SPS Inc. of Tilsonburg, Ontario, has developed a new flow mold system designed to produce large dimension plastic timber wood plastic composite material products at high throughput. The new design reduces shrinkage and voiding and can produce parts with reproducible dimensions.
The system employs a unique mold design that maintains pressure in the cavity during cooling to eliminate large voids, and surface shrinkage. High productivity is achieved by use of a unique filling station that that employs a diverter valve system to fill and switch molds without interrupting the melt flow from the extruder. The reputation,quality,service valve design eliminates extruder back-pressure swings during the mold fill and switch cycle. The molds are transferred to a cooling bath by an automated carriage system that moves them sequentially through the cooling process. The system utilizes multiple molds to achieve very high throughputs. An automated line to produce railway ties is run by a single operator.
SPS also offers processing equipment to convert baled film plastic to densified feedstock. The large cross-section timber produced can tolerate higher levels of contamination in the finished product and this reduces the level of cleaning required, which (in turn) reduces the capital needed to process the recycled polymers. The process can produce parts with simple blends of mixed plastic with up to 50 ercent “non-melts”, or can be used to wood plastic composite boards produce complex composites with more emanding structural requirements, such as railway ties.
An automated line to produce railway ties can mold up to one tie per minute. Throughputs of 5,000 pounds per hour are attainable when producing large timber cross-sections. It is worth noting that thick cross-sections of molten polymer take very long times to cool and crystallize. Cooling cycles could be well over one hour for a 12”x 12” cross-section. A continuous extrusion process would require a water spray cooling line measured in kilometers to achieve the cooling necessary for dimensional stability. Once a plastic profile increases beyond two inches in thickness, this new flow mold system is most likely the process of choice.
Tie Tek (Houston, Texas) and U.S. wood plastic composite lumber (Ocala, Florida) have qualified railway ties made on the SPS system through extensive testing at the Railway Test Center in Pueblo, Colorado. Plastic ties meet all the requirements for wood ties, but do not require the use of toxic preservatives and are expected to have at least double the lifespan. It is estimated that 18 million railway ties are replaced each year in North America. SPS Inc. is also the equipment supplier to Nova Plastics Products Inc. in Newfoundland, which produces large timbers for marine applications.
没有评论:
发表评论