Role of finger tip area on flexural strength properties of finger-jointed sections

Abstract

This study reports the effect of two finger profiles on the static bending parameters of Eucalyptus tereticornis samples when joined with urea formaldehyde adhesive. Two sets of finger profiles with tip thicknesses of 0?11 and 0?14 cm were used. Interestingly, the profile with the thinner tip produced weaker joints. This behaviour is attributed to the larger contribution of the tip area to the total joint area in a joint when using the thinner tipped profile. The study suggests that for a given geometry, one needs to reduce the tip area in relation to the total area encountered in a joint. This gives the manufacturer an opportunity to make not too thin and fragile tips but still making it possible to design a profile which can result in useful strength parameters. The results obtained on the effect of tip area on bending parameters were confirmed by using another adhesive.

Bending strength enhancement of finger joints by inclusion of nanoclay in low concentrations into Urea formaldehyde adhesive

“…Fingers of 20 mm length, 5 mm pitch and 0.8 mm tip thickness were profiled on a commercial finger shaping machine. Urea Formaldehyde (UF) adhesive with 57.6% solid content was prepared using commercial STRONGBOND-P-101G as reported earlier [7].…”

“…These mixtures were homogenized using Dynaken WT 500 Homogenizer at 20000 rpm for 10 minutes or till no visible lumps could be detected. The required hardener [7] was mixed to the adhesives just before applying to the fingers.…”

“…The static bending measurements on the 32 finger-jointed samples were carried out on an automatic Universal testing machine as described elsewhere [7]. The span of the test was kept at 700 mm irrespective of the thickness of the samples.…”

“…However, finger jointed sections of M. azedarach resulted in less than 50% efficiency in bending strength compared to its unjointed solid wood when a profile with thicker finger tips was used [6]. The performance of UF with Eucalyptus sections was equally unsatisfactory [7]. It thus became imperative that suitable adhesive combinations should be investigated for such hardwood species for obtaining strong finger joints.…”