Freeze dryer barrel heat insulation foam forming quality control method

Abstract

The invention provides a freeze dryer barrel heat insulation foam molding quality control method, which belongs to the field of material molding, and comprises the steps of freeze dryer barrel heat insulation foam mold device assembling, parameter setting, foaming preparation, polyurethane material injection, foaming molding, foam surface inspection, and surface defect rate statistics. The mold device comprises a mold body, a fixed heating water pipe and a temperature sensor, and definite and effective planning guidance is provided for the surface forming quality of the polyurethane foam by establishing the quantitative relation between the surface defect rate of the formed polyurethane foam and the mold temperature, the filling coefficient of the injected polyurethane material for forming and the injection temperature. The surface quality is effectively controlled, meanwhile, the forming uniformity in the foam is guaranteed, and the overall quality of the formed polyurethane foam is improved.

Description

Technical Field

[0001] The invention relates to the field of polyurethane foam molding, and in particular to a freeze dryer barrel insulation foam molding quality control method. Background Art

[0002] Polyurethane foam has been widely used due to its excellent mechanical properties, thermal insulation effect and low preparation cost. Under the existing technology, the barrel of the food freeze dryer has a layer of polyurethane foam to isolate the heat transmitted by the air during the freeze-drying process, effectively reducing the energy consumption of the equipment. The thermal insulation foam of the food freeze dryer is formed by fitting the outer wall of the metal barrel. The metal barrel will be cooled to -40℃ to -60℃ during use. The thermal insulation foam layer outside the barrel needs to frequently withstand temperature changes between low temperature and normal temperature. Therefore, there are extremely high requirements for the molding quality and structural uniformity of this layer of thermal insulation foam to ensure that the foam layer will not break due to stress accumulation during the repeated temperature increase and decrease of the freeze dryer, thereby maintaining the long-term durability of the freeze dryer.

[0003] Existing quantitative detection methods for polyurethane foam molding quality include physical experiments, destructive tests, and microstructure observation tests. Physical experiments require the foam products to be taken offline and tested for density and pressure. Destructive tests require the products to be sampled regularly or in batches for destructive inspection. Microstructure observation tests such as metallography and ultrasound also require the products to be taken offline and inspected using corresponding instruments. Among the above methods, except for destructive tests, which are used regularly in batches by freeze dryer manufacturers, other methods are not used due to high test costs and low efficiency. In general, there is currently a lack of online control methods for foam molding quality suitable for small and medium-sized enterprises such as freeze dryer manufacturers. Even if destructive tests are applied, the real-time foam molding quality fluctuations on the production line cannot be captured and corrected in a timely manner, which can easily lead to poor batch molding quality problems.

[0004] Therefore, there is an urgent need for an online quality control method for polyurethane foam, so that freeze dryer manufacturers and more small and medium-sized enterprises can conduct online foam quality inspections efficiently and at low cost to ensure the molding quality of polyurethane foam products. Summary of the invention

[0005] The object of the present invention is to provide a freeze dryer barrel insulation foam molding quality control method:

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A freeze dryer barrel insulation foam molding quality control method comprises the following steps:

[0008] S100. Assemble the freeze dryer barrel insulation foam mold device: the freeze dryer barrel insulation foam mold device includes a mold body, a heating water circuit and a temperature sensor; the mold body includes a lower mold, a left mold door, a right mold door and a mold upper cover; the lower mold is movably connected to the left mold door, the right mold door and the mold upper cover respectively by means of hinges; the bottom of the lower mold has an opening, the shape of the opening is adapted to the outer shape of the barrel body, and is used to allow the barrel body to be inserted with the opening facing downward, so that the barrel body and the mold body are enclosed to form a molding space; the surface of each component of the mold body is equipped with a plurality of sections of fixed heating water pipes for heating the mold body; each section of the fixed heating water pipe is connected by an external pipeline to form a continuous serial heating water circuit; the surface of the mold body is embedded with a temperature sensor and is electrically connected to an external control system.

[0009] S200, parameter setting: setting the barrel insulation layer foam molding process parameters according to the process quality requirements of the barrel insulation foam, the process parameters including the mold temperature T1, the filling system C for filling polyurethane material, and the filling temperature T2; the process quality requirements include that the mold temperature T1 and the filling temperature T2 are in the temperature control reaction and the surface defect rate x of the formed insulation foam is less than or equal to the threshold value x', that is, the following relationship is satisfied:

[0010] T1'≤T1≤T1"

[0011] T2'≤T2≤T2"

[0012] x≤x'

[0013]

[0014] Among them, k1~k3 are adjustment coefficients; C is the filling coefficient of the injected material; T1 is the mold temperature, ℃; T2 is the injected material temperature, ℃; the surface defect rate x refers to the ratio of the total statistical surface defect area of ​​the thermal insulation foam layer of a batch of products to the total appearance area of ​​the thermal insulation foam layer of this batch. This ratio not only quantitatively specifies the appearance quality of the polyurethane foam, but also effectively reflects the internal molding quality level of the foam.

[0015] The filling coefficient C of the polyurethane material is the ratio of the density of the polyurethane foam formed in the mold to the density of the polyurethane foam foamed to a stable volume in a free state. The larger the coefficient, the tighter the foaming effect of the polyurethane material in the mold, and the greater the restriction on the growth of the foam cells. Therefore, the foam cell size after molding is smaller and more uniform, and the internal uniformity and surface quality of the foam are also higher; the material injection temperature T2 mainly affects the speed of the entire reaction. Before the foaming reaction, the material temperature rises mainly due to its own reaction heat. The higher the injection temperature, the faster the reaction speed, the more complete the reaction in the same molding time, and the higher the internal uniformity and surface quality of the foam; the mold temperature T1 mainly affects the internal and external uniformity of the foam during the foaming process. The higher the mold temperature, the smaller the tendency of the foam close to the mold to cool due to the principle reaction material, the more uniform the pore growth of the foam in the entire mold, and the higher the internal uniformity and surface quality of the foam.

[0016] According to the reaction characteristics of polyurethane foam, the mold temperature and the filling material temperature are set within the appropriate range to ensure that the filling material temperature rises and the reaction process remains moderate and mild to ensure the quality of foam molding.

[0017] S300, foaming preparation: circulating water is introduced into the serial heating water circuit, and the circulating water is heated by an external heat source, and at the same time, the barrel body is inserted into the opening at the bottom of the lower mold with the opening facing downward; after the feedback value of the temperature sensor to the external control system reaches the preset mold temperature T1, the external heat source is switched to the insulation mode, and the left and right doors of the mold are closed at the same time.

[0018] S400, injecting polyurethane material: using an external polyurethane injection machine to inject a polyurethane mixed material with a temperature of T2 and a filling factor of C into the space enclosed by the lower mold, the left mold door, the right mold door and the barrel body, and closing the mold cover.

[0019] S500, foaming molding: the injected polyurethane material completes a series of reactions in the molding space, and the foam fills the entire molding space and has corresponding strength and hardness; after the process timing is reached, the mold upper cover, the mold left hatch and the mold right hatch are opened, and the barrel body together with the formed foam layer are taken out from the lower mold.

[0020] S600, foam surface inspection: perform surface inspection on the formed foam layer, mark surface defects with a size greater than or equal to 2.0 mm and a depth greater than or equal to 0.5 mm, and measure the total surface area S of all marked defects. x , and then perform the following judgment processing:

[0021] If there are surface defects with a size greater than or equal to 5.0 mm and a depth greater than or equal to 0.5 mm, the process will be redone, and the foam layer will be peeled off and redone;

[0022] If there are no surface defects with a size greater than ≥5.0mm and a depth ≥0.5mm, the product will enter the rework process to repair the existing marking defects before being sent to the next processing step.

[0023] S700, Statistical surface defect rate: Statistical surface defect rate x of a batch of products, Where S is the appearance area of ​​the foam layer of a single product, which is compared with the parameters set by S200 and the target value of the surface defect rate, and the molding parameters are continuously optimized to make the surface defect rate reach the set target.

[0024] Furthermore, the outer cross-section of the fixed heating water pipe is rectangular and the inner cross-section is circular.

[0025] Furthermore, the installation position of the temperature sensor is located next to the outlet of the last section of the fixed heating water pipe in the water flow direction of the serial heating water circuit.

[0026] Furthermore, the mold device is provided with exhaust holes, and the exhaust holes are evenly distributed circumferentially on the closed surface of the mold upper cover and the lower mold, the mold left hatch, and the mold right hatch.

[0027] Furthermore, before inserting the barrel body into the opening of the lower mold in step S300, a layer of film is laid on the lower mold for subsequent demoulding, and the material of the film is polyethylene.

[0028] The beneficial effects of the present invention are as follows:

[0029] (1) The surface defect rate of molded foam is introduced to evaluate the molding quality of polyurethane foam products. It can not only quantitatively indicate the appearance quality of polyurethane foam products, but also effectively reflect the internal molding quality of foams. It is convenient for freeze dryer manufacturers to quickly and efficiently monitor the molding quality of the thermal insulation foam of the freeze dryer barrel on the production line, and ensure that the formed thermal insulation foam can be used in low-temperature freezing occasions for a long time.

[0030] (2) By laying fixed heating water pipes on the molding mold and controlling the temperature of the mold during the molding process, a quantitative relationship between the surface defect rate of the molded foam and the mold temperature, the filling coefficient of the filling material, the filling temperature and the appearance area of ​​the molded foam is established. Based on the quantitative relationship, clear and effective guidance can be provided for the surface quality control of polyurethane foam in actual production. By monitoring and adjusting relevant molding parameters, the foam surface quality can be made to meet the production requirements, thereby providing guarantee for the surface and internal structure quality of the molded foam. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic structural diagram of the freeze dryer barrel insulation foam molding mold in an open state of the present invention;

[0032] Figure 2This is a schematic structural diagram of the freeze dryer barrel insulation foam molding mold in a closed state of the present invention;

[0033] Figure 3 This is a cross-sectional view of the heat-insulating foam forming mold for the freeze dryer barrel of the present invention;

[0034] Figure 4 is a curve diagram of the mold temperature T2 and the surface defect rate in this embodiment;

[0035] In the figure, 1-mold body, 11-lower mold, 111-cylindrical opening, 12-mold left hatch, 13-mold right hatch, 14-mold upper cover, 2-fixed heating water pipe, 3-barrel body, 4-molding space. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments given here are only used to illustrate and explain the present invention, and cannot be used to limit the present invention.

[0037] It should be noted that many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention may also have other implementations and variations thereof. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0038] like Figures 1 to 4 As shown, a freeze dryer barrel insulation foam molding quality control method comprises the following steps:

[0039] S100, assemble the freeze dryer barrel insulation foam mold device: the freeze dryer barrel insulation foam mold device includes a mold body 1, a heating water channel 2 and a temperature sensor; the mold body 1 includes a lower mold 11, a mold left hatch 12, a mold right hatch 13, and a mold cover 14; the lower mold 11 is movably connected with the mold left hatch 12, the mold right hatch 13 and the mold cover 14 by hinges; the bottom of the lower mold 11 has an opening 111, the shape of the opening 111 is adapted to the shape of the barrel body, and is used to allow the barrel body 3 to be inserted with the opening downward, so that the barrel body 3 and the mold body 1 enclose a molding space 4; each of the mold body 1 Several sections of fixed heating water pipes 2 are installed on the surface of the components for heating the mold body 1. The outer cross-section of the fixed heating water pipes 2 is rectangular and the inner cross-section is circular. Each section of the fixed heating water pipes 2 is connected by an external pipeline to form a continuous serial heating water circuit. A temperature sensor is embedded on the surface of the mold body 1 and is electrically connected to an external control system. The temperature sensor is installed next to the outlet of the last section of the fixed heating water pipe 2 in the water flow direction of the serial heating water circuit. The mold device is provided with exhaust holes (not shown in the figure), which are evenly distributed circumferentially on the closed surface of the mold upper cover 14 and the lower mold 11, the mold left hatch 12, and the mold right hatch 13.

[0040] S200, parameter setting: according to the process quality requirements of the barrel insulation foam, the barrel insulation layer foam molding process parameters are set, the process parameters include the mold temperature T1, the filling system C of the polyurethane material, and the filling temperature T2; the process quality requirements include that the mold temperature T1 and the filling temperature T2 are in the temperature control reaction and the surface defect rate x of the formed insulation foam is less than or equal to the threshold value x', that is, the following relationship is satisfied:

[0041] T1'≤T1≤T1"

[0042] T2'≤T2≤T2"

[0043] x≤x'

[0044]

[0045] Among them, k1~k3 are adjustment coefficients; C is the filling coefficient of the injected material; T1 is the mold temperature, °C; T2 is the injected material temperature, °C; the surface defect rate x refers to the ratio of the total statistical surface defect area of ​​a batch of molded thermal insulation foam layers to the total appearance area of ​​the batch of thermal insulation foam layers;

[0046] The outer diameter of the barrel of the embodiment is 0.184m, the black polyurethane material adopts Covestro's Deshimodu 44V20L, the white material adopts Hongshi Material's HS-1203, the outer diameter of the molded foam layer is 0.204m, the height is 0.530m, the appearance area is 0.708㎡, the filling coefficient C of the injected mixed material is 2.6, the temperature T2 is 25℃, and the mold temperature T1 is changed by adjusting the temperature of the circulating water to obtain the experimental data of the surface defect rate x, see the following table:

[0047]

[0048]

[0049] Fit the data in the above table to determine the adjustment coefficient k 1、 k2 and k3 are 5.68×10 -4 , 1.87×10 -3 , 5.23×10 -8 , the complete quantitative relationship of the surface defect rate x is obtained as follows:

[0050]

[0051] x≤1.42×10 -5

[0052] According to the reaction characteristics of polyurethane foam, the temperature T2 of the mixed material is between 20 and 35℃, the internal structure uniformity and closed cell rate of the foam are in a reasonable range, and the mold temperature T1 is between 20 and 70℃ to ensure that the temperature rise and reaction process of the filled material are maintained in a moderate state; when the mold temperature T1 is greater than 58℃, the surface defect rate of the molded foam is less than 1.42×10 -5 The average surface defect area of ​​each barrel foam layer is less than 10.0mm 2 Compared with the case where the mold temperature is not controlled, the surface defect rate is 8.58×10 -5 to 5.90×10 -5 The quality has been greatly improved, effectively optimizing the surface quality and internal molding uniformity of the molded foam, ensuring the good appearance and long-term durability of the foam; different polyurethane material filling coefficients are set for different foam sizes and different foam layer usage occasions, and the corresponding matching material temperature is determined. Then, the appropriate mold temperature is set according to the surface quality design requirements of the product to ensure the best surface quality and internal quality of the molded foam.

[0053] S300, foaming preparation: circulating water is introduced into the serial heating water circuit, and the circulating water is heated by an external heat source; a film is laid on the lower mold 11, and the material of the film is polyethylene; the barrel 3 is inserted into the opening at the bottom of the lower mold 11 with the opening facing downward; after the feedback value of the temperature sensor to the external control system reaches the preset mold temperature T1, the external heat source is switched to the insulation mode, and the left mold door 12 and the right mold door 13 are closed at the same time.

[0054] S400, injecting polyurethane material: using an external polyurethane injection machine to inject a polyurethane mixture material with a temperature of T2 and a filling factor of C into the space enclosed by the lower mold 11, the left mold door 12, the right mold door 13 and the barrel body 3, and closing the mold cover 14.

[0055] S500, foaming molding: the injected polyurethane material completes a series of reactions in the molding space 4, and the foam fills the entire molding space 4 and has corresponding strength and hardness; after the process timing is reached, the mold upper cover 14, the mold left hatch 12 and the mold right hatch 13 are opened, and the barrel body 3 together with the molded foam layer are taken out from the lower mold 11.

[0056] S600, Foam surface inspection: Conduct surface inspection on the formed foam layer, mark surface defects with a size of ≥2.0mm and a depth of ≥0.5mm, and measure the total surface area S of all marked defects. x , and then perform the following judgment processing:

[0057] If there are surface defects with a size greater than or equal to 5.0 mm and a depth greater than or equal to 0.5 mm, the process will be redone, and the foam layer will be peeled off and redone;

[0058] If there are no surface defects with a size greater than ≥5.0mm and a depth ≥0.5mm, the product will enter the rework process to repair the existing marking defects before being sent to the next processing step.

[0059] S700, Statistical surface defect rate: Statistical surface defect rate x of a batch of products, Where S is the appearance area of ​​the foam layer of a single product, which is compared with the parameters set by S200 and the target surface defect rate, and the molding parameters are continuously optimized to make the surface defect rate reach the set target.

[0060] It should be understood that the above-mentioned embodiments are one or more embodiments of the present invention, and there are many other embodiments and variations thereof based on the present invention; the variations and modifications made by ordinary technicians in this industry through the present invention without making pioneering innovations all fall within the scope of protection of the present invention.

Claims

1. A freeze dryer barrel insulation foam molding quality control method, characterized in that: The following steps are involved: S100, assemble the freeze dryer barrel insulation foam mold device: the freeze dryer barrel insulation foam mold device includes a mold body, a heating water circuit and a temperature sensor; the mold body includes a lower mold, a left mold door, a right mold door and a mold upper cover; the lower mold is movably connected with the left mold door, the right mold door and the mold upper cover respectively by hinges; the bottom of the lower mold has an opening, the shape of the opening is adapted to the shape of the barrel body, and is used to allow the barrel body to be inserted with the opening facing downward, so that the barrel body and the mold body are enclosed to form a molding space; the surface of each component of the mold body is equipped with a plurality of sections of fixed heating water pipes for heating the mold body; each section of the fixed heating water pipe is connected by an external pipeline, so as to form a continuous serial heating water circuit; the surface of the mold body is embedded with a temperature sensor and is electrically connected to an external control system; S200, parameter setting: setting the barrel insulation layer foam molding process parameters according to the process quality requirements of the barrel insulation foam, the process parameters including the mold temperature T1, the filling system C for filling polyurethane material, and the filling temperature T2; the process quality requirements include that the mold temperature T1 and the filling temperature T2 are in the temperature control reaction and the surface defect rate x of the formed insulation foam is less than or equal to the threshold value x', that is, the following relationship is satisfied: T1'≤T1≤T1" T2'≤T2≤T2" x≤x' Among them, k1~k3 are adjustment coefficients; C is the filling coefficient of the injected material; T1 is the mold temperature, °C; T2 is the injected material temperature, °C; S300, foaming preparation: circulating water is introduced into the serial heating water channel, and the circulating water is heated by an external heat source, and the barrel is inserted into the opening at the bottom of the lower mold with the opening facing downward; after the feedback value of the temperature sensor to the external control system reaches the preset mold temperature T1, the external heat source is switched to the heat preservation mode, and the left and right doors of the mold are closed at the same time; S400, injecting polyurethane material: using an external polyurethane injection machine to inject a polyurethane mixed material with a temperature of T2 and a filling factor of C into the space enclosed by the lower mold, the left hatch of the mold, the right hatch of the mold and the barrel, and closing the mold cover; S500, foaming molding: the injected polyurethane material completes a series of reactions in the molding space, and the foam fills the entire molding space and has corresponding strength and hardness; after the process timing is reached, the mold upper cover, the mold left hatch and the mold right hatch are opened, and the barrel body together with the formed foam layer is taken out from the lower mold; S600, foam surface inspection: perform surface inspection on the formed foam layer, mark surface defects with a size greater than or equal to 2.0 mm and a depth greater than or equal to 0.5 mm, and measure the total surface area S of all marked defects. x , and then perform the following judgment processing: If there are surface defects with a size greater than or equal to 5.0 mm and a depth greater than or equal to 0.5 mm, the process will be redone, and the foam layer will be peeled off and redone; If there are no surface defects with a size greater than 5.0 mm and a depth greater than 0.5 mm, the process will enter the rework process, and the existing marking defects will be reworked before being sent to the next processing process; S700, Statistical surface defect rate: Statistical surface defect rate x of a batch of products, Where S is the appearance area of ​​the foam layer of a single product, which is compared with the parameters set by S200 and the target surface defect rate, and the molding parameters are continuously optimized to make the surface defect rate reach the set target.

2. The freeze dryer barrel insulation foam molding quality control method according to claim 1 is characterized in that: The fixed heating water pipe has a rectangular outer cross section and a circular inner cross section.

3. The freeze dryer barrel insulation foam molding quality control method according to claim 1 is characterized in that: The installation position of the temperature sensor is located beside the outlet of the last fixed heating water pipe in the water flow direction of the serial heating water circuit.

4. The freeze dryer barrel insulation foam molding quality control method according to claim 1, characterized in that: The mold device is provided with exhaust holes, and the exhaust holes are evenly distributed circumferentially on the closed surface of the mold upper cover and the lower mold, the mold left hatch, and the mold right hatch.

5. The freeze dryer barrel insulation foam molding quality control method according to claim 1, characterized in that: In step S300, before inserting the barrel body into the opening of the lower mold, a layer of film is laid on the lower mold for subsequent demoulding, and the material of the film is polyethylene.

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