Epoxy granite, also known as synthetic granite, is a mixture of epoxy and granite commonly used as an alternative material for machine tool bases. Epoxy granite is used instead of cast iron and steel for better vibration damping, longer tool life, and lower assembly cost.
Machine tool base
Machine tools and other high-precision machines rely upon high stiffness, long-term stability, and excellent damping characteristics of the base material for their static and dynamic performance. The most widely used materials for these structures are cast iron, welded steel fabrications, and natural granite. Due to the lack of long-term stability and very poor damping properties, steel fabricated structures are seldom used where high precision is required. Good-quality cast iron that is stress-relieved and annealed will give the structure dimensional stability, and can be cast into complex shapes, but needs an expensive machining process to form precision surfaces after casting.
Good-quality natural granite is becoming more and more difficult to find, but has a higher damping capacity than cast iron. Again, as with cast iron, the machining of natural granite is labour-intensive and expensive.
Precision granite castings are produced by mixing granite aggregates (which are crushed, washed, and dried) with an epoxy resin system at ambient temperature (i.e., cold curing process). Quartz aggregate filler can also be used in the composition. Vibratory compaction during the molding process tightly packs the aggregate together.
Threaded inserts, steel plates, and coolant pipes can be cast-in during the casting process. To achieve an even higher degree of versatility, linear rails, ground slide-ways and motor mounts can be replicated or grouted-in, therefore eliminating the need for any post-cast machining. The surface finish of the casting is as good as the mould surface.
Advantages and disadvantages
Advantages include:
■ Vibration damping.
■ Flexibility: custom linear ways, hydraulic fluid tanks, threaded inserts, cutting fluid, and conduit piping can all be integrated into the polymer base.
■ Inclusion of inserts etc. allows greatly reduced machining of the finished casting.
■ Assembly time is reduced by incorporating multiple components into one casting.
■ Does not require a uniform wall thickness, allowing for greater design flexibility of your base.
■ Chemical resistance to most common solvents, acids, alkalis, and cutting fluids.
■ Does not require painting.
■Composite has a density approximately the same as aluminum (but pieces are thicker to achieve equivalent strength).
■ The composite polymer concrete casting process uses much less energy than metallic castings. Polymer cast resins use very little energy to produce, and the casting process is done at room temperature.
Epoxy granite material has an internal damping factor up to ten times better than cast iron, up to three times better than natural granite, and up to thirty times better than steel fabricated structure. It is unaffected by coolants, has excellent long-term stability, improved thermal stability, high torsional and dynamic stiffness, excellent noise absorption, and negligible internal stresses.
Disadvantages include low strength in thin sections (less than 1 in (25 mm)), low tensile strength, and low shock resistance.
An introduction to mineral casting frames
Mineral-casting is one of the most efficient, modern construction materials. Manufacturers of precision machines were among the pioneers in the use of mineral casting. Today, its use with regards to CNC milling machines, drill presses, grinders and electric discharge machines is on the rise, and the advantages are not limited to high speed machines.
Mineral casting, also referred to as epoxy granite material, composes of mineral fillers like gravel, quartz sand, glacial meal and binders. The material is mixed according to precise specifications and poured cold into the molds. A solid foundation is the basis for success!
State-of-the-art machine tools must run faster and faster, and provide more precision than ever. However, high travel speeds and heavy-duty machining produce unwanted vibrations of the machine frame. These vibrations will have negative effects on the part surface, and they shorten the tool life. Mineral-casting frames quickly reduce vibrations – about 6 times faster than cast-iron frames and 10 times faster than steel frames.
Machine tools with mineral casting beds, such as milling machines and grinder, are significantly more accurate and achieve a better surface quality. In addition, tool wear is significantly reduced and service life is extended.
composite mineral (epoxy granite) casting frame brings several advantages: :
- Shaping and strength: The mineral casting process provides an exceptional degree of freedom with respect to the shape of the components. The specific characteristics of the material and of the process result in a comparatively high strength and a significantly lower weight.
- Integration of infrastructure: The mineral casting process enables the simple integration of the structure and additional components such as guideways, threaded inserts and connections for services, during the actual casting process.
- The manufacturing of complex machine structures: What would be inconceivable with conventional processes becomes possible with mineral casting: Several component parts can be assembled to form complex structures by means of bonded joints.
- Economical dimensional accuracy: In many instances the mineral cast components are cast to the final dimensions because practically no contraction takes place during hardening. With this, further expensive finishing processes can be eliminated.
- Precision: Highly precise reference or supporting surfaces are achieved by further grinding, forming or milling operations. As a result of this, many machine concepts can be implemented elegantly and efficiently.
- Good thermal stability: Mineral casting reacts very slowly to temperature changes because the thermal conductivity is significantly lower than metallic materials. For this reason short-term temperature changes have significantly less influence on the dimensional accuracy of the machine tool. A better thermal stability of a machine bed means the overall geometry of the machine is better maintained and, as a result, geometrical errors are minimized.
- No corrosion: Mineral-cast components are resistant against oils, coolants and other aggressive liquids.
- Greater vibration damping for longer tool service lives: our mineral casting achieves up to 10x better values of vibration damping than steel or cast iron. Thanks to these characteristics, an extremely high dynamic stability of the machine structure is obtained. The benefits that this has for machine tool builders and users are clear: better quality of surface finish of the machined or ground components and longer tool life leading to lower tooling costs.
- Environment: The environmental impact during manufacture is reduced.
Mineral casting frame vs cast iron frame
See below the benefits of our new mineral casting vs cast iron frame previously used:
| Mineral Casting (Epoxy Granite) | Cast Iron | |
| Damping | High | Low |
| Heat Performance | Low heat conductivity
and high spec. heat capacity |
High heat conductivity and
low spec. heat capacity |
| Embedded Parts | Unlimited design and
One-piece mold and seamless connection |
Machining necessary |
| Corrosion Resistance | Extra high | Low |
| Environmental
Friendliness |
Low energy consumption | High energy consumption |
Conclusion
Mineral casting is ideal for our CNC machine frame structures. It offers clear technological, economic and environmental advantages. Mineral casting technology provides excellent vibration damping, high chemical resistance and significant thermal advantages (thermal expansion similar to that of steel). Connection elements, cables, sensor and measurement systems can all be poured into the assembly.
What are the benefits of the mineral casting granite bed machining center?
Mineral castings (man-made granite aka resin concrete) have been widely accepted in the machine tool industry for over 30 years as a structural material.
According to statistics, in Europe, one out of every 10 machine tools uses mineral castings as the bed. However, the use of inappropriate experience, incomplete or incorrect information can lead to suspicion and prejudice against Mineral Castings. Therefore, when making new equipment, it is necessary to analyze the advantages and disadvantages of mineral castings and compare them with other materials.
The base of construction machinery is generally divided into cast iron, mineral casting (polymer and/or reactive resin concrete), steel/welded structure (grouting/non-grouting) and natural stone (such as granite). Each material has its own characteristics, and there is no perfect structural material. Only by examining the advantages and disadvantages of the material according to the specific structural requirements, can the ideal structural material be selected.
The two important functions of structural materials—guarantee the geometry, position and energy absorption of components, respectively put forward performance requirements (static, dynamic and thermal performance), functional/structural requirements (accuracy, weight, wall thickness, ease of guide rails) for materials installation, media circulation system, logistics) and cost requirements (price, quantity, availability, system characteristics).
I. Performance requirements for structural materials
1. Static characteristics
The criterion for measuring the static properties of a base is usually the stiffness of the material—minimum deformation under load, rather than high strength. For static elastic deformation, mineral castings can be thought of as isotropic homogeneous materials obeying Hooke's law.
The density and elastic modulus of mineral castings are respectively 1/3 of those of cast iron. Since mineral castings and cast irons have the same specific stiffness, under the same weight, the rigidity of iron castings and mineral castings is the same without considering the influence of shape. In many cases, the design wall thickness of mineral castings is usually 3 times that of iron castings, and this design will not cause any problems in terms of mechanical properties of the product or casting. Mineral castings are suitable for working in static environments that carry pressure (eg beds, supports, columns) and are not suitable as thin-walled and/or small frames (eg tables, pallets, tool changers, carriages, spindle supports). The weight of structural parts is usually limited by the equipment of mineral casting manufacturers, and mineral casting products above 15 tons are generally rare.
2. Dynamic characteristics
The greater the rotational speed and/or acceleration of the shaft, the more important the dynamic performance of the machine is. Rapid positioning, rapid tool replacement, and high-speed feed continuously strengthen mechanical resonance and dynamic excitation of machine structural parts. In addition to the dimensional design of the component, the deflection, mass distribution, and dynamic stiffness of the component are greatly affected by the damping properties of the material.
The use of mineral castings offers a good solution to these problems. Because it absorbs vibrations 10 times better than traditional cast iron, it can greatly reduce the amplitude and natural frequency.
In machining operations such as machining, it can bring higher precision, better surface quality, and longer tool life. At the same time, in terms of noise impact, the mineral castings also performed well through the comparison and verification of the bases, transmission castings and accessories of different materials for large engines and centrifuges. According to the impact sound analysis, the mineral casting can achieve a local reduction of 20% in the sound pressure level.
3. Thermal properties
Experts estimate that about 80% of machine tool deviations are caused by thermal effects. Process interruptions such as internal or external heat sources, preheating, changing workpieces, etc. are all causes of thermal deformation. In order to be able to select the best material, it is necessary to clarify the material requirements. The high specific heat and low thermal conductivity allow mineral castings to have good thermal inertia to transient temperature influences (such as changing workpieces) and ambient temperature fluctuations. If rapid preheating is required like a metal bed or the bed temperature is prohibited, heating or cooling devices can be directly cast into the mineral casting to control the temperature. Using this kind of temperature compensation device can reduce the deformation caused by the influence of temperature, which helps to improve the accuracy at a reasonable cost.
II. Functional and structural requirements
Integrity is a distinguishing feature that distinguishes mineral castings from other materials. The maximum casting temperature for mineral castings is 45°C, and together with high-precision molds and tooling, parts and mineral castings can be cast together.
Advanced re-casting techniques can also be used on mineral casting blanks, resulting in precise mounting and rail surfaces that do not require machining. Like other base materials, mineral castings are subject to specific structural design rules. Wall thickness, load-bearing accessories, rib inserts, loading and unloading methods are all different from other materials to a certain extent, and need to be considered in advance during design.
III. Cost requirements
While it is important to consider from a technical point of view, cost-effectiveness is increasingly showing its importance. Using mineral castings allows engineers to save significant production and operating costs. In addition to saving on machining costs, casting, final assembly, and increasing logistics costs (warehousing and transport) are all reduced accordingly. Considering the high-level function of mineral castings, it should be viewed as a whole project. In fact, it is more reasonable to make a price comparison when the base is installed or pre-installed. The relatively high initial cost is the cost of mineral casting molds and tooling, but this cost can be diluted in long-term use (500-1000 pieces/steel mold), and the annual consumption is about 10-15 pieces.
IV. Scope of use
As a structural material, mineral castings are constantly replacing traditional structural materials, and the key to its rapid development lies in mineral casting, molds, and stable bonding structures. At present, mineral castings have been widely used in many machine tool fields such as grinding machines and high-speed machining. Grinding machine manufacturers have been pioneers in the machine tool sector using mineral castings for machine beds. For example, world-renowned companies such as ABA z&b, Bahmler, Jung, Mikrosa, Schaudt, Stude, etc. have always benefited from the damping, thermal inertia and integrity of mineral castings to obtain high precision and excellent surface quality in the grinding process.
With ever-increasing dynamic loads, mineral castings are also increasingly favored by world-leading companies in the field of tool grinders. The mineral casting bed has excellent rigidity and can well eliminate the force caused by the acceleration of the linear motor. At the same time, the organic combination of good vibration absorption performance and linear motor can greatly improve the surface quality of the workpiece and the service life of the grinding wheel.
As for the single part. Within 10000mm of length is easy for us.
What is the minimum wall thickness?
In general, the minimum section thickness of the machine base should be at least 60mm. Thinner sections (eg 10mm thick) can be cast with fine aggregate sizes and formulations.
The shrinkage rate after pouring is about 0.1-0.3mm per 1000mm. When more precise mineral casting mechanical parts are required, tolerances can be achieved by secondary cnc grinding, hand lapping, or other machining processes.
Our Mineral casting material is choosing nature Jinan Black granite. Most of companies just choose normal nature granite or normal stone in building construction.
· Raw materials: with the unique Jinan Black Granite (also called ‘JinanQing’ granite) particles as aggregate, which is world famous for high strength, high rigidity and high wear resistance;
· Formula: with the unique reinforced epoxy resins and additives, different components using different formulations to ensure optimal comprehensive performance;
· Mechanical properties: the vibration absorption is about 10 times that of cast iron, good static and dynamic properties;
· Physical properties: density is about 1/3 of the cast iron, higher thermal barrier properties than metals, not hygroscopic, good thermal stability;
· Chemical properties: higher corrosion resistance than metals, environmental friendly;
· Dimensional accuracy: linear contraction after casting is about 0.1-0.3㎜/m, extremely high form and counter accuracy in all planes;
· Structural integrity: very complex structure can be cast, while using natural granite usually requires assembling, splicing and bonding;
· Slow thermal reaction: reacts to short term temperature changes is much slower and much less;
· Embedded inserts: fasteners, pipes, cables and chambers can be embedded into the structure, inserts materials including metal, stone, ceramic and plastic etc.