For more technical information:
North American Die Casting Association ~ www.diecasting.org
Frequently
Asked Questions
If you have any questions, please ask by filling out this online form.
You can expect an answer within 48 hours. Questions of general interest
will be added to our list for all to see. Check back often for new information.
1: From
what material should hot chamber zinc die casting nozzles and noses be made?
2: What material is recommended for plunger rods?
3: Why do my nozzles wash out?
4: What are the differences between tool steel and cast iron plungers?
5: How much clearance is required between the plunger and the gooseneck
in a conventional hot chamber zinc machine?
6: Are there standard shot-end parts for my machine?
7: How can we recondition the sealing surfaces of our nozzles?
8: What are the various methods of supplying water to the plunger
tip in a cold chamber shot end?
9: How can I minimize the cost of re-sleeving my gooseneck?
1:
From what material should hot chamber zinc die casting nozzles and noses be
made?
The material that is most widely specified is H-13. This is the same
material that is used for most cavity blocks and inserts. Its chemical
composition resists washout, and its mechanical properties withstand
the severe compressive loads associated with zinc die casting.
Top
2: What material is recommended for plunger rods?
Plunger rods for cold chamber machines are produced from AISI 4150
HT. This material possesses high mechanical strength, good toughness
characteristics, and can be machined in its pre-hardened condition
(28-32 Rc). Due to the high mechanical loads associated with cold chamber
die casting, use of a lesser quality material results in unsatisfactory
plunger rod life.
Top
3: Why do my nozzles wash out?
The primary cause for nozzle washout is excessive nozzle temperature.
While the casting temperature of zinc alloy is usually 800 degrees
F, nozzles are often heated in excess of 1000 degrees F. This excessive
temperature is the primary cause for nozzle washout. Other contributing
factors are the type of alloy being cast, and high aluminum content.
Top
4: What are the differences between tool steel
and cast iron plungers?
Plungers for zinc die casting are commonly produced in either cast
iron, or tool steel (H-13). Cast iron plungers can be produced in a
near net shape, reducing the amount of machining required to produce
a functional part. However, they are susceptible to mechanical failure
due to the nature of the casting.
Tool steel plungers are produced from bar stock, and require extensive
machining to produce a comparable finished part. The mechanical properties
of the tool steel plunger are far superior to those of cast iron, which
usually justifies the increased cost. Heat treating can increase the
durability of the part even further.
Top
5: How much clearance is required between the
plunger and the gooseneck in a conventional hot chamber zinc machine?
The general rule for clearance between the plunger and the gooseneck
sleeve for a conventional hot chamber zinc machine is .002" per
inch of plunger diameter.
For example, a 2-1/2" plunger would have .002" x 2-1/2 or .005" clearance.
This clearance allows the plunger to move freely in the sleeve, while the
rings seal the plunger and provide the necessary injection pressure.
Top
6: Are there standard shot-end parts for my machine?
While there are standard items for the shot-ends of various casting
machines, most die casters benefit from customizing the shot-end tooling
to the particular job they are running. In many cases, shot-end tooling
is an extension of the gating system, and will have a definite impact
on die performance.
Top
7: How can we recondition the sealing surfaces
of our nozzles?
The refacing of nozzles is done in a lathe. The best method is to
use a single point tool, sweeping it through an arc to produce the
proper radius. (See
photo) Form tools can be used, but are susceptible to chatter.
It is crucial to have a good surface finish to ensure a good seal.
Another important point to consider when resurfacing nozzles is that
although the outside of the nozzle may look fine, the nozzle may be
washing out from the inside. Remove nozzles from the machine while
still hot, and drain any zinc from the nozzle. This will allow inspection
of the inside of the nozzle for any washout that may have occurred. (See
photo)
Brach Machine can reface nozzles for you at a fraction of the
cost of a new nozzle. We inspect the I.D. and mark each piece, in order
to track how many times a nozzle has been in service. Please call for
details.
Top
8: What are the various methods of supplying
water to the plunger tip in a cold chamber shot end?
There are several methods of supplying water to the plunger tip. Most
shot rods have a center hole drilled through them, allowing the insertion
of a baffle tube. Water flows into the plunger tip through the tube,
cools the plunger tip, and flows out in the area between the tube and
center hole. This tube is usually made from thin wall brass or stainless
steel.
With some of the newer high velocity shot-ends, customers have experienced
problems with this type of baffle tube breaking off or loosening. This
problem can be overcome by drilling two separate holes in the shot
rod. These holes act as independent channels for cooling water, and
have no separate parts that can come loose while in use. (See
example)
Top
9: How can I minimize the cost of re-sleeving
my gooseneck?
Removing any nozzles, heaters, thermocouples, and excess zinc before
you ship the gooseneck will reduce additional charges. These parts
are much easier to remove while the gooseneck is in the machine and
up to operating temperature.
In addition, it is important for the customer to evaluate the condition
of the gooseneck before it is shipped to us. If the gooseneck cannot
be re-sleeved, a minimum fee for "de-zincing", inspection,
and return freight (if applicable) will be charged.
|
