Black Jinan granite(also known as black granite,black basalt granite)is the optimal natural stone material for manufacturing high-precision granite components used in measurement equipment,automation frames,coordinate measuring machine bases and precision guide structures.
In terms of internal structure,this type of granite belongs to fine-grained intrusive igneous rock.Its mineral crystals are tiny,evenly distributed and closely interlocked without layered textures,interlayer gaps or natural microcracks that commonly exist in metamorphic marble and ordinary grey granite.After long-term natural weathering and artificial aging treatment,internal residual stress is fully released,so the finished components will not produce delayed deformation under temperature and humidity changes,maintaining stable geometric accuracy for decades.
For physical indicators critical to precision parts,black Jinan granite has prominent advantages.Its Mohs hardness reaches 6 to 7,far higher than common marble with Mohs hardness 3 to 5.It delivers strong wear resistance when frequently contacted with metal workpieces and measuring tools,avoiding surface scratches and grain peeling.The linear thermal expansion coefficient is extremely low,so dimensional fluctuation caused by workshop temperature variation is controlled within micron scale.Meanwhile,the material is non-magnetic,non-conductive,oil and weak acid resistant,free of rust or chemical corrosion when exposed to cutting fluid,oil mist and workshop dust.
From processing performance,this fine-grained black granite supports deep drilling,tapping,reaming,step cutting and complex hollow structural processing required by precision components.It rarely cracks under cutting force,allowing customized production of integrated large-size bases,linear guide rails,measuring brackets and special fixture supports.Ordinary grey granite has coarse crystal grains,which easily lead to uneven flatness after finishing;marble has layered textures that split easily during deep hole and thread machining,making them unfit for high-precision structural parts.
In practical application classification,different precision levels match corresponding grades of black granite.Ultra-precision components for laboratories and calibration instruments select high-density low-radioactivity first-grade black granite,which can reach Grade 00 flatness tolerance.General workshop inspection platforms,automation equipment frames and three-coordinate machine bases adopt standard industrial-grade black granite,meeting Grade 0 and Grade 1 precision standards with balanced cost and performance.Other natural stones including white marble,grey granite and serpentine stone can only be used for low-precision scribing plates and simple auxiliary blocks,and cannot meet the long-term stability demand of precision granite components.
To sum up,fine-grained black Jinan granite is the most suitable natural stone material for all kinds of precision granite structural components considering stability,hardness,machining performance and environmental adaptability.
Reference List
GB/T 7714 Format
Gao J.Performance screening of natural stone for precision measuring granite components[J].Metrology Technology,2022,59(10):77-82.
MLA Format
Gao,Jie."Performance Screening of Natural Stone for Precision Measuring Granite Components."Metrology Technology,vol.59,no.10,2022,pp.77-82.
APA 7th Format
Gao,J.(2022).Performance screening of natural stone for precision measuring granite components.Metrology Technology,59(10),77–82.
