Direct Gate or Sprue Gate

What is Gate ?
The entrance through which molten plastic flows into the cavity of the mold from the runner. This is where the flow or melting of molten plastic is controlled by control type of gate or gate dimension. It is positioned at the thickest area of a part.
other function of gate is the gate makes it easier for the runner, which will be unnecessary after molding, to be separated from the part.is recommended to consider gating options early in part design.

Direct Gate
direct gate or sprue gate we can define as connecting directly end sprue to the molding and used as a gate,
this type of gate is commonly used for single cavity molds, where sprue feeds the material to cavity molds directly rapidly with minimum pressure drop.

this type of gate is applied to molding of boxes or cups like bathtub, plastic bucket, and others, particularly large sized products. like at the picture above, shown cups product with direct gate before cutting.

Dimensions and Construction
from picture below we can concluded that direct gate is very easy to design,

from picture above the construction of direct gate is one parts with the product, after injection process, the sprue will cut manually.
parting line between cavity and core can directly placed at top surface of product or more lower from top surface product, it very depending of product shape and characteristics.
starting sprue diameter is controlled by nozzle of injection

- then, make sure the diameter of sprue orifices must be larger than nozzle exit diameter, choose from 1-2 mm or about 1/32 inch.
- give taper at the sprue from orifice diameter to product about 1-3 degree, it is will made the product demolded from cavity side more easy.
- in general the diameter of the gate much greater than the thickness of the product.

Advantages
- Low cost of design.
- The injection pressure was reduced due to direct cavity filling.
- Simple way to design gate and runner system.
- easy design and maintenance.

Disadvantages
some disadvantage of direct sprue are:
- since excessive stress is left easily around the gate, cracking often starts around the gate.
- when using non standard sprue tapers, will more expensive with little gain.
- gate mark left on part surface after runner of sprue trimmed of.
- This gate type can only produce one part per shot.
- The gate has to be cut manually by a cutter.
- Not applicable in little size product.

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Basic Functions of Mold Base Parts

A mold plate is any plate required to built a complete mold, in all plate use for molds have the main requirements, they are :
1. Good corrosion resistant
2. Good Machinability.
3. Easy to clean
3. Good heat transfer.
4. Homogeneity of steel.
5. Easy ability.
6. Low Cost.

at picture below you can see 3 plate mold base type with closed position, basically 3 plate type and 2 plate type has some main plate, see explanation about mold construction type to understand more,


explanation below based on number at those picture
1. Fixed Clamping Plate or Top Plate
Holds The fixed side of the mold to attached at the fixed platen of the injection machine. at this plate will attach locating ring, eye bolt, and sprue bush.
2. Runner Stripper Plate
this plate only used in 3 plate molds type, the function is to cut resin from nozzle in top of sprue bush, and pull the runner by runner locking pin.
3. Fixed Mold Plate or Cavity plate.
use to hold cavity side of product, leader pin, support pin, Puller bolts, and Angular pin when slider attached.
4. Movable Cavity Plate or Cavity plate
it used to attach core side of product, return pin, leader bush and slider core if needed.
5. Back up Plate or Support plate
used to support cavity plate, attach the hole for return pin's spring, and cooling channel when in cavity plate can not make it.
6. Spacer Block
Mounted between the movable clamping plate (bottom plate) and the movable cavity plate to give space and allow the ejector plate to move when ejecting the
part. the required length of spacer block depend on ejector stroke that needed to eject product.
7.Ejector retainer plate
to hold the ejector, Z pin, shoulder bolts,and give space to ejector leader pin and support pillar.
8. Ejector Plate
Pushes the ejector pins and return pins, connected with ejector rods.
9. Movable Clamping Plate or Bottom plate
Holds The movable side of the mold like spacer block, support plate, cavity plate and ejector mechanism to the movable platen of the injection machine.


and look at picture below, shown 3 plate molds type in opening position, but at picture below, Bottom plate or movable clamping plate is number 7, number 8 is ejector retainer plate, and number 9 is ejector plate.

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Paralel and series Cooling methode at flat type plate of Mold Base

almost mold designer know that cooling is biggest part that effect cycle time of injection mold, a good design in cooling will make heat exchange between resin after injected and mold will reduce cycle time and give good product.
at flat type of mold base plate like stripper (Plate number2) plate between top plate and cavity plate, top plate it self, and support plate after core plate, at the top plate cooling not always used, it very depend on resin type,and product shape.
the picture below shown some flat mold base that we can use parallel or series cooling methods


How about core and cavity of Mold base ?

we can use both type of cooling series and parallel when design cooling at core and cavity plate, but you must careful place the cooling, because beside cavity molds it self, they are ejector at the core plate then sprue and runner system at cavity plate. the construction and how to connecting cooling at mold plate with cavity mold cooling will discuss later.

Parallel Cooling Channel
picture below shown parallel cooling channels concept























basic mold base cooling have four parts, they are :
1. Main Cooling pipe
commonly cooling pipe make by drilling using bore,the longer drilled hole, it recommended have length about 6 mm if using long nipple joint to connect with outer tube, if using nipple or inner joint plug each cooling pipe minimum have 12 mm.
2. stopper plugs, like at slider cooling and cavity cooling stopper plugs is prevent water or oil coolant flow to undesirable way.
3. Inner stopper plugs, the function is same as stopper plugs, but assembly methods and location is different, it assembled at inner of cooling pipe.

parallel cooling channels are drilled straight trough supply manifold cooling pipe, due the parallel design flow characteristics, the flow rate along various cooling will different, because each cooling pipe have their own flow resistance. as a results, cooling of the mold will not uniform. so it's clear that parallel circuit of cooling in molds are very poor flow rates.

Series Cooling
picture below shown basic series cooling construction and methods






















the parts is same with parallel cooling type, but the construction is different, at the series cooling channel types, it connected in single loop from the coolant inlet until its outlet, we can configure the flow by adjust the inner stopper plug type.
when design it is recommended to use same size of diameter cooling, because it's can maintain the turbulent flow, turbulent flow enables heat to be transferred more effectively.

Long and Shorts Nipple joint plug Assembly methods
considering mold base material strength,closer distance between two nipple plug type are not advisable, look at picture below

assembly between long type and shorts type is different, by using long type minimum length from both side is 6 mm, except for little diameter hole, less then 5 mm, smaller length spacing my be acceptable.
Short nipple joint types almost assembly in inner mold base, because of that minimum length space is 12,5 mm, although 10 mm my acceptable but will difficult to assembly it using hand.

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Cavity mold cooling construction design

In commonly mold designer know that Cooling conditions affect cycle time, part dimensions, surface finish, and warpage. but some junior mold designer still confuse to make layout and construction of cooling in mold.

before this posting, i havepost about cooling construction in slider, beside slider mold cavity also important to fill cooling, why because almost product 70-80 % is molded shape in mold cavity.

picture above shown core side of cavity mold, the basic construction is
1. Plug (Plug is for prevent water flow out from desire flow layout)
2. cooling pipe (as those picture cooling pipe doesn't shown, almost cavity cooling pipe processing using jig bor to make a long hole that becoming cooling pipe)
3. In / Out Hole, it's hole also make using jig bore. this hole will attach in cavity plat that will match with cooling layout in mold base.
orange color indicate product insert hole shape.

here i post basic construction in single cavity, see picture below to learn more

picture above is shown flow of cooling process of cavity mold from top view.
then which hole water flow in and flow out, see picture below

at this wireframe method picture, we should make hole at bottom side of core to connected cavity and cooling layout of mold base.

Tips Design Cooling pipe for cavity
1. make sure side of cooling pipe have enough length from insert, minimum 3 cm
2. choose a good diameter for the hole, like 6 cm, 8 cm, or 10 cm.
3. when injection proses begin make sure using calculation so you have turbulent flow in cooling pipe.
4. make the pipe more long is useful for make turbulent flow.


then how the layout and construction of cooling in mold base ?
just wait for new post

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Mold Cooling Design at Slider

Why mold need cooling ? as we know that cooling conditions affect cycle time, part dimensions, surface finish, and warpage, Mold cooling time is the biggest contributor to the overall cycle time, it could be as two-thirds or 70-80% of total cycle time.

from those reason design an efficient cooling circuit can reduces the cooling time, beside that uniform cooling improve part quality by reducing residual stress, stability of heat transfer, and accuracies of part after cooled.

Why Slider Need Cooling?
Some product have long dimension that need slider, to prevent warpage, residual stress, and stability of shrinkage behavior, for that reason slider need cooling.

Mold Cooling Construction
picture below shown cooling construction at slider insert from top side.


annotation number at picture upper indicate part of slider, they are
1. Plug
2. Slider Insert
3. Cooling Pipe
4. Guide Rel of slider core
5. Locking Block slider
6. Long Nipple

Pipe with blue color indicate flow of water when cooling process working. number 1 part (Plug) prevent water flow to side of slider inserts.
When design nipple,make sure that nipple is long enough to reach outer side of mold base.

to get understand more look at picture below, at this picture still shown cooling at slider from left side.


additional number of slider parts are
7. slider core (this part is one of slider main part, where slider insert attached)
8. Angular slider ( the main function of angular is change the moving 90 degree, so slider can move)

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Plastic Processing Methode Types

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


1. Molding Methode
this method usually use mold to melt the plastic, deformed with applied pressure and the product shape will 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 material is 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. look at picture below to 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. you should learn about various injection molds type at mold construction post
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 you can see at picture below

to learn more about injection mold you should open introduction of injection molds post
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 you can see at picture below


we can divided blow mold four types as :
* Extrusion blow molding
* Injection blow molding
* Stretch blow molding
* Reheat and blow molding.
the picture above shown Stretch blow mold type, you should see more at Blow Mold Posting

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


Reaction Injection Molding (RIM)
the concept of RIM is Two reactant liquids are heated and brought together under high pressure. one example process is polyurethane RIM, At the heart of the polyurethane RIM process is a chemical reaction between the two liquid components, which are held in separate, temperature-controlled feed tanks equipped with agitators. From these tanks, the isocyanate and polyol feed through supply lines to metering units that precisely meter both components, at high pressure, to a mixhead device (http://www.rimmolding.com/rim/index.html), look at picture below, those picture shown two chemical reaction process mold isocyanete (blue tank) and polyol (red tank) .
the advantages of RIM is Strong, flexible, lightweight parts which can easily be painted. Quick cycle times compared to typical vacuum cast materials, the disadvantage is slow cycle time because must mixed before formed by mold.
Transfer Mold
transfer Mold or resin transfer mold (RTM)
like compression molding, is a process where the amount of molding material (usually a thermoset plastic) is measured and inserted before the molding takes place. The molding material is preheated and loaded into a chamber known as the pot. A plunger is then used to force the material from the pot through channels known as a sprue and runner system into the mold cavities. The mold remains closed as the material is inserted and is opened to release the part from the sprue and runner. The mold walls are heated to a temperature above the melting point of the mold material; this allows a faster flow of material through the cavities.


Thermoforming
is a manufacturing process for thermoplastic sheet or film by Heating a thermoplastic sheet and using a vacuum to pull the sheet over perforated mold. the product of this method is Fast food containers, advertising signs, panels for shower stalls



Pultrusion
Pultrusion is a continuous process of manufacturing of composite materials with constant cross-section whereby reinforcing fibers are pulled through a resin, possibly followed by a separate preforming system, and into a heated die, where the resin undergoes polymerization. Many resin types may be used in pultrusion including polyester, polyurethane, vinylester and epoxy.(Wikipedia)


2. Casting Mold
Casting is a manufacturing process by which a liquid plastic introduced into a mould, allowed to solidify within the mould, this characteristic of this molds is filling a molds by gravity, this kind type of casting molds are :
Liquid resins (epoxy)
Hot melted plastic poured into a casting (nylon)
Slush casting for thin walled products (snow boots, gloves, toys)
Wet spinning -fibers formed by spinning the solution through multi-hole dies
Rotational Mold
Rotational molding or moulding is a versatile process for creating many kinds of mostly hollow plastic Parts. The phrase is often shortened to rotomolding or rotomoulding.
molding of large products such as storage tanks and containers,
cPrnpIex toys, mannequins (display figures), etc., is achieved using rotational
molding. Lately, there are more and more applications for this technology.
.

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