What Is The Main Raw Material For The SMC Basin Mold

Raw Material Selection for SMC Basin Molds

The selection of raw materials for SMC basin molds directly determines their strength, precision, service life, and molding stability. It mainly centers on two categories: mold base materials (steel) and functional auxiliary materials. Different materials must match the hot-press molding characteristics of SMC (Sheet Molding Compound) materials-withstanding a high temperature of 140-160℃ and a pressure of 30-100MPa. The specific classification and key parameters are as follows:

 

I. Core Base Material: Mold Steel (Determines the Basic Performance of the Mold)

Mold steel is the main material of SMC basin molds and must meet four core requirements simultaneously: high rigidity, high-temperature resistance, easy polishing, and fatigue resistance. Due to differences in stress and functions of different parts (cavity, mold base, guide parts), different steel grades are selected:

 

1. Steel for Cavities (Core Part of the Mold, in Direct Contact with SMC Materials)

The cavity is the direct molding area for the basin shape and must have extremely high surface finish (to ensure no defects on the basin surface) and wear resistance (to resist friction from glass fibers in SMC materials). The following two types of steel are mainly used:

NAK80 (Pre-hardened Mirror Mold Steel)Core characteristics: The factory hardness reaches HRC37-43, requiring no subsequent heat treatment. It can be directly processed and polished to a mirror effect (surface roughness Ra≤0.02μm), avoiding cavity deformation caused by heat treatment. It has excellent thermal fatigue resistance and is less prone to cracks under repeated hot pressing at 140-160℃.Application scenarios: Mid-to-high-end SMC basin molds (such as household bathroom basins, customized special-shaped basins), especially suitable for products with high surface texture requirements (such as basins imitating marble texture).Market positioning: The price of domestic NAK80 is about 18,000-22,000 RMB per ton, and imported NAK80 (from Daido, Japan) is about 35,000-40,000 RMB per ton. It is the first choice for mainstream mid-to-high-end molds.

718H (Pre-hardened Plastic Mold Steel)Core characteristics: With a hardness of HRC32-38, it has higher toughness than NAK80 and strong impact resistance (suitable for scenarios with high glass fiber content in SMC materials). It has good polishing performance (Ra≤0.05μm) and its cost is 15%-20% lower than that of NAK80.Application scenarios: Mass-consumption SMC basin molds (such as under-counter basins for engineering projects, economical hand basins), or molds with complex cavity structures (such as those with overflow holes and storage grooves).

2. Steel for Mold Bases (Mold Frame, Playing a Supporting and Positioning Role)

The mold base does not need to be in direct contact with SMC materials, and its core requirement is high rigidity and easy processability. The main choice is:

S50C (High-Quality Carbon Structural Steel)

Core characteristics: With a hardness of HB170-210, it has moderate strength and excellent welding and cutting performance. Local hardness can be improved through quenching and tempering (such as guide pillar mounting holes). Its cost is low, at about 5,000-8,000 RMB per ton.

Application scenarios: The main body of the mold base for all SMC basin molds, including upper mold base, lower mold base, support plate, etc.

 

3. Steel for Guide and Positioning Parts (Ensuring Mold Opening and Closing Precision)

Guide parts (guide pillars, guide bushes) and positioning parts (positioning pins, limit blocks) need to withstand repeated friction and impact, so they require high wear resistance and high precision. The selected steel is:

SUJ2 (High-Carbon Chromium Bearing Steel)

Core characteristics: After quenching and tempering, its hardness reaches HRC60-62, with extremely strong wear resistance and good dimensional stability (tolerance can be controlled within 0.005mm). It can be processed into high-precision guide pillars and guide bushes, ensuring that the cavity alignment error is ≤0.01mm when the mold is opened and closed.

Application parts: All guide pairs (guide pillars + guide bushes) and positioning pins. They are key components to ensure uniform basin wall thickness (error ≤0.3mm).

 

II. Functional Auxiliary Materials (Guaranteeing Mold Molding Efficiency and Service Life)

Although not the main body of the mold, these materials directly affect the molding quality of SMC basins and the mold maintenance cost. They mainly include:

1. Materials for Heating Systems (Providing the Temperature Required for SMC Curing)

SMC molding requires the mold to maintain a uniform temperature of 140-160℃, so the materials for heating systems must be high-temperature resistant and have uniform thermal conductivity:

Heating Tubes/Heating Rods: 304 stainless steel (withstanding temperatures above 600℃ and corrosion resistance) or Incoloy 800 alloy (withstanding temperatures above 1000℃, suitable for high-temperature SMC materials) is selected. The power is designed according to the mold size (usually 2-3kW of heating power is allocated per square meter of cavity).

Heat Transfer Medium: If oil heating or water heating is adopted, special heat transfer oil (such as No. 320 heat transfer oil, with a maximum service temperature of 320℃) or deionized water (to avoid scale blocking the heating channel) must be used.

 

2. Release and Surface Treatment Materials (Preventing SMC Sticking to the Mold and Improving Surface Quality)

Release Agent Coating: The cavity surface needs to be sprayed with PTFE (polytetrafluoroethylene) or TiN (titanium nitride) coating. PTFE coating is temperature-resistant up to 260℃ and has a low friction coefficient (0.04), which can reduce the adhesion between SMC materials and the cavity. TiN coating has a hardness of over HV2000, which combines release property and wear resistance, extending the mold polishing cycle (from 3,000 mold cycles per polishing to 8,000 mold cycles per polishing).

 

Sealing Rings: High-temperature resistant silicone sealing rings (such as fluororubber O-rings, temperature-resistant from -20℃ to 250℃) are used at the mold parting surface and heating channel interfaces to prevent high-temperature resin overflow or heat transfer medium leakage.

 

3. Structural Reinforcement Materials (Improving Local Strength of the Mold)

Prestressed Tie Rods: Large SMC basin molds (such as integrated basin molds with a length >1.2m) need to be equipped with tie rods made of 40Cr alloy steel on both sides of the mold base to prevent mold base deformation during hot pressing (the yield strength of the tie rods is ≥800MPa).

 

Venting Plugs: Copper venting plugs (with good thermal conductivity and easy processing of micro-holes) need to be installed at the dead corners of the cavity. The hole diameter is 0.5-0.8mm, which is used to discharge the gas generated during SMC molding (to avoid bubbles and material shortage in the basin).

 

III. Core Influencing Factors for Raw Material Selection

Mold Positioning: For high-end molds (exported to Europe and the United States, supporting international sanitary brands), imported NAK80 + SUJ2 + TiN coating is preferred, and the cost accounts for 40%-50% of the total mold price. For mid-to-low-end molds (domestic engineering orders), domestic 718H + S50C + PTFE coating is selected, and the material cost accounts for 25%-30%.

Basin Characteristics: Thin-walled basins (wall thickness ≤3mm) require NAK80 steel with higher precision to avoid uneven wall thickness caused by cavity deformation. Thick-walled basins (wall thickness ≥5mm) can use 718H with better toughness to reduce the risk of mold cracking.

Production Batch: For small-batch customized molds (output <10,000 pieces), domestic steel with lower cost can be selected. For large-batch molds (output >100,000 pieces), imported steel + reinforced coating is required to reduce the unit cost by extending the mold service life.