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Other Joint Construction Betwen Cooling in Cavity and Mold Base with O Ring

Today, they are various plastic processing method available in industrial process, from the method of processing plastic, we can divided into two big methods:

I. Molding Methode

This method usually uses mold to melt the plastic, deformed with applied pressure and the product shape will be as same as the mold shape.

Various molding type method can be divided as:

Extrusion Molding Method

This process can produce along product with fixed cross-sectional profile such as wire and cable coating, plastic tube for printer ink, some hollow profile and various solid profile. The materials are pallet or plastic chips that are usually dried in a hopper before going to the feed screw. To process extrusion method used injection machine, the plastic heated at barrel to molten state then forced through a plastic mold die that is in desired shape. Let us learn more about extrusion mold.

Injection Mold

Injection molding involves taking plastic in the form of pellets or granules and heating this material until a melt is obtained. Molten plastic is injected at high pressure into a mold, which is the inverse of the product's shape. Then it is allowed to cooling into the desired shape. The mold is then opened and the part is ejected, at which time the cycle is repeated.

injection mold method have various kind of techniques like Thermoplastic Foam Injection Molding, Multi injection mold (sandwich mold, bi-injection mold) gas assist injection molds and other, basic injection machine for injection mold.

Blow Molding Process

A thermoplastic resin is heated to a molten state It is then extruded through a die head to form a hollow tube called a parison. The parison is dropped between two mold halves, which close around it, the concept of blow mold.

There divided four types of blow mold:

•Extrusion blow molding

•Injection blow molding

•Stretch blow molding

•Reheat and blow molding

Compression Molds

Compression molding is a method of molding in which the plastic, generally preheated, is first placed in an open, heated mold cavity. There are four steps in compression molds. it is loaded charge, charge compressed, cured the charge and ejecting process of product. The main construction is Punch (cavity side), core molds and ejection system.

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.

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.

O ring typically used in one of two seal designs, axial or radial, in mold design to attaching cavity to mold base axial, face types are commonly used then radial type. Because axial type is more easy to assembly in mold than radial type.

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 shots.

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 gives 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.

• 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.