An investigation on the permeability of different wood furnish materials

Holzforschung ◽  
2008 ◽  
Vol 62 (2) ◽  
pp. 215-222 ◽  
Author(s):  
Heiko Thoemen ◽  
André Klueppel
Keyword(s):  
Hot Pressing ◽  
Gas Permeability ◽  
Core Layer ◽  
Raw Material ◽  
Cross Sectional ◽  
Wood Particles ◽  
Order Of Magnitude ◽  
Lower Permeability ◽  
Size Of Particles ◽  
Wood Based Composite

Abstract In wood-based composite mats, mass and heat transfer are substantially influenced by their gas permeability. Thus, reliable permeability data are needed if one wants to model and simulate those processes taking place prior, during, and after hot-pressing operations of the mat. In this study, wood particles of surface and core layer type were obtained from two particleboard manufacturers, using impact mills and knife ring flakers, respectively. The permeability measurements were performed on the initial materials, as well as on subsets of it obtained by laboratory sieving. Additionally, medium density fibreboard (MDF) fibres from three species, namely pine (Pinus sylvestris), spruce (Picea abies) and rubberwood (Hevea Brasiliensis) were investigated. Cross-sectional and within-plane permeability was measured for densities from 250 to 1000 kg m-3. The permeability of the core particle materials was determined on solidified samples. On the other hand, the surface particles and MDF fibres were investigated by means of a rapid testing method on loose furnish materials (without solidification). MDF mats exhibited lower permeability values than particle mats at low densities, but values were found in the same order of magnitude for high densities. Mainly, the small particles determine the pore structure and permeability of particle mats. Thickness and in-plane size of particles affect the mat permeability, with the in-plane size becoming primarily effective at elevated densities. The permeability of MDF fibre mats depends more on the anatomy of the raw material than on its size distribution. We suggest, based on computer simulations, that only the within-plane permeability has a strong effect on gas pressure and temperature conditions during hot pressing. The cross-sectional permeability does not play an essential role in this regard.

Investigation of Furfural Formation and Mechanical Properties of Suberinic Acids-Bonded Particleboards Depending on their Preparation Parameters

2021 ◽  
Vol 903 ◽  
pp. 235-240
Author(s):  
Raimonds Makars ◽  
Daniela Godiņa ◽  
Janis Rizhikovs ◽  
Aigars Paze ◽  
Ramunas Tupciauskas ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Hot Pressing ◽  
High Performance ◽  
Bending Strength ◽  
Ph Value ◽  
Raw Material ◽  
Technological Parameters ◽  
Pressing Temperature ◽  
Outer Bark ◽  
Wood Particles

Silver birch (Betula pendula) outer bark suberin can be used as a raw material to make an adhesive for particleboards (PBs). It is a promising formaldehyde-free alternative to traditional synthetic resins. However, the adhesive is acidic, which can catalyse furfural (FUR) formation from xylans in wood particles that are used for the preparation of PBs. FUR being a volatile organic compound can be emitted from the PBs and exposure to it can have harmful effects on humans. In the scope of this study, the effects on technological parameters (wet adhesive pH: 3, 6 and 9), glycerol as an additive to adhesive and hot-pressing temperature (180...230 °C) were investigated on the FUR formation in PBs. The FUR content was determined with high-performance liquid chromatography-ultraviolet spectroscopy system from the extracts of milled PBs. Mechanical properties (modulus of elasticity, bending strength, and thickness swelling) of the PBs were also studied. When using an adhesive with a pH 6 at hot-pressing temperature 230 °C with no glycerol added, it was possible to obtain PBs that satisfied the requirements of EN 312 P2 (boards for interior fitments). The FUR yield of these boards were more than 6 times lower than for the PBs pressed at 230 °C with a wet adhesive pH value 3.

Diagnostics of metal samples using the results of experimental and theoretical study of positively charged microparticles formed upon sample destruction

2018 ◽  
Vol 84 (10) ◽  
pp. 23-28
Author(s):  
D. A. Golentsov ◽  
A. G. Gulin ◽  
Vladimir A. Likhter ◽  
K. E. Ulybyshev
Keyword(s):  
Experimental Data ◽  
Early Stage ◽  
Experimental Studies ◽  
Material Model ◽  
Total Charge ◽  
Cross Sectional ◽  
Practical Applications ◽  
Mechanical And Electrical Properties ◽  
Order Of Magnitude ◽  
Using Data

Destruction of bodies is accompanied by formation of both large and microscopic fragments. Numerous experiments on the rupture of different samples show that those fragments carry a positive electric charge. his phenomenon is of interest from the viewpoint of its potential application to contactless diagnostics of the early stage of destruction of the elements in various technical devices. However, the lack of understanding the nature of this phenomenon restricts the possibility of its practical applications. Experimental studies were carried out using an apparatus that allowed direct measurements of the total charge of the microparticles formed upon sample rupture and determination of their size and quantity. The results of rupture tests of duralumin and electrical steel showed that the size of microparticles is several tens of microns, the particle charge per particle is on the order of 10–14 C, and their amount can be estimated as the ratio of the cross-sectional area of the sample at the point of discontinuity to the square of the microparticle size. A model of charge formation on the microparticles is developed proceeding from the experimental data and current concept of the electron gas in metals. The model makes it possible to determine the charge of the microparticle using data on the particle size and mechanical and electrical properties of the material. Model estimates of the total charge of particles show order-of-magnitude agreement with the experimental data.

Should Weights and Risk Categories Be Used for Inspection Scores To Evaluate Food Safety in Restaurants?

2016 ◽  
Vol 79 (3) ◽  
pp. 501-506 ◽  
Author(s):  
DIOGO THIMOTEO da CUNHA ◽  
VERIDIANA VERA de ROSSO ◽  
ELKE STEDEFELDT
Keyword(s):  
Food Safety ◽  
Food Service ◽  
Safety Evaluation ◽  
Cross Sectional Study ◽  
Raw Material ◽  
Risk Category ◽  
Cross Sectional ◽  
Evaluation Bias ◽  
Risk Categories ◽  
Food Safety Evaluation

ABSTRACT The objective of this study was to verify the characteristics of food safety inspections, considering risk categories and binary scores. A cross-sectional study was performed with 439 restaurants in 43 Brazilian cities. A food safety checklist with 177 items was applied to the food service establishments. These items were classified into four groups (R1 to R4) according to the main factors that can cause outbreaks involving food: R1, time and temperature aspects; R2, direct contamination; R3, water conditions and raw material; and R4, indirect contamination (i.e., structures and buildings). A score adjusted for 100 was calculated for the overall violation score and the violation score for each risk category. The average violation score (standard deviation) was 18.9% (16.0), with an amplitude of 0.0 to 76.7%. Restaurants with a low overall violation score (approximately 20%) presented a high number of violations from the R1 and R2 groups, representing the most risky violations. Practical solutions to minimize this evaluation bias were discussed. Food safety evaluation should use weighted scores and be risk-based. However, some precautions must be taken by researchers, health inspectors, and health surveillance departments to develop an adequate and reliable instrument.

Numerical Prediction of Flow and Heat Transfer in a Parallel Plate Channel With Staggered Fins

1987 ◽  
Vol 109 (1) ◽  
pp. 25-30 ◽  
Author(s):  
K. M. Kelkar ◽  
S. V. Patankar
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Periodic Variation ◽  
Local Heat ◽  
Temperature Fields ◽  
Parallel Plates ◽  
Constant Property ◽  
Cross Sectional ◽  
Flow And Heat Transfer ◽  
Order Of Magnitude

Fluid flow and heat transfer in two-dimensional finned passages were analyzed for constant property laminar flow. The passage is formed by two parallel plates to which fins are attached in a staggered fashion. Both the plates are maintained at a constant temperature. Streamwise periodic variation of the cross-sectional area causes the flow and temperature fields to repeat periodically after a certain developing length. Computations were performed for different values of the Reynolds number, the Prandtl number, geometric parameters, and the fin-conductance parameter. The fins were found to cause the flow to deflect significantly and impinge upon the opposite wall so as to increase the heat transfer significantly. However, the associated increase in pressure drop was an order of magnitude higher than the increase in heat transfer. Streamline patterns and local heat transfer results are presented in addition to the overall results.

The stress generated in a non-dilute suspension of elongated particles by pure straining motion

1971 ◽  
Vol 46 (4) ◽  
pp. 813-829 ◽  
Author(s):  
G. K. Batchelor
Keyword(s):  
Theoretical Formula ◽  
Rigid Sphere ◽  
Cross Sectional ◽  
Outer Flow ◽  
Rigid Particles ◽  
Bulk Stress ◽  
Order Of Magnitude ◽  
Sectional Plane ◽  
Dilute Suspension ◽  
A Minor

In a pure straining motion, elongated rigid particles in suspension are aligned parallel to the direction of the greatest principal rate of extension, provided the effect of Brownian motion is weak. If the suspension is dilute, in the sense that the particles are hydrodynamically independent, each particle of length 2l makes a contribution to the bulk deviatoric stress which is of roughly the same order of magnitude as that due to a rigid sphere of radius l. The fractional increase in the bulk stress due to the presence of the particles is thus equal to the concentration by volume multiplied by a factor of order l2/b2, where 2b is a measure of the linear dimensions of the particle cross-section. This suggests that the stress due to the particles might be relatively large, for volume fractions which are still small, with interesting implications for the behaviour of polymer solutions. However, dilute-suspension theory is not applicable in these circumstances, and so an investigation is made of the effect of interactions between particles. It is assumed that, when the average lateral spacing of particles (h) satisfies the conditions b [Lt ] h [Lt ] l, the disturbance velocity vector is parallel to the particles and varies only in the cross-sectional plane. The velocity near a particle is found to have the same functional form as for an isolated particle, and the modification to the outer flow field for one particle is determined by replacing the randomly placed neighbouring particles by an equivalent cylindrical boundary. The resulting expression for the contribution to the bulk stress due to the particles differs from that for a dilute suspension only in a minor way, viz. by the replacement of log 2l/b by log h/b, and the above suggestion is confirmed. The relative error in the expression for the stress is expected to be of order (log h/b)−1. Some recent observations by Weinberger of the stress in a suspension of glass-fibre particles for which 2l/h = 7·4 and h/2b = 7·8 do show a particle stress which is much larger than the ambient-fluid stress, although the theoretical formula is not accurate under these conditions.

Comparison of Mo-10Nb Alloy Target Materials Prepared by Different Techniques

2017 ◽  
Vol 726 ◽  
pp. 316-320 ◽  
Author(s):  
Jie Gao ◽  
You Jun Lu ◽  
Jun Feng Hou ◽  
Zhen Xia Yuan ◽  
Wen Luo ◽  
...  
Keyword(s):  
Hot Pressing ◽  
Element Distribution ◽  
Raw Material ◽  
Elemental Distribution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Alloy Target ◽  
Hot Pressing Sintering ◽  
Sintering Condition ◽  
Scanning Electron

The Mo powder and Nb powder was used as raw material, the Mo-10Nb alloy target was prepared by different sintering condition (non-pressure sintering and hot pressing sintering). The density, phase composition, microstructure and elemental distribution of Mo-10Nb alloy targets were determined by X-ray diffraction and scanning electron microscopy. The results showed that prepared by hot pressing Mo-10Nb alloy target density of 9.618 g/cm3, grain size 20 ~ 30μm, Mo and Nb element distribution.

scholarly journals Effect of Post-Process Curing and Washing Time on Mechanical Properties of mSLA Printouts

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 4856
Author(s):  
Bartłomiej Nowacki ◽  
Paweł Kowol ◽  
Mateusz Kozioł ◽  
Piotr Olesik ◽  
Jakub Wieczorek ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Bending Strength ◽  
Curing Time ◽  
Cross Sectional ◽  
Post Process ◽  
Order Of Magnitude ◽  
Static Tensile ◽  
High Roughness ◽  
Ambiguous Effect

The article discusses the influence of the post-process on the mechanical properties of elements produced with the use of the mask stereolithography (mSLA) method. Printed samples were subjected to the following post-process steps: Washing and post-curing, at various times. Then, static tensile and static bending tests were carried out, as well as Shore D hardness measurements for the inner and surface part of the sample, as well as profilographometric analysis of the surface. The post-curing time has been found to strongly affect the tensile and bending strength of printouts, and to improve their surface quality. Washing has an ambiguous effect on the strength of the printouts, but, in the end, it was found that extended washing slightly reduces the strength. Washing significantly affects the quality of the printout surface. A washing time that is too short results in a surface that strongly resembles the printing process, with high roughness. Increasing the washing time to 10 min lowers the roughness by one order of magnitude. Post-curing has also been shown to be beneficial for the cured sample with the application of shielding water. This approach results in an improvement in the flexural strength of the printouts. In general, the obtained research results indicate that, for printouts with cross-sectional dimensions of several mm, the optimal washing time is no more than 10 min and the post-curing time is at least 30 min.

Natural cellulosic fiber from Cordyline Australis leaves for textile application: extraction and characterization

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Atin Sumihartati ◽  
Wiah Wardiningsih ◽  
Naelly Al Kautsar ◽  
Muhammad Permana ◽  
Samuel Pradana ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Friction Coefficient ◽  
Average Length ◽  
Natural Fibers ◽  
Longitudinal Section ◽  
Raw Material ◽  
Scientific Article ◽  
Cross Sectional ◽  
Moisture Regain ◽  
Content Type

Purpose The purpose of this study is to explore the potential of Cordyline Australis fibers as an alternate raw material for textile. Design/methodology/approach The water retting method was used to extract the fiber. Cordyline Australis fibers were characterized in terms of the morphology of fibers (fiber cross-sectional and longitudinal), fiber chemical functional groups, tensile strength and elongation, fineness, fiber length, moisture regain and friction coefficient. Findings Cordyline Australis fiber strands consist of several individual fibers. At the longitudinal section, the fiber cells appeared as long cylindrical tubes with a rough surface. The cross-section of the Cordyline Australis fibers was irregular but some were oval. The key components in the fibers were cellulose, hemicellulose and lignin. The tensile strength of the fiber per bundle was 2.5 gf/den. The elongation of fibers was 13.15%. The fineness of fiber was 8.35 Tex. The average length of the fibers was 54.72 cm. Moisture Regain for fiber was 8.59%. The friction coefficient of fibers was 0.16. The properties of the fiber showed that the Cordyline Australis fiber has the potential to be produced into yarn. Originality/value To the best of the author's knowledge, there is no scientific article focused on the Cordyline Australis fibers. Natural fibers from the leaves of the Cordyline Australis plant could be used as an alternate material for textile.

scholarly journals Environmentally-Friendly High-Density Polyethylene-Bonded Plywood Panels

Polymers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1166 ◽  
Author(s):  
Pavlo Bekhta ◽  
Ján Sedliačik
Keyword(s):  
Mechanical Properties ◽  
Hot Pressing ◽  
High Density Polyethylene ◽  
Phenol Formaldehyde ◽  
Urea Formaldehyde ◽  
Physical And Mechanical Properties ◽  
Core Layer ◽  
High Density ◽  
Pressing Pressure ◽  
Pressing Time

Thermoplastic films exhibit good potential to be used as adhesives for the production of veneer-based composites. This work presents the first effort to develop and evaluate composites based on alder veneers and high-density polyethylene (HDPE) film. The effects of hot-pressing temperature (140, 160, and 180 °C), hot-pressing pressure (0.8, 1.2, and 1.6 MPa), hot-pressing time (1, 2, 3, and 5 min), and type of adhesives on the physical and mechanical properties of alder plywood panels were investigated. The effects of these variables on the core-layer temperature during the hot pressing of multiplywood panels using various adhesives were also studied. Three types of adhesives were used: urea–formaldehyde (UF), phenol–formaldehyde (PF), and HDPE film. UF and PF adhesives were used for the comparison. The findings of this work indicate that formaldehyde-free HDPE film adhesive gave values of mechanical properties of alder plywood panels that are comparable to those obtained with traditional UF and PF adhesives, even though the adhesive dosage and pressing pressure were lower than when UF and PF adhesives were used. The obtained bonding strength values of HDPE-bonded alder plywood panels ranged from 0.74 to 2.38 MPa and met the European Standard EN 314-2 for Class 1 plywood. The optimum conditions for the bonding of HDPE plywood were 160 °C, 0.8 MPa, and 3 min.

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