A special sand for the flow channels of a dual-flow turbocharger housing and its preparation method

Abstract

This invention belongs to the field of molding materials technology, specifically relating to a special sand for the flow channels of a dual-flow turbocharger housing and its preparation method. The special sand for the flow channels of a dual-flow turbocharger housing comprises the following raw materials: aggregate-based sand, resin binder, hardener, and release agent; wherein: the aggregate-based sand is composed of the following raw materials by weight percentage: 60-100% 70 / 140 mesh granulated sand, 0-20% 70 / 140 mesh recycled sand, and 0-20% 50 / 100 mesh recycled sand; the resin binder accounts for 1.1-1.3% of the aggregate-based sand by weight; the hardener accounts for 16% of the resin binder by weight; and the release agent accounts for 0.13-0.15% of the aggregate-based sand by weight. The special sand for the flow channels of a dual-flow turbocharger housing has higher thermal stability and strength, effectively resisting thermal stress and expansion pressure at high temperatures, preventing core cracking and the formation of fissures.

Description

Technical Field

[0001] This invention belongs to the field of molding materials technology, specifically relating to a special sand for the flow channels of a dual-flow turbocharger housing and its preparation method. Background Technology

[0002] Twin-scroll turbochargers produce similar effects to twin-turbochargers, but due to their smaller size, they reduce vehicle weight and cost. They further eliminate exhaust interference, improve exhaust efficiency, and reduce turbo lag. Compared to conventional single-scroll turbochargers, twin-scroll turbochargers offer 7-8% higher intake combustion efficiency and 7-8% better performance. This increased efficiency requires less fuel to achieve the same acceleration performance, thus improving fuel economy. This represents a new turbocharging technology.

[0003] The casting of twin-scroll turbocharger housings is generally produced using coated sand shell casting. However, in the casting process, the twin-scroll turbocharger housing is composed of two flow channel cores, with the thinnest part of the sand core being 2 to 2.5 mm. This places high demands on the performance of the coated sand used to produce the flow channel cores.

[0004] When using coated sand prepared using traditional processes for core making in casting production, its poor thermal stability and low strength at high temperatures make it unable to withstand the thermal stress generated by the expansion of the sand core. This leads to core cracking, allowing molten metal to seep in and causing raised cracks in the casting (commonly known as core cracking). It also easily causes sand adhesion. These problems increase the cleaning work on the surface of the casting and may even lead to the scrapping of the casting, thereby increasing casting costs and reducing production efficiency.

[0005] In other words, existing coated sand cannot solve casting defects such as incomplete sand core injection, product porosity, sand adhesion in the flow channel, and core cracking in the product during the casting process.

[0006] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a special sand for the flow channels of a dual-flow turbocharger housing, comprising the following raw materials: aggregate-based sand, resin binder, hardener, and release agent; wherein:

[0008] The aggregate base sand is composed of the following raw materials by weight percentage: 60-100% granulated sand, 0-20% 70 / 140 mesh recycled sand, and 0-20% 50 / 100 mesh recycled sand. Through repeated verification by the inventors, the granulated sand and recycled sand in the above proportions and particle sizes have the optimal particle shape and distribution. This not only results in the best interlocking density but also ensures sufficient gaps between the sand particles when they expand due to heat, preventing deformation caused by squeezing and impact. Ensuring appropriate gaps between the sand particles effectively offsets the thermal expansion and stress, thereby preventing the sand core from cracking or developing fissures due to particle expansion.

[0009] The weight of the resin binder is 1.1 to 1.3% of the weight of the aggregate-based sand;

[0010] The weight of the hardener is 16% of the weight of the resin adhesive;

[0011] The release agent is 0.13 to 0.15% of the weight of the aggregate-based sand.

[0012] Preferably, the resin binder is a solid thermoplastic phenolic resin.

[0013] Preferably, the hardener is hexamethylenetetramine.

[0014] Preferably, the release agent is calcium stearate.

[0015] To facilitate understanding of this invention, the raw materials used in this invention are explained as follows:

[0016] Ceramic refractory sand is a near-spherical, high-strength, and high-hardness alumina-silicon refractory material, also known as "fused ceramic sand for foundrying." It is a type of artificial foundry sand of varying particle sizes, produced from calcined bauxite with alumina (Al₂O₃) as its main component, through melting, blowing, and sieving. Its mineral phases are primarily corundum and mullite, with trace amounts of amorphous phases. The main chemical components of cinnamic refractory sand are alumina (Al₂O₃) and silicon dioxide (SiO₂), and its physical properties include a particle size generally between 0.053 and 3.35 mm. It has a refractoriness greater than 1800℃, and at 1800℃, the sand particles do not expand or sinter.

[0017] Recycled sand: It is an environmentally friendly foundry sand that is recycled after impurities are removed from natural silica sand used for casting.

[0018] Solid thermoplastic phenolic resin: This is a linear resin that only melts when heated and cannot become insoluble or infusible. However, it can be transformed into a thermosetting resin by adding a hardener (such as hexamethylenetetramine). It is produced from difunctional or trifunctional phenols in an acidic solution when the molar amount of phenol is greater than that of aldehyde. Due to the use of an acidic catalyst and the excess of phenol, a soluble and fusible linear phenolic resin is obtained. Thermoplastic phenolic resin requires a hardener to cure at high temperatures. The resin-coated sand made from this material, combined with other raw materials, exhibits excellent performance characteristics, fully meeting the manufacturing process requirements for core-making applications in casting hot core box processes, producing dual-channel vortex sand cores with a minimum thickness of 2-2.5 mm.

[0019] Urotropine: also known as "hexamethyltetramine", is a thermoplastic phenolic resin curing agent.

[0020] Calcium stearate: used as an additive for toughening and lubrication during demolding.

[0021] Based on the same technical concept, another aspect of the present invention is to provide a method for preparing special sand for the flow channels of a dual-flow turbocharger housing, the preparation method comprising the following steps:

[0022] (1) Heat the aggregate base sand and then add the sand;

[0023] (2) Add resin binder and perform a first mixing process to obtain the first mixed mixture;

[0024] (3) Add a hardener to the first mixture and perform two-stage mixing to obtain a second mixture;

[0025] (4) Add a release agent to the second mixture and break it up. Then, discharge the sand, vibrate the screen and cool it in sequence to obtain special sand for the flow channel of the dual-flow turbocharger housing.

[0026] Preferably, in step (1), the heating temperature is 125-155℃; and the sand pouring time is 23-27s. It should be noted that in practice, during the heating process of the aggregate base sand, a rotary heating barrel is used to accurately control the heating temperature so that the base sand is heated evenly; and to avoid the sand temperature drop that may be caused by the sand pouring process taking too long, the sand pouring time must be controlled to ≤30 seconds.

[0027] Preferably, in step (2), the mixing time is 45 to 65 seconds.

[0028] Preferably, in step (3), the time for the two-stage mixing is 50 to 70 seconds.

[0029] Preferably, in step (4), the time for dispersing is 15-35s; the time for removing sand is 23-27s; and the temperature after cooling is 43-70℃.

[0030] It should be emphasized that, through repeated verification by the inventors, it was found that: the heating temperature in step (1) and the first mixing time in step (2) determine the thickness and uniformity of the resin binder coating layer on the surface of the sand particles; the second mixing time in step (3) and the dispersing time in step (4) affect the timing of adding the hardener to the mixing process, thereby determining whether the hardener and release agent can be evenly distributed on the outer layer of the resin film, and thus determining the stability during subsequent core making and the strength performance during molten iron casting.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. The special sand for the flow channels of the dual-flow turbocharger housing described in this invention, through scientific proportioning and a specific feeding method, possesses higher thermal stability and strength, effectively resisting thermal stress and expansion pressure at high temperatures, and preventing core cracking and the formation of fissures. Furthermore, the coated sand of this invention also exhibits good fluidity, meeting the requirements for flow channel sand cores in dual-flow volute casting production, thereby reducing casting defects.

[0033] 2. The special sand for the flow channels of the dual-flow turbocharger housing described in this invention is a sand core material with high thermal stability, high strength, and good fluidity, suitable for dual-flow volute casting production. Its application will help improve casting quality and production efficiency, reduce production costs, and promote the development of the casting industry. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] To better implement this invention, the performance indicators of the special sand must first be determined. The basic requirements for these performance indicators are shown in Table 1. The performance indicators designed in this invention are higher than the basic requirements, as shown in Table 2.

[0036] Table 1 Basic Indicators of Special Sand

[0037]

[0038] Table 2 Design Specifications of the Invention

[0039]

[0040] The formulations designed in the examples are shown in Table 3.

[0041] Table 3 Raw Material Formula

[0042]

[0043] Table 3 (continued)

[0044]

[0045]

[0046] The preparation method used in the examples includes the following steps:

[0047] (1) Heat the aggregate base sand and then add the sand;

[0048] (2) Add resin binder and perform a first mixing process to obtain the first mixed mixture;

[0049] (3) Add a hardener to the first mixture and perform two-stage mixing to obtain a second mixture;

[0050] (4) Add a release agent to the second mixture and break it up. Then, discharge the sand, vibrate the screen and cool it in sequence to obtain special sand for the flow channel of the dual-flow turbocharger housing.

[0051] More specifically, the design process parameters are shown in Table 4.

[0052] Table 4 Process Parameters

[0053]

[0054] Table 4 (continued)

[0055]

[0056] The present invention designed a total of 25 sets of embodiments and 10 sets of comparative examples, and conducted performance tests on the special sand obtained in each set of embodiments and comparative examples. The specific correspondence and test results are shown in Table 5.

[0057] Table 5 Test results for each set of examples and comparative examples

[0058]

[0059]

[0060]

[0061] Table 5 (continued)

[0062]

[0063]

[0064]

[0065] After comparing the data in Table 5, the best-performing coated sand for each formula under five different process parameters was selected and used in the core molding and casting of the double-flow-channel vortex shell. The final casting inspection and verification results are shown in Table 6.

[0066] Table 6. Inspection Results of Castings

[0067]

[0068] Table 6 (continued)

[0069]

[0070]

[0071] Note: The standard for casting inspection usually adopts the industry default standard, which means that defects such as protrusions and depressions in the flow channels are not allowed, and there are also roughness requirements for the appearance of the flow channels. Specifically, protrusions and depressions in the flow channels are detected by endoscopy, and the roughness of the flow channel appearance is detected by profilometer and roughness comparison block.

[0072] The verification results show:

[0073] 1. The dual-flow turbocharger housing castings produced by the special sand obtained in Examples 3, 7, 13, 18, and 22 did not produce any defects.

[0074] 2. The twin-scroll turbocharger housing castings produced from the special sand obtained in Comparative Example 3 had a defect rate of 15-20%, which did not meet the requirements.

[0075] 3. The twin-scroll turbocharger housing castings produced from the special sand obtained in Comparative Example 7 had a defect rate of 30-40%, which did not meet the requirements.

[0076] Further analysis shows that Comparative Example 3 is the best example in Formula 6, and Comparative Example 7 is the best example in Formula 7. However, neither Comparative Example 3 nor Comparative Example 7 meets the requirements, meaning that Comparative Examples 1 to 10 also fail to meet the requirements.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A special sand for the flow channels of a dual-flow turbocharger housing, characterized in that, It includes the following raw materials: aggregate-based sand, resin binder, hardener, and release agent; wherein: The aggregate base sand is composed of the following raw materials by weight percentage: 60-90% 70 / 140 mesh granulated sand, 5-20% 70 / 140 mesh recycled sand, and 5-20% 50 / 100 mesh recycled sand; The resin binder is a solid thermoplastic phenolic resin, and the weight of the resin binder is 1.1~1.3% of the aggregate-based sand. The hardener is hexamethylenetetramine, and the weight of the hardener is 16% of the resin adhesive. The release agent is calcium stearate, and the weight of the release agent is 0.13~0.15% of the aggregate-based sand. The preparation method of special sand for the flow channels of a dual-flow turbocharger housing includes the following steps: (1) The aggregate base sand is heated and then poured into the sand; wherein the heating temperature is 125~155℃; and the sand pouring time is 23~27s; (2) Add resin binder and perform a first mixing to obtain a first mixed mixture; wherein the first mixing time is 45~65s; (3) Add a hardener to the first mixture and perform a second mixing stage to obtain a second mixture; wherein the second mixing stage takes 50-70 seconds. (4) Add a release agent to the second mixture and break it up. Then, discharge sand, vibrate and cool it in sequence to obtain special sand for the flow channel of the dual-flow turbocharger housing. The dispersing time is 15~35s; the sand discharge time is 23~27s; and the temperature after cooling is 43~70℃.

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