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Bugweed, a short fibre source of high potentialHoto, N. A. (Nceba Antony) 03 1900 (has links)
Thesis (MFor ) -- University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The bulk of paper grades destined for the printing industry are produced on modern
paper machines which continuously become wider and faster. In order to improve
printability, print quality and dimensional stability, such papers contain a large
percentage of mineral pigments either in the form of internal loading or external
coatings. Although mineral pigments exercise a substantial beneficial effect on paper
surface quality, unfortunately these minerals do not contribute towards sheet strength
and machine runnability. Today's papermakers are faced with the dilemma of
producing highly filled and coated printing papers with low grammages on faster
running paper machines, but often lacking the required quality of fibre resources to
secure a smooth runnability of such at high speeds. Standard fibre furnishes will have
to be upgraded with special types of reinforcing fibres in order to meet the demands
of sheet strength and machine runnability. The investigation had succeeded to identify
a new suitable fibre resource, which would satisfy the demand of a reinforcing type
natural material. / AFRIKAANSE OPSOMMING: Die oorgrootte meerderheid tipes papier wat vir die drukkersbedryf bestem is, word
op moderne papiermasjiene vervaardig wat steeds breër en vinniger word. Om die
drukbaarheid, drukkwaliteit en dimensionele stabiliteit te verbeter, bevat sulke papiere
groot hoeveelhede minerale pigmente wat in die vorm van interne ladings of as
eksterne bestrykings teenwoordig is. Alhoewel minerale pigmente -n merkbare
voordelige effek op die papier oppervlakte-kwaliteit uittoefen, dra sulke pigmente
ongelukkig nie by tot die sterkte en loopvermoë van die papier nie. Die hedendaagse
papiervervaardiger word konfronteer met die dilemma om swaar gevuldeen bestrykte
drukpapiere met lae oppervlaktegewig op vinniger lopende papiermasjiene te
vervaardig. Dit gebeur dikwels sonder die beskikbaarheid van die nodige hoëkwaliteit
veselbronne om te verseker dat die loopvermoë van die papier teen hoë
spoed nie benadeel word nie. Standaard veselsamestellings salopgegradeer moet
word met spesiale tipe versterkingsvesels om aan die uitdaging van hoë velsterkte en
masjien-Ioopvermoë te voldoen. Hierdie ondersoek het daarin geslaag om 'n nuwe
geskikte veselbron te dentifiseer en wat aandie behoeftes van 'n versterkingsvesel sal
voldoen.
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'n Ontleding van die hidrologiese eksperimente in die Cathedral Peak opvanggebiedeBosch, Jan Michael 12 1900 (has links)
Thesis (MScFor)--Stellenbosch University, 1980. / No Abstract Available
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Operation and performance of a solar hardwood drying kiln utilizing natural dehumidificationMuller, Richard B. 03 1900 (has links)
Thesis (MSc (Forest and Wood Science))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Saasveld solar kiln, valued at US$ 10,000 (R 70,000), is a greenhouse-type solar kiln requiring
no additional heating. A unique auto-regulated process of natural dehumidification at night controls
the humidity, and uses no venting system, nor any human/controller intervention. The natural
dehumidification is achieved by circulating the humid kiln air through an air jacket on the periphery
of the solar kiln. Diurnal temperature fluctuations allow condensation in the air jacket when air is
cooled to below its dew-point temperature. The process is simple as colder night temperatures are
a certainty. Almost no research has been done on similar kilns.
The purpose of this thesis was to study the operation and performance of a solar drying kiln to dry
high density hardwoods utilising natural dehumidification. The kiln load consisted of 20.1m
3
of a
high density hardwood, Eucalyptus diversicolor, with air-dry density of 893kg/m
3
.
The ZA Dry Q drying quality assessment indicated outstanding moisture distribution with little
drying stress, a few surface checks and no internal checks, collapse, short bow or surface
discolouration. The results conformed to the ZA Dry Q softwood appearance grade specification,
except for end checks – remarkable for the drying of any hardwood. The final moisture content
(MC) distribution was extremely tight with MC average of 11.5 per cent (%), standard deviation of
0.97% and the moisture gradient averaged 1.49%, standard deviation of 0.5%. The MC and MG
were equally distributed in all three geometric directions throughout the load. The timber dried in
130 days.
The kiln operation was analysed by temperature and humidity parameters at five positions inside
and outside the kiln while monitoring the MC. The extent of moisture evaporation from the timber
and the dehumidification of air were derived from this data.
The results showed that the average of the daily kiln temperature, independent from the external
temperature, increased from 18.0°C initially to 25.7°C. A maximum temperature of 38.1°C was
recorded at the end of drying. Cell collapse did not occur under these low temperatures.
Evaporation occurred generally from 07h30 to 16h45. The rate reduced at lower moisture contents.
There was no effect of stack width. Natural dehumidification by condensation happened generally
from 17h00 to 07h30.
The equilibrium moisture content (EMC) decreased automatically from an initial daily average of
18.1% (variation 5%) to 8% (variation 2%) finally. It was similar to a smoothed T3C2–schedule. The mild drying conditions, with EMCs above 7.3%, ensured minimal moisture gradients and
drying stresses. This reduced surface and internal checks. Nocturnal equalising and conditioning,
comparable to intermittent schedules, resulted from: no evaporation, improved diffusion of heated
timber and adsorption of moisture on the wood surface. The kiln protected the timber in extreme
climatic conditions.
It was found that the main circulating fan could be switched off from 17h00 to 07h30. A 30-minute
manual venting at noon was permitted once fibre saturation point had been reached.
Beneficiaries to this study can include hardwood processors who need to dry high density
hardwoods within a reasonable time to an excellent drying quality. Processors in developing
countries or who have little drying expertise could also benefit. / AFRIKAANSE OPSOMMING: Die Saasveld sondroër, met ‘n beraamde waarde van US$ 10,000 (R70,000), is ‘n groentetonneltipe sondroër met geen addisionele verhitting nie. ‘n Unieke auto-reguleerder beheer die humiditeit
snags deur natuurlike dehumidifikasie. Dit gebruik geen ventileerder of enige
menslike/kontroleerder inmenging nie. Die natuurlike dehumidifikasie word verkry deur die vogtige
lug te sirkuleer deur ‘n lugkussing op die omtrek van die tonnel. Dag-en-nag temperatuur
skommelings laat kondensasie toe binne-in die lugkussing sodra die lug benede die doupunttemperatuur afkoel. Dit is ‘n eenvoudige proses aangesien kouer nagte ‘n gegewe is. Byna geen
navorsing is nog op soortgelyke sondroërs gedoen nie.
Die doel van die tesis was om die werking en werkverrigting van ‘n sondroër wat hoë digtheid
loofhout met behulp van natuurlike dehumidifikasie droog, te bestudeer. Die houtvrag het bestaan
uit 20.1m
3
van hoë digtheid loofhout, Eucalyptus diversicolor, met ‘n gemiddelde lug-droë digtheid
van 893 kg/m
3
.
Die ZA Dry Q drogingskwaliteit toets het uitstaande resultate getoon. Daar was min
drogingspannings, ‘n paar oppervlak krake en geen interne krake, sel-ineenstorting, kort-boog of
oppervlak-verkleuring nie. Die resultate bevredig die ZA Dry Q naaldhout voorkomsgraad
spesifikasie, behalwe vir end-krake – merkwaardig vir die droging van enige hoë digtheid loofhout.
Die finale vogverspreiding was nou-verspreid met ‘n gemiddelde voggehalte van 11.5%, standaard
afwyking van 0.97% en ‘n gemiddelde vog-gradiënt van ‘n 1.49%, standaard afwyking van 0.5%.
Die voggehalte en vog-gradiënt was eweredig verspreid in al drie geometriese rigtings van die
houtvrag. Die hout het in 130 dae gedroog.
Die werking van die sondroër is geanaliseer deur temperatuur- en humiditeits-parameters by vyf
posisies binne- en buite die droogkamer tegelykertyd met die voggehalte te monitor. Die omvang
van vogverdamping uit die hout en dehumidifikasie van die lug is afgelei van hierdie data.
Die gemiddelde daaglikse sondroër-temperatuur, wat onafhanklik van die buite temperatuur was,
het verhoog van 18.0°C aanvanklik tot 25.7°C. Die maksimum temperatuur van 38.1°C is gemeet
aan die end van droging. Sel-ineenstorting het nie voorgekom by hierdie lae temperature nie.
Verdamping het algemeen voorgekom vanaf 07h30 tot 16h45, teen ‘n vertragende
verdampingstempo by laer voggehaltes. Die stapelwydte-effek was van geen belang nie.
Natuurlike dehumidifikasie deur kondensasie het gereeld voorgekom vanaf 17h00 tot 07h30. Die ewewigsvoggehalte (EVG) het outomaties verminder vanaf ‘n aanvanklike daaglikse
gemiddelde van 18.1% (variasie van 5%) na 8% (variasie van 2%). Dit was soortgelyk aan ‘n
gelykmatige T3C2 –drogingskedule. Die matige drogingskondisies, met EVG bokant 7.3%, het
minimale vog-gradiënte en drogingspannings verseker wat oppervlak-krake en interne-krake
verhoed het. Nagtelike houtvog egalisasie en kondisionering, vergelykbaar met puls-humiditeit
skedules, was die gevolg van: geen verdamping, verbeterde diffusie in verhitte hout en adsorpsie
van vog op die hout oppervlak. Die droogkamer het die hout beskerm teen buitengewone
klimaatstoestande.
Daar is gevind dat die hoof-waaier afgeskakel kan word vanaf 17h00 tot 07h30 en dat ‘n 30-minute
nie-outomatiese ventilering smiddae kan plaasvind sodra veselversadigingspunt bereik is.
Hierdie studie sal van nut wees vir die loofhout verwerkers wat hoë-digtheid loofhout moet droog
binne ‘n redelike tydperk met ‘n uitstekende drogings-kwaliteit, asook houtverwerkers in
opkomende lande of met gebrekkige drogingsvaardighede.
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Development of a time/temperature logging device to characterise the burning characteristics of biofuelsSmit, Hendrik Christiaan 03 1900 (has links)
Thesis (MScFor (Forest and Wood Science))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: A lab scale combustion unit was designed, in order to characterise the performance of
various woody and wood-based biofuels commonly used for energy production, cooking
and heating. The unit was constructed in a way that it could be repeatedly reused and
provide similar testing conditions, such as airflow for all samples. The requirements
were that it was big enough to contain a fire large enough to yield good
time/temperature profiles and at the same time easy to handle, operate and clean. It
also had to allow the insertion of the thermocouples and flue gas probe.
Time / temperature profiles were obtained and O2, CO2 and CO levels in the flue gas
determined for each biofuel. The samples consisted of the five most commonly used
fuel wood species in the Western Cape, namely Rooikrans, Camelthorn, Bluegum,
Black wattle and vine stumps and five processed products, namely wood pellets, wood
briquettes, commercial charcoal, commercial briquettes and handmade briquettes.
Combustion time/temperature profiles were obtained for all samples and characteristic
values, such as the maximum temperature and coal temperature compared. This
allowed an indication of which product performed better than others in the different
combustion phases and is more suitable for different requirements, such as industrial
heating, or domestic cooking. Even though Bluegum and Camelthorn performed best
overall they were not necessarily suited, for example, for large scale industrial use. It
was found that wood pellets and charcoal were the best biofuel for industrial purposes,
whereas Rooikrans was found to be the best option for small scale use. / AFRIKAANSE OPSOMMING: ‘n Laboratoriumskaal verbrandingseenheid was ontwerp vir die toets en karakterisering
van verskeie houtgebaseerde biomassa soorte algemeen in gebruik vir energie
opwekking, kook en verhitting. Daar was besluit om ‘n eenheid te bou vir herhaalde
gebruik wat die omstandinghede vir elke toets konstant kan hou, bv. ‘n damper om
lugvloei deur die sisteem the beheer. Die eenheid moet groot genoeg wees om veilig ‘n
groot genoeg vuur the bevat waarmee ‘n goeie tyd/temperatuur profiel verkry kan word,
maar terselfdetyd klein genoeg wees om te hanteer, operateer en skoon te maak. Die
eenheid moes ook voorsiening maak vir die insteek van die termostate en gas peilstif.
Tyd/temperatuur profiele is verkry en O2, CO2 en CO vlakke in die uitlaatgas is bepaal
vir elke bio-brandstof. Die monsters was saamgestel uit vyf van die mees algemeen
gebruikte brandhout spesies in die Wes Kaap, naamlik Rooikrans, Kameeldoring,
Bloekom, Swartwattel en wingerdstompies, asook vyf geprosesseerde produkte naamlik
houtpille, houtbrikette, kommersiële steenkool, kommersiële brikette and handgemaakte
brikette.
Verbranding tyd/temperatuur profiele is verkry vir al die monsters en verteenwoord
waardes is daarvan afgelees, bv. die maksimum temperatuur wat bereik is of die
temperatuur waar die vlamme uitgesterf het en slegs koolhitte gemeet word. Hierdie
profiele het dit moontlik gemaak om te identifiseer watter produk het beter gevaar as
ander gedurende die verskillende verbrandingsfases en is beter gepas vir verskillende
gebruike, bv. huishoudelike kook en verhitting. Resultate het gedui dat die Bloekom en
Kameeldoring die beste gevaar het oor all die toetse heen, maar was nie noodwendig
ideaal vir elke spesifieke doel nie. Dit was bevind dat die steenkool en houtpille die
beste gepas is vir industriele gebruik en dat die Rooikrans beter geskik is vir
huishoudelike en kleinskaalse gebruik.
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Development of potential height growth and diameter increment models for the parameterisation of an individual tree growth model for Pinus elliottii plantations in South AfricaLindner, Gerard Eckard 04 1900 (has links)
Thesis (MScFor)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Individual tree models, as opposed to stand models, have the potential to greatly improve sensitivity
of forest growth models to changing conditions such as silvicultural amendments, irregular stand
structures, etc. It was the purpose of this study to extend two sub-components of a European
individual tree growth model to introduce individual tree growth modelling concepts in South Africa
using Pinus elliottii as a study species. Two main objectives were established: Modelling the
potential height of stands across different site qualities and modelling diameter increment using a
potential modifier approach with a combination of competition indices that change in importance
according to the edaphic conditions of the site.
Potential height modelling used three steps in order to achieve this objective. The first was to
compare site index models based on different model fitting techniques, namely nonlinear least
squares, generalised nonlinear least squares and nonlinear mixed effects models. The nonlinear
mixed effects model proved to be superior in terms of achieving the principles of regression
assumptions and model fit for the data range observed. The second step was to fit potential height
using nonlinear quantile regression on observed spacing trial height measurements. This proved to
be a robust technique able to capture potentials according to the defined Chapman-Richards model
structure. The final step was to use the predicted site index as a site classification variable in order to
predict potential height. While some small deviation occurred, potential height seems to be well
correlated to site index and validation on selected sites suggested that site index can be used to
model potential height until a more sophisticated site classification model is used for future
improvement of the model. Diameter increment modelling followed six major steps in order to apply the full parameterisation
methodology of an age-independent diameter increment model dependent on tree diameter and
competition. Diameter increment potentials were fit using site index as a predictor of the potential
height curves. Multiple competition indices were tested on two sites to obtain a combination of two
indices, which can capture overtopping and local crowding effects. Principle components analysis
and variance inflation factors calculation were applied to test for collinearity between indices.
Suitable combinations were tested resulting in a combination of the KKL and Local Basal Area
competition indices. Changing importance of the two indices were observed on the two sites tested
indicating a shift in the mode of competition according to a water gradient.
These were combined in a deterministic potential modifier model, which mimicked competitive
stages over age; however the validation showed a skewed distribution, which was not sensitive to
stand density gradients. A stochastic model was constructed to model variance from observed
residual plots using linear quantile regression to determine bounds for a truncated normal
distribution which generates random deviates for a predicted increment. The stochastic element
significantly improved the performance and sensitivity of the model, however the model was still
not sensitive enough at very high and very low spacing densities. All in all two key models for an
adaptation of an individual tree growth simulator to South African conditions were successfully
demonstrated. The two main objectives were achieved; however some indicated improvements
could be made, especially for the competition indices where the sensitivity of competition to
changing resource limitation according to site and temporal scales needs to be further investigated. Furthermore, the full set of models for simulating individual tree growth still needs to be applied.
Overall, as a methodological approach, the study outlined problems and future improvements,
introduced new concepts and can serve as a guideline for future parameterisation of an individual
tree growth model. / AFRIKAANSE OPSOMMING: In vergelyking met vakgroeimodelle, het individuele-boomgroeimodelle die potensiaal om die
sensitiwiteit van plantasiegroeimodelle vir veranderende omstandighede soos aanpassings in
boskultuur, onreëlmatige vakstrukture, ensovoorts, drasties te verbeter. Die doel van hierdie studie
was om twee subkomponente van ‘n Europese individuele-boomgroeimodel uit te brei om
sodoende individuele-boomgroei modelleringskonsepte in Suid-Afrika bekend te stel. Pinus elliottii is
gebruik as studiespesie. Twee hoofdoelstellings is bepaal. Eerstens, die modellering van hoogtegroei
potensiaal van opstande oor verskeie vlakke van groeiplek kwaliteit. Tweedens, die modellering van
deursnee-aanwas deur gebruik te maak van ‘n potensiaal matigingsbenadering “potential modifier
approach“ met ‘n kombinasie van kompetisie-indekse waarvan die belangrikheid verander volgens
die edafiese toestande van die groeiplek.
Die hoogtepotensiaalmodellering bestaan uit drie stappe. Tydens die eerste stap word groeiplek
bonniteitsmodelle vergelyk op grond van verskillende modelpassingstegnieke, naamlik nie-lineêre
minimum kwadrate, algemene nie-lineêre minimum kwadrate en nie-lineêre gemengde effek
modelle. Laasgenoemde het die beste gevaar in terme van die beginsels van regressiemodelle asook
die mate waarin die model die waargeneemde data pas. Tweedens is hoogtegroei potensiaal
gemodelleer deur nie-lineêre kwantielregressie op waargeneemde hoogtes van
spasiëringseksperimente toe te pas. Die metode is robuust en in staat om potensiale volgens die
gedefinieerde Chapman Richards modelstruktuur vas te vang. Laastens is die voorspelde bonniteits
indeks as ‘n groeiplek klassifasie veranderlike gebruik om sodoende die hoogtegroei potensiaal te
voorspel. Alhoewel klein afwykings voorgekom het, blyk hoogtegroei potensiaal goed gekorreleer te
wees met bonniteits indeks. Uit validasie op geselekteerde groieplekke blyk dit dat bonniteits indeks
gebruik kan word om hoogtegroei potensiaal te modelleer totdat ‘n meer gesofistikeerde groeiplek
klassifikasiemodel beskikbaar is wat die model verder sal kan vebeter. Die volledige parametriseringsmetodiek van ‘n ouderdoms-onafhanklike deursnee-aanwas model
wat afhanklik is van boomdeursnee en kompetisie bestaan uit ses hoof prosesse. Nie-lineêre
kwantielregressie is gebruik om deursnee-aanwaspotensiale te pas vir verskeie groeiplekke. Dié is
gekombineer met ‘n bonniteits indeks om ‘n nuwe model te vorm waarmee hoogtegroeipotensiaal
kurwes voorpel kon word. Daar is met veelvuldige kompetisie-indekse op twee groeiplekke
geëksperimenteer om ‘n kombinasie van slegs twee indekse te vind wat die effekte van
oorskaduwing en plaaslike verdringing kan vasvang, te vind. Hoof komponent analise “Principle
components analysis” en variansie inflasie faktore berekening “variance inflation factors calculation”
is gebruik om vir kollineariteit tussen die indekse te toets. Gepaste indekskombinasies is getoets. ‘n
Kombinasie van die KKL en plaaslike basale oppervlakte “Local Basal Area” kompetisie-indekse het
die beste resultate gelewer. Die twee indekse is as volg geselekteer. Veranderings in die
belangrikheid van elk van die indekse is waargeneem op die twee toetspersele. Dit dui op ‘n
verskuiwing in die modus van kompetisie afhangend van ‘n watergradiënt.
Die twee indekse is gekombineer in ‘n deterministiese potensiaal matigings model wat die
kompeterende stadiums oor ouderdom naboots. Validasie het egter ‘n skewe verdeling wat nie
sensitief vir opstandsdigtheidsgradiënte is nie, gewys. ‘n Stogastiese model is ontwikkel om variansie
in die residuele grafieke te modelleer. Lineêre kwantielregressie is gebruik om grense vir ‘n afgestompte normaalverdeling wat ewekansige afwykings vir ‘n voorspelde aanwas te bepaal. Die
stogastiese element het die prestasie van die deterministiese model merkbaar verbeter. Selfs met
die stogastiese element, is die model egter steeds nie sensitief genoeg vir baie hoë en baie lae
opstandsdigthede nie.
Ter opsomming is twee modelle vir ‘n aanpassing van ‘n individuele-boomgroeisimuleerder vir Suid-
Afrikaanse toestande suksesvol gedemonstreer. Die twee hoofdoelstellings is bereik. Daar is egter
steeds ‘n paar aangeduide verbeterings wat aangebring kan word. Die sensitiwiteit van die
kompetisie-indekse op hulpbronbeperkings wat verander op grond van die ruimtelike en temporale
skale moet veral verder bestudeer word. Verder moet die volle stel modelle wat benodig word om
individuele-boomgroei te modelleer nog toegepas word. As ‘n metodologiese benadering, het die
studie probleme uitgewys en toekomstige verbeterings aangedui, nuwe konsepte bekendgestel en
kan dus dien as ‘n riglyn vir toekomstige parametrisering van individuele-boomgroeimodelle.
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’n Ekonomiese ondersoek na die produksie van timmerhout uit uitheemse naaldhoutplantasies in die unie van Suid-AfrikaDe Villiers, P. C. 06 1900 (has links)
Thesis (DSc (Forest and Wood Science))-- Stellenbosch University, 1954. / No abstract
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Moisture content and drying defects in kiln-dried Eucalyptus grandis polesMugabi, Paul 12 1900 (has links)
Thesis (PhD (Forest and Wood Science))--Stellenbosch University, 2007. / ENGLISH ABSTRACT: There has been a reported reduction in the durability of creosote treated, wooden utility poles in
South Africa in recent years. Several factors could have been responsible for this. In this study,
Eucalyptus grandis pole drying schedules currently used, methods of measurement of moisture
content (MC) after drying and drying defects were investigated. Relationships involving drying
defects and MC gradient before treatment which may help in the development of simple nondestructive
methods of assessing defects such as surface checking, honeycomb and collapse,
and MC gradient were also explored. The long term goal of this study was to increase the
durability of treated poles by avoiding unacceptable drying defects and MC values before
treatment. The results of this investigation are presented in the following chapters:
an introduction motivating the aims of the investigations (Chapter 1);
a review of literature relevant to MC and drying defects in sawn or round wood
(Chapter 2);
ready for press manuscripts on MC and drying defects in kiln-dried E. grandis poles
(Chapters 3 to 7) and
a general conclusion that links up chapters 3 to 7, and recommendations (Chapter 8).
The auger drill method gave reliable MC values when samples in increments of 25 mm depths
into the pole were taken. However, when single samples of 50 mm and 75 mm depths were
considered, the auger drill MC measurements were unreliable. It was concluded that SABS SM
983 (2000), which specifies taking single radial auger drill samples of depth 70±5 mm at pole
mid length, is not a reliable method of measuring MC in a kiln-dried E. grandis pole.
Correlation results indicated that tree growth factors such as sapwood depth, green MC and
heartwood percentage were related to final drying defects and may be used as criteria for pole
sorting before kiln drying. Also, the number of valleys per unit length (VPUL) of the
circumference at the theoretical ground line (TGL) was positively correlated with honeycomb
and closed surface checks, implying that VPUL as a parameter of the pole circumference
profile can be used to assess invisible, internal defects.
The dry bulb temperature (Tdb) of 80oC, used to dry poles in industry, was too high and resulted
into unacceptable levels of drying defects in kiln dried E. grandis poles. In addition, the drying
period of 8 days was too short to attain an acceptable MC gradient in poles.
It is, therefore, recommended that:
To use the auger drill method to reliably determine the moisture content of a pole,
samples in increments of 25 mm should be taken.
MC measurements should be made at the most critical zones of a pole such as the TGL
and not higher up since there is normally considerable MC variation in the longitudinal
direction. It is also important to consider sampling more than one position on the pole
circumference to cater for the MC variation in the tangential direction.
For poles with large sapwood depths i.e. >15mm, mild drying conditions at the
beginning of a drying run should be used, since such poles may be more susceptible to
surface checking. Poles with large heartwood percentages should also be dried with
suitable kiln schedules, i.e. with low Tdb to minimise honeycomb and collapse. In
general, Tdb lower than 80oC should be considered in order to reduce the defects to
acceptable levels.
Poles should be dried for longer than 8 days even at Tdb as high as 80oC to reduce the
MC to acceptable values and gradients.
Since only three schedules were tested, more drying schedules should be investigated to
make reliable conclusions about the effect of schedule on drying defects. In addition,
more poles per schedule should be considered in order to obtain statistically reliable
results.
The relationship of pole diameter and drying defects also requires further investigation.
Since a limited sample was used to test for the effect of source of poles and drying
schedules on defect correlations, further studies should be done on sufficient samples to
come up with more reliable conclusions. It is also necessary to further investigate the
possible variation in correlation of VPUL and internal defects on a large sample of poles
from specific sources and drying schedules. / AFRIKAANSE OPSOMMING: Die afgelope paar jaar is waargeneem dat kreosootbehandelde transmissiepale 'n afname in
duursaamheid toon. Verskeie faktore kan hiervoor verantwoordelik wees. In hierdie studie is
huidige Eucalyptus grandis oonddrogingskedules en voggehalte- (VG) bepalingsmetodes vóór
en na droging asook drogingsdefekte ondersoek. Verwantskappe tussen drogingsdefekte en
VG-gradiënt vóór behandeling wat kan meehelp om nie-destruktiewe metodes te ontwikkel om
defekte soos oppervlaktekrake, interne barste en instorting en VG-gradiënt te bepaal, is ook
bestudeer. Die langtermyn doelwit van hierdie studie is om die duursaamheid van behandelde
pale te verbeter deur onaanvaarbare drogingsdefekte en voggehaltes vóór behandeling te vermy.
Die resultate van hierdie ondersoek word in die volgende hoofstukke bespreek:
'n inleiding waarin die doelwitte van die onderskeie ondersoeke motiveer word
(Hoofstuk 1);
'n oorsig van die literatuur relevant tot VG en drogingsdefekte in gesaagde en
rondehout (Hoofstuk 2);
persklaar manuskripte oor VG en drogingsdefekte in oondgedroogde E. grandis
pale (Hoofstukke 3 tot 7) en
'n algemene gevolgtrekking wat bevindings uit hoofstukke 3 tot 7 saamvat gevolg
deur aanbevelings (Hoofstuk 8).
Die augerboor-metode kon betroubare VG-waardes lewer indien monsters van 25mm diepteinkremente
in die paal geneem is. Augerboor-voggehaltemetings met enkel 50mm en 75mm
monsters was egter onbetroubaar. Daar is bevind dat SABS SM 983 (2000), wat 'n enkel
radiale augerboormonster tot op 'n diepte van 70±5 mm in die middel van die lengte van die
paal spesifiseer, nie 'n betroubare VG-bepalingsmetode vir oondgedroogde E. grandis pale is
nie.
Die resultate het aangetoon dat boomgroeifaktore soos spinthoutdiepte, groen voggehalte en die
persentasie kernhout aan drogingsdefekte verwant is en as basis vir sortering van pale vóór
oonddroging gebruik kan word. Ook kon die aantal valleie per eenheidslengte (e. VPUL) van
die omtrek by die teoretiese grondlyn (TGL) positief met interne barste en geslote
oppervlaktekrake korreleer word wat impliseer dat VPUL as parameter van die omtrekprofiel
van die paal gebruik kan word om onsigbare, interne defekte mee vas te stel.
Die droëbaltemperatuur (Tdb) van 80oC wat in die industrie gebruik word, was te hoog omdat
dit onaanvaarbare vlakke van drogingsdefekte in oondgedroogde E. grandis veroorsaak het.
Daarbenewens was die drogingsperiode van 8 dae by 'n Tdb van 80oC te kort om 'n aanvaarbare
VG-gradiënt te lewer.
Die volgende word derhalwe aanbeveel:
Om betroubare VG-resultate d.m.v. die augerboormetode te verkry, behoort monsters in
inkremente van 25mm geneem te word.
VG-metings behoort in die mees kritiese dele van 'n paal gedoen te word byv. by TGL
en nie hoër nie omdat daar normaalweg beduidende VG-variasie in die longitudinale
rigting is. Dis ook belangrik om op meer as een posisie op die omtrek te meet om vir die
variasie in die tangensiale rigting voorsiening te maak.
Ligte drogingstoestande behoort aan die begin van die drogingsproses by pale met groot
spinthoutdieptes, bv. > 15mm, gebruik te word omdat sulke pale meer geneigd tot
oppervlaktekrake is. Pale met hoë kernhoutpersentasies moet ook met geskikte
drogingskedules, bv. met lae Tdb, gedroog word om interne barste en ineenstorting te
verminder. Oor die algemeen behoort Tdb laer as 80oC oorweeg te word om die omvang
van defekte by aanvaarbare vlakke te hou.
Selfs by Tdb so hoog as 80oC behoort pale langer as 8 dae te droog om die VG tot by
aanvaarbare waardes en 'n gradiënt te bring.
Omdat slegs drie skedules evalueer is, behoort meer skedules ondersoek word om
betroubare gevolgtrekkings oor die effek van skedule op drogingsdefekte te verskaf.
Addisioneel behoort meer pale per skedule oorweeg word om statisties betroubare
resultate te verkry.
Die verwantskap tussen paaldeursnee en drogingsdefekte benodig ook verdere
ondersoek.
Aangesien 'n beperkte aantal pale gebruik is om die herkoms en drogingskedule met
defekte te korreleer, behoort verdere studie op genoeg pale gedoen te word om meer
betroubare gevolgtrekkings te kry. Dit is ook noodsaaklik om die moontlike variasie in
die korrelasie tussen VPUL en interne defekte op 'n groot aantal pale van spesifieke
herkoms en drogingskedules vas te stel.
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Nasionale bosbeleid in Suid-AfrikaUys, H. J. E. 12 1900 (has links)
Thesis (MSc (Forest and Wood Science))--University of Stellenbosch, 1979. / 368 leaves printed on single pages, preliminary pages i-vii and numbered pages 1-211. Includes bibliography, list of figures. / Digitized at 600 dpi grayscale to pdf format (OCR), using a Bizhub 250 Konica Minolta Scanner.
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19 |
Die ekonomiese ontwikkeling van die bosbou-onderneming in Suid-AfrikaDe Villiers, P. C. 05 1900 (has links)
Thesis (MSc)-- Stellenbosch University, 1951. / No abstract.
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20 |
The effect of sodium lauryl sulphate on blue stain, mould growth and surface properties of SA pinePerold, Maurits 3 1900 (has links)
Thesis (MScFor (Forest and Wood Science))--University of Stellenbosch, 2006. / Producing high quality end products, rather than focusing on volume production, is
slowly but surely becoming the main driving force in the wood processing industry of
South Africa. Drying defects such as surface checks and discolouration by yellow
stain and kiln brown stain are major factors in softwood timber downgrades when
selecting furniture grade timber. Previous efforts to control these defects have
focused on schedule adaptation, but as the industry is still mainly concerned with
volume production, and because of the varying lumber price, longer schedules to
control these drying defects have not yet been that attractive for the larger sawmills.
In ongoing research in this laboratory, a dip treatment of freshly sawn softwood boards
in an aqueous solution containing a surfactant called sodium lauryl sulphate (SLS)
was used to try to influence the mechanism involved in the development of these
stains. Further, complementary research is reported in this study. Firstly, the
possibility of using SLS solutions to control surface mould development and bluestain
was investigated. Results showed that SLS did control the development of blue stain
and mould growth in open-stacked boards for up to three weeks, using concentrations
as low as 0.1%, and up to two weeks in closed-stacked timber when using
concentrations of 0.2%.
Secondly, it was investigated whether SLS treatment would have a detrimental effect
on downstream product quality; in particular, kiln dried boards and glued components
for furniture manufacturing. Since SLS influenced fluid water flow during kiln drying,
the treatment could have exacerbated the occurrence of surface checking due to
altered moisture distribution profiles. Results of this investigation showed that the SLS
treatment did not result in increased surface checking.
Thirdly, as furniture quality timber treated with SLS would be glued, (and also finished
with surface coatings), it was further considered important to determine if SLS
treatment influenced adhesion properties of wood surfaces. Based on shear test
results, it was established that SLS did not influence the adhesion properties of wood
when glued with two most commonly used glues in the furniture industry i.e. polyvinyl
acetate (PVAc) and urea formaldehyde (UF).
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