これは鋳物砂の透水性を測定するための精密機器です。標準装備として、AFS（直径2インチ×2インチ）またはメトリック（直径50mm×50mm）試験片の絶対透水性を測定できます。

アタッチメントの助けを借りて測定することもできます

• カビの相対透過率（4.2.1参照）
• コアの絶対透磁率（4.2.2参照）
• 非結合砂の絶対透水性（4.2.3 参照）。

製品名:	デジタル透磁率計
製品コード:	VPD1
注文参照コード:	V0000107
必要な電源:	230V 50Hz AC（デフォルト） 110V 60Hz AC（オプション） 単相、過電圧/低電圧カットオフで安定化。
電気プラグ:	Mタイプ：15アンペアプラグ
標準最大電流:	230Vで2.2A
圧縮空気供給:	操作を完全に自動化するには、2 Kg/cm2 の乾燥圧縮空気が必要です。 エアドラムをオペレーターが持ち上げることができる場合はオプションです。
コミュニケーション：	RS485 MODBUS RTU RS232シリアル イーサネット（オプション） V-Syncを使用したCloudSync
寸法:	500 x 320 x 460 mm（幅x奥行x高さ）
梱包寸法:	600 mmx 450 mm x 625 mm (幅x奥行x高さ) 標準
正味重量：	約25kg
総重量：	約30kg
色：	工場出荷時のデフォルト
測定範囲:	0～100 mmWC および関連測定値 AFS 透過率測定チャートがデジタル表示されます。
追跡可能:	メーカー規格
最小数:	1mmWC
標本の要件:	圧縮型試験片
動作温度:	0～50℃
試験基準:	BIS: 標準 AFS: オプション
校正頻度:	22500回のテストサイクルまたは年に1回

• デジタル透磁率計。
• 大きな開口部。
• サイフォンポンプ。
• 校正証明書。
• 取扱説明書。

砂割り機：代表的なサンプルを得るため

標準 AFS またはメートル法圧縮試験片を作成するための試験片準備装置。

選択できるキャリブレーション キットには次の 4 つのタイプがあります。

VKPA: 標準試験片タイプ付き小口径

VKPB: 大型オリフィス用標準試験片タイプ

VKPC:小口径用ゴムボス付き

VKPD: 大口径用ゴムボス付きタイプ

• VPR: モールドパーマテスター
• VD: コア透過性チューブ
• VBP: 基礎透水性管
• 小さな開口部

• 透水性計VP（教育用）
• 電気透過率計VEP
• VCATマルチテスター
• デジタル透磁率計 VPD
• デジタル透磁率計 VPD II

• 脱塩水
• ゴムボスアセンブリ（部品番号 V4500259）

The Unseen Pillar of Casting: A Deep Dive into Sand Permeability

Permeability. This is the measure of a sand mold's ability to allow gases to pass through it. It is a fundamental requirement for producing sound, defect-free castings. A mold that cannot effectively vent the massive volume of gases generated during pouring is a recipe for disaster, leading to defects that can render a casting useless.

The Theory and Importance of Permeability Testing

At its core, permeability is a measure of how easily a fluid—in this case, gas—can flow through a porous medium like compacted sand. The scientific principle governing this is Darcy's Law, which establishes a relationship between the flow rate, the properties of the fluid, the pressure gradient, and the permeability of the medium.

In a foundry setting, the standard method for quantifying this property is the American Foundry Society (AFS) Permeability Test. This test involves taking a standard cylindrical specimen of prepared sand (2 inches in diameter and 2 inches high), ramming it with a standard force, and then measuring the time it takes for a specific volume of air (2000 cc) to pass through it under a constant pressure. The result is expressed as a Permeability Number. A higher number signifies a more permeable sand, meaning gases can escape more easily.

The importance of this test cannot be overstated. When molten metal enters the mold cavity, it rapidly heats the sand and any moisture or organic binders present. This process generates a significant volume of gases, including steam, hydrogen, carbon monoxide, and carbon dioxide. This gas volume can be many times greater than the volume of the mold itself. If these gases cannot escape through the sand pores quickly and efficiently, they will become trapped, building up pressure within the mold. This pressure can resist the inflow of metal, leading to incomplete castings, or it can force its way into the solidifying metal, creating a variety of gas-related defects.

Therefore, permeability is a critical balancing act:

• Too Low Permeability: Traps gases, causing defects like blowholes and pinholes.
• Too High Permeability: Can lead to a poor surface finish on the casting and may cause defects like metal penetration, where the molten metal seeps into the large pores between sand grains.

Factors Influencing Sand Permeability

Permeability is not a fixed property but is influenced by several interconnected factors related to the sand and the molding process. Understanding these factors is key to controlling the final outcome.

• Grain Size and Shape: This is the most significant factor. Coarser, more uniform sand grains create larger voids between them, resulting in higher permeability. Finer sands pack more densely, leading to smaller voids and lower permeability. Similarly, rounded grains will have larger pore spaces than angular grains, which can interlock more tightly.
• Grain Distribution: A sand with a wide distribution of grain sizes will have lower permeability. The smaller grains will fill the voids between the larger grains, reducing the overall porosity. Foundries often aim for a sand with three to four sieve distributions to create a balance between strength and permeability.
• Binder Content and Type: The type and amount of binder (such as clay or chemical resins) directly impact permeability. An excess of binder can fill the voids between sand grains, drastically reducing permeability.
• Moisture Content: In green sand systems, water content is critical. A small amount of water is necessary to activate the clay binder, but excessive moisture generates more steam during pouring and can also reduce permeability by filling pore spaces.
• Ramming Density: The more a sand is compacted or rammed, the smaller the voids between the grains become, and the lower the permeability. The ramming energy must be carefully controlled to achieve the desired mold hardness and permeability.

Permeability of Different Sand Types:

• Silica Sand: The most common foundry sand. Its permeability can be easily controlled by managing grain size and distribution.
• Zircon Sand: Being finer and having a different grain shape, zircon sand typically has lower permeability than silica sand but offers higher refractoriness and a better surface finish.
• Chromite Sand: Similar to zircon, chromite is used for its high thermal conductivity and chill effect. Its angular grain shape can lead to lower permeability if not managed properly.

Permeability as a Diagnostic Tool for Casting Defects

An out-of-spec permeability reading is a major clue when diagnosing casting defects. By analyzing the permeability number in conjunction with the type of defect observed, foundry engineers can pinpoint the root cause.

• Blowholes and Gas Porosity: These are cavities within the casting caused by trapped gas. They are the classic symptom of low permeability. If the sand is too fine, has too much binder or moisture, or is over-rammed, gases cannot escape, and they form bubbles in the metal.
• Metal Penetration: This occurs when molten metal seeps into the sand mold, resulting in a rough, sandy surface on the casting. This is often a sign of excessively high permeability, where the pores between sand grains are too large for the surface tension of the metal to bridge.
• Scabs, Cuts, and Washes: These defects, where a portion of the mold surface breaks away and is embedded in the casting, can be indirectly related to permeability. Low permeability can cause high gas pressure at the mold-metal interface, which can lift or erode the sand surface.
• Incomplete Fill (Misrun): If the back-pressure from trapped gases due to low permeability is high enough, it can prematurely halt the flow of molten metal, preventing it from completely filling the mold cavity.

The Modern Approach: Online Testing and Automation

Traditionally, sand testing has been a manual, batch-based process performed in a laboratory. While essential, this method has a time lag; by the time a problem is detected, a significant amount of defective sand may have already been used, resulting in scrap castings.

The modern trend is a move towards online and automated sand testing. Advanced systems are now available that can be integrated directly into the sand preparation and molding line. These systems automatically sample the sand at critical points (e.g., after the muller or before the molding machine) and provide near-instantaneous readings for key properties, including permeability, compactability, and moisture.

この進化の重要性は計り知れません。

• リアルタイム制御:制御システムはライブ データを使用することで、水やバインダーの添加量の変更など、砂の混合物を即座に自動的に調整できます。
• プロセスの安定性:自動化により人的要素が最小限に抑えられ、バッチごとに非常に厳しい制御ウィンドウ内で砂の特性が維持されます。
• 欠陥防止:逸脱が発生したときにそれを捕捉することで、これらのシステムは欠陥のある金型の製造を防ぎ、廃棄率を大幅に削減します。
• データ駆動型改善:継続的にデータを収集することで高度な分析が可能になり、鋳造所が砂の変数と鋳造結果の複雑な相互作用を理解するのに役立ち、さらなるプロセス最適化 (インダストリー 4.0) への道が開かれます。

透過性を制御する正しい方法

鋳造工場では、透水性を効果的に管理することが日常業務です。そのためには、材料、プロセス、試験を網羅した体系的なアプローチが必要です。

砂の選定と管理：製造する鋳物の種類に適した粒度分布（GFN）を持つベース砂から始めます。定期的にふるい分け分析を実施し、劣化や汚染による粒度分布の変化を監視します。

バインダーと添加剤の管理：粘土、樹脂、その他の添加剤の添加量を正確に管理します。メチレンブルー粘土試験などの試験を用いて、システム内の活性粘土の量を測定します。細孔を塞ぐ可能性のある過剰な添加は避けてください。

水分管理：生型砂の場合、水分管理は特に重要です。混練機での水分添加量を管理するには、主に圧縮性試験を実施してください。これにより、一定の「テンパー」状態が確保され、透水性が安定します。

圧縮制御：成形時に適用される圧縮エネルギーを標準化・制御します。これにより、金型の密度が一定になり、ひいては通気性も一定になります。

混練効率：混練機が正しく作動していることを確認してください。適切な混練は、砂粒を過度に砕くことなく、バインダーで砂粒を均一にコーティングします。砕くと、細粒分が増加し、透水性が低下します。