Cooling Layout and Cooling method between core/cavity and mold base

Cooling is most important parameter when talking about cycle time reduce, some of my friend who very interest in injection mould still confuse how to design cooling system in injection mould, before talking about optimal design, first we must be familiar with the term and design standard that will be used.

Basic Cooling Layout

in principle, the more uniform temperature in the cavity, the better the resulting product, the more uniform and rapid heat transfer processes during the process of solidification occurs, the faster the cooling process, and of course the faster the cycle time that happened.when designing, to keep the cooling process is rapid and uniform cooling channels should be sought closer to the wall of the product, especially for regions of high and thick walls. therefore the cavity cooling channels is essential.

in the image above, is an example of basic connections cooling layout, its parts are
A. cavity colored with blue
2. green is mold base
3. yellow is cooling joint plug
4. white is hose connection to connecting cooling joint plug

on the left side of mold in above picture, we see that two pcs of cooling joint plug (yellow color) in that side, is for input and output of cooling mold base and cooling channel from the machine.

Rectangle Like Layout
depend one cooling layout is a favorite around the product, because the drilling process should be straight, then the shape is rectangle, except in the form of circular gear will be retained.

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Other Joint Construction Betwen Cooling in cavity and Mold base with O Ring

What is O ring
o-ring is a loop of elastomer with a round (o-shaped) cross-section used as a mechanical seal or gasket. They are designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface. (wikipedia.com)
O-Rings are torus-shaped (i.e. doughnut-shaped) objects made from elastomeric compounds such as natural or synthetic rubber, and are used to seal mechanical parts against fluid movement (air or liquid). O-Rings perform their sealing action by deforming to take the shape of their cavity, after being oversized to guarantee an predetermined interference fit.( efunda.com)


O ring typically used in one of two seal designs, axial or radial, in mold design to attaching cavity to mold base axial, face type are commonly used then radial type, because axial type is more easy to assembly in mold than radial type.
2D O ring drawing like picture below


Static seals exist where there is no relative motion between the mating surfaces being sealed.





at previous post about basic construction for joining cooling system in cavity and mold base , we can learn how to joint pipe from mold base of mold to cavity site.

various construction can be develop from basic construction, previous post basic construction is fast and cheap construction model, but it isn't good when you in large mold and mass production mold, why? becouse production mold must have endurance until 1000 000 shot.

Picture below shown develop construction of joining cooling pipe








blue color indicate mold base side and yellow color indicate cavity side.
basic rule from those picture are :
1. T is height of O ring
2. part of O ring that will receive pressure form cavity plate. 15-30% from it's height is best. this little pressure give to prevent leak when water flow in cooling system.
3. t2 value is same with t, but t2 is horizontal, becouse O ring always made from elastomer plastic, by little pressure we can add O ring to O ring hole.
4. L is Gap between cooling channel and O ring hole.

O-Ring Design Considerations
1. Proper Squeeze
•Compression expressed as a percentage of the free-state cross-sectional thickness:








•Face Seal: 20-30%
•Static Male/Female: 18-25%
•Reciprocating: 10-20%
•Rotary: 0-10%
2. In static seals, where the O-Ring is not in axial motion in the bore, the recommended maximum compression is approximately 40%.
3. The O-Ring must be compressed by a predetermined amount, and this compression determines the O-Ring cross-section diameter.
4. The O-Ring inner diameter is typically chosen to be close to the groove's inner diameter; by selecting it to be slightly less than the groove's inner diameter, the O-Ring will stretch and hug the groove.
5. The Groove Width must be larger than the O-Ring cross-section diameter, to accommodate the radial expansion of the O-Ring when it's axially compressed in the gland.
6. stretch,
- Excessive stretch can overstress material, thin cross section, and reduces % squeeze
- % cross section reduction due to stretch about half of the % ID stretch
7. Sharp Corners, make R in cornet to prevent damage during seal installation.
8. Pressure and Clearance Gap.
Most elastomeric seals are designed to operate within ambient pressure to about 1,500 psi. At very high pressures, the seal must have sufficient strength to resist extrusion into the clearance gap. The chart at right illustrates the recommended limits of the combination of clearance gap (diametral), seal hardness, and pressure differential. picture below shown graph between clearance gap and pressure



















9. When it is said that an elastomer is good for an application it is meant that some compounds which include that material are acceptable. Not All. For instance, some compounds of EP are good for brake fluid applications, but most are not acceptable.
10. DO NOT use a lubricant composed of the same material as the O-ring. For example, a silicone lubricant should NOT be used with a silicone O-ring.
11. Avoid using graphite-loaded compounds with stainless steel, as they tend to pit the stainless steel surface over time.

useful reference
http://www.rlhudson.com/O-Ring%20Book/designing-static.html
http://www.pspglobal.com/application-limits/04-watery-substances.html
http://en.wikipedia.org/wiki/O-ring
http://www.efunda.com/DesignStandards/oring/design_guidelines.cfm#axial
http://www.marcorubber.com
http://www.allorings.com/gland_static_axial.htm

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Construction of Cavity Cooling and Mold Base Cooling, O ring

here the basic construction of joining cavity cooling and mold base cooling, we can use from simple construction to joint cavity and mold base cooling with one O ring, or we can use more complex construction like using special plate, and various O ring seal type. here is basic construction to joint the cavity cooling and mold base cooling.


both circular type and straight type cooling can be joint use those construction,
those construction use in half circular type of cooling system like picture below


click the image to see more large

simple joint just need one O ring or rubber seal, O ring pocket is preferred make in horizontal face from assembly, becouse it's make assembly and machining process mold more easily,
basic rule and tolerance to prevent leak in O ring are like picture below













at the cross section of cavity and mold base cooling construction, blue color indicate mold base part, and light yellow indicate cavity block, green is indicate hole or pipe of cooling. light black is O ring before penetrate with cavity block.
however is the simplest construction to join cooling cavity and mold base.

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