Screw-holding, internal bond, and related properties of composite board products for furniture and cabinet manufacture: a survey of the Literature

This paper discusses selected properties of particleboard, hardboard, medium-densi­ ty fiberboard (MDF), and plywood related to their use in furniture and cabinet manu­ facture. Properties covered are screw-hold­ ing, internal bond, density profile, and edge appearance. Studies of direct screw with­ drawal of panel products indicate that re­ sistance to withdrawal from the edge is 75 to 80 percent of resistance to withdrawal from the face. In all cases, screw-holding powers of these products are considerably less than that of solid wood of the same den­ sity. Internal bond strength, density profile, and edge appearance are all related to each other to some degree and are largely gov­ erned by press conditions, particle or fiber characteristics, and adhesive content. A particular panel product can be ac­ cepted or rejected for use in furniture and cabinet manufacture for a variety of rea­ sons. In 1968, Suchsland (36) published the results of a survey on the use of panel ma­ terials by furniture and cabinet manufactur­ ers. Most frequently mentioned reasons for Madison, Wisconsin using particleboard,for example,were: ec­ onomics, dimensional stability, no tele­ graphing, no warping, sizes available, and uniform thickness. Reasons given for not using particleboard were: difficult edge treatment, fastening problems, customer objection, and low strength/high weight. Concerning customer objection, one manu­ facturer commented, "We are using parti­ cleboard whereverit is superior to any other material,but we would not like our custom­ ers to know about it." It is no surprise then that particleboard used in furniture is dis­ guised. To a great extent, the results of this sur­ vey are still valid. Component joints (espe­ cially where screws are used)and treatment of panel edges are still major concerns of furniture and cabinet manufacturers. This paper discussesscrew-holding, inter­ nal bond (IB),density profile, and edge ap­ pearanceof particleboard, hardboard, MDF, and plywood as they relate to performance of these products in furniture and cabinets. Additional important properties are covered in other papers in this proceedings. 30 Screw-holding: resistance to direct withdrawal The resistance of particleboard and MDF to direct screw withdrawal is considerably lower than solid wood of the same density (14,15,43,44). This is usually attributed to the reconstituted nature of the products. A limited amount of data available indicates that withdrawal resistance of plywood is also somewhat lower than that of solid wood of the same species. The standard ASTM method for deter­ mining the screw withdrawal resistance of wood-based panels (6) specifies a 1-inch­ long, No. 10 wood screw inserted into a 7/64-inch-diameter lead hole to a depth of 2/3 inch. Lead hole diameter is about 90 percent of the screw root diameter. The ANSI standards for particleboard (1)and MDF (2)call for a Type A or AB self-tapping screw instead of a wood screw. Whittington and Walters (43)and Johnson (18)indicate that there is little difference between the withdrawal resistance of self-tapping and wood screws in particleboard and plywood for the same depth of thread penetration. Superfesky (40) reported that the Type A screw averaged slightly greater withdrawal resistance from particleboard (+ 4%) and MDF (+ 10%) than did Type AB. Both types had a shank diameter of 0.190 inch. Threads in the Type A screw were cut deeper than those in the Type AB screw, which offset the fact that the Type AB had 16 threads per inch compared to 12 for the Type A. It is interesting that a special particleboard screw showed greater withdrawal resist­ ance than the wood or self-tapping screw from fiberboard, but not from particleboard (13). ANSI standards for particleboard and MDF (1,2) list minimum screw-holding (No. 10, self-tapping) requirements which vary by panel grade and type for particleboard and by panel thickness for MDF. Face with­ drawal resistance requirements for particle­ board vary from 125 pounds for Grade 1-L-2 (low-density door core) to 450 pounds for Grade 1-H-3, a highdensity product. Grades 1-M-2 and 1-M-3 are most often used in fur­ niture and cabinet manufacture. Face with­ drawal resistance requirements for these are 225 pounds and 250 pounds, respective­ ly. Face withdrawal resistance requirements for MDF are 325 pounds for panels 3/16­ inch-thick or less, and 300 pounds for pan­ els thicker than 13/16 inch. Screw with­ drawal resistance requirements for screws inserted into the edges of MDF or particle­ board panels average about 80 percent of face withdrawal requirements. This differ­ ence in face and edge screw-holding re­ quirements reflects the results of test data (13,20,33,37,40,44).Coefficientsofvariation for screw withdrawal resistance are about 10 to 15 percent for commercial particle­ board and MDF. Eckelman (14,15) used some of these published data to develop equations to provide furniture and cabinet designers with reasonable estimates of the screw-holding power of wood-base panels. Average ultimate withdrawal resistance from the face of particleboards is predicted by: F = 2655D1/2(L-D/3)5/4G2 [1] and from the edge of a panel by: F = 2055D1/2(L-D/3)5/4G2 [2] A comparable expression for MDF face withdrawal is: F = 3700D1/2(L-D/3)5/4G2 [3] A comparable expression for MDF edge withdrawal is: F = 2860D1/2(L-D/3)5/4G2 [4]