China Hollow Concrete Block Moulds
2.Hardness for shoes:HRC59-62
3.Carburized layer thickness:1.3-1.5mm
4.Unilateral clearance between presser foot and mold cavity: 0.2 mm ≤ Unilateral clearance ≤ 0.4mm
5.Flatness of the whole board: ≤ 0.5mm
6.Deviation in length and width dimensions of a single cavity model: -0.3 to+0.3mm
7.The dimensional deviation of the height (filling depth) of the lower model cavity is ± 0.5mm
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Product Details ofChina Hollow Concrete Block Moulds
China Hollow Concrete Block Moulds
The Core Pins Make the Difference
A hollow concrete block is defined by its holes. Those holes reduce weight, improve insulation, and lower material costs. But the holes also create the single most vulnerable point in the moulding process: the core pins.
Chinese manufacturers have made significant advances in core pin technology over the past decade. Understanding these advances helps buyers distinguish between moulds that will last 80,000 cycles and those that will fail at 30,000.
UNIK has been manufacturing hollow concrete block moulds in Quanzhou, Fujian since 2010, exporting to 28 countries. This page focuses on the core pin-the component that separates a reliable hollow block mould from a problematic one.
Why Core Pins Determine Hollow Block Mould Quality
Core pins are the steel rods that form the holes in hollow blocks. They extend into the mould cavity from the top or side, displacing concrete to create voids. Each cycle, concrete flows around these pins, compacts against them, and then releases as the block is ejected.
This repeated action subjects core pins to three types of stress:
Abrasion – Concrete aggregates slide against the pin surface during every fill and ejection cycle.
Bending – Off-center fill or uneven compression can push pins out of alignment.
Fatigue – Vibration cycles eventually cause microscopic cracks that grow over time.
A mould can have perfect cavity walls and still fail early if the core pins are substandard. Conversely, a mould with high-quality pins can continue producing accurate blocks long after the cavity surfaces have begun to wear.
Core Pin Specifications That Matter
When evaluating hollow concrete block moulds from Chinese suppliers, request the following core pin specifications:
Steel grade – Core pins require higher hardness than cavity walls because they experience concentrated abrasion. Acceptable grades include Cr12MoV, 9CrSi, or high-speed steel equivalents. Pins made from standard structural steel will wear rapidly.
Surface hardness – Core pins should achieve HRC58-62 after heat treatment. Some suppliers apply surface hardening only; pins that are not hardened through risk cracking under repeated bending stress.
Surface finish – Pin surfaces should be polished to Ra 0.8 or better. Rough pins cause concrete to stick, creating drag during ejection that can pull pins out of alignment.
Taper – Core pins typically have a 1-2 degree taper to aid ejection. Straight pins without taper increase friction and wear.
Base mounting – Pins must be securely mounted to the pin plate. Loose pins shift position over time, producing blocks with uneven wall thickness.
Common Core Pin Problems and Solutions
| Problem | Cause | Solution |
|---|---|---|
| Pins bend or break | Off-center concrete fill; excessive compression pressure | Adjust fill distribution; reduce compression; use hardened pins |
| Uneven wall thickness | Pins shifted in loose mounts | Replace pin plate; use pinned or bolted mounting instead of press-fit |
| Concrete sticks to pins | Rough pin surface; insufficient taper | Polish pins to Ra 0.8; increase taper to 1-2 degrees |
| Pin surface pitting | Corrosion from concrete moisture | Use stainless steel pins or apply anti-corrosion coating |
| Early pin wear | Soft steel; inadequate heat treatment | Specify Cr12MoV with HRC60+ hardness |
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A hollow block mould's service life is typically limited by core pin wear, not cavity wear. When pins wear beyond tolerance, the entire mould becomes unusable even if the cavity is still good. This makes pin quality disproportionately important to total cost.
A mould with soft pins (HRC50-55) might produce 30,000-40,000 blocks before pins wear out. A mould with properly hardened pins (HRC58-62) produces 80,000-100,000 blocks. The price difference between the two moulds is typically 15-25%. The production difference is 100-150% more blocks per mould.
For buyers, this calculation is straightforward: pay slightly more for proper pin hardening, or replace the entire mould twice as often.
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