Simple Solutions That Work! Issue 11

60 much better way to do this now. The old-style heaters would use up many elements per season due to the thermal shock of going from ‘red hot’ to ‘off’ hundreds of times a day, as well as wearing out the contactors that connected and disconnected power to each bank. Now, with affordable and precise SCR controls all elements can be installed in one bank, which results in only the needed volume of power being applied to the elements. As a result, the elements rarely exceed 250°F, which extends element life almost indefinitely, and also increases accuracy and repeatability for sand-discharge temperature. It is not uncommon for this style of heater to operate for years with zero maintenance costs. Inlet butterfly valve, with timer and bypass. All Palmer electric- resistance heaters are equipped with a summer bypass, which allows the sand simply to bypass the heating chamber under gravity. In the non-heating season the sand can flow directly from supply to the mixer. Normally this is a manual valve, however it also can be configured with a powered valve with proof of position. There is another butterfly valve above the summer bypass that opens when heated sand is called for, when the mixer is shut down. This butterfly valve closes immediately but the fluidizing air stays on in the heater for an adjustable period of time, and keeps the sand in a homogeneous condition so that there are no temperature spikes if the mixer is cycled off and on. mixer, batch mixer, transporter, or any other process. It is important to always consider temperature losses when installing either type mixer if the discharge isn’t going directly into the next process. Piping, interim hoppers, transport distance, etc., must all be taken into consideration when installing these heaters. The traditional mount method is with threaded rods in each corner or the upper end of the heater although this may differ from manufacturer. It is usually a simple matter to run some structural steel in the support steel of the silo to hold these threaded rods – while these heaters are not small, the support structure for these heaters is usually more than sufficient to handle this comparatively small additional weight. Since the fluidization of this design heater can sometimes be powerful, a bracket towards the bottom of the heater tying it to a beam close by will eliminate any lateral movement. In standard design, all sides of the heater plus the bottom need to be accessible so it is important any support structure keeps all sizes and the bottom of the heater open. When installing, it usually is a small amount of work to add in a catwalk to make servicing of these heaters simpler and safer – obviously these catwalks will need to meet all applicable requirements for safety of design: railings, ladder access, tie off points etc. The alternative is ladder work which should be avoided at all times If the elements are working hard to heat the sand to set-point they could be at a fairly high temperature. If the fluidization simply stops when the mixer is shut down, all of the residual heat in the elements goes directly to the surrounding sand, and the result will be that the temperature of the next sand coming out of the heater will be substantially higher than set-point for at least a few minutes, which can be highly detrimental to the molding process. High-temp safety system. All heaters should be equipped with a high-temperature safety system so that if there is a component failure, the system shuts off and an alarm alerts the operator. The Palmer design is normally set at 150°F, so that if there is a problem the power to the heater will be cut off. This is rare, but it’s necessary to ensure a safe and reliable operation. The water-pipe heater/coolers have a number of advantages over the electric-resistance type. While a water-pipe design is roughly two to three times higher in cost, the accuracy and lower power requirements easily can offset the higher price. When performing the suitability analysis for one design versus the other, all associated costs and operating efficiencies need to be included. INSTALLATION Installation of these 2 types of heaters is quite different mainly due to their respective size difference. The electric-resistance style can usually be simple mounted below the supply silo between the silo discharge and the piping to the mixer inlet or the next process be it a continuous