How Can Foundries Strictly Control Raw and Auxiliary Materials for V-Process Casting? A Comprehensive Guide to Implementing Standard Acceptance Specifications

Zunhua Shengjian Fanrong Machinery Parts Co., Ltd. has deep expertise in V-process casting. This article provides a detailed interpretation of the company's internal document, "SJFR-ZD-045: Raw and Auxiliary Material Standards." It covers the full range of specifications—including silica sand, EVA film, scrap steel, and coke—and outlines acceptance procedures to help trace the root causes of defects such as porosity and sand adhesion.

In the foundry industry, the saying goes, "70% depends on raw materials, 30% on process." V-process casting relies on unique techniques involving plastic film covering and vacuum molding with dry sand; consequently, the quality of raw materials directly determines surface finish and dimensional accuracy. Substandard materials easily lead to batch defects such as porosity, surface wrinkling, sand adhesion, and mold collapse. Zunhua Shengjian Fanrong Machinery Parts Co., Ltd. issued the controlled document "SJFR-ZD-045: Raw and Auxiliary Material Standards and Acceptance Specifications" to fully implement quality control requirements. This document covers core areas—including national standards for V-process silica sand, EVA film control, sulfur and phosphorus limits in foundry pig iron, scrap steel grading, furan resin technical indicators, coke testing methods, and refractory brick inspection—categorized into three main sections: molding/core-making materials, metallic charge and refractory materials, and auxiliary consumables. It clearly defines physicochemical specifications, inbound inspection workflows, and non-conforming product handling rules, establishing a reusable quality control system for raw materials that other V-process foundries can adopt. Based strictly on the original specifications, this article breaks down the core standards and practical inspection methods, supported by professional data tables, to help V-process casting professionals rapidly implement standardized material intake controls and efficiently trace casting defects back to raw material issues. I. Standards for Key Materials in V-Process Molding: Specifications for Silica Sand, EVA Film, and Resin

The essential consumables for V-process casting include synthetic silica sand, EVA facing film, and PE backing film, used in conjunction with core-making resins and coatings. Raw material grain size, film thickness, and volatility characteristics directly impact the quality of vacuum-formed molds; all mandatory technical specifications adopted by Zunhua Shengjian Fanrong Machinery Parts Co., Ltd. are derived from the "SJFR-ZD-045" document.

1. Standards for the chemical composition of synthetic silica sand used in V-process molding

Particle size testing is conducted in accordance with the GB2684-81 standard. Sieve retention requirements are as follows: 50-mesh <0.2%, 70-mesh <5.4%, 100-mesh >26.0%, 140-mesh >46.5%, 200-mesh <19.2%, and 270-mesh + pan <2.4%. The particle size index for new sand is controlled within the 90–130 range, with specific sieve fraction percentages serving only as a reference. The silica sand grade for core making is ZGS85-50/100, with SiO₂ ≥85% and moisture content <0.3%; the use of dry sand (zero moisture) is essential for V-process vacuum molding to prevent subsurface porosity caused by gas generation from the heated film, a core requirement of the national standard for foundry silica sand.

2. Specifications for V-process specialized plastic films (EVA front film + PE back film)

Parameters fully comply with the original specifications:

EVA (Ethylene-Vinyl Acetate) front film: Vinyl acetate content 17.5–19%, thickness 0.15–0.25 mm, width 1800 mm; meets standards for heat-induced ductility; ensures no film breakage or vacuum leakage during the molding process.

PE (Polyethylene) back film: Thickness 0.03–0.04 mm; used to seal the back of the flask and prevent dry sand leakage.

Both types of film must be accompanied by a supplier certificate of conformity upon delivery and pass a V-process production trial; non-compliant materials will be rejected immediately.

3. Physicochemical parameters of auxiliary materials for V-process furan resin core making

The technical specifications for furan resin listed above are specific control parameters established by the company for V-process core making; the values strictly adhere to the company's internal standards.

4. Standards for phenolic resin used in V-process coatings

Incoming Inspection Requirements:The supplier must provide a complete certificate of conformity regarding physical and chemical properties. The material must appear as a reddish-brown, transparent liquid free of lumps. If the graphite coating prepared for the V-process fails to meet performance standards during trial use, it will be returned in accordance with the non-conforming product procedure.

General Rules for V-Process Auxiliary Material Inspection:All specialized V-process films, silica sand, resins, and graphite powders must be accompanied by a supplier's certificate of conformity. Incoming materials undergo a visual inspection followed by small-batch trial production (film coating and core making). Materials resulting in film breakage due to stretching, insufficient sand core strength, or coating peeling are prohibited from entering storage; this constitutes the fundamental quality control process for sand casting raw materials.

II. Inspection Standards for V-Process Melting Charge Materials: Graded control of pig iron, steel scrap, and iron scrap.

V-process vacuum casting demands higher purity in molten iron; excessive sulfur and phosphorus impurities significantly increase the likelihood of porosity and leakage defects. Zunhua Shengjian Fanhong Machinery Parts Co., Ltd. classifies materials according to standard *SJFR-ZD-045* and strictly enforces control standards for sulfur and phosphorus in foundry pig iron and grading standards for steel scrap.

1. Control Ranges for Silicon, Manganese, Phosphorus, and Sulfur in V-Process Foundry Pig Iron Grades (GB718-82)

The company prioritizes the procurement of "virgin" pig iron in grades Z18 through Z26, with a carbon content consistently exceeding 3.3%. Silicon content is categorized by gradient, while manganese, phosphorus, and sulfur are subject to multi-tier graded control. Standards for market-procured materials may be relaxed to: P ≤ 0.2%, S ≤ 0.15%, and Mn ≤ 0.50%. Iron blocks must be clean, free of slag and sand grains, and allow only minor traces of graphite or lime adhesion. Maximum incoming dimensions must not exceed 250mm, and all materials must comply with the established control indicators for sulfur and phosphorus throughout the process.

2. Thickness Grading and Composition Standards for V-Process Melting Steel Scrap

The specifications for thickness and chemical composition limits are fully consistent with the documented scrap steel grading standards.

3. Criteria for V-process scrap iron reuse (gray cast iron)

Chemical composition range: C 2.9–3.5%, Si 1.3–2.5%, Mn 0.4–1.5%; P and S both ≤0.15%; other impurities <0.8%;

Fracture appearance: Uniform gray cross-section; inclusion of white cast iron is strictly prohibited;

Impurity control: Mixing with lead, copper, or aluminum parts is prohibited; batches of similar scrap machine iron ≥2 tons require chemical re-testing via sampling;

Processing requirements: Maximum material dimension <250mm.

III. Summary of specifications for V-process melting refractories and metallurgical auxiliaries: Coke, ferrosilicon, and refractory bricks

The cupolas and pouring furnaces used in the V-process impose strict requirements regarding fuel calorific value and the high-temperature resistance of refractory materials; all auxiliary material specifications are derived directly from the company's standards.

1. Two standards for V-process-specific coke

① Grade II metallurgical coke (GB1996-80)

② Grade II Foundry Coke (GB8729-88)

Lump size: 100–150 mm; moisture ≤ 5%; ash ≤ 12%; sulfur ≤ 0.8%; volatile matter ≤ 1.5%.

Unified plant-wide visual inspection criteria for coke lump size: 80–150 mm. In the event of a quality dispute, an external third-party inspection may be commissioned; the complete testing procedure follows the standard testing methods for foundry coke.

2. Standards for adjusting ferrosilicon and ferromanganese alloy composition in molten iron (V-process)

Ferrosilicon (GB2272-87) FeSi75 series

Ferromanganese FeMn65C7.0

Mn content: 65–72%; C ≤ 7.0%; Si: 2.5–4.5%; P ≤ 0.4%; S ≤ 0.03%. Lump size specifications: for ferrosilicon, 40–80 mm (post-furnace) and ≤15 mm (pre-furnace); for ferromanganese, 40–80 mm (post-furnace) and ≤10 mm (pre-furnace); materials must be stored separately by category.

3. Appearance and physicochemical standards for clay/high-alumina refractory bricks used in V-process furnaces

Clay bricks (N4): Refractoriness ≥ 1690°C; cold crushing strength ≥ 200 kgf/cm². High-alumina bricks (LZ-75): Al₂O₃ ≥ 75%; refractoriness under load (0.2 MPa) ≥ 1520°C. General dimensional tolerance: ±2%; warpage: ≤2 mm; depth of chipped edges/corners: ≤7 mm; cracks with a width > 0.5 mm result in immediate rejection; these constitute the core criteria for incoming inspection of refractory bricks. IV. Standardized Acceptance Process for V-Process Casting Raw and Auxiliary Materials (Fully Compliant with Original Specifications)

Zunhua Shengjian Prosperity Machinery Parts Co., Ltd. has implemented standardized acceptance specifications for raw and auxiliary materials used in the V-process (vacuum casting). The acceptance procedures strictly adhere to the following requirements:

Document Verification: Upon arrival of materials—such as V-process EVA film, molding silica sand, pig iron, and coke—manufacturers' certificates of conformity and physicochemical test reports must be provided; warehousing is suspended if documentation is incomplete.

Preliminary Visual Inspection: EVA film must be free of black spots or damage; silica sand must be dry and free of clumps; liquid resin must show no phase separation; metal furnace charges must be sorted to remove non-ferrous metals and heavily rusted scrap.

Sampling and Testing:

Silica Sand: Sampling and particle size sieving are conducted according to the GB2684 standard; if moisture content exceeds limits, a re-test with double the sample size is performed.

Pig Iron/Alloys: Sampling is conducted in accordance with GB719; rapid analysis of carbon, sulfur, silicon, phosphorus, and manganese is performed using combustion and photometric methods, with arbitration testing following GB223.1–223.5-81.

Coke: Samples are collected from three fixed points and reduced using the cone-and-quartering method; moisture, ash, volatile matter, fixed carbon, and total sulfur content are tested.

Re-testing and Disposition: If preliminary tests fail, re-testing is conducted with double the sample size; if re-test results exceed limits, the "Management Regulations for Handling Non-conforming Raw and Auxiliary Materials" (No. QB/HXTMS-B-028-2009) are enforced, resulting in material isolation and return.

Sample Retention and Traceability: Test samples of coke, metal furnace charges, and V-process film are retained for 7 days; in the event of V-process casting defects, these samples are used for re-testing and traceability analysis to link defects back to the raw materials. V. Summary of Common Pitfalls in Raw Material Control for V-Process Casting

Drawing on years of frontline quality control experience in V-process casting at Zunhua Shengjian Rongrong Machinery Parts Co., Ltd., we have compiled a list of industry misconceptions. All standards cited herein adhere to the company's internal specifications:

Checking certificates without conducting on-site trial production with film application: EVA films failing to meet specifications for ethylene-vinyl acetate content or thickness may rupture during heating and stretching, causing vacuum leaks—a violation of fundamental quality control requirements for sand casting raw materials;

Lax control of silica sand moisture content: Failure to strictly adhere to national standards for foundry silica sand; moisture-laden sand releases excessive gas when heated, leading to widespread subcutaneous porosity in castings;

Mixing thin-gauge scrap steel with other scrap: Failure to implement scrap grading standards; substandard materials (e.g., <3mm thickness) oxidize in the furnace, creating fumes and dust that contaminate the vacuum mold cavity, resulting in surface pitting and inclusions on castings;

Rosin/resin assessment based solely on visual inspection without process verification: Neglecting to measure technical parameters (such as acid value and viscosity) of furan resin leads to issues like sand core cracking, sand shedding, and sand adhesion during pouring;

Coke contaminated with fines/dust: Failure to follow testing protocols for foundry coke; dust adheres to the mold cavity via the vacuum airflow, resulting in poor casting surface finish.

Conclusion

Amidst intensifying quality-based competition in the V-process casting industry, standardized acceptance specifications for raw and auxiliary materials are crucial for reducing scrap rates and ensuring consistent vacuum molding quality. The document *SJFR-ZD-045: Standards and Acceptance Specifications for Raw and Auxiliary Materials*, compiled by Zunhua Shengjian Rongrong Machinery Parts Co., Ltd., integrates national (GB) and industry standards with the practical operational needs of V-process vacuum casting. It covers the entire lifecycle—from procurement and warehousing to testing and the disposal of non-conforming items—for materials such as specialized V-process films, dry sand, metal furnace charges, and refractory materials. V-process foundries can use the metrics in the tables provided here to establish their own raw material quality control systems, enabling the traceability of casting defects back to the source material and preventing mass production losses caused by raw material issues.