A starters guide on compression moulding and autoclave

Machinery
World
Rubber & Tyre Knowledge On-The-Go Special Supplement
http://rubbermachineryworld.com
A Starter’s
GUIDE
Vulcanizing Autoclave
Compression Moulding Press
Inside:
How To Select?

This edition features two key machinery used in the
rubber industry viz. Autoclave and Compression
Moulding.
Autoclave is a vulcanizing equipment, and the other
is the equipment used in your most common rubber
moulding technique - compression moulding. These
contents first appeared on our portal and witnessed
high traffic.
This high interest level, prompted us to publish the
details in this Knowledge On-The-Go Special
Supplement.
Our previous issue on Mixing Mills was well-received.
Thanks again to each of you - esteemed readers and
supportive advertisers.
While, the last edition was tracking the advancements
of a very popular rubber machinery, this edition is
aimed at fulfilling the curiosity of the new generation
of business leaders - who are either taking over from
their parents or those young entrepreneurs setting up
their own venture.
Hence, the theme - ‘A Starter’s Guide’.
I hope you find this special supplement different and
informative.
As always, I welcome your feedback on
rubbermachineryworld@gmail.com.
BestRegards
Prasanth Warrier
| Editor’s Note |
A Starter’s Guide
Autoclave is a
vulcanizing
equipment, and the
other is used in your
common rubber
moulding technique
viz. compression
moulding.
3
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Special Supplement - Rubber Machinery World OCT 2015|

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| COMPRESSION MOULDING |
Image: Bharaj Machineries Make Automatic Compression Moulding Press

5
COMPRESSION
MOULDING
MACHINERY
Compression moulding is the
most common moulding
technique you will notice in
the rubber industry.
The other two are transfer
moulding and injection
moulding.
Compression moulding is a
closed mould process and you
apply high pressure on the job.
It is best used when you have
low to medium production
volumes for larger parts
where tightest tolerances and
flawless finishes are not
required.
Examples may include
diaphragms, valves and
gaskets, Dampers, O-rings,
seals, rubber wear parts, etc
depending upon their areas of
application.
Prasanth Warrier

Schematic From JW Elastomer Engineering Guide
As shown in the schematic here, in
compression moulding, you place an
uncured rubber profile in a heated
mould. Then you soften the uncured
rubber by the heat and press them
forcing the rubber compound to fill
the mould cavity. The rubber is thus
made to conform to the shape of the
mould and then you cure it to
produce your finished article.
6
Santec Group Make Compression Moulding Machines inside their Plant

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Compression Moulding Press:
The machinery you will use is
called Compression Moulding
Press. These presses are mostly
hydraulically driven, where a
hydraulic pump powers a
hydraulic cylinder (or cylinders)
that drive the ram or slide.
(Caution: there are pneumatically
powered presses too).
Hence, the terms that apply to a
standard hydraulic press are
relevant here.
Hydraulic Press Terms
Stroke: The amount of possible ram travel.
Stroke is the total distance that the ram can
travel, from full extension to full retraction.
Shut Height: The distance between the bed
bolster and the ram bolster when the ram is
fully extended. This is also commonly
known as the Closed Height. As standard,
this dimension is usually within “0.25” due
to assembly processes.
Daylight: The distance between the bed
bolster and the ram bolster when the ram is
fully retracted. This is also commonly
known as the Open Height.
Bolster: The removable plate that serves as
the working surface for the bed and ram.
8
Terms & Image Taken from Beckwood Hydraulic Presses and Machinery
The plate is usually bolted to the bed and
rams substructures.
Bed Height: Bed Height is the distance from
the bottom of the hydraulic press structure
to the working height or top of the bed bolster.
Remote Power Skid: Some press applications
may require that the hydraulics be located
remotely from the press itself. Others may
preclude the power system from being able
to be installed at the top around the crown
structure of the press. In these cases, the
power system and even the controls may be
designed into a separate unit capable of being
placed adjacent to the press or away from the
press.
Heated Platens: These are plates that have
heating capabilities.

Image: A 60" Mixing Mill With Advanced Features,
Controls, and Automation from Bharaj Machineries.
Hydraulic presses are
preferred by your peers in the
industry because they give
Performance, Reliability, and
Versatility. This means you can
get full pressing force (or
tonnage) anywhere in the
range of stroke using hydraulic
press unlike a mechanical
press.
By varying the ram speed and
other operating parameters,
you can optimize cycle time for
each of your job. Further, you
could customize your bed size;
say lower tonnage on a larger
work area or higher tonnage
on a smaller area of work.
You will see that compression
moulding presses offered by
most reputed manufacturers
are vertical and the moulds
can be heated using electric
rods, steam, oil, water or other
medium.
Depending on requirement,
your moulds may be fixed to
both the platens; or part fixed
to a platen, or totally free to be
drawn out. When you have
free loose moulds, your
operators need to load and
unload them on a press table
manually. You call it charging
(loading) and stripping
(unloading) by hand.
On the other hand, the
presence of ejector pins
or strippers on fixed
mould presses will speed
up your operation.
One of the platens is
fixed in your
compression moulding
press. When the lower platen
is raised or lowered in the
vertical plane, you call it
upstroking; while in down-
stroking, the upper platen is
the driven plate (moving up
and down).
Hydraulic presses are preferred by your
peers in the industry because they give
Performance, Reliability, and Versatility.
Bharaj Machineries Make Automatic Vacuum Type
Compression Moulding Press10

How will you decide (select)?
Apart from safety and ease of
operations, your final choice
of a compression moulding
press depends on these six
important considerations:
1. Calculation of the proper
amount of rubber for your
product.
2. Calculating the minimum
amount of energy required
to heat your rubber.
3. Calculating the minimum
time required to heat your
rubber.
4. Identifying the appropriate
heating technique.
5. Predicting the required
force, to ensure that stroke
attains the proper shape for
your rubber.
6. Designing the mould for
rapid cooling after the
rubber has been compressed
into the mould.
You try to optimize the Time,
Temperature and Pressure
– the three critical
parameters for your
moulding process.
Manufacturers compete to
offer your robust hydraulic
presses with superior drives
and controls, advanced levels
of hydraulics and
instrumentation features.
A Reconditioned Press
By Pelmar Engineering
Your final choice of a compression
moulding press depends on these six
important considerations.
12
Santec Group Make Compression Moulding Press

Advantages and Disadvantages
of Compression Moulding
Process
The advantages of compression
rubber moulding are lower cost
of your moulds, the large sizes of
mouldings possible, and the
relatively quick changeover
between different moulds
helping you expedite shorter
production runs.
Additionally, there are no tooling
features like gates, spruces or
runners that could increase the
time for your mould to enter the
cavity or potentially affect the
aesthetics of your product.
The main disadvantage is your
output when loaded and
unloaded manually. This
increases your cost on skilled
labour.
There is product wastage too
as compression moulding is
not precise like injection
rubber moulding. Since
thermal conductivity of
rubber is poor and you
often place your profile
into the cavity ‘cold’,
your cure times are
longer.
Additional difficulties
you face will be from
positioning the blank
properly in the cavity
and the difficulty to
control the ‘flash’
that results from the
additional material
placed in the cavity.
Unsuitable for complex
moulding, compared to a
transfer moulding or
injection moulding, your
product contamination is also
higher in compression
moulding.
Summarizing, compression
moulding is the most
common moulding technique
that you will find in rubber
industry and the common
machinery for this process is
the a hydraulic compression
moulding press.
Presses Inside A Plant of Elastomer Engineering Ltd UK
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14
| AUTOCLAVE |
VULCANIZING AUTOCLAVE
You use an Autoclave or Vulcanizer
(Vulcanizing autoclave) to convert natural
rubber into a cured and chemically
cross-linked rubber product. A vulcanized
rubber is less sticky and gives you
superior mechanical properties.
Rubber Vulcanization (a term coined by
Thomas Hancock) “process” was
discovered accidentally by Charles
Goodyear in 1839.
If you are curious about history, this is
how it goes – Charles Goodyear left a piece
of natural rubber mixed with sulphur on a
hotplate one evening. Overnight, it turned
into elastic rubber and that caught his
attention! Since sulphur and heat were
associated with the ancient Roman god
Vulcan, the process was named
vulcanization (or vulcanisation).
Your friends in rubber industry use
autoclaves to cure tires, hoses, and many
other products but not limited to
vulcanization and forming of extrudates
(like car radiator hoses), rubber mats,
sleeves, joints, gaskets and boots. Typically
these are products that you cannot achieve
on a standard press-based compression
moulding process.
Depending on the type of your rubber, the
vulcanizing process can occur from room
temperature (as in Silicone) up to 350°F
(170°C) or more like in case of Tire.
Image: Bondtech Autoclave
Prasanth Warrier

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| AUTOCLAVE |
The Machinery
Autoclaves are predominantly cylindrical
pressure vessels with lids or doors to
process your rubber parts that require
exposure to elevated pressure and
temperature. They are available in a wide
range of sizes and design pressures in
horizontal (or sometimes vertical)
configuration.
The key component of your autoclave is
the door. For a manufacturer, this is also
the critical component in cost of autoclave
construction. On one hand, your operator
must be able to open and close the door
quickly and easily; on the other, the door
must satisfy stringent safety requirements
of manufacturing and usage.
Let me explain.
Rubber vulcanizing is a batch process. Your
autoclave door must be of full diameter to
allow easy access to the chamber inside. So
you need a fast-acting door to reduce batch
change time and increase productivity.
Depending on the size of your autoclave
and manufacturer’s offered features, there
are several types of fast-opening doors.
An autoclave design is driven by various
safety standards, primary among them
being the ASME Pressure Vessel Code.
Autoclave Image From Web
Tyre Vulcanizing in Autoclaves (Web)
Rubber vulcanizing is a batch
process. Your autoclave door
must be of full diameter to
allow easy access to the
chamber inside.
16

| AUTOCLAVE |
Of all safety-related concerns, the most
critical are those which relate to the door’s
operation. The manufacturer of your
autoclave should ensure that the door seals
tightly against rated pressure at the highest
shell temperature; operate readily and
quickly and meets all safety guidelines of a
pressure vessel.
Regular testing is a must along with fool
proof interlock mechanisms to prevent
door opening under pressure.
Leading manufacturers deploy Solid-
Modelling and Finite Element Analysis
(FEA) to design and validate autoclave
pressure vessels and quick-opening doors.
CE Standard in Europe applies to vessels as
well as to electrical controls.
The process medium in autoclaves may be
steam, a combination of steam and air or
inert gas, “Dry Heat” produced by electrical
heaters, steam or hot oil autoclave jackets,
or circulating hot gases. Despite electric
heat being 100 per cent efficient, most
precise to control, and lowest maintenance;
the cost per kilowatt-hour makes them
expensive for your use.
And because rubber vulcanizing cannot be
done in an air atmosphere, you mostly use
steam.
Two types of autoclaves are in common use
– Non-jacketed and Jacketed.
In the non-jacketed type, steam is
introduced directly into the autoclave
chamber. The steam condenses on the walls
of your autoclave and on the surface of your
rubber products under vulcanization.
However, this leaves behind a mark on the
surface of your product.
And when you adopt preventive measures,
you end up getting a dull finish on your
rubber products. For some products like
Radiator hoses for cars, you can cure in open
steam.
Inside View of an Autoclave
Your manufacturer should
ensure that the door seals
tightly against rated pressure at
the highest shell temperature;
operate readily and quickly and
meets all safety guidelines of a
pressure vessel.
18

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(MFRS. OF RUBBER INDUSTRIAL MACHINERY)
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Phone Off: +91- 481-2430325. Fax: +91- 481-2430596
e-mail: km1912@gmail.com

20
| AUTOCLAVE |
The jacketed autoclaves has a double wall.
Steam is circulated in the jacket to provide
heating. There is no direct contact of
steam with your rubber products. An
inert gas (like Nitrogen) is then introduced
in the autoclave to eliminate oxidation.
(Oxidation aids polymer degradation and
hence you need to eliminate them).
Gases are normally poor conductors of
heat and thus increases the curing time.
You may also come across this process
referred to as “gas curing” by technologists.
Additionally, if you have brightly colored
articles, the jacketed autoclave lends a
good surface finish on your rubber product.
The vulcanizing process in an autoclave is
a function of temperature and time.
Traditionally, in most applications there is
no indication of when your cure is
complete. For this reason, to ensure that all
components in the autoclave have been
universally cured, your process cycle times
are usually longer than is necessary.
Modern autoclaves come with PLC
controlled systems and offer extended
features including variable temperatures,
pressures, cycle times, cycle and system
alarms, multiple cycle recipe storage and
selection.
Operator Consoles with HMI provide an
operator friendly interface with touch
screens, for cycle parameter entry, cycle/
system/alarm status monitoring, operating
and diagnostic messages.
Separate Images of Controls and HMI Screen (Inset) from different sources
on web (Only for representation purpose).

| AUTOCLAVE |
When you invite offers to purchase an
autoclave, you should not be surprised if
price variations confuses you or you are
unable to comprehend immediately – be
it prices among manufacturers and
between features.
Price is sensitive to some factor and
insensitive to others.
For eg:, doubling the design pressure
might increase the cost of the autoclave
by over fifty percent. And doubling the
diameter might more than double your
purchase price. On the other hand, you
may find that increases in length are
inexpensive (relatively).
So, your purchase price varies as a
function of what has been designed and
built into your proposed autoclave.
Options of features offered by your suppliers
has to be carefully decided so as to optimize
your overall investment.
Operation Cycle
Your typical cycle of autoclave curing has the
following steps.
The autoclave is loaded with your rubber
component, and the connections are made
to the autoclave. The door is closed and
locked. Pressure is applied until the required
level is attained. The circulation fan starts.
Heating begins and is maintained at a
specified ramp up rate. Once the required
Price is sensitive to some factor
and insensitive to others.
21

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| AUTOCLAVE |
temperature is reached, a timed soak
at that temperature begins and runs for
the necessary duration. At the end of
the soak period, the cooling function
brings the temperature down to a set
value at a specified ramp rate. The
vessel is depressurized and the
circulation stopped.
Steam curing requires a great deal of
manual work from one processing
stage to the other, and this also
contributes to the high cost of your
autoclave cured products.
RMW
Hence, some of your new generation
peers advocate the more advanced
microwave process.
Summarizing autoclaves are pressure
vessels for rubber product
vulcanization, available in a wide
range of sizes. A discontinuous curing
method, the curing of your rubber
component takes place in a vessel
(autoclave) where pressurized steam
is the medium of heating.
22

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A starters guide on compression moulding and autoclave

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