Improved pallet base designs for citrus export : a structural and airflow study

Thesis (MScFor)--Stellenbosch University, 2023.

ENGLISH ABSTRACT: The overall aim of this study was to investigate and develop pallet base designs for the citrus export industry that have sufficient mechanical strength and stiffness to handle the rigors of the export process. Pallet designs should also facilitate good airflow penetration for an efficient cold chain during shipping. Six existing pallet designs were tested for strength and stiffness performance to obtain a baseline data set. Airflow penetration was also modelled for these designs. An existing pallet testing rig that has the capability of testing various aspects of pallet strength and stiffness, was used to evaluate racking bending strength/stiffness, forklift bending strength/stiffness, and impact strength. Results from these tests assisted with the identification of weaknesses in each of the pallet designs. The information was used to create improved pallet designs which were subsequently manufactured and compared to the original designs. In designs where the thickness of the structural members were increased, it resulted, as expected, in a stiffer pallet. The most breakages occurred in the stringers and especially where there were knots present on the stringer, indicating that this specific member should be a focus of improvement. The orientation of the deck boards also played a role in the stiffness of the pallet as it affected the orientation of the corner blocks. If the corner blocks were parallel to the length of the pallet, they effectively reduced the span of bearers and therefore increased the pallet stiffness. In the improved designs, an extra nail was added on the corner block for better impact performance. This inadvertently increased pallet stiffness by aiding the connections between the bearer and the corner blocks. Mixed species pallets, where Eucalyptus grandis stringers were used with other members being Pinus, also resulted in stiffer pallets. The accuracy of the nailing pattern had a large effect on the performance of the pallet during impact testing. Airflow of all the improved pallets could be enhanced by better slat spacings. Apart from improving pallet designs, it is recommended that the manufacturers and buyers of pallets should implement more stringent quality control measures. A citrus pallet quality control working group consisting of users and manufacturers of pallets can aid in this process and should be considered by the South African citrus industry.

AFRIKAANSE OPSOMMING: Die oorkoepelende doel van hierdie studie was om palet-ontwerpe vir die sitrusuitvoerbedryf te ondersoek en te verbeter sodat dit voldoende meganiese sterkte en styfheid het om die uitdagings van die uitvoerproses te hanteer. Paletontwerpe moet ook goeie lugvloeipenetrasie toelaat vir 'n doeltreffende koueketting tydens verskeping. Ses bestaande paletontwerpe is getoets vir sterkte en styfheid om 'n basislyn datastel te verkry. Lugvloeipenetrasie is ook vir hierdie ontwerpe gemodelleer. ’n Bestaande palettoetstoestel wat die vermoë het om verskeie aspekte van paletsterkte en -styfheid te toets, is gebruik om rakbuigsterkte/-styfheid, vurkhyserbuigsterkte/-styfheid en impaksterkte te evalueer. Resultate van hierdie toetse het gehelp met die identifisering van swakhede in elk van die paletontwerpe. Die inligting is gebruik om verbeterde paletontwerpe te skep wat daarna vervaardig en met die oorspronklike ontwerpe vergelyk is. In ontwerpe waar die dikte van die strukturele lede vergroot is, het dit, soos verwag, gelei tot 'n stywer palet. Die meeste breuke het op die dwarsbalke voorgekom en veral waar daar kwaste op die dwarsbalk was, wat aandui dat hierdie spesifieke lid 'n fokus van verbetering behoort te wees. Die oriëntasie van die dekplanke het ook 'n rol gespeel in die styfheid van die palet aangesien dit die oriëntasie van die hoekblokke beïnvloed het. As die hoekblokke parallel aan die lengte van die palet was, het dit effektief die span van draers verminder en dus die paletstyfheid verhoog. In die verbeterde ontwerpe is 'n ekstra spyker op die hoekblok bygevoeg vir beter impakprestasie. Dit het ook paletstyfheid verhoog deur die verbindings tussen die draer en die hoekblokke te help. Gemengde spesies palette, waar Euclyptus grandis dwarsbalke gebruik is met ander lede van Pinus, het ook stywer palette tot gevolg gehad. Die akkuraatheid van die spykerpatroon het 'n groot effek op die werkverrigting van die palet tydens impaktoetsing gehad. Lugvloei van al die verbeterde palette kan verbeter word deur beter dekplankspasiëring. Afgesien van die verbetering van paletontwerpe, word dit aanbeveel dat die vervaardigers en kopers van palette strenger gehaltebeheermaatreëls moet implementeer. ’n Sitruspalletkwaliteitbeheerwerkgroep bestaande uit gebruikers en vervaardigers van palette kan in hierdie proses help en behoort deur die Suid- Afrikaanse sitrusbedryf oorweeg te word.

Masters