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How to keep temperature sensors for aluminum casting in optimal condition?
Temperature is one of the primary variables in an aluminum casting process. It is necessary to monitor and maintain control of the temperature of the molten aluminum, since some physical properties that we seek for the final piece, such as tensile strength, can be affected in the case of having sensors with faulty maintenance.
It's advisable to measure the temperature in the melt itself, using thermocouples protected with special sheaths (pyrometric tubes for aluminum smelting). This will make the measurement more precise and tailored to the process we want to perform.
The lower scrap volume, resulting from a proper process thanks to thorough temperature control, leads to a reduction in operating costs.
MAINTENANCE
In aluminum foundry, correct maintenance of the pyrometric tubes during the processes is a decisive advantage to achieve high-quality production in terms of castings. Too hot molten aluminum can damage the molds, excessively low temperature will hinder production and reduce fluidity, especially in the most demanding parts of the foundry when it comes to detailing the casting characteristics and the precision of the control.
A melt that does not reach the ideal heat will show insufficient metal flow into the passages of the mold and may cause bubbles or holes. The temperature also has consequences on the physical capabilities of the product to be achieved.
Difficulties are likely to arise during post-welding or machining. Even worse is the realization that defects cannot be identified until the final products are used and integrated with other parts. Poor temperatures will produce brittle castings, prone to wear and material fatigue.
CALIBRATION
It's a good idea to periodically calibrate temperature sensors and controllers to ensure proper measurement of all equipment. Remember that coolants can cause corrosion and impair sensor response, so take the time to properly secure the sensor bracket and place it in the correct location.
Isolating it from impurities is also important, since they could clog the ducts, and hinder the sensors when making the relevant readings. For this, jacketed thermocouples are used that isolate the sensor from these drawbacks.
REPLACEMENT
Replace the sensor if it verifies that the specified checks are not within the limit values marked for its manufacture.
It is very important to have a good support for the pyrometric rods in both melting and maintenance furnaces, since if they are not properly fastened they can have sudden movements and receive blows (with ingots, against the crucible wall, etc.)
Our cases at room temperature can resist shock well but when immersed in aluminum at 700ºC they are all fragile. Before immersing them in aluminum at 700ºC, it is recommended to preheat them to avoid breakage due to thermal shock.
INSTRUCTIONS FOR USE OF SRC COVERS
Our covers are made of materials for non-ferrous casting and have excellent characteristics such as high resistance to impacts, corrosion and thermal shock. These features give these sleeves a long life in temperature measurement of molten aluminum, zinc and copper alloys.
The covers have an optional support with or without tilting system (anti-shock protection).
SRC can supply all its models of covers mounted on pyrometric reeds tailored to the customer.
Once you receive our cover, proceed to inspect it. In case of breakage, contact your nearest distributor.
INTERIOR INSTALLATION
If the protective sheath is attached to a thermocouple, a space must be left between the bottom of the sheath and the thermocouple tip. There is a significant difference in the coefficient of thermal expansion between the thermocouple (NiCr-Ni: 13×10-6) and the SRC sheath (3×10-6).
The bottom of this will break when the above mentioned space is insufficient.
Enough Space = Temperature x Length x (10×10-6) x Safety Coefficient
Example using working temperature 700ºC Length 1000 mm.
Enough Space = 700 x 1000 x 10 x 10-6 x 1.3 = 9.1 mm.
INSERTION INTO THE BROTH
Before immersing the sheath in a bath of molten metal, it must be preheated for 5 minutes on the surface of the furnace or molten metal. Subsequently submerge the sheath into the molten metal slowly (up to 5 cm for 10-20 seconds).
REMOVING FROM THE OVEN
After taking the sleeve out of the molten metal bath, hang it in a special, marked place in your factory. It should never drip, be placed on the ground directly or put in contact with a cold wall (metallic or non-metallic). They must remove any excess metal or dirt each time they remove the cover from the bathroom, since the accumulation of metal can crack it.
The covers have excellent properties but misuse considerably shortens their life.
CLEANING THE COVER
To remove excess metal and dirt from the sleeves, scrape them longitudinally with a steel spatula while the sleeve is still hot. Never hit the sleeve.
surface or metals stuck to the sleeve with a hammer as this may damage or break the sleeve.
Never leave the casing inserted in the aluminum when it solidifies or when loading with ingots, scrap or stock as the casing can be damaged. The mechanical stress produced by these actions at high temperatures can cause breaks or cracks that considerably shorten the life of this product.
CAUTION !
DRY THE COVER BEFORE USE
Do not insert the wet sheath into molten metal, molten metal could splash and this is very dangerous as you could get burned or start a fire.
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