External corrosion of tinplate cans containing food products, although less frequent and comparatively less dangerous than internal corrosion, should anyhow be studied more in depth, since the consumer requires not only high-quality products, but also cans having a good appearance. The objective of this experimental work was to study the influence of the main ions present in cooling waters on the corrosion of metal food cans. After a short introduction on tinplate corrosion phenomena and on the chemical and processing factors affecting it, the results are shown which were obtained from electrochemical corrosion trials performed using model solutions at various concentrations as well as cooling water samples directly taken from food plants. This research work yielded information on the corrosion mechanisms (extent and morphology) of the various species and parameters affecting the aggressivity of industrial waters (presence of additives, free chlorine content and conductivity) | La corrosione esterna delle scatole di banda stagnata contenenti prodotti alimentari, sebbene meno frequente e relativamente meno pericolosa della corrosione interna, deve comunque essere oggetto di maggiore attenzione, in quanto il consumatore richiede, oltre a prodotti di alta qualita', contenitori di aspetto accettabile. Oggetto del lavoro sperimentale e' stato lo studio dell'influenza dei principali ioni presenti nelle acque di raffreddamento sulla corrosione delle scatole metalliche per alimenti. Dopo una breve introduzione sui fenomeni di corrosione della banda stagnata e sui fattori chimici e di processo che la condizionano, il lavoro illustra i risultati ottenuti nelle prove di corrosione elettrochimiche effettuate con soluzioni modello a diverse concentrazioni e con acque di raffreddamento prelevate direttamente presso industrie alimentari. A conclusione della ricerca sono state ottenute informazioni sul meccanismo di corrosione (intensita' e morfologia) delle diverse specie e sui parametri che influenzano l'aggressivita' delle acque industriali (presenza di additivo, concentrazione di cloro libero e conducibilita')

There has been developed a two-stage method for cooling jars with preserved food after sterilization. The first stage comprises cooling preserves up to t 75-80 deg. C in the air flow, the air velocities being 2.75, 3.7, 4.8, and 5.8 m/sec. The time of cooling reduced as the air velocity increases to be 11, 9, 8.5 and 8 min, respectively. The average speed of cooling gradually increases from 1.82 deg. C/min to 2.5 deg. C/min. The second stage comprises continuing cooling to apply a water film of 60-65 deg. C to the jar surface at 5-10 sec interval. During the process a jar is with a certain frequency is overturned down from the bottom to the cap. The average speed of cooling product is 3.33 deg. C/min at cooling air velocity of 2.75 m/sec and it is gradually increasing to reach 5.4 deg. C/min. Experimentally range of optimum cooling air velocities has been determined to be 4.8-5.8 m/sec, cooling time being decreased by 0.6 min only. A mathematical model has been has been developed describing the two-stage air and water vaporizing cooling time of stewed fruit jars depending on some factors. Relative error in comparing target values with experimental values did not exceed 8%. The developed method is recommended to be used at food canning industry enterprises and for designing continuously operating devices. | Разработан двухэтапный способ охлаждения банок с консервированными продуктами после стерилизации. На первом этапе (до t 75-80 град. С) охлаждение консервов производят в потоке атмосферного воздуха при различных скоростях охлаждающего воздуха – 2,75; 3,7; 4,8 и 5,8 м/с. Продолжительность охлаждения с увеличением скорости охлаждающего воздуха снижается и составляет соответственно 11,0; 9,0; 8,5 и 8,0 мин. При этом средняя скорость охлаждения продукта постепенно увеличивается с 1,82 град. С/м до 2,5 град. С/мин. На втором этапе охлаждение продолжается с нанесением на поверхность банки водяной пленки температурой 60-65 град. С с интервалом 5-10 с, при этом в процессе охлаждения банку с определенной частотой переворачивают с донышка на крышку. Средняя скорость охлаждения продукта составляет 3,33 град. С/мин при скорости охлаждающего воздуха 2,75 м/с и постепенно увеличивается, достигая 5,4 град. С/мин. Экспериментально определен интервал оптимальных скоростей охлаждающего воздуха (4,8-5,8 м/с), при котором продолжительность процесса охлаждения сокращается всего на 0,6 мин. Составлена математическая модель, описывающая продолжительность двухэтапного воздушно-водоиспарительного охлаждения банок с компотами в зависимости от ряда факторов. Относительная погрешность при сопоставлении расчетных значений с опытными не превышала 8%. Разработанный способ рекомендуется для применения на предприятиях консервной промышленности и при проектировании аппаратов непрерывного действия.