Many mold systems require heat within the manufacturing process. Within the plastics industry, heaters will be the key ingredient to maintaining temperature in the molten plastic. The plastic flows through the mold base, sprue nozzle, manifold, in a die head, or through an injection barrel. Without heat, the mold or machine is useless.
The heater should be thought about in the first place, since it is an integral part of the general system. There are numerous heater configurations available. However, when examining the heater bands from an insulation standpoint, there are actually three common heater types available in the marketplace: mica, ceramic knuckle and mineral insulated.
When contemplating heater type, you need to understand the performance capabilities and limitations of each heater type. The part geometry, temperature and also heat-up time requirements generally dictate the particular heater to make use of.
All the three heater types has distinctive characteristics. The unique material that differentiates these heaters will be the interior insulation that provides the appropriate dielectric strength while the heater heats the part. The insulation in each heater plays a significant role in determining heater life and gratifaction.
Mica is primarily taken from Paleozoic rocks and can be obtained from many areas around the world, including India, southern Africa, and Russia, along with the American continents. Mica is utilized in appliances, like toasters and microwaves, in addition to band and strip heaters. Mica falls into the aluminum silicates category, meaning that chemically they contain silica (SiO4). The insulation materials used in mica heaters offers excellent physical characteristics such as thermal, mechanical, electrical and chemical properties. There are two primary types of mica: (1) muscovite, that contains a lot of potassium promoting strong mechanical properties and (2) phlogopite containing various quantities of magnesium, which enables it to withstand higher temperatures than muscovite.
Mica carries a unique characteristic in that you can obtain very thin flakes having a consistent thickness. It conducts low levels of heat, especially perpendicular to the strata. Furthermore, it really is non-flammable, flame-retardant and will not emit fumes. From your heating perspective, mica is a solid option because of its resistance to erosion and arcing, and its particular dielectric strength. Additionally, mica is resistant against chemicals and water, and possesses excellent compressive strength. Furthermore, it holds up to bending stresses due to its high elasticity.
Although some mica types can withstand temperatures greater than 1000°C (1830°F), the mica temperature ought not exceed 600°C (1112°F) when utilized in a heater assembly. When temperatures exceed that level, deterioration begins in the binder and a weakening in the dielectric strength will occur.
These characteristics are important since the mica band heater is curved under perpendicular pressure to create a specific diameter. The typical mica band heater is approximately 3/16-inch thick and can accommodate many geometries and special features for example holes and notches. Its design versatility lends itself well for most applications and markets.
The mica bands’ greatest disadvantage may be the maximum temperature ability of 480°C (900°F) sheath temperature. You will find an increasing number of processes that require higher temperatures than mica heaters can offer.
Steatite is a kind of ceramic comprised primarily of aluminum oxide (Al2O3), silica (SiO2) and magnesium oxide (MgO). Steatite is actually created when these materials are mixed within the correct proportion and fired at a certain temperature. L-3 and L-5 are the most frequent grades of steatite. L-3 is used in most applications. However, L-5 is required where low electrical loss is crucial. The ceramic is actually created using industry specific processing methods and will readily be machined or net shape sintered into a variety of designs.
Ceramic knuckle band heaters are manufactured together with the L-5 kind of material because of its superior electrical characteristics. According to Jim Shaner of Saxonburg Ceramics Inc., “A specific L-5 formula is ready, that contains the proper proportions of Al2O3, SiO2, and MgO, in addition to binders, plasticizers, release agents, and other additives to assist in the processing. The components are then mixed for any specified time period and the batch is shipped to the presses.” A press competent at pressures up to 30 tons is commonly used to press the powder into its finished shape. The very last step is always to fire the ceramic to some temperature of 2320ºF.
The ceramic knuckle heater is designed to handle as much as 760ºC (1400ºF). This degree of performance is a direct result of the heaters’ excellent insulating properties of your ceramic knuckle segments. The knuckles interact comparable to a ball-and-socket from the knee or elbow to produce the heater diameter. Unfortunately, the ceramic’s strength can also be its weakness as it stores heat generated with the element wire, which creates difficulty in managing the heater temperature. This might lead to unnecessary scrap, especially in the early stages of the plastic manufacturing process.
Mineral insulated heaters dominate the marketplace when it comes to overall heater performance. Mineral insulated heaters contain magnesium oxide generally known as MgO, which is the oxide of metal magnesium. Magnesium oxide or mineral insulation can be a fine granular powder in big amounts form. It can be layered between the resistance element and also the heater sheath. In several mineral insulated heaters, the MgO is compacted in a thin solid layer. The compacted MgO offers excellent thermal conductivity and great dielectric strength.
MgO has a upper useful temperature limit greater than 1094°C (2000°F). This is usually never reached, since the heater’s nichrome resistance wire has a lower operating temperature of about 870°C (1598°F). Generally speaking of thumb, the temperature of the mineral-insulated band ought not exceed 760°C (1400°F). The ability 96dexnpky a thin layer of insulation to face up to current flow, yet allow quick heat transfer, creates an efficient performance heater.
With a heater thickness of only 5/32-inch, a mineral insulated heater provides rapid heat-up and funky down in comparison to mica and ceramic knuckle heaters. The compacted insulation also enables higher watt densities that enable the thermocouple to heat up the part faster, which means a decrease in scrap upon machine startup. The mineral insulated band is tremendously responsive to precise heat control due to the thin construction and low mass. Less thermal lag and minimum temperature overshoot cause faster startup and reduced cycle time. Other heaters that utilize mineral insulation are tubular, cable and cartridge heaters.