Criterion of strength for hinged doors of vertical rotation axis is the value of force resulting in breaking out of the hinge form the slot made in the particle board constituting side wall of the body. Distribution of internal forces acting on the hinge
has been shown in Fig. 7.76. Taking into account the weight of the door, the resultant W of the forces RA and HA acting on the lower hinge must be determined:
W resultant force,
P operational load,
V volume of the door board, p density of element material, g 9.81 m/s2, h height of the door, a height of the setting of hinges and b width of the door.
Fig. 7.77 Scheme of door deformation
Results of studies on the strength of box hinges mounted in particle boards of various densities indicate that the criterion of strength for hinges refers to the plasticity limit, Re, designated from the experimental graph of the load-deformation function P = /(Ah). Theoretically established value of the force W should not be greater than the experimentally designated plasticity limit Re:
W < Re. (7.262)
The value Re for box hinges, mounted in a board with a density from 650 to 700 kg/m3, is at a medium level of 365 N. An additional criterion for the evaluation of the quality of hinged joints of vertical rotation axis is the stiffness of the joints. For aesthetic reasons, the value of the door hanging down during use should be limited to 2 mm (Fig. 7.77). This value results from the possibility of improving the geometric fault through adjusting the position of the screws on the assembly plate of box hinges.
A necessary and sufficient condition is, therefore, that the displacement Ah fulfils the condition of inequality:
k1, k2 stiffness of the upper and lower hinge determined on the basis of the results of laboratory tests (N/mm).