Blog: Cookie weight variation – the causes and the cures
The system maximises heat removal from the agitator shafts, screw elements and barrel to minimise the risk of pre-curing. This enables extrudate temperatures to be driven down below 100°C, allowing material with low curing temperatures to be produced.
It is standard on the new generation of Baker Perkins MPX 50, 65 and 80 machines.
The powerful cooling capacity of Baker Perkins’ twin-screw extruders is due to a new barrel, and through-shaft cooling.
The surface area of new multi-directional barrel cooling channels has been increased by 138%, and the channels are now closer to the barrel bores to increase heat transfer. Rates of cooling can be controlled and adjusted to suit each individual product profile.
Preventing the screws overheating is crucial, because if this happens the product can pre-cure on the screws. At best this reduces product quality and output; at worst it results in an expensive machine shutdown to clean them. In both cases, there is a costly loss of production through downtime and waste.
Increased heat removal from the shaft and screw elements raises product quality by removing hot spots, linked to temperature sensitive materials, from the mixing edges. Improved cleanliness is another bonus.
Baker Perkins’ design for through-shaft cooling feeds the cooling water from the rear of the gearbox. This feature is unique to Baker Perkins: extruders from other manufacturers feed cooling water either at the gearbox/shaft coupling or the extruder discharge. The coupling is a highly stressed area, which increases the likelihood of leaks, while feeding water into the discharge end risks water entering the product area: when that happens, the product is ruined and there is yet more loss of production.
These features provide a highly efficient cooling system that can cope with the wide range of heat levels created by handling resins with both low and high melt temperatures, and formulations requiring high intensity mixing.
The features have been developed specifically for the powder coating industry, and are not found on general-purpose industrial or plastics extruders. They are examples of the specialisation that make choosing Baker Perkins’ twin-screw extruders for powder coating an easy decision. They handle all types of powder coating formulations, including epoxy, hybrids, polyester, acrylics and fines recycling and provide continuous production at outputs from 100 to 2,900kg/hour.
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