How to Prepare Drawings for Custom Mould Manufacturing: A Guide for Brick Plant Engineers
For brick plant engineers, preparing accurate technical drawings is the most critical step in procuring a custom mould. The drawing communicates your exact requirements to the manufacturer and becomes the binding specification for production, inspection, and acceptance.
A well-prepared drawing eliminates guesswork, reduces the risk of dimensional errors, and ensures the mould you receive fits your machine and produces blocks to your exact specifications. This guide outlines the essential information your drawing must include, based on UNIK's experience serving block producers across 28 countries.
The Core Principle: The Drawing Is the Contract
Once a mould is manufactured to your drawing, dimensional changes are prohibitively expensive. The drawing serves as the definitive specification for:
Cavity dimensions and tolerances
Interlocking geometry and features
Mounting interface and bolt patterns
Surface finish requirements
Material and heat treatment specifications
Engineers should treat drawing preparation as a formal engineering process, not a casual sketch.
Essential Information Your Drawing Must Include
1. Machine Brand, Model, and Mounting Specifications
The drawing must clearly identify the block machine the mould will be used on. This is non-negotiable. A mould that does not fit your machine is unusable, regardless of its quality.
Required information:
Machine brand (e.g., Hess, Masa, Zenith, Tiger, Besser, Columbia, Qunfeng, Hengxing)
Machine model number
Mounting hole positions, sizes, and patterns
Overall envelope dimensions (length, width, height)
Interface specifications for the press head and lower mould
For machines not listed, provide drawings or measurements of your existing mould or machine mounting plate .
2. Block Dimensions with Tolerances
The cavity dimensions determine the finished block size. Include both nominal dimensions and acceptable tolerances.
Critical dimensions:
Length, width, and height of the finished block
Cavity dimensions (which account for concrete shrinkage)
Wall thickness for hollow blocks
Core pin positions and diameters
Interlocking feature dimensions (lips, pins, grooves)
Recommended tolerances:
Single cavity dimension: ±0.1 mm
Cavity height (filling depth): ±0.5 mm
Overall mould plate flatness: ≤0.5 mm
3. Corner Radii and Draft Angles
Two design features that are frequently overlooked but critically important:
Corner Radii (3–5 mm):
All internal corners of the cavity should include a radius of 3–5 mm
Sharp 90-degree corners create stress concentration points where cracks initiate
The radius allows stress to flow around the curve rather than concentrating at a point
Draft Angle (1–3° per side):
A slight taper on vertical cavity walls is essential for clean demoulding
Without a draft angle, blocks will stick regardless of release agent quality
The exact angle depends on block height, surface finish, and concrete mix
4. Surface Finish Requirements
The cavity surface finish directly affects demoulding performance and block surface quality.
Standard specification: Ra 1.6 or better
Why it matters: A polished cavity surface reduces friction, allowing blocks to release cleanly. UNIK's cavity polishing technologies improve demoulding performance by up to 30% .
5. Cavity Count and Layout
Specify the number of cavities per mould and their arrangement.
Considerations:
Number of cavities impacts production rate and mould size
Layout affects material flow and filling balance
For multi-cavity moulds, specify cavity-to-cavity spacing
Additional Information That Improves Outcomes
Concrete Mix Details
Providing information about your concrete mix helps the manufacturer select the optimal steel grade:
Standard mixes (rounded aggregates): 42CrMo steel provides cost-effective performance
Abrasive mixes (sharp sand, recycled aggregates, high silica): Tool steel (Cr12MoV) extends cavity life
Expected production volume and daily output
Block Type and Application
Different block types require different mould features:
Hollow blocks: Core pin positions and diameters
Retaining wall blocks: Interlocking geometry, rear lip dimensions
Pavers: Surface texture requirements, edge profiles
Sample Block or Existing Mould
If available, providing a sample block or an existing mould helps the manufacturer verify dimensions and features.
Common Drawing Mistakes to Avoid
Mistake 1: Missing Mounting Specifications
A mould that doesn't fit your machine is scrap. Always include machine brand, model, and mounting hole details.
Mistake 2: No Corner Radii
Sharp corners cause cracking. Specify 3–5 mm radii on all internal corners.
Mistake 3: Insufficient Draft Angles
Blocks will stick without proper draft angles. Include 1–3° taper per side on vertical cavity walls.
Mistake 4: Unclear Tolerances
Without specified tolerances, manufacturers apply their standard tolerances-which may not match your requirements. Always state acceptable deviations.
The Drawing Approval Process at UNIK
UNIK follows a structured process to ensure every drawing is accurate before production begins :
Step 1 – Information Gathering: You provide machine brand and model, block size, number of cavities, and daily production target.
Step 2 – Drawing Preparation: Within 48 hours, UNIK sends a dimensional drawing for your approval. The drawing includes cavity dimensions, interlocking features, corner radii, mounting hole positions, and overall envelope sizes.
Step 3 – Drawing Approval: You review the drawing and confirm all dimensions match requirements. If changes are needed, UNIK revises the drawing and resubmits.
Step 4 – Production: After drawing approval, UNIK cuts steel and begins machining.
Conclusion
A well-prepared drawing is the foundation of a successful custom mould project. Include complete machine specifications, precise dimensions with tolerances, corner radii (3–5 mm), draft angles (1–3°), and surface finish requirements (Ra 1.6). The extra effort invested in drawing preparation saves time and cost by eliminating errors before production begins.
For guidance on preparing drawings for your specific application, contact UNIK's engineering team.
