Many mold systems require heat included in the manufacturing process. Inside the plastics industry, heaters will be the key ingredient to maintaining temperature in the molten plastic. The plastic flows from the mold base, sprue nozzle, manifold, into a die head, or using an injection barrel. Without heat, the mold or machine is useless.
The heater should be considered from the beginning, since it is an integral part of the overall system. There are several heater configurations available. However, when viewing the heater band from an insulation standpoint, there are actually three common heater types available in the industry: mica, ceramic knuckle and mineral insulated.
When it comes to heater type, you need to understand the performance capabilities and limitations of each and every heater type. The part geometry, temperature and also heat-up time requirements generally dictate the sort of heater to utilize.
All the three heater types has distinctive characteristics. The unique material that differentiates these heaters will be the interior insulation which offers the needed dielectric strength even though the heater heats the part. The insulation in each heater plays a tremendous role in determining heater life and satisfaction.
Mica is primarily obtained from Paleozoic rocks and are available in many areas worldwide, including India, southern Africa, and Russia, along with the American continents. Mica is commonly used in appliances, including toasters and microwaves, as well as band and strip heaters. Mica falls to the aluminum silicates category, which means chemically they contain silica (SiO4). The insulation materials used in mica heaters offers excellent physical characteristics including thermal, mechanical, electrical and chemical properties. The two main primary kinds of mica: (1) muscovite, that contains considerable amounts of potassium promoting strong mechanical properties and (2) phlogopite containing various amounts of magnesium, which enables it to stand up to higher temperatures than muscovite.
Mica includes a unique characteristic in that you can obtain very thin flakes having a consistent thickness. It conducts low quantities of heat, especially perpendicular to its strata. In addition, it is non-flammable, flame-retardant and does not emit fumes. From your heating perspective, mica is really a solid option due to its effectiveness against erosion and arcing, as well as its dielectric strength. Additionally, mica is immune to chemicals and water, and it has excellent compressive strength. Additionally, it holds up to bending stresses due to its high elasticity.
Even though some mica types can withstand temperatures greater than 1000°C (1830°F), the mica temperature ought not exceed 600°C (1112°F) when found in a heater assembly. When temperatures exceed that level, deterioration begins inside the binder as well as a weakening of the dielectric strength will occur.
These functions are important ever since the mica band heater is curved under perpendicular pressure to create a specific diameter. The normal mica band heater is around 3/16-inch thick and might accommodate many geometries and special features like holes and notches. Its design versatility lends itself well for many applications and markets.
The mica bands’ greatest disadvantage is definitely the maximum temperature ability of 480°C (900°F) sheath temperature. You will find progressively more processes which require higher temperatures than mica heaters can offer.
Steatite the type of ceramic comprised primarily of aluminum oxide (Al2O3), silica (SiO2) and magnesium oxide (MgO). Steatite is created when these materials are mixed in the correct proportion and fired with a certain temperature. L-3 and L-5 are the most typical grades of steatite. L-3 is used in the majority of applications. However, L-5 is suggested where low electrical loss is critical. The ceramic is created using industry specific processing methods and can readily be machined or net shape sintered into a variety of designs.
Ceramic knuckle band heaters are produced together with the L-5 sort of material for its superior electrical characteristics. Based on Jim Shaner of Saxonburg Ceramics Inc., “A specific L-5 formula is ready, that contains the appropriate proportions of Al2O3, SiO2, and MgO, together with binders, plasticizers, release agents, or other additives to help in the processing. The constituents are then mixed to get a specified time period and also the batch is shipped to the presses.” A press effective at pressures up to 30 tons is used to press the powder into its finished shape. The ultimate step is usually to fire the ceramic to a temperature of 2320ºF.
The ceramic knuckle heater is designed to handle up to 760ºC (1400ºF). This degree of performance is a direct reaction to the heaters’ excellent insulating properties in the ceramic knuckle segments. The knuckles work together just like a ball-and-socket inside the knee or elbow to generate the heater diameter. Unfortunately, the ceramic’s strength is additionally its weakness because it stores heat generated from the element wire, which creates difficulty in controlling the heater temperature. This may lead to unnecessary scrap, particularly in the initial phases of your plastic manufacturing process.
Mineral insulated heaters dominate the marketplace when it comes to overall heater performance. Mineral insulated heaters contain magnesium oxide known as MgO, which is the oxide of metal magnesium. Magnesium oxide or mineral insulation is a fine granular powder in bulk form. It can be layered involving the resistance element and the heater sheath. In numerous mineral insulated heaters, the MgO is compacted into a thin solid layer. The compacted MgO offers excellent thermal conductivity and great dielectric strength.
MgO comes with an upper useful temperature limit greater than 1094°C (2000°F). This is usually never reached, as the heater’s nichrome resistance wire carries a much lower operating temperature of about 870°C (1598°F). As a rule of thumb, the temperature of your mineral-insulated band ought not exceed 760°C (1400°F). The power 96dexnpky a thin layer of insulation to face up to current flow, yet allow quick heat transfer, creates a competent performance heater.
With a heater thickness of just 5/32-inch, a mineral insulated heater provides rapid heat-up and funky down when compared with mica and ceramic knuckle heaters. The compacted insulation also provides for higher watt densities which allow the thermocouple temperature sensor to warm the part faster, meaning a reduction in scrap upon machine startup. The mineral insulated band is tremendously responsive to precise heat control because of its thin construction and low mass. Less thermal lag and minimum temperature overshoot lead to faster startup and reduced cycle time. Other heaters that utilize mineral insulation are tubular, cable and cartridge heaters.