Molded composites made primarily from crushed stone have substantial potential to replace plastic according to a Chinese invention that was awarded a US Patent last year.
In the patent, Haitian Plastics Machinery Group (Zhejiang Province, China) says: “The product is capable of substituting the majority of thermoset plastics and thermoplastics, thus reducing the usage amount of plastic products and providing powerful support and safeguard for creating resource-conservation and environment-friendly industry.”
Materials in the composite are stone, unsaturated polyester, fiber glass and various additives. The polyester is a thermoset plastic that acts like glue holding the other materials together.
This is a description of the Haitian process: Stones are placed into a charging device and then pushed into a preforming machine barrel. Temperatures rise from ambient to 151ºF (shear heat) as the composite mixture is compacted with a screw, and moved to a block where it is injected into a mold at a force of 10-80 Mpa. The mold cavity is heated as high as the boiling point of water. Curing time is 40 to 300 seconds, depending on size of the part.
Haitian is the world’s largest manufacturer of injection molding machines, having shipped 30,000 machines to 130 countries in 2010. Data for 2011 is not yet available. The company broke into the injection molding machinery business with low cost machines for the Chinese market, but has been placing emphasis on developing new technology. One example is a high-level injection molding machine developed with a German partner for the medical market. Its North American debut will be at NPE2012 in Orlando, FL April 1-5.
Haitian became interested in the invention because there is a significant amount of stone available in China as a byproduct of other businesses. A process that had been developed to process the stones into finished shapes worked poorly and has fallen into disfavor.
The idea of using stone to replace large amounts of oil in molded parts is attractive in China because of the dearth of fossil fuels, the abundance of stone, and the explosion in demand for manufactured goods.
As might be imagined, the machinery to process the stone is interesting and is significantly different from injection molding machinery used to process plastics. It consists primarily of a preforming device, a sealing device and an injection device.
The $64,000 question, of course, is what kinds of products can you make with a stone composite, and how good are they?
The patent makes these statements:
“The products produced by the method for producing products provided by the invention are high and stable in quality. The method is capable of being used to produce products requiring high quality and ones with complicated structure and special surface treatment. Such products can completely substitute such existing precision components such as automobile component, electrical component or parts and the like.”
The patent also states that the molded stone composites have high mechanical strength, good fire resistance, thermal stability, corrosion resistance, electrical property, low cost and very wide application range.
Specific potential applications are car light reflectors, heater cases, automobile igniters, and even hoods! The stone composites might be strong and inexpensive, but they would not help solve weight problems in cars. The ability to mold high-quality hoods from stone composites is arguable. Even very high-quality thermoplastic/glass composites shown in concept cars such as the original Chevy Volt did not make the production cut.
Potential electrical components cited in the patent include high-voltage devices, relay bases, coil framework, knife switch tables, and fuse boxes.
Other products mentioned as sanitary products urinals and bathtubs. Composite stone is already used to make bathtubs, but we’re talking about quite a machine to mold a bathtub.
Haitian is very hopeful: “The main components of the products are stone, the density and strength of which are higher than those of plastics, thus the products have better performance than plastics and the products can be applied to more fields.”