Hot Runner Molding
What is hot runner mold
A hot runner mold is a type of injection molding system that uses heated material feed channels, or “hot runners,” to maintain the temperature of the plastics as it flows through the injection mold. This allows for a more consistent and efficient molding process, as the plastic does not have to be reheated between shots so the cycle time will be reduced and will save the waste runner materials ( sometimes has no any runner with hot runner systems). Hot runner systems are commonly used in the production of large quantities of plastic parts, such as in the automotive and consumer goods industries, or used in the stack mold.
DONGGUAN SINCERE TECH CO.LTD(SINCERE TECH) provides plastic injection mould solutions to industries of all types and sizes. For almost 20 years DST has designed, built, and worked on almost every type of mold existing in the plastic industry.
We are experienced in building custom plastic molds for a variety of hot runner mold systems, from hot runner manufacturers like:
Our state-of-the-art mold building facilities include High precision CNC machines, automatic CMM measurement machine, and Two heads of EDM Machines to create many types of custom molds, including complex specialty injection molds, insert molds, unscrewing molds, overmolding, hot runner mold, cold runner mold, stack mold, gas-assisted injection molds, double injection molds (2k molding), etc. We can build molds for both cold runner systems and hot runner systems.
Hot Runner Molding: Efficient High Production
Each system offers advantages and disadvantages. Choosing the system to employ depends on the requirements of the part to be produced. A few of the considerations include:
- Type of material to use – virgin or “regrind”
- Colour changes during the production run
- Single or multiple design production
- Part complexity
- Colour requirements
- Physical characteristics of the material
The primary difference between the two systems is that the hot runner eliminates the excess material retained in the feed channels of a cold runner mold. This feature reduces the number of production steps required and saves in material and energy costs.
Furthermore, mostly hot runners use 100% virgin resins; no reprocessed or “re-grind” material is added. This is an important feature for specific applications where regrinding can cause the material to yellow, or detracts from the material properties, such as clarity in light pipe or lens production, where long-lasting transparency is a specific requirement.
Hot runner molding systems normally inject melted material directly into the individual mold cavity. Hot runner is almost always used for large volume production of thermoplastic injection molded parts, or multiple part production using multi-cavity molds and stack-molding technology.
Hot runner molds are two plate molds with a heated runner system inside one half of the mold. A hot runner system is divided into two parts:
- The manifold has channels that convey the plastic on a single plane, parallel to the parting line, to a point above the cavity
- The drops, situated perpendicular to the manifold, convey the plastic from the manifold to the part
Hot-Runner Systems: The advantages and disadvantages
Primary advantages of hot runner systems include:
- Shorter, faster cycle times – most of them have no runners to cool
- Smaller machines – reduced shot volume into runners
- Automated processing – runners do not need to be separated from the parts
- Gates at the best position for economical design
- Elimination of runners means
- Materials cost savings – no runner to regrind or reprocess
- Least expensive cost/piece
- Reduction of energy costs
- No runners to remove or regrind
- Reduces the possibility of contamination
- Lower injection pressures
- Lower clamping pressure
- Consistent heat within the cavity
- Shorter cooling time
- Shot size reduced
- Cleaner molding process
- Eliminates nozzle freeze
There are, however, a few disadvantages to hot runner mold systems that need to be considered:
- Hot runner molds are more complex and expensive to build than cold runner molds
- Higher initial start-up costs than for cold runner systems
- Complex initial setup prior to running the mold
- Higher maintenance costs – more susceptible to:
- Heating element failure
- Wear caused by filled materials
- Risk of thermal damage to sensitive materials
- Elaborate temperature control required
- The colors change is more complex than the cold runner, sometime you will spend lots of time and cost to clean up the hot runner systems, especially for transparency and white color parts.
Hot Runner Molds: Applications & Possibilities
Hot-runner systems are almost always used when large runs have to be manufactured in highly automated production. Additionally, technological advances enable us to build molds with gates positioned to yield the best quality molded parts.
Hot runner molds are sometimes connected to needle valve nozzles, which are activated with precise computer-controlled timing. This allows for a number of advanced processes, including:
- In-Mold Decoration – lamination with a colored film coating
- Multi-Cavity Molds – cavities with different geometries and/or volumes
- Parts that belong together produced in one mold
- Injection valve opening and closing can be adjusted to the conditions of each individual cavity
- Injection pressure and holding pressure may be adjusted independently of each other
- Controlled Volume Balancing – a weld line can be shifted into a non-critical area of the molded part
- Stack Molding – two or more mold bases in production simultaneously creating multiple parting lines
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