Preparation method of high-precision foaming product

Abstract

The invention provides a preparation method of a high-precision foamed product, which comprises the following steps: pouring dried TPU and EVA composite particles into a hopper of a foaming machine, enabling the particles to enter a material injection pipe under the action of gravity, and enabling the material to be quickly foamed in the material injection pipe at high temperature. And the foamed material is injected into the mold cavity through the material injection pipe. The foaming material is rapidly cooled in a low-temperature environment of the mold, shaping is completed in a short time, the strict requirement of a high-precision product for dimensional tolerance can be met, the qualified rate of the product is greatly improved, the production difficulty is reduced, the production efficiency is improved, and meanwhile the production cost is also reduced. EVA and TPU are compounded and have a synergistic effect, so that the comprehensive physical performance of the product is improved while the precise size is ensured. The EVA foaming machine is used for foaming the TPU composite material, the EVA foaming machine has the advantage of stable control, the size accuracy of a foamed product is further improved, the mold temperature is lower than 70 DEG C, the product can be conveniently taken out, and the operation safety is improved.

Description

Technical Field

[0001] This invention relates to the field of foam material molding technology, and in particular to a method for preparing high-precision foamed products. Background Technology

[0002] In current applications of foamed materials, ethylene-vinyl acetate copolymer (EVA) is an extremely common foamed material, widely used in numerous industries. Its foaming process is typically accomplished using an EVA foaming machine. In traditional processes, EVA material is injected into a mold through an injection tube. However, EVA material does not foam within the injection tube; it only begins foaming after being transported to a high-temperature mold. The mold must be maintained at a temperature above 170°C because the high temperature causes the foaming agent inside the EVA material to decompose, releasing gas and causing the EVA material to expand and foam. After foaming, as the mold opens, the product undergoes a significant dimensional change. The product expands rapidly due to the sudden drop in pressure inside the mold upon opening, causing the gas inside the material to diffuse rapidly and increase in volume; subsequently, the product shrinks. Taking a product with a required size of 240mm as an example, due to the expansion and contraction after mold opening, the cavity size within the mold cannot be simply set to 240mm. In practice, the cavity size needs to be set to about 170mm. After the mold is opened, the product will first expand to about 340mm and then shrink to about 240mm.

[0003] While traditional EVA foaming processes can produce foamed products that meet certain requirements, they have significant shortcomings in dimensional control. After mold opening, the expansion and contraction of the product are affected by various factors, including the properties of the EVA material itself, the uniformity of mold temperature, the distribution of the foaming agent, and the mold opening speed. The complexity of these factors makes it extremely difficult to accurately control the dimensions of the product after shrinkage, making it hard to guarantee that the final product size will accurately reach 240mm, and dimensional deviations are often unavoidable.

[0004] In modern industrial production, the demand for high-precision foamed products is increasing. For example, the manufacturing of components for high-end electronic products, the production of cushioning materials for precision instruments, and the manufacturing of special components in the aerospace field all place extremely high demands on the dimensional accuracy of foamed products. Traditional EVA foaming processes, due to their inherent limitations in dimensional control, are no longer sufficient to meet the production needs of these high-precision fields. Therefore, it is urgent to develop a method for preparing high-precision foamed products to solve these problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-precision foamed products to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing high-precision foamed products includes the following steps:

[0008] Step S1, Raw material preparation: Weigh thermoplastic polyurethane elastomer (TPU) granules and ethylene-vinyl acetate copolymer (EVA) granules. The mass percentage of TPU granules to EVA granules is 65%:35%~75%:25%. Place them in a forced-air drying oven and set the drying temperature to 100℃~110℃ for more than 3 hours.

[0009] Step S2, Equipment Preparation: Inspect and debug the EVA foaming machine, set the heating system of the injection pipe to 170℃~190℃ to ensure that the injection pipe reaches the required high temperature environment. At the same time, install the mold on the foaming machine and connect the mold cooling system, and set the mold temperature to 55℃~65℃.

[0010] Step S3, Foaming and Molding: Pour the dried TPU and EVA composite granules into the hopper of the foaming machine. The granules enter the injection tube under the action of gravity. In the injection tube, the material foams rapidly. The foamed material is injected into the mold cavity through the injection tube. The foamed material cools down and solidifies rapidly. The mold holding pressure and cooling time is 5 to 10 seconds.

[0011] Step S4, Mold Opening Inspection: After the mold has been held under pressure and cooled, open the mold, take out the molded foamed product, and use a vernier caliper to measure the dimensions of the product.

[0012] Further description of the present invention: In step S1, the mass percentage of TPU particles to EVA particles is 70%:30%.

[0013] Further description of the present invention: In step S1, the drying temperature is set to 105°C and the drying time is 3.5 hours to 5 hours.

[0014] Further description of the present invention: In step S2, the temperature of the injection tube is set to 175°C for the first section, 180°C for the second section, and 185°C for the third section, with the first to third sections arranged along the injection direction.

[0015] Further description of the present invention: In step S2, the mold temperature is set to 60°C.

[0016] Further description of the present invention: In step S3, the error between the size of the foamed product and the size of the mold cavity is within ±0.5%.

[0017] Further description of the present invention: In step S4, the mold holding and cooling time is 5 seconds.

[0018] The beneficial effects of this invention are as follows: From the perspective of dimensional control, the expansion and contraction of products after mold opening in traditional processes make it difficult to control the dimensions precisely. However, this invention, through the composite of TPU and EVA, first completes the foaming in the injection tube, and then injects it into the mold for pressure holding and cooling. This completely eliminates the unstable process of product expansion and contraction after mold opening in traditional processes, making the product dimension stable after mold opening with minimal deviation. This can meet the strict requirements of high-precision products for dimensional tolerances and greatly improve the product qualification rate.

[0019] In terms of process complexity, this invention simplifies the production process. Traditional processes require complex calculations and adjustments to the mold cavity dimensions based on the expansion and contraction characteristics of the product. In contrast, the mold cavity dimensions of this invention only need to match the required dimensions of the product, reducing uncertainties in the production process, lowering production difficulty, improving production efficiency, and also reducing production costs.

[0020] In terms of product quality, EVA and TPU are used as a composite material. TPU gives the product better wear resistance, toughness and resistance to compression set, while taking advantage of EVA's cost advantage and foaming properties. The two work together to improve the overall physical properties of the product while ensuring precise dimensions.

[0021] This invention uses an EVA foaming machine to foam TPU composite materials. The EVA foaming machine has the advantage of stable control, which further improves the dimensional accuracy of the foamed products. On the other hand, in this invention, the mold temperature is below 70°C, which makes it easier to remove the products and improves the safety of operation. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments and comparative examples:

[0023] A method for preparing high-precision foamed products includes the following steps:

[0024] Step S1: Raw Material Preparation: Weigh thermoplastic polyurethane elastomer (TPU) granules and ethylene-vinyl acetate copolymer (EVA) granules. The TPU granule type is TH95A, and the EVA granule type is Formosa Plastics 7350. The mass percentage of TPU granules to EVA granules is 65%:35%~75%:25%. Place these granules in a forced-air drying oven, set the temperature to 100℃~110℃, and dry for 3 to 4 hours. In summer, when the temperature and humidity are high, extend the drying time by 1 to 2 hours to remove moisture from the material. After drying, remove the material and use a high-precision moisture meter to test the moisture content of the granules, ensuring that the moisture content is less than 0.03%.

[0025] Step S2, Equipment Preparation: Inspect and debug the EVA foaming machine, and set the heating system of the injection pipe to 170℃~190℃ to ensure that the injection pipe reaches the required high-temperature environment. At the same time, install the mold on the foaming machine and connect the mold's cooling system, setting the mold temperature to 55℃~65℃.

[0026] Step S3, Foaming and Molding: The dried TPU and EVA composite granules are poured into the hopper of the foaming machine. Under gravity, the granules enter the injection tube, where the high temperature causes the material to foam rapidly. The foamed material is then injected into the mold cavity through the injection tube. The low temperature environment of the mold allows the foamed material to cool down rapidly, completing the shaping process in a short time. The mold holding and cooling time is 5 to 10 seconds.

[0027] Step S4, Mold Opening Inspection: After the mold has cooled and been pressurized, open the mold, remove the molded foamed product, and measure the dimensions of the product using a vernier caliper with an accuracy of 0.01mm. The error between the dimensions of the foamed product and the mold cavity dimensions should be within ±0.5%. Inspect the appearance of the foamed product; the surface should be smooth, without obvious defects or bubbles.

[0028] Compared with traditional EVA foaming processes, this invention has several significant advantages. From a dimensional control perspective, the expansion and contraction of products after mold opening in traditional processes makes precise dimensional control difficult. However, this invention, through the composite of TPU and EVA, first completes foaming in the injection tube and then injects it into the mold for pressure holding and cooling. This completely eliminates the unstable process of product expansion and contraction after mold opening in traditional processes, resulting in stable product dimensions with minimal deviation after mold opening. This meets the stringent dimensional tolerance requirements of high-precision products and greatly improves the product yield.

[0029] In terms of process complexity, this invention simplifies the production process. Traditional processes require complex calculations and adjustments to the mold cavity dimensions based on the expansion and contraction characteristics of the product. In contrast, the mold cavity dimensions of this invention only need to match the required dimensions of the product, reducing uncertainties in the production process, lowering production difficulty, improving production efficiency, and also reducing production costs.

[0030] In terms of product quality, EVA and TPU are used as a composite material. TPU gives the product better wear resistance, toughness and resistance to compression set, while taking advantage of EVA's cost advantage and foaming properties. The two work together to improve the overall physical properties of the product while ensuring precise dimensions.

[0031] This invention uses an EVA foaming machine to foam TPU composite materials. The EVA foaming machine has the advantage of stable control, which further improves the dimensional accuracy of the foamed products. On the other hand, in this invention, the mold temperature is below 70°C, which makes it easier to remove the products and improves the safety of operation.

[0032] Example 1:

[0033] Step 1: Weigh thermoplastic polyurethane elastomer (TPU) granules and ethylene-vinyl acetate copolymer (EVA) granules at a mass ratio of 7:3. The TPU granules are model TH95A, and the EVA granules are model Formosa Plastics 7350. Place these granules in a forced-air drying oven, set the temperature to 105℃, and dry for 3.5 hours to remove moisture from the materials. After drying, remove the materials and use a high-precision moisture meter to test the moisture content of the granules, ensuring that the moisture content is less than 0.03%.

[0034] Step 2: Inspect and adjust the EVA foaming machine. Set the temperature of the injection tube to 175℃ for the first section, 180℃ for the second section, and 185℃ for the third section (the first to third sections are arranged along the injection direction) to ensure that the injection tube reaches the required high-temperature environment. At the same time, install the mold on the foaming machine and connect the mold's cooling system. Set the mold temperature to 60℃, and precisely machine the mold cavity dimensions to 240mm × 100mm × 20mm.

[0035] Step 3: Pour the dried TPU and EVA composite granules into the hopper of the foaming machine. Under gravity, the granules enter the injection tube, where the high temperature causes the material to foam rapidly. The foamed material is then injected into the mold cavity through the injection tube. The low-temperature environment of the mold allows the foamed material to cool rapidly, completing the shaping process in a short time. The mold holding and cooling time is 5 seconds.

[0036] Step 4: After the mold has cooled and been pressurized, open the mold, remove the molded foamed product, and measure its dimensions using a vernier caliper with an accuracy of 0.01mm. The measured dimensions are 240.5mm × 100.2mm × 20.07mm, and the error between the foamed product dimensions and the mold cavity dimensions is within ±0.5%. Inspect the appearance of the foamed product; the surface is smooth, with no obvious defects or bubbles.

[0037] Example 2:

[0038] Step 1: Conduct the experiment under high temperature and humidity conditions in summer. The simulated ambient temperature is 30℃ and the relative humidity is 75%. Thermoplastic polyurethane elastomer (TPU) granules and ethylene-vinyl acetate copolymer (EVA) granules are weighed at a mass ratio of 7:3. The TPU granules are model TH95A, and the EVA granules are model Formosa Plastics 7350. These granules are placed in a forced-air drying oven, set at 105℃, and dried for 5 hours to remove moisture from the materials. After drying, the materials are removed, and the moisture content of the granules is tested using a high-precision moisture meter to ensure that the moisture content is less than 0.03%.

[0039] Step 2: Inspect and adjust the EVA foaming machine. Set the temperature of the injection tube to 175℃ for the first section, 180℃ for the second section, and 185℃ for the third section (the first to third sections are arranged along the injection direction) to ensure that the injection tube reaches the required high-temperature environment. At the same time, install the mold on the foaming machine and connect the mold's cooling system. Set the mold temperature to 60℃, and precisely machine the mold cavity dimensions to 240mm × 100mm × 20mm.

[0040] Step 3: Pour the dried TPU and EVA composite granules into the hopper of the foaming machine. Under gravity, the granules enter the injection tube, where the high temperature causes the material to foam rapidly. The foamed material is then injected into the mold cavity through the injection tube. The low-temperature environment of the mold allows the foamed material to cool rapidly, completing the shaping process in a short time. The mold holding and cooling time is 5 seconds.

[0041] Step 4: After the mold has cooled and been pressurized, open the mold, remove the molded foamed product, and measure its dimensions using a vernier caliper with an accuracy of 0.01 mm. The measured dimensions are 241.0 mm × 100.4 mm × 20.08 mm, and the error between the foamed product dimensions and the mold cavity dimensions is within ±0.5%. Inspect the appearance of the foamed product; the surface is smooth, with no obvious defects or bubbles.

[0042] Comparative example:

[0043] Products of the same specifications are produced using traditional pure EVA foaming technology. The mold cavity dimensions need to be designed as 170mm × 70mm × 14mm (calculated based on empirically estimated shrinkage rate). After foaming and molding in the mold at 175℃, the product expands to approximately 340mm × 140mm × 28mm at the moment of mold opening, and then slowly shrinks, finally yielding a product with dimensions of 235mm × 97mm × 20.2mm. The error between the dimensions of the foamed product and the mold cavity dimensions is within ±0.5%.

[0044] The above does not limit the technical scope of the present invention in any way. Any modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the technical scope of the present invention.

Claims

1. A method for preparing high-precision foamed products, characterized in that, Includes the following steps: Step S1, Raw material preparation: Weigh thermoplastic polyurethane elastomer (TPU) granules and ethylene-vinyl acetate copolymer (EVA) granules. The mass percentage of TPU granules to EVA granules is 65%:35%~75%:25%. Place them in a forced-air drying oven and set the drying temperature to 100℃~110℃ for more than 3 hours. Step S2, Equipment Preparation: Inspect and debug the EVA foaming machine, set the heating system of the injection pipe to 170℃~190℃ to ensure that the injection pipe reaches the required high temperature environment. At the same time, install the mold on the foaming machine and connect the mold cooling system, and set the mold temperature to 55℃~65℃. Step S3, Foaming and Molding: Pour the dried TPU and EVA composite granules into the hopper of the foaming machine. The granules enter the injection tube under the action of gravity. In the injection tube, the material foams rapidly. The foamed material is injected into the mold cavity through the injection tube. The foamed material cools down and solidifies rapidly. The mold holding pressure and cooling time is 5 to 10 seconds. Step S4, Mold Opening Inspection: After the mold has been held under pressure and cooled, open the mold, take out the molded foamed product, and use a vernier caliper to measure the dimensions of the product.

2. The method for preparing a high-precision foamed product according to claim 1, characterized in that: In step S1, the mass percentage of TPU particles to EVA particles is 70%:30%.

3. The method for preparing a high-precision foamed product according to claim 1, characterized in that: In step S1, the drying temperature is set to 105°C and the drying time is 3.5 to 5 hours.

4. The method for preparing a high-precision foamed product according to claim 1, characterized in that: In step S2, the temperature of the injection tube is set to 175°C for the first section, 180°C for the second section, and 185°C for the third section, with the first to third sections arranged along the injection direction.

5. The method for preparing a high-precision foamed product according to claim 1, characterized in that: In step S2, the mold temperature is set to 60°C.

6. The method for preparing a high-precision foamed product according to claim 1, characterized in that: In step S3, the error between the size of the foamed product and the size of the mold cavity is within ±0.5%.

7. The method for preparing a high-precision foamed product according to claim 1, characterized in that: In step S4, the mold holding and cooling time is 5 seconds.