Effective return sand conditioning

• capacity range 30 to 250 t/h
• integrated control system
• maximum cooling capacity
• optimum moistening and homogenization

The task: Return sand conditioning

Continually increasing demands on foundries in respect of quality, dimensional accuracy, surface finish and efficiency of casting production create the necessity for an effective cooling of hot return sand following the separation of sand and casting. The conditioning mainly comprises the screening, cooling, homogenization, moistening and optionally the predosage of additives.

The subsequent storage in a return sand hopper plant allows a relaxing of the return sand which is delivered to the moulding sand mixer at an almost uniform moisture and composition through a hopper management system.

The Solution

The continuous KW mixer-cooler type ASK excellently fulfils the requirements of modern high-capacity plants with regard to a homogenous, reliable and efficient cooling of the hot return sand and a uniform nominal moisture.

The blending and aeration of the return sand in the cooling chamber takes place with the help of two agitating tools. The agitating tools are actuated by a central drive motor via two high-performance reducing gears. A common intermediate shaft ensures synchronism of the agitating tools. The sand flow is controlled electronically. In this way the volume of sand inside the sand cooler is maintained at a constant level. The hot and moistened return sand is aerated by a blower with centrifugal fan thus ensuring an evaporative cooling of the return sand. The outgoing cooling air is conducted through a cyclone. Any fines extracted from the hot return sand are filte- red out from the exhaust air by the cyclone and can be returned to the return sand directly after the sand cooler.

An automatic control system regulates the addition of water in dependence on the sand temperature and ensures a uniform moisture content of the cooled return sand within narrow tolerances.

The working principle of the continuous mixer-cooler allows an automatic dosage of additives as powder or in form of a suspension during the cooling process. The homogenised return sand having a moisture content of approx. 2.5 % is stored in a hopper plant where the swelling of the thermally different bentonite and of the fresh bentonite takes place.

The optimum dimensioning of the return sand hoppers allows a sufficient relaxing of the return sand.

Safe and proven technique

Continuous KW mixercoolerstype ASK are particularly servicefriendly. Based on many years ofexperience a special material has been chosen for the agitating tools and the bottom liners of the cooling chamber inorder to minimise the maintenance costs.

An optimum dimensioning of the sandlayer, the moistening systems and the areaabove the sand layer ensure an in-time moistening of the return sand, a sufficient hold time inside the sand cooler and minimisethe extraction of fines. The continuous KW mixercoolers ASK ensure an approx. 5 °C loweroutlet temperature of the cooled sandcompared with similar units.

User-friendly process control and visualisation system

The basic version of the KW process control and visualisation system, designed on the basis of the latest control technology, provides already for all required functions:

• message and diagnostic system for process monitoring
• management of the moistening level and the dosage of additives
• control features for automatic and manual operation

Integrated control of the conditioning

Measuring and control equipment for the sand volume and the air flow.

Measuring and control equipment for the amount of water required for cooling and moistening as well as for the outlet moisture of the cooled moulding sand.

Data collection, data evaluation and control of the drive units by means of the central user-programmable control system of the sand preparation plant or, application-oriented and/or upon customer’s request, by means of a separate user-programmable control system.

Analyisis

Special features of the continuous KW mixer-coolers ASK are:

• an electronically controlled sand discharge gate provided with an electric actuating drive stabilising the sand flow and ensuring a uniform sand volume inside the sand cooler
• particularly service-friendly design and long-life agitating tools
• Optimum conditioning of the return sand by:
  an intensive blending of the contents of several poured moulds
  effective cooling of the return sand to a temperature appropriate for the mixing and moulding process
  a uniform moistening to keep a defined value with a tolerance of ±0.2 %
  optional equipment for the dosage of new sand and additives as powder or suspension (patent DE 195 45 917, CN 1 157 760)