Analysis of Types and Characteristics of Molding Sand for V-Process Casting

1. Types of Molding Sand

The raw sand used in V-process casting can be divided into two main categories according to its basic composition: silica sand (quartz sand) and special sands (non-quartz sands).

At present, silica sand is the mainstream choice in the foundry industry, mainly due to its abundant resources and low cost, which can meet the production requirements of most castings. For castings with special performance requirements or specific process demands, special sands with superior properties must be selected as raw sand.

Classification of Silica Sand

According to its origin and processing method, silica sand can be classified as follows:

(1) Natural Silica Sand

Based on geological formation conditions, it can be divided into:

Mountain sand

River sand

Lake sand

Sea sand

Aeolian (wind-deposited) sand

Lake sand and sea sand can be further subdivided into:

Beach sand

Sedimentary sand

Accumulated sand

(2) Artificial Silica Sand

Classification of Special Sands

Special sands mainly include:

Limestone sand (including limestone, marble, and dolomite types)

Zircon sand (zircon mineral sand)

Magnesia sand and olivine sand

Chromite sand and ilmenite sand

Corundum sand

Refractory clinker (bauxite sand, chamotte sand, coal gangue sand)

Carbonaceous sand (graphite and coke)

Titanium slag sand (including chromium slag and vanadium slag), etc.

2. Analysis of Molding Sand Characteristics

Characteristics of Silica Sand

Silica sand has the following features:

(1) Advantages

Widely available with economical cost

Capable of meeting the basic requirements of general castings

(2) Limitations

Its acidic nature readily reacts with metal oxides to form low-melting-point silicates, leading to sand adhesion defects

High thermal expansion coefficient, which easily causes sand inclusion defects

Prone to crushing and fines generation under thermal stress, resulting in reduced reusability

Difficult to meet the special requirements of large steel castings, especially alloy steel castings

Characteristics of Special Sands

Special sands offer significant advantages:

(1) Performance Characteristics

High refractoriness and excellent thermal conductivity

Low thermal expansion coefficient and good thermo-chemical stability

Strong resistance to slag penetration and erosion

Available in different chemical natures (acidic, basic, and neutral)

(2) Application Advantages

Particularly suitable for alloy steel castings and carbon steel castings prone to sand adhesion

Suitable for castings with slow solidification, difficult sand removal, and high sand adhesion tendency

Ensures dimensional stability of castings and reduces thermal stress

Helps improve dimensional accuracy and prevent crack defects

(3) Usage Limitations

Mostly produced through beneficiation or calcination processes

Higher cost and relatively limited resources