Development of home compostable materials based on bioavailable polymers is of high strategic interest as they ensure a significant reduction of the environmental footprint in many production sectors.In this work,the ...Development of home compostable materials based on bioavailable polymers is of high strategic interest as they ensure a significant reduction of the environmental footprint in many production sectors.In this work,the addition of thermoplastic starch to binary PLA/PBAT blends was studied.The compounds were obtained by a reactive extrusion process by means of a co-rotating twin screw extruder.Thermomechanical,physical and chemical characterization tests were carried out to highlight the effectiveness of the material design strategy.The compounds were subsequently reprocessed by cast extrusion and thermoforming in order to obtain products suitable for the storage of hot food.The extruded films and the thermoformed containers were further characterized to highlight their thermo-mechanical,physical and chemical properties.Thermo-rheological,mechanical and physical properties of the material and of the cast film were analyzed thoroughly using combined technique as capillary rheometer,MFI,DSC,VICAT/HDT,XRD,FTIR,UV-Vis,SEM,permeability and,lastly,running preliminary chemical inertness and biodegradation tests.Particular attention was also devoted to the evaluation of the thermo-mechanical resistance of the thermoformed containers,where the PLA/PBAT/TPS blends proved to be very effective,also presenting a high disintegration rate in ambient conditions.展开更多
Wearing a mouthguard reduces the risk of sports-related injuries, but the material and thickness of the mouthguard has a substantial impact on its effectiveness and safety. The aim of this study was to establish a the...Wearing a mouthguard reduces the risk of sports-related injuries, but the material and thickness of the mouthguard has a substantial impact on its effectiveness and safety. The aim of this study was to establish a thermoforming technique in which the model position is moved just before formation to suppress the reduction in thickness. Mouthguards were vacuum formed using ethylene-vinyl-acetate sheets with a thickness of 2.0, 3.0, and 4.0 mm. The working model was trimmed to the height of 25-mm at the maxillary central incisor and 20-mm at first molar. The model was placed with its anterior rim positioned 40-mm from the front of the forming table. Two forming methods were compared: 1) the sheet was formed when it sagged 15-mm at the top of the post under normal conditions (control);and 2) the sheet frame at the top of the post was lowered and the model was covered when the sheet sagged 15-mm, the rear side of the model was pushed forward 20-mm, and the mouthguard was formed (MP;model position). Sheet thickness after fabrication was determined for the incisal edge, labial surface, and buccal surface using a specialized caliper accurate to 0.1-mm. The difference in the reduction in thickness depending on the forming methods and sheet thicknesses were analyzed by two-way ANOVA and Bonferroni’s multiple comparison tests. Reduction in thickness was greater for thicker sheets, and the reduction in thickness for the MP was less than that for the control. The reduction in labial for the MP was an exception;the reduction in thickness was only about half that of the control. The thermoforming technique of moving the model forward just before vacuum formation was effective for suppressing the mouthguard thickness reduction, which in thickness of the labial side can be reduced to about half of the normal forming method.展开更多
Wearing a mouthguard reduces the risk of sports-related injuries, but a more comfortable design is required in order to increase the wearing rate. The aim of this study was to investigate a thermoforming method that d...Wearing a mouthguard reduces the risk of sports-related injuries, but a more comfortable design is required in order to increase the wearing rate. The aim of this study was to investigate a thermoforming method that decreases palatal thickness while maintaining labial and buccal thickness. Mouthguards were fabricated from an ethylene-vinyl acetate sheet (thickness: 4.0 mm) by using a vacuum forming machine. Four working models were prepared: 1) the anterior height was 25-mm and the posterior height was 20-mm (model A), 2) model A with the palate trimmed (model B), 3) heights 5 mm greater than model A (model C), and 4) model C with the palate trimmed (model D). The two forming conditions were as follows: 1) The sheet was formed when it sagged 15 mm below the level of the sheet frame at the top of the post under ordinary use (control);2) The sheet frame at the top of the post was lowered and the sheet covered the model when it sagged by 15 mm. The rear side of the model was pushed to move the model forward 20 mm, and then the sheet was formed (MP). Differences in mouthguard thickness due to forming conditions and model forms were analyzed by two-way analysis of variance and Bonferroni’s multiple comparison tests. Difference in forming conditions was similar for all model forms;for the MP, the thickness of the incisal edge, labial surface, cusp and buccal surface were greater, and the palatal surface was thinner than the control. On the labial and buccal surface, the thickness difference due to the model form was observed only for the MP, and models A and B were thicker than models C and D. The palatal thickness tended to be thin in the models with the trimmed palate. This study suggested that the labial and buccal thickness of the mouthguard can be maintained, and the palatal thickness can be decreased by using the model with the palate trimmed with the forming method in which the model position is moved forward immediately before the vacuum formation.展开更多
Mouthguards can reduce the risk of sports-related injuries, but the sheet material and thickness have a large effect on their efficacy and safety. This study was intended to predict the changes in thickness of molded ...Mouthguards can reduce the risk of sports-related injuries, but the sheet material and thickness have a large effect on their efficacy and safety. This study was intended to predict the changes in thickness of molded products by clarifying the effect of the time interval between repeat moldings during the continuous use of a vacuum-forming machine. Ethylene vinyl acetate mouthguard sheets were used for thermoforming with a vacuum-forming machine. The working model was trimmed to a height of 23 mm at the maxillary central incisor and 20 mm at maxillary first molar. Five molding conditions were investigated: 1) molding was carried out after the sag at the center of the softened sheet was 15 mm (control);2) sheet heating was started 5 min after the molding of the control (AF5-Re1);3) sheet heating started 5 min after the molding of AF5-Re1 (AF5-Re2);4) sheet heating started 10 min after the molding of the control (AF10-Re1);and 5) sheet heating started 10 min after the molding of AF10-Re1 (AF10-Re2). Sheet thickness after fabrication was determined for the incisal edge, labial surface, cusp, and buccal surface using a special caliper accurate to 0.1 mm. Thickness differences of the molding conditions were analyzed by two-way analysis of variance. Significant differences between the control and AF5-Re1 were observed at all measurement points (p < 0.01), but not between the control and AF10-Re1. AF10-Re2 became thinner than AF10-Re1 (p < 0.01). Reproducible molding results were obtained by waiting 10 min between the first and second moldings, but the third molded mouthguard was significantly thinner, despite this 10 min wait interval.展开更多
Mouthguard thickness is affected by the softened state of the sheet during thermoforming. The aim of this study is to establish an effective method for controlling the softened state of the sheet to prevent the mouthg...Mouthguard thickness is affected by the softened state of the sheet during thermoforming. The aim of this study is to establish an effective method for controlling the softened state of the sheet to prevent the mouthguard thickness from decreasing during mouthguard fabrication using a vacuum-forming machine. Mouthguards were thermoformed using an ethylene-vinyl acetate sheet (thickness: 4.0 mm) and a vacuum-forming machine. The working model was trimmed to the anterior height of 25 mm and the posterior height of 20 mm. The following two heating methods were compared: 1) the sheet was formed when it sagged 15 mm below the level of the sheet frame at the top of the post (condition T);and 2) the sheet frame was lowered to and heated at 50 mm below its usual height and the sheet was formed when it sagged 15 mm below the level of the sheet frame (condition L). For each heating method, the vacuum was applied immediately (T0, L0) or 5 s (T5, L5) after the sheet frame was lowered to the forming unit. The sheet surface temperature immediately before the vacuum was applied under each condition was measured. The differences in mouthguard thickness due to forming conditions were analyzed by one-way ANOVA and Bonferroni’s multiple comparison tests. The temperature difference between the center and the posterior depending on the condition decreased in the order T0 > T5 > L0 > L5, and that was 20<span style="white-space:nowrap;">°</span>C or higher for T0 and T5, and 10<span style="white-space:nowrap;">°</span>C or less for L0 and L5. At the incisal edge and the cusp, L0 and L5 were significantly thicker than T0. No significant differences were observed between conditions L0 and L5 at any measurement points. For the labial and buccal surfaces, significant differences in thicknesses among all conditions, except L0 and L5, were observed and were in the order T0 < T5 < L0 and L5. This study was suggested that the lowering the sheet frame and heating was more effective than adjusting the vacuum timing for uniform softening of the sheet.展开更多
Effectiveness and safety of mouthguards are greatly affected by its thickness. The aim of this study was to clarify the effect of model height and model position on the forming table on the mouthguard thickness in the...Effectiveness and safety of mouthguards are greatly affected by its thickness. The aim of this study was to clarify the effect of model height and model position on the forming table on the mouthguard thickness in thermoforming using a circular frame. Mouthguards were thermoformed using 4.0-mm-thick ethylene-vinyl-acetate sheets and a vacuum forming machine. The sheet was sandwiched between circular frames and fixed to the clamp of the forming machine. Working models were two types of hard gypsum models trimmed so that the height of the anterior part was 25 mm (Model A) and 30 mm (Model B). The model was placed with its anterior rim positioned 40 mm (P40), 30 mm (P30), 20 mm (P20), or 10 mm (P10) from the front of the forming table. Differences in the reduction rate of the thickness due to the model height and model positions were analyzed by two-way ANOVA and Bonferroni’s multiple comparison test. Differences depending on the model height were observed at P40 at the incisal edge and P30, P20, and P10 on the labial surface, and the reduction rate of the thickness was significantly smaller in Model A (P < 0.01). As the distance from the model anterior rim to the front of the forming table was smaller, the rate of the thickness of the incisal edge and the labial surface decreases became larger. The rate of decrease in the thickness of the cusp and buccal surface was the smallest at P20. This study indicated that the difference in the thickness of the single-layer mouthguard depending on the model position on the forming table is affected by the model height. However, that is only the anterior part of the mouthguard, and the difference in thickness reduction rate is less than 5%. Additionally, in order to perform stable forming, it is useful to increase the distance from the model to the frame, and it is important to position the part whose thickness is desired to be maintained in the center of the forming table.展开更多
The height of the working model affects the mouthguard thickness. The aim of this study was to clarify the difference in the effect of model height on the thickness between single- and double-layered mouthguards. Mout...The height of the working model affects the mouthguard thickness. The aim of this study was to clarify the difference in the effect of model height on the thickness between single- and double-layered mouthguards. Mouthguards were thermoformed using ethylene-vinyl-acetate sheets and a pressure molding machine. Working models were three hard gypsum models with the height of the anterior part trimmed to 25 mm (model A), 30 mm (model B), and 35 mm (model C). Three molding conditions were compared: a single-layered mouthguard using a 4.0-mm thick-sheet (S4);a double-layered mouthguard using a 3.0-mm-thick sheet on the first-layer and a 2.0-mm-thick sheet on the second-layer (L32);and a double-layered mouthguard using 3.0-mm-thick sheets on first- and second-layers (L33). Analysis was performed by two-way ANOVA and a simple main effect test for the differences in the mouthguard thickness depending on the model height and the molding condition. Under all molding conditions, the labial and buccal thicknesses tended to become thinner as the model height increased, and models B and C were thinner by about 6% - 7% and about 14% - 16% than model A, respectively. The cusp thickness was not affected by the model height in L32 and L33, but in S4, models B and C were thinner about 14% or more than model A. Significant differences were observed among molding conditions, and S4 P < 0.01). This study suggested that the degree of the decrease in mouthguard thickness due to the increase the model height was similar for the single- and double-layered mouthguards on the labial and buccal sides, and increasing the model height by 5 mm and 10 mm decreased the thickness by about 6% - 7% and about 14% - 16%, respectively. At the cusp, only the single-layered mouthguard was affected by the model height.展开更多
The effectiveness and safety of the mouthguard depend on the sheet material thickness. The thickness of the thermoformed mouthguard is affected by the model undercut and the thermal shrinkage that occurs when the extr...The effectiveness and safety of the mouthguard depend on the sheet material thickness. The thickness of the thermoformed mouthguard is affected by the model undercut and the thermal shrinkage that occurs when the extruded-molded sheet is reheated. The aim of this study was to clarify the influence of the undercut amount of the model and the thickness of the sheet material on the thermal shrinkage of the extruded sheet. The mouthguard sheet used ethylene-vinyl acetate resin with a thickness of 4.0 mm (4M) and 3.0 mm (3M) and was manufactured by extrusion molding. The working models were three hard gypsum models with the undercut amount on the labial side trimmed to 0? (U0), 10? (U10), and 20? (U20). Mouthguard thickness after vacuum formation was compared between the conditions formed so that the extrusion direction was vertical (condition V) or parallel (condition P) to the model midline. Differences in the reduction rate of the mouthguard thicknesses of the labial and buccal side depending on the sheet extrusion direction, model angle, and sheet material thickness were analyzed by three-way ANOVA and Bonferroni method. The reduction rate of the thickness in condition P was significantly greater than in condition V under all conditions except U0-4M on the labial side and U0-4M and U10-4M on the buccal side. In all models, the reduction rate of the thicknesses was significantly greater in 3M than in 4M in the same extrusion direction. In both 4M and 3M, the reduction rate of the thicknesses tended to increase as the amount of undercut increased in each extrusion direction. This study suggested that a model with a large amount of undercut on the labial side or a thin sheet had a significant effect on the thermal shrinkage of the mouthguard sheet during thermoforming, which leads to the thinning of the mouthguard.展开更多
Effectiveness and safety of a sports mouthguard depend on its thickness and material, and the thermoforming process affects these. The purpose of this study was to clarify the effects of differences in molding mechani...Effectiveness and safety of a sports mouthguard depend on its thickness and material, and the thermoforming process affects these. The purpose of this study was to clarify the effects of differences in molding mechanisms on the lower molding temperature limit and molding time in dental thermoforming. Ethylene vinyl acetate resin mouthguard sheet and two thermoforming machines;vacuum blower molding machine and vacuum ejector/pressure molding machine were used. The molding pressures for suction molding were −0.018 MPa for vacuum blower molding and −0.090 MPa for vacuum ejector molding, and for pressure molding was set to 0.090 MPa or 0.450 MPa. Based on the manufacturer’s standard molding temperature of 95˚C, the molding temperature was lowered in 2.5˚C increments to determine the lower molding temperature limit at which no molding defects occurred. In order to investigate the difference in molding time depending on the molding mechanism, the duration of molding pressure was adjusted in each molding machine, and the molding time required to obtain a sample without molding defects was measured. The molding time of each molding machine were compared using one-way analysis of variance. The lower molding temperature limit was 90.0˚C for the vacuum blower machine, 77.5˚C for the vacuum ejector machine, 77.5˚C for the pressure molding machine at 0.090 MPa, and 67.5˚C for the pressure molding machine at 0.45 MPa. The lower molding temperature limit was higher for lower absolute values of molding pressure. The molding time was shorter for pressure molding than for suction molding. Significant differences were observed between all conditions except between the pressure molding machine at 0.090 MPa and 0.45 MPa (P < 0.01). A comparison of the differences in lower molding temperature limit and molding time due to molding mechanisms in dental thermoforming revealed that the lower molding temperature limit depends on the molding pressure and that the molding time is longer for suction molding than for pressure molding.展开更多
Introduction Jiangmen Underground Neutrino Observation(JUNO)focuses on determining neutrino mass hierarchy and other physical purposes.The central detector is one of the keys to the JUNO.The main structure of the cent...Introduction Jiangmen Underground Neutrino Observation(JUNO)focuses on determining neutrino mass hierarchy and other physical purposes.The central detector is one of the keys to the JUNO.The main structure of the central detector is an acrylic spherical container with a diameter of 35.4 m,which will be the largest acrylic spherical vessel in the world.Its construction will inevitably face many great challenges and difficulties.Method The thermoforming process of large acrylic spherical panel is introduced,which is a very important step in panel production.The effect of temperature on the curvature of panel during thermoforming is discussed.The thermal deformation of panel in thermoforming process is analyzed by finite element method.The bending experiment and curvature measurement are carried out,and the influence of deformation of the panel under gravity on the curvature of the panel is analyzed.Results The current thermoforming process makes the curvature of panel smaller than that of mold.The measurement results show that the curvatures are different due to the influence of gravity when the panel is placed on the mold or vertically.Some suggestions for improving the shape of spherical panels are put forward.In the thermoforming process,the temperature of the concave-convex surfaces of the panel should be controlled at the same level as far as possible.Another feasible method is to increase the radius of the forming mold to obtain a spherical panel with designed radius.展开更多
In this study,the influence of thermoforming conditions on the resulting material properties was investigated,which aimed at developing advanced wood-fiber-based materials for the replacement of fossil plastics.Two bl...In this study,the influence of thermoforming conditions on the resulting material properties was investigated,which aimed at developing advanced wood-fiber-based materials for the replacement of fossil plastics.Two bleached softwood pulps were studied,i.e.,northern bleached softwood Kraft pulp(NBSK)and chemi-thermomechanical softwood pulp(CTMP).The thermoforming conditions were varied between 2–100 MPa and 150–200℃,while pressing sheets of 500 g/m^(2)for 10 min to represent thin-walled packaging more closely.As our results showed,the temperature had a more pronounced effect on the CTMP substrates than on the Kraft pulp.This was explained by the greater abundance of lignin and hemicelluloses,while fibrillar dimensions and the fines content may play a role in addition.Moreover,the CTMP exhibited an optimum in terms of tensile strength at intermediate thermoforming pressure.This effect was attributed to two counteracting effects:1)Improved fiber adhesion due to enhanced densification,and 2)embrittlement caused by the loss of extensibility.High temperatures likely softened the lignin,enabling fiber collapse and a tighter packing.For the Kraft substrates,the tensile strength increased linearly with density.Both pulps showed reduced wetting at elevated thermoforming temperature and pressure,which was attributed to hornification and densification effects.Here,the effect of temperature was again more pronounced for CTMP than for the Kraft fibers.It was concluded that the thermoforming temperature and pressure strongly affected the properties of the final material.The chemical composition of the pulps will distinctly affect their response to thermoforming,which could be useful for tailoring cellulose-based replacements for packaging products.展开更多
Future large-scale radio telescope observatories,such as the next-generation Very Large Array,involve extremely large collection areas.These collection areas are divided into smaller shaped panels,which typically requ...Future large-scale radio telescope observatories,such as the next-generation Very Large Array,involve extremely large collection areas.These collection areas are divided into smaller shaped panels,which typically require their own unique molds to manufacture.For these projects to be cost-effective,an efficient fabrication method for the shaped panels is needed.This paper outlines the development and success of a novel adaptive freeform panel molding technology that greatly improves manufacturing efficiency due to its repeatable and reusable nature.Moreover,it presents an analysis of a proposed panel structural design for the shaped panels,which incorporates a study on surface deformation due to gravity and wind loading under realistic operational conditions.展开更多
文摘Development of home compostable materials based on bioavailable polymers is of high strategic interest as they ensure a significant reduction of the environmental footprint in many production sectors.In this work,the addition of thermoplastic starch to binary PLA/PBAT blends was studied.The compounds were obtained by a reactive extrusion process by means of a co-rotating twin screw extruder.Thermomechanical,physical and chemical characterization tests were carried out to highlight the effectiveness of the material design strategy.The compounds were subsequently reprocessed by cast extrusion and thermoforming in order to obtain products suitable for the storage of hot food.The extruded films and the thermoformed containers were further characterized to highlight their thermo-mechanical,physical and chemical properties.Thermo-rheological,mechanical and physical properties of the material and of the cast film were analyzed thoroughly using combined technique as capillary rheometer,MFI,DSC,VICAT/HDT,XRD,FTIR,UV-Vis,SEM,permeability and,lastly,running preliminary chemical inertness and biodegradation tests.Particular attention was also devoted to the evaluation of the thermo-mechanical resistance of the thermoformed containers,where the PLA/PBAT/TPS blends proved to be very effective,also presenting a high disintegration rate in ambient conditions.
文摘Wearing a mouthguard reduces the risk of sports-related injuries, but the material and thickness of the mouthguard has a substantial impact on its effectiveness and safety. The aim of this study was to establish a thermoforming technique in which the model position is moved just before formation to suppress the reduction in thickness. Mouthguards were vacuum formed using ethylene-vinyl-acetate sheets with a thickness of 2.0, 3.0, and 4.0 mm. The working model was trimmed to the height of 25-mm at the maxillary central incisor and 20-mm at first molar. The model was placed with its anterior rim positioned 40-mm from the front of the forming table. Two forming methods were compared: 1) the sheet was formed when it sagged 15-mm at the top of the post under normal conditions (control);and 2) the sheet frame at the top of the post was lowered and the model was covered when the sheet sagged 15-mm, the rear side of the model was pushed forward 20-mm, and the mouthguard was formed (MP;model position). Sheet thickness after fabrication was determined for the incisal edge, labial surface, and buccal surface using a specialized caliper accurate to 0.1-mm. The difference in the reduction in thickness depending on the forming methods and sheet thicknesses were analyzed by two-way ANOVA and Bonferroni’s multiple comparison tests. Reduction in thickness was greater for thicker sheets, and the reduction in thickness for the MP was less than that for the control. The reduction in labial for the MP was an exception;the reduction in thickness was only about half that of the control. The thermoforming technique of moving the model forward just before vacuum formation was effective for suppressing the mouthguard thickness reduction, which in thickness of the labial side can be reduced to about half of the normal forming method.
文摘Wearing a mouthguard reduces the risk of sports-related injuries, but a more comfortable design is required in order to increase the wearing rate. The aim of this study was to investigate a thermoforming method that decreases palatal thickness while maintaining labial and buccal thickness. Mouthguards were fabricated from an ethylene-vinyl acetate sheet (thickness: 4.0 mm) by using a vacuum forming machine. Four working models were prepared: 1) the anterior height was 25-mm and the posterior height was 20-mm (model A), 2) model A with the palate trimmed (model B), 3) heights 5 mm greater than model A (model C), and 4) model C with the palate trimmed (model D). The two forming conditions were as follows: 1) The sheet was formed when it sagged 15 mm below the level of the sheet frame at the top of the post under ordinary use (control);2) The sheet frame at the top of the post was lowered and the sheet covered the model when it sagged by 15 mm. The rear side of the model was pushed to move the model forward 20 mm, and then the sheet was formed (MP). Differences in mouthguard thickness due to forming conditions and model forms were analyzed by two-way analysis of variance and Bonferroni’s multiple comparison tests. Difference in forming conditions was similar for all model forms;for the MP, the thickness of the incisal edge, labial surface, cusp and buccal surface were greater, and the palatal surface was thinner than the control. On the labial and buccal surface, the thickness difference due to the model form was observed only for the MP, and models A and B were thicker than models C and D. The palatal thickness tended to be thin in the models with the trimmed palate. This study suggested that the labial and buccal thickness of the mouthguard can be maintained, and the palatal thickness can be decreased by using the model with the palate trimmed with the forming method in which the model position is moved forward immediately before the vacuum formation.
文摘Mouthguards can reduce the risk of sports-related injuries, but the sheet material and thickness have a large effect on their efficacy and safety. This study was intended to predict the changes in thickness of molded products by clarifying the effect of the time interval between repeat moldings during the continuous use of a vacuum-forming machine. Ethylene vinyl acetate mouthguard sheets were used for thermoforming with a vacuum-forming machine. The working model was trimmed to a height of 23 mm at the maxillary central incisor and 20 mm at maxillary first molar. Five molding conditions were investigated: 1) molding was carried out after the sag at the center of the softened sheet was 15 mm (control);2) sheet heating was started 5 min after the molding of the control (AF5-Re1);3) sheet heating started 5 min after the molding of AF5-Re1 (AF5-Re2);4) sheet heating started 10 min after the molding of the control (AF10-Re1);and 5) sheet heating started 10 min after the molding of AF10-Re1 (AF10-Re2). Sheet thickness after fabrication was determined for the incisal edge, labial surface, cusp, and buccal surface using a special caliper accurate to 0.1 mm. Thickness differences of the molding conditions were analyzed by two-way analysis of variance. Significant differences between the control and AF5-Re1 were observed at all measurement points (p < 0.01), but not between the control and AF10-Re1. AF10-Re2 became thinner than AF10-Re1 (p < 0.01). Reproducible molding results were obtained by waiting 10 min between the first and second moldings, but the third molded mouthguard was significantly thinner, despite this 10 min wait interval.
文摘Mouthguard thickness is affected by the softened state of the sheet during thermoforming. The aim of this study is to establish an effective method for controlling the softened state of the sheet to prevent the mouthguard thickness from decreasing during mouthguard fabrication using a vacuum-forming machine. Mouthguards were thermoformed using an ethylene-vinyl acetate sheet (thickness: 4.0 mm) and a vacuum-forming machine. The working model was trimmed to the anterior height of 25 mm and the posterior height of 20 mm. The following two heating methods were compared: 1) the sheet was formed when it sagged 15 mm below the level of the sheet frame at the top of the post (condition T);and 2) the sheet frame was lowered to and heated at 50 mm below its usual height and the sheet was formed when it sagged 15 mm below the level of the sheet frame (condition L). For each heating method, the vacuum was applied immediately (T0, L0) or 5 s (T5, L5) after the sheet frame was lowered to the forming unit. The sheet surface temperature immediately before the vacuum was applied under each condition was measured. The differences in mouthguard thickness due to forming conditions were analyzed by one-way ANOVA and Bonferroni’s multiple comparison tests. The temperature difference between the center and the posterior depending on the condition decreased in the order T0 > T5 > L0 > L5, and that was 20<span style="white-space:nowrap;">°</span>C or higher for T0 and T5, and 10<span style="white-space:nowrap;">°</span>C or less for L0 and L5. At the incisal edge and the cusp, L0 and L5 were significantly thicker than T0. No significant differences were observed between conditions L0 and L5 at any measurement points. For the labial and buccal surfaces, significant differences in thicknesses among all conditions, except L0 and L5, were observed and were in the order T0 < T5 < L0 and L5. This study was suggested that the lowering the sheet frame and heating was more effective than adjusting the vacuum timing for uniform softening of the sheet.
文摘Effectiveness and safety of mouthguards are greatly affected by its thickness. The aim of this study was to clarify the effect of model height and model position on the forming table on the mouthguard thickness in thermoforming using a circular frame. Mouthguards were thermoformed using 4.0-mm-thick ethylene-vinyl-acetate sheets and a vacuum forming machine. The sheet was sandwiched between circular frames and fixed to the clamp of the forming machine. Working models were two types of hard gypsum models trimmed so that the height of the anterior part was 25 mm (Model A) and 30 mm (Model B). The model was placed with its anterior rim positioned 40 mm (P40), 30 mm (P30), 20 mm (P20), or 10 mm (P10) from the front of the forming table. Differences in the reduction rate of the thickness due to the model height and model positions were analyzed by two-way ANOVA and Bonferroni’s multiple comparison test. Differences depending on the model height were observed at P40 at the incisal edge and P30, P20, and P10 on the labial surface, and the reduction rate of the thickness was significantly smaller in Model A (P < 0.01). As the distance from the model anterior rim to the front of the forming table was smaller, the rate of the thickness of the incisal edge and the labial surface decreases became larger. The rate of decrease in the thickness of the cusp and buccal surface was the smallest at P20. This study indicated that the difference in the thickness of the single-layer mouthguard depending on the model position on the forming table is affected by the model height. However, that is only the anterior part of the mouthguard, and the difference in thickness reduction rate is less than 5%. Additionally, in order to perform stable forming, it is useful to increase the distance from the model to the frame, and it is important to position the part whose thickness is desired to be maintained in the center of the forming table.
文摘The height of the working model affects the mouthguard thickness. The aim of this study was to clarify the difference in the effect of model height on the thickness between single- and double-layered mouthguards. Mouthguards were thermoformed using ethylene-vinyl-acetate sheets and a pressure molding machine. Working models were three hard gypsum models with the height of the anterior part trimmed to 25 mm (model A), 30 mm (model B), and 35 mm (model C). Three molding conditions were compared: a single-layered mouthguard using a 4.0-mm thick-sheet (S4);a double-layered mouthguard using a 3.0-mm-thick sheet on the first-layer and a 2.0-mm-thick sheet on the second-layer (L32);and a double-layered mouthguard using 3.0-mm-thick sheets on first- and second-layers (L33). Analysis was performed by two-way ANOVA and a simple main effect test for the differences in the mouthguard thickness depending on the model height and the molding condition. Under all molding conditions, the labial and buccal thicknesses tended to become thinner as the model height increased, and models B and C were thinner by about 6% - 7% and about 14% - 16% than model A, respectively. The cusp thickness was not affected by the model height in L32 and L33, but in S4, models B and C were thinner about 14% or more than model A. Significant differences were observed among molding conditions, and S4 P < 0.01). This study suggested that the degree of the decrease in mouthguard thickness due to the increase the model height was similar for the single- and double-layered mouthguards on the labial and buccal sides, and increasing the model height by 5 mm and 10 mm decreased the thickness by about 6% - 7% and about 14% - 16%, respectively. At the cusp, only the single-layered mouthguard was affected by the model height.
文摘The effectiveness and safety of the mouthguard depend on the sheet material thickness. The thickness of the thermoformed mouthguard is affected by the model undercut and the thermal shrinkage that occurs when the extruded-molded sheet is reheated. The aim of this study was to clarify the influence of the undercut amount of the model and the thickness of the sheet material on the thermal shrinkage of the extruded sheet. The mouthguard sheet used ethylene-vinyl acetate resin with a thickness of 4.0 mm (4M) and 3.0 mm (3M) and was manufactured by extrusion molding. The working models were three hard gypsum models with the undercut amount on the labial side trimmed to 0? (U0), 10? (U10), and 20? (U20). Mouthguard thickness after vacuum formation was compared between the conditions formed so that the extrusion direction was vertical (condition V) or parallel (condition P) to the model midline. Differences in the reduction rate of the mouthguard thicknesses of the labial and buccal side depending on the sheet extrusion direction, model angle, and sheet material thickness were analyzed by three-way ANOVA and Bonferroni method. The reduction rate of the thickness in condition P was significantly greater than in condition V under all conditions except U0-4M on the labial side and U0-4M and U10-4M on the buccal side. In all models, the reduction rate of the thicknesses was significantly greater in 3M than in 4M in the same extrusion direction. In both 4M and 3M, the reduction rate of the thicknesses tended to increase as the amount of undercut increased in each extrusion direction. This study suggested that a model with a large amount of undercut on the labial side or a thin sheet had a significant effect on the thermal shrinkage of the mouthguard sheet during thermoforming, which leads to the thinning of the mouthguard.
文摘Effectiveness and safety of a sports mouthguard depend on its thickness and material, and the thermoforming process affects these. The purpose of this study was to clarify the effects of differences in molding mechanisms on the lower molding temperature limit and molding time in dental thermoforming. Ethylene vinyl acetate resin mouthguard sheet and two thermoforming machines;vacuum blower molding machine and vacuum ejector/pressure molding machine were used. The molding pressures for suction molding were −0.018 MPa for vacuum blower molding and −0.090 MPa for vacuum ejector molding, and for pressure molding was set to 0.090 MPa or 0.450 MPa. Based on the manufacturer’s standard molding temperature of 95˚C, the molding temperature was lowered in 2.5˚C increments to determine the lower molding temperature limit at which no molding defects occurred. In order to investigate the difference in molding time depending on the molding mechanism, the duration of molding pressure was adjusted in each molding machine, and the molding time required to obtain a sample without molding defects was measured. The molding time of each molding machine were compared using one-way analysis of variance. The lower molding temperature limit was 90.0˚C for the vacuum blower machine, 77.5˚C for the vacuum ejector machine, 77.5˚C for the pressure molding machine at 0.090 MPa, and 67.5˚C for the pressure molding machine at 0.45 MPa. The lower molding temperature limit was higher for lower absolute values of molding pressure. The molding time was shorter for pressure molding than for suction molding. Significant differences were observed between all conditions except between the pressure molding machine at 0.090 MPa and 0.45 MPa (P < 0.01). A comparison of the differences in lower molding temperature limit and molding time due to molding mechanisms in dental thermoforming revealed that the lower molding temperature limit depends on the molding pressure and that the molding time is longer for suction molding than for pressure molding.
基金This work has been supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA10010200)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.292020000087).
文摘Introduction Jiangmen Underground Neutrino Observation(JUNO)focuses on determining neutrino mass hierarchy and other physical purposes.The central detector is one of the keys to the JUNO.The main structure of the central detector is an acrylic spherical container with a diameter of 35.4 m,which will be the largest acrylic spherical vessel in the world.Its construction will inevitably face many great challenges and difficulties.Method The thermoforming process of large acrylic spherical panel is introduced,which is a very important step in panel production.The effect of temperature on the curvature of panel during thermoforming is discussed.The thermal deformation of panel in thermoforming process is analyzed by finite element method.The bending experiment and curvature measurement are carried out,and the influence of deformation of the panel under gravity on the curvature of the panel is analyzed.Results The current thermoforming process makes the curvature of panel smaller than that of mold.The measurement results show that the curvatures are different due to the influence of gravity when the panel is placed on the mold or vertically.Some suggestions for improving the shape of spherical panels are put forward.In the thermoforming process,the temperature of the concave-convex surfaces of the panel should be controlled at the same level as far as possible.Another feasible method is to increase the radius of the forming mold to obtain a spherical panel with designed radius.
文摘In this study,the influence of thermoforming conditions on the resulting material properties was investigated,which aimed at developing advanced wood-fiber-based materials for the replacement of fossil plastics.Two bleached softwood pulps were studied,i.e.,northern bleached softwood Kraft pulp(NBSK)and chemi-thermomechanical softwood pulp(CTMP).The thermoforming conditions were varied between 2–100 MPa and 150–200℃,while pressing sheets of 500 g/m^(2)for 10 min to represent thin-walled packaging more closely.As our results showed,the temperature had a more pronounced effect on the CTMP substrates than on the Kraft pulp.This was explained by the greater abundance of lignin and hemicelluloses,while fibrillar dimensions and the fines content may play a role in addition.Moreover,the CTMP exhibited an optimum in terms of tensile strength at intermediate thermoforming pressure.This effect was attributed to two counteracting effects:1)Improved fiber adhesion due to enhanced densification,and 2)embrittlement caused by the loss of extensibility.High temperatures likely softened the lignin,enabling fiber collapse and a tighter packing.For the Kraft substrates,the tensile strength increased linearly with density.Both pulps showed reduced wetting at elevated thermoforming temperature and pressure,which was attributed to hornification and densification effects.Here,the effect of temperature was again more pronounced for CTMP than for the Kraft fibers.It was concluded that the thermoforming temperature and pressure strongly affected the properties of the final material.The chemical composition of the pulps will distinctly affect their response to thermoforming,which could be useful for tailoring cellulose-based replacements for packaging products.
基金This work was funded by the National Science Foundation(NSF)Award 2009384.
文摘Future large-scale radio telescope observatories,such as the next-generation Very Large Array,involve extremely large collection areas.These collection areas are divided into smaller shaped panels,which typically require their own unique molds to manufacture.For these projects to be cost-effective,an efficient fabrication method for the shaped panels is needed.This paper outlines the development and success of a novel adaptive freeform panel molding technology that greatly improves manufacturing efficiency due to its repeatable and reusable nature.Moreover,it presents an analysis of a proposed panel structural design for the shaped panels,which incorporates a study on surface deformation due to gravity and wind loading under realistic operational conditions.
