End joint

Shipping cartons for hquids in cans and bottles, bulk solids in jars, pouches, and folding boxes, and briquetted items with or without individual packaging are usually made or corrugated kraft paper. The most common styles are the regular slotted caiton (RSC), the end-opening RSC, and the center special-full overlap slotted container (SFF). End joints may be stapled, stitched, glued, or taped. 

A flexible-end Joint connects a generator or transformer to a bus system or a bus system to a pow er panel. 

Depending on the rating and length of the bus system, a flexible-end joint may be necessary at the panel end also to absorb expansion of the busbars and also to assist in making the end connections when the configurations of the bus sections in the equipment are different or have a mismatch, although there are no vibrations at the panel end. 

Fig. 1. Schematic representation of the structure of a crystallizable rigid-chain polymer point defects are located at end joints...

Although preliminary studies suggest that face-laminations can be obtained using adhesives made from condensed tannins that pass the standards of the American Institute of Timber Construction (< ), less is known about how to formulate adhesives using these materials for end-jointing of wood. This study, funded by the USDA Small Business Innovation Research Program, was undertaken to develop adhesive formulations containing 50% of sulfite extracts obtained from the bark of southern pine trees and demonstrate their use in... 

At the time the end-joint test unit was being built, the industry used both horizontal and vertical end-joint profiles. This question/dilemma was eliminated by designing the unit for a lumber cross-section of 1.5 x 1.5 inches. Restriction to this dimension was also necessary to keep the power requirements within reasonable limits. At present, the unit is limited to approximately 3,000 psi in tension, at which point the hydraulically-driven grips begin to slip. The unit thus allows one to determine the strength development in the joint during the... 

Selection of the End-Joint Profile. Because the purpose of this work was to determine whether a portion of the phenol-resorcinol-formaldehyde adhesive used in structural end-joints could be replaced by tannin extracts from southern pine bark, it was necessary to use a structural end-joint profile design. The profile chosen was the design used by many U.S. plants for the manufacture of structural end-joints. A reproduction in natural size with a drawing showing the exact dimensions is shown in Figure 1. 

When the components A and B were applied separately to the mating surfaces of the end-joint profiles, the tensile strength of the joints increased at very similar rates, advancing to a level of about 3,000 psi in 20 to 30 minutes at ambient temperature in both resin systems (Figure 2). Because of the negligible difference in tensile strength development and the comparatively low cost of the PRF resin, the Borden LT-75 resin was used in the component B in all further testing. 

In adhesives formulated in the F- and M-Series (Table I), approximately 5 to 10 minutes at ambient temperature was required to reach an end-joint tensile strength of 500 psi, a value deemed adequate to permit gentle handling of the end-jointed members. Between 15 and 20 minutes at ambient temperature was required to reach a tensile strength of 1,500 psi (11). 

Ultimate Tensile Strength. The tensile strengths of fully cured end-joints in lodgepole pine or Douglas-fir when tested dry after vacuum-pressure water... 

Table II. Gluebond Quality of Lodgepole Pine End-joint and Douglas-fir Parallel Laminates Obtained with the F-Series Adhesive Formulations...

Resin Strength or Wood Fail (WF) End-joint Parallel Laminate ... 

Although not normally measured and not a requirement of an industry standard, the high wood failure values of the end-joints obtained with these adhesives are further evidence of water-resistant bonds. It was difficult to discern differ-... 

Extracts from southern pine bark obtained by extracting finely ground bark with 4.0% sodium sulfite and 0.4% sodium carbonate at 100 °C can be used to replace 50% of the PRF resin in a honeymoon system forbonding exterior quality structural end-joints in lodgepole pine or Douglas-fir. 

This work was funded by the USDA Small Business Innovation Research Grant No. 86-SBIR-8-0126. The authors thank Mr. Gary Smith for his assistance in testing specimens. Weyerhaeuser Company kindly made the end-joint test unit and provide laboratory space available. The Borden Chemical Company provided the PRF resin LT-75 and the hardener FM-260. The Chembond Company provided the resin RF-900. Boise Cascade Corporation kindly provided southern pine bark from its plywood plant at Oakdale, Louisiana. 

Kreibich, R. E., Use of Bark Tannins in End-Joint Adhesives for Wood. Final Report-Phase I to the USDA Small Business Innovation Research Program on grant 86-SBIR-8-0126, R. E. Kreibich, Auburn WA., 1987. 

There are four steps in the manufaeturing proeess (i) drying and grading the timber, (ii) end jointing, (hi) faee bonding, and (iv) finishing and fabrieation. 

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