Hot runner system represent the most extensive technological development from conventional runner system to a system ready to be installed.
Large moulding such as automotive dash boards , bumpers,computer housing etc. could be produced in practice without multiple melt supply.
Nozzles upto 8mm length and runners upto 1800mm are applied in such large moulds.
All materials can be moulded in hot runners,even reinforced plastics and structural foam.Certain limitation are applicable for thermally sensitive plastics and in particular flame resistant material.
Saving in material for runner cost for regrind
Shorter cycles,time for demoulding runner system is omitted, cooling time is not determined by slow freezing,no runner break off.
Smaller machines are adequate, runner system does not create reactive forces,short size is reduced by volume for runners or larger shot size is available for filling larger number of cavities,shorter opening stroke than for three plate moulds.
mould making has recourse to mould standards.
Omission of demoulding the runner system permits simpler automation of processing.
Heated runners allow the realization of long flow paths. Option to place the gate at an optimum location.
Diameter of runners can be kept large resulting in less pressure
loss
Longer holding pressure is made possible
Balancing of the runner system can be done by temperature control or mechanically
Use of shut-off nozzles may avoid formation of knit lines
More rejects at least during start up
More work in mould design
Higher mould costs for installation More susceptible to trouble such as leak or failure of heating elements.
Hazard of thermal degradation of sensitive materials because of long flow path and high shear velocity
No pressure control from gates
HOT RUNNER SYSTEMS
The sprueless moulding principles have been well known since the ‘50s, even though their
use on a vast scale only dates back to the beginning of the ‘70s. Hot runner injection moulds are gaining wide acceptance as they give cheaper production as a result of shorter
cycle times and scrap reduction. The advantages are that they have no sprues, no runners and that the machine plasticising capacity is used almost
completely
HOT RUNNER SYSTEMS
In fact, the molten material remains under optimum viscosity conditions while it is being
transferred from the feed bush through the runners up to the mould cavities. In the feed
runners, the mass of molten material should be kept constantly hot, that is in a fluid state, ready for the new shot. On the conceptual standpoint,
hot runners are not thermally influenced by moulding breaks and across their cross sections
temperature is always constant
HOT RUNNER SYSTEMS
Hot runner cross sections may be very small, thereby ensuring constant filling stages over time. Runners into which resin flows must be
designed in such a way to have special characteristics
HOT RUNNER SYSTEMS
- the size must be such not to create high shear speeds which would result in pressure drops and overheating;
- cross sections must not be too small to avoid material degradation and
problems in colour change; - runners are to be balanced and sized
in such a manner not to cause problems when filling the impressions.
HOT RUNNER SYSTEMS
HOT RUNNER SYSTEMS
Furthermore, a number of practical and easy-to-service systems are used to get even temperature. Types most
broadly used are: heater bands, cartridge bands, spiral bands, low or
high voltage bands, heat tubes. Another critical design element is the gate, both for the nozzle construction
and quality of moulded part.
HOT RUNNER SYSTEMS
Gates are divided into four types: - circular gate;
- ring gate; - side (edge) gate;
- valve gate; .
HOT RUNNER SYSTEMS
- Circular shape nozzles, used for non critical materials and applications, are made from high
conductivity metals. Thus, they are heated up by simple contact with the distributor; in addition, at
the border they are insulated by means of the same resin to inject which flows inside a hollow space located between the bush and mould. In order to
maintain even thermal profile along the nozzle, the nozzles must not be too long, in particular L = 2*D. The nozzle can sometimes be equipped with a hot
tip .
HOT RUNNER SYSTEMS
HOT RUNNER SYSTEMS - Circular shape nozzles, used for non critical materials and applications, are made from high conductivity metals. Thus, they are
heated up by simple contact with the distributor; in addition, at the border they are
insulated by means of the same resin to inject which flows inside a hollow space located between the bush and mould. In
order to maintain even thermal profile along the nozzle, the nozzles must not be too long,
in particular L = 2*D. The nozzle can sometimes be equipped with a hot tip.
HOT RUNNER SYSTEMS Ring type nozzles are similar to circular ones. The only difference is that ring types have a central tip
which prevents the nozzle from cooling prematurely. The tip may be constructed in a variety of shapes and materials. High thermal conductivity materials can be
used (Be-Cu alloys). Sometimes, tips are to be subject to nickel plating processes for major
protection as certain polymers (e.g.: PA) react with these alloys; in some other cases, when abrasive
resins are to be processed, hard metal is used
HOT RUNNER SYSTEMS
HOT RUNNER SYSTEMS SIDE (EDGE) GATE
Gates with side entrance are more critical that previous gate styles. They allow side gating of parts and are used for pieces which must be injected at the centre of a hole with multiple injections or for
parts which do not accept capillary gate. The insulating material at the bottom of the nozzle is
very near to the part surface in the injection area. The width of the gate is to be less than part
thickness. Therefore hot resin must be brought very close to the part (0.5-1 mm), but this makes the local, mechanical resistance of the mould quite
critical and the part itself is overheated.
HOT RUNNER SYSTEMS
HOT RUNNER SYSTEMS Valve gate systems control gate opening and
closing through a rod operated via a pneumatic circuit. In this case it is possible to operate with high injection diameters without affecting the part aesthetical appearance. In
addition, the larger injection diameter permits very low filling times to be achieved
without incurring in speed gradients in excess. This also permits cycle time
improvements since lower temperature of both molten material and mould can be used.
This also results in shorter cooling times
HOT RUNNER SYSTEMS
HOT RUNNER SYSTEMS Valve gate systems control gate opening and
closing through a rod operated via a pneumatic circuit. In this case it is possible to operate with high injection diameters without affecting the part aesthetical appearance. In
addition, the larger injection diameter permits very low filling times to be achieved
without incurring in speed gradients in excess. This also permits cycle time
improvements since lower temperature of both molten material and mould can be used.
This also results in shorter cooling times
HOT RUNNER SYSTEMS Valve gate systems control gate opening and
closing through a rod operated via a pneumatic circuit. In this case it is possible to operate with high injection diameters without affecting the part aesthetical appearance. In
addition, the larger injection diameter permits very low filling times to be achieved
without incurring in speed gradients in excess. This also permits cycle time
improvements since lower temperature of both molten material and mould can be used.
This also results in shorter cooling times
HOT RUNNER SYSTEMS Valve gate systems control gate opening and
closing through a rod operated via a pneumatic circuit. In this case it is possible to operate with high injection diameters without affecting the part aesthetical appearance. In
addition, the larger injection diameter permits very low filling times to be achieved
without incurring in speed gradients in excess. This also permits cycle time
improvements since lower temperature of both molten material and mould can be used.
This also results in shorter cooling times
The objective of a Hot Runner System is to distribute the material from the machine nozzle to each gate, while minimizing adverse effects to the material’s properties.
Two hot runner system types:
• Complete Hot Runner System
• Manifold System
A complete hot runner system is supplied to the customer as a fully assembled unit, ready to be fastened to the cavity plate
and installed into the machine press
A manifold system includes all components that make up the heated flow path except the hot runner plates. Drawings that outline the necessary plate machining to accommodate the manifold and related components are included with every shipped manifold system
The simplest hot runner mould for replacing the conventional sprue bushing including the reversed sprue busing with a hot sprue bushing or heated nozzle.It feeds directly into the cavity and has the the following advantages:
-Control of temperature
-Substantial independence of material and cycle
-Suitable for large moulds
-Less pressure drop and clean gate separation.
The purpose of the nozzle is to provide a now path for the plastic melt from the machine's cylinder to the mould. In the simplest design the nozzle butts on to the sprue bush of the mould. There are two standard designs in common use and they differ only with respect to the form of seating that is made with-the sprue bush .One design incorporates a hemispherical end and the other design is flat-ended. The small length of reverse taper in the bore at the front end of the nozzle is such that the sprue is broken just. inside the nozzle. This helps to keep the nozzle face clean and assists in maintaining a leak-free sealing face. The standard nozzle of either design is provided by the machine manufacturer und, so that moulds are interchangeable, it is advantageous for a company to standardize on one particular design.
It is an advantage to keep the length of the sprue gate as short as possible to minimise the pressure drop across the gate and also to minimise the blemish left on the moulding when the sprue gate is removed.With the standard nozzle design the length of the sprue gate is controlled by the depth of the mould plate. The length of the sprue gate can be reduced quite simply, however, by designing a special nozzle variously termed a long reach nozzle or extended nozzle which protrudes into a pocket
machined in the mould plate
Some means of heating the nozzle must be provided lo prevent undue cooling of the plastics material. One method is to fit a resistance-type band heater on to the parallel length of the nozzle and to control the temperature by means of a controller via a thermocouple- The thermo couple is fitted into a slot machined into the parallel section of the nozzle directly beneath the heater band.To minimise the transfer of heat from the heated nozzle to the mould, a circumferential clearance of at least 7 mm must be provided between the two parts
The conventional sprue gate results in a sizeable blemish being left at the injection point. Now, for the majority of components this blemish is unimportant, but there are occasions where it is undesirable. To reduce it to a minimum some form of pin gate is necessary. One method of achieving this form of gate is by the use of a special nozzle in conjunction with a reverse tapered sprue.This special nozzle is variously termed as barb nozzle or Italian nozzle.
The barb nozzle is similar to the standard nozzle except that there is a projection at the front which incorporates barbs It is this portion of the nozzle which is accommodated in the reverse-tapered -sprue. Leakage of material is prevented by ensuring that the flat face the nozzle seats on to the sprue bush .The sprue is normally removed manually from the nozzle which of necessity, lengthens the moulding cycle. An alternative design incorporates a local stripper plate, to strip the sprue from the barbs. The barb nozzle design has largely been superseded by ante-chamber and hot sprue bush
designs.
In this design, also known as the hot well design, a small mass of plastic material is retained in the antechamber The plate material adjacent to the mould wall partially insulates the central core plastic material in antechamber. Thus, by suitable adjustment and control of the nozzle temperature and the moulding cycle, the material remains sufficiently fluid to allow it to pass intermittently through the ante chamber into the impression,
As it is not necessary to remove the sprue from the mould, fast moulding cycles can be achieved. Note that with a standard nozzle the moulding cycle, particularly with thin-walled components, is often controlled by the waiting period for the sprue to cool sufficiently to permit its extraction.
A part-section through a mould for a thin-walled beaker which incorporates the antechamber design is illustrated .In this single impression mould, the integer cavity is adopted for rigidity. A local insert forms the base of the impression, and also incorporates the antechamber . The nozzle has a seat on the insert
There are two heated sprue systems which can be used for feeding directly into an impression. In one system, in which the conventional sprue bush is replaced by an internally healed sprue bush. the concept of the injection machine's nozzle abutting onto the sprue bush is retained. In the alternative system the sprue bush is dispensed with. being replaced by an internally heated extension nozzle.
Internally heated sprue bush: The principle of this design is that a healing element is incorporated on the centre line of the sprue bush in the flow-way between the injection machine's nozzle and the gate (entry) into the impression. By this means, the polymer material may be held at an elevated, controlled temperature up to a position relatively close to the gate- A standard injection machine nozzle, with either a flat or a radius end, is used in conjunction with this design
Internally heated sprue bush: One design of internally heated sprue bush is illustrated in Figure and consists of five basic parts: (a) body-outer, (b) body-inner, (c) torpedo, (d) torpedo tip and (e) cartridge heater. The cartridge heater is housed within the torpedo assembly, as shown. The heater wires pass through one of the torpedo legs via an internal insulator and adaptor (f). The torpedo assembly is mounted within the body-inner which is then screwed into the body-outer to form the sprue bush.
A part-section through a mould for a thin-walled beaker which incorporates the antechamber design is illustrated .In this single impression mould, the integer cavity is adopted for rigidity. A local insert forms the base of the impression, and also incorporates the antechamber . The nozzle has a seat on the insert
A part-section through a mould for a thin-walled beaker which incorporates the antechamber design is illustrated .In this single impression mould, the integer cavity is adopted for rigidity. A local insert forms the base of the impression, and also incorporates the antechamber . The nozzle has a seat on the insert
Cavity Design Design Guidelines
Recessed Gate AreasWhen designing gates into recessed areas such as dimples, agenerous radius should be incorporated to avoid extended thinsections of plate steel (see figure at right).Nozzle Seal off DiameterTo provide a durable nozzle seal diameter surface in the gatebubble, a surface hardness range between 49 - 53 Rc isrecommended (see figure at right). If softer materials are used(e.g. BeCu), these should be hard chrome plated to increasehardness.
Gate Cooling
Gate area cooling is required to remove excess heat generated by
the system. Sufficient cooling provides many benefits including:
• Consistent gate quality
• Consistent gate vestige
• Greater control over material stringing
• Greater control over resin drool
• Greater control of gate blushing
• Faster cycles
Optimized Gate Cooling (Key Elements)
1) Minimize the distance from the cooling channel to the gate detail The maximum recommended distance between the cooling channel and the gate detail is 1.5 times the cooling channel diameter.
2) Cooling should surround the insert. The cooling water shouldreach flow speeds that cause effective mixing of the fluid. For most inserts, a flow rate of about 6.8 - 8.3 liters perminute is sufficient.
3) The gate insert material affects heat dissipation and longevity.Insert materials such as H13 (material of choice) and 420 SS are 7x less heat conductive than BeCu Alloys. The trade-off with conductivity is hardness and gate life. Material choice will depend upon the number of projected cycles and the cycle time goals,
Gate Inserts
Gate inserts provide an effective method of cooling the gate area, since the entire circumference is cooled. Cooling circuits for the gate insert should be independent from the plate cooling circuit to provide better control. The gate insert is a replaceable wear item.
Nozzle selection chart
Following data have to be taken into consideration: flow length, shear rate of resin, wall thickness and configuration of the molded part.
Sprue gate nozzles
Used where a small sprue on the part or runner is not objectionable.Its unrestricted channel is recommended for molding filled materials, or larger parts requiring maximum flow. Provides extra stock on front face for machining runner profiles and part contours.
Ring gate nozzles
Used where a small circular gate mark is permissible. Nickel plated beryllium copper gate tip controls plastic flow, provides uniform heat transfer and improves gate cosmetics.
Stack Mold
Stack Mold
Stack Mold
Extended sprue gate tips
Stack Mold
Stack Mold
Stack Mold
Multiple gate nozzles
System of operations:
The key to the system’s operation is the method employed to open and close each gate. In operation each gate is opened or closed independently and positively by a hydraulic cylinder. Each valve is open for only the time it takes to reach optimum fill. This enables the molder to eliminate the over packing of filled cavities while trying to fill others.The Full-body type nozzle is suggested when a circular gate mark is allowed. Feeding the part or runner, it features a unique removable tip for easy replacement and longer nozzle life. The Body less type Gate offers excellent cosmetics, feeding directly into the part.
Hot-One system
Hot-One system
Galaxy Hot Runner Systems are engineered to reduce cycle times and simplify start ups.Designed for high cavity applications, without any performance compromises. Close center-to-center dimensions yield more parts per cycle.
Galaxy nozzles are innovative and feature quick-change modular assemblies for reduced service time. Galaxy nozzles offer a choice of tips: standard, wear-reistant and thru-hole. A modular nozzle construction enables a wide range of nozzle lengths to suit a variety of mold stack heights. Nozzle tips, heaters and thermocouples are front loaded and easily replaced right in the machine.
Cold-runner Systems
- The standard single nozzle plunges centraliy into the tool
- The single nozzle is fitted to the machine nozzle to suit the machine
- The needle is actuated by means of an external cylinder/lever unit
- The needle shut-off nozzle is opened and closed by the machine control unit
- Optimum thermal separation of sprue system and contour unit as far as the feed orifice area
- Specially for the filling of large-volume cavities
Cold-runner System, Single decentralised nozzle
Cold-runner System,4-nozzle low system
Cool-One system - Basic concept
Cool-One system - Basic concept
Cool-One system - Basic concept
Multiple probes - complete
Guidelines for the construction of a distributor block
Hot sprue bushings