1. Introduction
The rigidity of furniture and other wooden furniture accessories depends on the type and thickness of the wood, as well as how the wooden pieces were put together. Screws and nails are widely used as joint components of furniture construction and since each wood species has its own properties, they also have different screw and nail withdrawal resistances. Therefore, it is important for both producers and consumers to be aware of the best screw and nail withdrawal resistance for the various wood species.
Ferah performed nail withdrawal resistance experiments at tangential, radial and cross-section angle penetration into wood of two different humidity levels (12% and 30%) [1]. Tangential surface screw withdrawal resistance experiments were performed according to TS 6094 and ASTM-D1761 standards on seven wood species that were obtained in the “Elmali Ciglikara Sedir Research Forest” and “Abant-Bolu region”. They determined that Sessile oak had the maximum screw withdrawal resistance value, followed by Fagus orientalis, red pine, black pine, Lebanese cedar and respectively. Uludag Fir was found to have the minimum screw withdrawal resistance value, while the maximum value was obtained from Sessile oak, followed by Fagus orientalis, red pine, black pine, Lebanese cedar and respectively, and the lowest value was obtained from Uludag fir.
Doganay determined parallel and perpendicular screw withdrawal resistance for three types of screws (17×17, 18×25 and 20×30 types) commonly used in Werzalit wood furniture production [2]. The results of the experiments show that the most effective material in screw withdrawal resistance from both directions is the Fagus orientalis wood, followed by Werzalit, MDF and particleboard, respectively.
Raczkowscha determined that the nail withdrawal resistance of Scotch pine juvenile wood is lower than that of heartwood [3]. This was found in 30% perpendicular to grain and 10% parallel to grain. He also stated that there is a linear relationship between nail withdrawal resistance and the density of wood; nail withdrawal resistance perpendicular to grain in juvenile wood is lower than in older wood with the same density.
Fujita determined that investigations were carried out on a withdrawal-resistance, in the case when nails were driven on a specimen in air drying condition through the five kinds of Sugi-woods (Cryptomeria japonica) growing at Takakuma University Forest, Kagoshima Prefecture [4]. The five kinds of Sugi-wood are Yakusugi-, Measasugi-, Yoshinosugi-, Kumotoushisugi- and Obiarakawasugi-wood aged 52,27,28 and 28, respectively. In this paper, 1. Concerning the withdrawal-resistance the highest value was noted in Yakusugi-wood, and the lowest one in Obiarakawasugi-wood. 2. A average withdrawal-resistance was ascertained to be dependent on the specific gravity of Sugi-wood growing at Takakuma University Forest. 3. Withdrawal-resistance to respective nail types, which were assorted into chequered-head countersunk-smooth type and -screw type, was decreasing in accordance with the width of average annual ring. But a withdrawal-resistance to wood screw was independent of the width of annual ring.
Broker and Krause performed static and dynamic screw withdrawal experiments on three layered particleboard, European Spruce grown in Norway, and European Birch wood with 9 types of screws. They concluded that the screw withdrawal resistance value is linearly proportional with screw length and screw diameter [5].
Bues and his colleagues pounded 2×40 mm sized nails into 250 20×20×110 dimensional wood samples which were obtained from scattered cuttings of pine wood and measured their withdrawal resistances [6]. They used screws of 20 mm groove length, 1.8 mm cog step, and 60° cog angle on nail holes of 2 mm diameter. After suitable conditioning, they measured screw and nail withdrawal resistances on radial and tangential directions as 50 N/s, and determined the relationship between the density and screw and nail withdrawal resistance [6]. As a result, they determined average nail withdrawal resistance as 1.27 KN in radial direction, 1.06 KN in tangential direction with 0.50 g/cm3 average density and with 12% humidity. They also determined average screw withdrawal resistance as 1.48 KN in radial direction and 1.42 KN in tangential direction at the same conditions. The meaningful differences in the screw and nail withdrawal resistance values in the tangential and radial directions were established by 20% of nails and 4% of screws. They determined that screw withdrawal resistance of the screws was 16% higher in radial direction and 34% higher in tangential direction than nails.
Reardon and Boughton examined 6 types of grooved nails on 7 species of pine [7]. They determined that nail withdrawal resistances of grooved nails are 2–3 times higher than that of smooth trunk nails. However, there is no relationship between the density of wood types and withdrawal resistance values.
Kim concluded the effect of nail direction and time elapse after nailing into the static withdrawal resistance by nailing 4.9–5.1 mm length and 0.25–0.26 mm diameter nails into pine and larix wood [8]. As a result, Kim determined that there is a linear relationship between static withdrawal resistance and humidity amount. Kim presented the relationship in both species of wood in tangential, radial and longitudinal directions.
Kanamori and his coworkers measured withdrawal resistance of nails that were nailed into dried wood samples of Picea jezoensis, Larix leptolepis and Quercus crispula [9]. Five humidity levels were analyzed. It was determined that nail withdrawal resistance of circular ribbed nails (max. 2.9 mm diameter) decreases during the process. The majority of this decrease occurs in the first phase. For the helical ribbed nails (max 3.2 mm diameter), nail withdrawal resistance does not change or increase unessential. In addition, nail withdrawal resistance of Quercus crispula is twice as that of the two other wood types. Kanamori and his coworkers compared nail withdrawal resistance of common wire nails, helitical ribbed nails and galvanized circular ribbed nails that were nailed tangentially, radially and longitudally nailed into three types of wood (Picea jezoensis, Larix leptolepis and Quercus crispula) [10]. They performed experiments in three different conditions; nailed into undried wood over a 6 month drying period, nailed into dried wood, over a 7 month humidity taken and humidity release period, nailed into dried wood over 15 months at equilibrium humidity.
Kjucukov and Encev measured screw withdrawal resistance of screws with different lengths (13–60 mm) and different diameters (1.5–8 mm) that were screwed into Abies alba wood in three directions [11]. As a result, they determined that there is no relationship between screw withdrawal resistance and screw length, and there is a linear relationship between screw withdrawal resistance and screw diameter.
Kjucukov and Encev performed with 1.5–6.0 mm diameters screws on Fagus orientalis and determined that there is a linear relationship between screw withdrawal resistance and screw diameter [12]. This result confirms the experiment results on fir wood.
Lexa concluded nail withdrawal resistances of steal nails covered with an epoxy resin that was nailed into dried and green spruce, fir, and Fagus orientalis wood [13]. He determined that the nail withdrawal resistances of covered nails are smaller, the nail withdrawal resistances of covered nails are higher on the dried wood, and the nail withdrawal resistances of covered nails are slowly diminished.
Bacher nailed nails on wood with 60% humidity and measured the nail withdrawal resistance during the drying period from 60% humidity to 0% [14]. As a result, he determined that nail withdrawal resistance diminishes when the wood humidity amount decreased to the leaf saturation point.
Hellawel concluded nail withdrawal resistance in the wood samples at fresh, air dried, partially dried and moistened conditions just after nailing, and the effect of drying and time on this property [15]. He concluded that Rimu wood generally has higher nail withdrawal resistance than Radiata pine wood.
Noguchi and Sugihara compared nail withdrawal resistance of chrome nickel and iron nails that were nailed longitudinally, radially, tangentially at static and dynamic conditions on 6×6×30 cm experiment samples of Cryptomeria japonica, Fagus crenata and Chamaecyparis [16]. They determined that nail withdrawal resistance at static nailing is higher than dynamic nailing. They concluded that nail withdrawal resistance decreases with time in the density of wood in both nailing types. It was also found that the nail withdrawal resistance is maximized for tangentially nailing nails. They formulated equations on nail withdrawal resistance and wood density, nail diameter and time after nailing.
Mack compared static nail withdrawal resistance of flat and ribbed nails on wet and air dried Radiata pine and Eucalyptus wood after different periods [17]. He concluded that ribbed nails show high nail withdrawal resistance values on soft and hard wood during and after the nailing period.
Scholten found that the highest nail withdrawal resistance values were obtained from sharp tip nails on wood with low density [18]. Wood with high density did not divide after nailing. He proposed common nails for wood with high division resistances.
Stern and Price measured nail withdrawal resistance of different shaped nails on the structural quality of southern yellow pine [19]. As a result, they concluded that circular ribbed and screw dented nails show higher resistances than common wire nails. There was also a linear relationship between nail withdrawal resistance and nail diameter in big diameter nails and this relationship was higher than predicted.
Ayyildiz and Malkocoglu, carried on the screw withdrawal resistance of stem wood material of Fagus orientalis Lipsky., Alnus glitunosa subsp. barbata (C.A.Mey) Yalt., Castenea sativa Mill., Picea orientalis (L.) Link., and Pinus sylvestris L. [20]. The wood samples of these tree species were collected from forest districts in Gümüshane, Trabzon and Artvin located in Eastern Black Sea region of Turkey. Tests were carried out according to the TS 6094 and ASTM-D 143 and ASTM-D 1761 on 60 samples of each one of the tree species. Half of the samples had 12% and the other half had 30% moisture contents. The dimensions of wood materials on which the tests were carried out were 50×50×150 mm. Screws used for withdrawal tests were 4.5 mm in diameter and 40 mm in length. Two screws were inserted into lead holes at right angles on the tangential surface, 26 mm penetration. In this study, the results presented that the highest screw withdrawal resistance was found for oriental beech among the five tree species. The order of screw withdrawal resistance from the higher to the lower was found as follows; alder, chestnut, pine, spruce. In regards to moisture effects, the screw withdrawal resistances were found to be higher at the 12% moisture content.
In this study, screw and nail withdrawal resistance of fir (Abies nordmanniana), oak (Quercus robur L.) black pine (Pinus nigra Arnold) and Stone pine (Pinus pinea L.) wood were determined and compared. This study includes the comparison of nail and screw withdrawal resistances for the same species and between other species. The resistance values were obtained from all of the directions (radial, tangential, longitudinal) of wood specimens. The data represent the testing of withdrawal resistance of three types of screws as smart, serrated and conventional and common nails.
3. Results and Discussion
As a result of the experiments, data were obtained by using 4 types of wood: oak (Quercus robur L.), Stone pine (Pinus pinea L.), fir (Abies nordmanniana) and black pine (Pinus nigra Arnold), 3 types of screws (smart screw, serrated screw, and conventional screw), and one type (2,5×5) of nail. These data represent resistance values of three different directions (tangential, longitudinal, and radial).
3.1. Withdrawal resistances for radial direction
In this section, nail and screw withdrawal resistance of wood specimens for radial direction were compared. Representative statistical data of withdrawal resistances for radial direction are presented in Table 1. Radial direction resistance values of nails have lower values with respect to that of screws.
According to results, the highest resistance value for radial direction was obtained from oak as 439.75 kgf with conventional type screw. Conventional screws also performed best for every species except Stone pine.
Nail and screw withdrawal resistances for radial direction were presented in Figure 1. According to data, oak and Stone pine performed similarly. The lowest values were obtained from fir wood.
3.2. Withdrawal resistances for tangential direction
The highest value was obtained from oak with conventional type screws as 445.70 kgf. Besides, Stone pine performed quite similarly with serrated screw. The results related to tangential withdrawal direction resistance, are tabulated and presented in Table 2.
According to Figure 2, oak, Stone pine and black pine performed quite similarly. Fir had the lowest values for every screw and nail tested.
3.3. Withdrawal resistances for longitudinal direction
In this section, nail and screw withdrawal resistance of wood specimens for longitudinal direction were compared. According to results, the highest resistance values for longitudinal direction were obtained from oak and black pine as 362.85 kgf and 257.25 kgf respectively with conventional type screw. The lowest resistance value was obtained from black pine as 197.10 kgf with smart screw.
The results related to tangential withdrawal direction resistance, are tabulated and presented in Table 3.
According to results, oak, Stone pine, black pine and performed quite similarly (Figure 3). Fir performed lowest values for every screw and nail.
3.4. Nail and screw withdrawal resistances for wood species
In this work, results were obtained from experiments on samples that were prepared by the TS 6094 fundamentals at 12% humidity for nail and three different screw types at different sample directions (radial, tangential and longitudinal).
According to results, the highest value among all of the directions and connection materials, oak with conventional screws performed the best following by Stone pine with serrated screws. In general, oak performed quite satisfactorily. These results are presented in Tables 4.
The difference between screw withdrawal resistances of serrated screws and conventional screws are not notable. The screw withdrawal resistances are Stone pine, oak, black pine and fir, respectively.
The conventional screw gave the maximum screw withdrawal resistance on oak wood followed by Stone pine, black pine and fir wood, respectively.
There is no big screw withdrawal resistances difference between radial and tangential direction at sample directions. It was seen that the radial direction resulted the maximum screw withdrawal resistance values. Tangential direction follows it, but resistance values are close to the radial direction. The minimum screw withdrawal resistance value is presented by the longitudinal direction. The screw withdrawal resistances at the longitudinal direction are lower with respect to the radial and tangential directions.
It was seen that oak wood, one of the hard wood species, yielded higher screw withdrawal resistances than softwood species. It was determined that oak shows the maximum screw withdrawal resistance except for serrated screw.
For three factors (wood species, screw type and sample direction), oak wood showed the maximum resistance value followed by Stone pine, black pine and fir respectively. The average nail withdrawal resistance values according to wood species and three different sample directions are presented in Table 5.
In Table 5, it is seen that oak wood showed higher nail withdrawal resistances than softwood species. It was also determined that oak shows the maximum nail withdrawal resistance in all types. In sample directions, the radial direction shows the maximum nail withdrawal resistance, tangential direction follows it but resistance values are close to radial direction. The nail withdrawal resistances at the longitudinal direction are lower with respect to radial and tangential directions.