on the provided core strength value and the determined nail pull value. The method includes displaying the calculated face paper stiffness value on a display device.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to composite building panels. More specifically, it relates to a method for determining structural parameters of gypsum wallboard. 
       BACKGROUND OF THE INVENTION 
       [0002]    Composite building panels, such as gypsum wallboard, are well known for interior wall and ceiling construction. Some of the main advantages of wallboard over other materials is that wallboard is less expensive, a fire retardant and easy to work with in construction applications. In construction, wallboard is typically secured to wood or metal supports of framed walls and ceilings using fasteners such as nails or screws. Because wallboard is relatively heavy, it must be strong enough to prevent the fasteners from pulling through the wallboard and causing the wallboard to loosen or fall away from the supports. 
         [0003]    Nail pull is an industry measure of the amount of force required for wallboard to be pulled away from the associated support and over the head of such a fastener. Preferable nail pull values for wallboard are in the approximate range of between 65-85 pounds of force. Nail pull is a measure of a combination of the wallboard core strength, the face paper strength and the bond between the face paper and the core. Nail pull tests are performed in accordance with the American Society for Testing Materials (ASTM) standard C473-00 and utilize a machine that pulls on a head of a fastener inserted in the wallboard to determine the maximum force required to pull the fastener head through the wallboard. Because the nail pull value is an important measure of wallboard strength, minimum required nail pull values have been established for wallboard. Accordingly, manufacturers produce wallboard that meets or exceeds the minimum required nail pull values. 
         [0004]    To ensure that wallboard meets the required nail pull values, conventional wallboard manufacturers adjust the structural parameters of the wallboard. Specifically, manufacturers typically adjust the face paper weight of wallboard having a known core strength value to meet the required nail pull value. During manufacturing, wallboard is tested to determine if it meets the required nail pull value. If the tested nail pull value of the wallboard is less than the required nail pull value, manufacturers increase the face paper weight on the wallboard. This process is repeated until the required nail pull value is met. 
         [0005]    Such a process is inaccurate and commonly causes the tested nail pull values to exceed the required nail pull values due to excess face paper weight added to the wallboard. Also, the excess face paper adds weight to wallboard and thereby increases manufacturing and shipping costs of wallboard. Further, there is the likelihood of wasting time and material until the desired nail pull values are achieved on the wallboard production line. 
         [0006]    Thus, there is a need for an improved technique of adjusting wallboard manufacturing systems to produce wallboard that meets specified nail pull values. 
       SUMMARY OF THE INVENTION 
       [0007]    These, and other problems readily identified by those skilled in the art, are solved by the present method of determining structural properties of composite building panels such as wallboard. 
         [0008]    The present method is designed for determining structural parameters of gypsum wallboard prior to manufacturing to reduce manufacturing and shipping costs as well as significantly reduce manufacturing time. 
         [0009]    More specifically, the present method determines structural parameters of wallboard and includes providing a core strength value of the wallboard, determining a required nail pull value and calculating a face paper stiffness value based on the provided core strength value and the determined nail pull value. The calculated face paper stiffness value is displayed on a display device for use by a manufacturer. 
         [0010]    In another embodiment, a method of manufacturing wallboard includes determining a required nail pull value, providing a core strength value of the wallboard and determining a face paper stiffness value based on the required nail pull value and the provided core strength value. The method includes determining a face paper weight based on the determined face paper stiffness value, selecting a face paper type based on the determined face paper weight and producing the wallboard using the selected face paper type and the provided core strength value. 
         [0011]    Determining the structural parameters prior to manufacturing enables manufacturers to save significant manufacturing and shipping costs by eliminating excess face paper weight that is typically added to wallboard to meet required nail pull values. Additionally, a significant amount of manufacturing time is saved because less time is needed to test the manufactured wallboard to determine the face paper weight needed to meet required nail pull values. Furthermore, the structural integrity and strength of wallboard is maintained, even though the additional weight and stress added by the excess face paper is reduced. 
     
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a table illustrating a comparison between measured nail pull data and predicted nail pull data for the same types of wallboard using different face papers. 
           [0013]      FIG. 2  is a graph illustrating nail pull as a function of the face paper stiffness at different core strength values. 
           [0014]      FIG. 3  is a graph illustrating nail pull as a function of the core strength at different face paper stiffness values. 
           [0015]      FIG. 4  is a graph illustrating the relationship between the face paper stiffness and the core strength at different required nail pull values. 
           [0016]      FIG. 5  is a graph illustrating the relationship between the face paper weight and the Tensile Strength Index Area (TSIA) values needed to achieve a required nail pull value of 77 lb f  at different core strength values. 
           [0017]      FIG. 6  is a table identifying certain face paper weight values and Tensile Strength Index Area (TSIA) values needed to achieve a required nail pull value of 77 lb f  at different core strength values based on the graph of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Nail pull values are critical to the strength and usefulness of gypsum wallboard. If a nail pull value for a particular wallboard is too low, the fastener holding the wallboard on a frame or other support can pull through the wallboard and cause the wallboard to crack, break or fall from the frame or support. Alternatively, if nail pull values are too high (i.e., significantly exceed required nail pull values), wallboard production resources are inefficiently applied and money is wasted during manufacturing. 
         [0019]    A problem in gypsum wallboard manufacturing is how to accurately determine the face paper weight that correlates to a required nail pull value for wallboard and a way that more efficiently utilizes manufacturing and shipping costs, as well as manufacturing time. As stated above, wallboard manufacturers perform tests on wallboard to determine if it meets a required nail pull value. If the required nail pull value is not met, manufacturers typically increase the face paper weight of the wallboard. These steps are repeated until the required nail pull value of the wallboard is met. This process is not accurate and often causes the wallboard to have excess face paper, which increases the overall weight of wallboard and thereby increases manufacturing and shipping costs as well as manufacturing time. 
         [0020]    The present method determines a face paper weight, or alternatively a face paper stiffness value, for wallboard prior to manufacturing that meets the required nail pull value. The method utilizes the following equation that correlates a required nail pull value with the face paper stiffness value and the core strength value of wallboard. The equation is as follows: 
         [0000]      Nail Pull (lb f )= a+[b ×(face paper stiffness (kN/m))]+[ c ×(core strength (psi))]  (1)
 
         [0000]    where a=4.2126759, b=0.009490606731, c=0.092421774 are constants determined from testing data that best fit the data shown in  FIG. 1 . 
         [0021]    Prior to manufacturing, the core strength value of wallboard is determined and the required nail pull value is determined for the wallboard to be manufactured (i.e., quarter inch, half inch, etc.). These values are entered in Equation (1) above to determine the face paper stiffness value of the wallboard. For example, the face paper stiffness value for wallboard having a core strength value of 400 pounds per square inch (psi) and a required nail pull value of 77 pound-force (lb f ) is as follows: 
         [0000]      77 lb f =(4.2126759)+[(0.009490606731)×(face paper stiffness (kN/m))]+[(0.092421774)×(400 psi)]
 
         [0000]    where the face paper stiffness value=3774 kiloNewton/meter (kN/m). 
         [0022]    The face paper stiffness value is a product of the face paper weight and the Tensile Stiffness Index Area (TSIA) value as shown in the following equation: 
         [0000]      Face Paper Stiffness (kN/m)=Face Paper Weight (g/m 2 )×TSIA (kNm/g)  (2)
 
         [0023]    Using the above example, the Face Paper Weight for the above wallboard having a core strength value of 400 psi, a required nail pull value of 77 lb f  and a TSIA of 26 kiloNewton-meter/gram (kNm/g) is as follows: 
         [0000]    
       
         
           
             
               
                 
                   
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         [0024]    In the above equation, the TSIA value is a measurement of the normalized face paper stiffness in all directions on the wallboard. Specifically, an ultrasonic Tensile Stiffness Orientation (TSO®) tester machine measures the Tensile Stiffness Index (TSI) in all directions on the wallboard to determine the TSIA. The stiffer the face paper, the larger the TSIA values. The approximate range of TSIA values for wallboard is 12 to 20 kNm/g. 
         [0025]    The face paper stiffness value and TSIA value are used to determine the weight of the face paper that is needed to achieve the required nail pull value for wallboard having a designated core strength value. The calculation for determining the face paper weight is therefore a two-step process of first determining the face paper stiffness and then determining the face paper weight for the wallboard being manufactured. 
         [0026]    Equations (1) and (2) are preferably stored in a memory of a computer, personal data assistant or other suitable device. The required nail pull values, core strength values and constants are also stored in the memory in a database or other searchable data format. The memory may be a read-only memory (ROM), random access memory (RAM), compact disk read-only memory (CD ROM) or any other suitable memory or memory device. A user or manufacturer inputs the required nail pull value and designated core strength value for the wallboard into the computer using a keyboard or other suitable input device. Alternatively, the required nail pull value and designated core strength value for the wallboard may be downloaded and stored in a file or folder in the memory. A processor, such as a microprocessor or a central processing unit (CPU), calculates the face paper weight for the wallboard using Equations (1) and (2), the inputted nail pull value and the inputted core strength value. The calculated face paper weight, or alternatively the face paper stiffness value, is displayed to a user on a display device such as a computer screen, monitor or other suitable output device or printed out by a printer. The user uses the calculated face paper weight to select the face paper or face paper type that is to be adhered to the core during manufacturing of the wallboard. The face paper selected using the present method typically reduces the face paper stiffness and weight needed to achieve the required nail pull value compared to conventional wallboard production techniques. Additionally, the present method reduces the overall weight of the manufactured wallboard, which reduces manufacturing and shipping costs. The present method also significantly reduces the manufacturing time associated with producing the wallboard because the intermediate testing of the wallboard to determine if the wallboard meets required nail pull values is no longer necessary. 
         [0027]      FIG. 1  is a table that illustrates a comparison between the measured nail pull data and the predicted nail pull data for different wallboard (sample nos. 1-11) using Equation (1). As shown in the table, the predicted average nail pull data using Equation (1) correlates well with the tested or measured average nail pull data of the wallboard. For example, the average tested or measured nail pull value for sample no. 4 was 83 compared to the predicted nail pull value of 82 using Equation (1). Similarly, the tested or measured average nail pull values for sample no. 5, sample no. 6 and sample no. 11 also differ by a value of one compared to the corresponding average predicted nail pull value using Equation (1) (e.g., 82,81; 80,79; 81,80). Furthermore, the predicted nail pull values for sample no. 8 and sample no. 10 wallboard were exactly the same as the corresponding tested or measured nail pull values (e.g., 80,80 and 77,77). Thus, the present method predicts the nail pull values for wallboard with a high degree of accuracy. 
         [0028]    Equations (1) and (2) can also be used to predict different structural parameters or values of wallboard to enhance the manufacturing process. 
         [0029]    For example, from Equation (1), nail pull data can be expressed as a linear function of the face paper stiffness at different core strength values ranging from 100 psi to 700 psi, as shown in  FIG. 2 . The core strength value of wallboard varies based on the type of wallboard being manufactured. The typical range of core strength values for the wallboard considered in  FIG. 1  is 400 to 500 psi. 
         [0030]    The nail pull data can also be plotted as a linear function of the core strength with the face paper stiffness values ranging from 1000 kN/m to 6000 kN/m, as shown in  FIG. 3 . Preferably, the face paper stiffness values range from 2500 to 4000 kN/m for wallboard. In  FIGS. 2 and 3 , it is apparent that increasing either the face paper stiffness value or the core strength value of wallboard increases the nail pull value. 
         [0031]      FIG. 4  shows a plot of the face paper stiffness value as a function of the core strength value at various different nail pull values. Specifically, line “A” illustrates the relationship between the face paper stiffness values and the core strength values at a target minimum nail pull value of 77 lb f . The ratio of the empirical constants c/b (=9.74) in Equation (1) provides the change in the face paper stiffness values with respect to the change in the core strength values. To maintain the required nail pull value of 77 lb f , a reduction (or increase) of 100 psi in the core strength values corresponds to a 974 kN/m increase (or decrease) in the face paper stiffness values. Furthermore using Equation (2), a higher face paper stiffness value can be accomplished by increasing either the face paper weight or the TSIA. 
         [0032]      FIG. 5  illustrates the relationship between the face paper weight and the TSIA that meets a required nail pull value of 77 lb f . The face paper weight requirements for different TSIA values are summarized in the table shown in  FIG. 6 . Note that increasing the TSIA value from 14 to 19.5 kNm/g tends to reduce the required face paper weight by an average of 28%, while maintaining the required nail pull value of 77 lb f . 
         [0033]    The present method enables wallboard manufacturers to determine important parameters and properties of the wallboard prior to manufacturing such as the face paper weight needed to achieve a required nail pull value. Obtaining these parameters prior to manufacturing helps to significantly reduce manufacturing time, as well as manufacturing costs and shipping costs. The present method also allows manufacturers to maintain the structural integrity and performance of wallboard without adding face paper weight on wallboard. 
         [0034]    While several particular embodiments of the present method have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.