Tekcast Spincasting

From: Mnr. D de Beer (DDEBEER@eng.tofs.ac.za)
Date: Mon Sep 30 1996 - 18:11:07 EEST


Terry, I will try to answer your questions:

Deon de Beer,

I read with interest your response to Yakov Horenstein's question "How efficient
is the TekCast spin-casting system for creating good metal parts from RP
masters?"

>From your response, it sounds like you have considerable experience
with RP and
TekCast. I am in search of a fast method of creating compression molds for shoe
soles. Do you feel that TekCast would be a good approach? If it's not much
trouble, could you please step through the TekCast process? What's a typical
cycle time?

I am not completely sure what the process concerning compression
molds for shoe soles entail, (for example the pressures involved),
but by judging the characteritics of spin-casting zinc alloys, I
assume that it will be a good option.

Here are some of the characteristics:

Impact strength: 43 ft-lb
Hardness (bhn): 120
Ulitimate Tensile Strength: 50 ksi

Spincasting through Tekcast's frontloading system involves six
easy steps:

1. Preparing the mold:

That is the physical making of the mold with
uncured silicon. This is allmost like playing with modelling clay,
except that you have to create split-lines, possible pull-out cores
etc. Through knowledge of planning or designing a mold, as well
as basic hand skills fairly complex molds (for instance the body of a
.38 police revolver) can be manufactured.(when our wek page is
running again I will post examples of these)

2. Vulcanization of the mold:

This is to cure the silicone rubber and
is done in a vulcanizing frame, where pressure and heat is applied
according to the volume of the mold. An index on the vulcanizer
inicates the time required per mold diameter and thickness. During
this phase the mold needs to be "bumped" to get rid of air trapped in
the rubber.

3. Gating and venting:

Gates and vents are cut by hand, using a
surgical knife. A centre-sprue is molded from which the runners and
gates are cut. With a little knowledge of physics (inertia of moving
particles, together with centrifugal forces) proper cavity lay-out,
in-gate positions and vents can be determined. (we are thinking of
starting a project which will do a numerical analysis of a mold,
before actually making the mold)

4. Placing the mold in the spin-caster.

The mold is clamped at a pre-set pressure (very important in the
limitation of shrinkage), rotated (again speed and direction will
be dependant of the mold size, shape of cavity and very
important, the density of the medium)

5. Pouring and spin-casting:

The spincaster will give an indication when the pre-set speed is
achieved, and now the pouring (by hand-ladle or with an automatic
dispenser) takes place. NB. This is done under pressure

6. Removal of the parts:

After solidification, parts are quickly removed from the mold.

With metal, 50-60 cycles per hour can be obtained. With plastics,
only 10-15 per hour is realistic.

In taking the full process into account: It is possible to make a
mold and start casting within one day, which is fairly unique for any
casting/reproduction system.

I hope this answers your questions Terry, but I will gladly address
any others that you may have. I have a full-colour broshure
available, which I will send to you if necessary.

Regards

Deon

Thank you, in advance, for your help. Let me know if there is anything I can do
for you in return.

Warm regards,

Terry Wohlers

Wohlers Associates, Inc.
OakRidge Business Park
1511 River Oak Drive
Fort Collins, CO 80525 USA
(970) 225-0086
Fax (970) 225-2027
twohlers@cis.compuserve.com
http://lamar.colostate.edu/~wohlers

*******************************************
* Deon de Beer *
* Department of Mechanical Engineering *
* Technikon Free State *
* PBag X20539 *
* Bloemfontein *
* 9300 *
* South Africa *
* *
* fax 27 51 4073199 *
*******************************************

*******************************************
* Deon de Beer *
* Department of Mechanical Engineering *
* Technikon Free State *
* PBag X20539 *
* Bloemfontein *
* 9300 *
* South Africa *
* *
* fax 27 51 4073199 *
*******************************************



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