Heating Element For Hot Runner Mold System Tubular Heaters

Heating Element For Hot Runner Mold System Tubular Heaters

Over the​ years, tubular heating systems for​ hot runner systems have changed as​ much as​ hot runners themselves have. the​ word “hot runner” itself explains the​ process and​ keeping the​ runner hot is​ a​ simple idea.Consider the​ hot runner as​ a​ body - the​ heating elements are the​ heart, the​ controller is​ the​ brain, and​ the​ thermocouples are the​ nerves that connect the​ entire system together. And, like a​ body, if​ one of​ these elements fails - no matter how much a​ company has spent - then the​ system will no longer work.

When selecting replacement parts for​ your heating system, cost should not be as​ critical as​ most companies make it. the​ cost of​ heating elements between a​ good manufacturer and​ a​ bad one is​ negotiable compared to​ the​ total investment. the​ production time and​ quality of​ the​ parts gained by selecting a​ respectable manufacturer will more than make up the​ difference. Keeping in​ mind the​ following tips when selecting a​ manufacturer will ensure less downtime due to​ a​ faulty product.
Manifold Heater, Cartridge Heater

Cartridge heaters are utilized around the​ flow channel to​ ensure uniform temperature. it​ is​ important to​ keep the​ distance between the​ heaters and​ the​ manifold equal or​ greater than 1x the​ diameter of​ the​ heating.
Thermocouple placement should be located equally distanced between the​ heating element and​ the​ flow channel and​ should be at​ least 1.5″ deep to​ ensure an​ accurate reading.
If an​ internal thermocouple is​ utilized, it​ is​ important to​ ensure that it​ is​ located towards the​ center of​ the​ heating element (at least 2″ away from the​ lead end) depending on whether the​ controller is​ grounded or​ ungrounded.
Some of​ the​ most common causes of​ failure include:

* Lead short out. This can be corrected by changing the​ lead type. if​ fiberglass leads were utilized, this could be the​ cause. Hot runners by nature create gases, which over time saturate the​ fiberglass material, allowing it​ to​ short between the​ leads. Depending on the​ ambient temperature around the​ lead area, Teflon leads can be utilized to​ correct this, as​ it​ is​ more resistant to​ gases. However, the​ temperature surrounding the​ leads cannot exceed 250′C.

* Internal thermocouple not reading correctly. This can be caused by two different reasons. One reason is​ the​ thermocouple must be located in​ the​ center of​ the​ heating element. if​ not, you will never obtain a​ correct temperature of​ the​ flow channel. the​ other reason is​ whether or​ not the​ unit is​ grounded or​ ungrounded. Consult your controller manufacturer to​ determine this.

* a​ performance issue. in​ a​ standard heater the​ resistance wire is​ evenly wound. to​ enhance performance, a​ distributed wattage heater is​ recommended. This is​ where the​ resistance wire is​ stacked at​ each end to​ compensate for​ the​ loss of​ heat due to​ various reasons. This allows for​ a​ more even heat curve.

Tubular Heating Elements

Tubular heating elements are inserted into a​ milled slot into the​ manifold. This allows for​ a​ more accurate location of​ heat at​ the​ areas that require the​ most (i.e., nozzle exits).Tubular heating elements are for​ the​ most part the​ heater of​ choice. They are reliable, relatively inexpensive and​ there is​ no extra cost for​ gun drilling the​ manifold. But more importantly, they perform the​ job well.
Tubular heaters do have two drawbacks. One is​ availability. it​ can take from six weeks standard delivery to​ as​ little as​ a​ week (if the​ manufacturer is​ running that diameter that week) to​ get a​ new part. Unlike cartridge heaters, tubular heaters have longer delivery times because of​ the​ machine setup time.
The other drawback is​ the​ design. if​ the​ manufacturer does not have a​ template of​ your system, it​ is​ extremely difficult to​ match some of​ the​ more complex layouts. for​ this reason, more companies are changing to​ highly flexible tubular heaters. These can be easily inserted into a​ manifold by anyone, resulting in​ shorter down time. This type of​ heater is​ capable up to​ 95 watts per square inch and​ is​ easily bent on site in​ minutes. a​ stainless steel plate or​ insulation plate is​ recommended to​ hold the​ heaters in​ place, and​ a​ dovetail design can replace this plate if​ a​ space is​ not available.
The thermocouple location should be maintained as​ explained above. if​ a​ problem arises with standard transfer heaters, it​ may be that the​ terminal area is​ not manufactured to​ bendable environment. Also, the​ slot may be too large or​ the​ diameter tolerance of​ the​ heater may be too wide, giving an​ uneven notch and​ an​ uneven temperature.
Nozzle Heaters

The torpedo system is​ one of​ the​ first hot runner heated nozzles introduced to​ the​ moldmaking industry. the​ concept is​ simple - a​ cartridge heater is​ inserted into a​ gun-drilled hole running through the​ center of​ several flow channels. When replacing a​ torpedo-style cartridge heater, several things should be remembered.

1. Does the​ hole have a​ flat bottom? This is​ important for​ the​ thermocouple to​ sense correctly, as​ air is​ an​ excellent insulator. With standard construction cartridge heaters, the​ disc end is​ concave due to​ the​ manufacturing process. to​ ensure an​ accurate measurement, a​ gun-drilled hole with a​ flat bottom and​ a​ flat bottom cartridge heater should be used to​ achieve optimum contact.

2. What is​ the​ diameter of​ the​ hole of​ the​ cartridge heater being inserted? it​ is​ important that close tolerances be maintained in​ this area. With the​ high watt density required within this type of​ heater, a​ centerless ground heater is​ highly recommended. Standard tolerances by most manufacturers are q 0.002″. With a​ centerless ground heater, a​ q 0.0008″ tolerance is​ achieved. This greatly increases the​ life of​ the​ unit due to​ more contact within the​ body of​ the​ nozzle, allowing a​ better transfer of​ heat from the​ cartridge heater to​ the​ nozzle body.

3. Where is​ the​ thermocouple located? the​ thermocouple must be located at​ the​ disc end to​ ensure proper temperature measurements.

4. What are the​ requirements for​ the​ internal thermocouple junction? as​ today’s manufacturers of​ controllers have different requirements, consult your controller manufacturer for​ these specs if​ you do not already have them.

External Heating (Coil Heater)

Coil heaters have been introduced to​ the​ hot runner system - greatly increasing the​ cycle speed and​ the​ quality of​ the​ product produced. Due to​ an​ even heat around the​ nozzle body, the​ material is​ not subject to​ excessive temperature changes, resulting in​ less degradation of​ material. When replacing a​ coil heater, consider these points:

1. the​ profile of​ the​ heating element. a​ flat or​ square cross section is​ far superior to​ a​ round profile. This is​ because of​ contact - greater contact provides for​ easier nozzle control and​ faster recovery time. With a​ round profile-heating element, the​ only contact is​ at​ the​ zenith of​ the​ arch. But with a​ flat profile, the​ contact is​ across the​ entire surface of​ the​ heating element. a​ special manufacturing process is​ required to​ obtain this contact with the​ nozzle.

2. the​ correct pitch of​ the​ coil heater.> to​ achieve an​ even pitch across the​ nozzle, the​ coil heater needs to​ be wound tight at​ each end and​ spaced in​ the​ middle. This allows the​ heat to​ re-disperse over the​ nozzle, allowing for​ custom profiling and​ ensuring even temperatures across the​ flow channel.

3. Internal thermocouple location. the​ internal thermocouple should be located as​ close to​ the​ tip as​ possible.

4. the​ thermocouple junction. the​ unit must be spec’ed out to​ match the​ controller being utilized.

5. the​ coil I.D. the​ coil I.D. should be smaller than the​ nozzle O.D. in​ order to​ achieve a​ good contact. for​ front load systems, a​ pressed-on or​ pushed-on sheath design is​ recommended if​ a​ clamping strap is​ too large to​ install.

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