cooling sys

8/7/2019 COOLING SYS

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DIE COOLING

During die casting process the molten metal is injected in to the die at very high

temperature, this raises the temperature of the die to a great extent. The die temperature

has to be maintained at certain value to get optimum production.

Even though die casting machines are operated at a pre-determined number of cycles in

order to control the die temperature; certain cross sections may retain more heat than

other. These cross sections- heavy walls & gating points, where the force & speed withwhich the metal is injected raise the temperature to a high level, must be maintained to

the correct temperature & this is done by cooling.

Cooling channels are drilled in the die & water is circulated through them. The

temperature of die at which it has to be maintained depends on the type of materials being

casted, shot wt, surface area of the cavity and the cycle speed.

The following table gives the temperature range of die & molten material,

Type Of Alloy Die Temperature (oC) Metal Temperature(oC)

Al 200 - 250 660 700

Zn 180 - 200 380 400

Mg 200 250 660 700

Brass 250 300 850 - 900

If the temperature of the die exceeds the working temperature range, then results in

Heat checking may occur

Longer cycle time

Sliding parts may jam due to expansion by overheating

If the temperature of the die falls below the working temperature range, then results in

Short fills & cold shuts

Poor surface finish

Weld lines may be formed

May result in more ejection force to eject the component

The die parts which need to be cooled are Inserts, Sprue Bush, Spreader & some timesplates are also cooled. In large die casting process, O Rings cannot be used as they cannot

withstand the high die temperature. This means the male hose ends have to be directly

threaded into the part to be cooled.


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Spreader Cooling (Baffle Cooling)

Baffle is a thin brass sheet normally of 2mm - 3mm thick. This is brazed to an MSadapter. Adapter is having BSP threads to spreader. Inlet & outlet holes are provided as

shown in figure.

Spreader Cooling (Bubbler System)Bubbler system consists of a thin Cu or Brass tube fitted tightly into the adapter. Adapteris having BSP threads, is threaded into the spreader. Cooling water enters through the

inner dia of the tube and flows out into the space between O.D of tube and the hole

drilled in spreader. Inlet & outlet are provided as shown in figure.

Sprue Cooling

In order to cool the sprue bush a M.S sleeve or cooling ring is shrunk fit on the sprue

bush. Inlet & outlet nozzles are provided in sleeve. Cooling groove is provided on ID ofthe sprue bush, where the water circulates. The inlet & outlet holes are angularly

positioned.


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Insert Cooling

For rectangular inserts, nozzles are directly threaded into the inserts.

For circular inserts, cooling ring (as incase of sprue bush cooling) is provided

alternatively cooling adaptor (as in case of spreader cooling) is provided.

Baffle Whole Cooling

Angle Whole Cooling


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Telescopic Cooling

Cooling Calculations

Heat Inflow into the Die (QA)

QA = (Shot Wt) X (Heat Factor for Al) X (No of Shots/Hr)

QA = A Kj/Hr Kcal/Hr 1 Joule = 4.2 Cal

Shot Wt in gmsHeat factor for Al = 145 Kcal/hr (for Al Alloys & Mg Alloys)

No of Shots/hr = 90 Shots/hr (for Al Alloys)

= 66 Shots/hr (for Cu Alloys)= 48 Shots/hr (for Zn Alloys)

Heat Transfer from the Die or Heat Loss to the Environment

Heat transfer by radiation is approximately 25% of the heat inflow.

Therefore, heat transfer from the die = 25% of A= (25/100) X A

Heat transfer from the die = B Kcal

Total Heat Removed From the Die

Total Heat Removed From the Die = Total Heat Removed From the Die- Heat Loss to theEnvironment

= A B

= C Kcal


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Heat Removed From Sprue Bush, Runner, Gate Area

= (0.3/1.3) X C 0.3/1.3 Factor for OF of Runner & Biscuit

= D Kcal

Heat to be removed from core & cavity

Heat to be removed from core & cavity = Total Heat Removed from the Die- Heat removed from runner & gate area

Heat to be removed from core & cavity = C D

Heat to be removed from core & cavity = E Kcal

Length of cooling channel

a) 10mm dia hole of 1cm length can remove 90 Kcals at gate area= (D/90) = F mm

b) 10mm dia hole of 1cm length can remove 4.5 Kcal at cavity & core

Length of cooling hole = E/4.5

= G mmHalf for core = G/2

Half for cavity = G/2

Weight of water to be circulated

In cooling system design, it is assumed only half of the heat accumulated on die is to beremoved by the cooling system. The other half is lost by Convection & Radiation.

Therefore, Heat to be transferred by cooling system/hour

Q w = QA/2

Mass of water (M1) to be circulated/hour

M1 = Q w / [ K (Tout - Tin)]

Where K = 0.64

Tout Tin = 5 oC (approximately)

cooling sys

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