Determining the Influence of the Thickness of an Adhesive Layer on A Change in the Angles of Contact and Tangent Angles

A method has been proposed for establishing experimentally the optimum ratio of the thickness of a W-shaped adhesive layer of the spine part of a book block sewn with threads to the necessary and sufficient efforts that are applied for its bending in the block opening process.The dependence of the effort applied to the opening of a block in a page or stochastic sequence, as well as a place of bending the spine's adhesive plate, influences the duration of the book's use until the beginning of irreversible destructive processes.It has been shown that increasing the thickness of the adhesive layer leads to an increase in efforts aimed at overcoming the elastic properties of the polymer plates, obtained after the polymerization of the applied adhesive, from the side of the curved outer surface of the block spine, as well as increases the surface tension of the concave surface of the adhesive layer, which is in direct contact with the sewing threads implanted in the structure of the adhesive and the paper of the spine folds of the book sections.An increase in the surface tension leads to a decrease in the indicators of the relative lengthening of the adhesive layer, which negatively influences the formation of the natural opening angles of the book blocks and requires additional efforts for the operational use of the book.It has been revealed that the location of the points at which efforts are applied for bending a spine's adhesive plate, in the zones that are limited by the angles of contact, and in the deltoid sections within the intra-section space, influences the magnitude of the applied effort.This paper describes the elastic-plastic state of the SH-shaped spine part of a book block in the form of the constructed algorithm showing stages in the influence of the adhesive layer thickness on the deformation of the spine part.The dependences of change in the angles of contact and tangent angles of an adhesive layer, at the stages of a discrete change in its thickness, are represented in the form of the inter-dependent graphic curves in a general coordinate system.The results derived from the established ratio of the thickness of a W-shaped adhesive layer to changes in the angles of contact and tangent angles have contributed to the elaboration of the new norms for quantitative adhesive us