Analiza određenih mehaničkih svojstava konstrukcijskog drva KVH i uslojenog drva PSL

This paper summarizes the results of the analysis of selected physical and mechanical properties of construction wood KVH and composite material Parallam 2.0 E (below Parallam). The following properties were determined: bending strength, local modulus of elasticity in bending, modulus of elasticity in pure bending, modulus of elasticity in shear by the constant span method, compression strength along the grain, compression strength across the grain, tensile strength across the grain, density and moisture content. The determined values were compared to each other and the best material was evaluated. The analyzed materials showed not only different values of monitored properties but also different behavior in particular tests. The presented tables and diagrams show that Parallam demonstrates better strength properties in many cases than construction wood KVH but with respect to the high purchase price of Parallam a manifold higher difference was expected. Comparing both analyzed materials from the aspect of purchase costs, two-fold higher values of the majority of analyzed mechanical properties of Parallam as against the construction wood KVH are irrelevant. The price of construction wood KVH is about EUR 250, and the price of Parallam is about EUR 1540 per m3. Such a high price is the main cause of the minimum use of Parallam as against construction wood KVH.U radu se iznose rezultati istraživanja određenih fizikalnih i mehaničkih svojstava konstrukcijskoga cjelovitog drva KVH (Konstruktionsvollholz) i uslojenog drva PSL (Parallel Strand Lumber). Određivana su ova svojstva: savojna čvrstoća, lokalni modul elastičnosti pri savijanju, modul elastičnosti pri čistom savijanju, modul elastičnosti pri smicanju, određen metodom konstantnog luka, tlačna čvrstoća duž vlakanaca, tlačna čvrstoća okomito na vlakanca, vlačna čvrstoća okomito na vlakanca, gustoća drva i sadržaj vode. Dobivene su vrijednosti istraživanih materijala uspoređene i procijenjeno je koji materijal ima bolja svojstva. Ispitivani materijali nisu pokazali samo različita svojstva već su se u testovima određivanja pojedinih svojstava različito i ponašali. Rezultati prikazani u tablicama i na dijagramima pokazuju da uslojeno drvo PSL u većini slučajeva ima bolju čvrstoću od konstrukcijskog drva KVH, ali s obzirom na mnogo veću cijenu uslojenog drva PSL, očekivana je i veća razlika u svojstvima tih materijala. Analizirajući svojstva obaju materijala, zaključeno je da su dva puta veće vrijednosti gotovo svih svojstava čvrstoće uslojenog drva PSL zanemarive s obzirom na višestruko veću cijenu. Cijena konstrukcijskog drva KVH kreće se oko 250 eura/m3, dok je cijena uslojenog drva PSL oko 1540 eura/m3. Tako visoka cijena glavni je razlog mnogo rjeđe uporabe uslojenog drva PSL od konstrukcijskog drva KVH

Optimizacija dijagrama prešanja pri prešanju OSB ploča

This paper summarizes the results of a pressing diagram optimization based on changes in pressure, temperature and distance between frames of a continuous press during Oriented Strand Boards (OSB) pressing. Tests of selected mechanical properties were carried out on OSB/3 boards with a nominal thickness of 18 mm - a basic type with urea-formaldehyd (UF) glue in surface layers and isocyanate glue (PMDI) in the central layer and further an ECO type with PMDI glue in all layers produced by a prominent manufacturer of OSB boards in the Czech Republic. OSB/3 boards are intended for structural purposes for use in wet environments. Changes in the pressing diagram were carried out at the stage of “press opening”, which signifi cantly affects mechanical and physical properties of OSB boards. In order to be able to compare the effects of changes in the pressing curve, the same setting of production parameters was used with all tested boards. The results of laboratory tests were compared with the values given in the ČSN EN 300 Standard. Optimization of the pressing process ranks among the most effective measures to increase the quality of particle boards at zero or minimum costs. The control of production processes is increasingly perfect thanks to the development of electronics, control and computer technology. At present, not only in our country but also worldwide, marked development of wooden constructions occurs thanks to the development of new types of wood-based composite materials and to the development of technologies in building industry. OSB boards are an important representative of wood-based composite materials for wooden constructions. As compared to natural material, OSB boards show a homogenous structure not including natural defects typical of solid wood. From the point of view of physical and mechanical properties, OSB boards are of orthotropic character.U radu se prikazuju rezultati optimizacije dijagrama prešanja utemeljeni na promjenama tlaka, temperature i udaljenosti između okvira kontinuirane preše pri prešanju ploča s usmjerenim iverjem – OSB ploča (Oriented Strand Boards). Mehanička svojstva mjerena su na pločama OSB/3, nominalne debljine 18 mm, na osnovnom tipu ploče s urea-formaldehidnim (UF) ljepilom u vanjskom sloju i izocijanatnim (PMDI) ljepilom u središnjem sloju te na ekološkom tipu ploče s PMDI ljepilom u svim slojevima, koje je proizveo priznati proizvođač OSB ploča u Republici Češkoj. OSB/3 ploče upotrebljavaju se za konstrukcijske svrhe u vlažnom okruženju. Promjene u dijagramu prešanja napravljene su u fazi “otvaranja preše”, koja bitno utječe na mehanička i fizikalna svojstva OSB ploča. Da bi se mogli uspoređivati učinci promjena u dijagramu prešanja, za sve su uzorke ploča upotrijebljeni jednaki parametri proizvodnje. Rezultati laboratorijskih mjerenja uspoređeni su s podacima iz norme ČSN EN 300. Optimizacija procesa prešanja pripada najučinkovitijim načinima povećanja kvalitete ploča iverica uz male troškove ili bez ikakvih izdataka. Kontrola procesa proizvodnje postala je bitno bolja zahvaljujući razvoju elektronike, kontrolne i računalne tehnologije. Trenutačno se u svijetu bilježi znatan porast upotrebe konstrukcijskog drva zahvaljujući razvoju novih kompozitnih materijala od drva i novih tehnologija građenja. OSB ploče važan su predstavnik kompozitnih materijala za drvene konstrukcije. U usporedbi s prirodnim materijalima, prednost OSB ploča je to što imaju homogenu strukturu bez grešaka koje su tipične za masivno drvo. Sa stajališta fizikalnih i mehaničkih svojstava, OSB ploče su ortotropan materijal

Analiza međusobnih odnosa gustoće, količine ljepila i mehaničkih svojstava OSB ploča

This paper deals with problems of the effect of changes in density and amount of glue on mechanical properties of OSB (oriented strand boards). Tests of mechanical properties were carried out on OSB/3, 18 and 15 mm thick, produced on an OSB production line of the prominent manufacturer of board composite materials in the Czech Republic. In the first stage of the experiment, density was decreased in manufactured OSB with a nearly the same amount of glue. In the second stage, density was constant and the amount of glue changed. Bending strength, modulus of elasticity and tensile strength perpendicular to the board surface were determined in OSB samples of particular variants. Results of laboratory tests were compared with values given by the ČSN EN 300 standard for category OSB/3.U radu se analizira utjecaj gustoće ploča i količine ljepila na mehanička svojstva ploča s usmjerenim iverjem – OSB ploča (Oriented Strand Boards). Mehanička svojstva mjerena su na pločama OSB/3, debljine 18 i 15 mm, koje je proizveo priznati proizvođač kompozitnih drvnih materijala u Republici Češkoj. U prvoj fazi eksperimenta proizvedene su ploče različite gustoće, uz približno jednaku količinu ljepila. U drugoj fazi proizvedene su ploče konstantne gustoće i s različitom količinom ljepila. Izmjerena je savojna čvrstoća, modul elastičnosti i vlačna čvrstoća okomito na površinu ploče svih ploča. Dobiveni rezultati uspore|eni su s vrijednostima koje su dane normom ČSN EN 300 za kategoriju ploča OSB/3

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Analysis of causes of warping the plywood sheets

The aim of the paper was to analyse the shape stability of plywoods. Following operations were monitored: storing the construction veneers, spreading the gluing mixtures, prepressing, pressing and the storage of plywoods. The shape stability of plywoods is affected by various factors and technological parameters of particular operations. It is one of the important parameters to assess the quality and use of plywood sheets in practice. On the basis of the analysis of the present condition of the problems a methodical procedure was prepared to determine causes of warping the plywood sheets. According to this procedure an experiment was created. Within this experiment parameters were determined, which affect warping the plywoods. The moisture and temperature of veneers and pressed plywood sheets rank among the most important parameters affecting shape stability. The size of the camber of pressed plywood sheets was also determined. Results showed that the warping of plywood sheets resulted particularly from the area distribution and variation of the moisture of veneers and plywoods, which was also related to temperature. These values of moisture and temperature result, e.g., from the relative air humidity and temperature, pressing parameters but also storing in stacks and appropriate storage. On the basis of the effect of determined parameters mentioned in this paper, the larger or smaller warping of plywood sheets originates, which is expressed by the shape change and size of their camber

Analysis of the shape stability of water-resistant plywoods

The paper analyses causes of disorders of the shape stability of water-resistant plywoods produced by an important producer in the CR. Deformations of plywoods are caused by many reasons, such as wood structure (the course of wood fibres), plywood construction (the construction balance as for size and material regularity), the moisture of processed veneers and boards, glue spread, actual pressing process, the storage and climatization of finished plywoods. Basic technological parameters affecting the shape stability of plywoods were analysed, such as parameters of the hydrothermic pre­pa­ra­tion of raw material, parameters of veneer drying and the moisture of peeled veneers after drying as well as pressing parameters. At the conclusion, recommendations to improve the shape stability of plywood sheets are presented

Effects of the ratio of mixing the UF adhesive and the UF adhesive with increased reactivity on mechanical properties and the content of formaldehyde

The paper includes results of research work dealing with the study of the effect of mixing the traditional urea-formaldehyde adhesive Kronores CB 1100 D and the urea-formaldehyde adhesive Kronores CB 1200 D characterised by increased reactivity for selected physical and mechanical properties of particleboards, the content of free formaldehyde and productivity of the production line of particleboards. Within the research, other potential factors affecting properties of particleboards were also studied. Present adhesive prescriptions (1) and five experimental prescriptions were eva­lua­ted. In conclusion, optimum prescriptions were determined fulfilling the CSN EN 312 standard requirements for physical and mechanical properties of particleboards of P 2 class and a pressing factor was defined substantially affecting the rate of a production line or production productivity