Polyvinyl alcohol solutions
Polyvinyl alcohol (PVOH, also referred to as PVA) is a versatile polymer that plays multiple roles in the manufacture of adhesives, sealants, cosmetics, paper, textiles and many other products.
Multi-Shaft Mixers are widely used in the preparation of PVOH solutions. Equipped with two or more independently-driven agitators working in tandem, Multi-Shaft Mixers deliver a robust combination of high shear agitation and laminar bulk flow within a wide viscosity range: from water-like consistency to several hundred thousand centipoise (cP).
The most economical design is the Dual-Shaft Mixer which features an anchor agitator and a high speed disperser. Turning at tip speeds around 5,000 ft/min, the saw-tooth disperser blade creates a vigorous vortex that quickly wets out dry PVOH powders or pellets as they are added into warm or room-temperature water (a defoamer may be pre-blended into the water). The sweeping action of the low-speed anchor agitator enhances the exchange of materials within the vessel, continuously “feeding” the disperser blade with fresh product.
For added versatility and shear capability, a rotor/stator assembly may be supplied in addition to the disperser blade and anchor agitator. This Triple-Shaft Mixer design is particularly ideal for applications where other raw materials are dispersed into the PVOH solution and a very tight particle size distribution is required in the finished product.
Plastisols
Formulated for a wide variety of coating, molding and screen printing applications, plastisols are dispersions of polyvinyl chloride (PVC) resin in a liquid plasticizer. Fillers, additives and colorants are also typical components of plastisols.
Multi-Shaft Mixers are well-proven equipment in the manufacture of plastisols. But formulations that undergo very high viscosity peaks (above 1 million cP) are better prepared in Planetary Dispersers and Double Planetary Mixers. These machines consist of two or more blades which rotate on their respective axes as they revolve around the mix vessel. Unlike the agitators in a Multi-Shaft Mixer which rotate from a fixed axis, the blades in a planetary-style mixer continually advance into the batch and are thus able to continuously contact fresh product.
Polymers and additives
Polymer additives such as lubricants, UV and heat stabilizers, colorants, preservatives, flame retardants and impact modifiers are commonly supplied as dry powders or pellets which are blended with virgin plastic feedstock prior to compounding. Thorough and accurate mixing is necessary to achieve a consistent finished product.
Innovations in concrete paving with new technology
The start of 2016 has seen major developments in the concrete paving sector - Mike Woof writes So far in 2016 there have been several major developments in the concrete paving equipment market. Many of the key players have introduced new models, broadening their ranges of machines on offer. US firms continue to dominate this niche area of the construction equipment market, with one European company being the only other major international player. At least two Chinese manufacturers have unveiled concrete
So far in 2016 there have been several major developments in the concrete paving equipment market. Many of the key players have introduced new models, broadening their ranges of machines on offer.
US firms continue to dominate this niche area of the construction equipment market, with one European company being the only other major international player.
At least two Chinese manufacturers have unveiled concrete pavers in the last few years. But these have not been proven on the international market and the designs may not suit global requirements, as well as having fewer capabilities and options than western models. The proven players from the US and Europe have all embraced 3D machine control technology for their machines, allowing these units to deliver high efficiency onsite but it is not clear if the Chinese machines are able to use these systems. For some time to come, the US and European firms will continue to lead this market.
GOMACO has a particularly strong presence in the concrete paving market and is looking to retain that position with the unveiling of two new slipformers, the GP3 and the latest version of its GT-3300.
The firm claims that the GP3 features a wide array of high performance capabilities, making it the most intelligent paver on the market. This paver can handle large road and runway jobs and offers a maximum paving width of 9.14m, achieved through the development of a novel dual-telescoping system. The firm has designed the frame widening system so that it is capable of multiple width changes, boosting its adaptability for a wide range of operations.
