BMC Bathroom Basin Mold

BMC (Bulk Molding Compound) has become the ideal material for modern integral bathroom floor slabs due to its excellent dimensional stability, water and corrosion resistance, impact strength, and good molding properties. As the core equipment for its molding, it directly determines the product's precision, surface quality, production efficiency, and service life. Therefore, its design and manufacture must be systematically planned around the characteristics of the BMC thermosetting compression molding process.

 

I. Core Design Principles for Molds

1. Cavity and Structural Design

▲Shrinkage Compensation: Precisely reserve according to the shrinkage rate of BMC material (0.3%–0.8%) to ensure the flatness of the floor slab, the drainage slope (typically 0.5%–1%), and the tolerance of installation holes; the draft angle should be ≥1.5° (the appearance side can be smaller, but the functional side should be ≥3°) to avoid scratches and sticking to the mold.

▲Integrated structure: One-time molding of the drainage outlet, water barrier edge, reinforcing ribs, pre-embedded nut positions and anti-slip textures; the anti-slip texture is preferably designed with concave-convex stripes (strip width 2-3mm, spacing 8-12mm, depth 0.8-1.2mm) or dot-shaped protrusions (diameter 3-5mm, spacing 10-15mm, height 1.0-1.5mm), with a dry static friction coefficient COF ≥ 0.65 and a wet static friction coefficient COF ≥ 0.6, meeting the anti-slip requirements for bathroom wet areas as stipulated in the JGJ industry standard "Anti-slip Technical Code for Building Floor Engineering", with an anti-slip grade reaching R10-R11, suitable for bathroom wet environments; at the same time, the anti-slip texture needs to be designed in coordination with the drainage slope to avoid water accumulation and residue affecting the anti-slip effect, and the height-to-width ratio of the reinforcing ribs should be ≤ 3, with a root R angle ≥ 0.5mm to prevent stress concentration and filling dead corners.

1. Parting line optimization: Prioritize non-external surfaces for the parting line, and use guide pins and precision locating pins to ensure mold closing accuracy and prevent flash.

2. Temperature control and heating system

The mold temperature is typically set at 140–160°C, with multi-zone heating tubes/heating plates evenly distributed to maintain a temperature difference of ±3–5°C. Water channels/heating holes are placed 15–25mm away from the cavity wall to prevent local overheating that could lead to uneven curing or material degradation. The mold should have preheating and constant temperature programs to ensure batch stability.

3. Venting and overflow design

During the curing process, a small amount of gas is released. Precision venting channels 0.01–0.03mm deep should be set at the end of the filling, parting lines, and dead corners to prevent bubbles and pinholes. Overflow channels should be provided to collect excess material and control flash thickness to ≤0.1mm, reducing post-processing costs.

4. Demolding and ejection system

A multi-point balanced ejection system (hydraulic cylinder/ ejector pin combination) should be used to avoid local stress-induced deformation. Ejector pin positions should avoid external surfaces, and the pins should be surface nitrided. Special high-temperature demolding agents should be used to improve demolding smoothness.

 

II. Mold Materials and Manufacturing Process

1. Material selection: High-quality mold steels such as P20, 718, and H13 are commonly used for the cavity, which are quenched and tempered to achieve a hardness of HRC32–44, balancing wear resistance and machinability. Standard components are used for the mold base to shorten the cycle and reduce costs.

2. Precision processing flow: Rough machining → heat treatment → semi-finishing → EDM (electrical discharge machining) → five-axis finishing → mirror polishing; the surface roughness of the cavity should be Ra≤0.2μm to ensure that the product surface can achieve a matte or high-gloss finish without additional grinding.

3. Surface strengthening: The cavity can be treated with hard chromium plating or TD treatment to enhance corrosion resistance and demolding performance, extending the mold's lifespan.

 

III. Matching Parameters for Molding Process

▲ Molding pressure: 3.5–10MPa (adjusted according to the wall thickness of the product);

▲ Curing time: Wall thickness × (1.2–1.5) min/mm (thick-walled parts require longer curing time to prevent under-curing);

▲ Material dosage: Precisely weigh based on the product volume × material density × 1.05–1.10 (flash factor) to avoid underfilling or excessive overflow. For anti-slip texture areas, the material dosage should be increased by 1%-2% to ensure full texture formation and prevent texture defects such as incomplete or collapsed textures, ensuring the anti-slip performance meets standards.

 

IV. Mold Maintenance and Lifespan Enhancement

1. Fully preheat before production (≥60 minutes) to avoid uneven curing due to cold molds;

2. Clean the cavity, venting channels, and overflow channels after each molding to prevent carbon buildup affecting the surface;

3. Regularly inspect the heating system, ejection mechanism, and seals, and perform lubrication and maintenance;

4. When not in use for a long time, apply anti-rust oil and store in a dry environment.

 

V. Product Advantages and Application Scenarios

Products formed by BMC bathroom floor molds have the advantages of being waterproof, moisture-resistant, crack-resistant, anti-slip, wear-resistant, lightweight (30% lighter than traditional ceramics or

stones), and easy to install. They are widely used in hotels, high-end residences, hospitals, and elderly care institutions where durability, safety, and assembly efficiency of bathroom facilities are highly demanded. Through multi-cavity molds or rapid mold change designs, they can also meet the customized requirements of different sizes and functions.

 

VI. Common Defects and Countermeasures

flaw	primary cause	countermeasure
Bubbles / Pinholes	Poor exhaust ventilation, uneven mold temperature, insufficient feeding volume	Encrypted exhaust channels, optimized heating zones, precise control of material quantity
Excessive flying edge	Inaccurate mold closure, excessive pressure, and unclean parting surface	Replace the precision positioning pins, reduce the molding pressure, and increase the frequency of cleaning.
Uneven surface flow marks / uneven luster	Low temperature, slow filling speed, and rough cavity surface	Increase mold temperature, optimize filling curve, and enhance polishing level
Demolding deformation	Inconsistent ejection, insufficient curing, and small ejection angle	Adjust the ejection point, extend the curing time, and increase the ejection angle.
Defective/collapsed anti-slip texture	Insufficient filling amount, insufficient molding pressure, and low mold temperature	Increase the amount of material in the anti-slip area, adjust the molding pressure to 5-8 MPa, and raise the mold temperature to 150-160℃

 

Conclusion

To sum up, the design, manufacturing, process matching, and operation of BMC bathroom chassis molds are the core factors that ensure product quality, enhance efficiency, and extend the lifespan of the molds. It is necessary to combine the characteristics of BMC materials, optimize the mold structure (including anti-slip texture parameters), strictly control the molding process, ensure that the core performance such as anti-slip of the products meets the standards, and meet the safety requirements of the bathroom. Huangyan Jiutai Molds has been deeply engaged in the SMC/BMC mold field for many years, specializing in the research and manufacturing of bathroom chassis and other bathroom molds. With rich industry experience, it adheres to this core principle and helps the industry develop.

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