The document provides an overview of compression molding processes for thermosetting plastics. It discusses how compression molding uses a heated press to mold thermosetting compounds into shape. It also describes transfer molding as a similar process using either a pot or plunger to force the compound into a mold. The document outlines several types of transfer molding and their advantages.

1. Processing Chapter 3
Compression Molding

2. Introduction
• In 1907 Dr. Leo Baekeland achieved a reaction
between Phenol, a caustic, crystalline acidic
compound and Formaldehyde, a colorless,
pungent gas, by heating these ingredients
under pressure in a reaction kettle.
• The resultant, hot liquid when cooled, became
a hard brittle solid. It lacked physical strength,
but possessed excellent thermal, chemical and
electrical insulating properties

3. Introduction
• The hard brittle resin in a pulverized from
could be mixed with fillers, reinforcement,
colorants, lubricants and catalyst. The end
product was a molding compound capable
of further processing on heated mills and
calendar mills.
• Thus the first thermosetting molding
compound was created.

4. Introduction
• In the following years additional thermoset
resin systems were developed to meet the
requirements of diverse applications in
automotive, communications,
construction, transportation, household
appliances, business machines, aircraft
and aerospace fields.

5. Thermoset Definition:
• A polymeric material which can be
formed by the application of heat and
pressure, but as a result of chemical
reaction permanently crosslinks and
cannot be reformed upon further
application of heat
– Chemical crosslinking must occur for the
resultant product to be called a thermoset.
– Monomeric precursors may or may not be
polymeric

6. Thermoset Families
– Allyls
– Aminos
– Epoxies
– Phenolics
– Polyesters
– Polyurethanes
– Silicones
– Crossed linked thermoplastics

7. Classifications
• General Purpose – Average mechanical
properties, lower resistance to heat, higher
coefficient of expansion, low cost and
commodity production.(Phenolics, Aminos and
polyesters)
• Engineering – Higher mechanical properties
and temperature resistance and more durable.
More expensive with moderate production
rates. (Epoxies and Polyurethanes)

8. Classifications
• Specialty – one or more highly specific
and unusual properties. Very expensive
and produced in small quantities.
(Silicones, Allyls, Crossedlinked
Thermoplastics)

9. General Properties
– Thermal and dimensional stability
– Electrical insulation
– Chemical resistance
– High flexural modulus
– Toughness
– Surface hardness
– Moldablilty
– Cost effectiveness

10. Phenolics

11. Introduction
• First thermosetting plastic, first synthetic
commercially available plastic resin
• Produced by chemical reaction between
phenol (resin) and formaldehyde (curing
agent)
• First made by Dr. Leo Baekeland in 1907
• By far the most widely used of all
thermosets for molding applications

12. Chemistry
– Phenol – Formaldehyde resins are general
purpose thermosets formed mainly by the
polycondensation reaction between phenol
and formaldehyde
– Resole process, other main process is
Novalac
– Raw Materials
• Phenol
– Show phenol structure
• Formaldehyde
– Show formaldehyde structure

13. Phenol
• Cumene process for making phenol

14. Formaldehyde
• Formaldehyde is produced by the
controlled catalytic oxidation of methanol

15. Phenolic Reaction
• Phenolic resin reaction process

16. Phenolic curing process
• The curing process to the final thermoset
material can be initiated by just heating the
resin in a mold above its gel temperature
• When heated, the resin forms larger
molecules without the use of additional
catalyst
• The reaction is a typical polycondensation,
since water is given off as a by product

17. Phenolic curing process

18. Processes that use Phenolics
• Compression Molding
• Transfer molding
• Injection Molding

19. Properties of Phenolics
• Physical
• Excellent dimensional stability
• Low water absorption
• High surface hardness
• High creep resistance
• Mechanical
• High compressive strength
• High modulus, stiffness

20. Properties of Phenolics
• Thermal
• Phenolics retain a high percentage of properties
at elevated temperatures
• Low coefficient of thermal expansion
• Good heat resistance

21. Properties of Phenolics
• Electrical
• Good electrical resistance
• Chemical
• Good chemical resistance
• Other
• Good weather resistance
• Easily molded
• Good machining properties

22. Applications for Phenolics
• Appliances 17%
• Closures 7%
• Electrical 38%
• Housewares 23%
• Industrial 4%
• Transportation 11%

23. Molding and Molding
Techniques

24. Introduction
• There are three fundamental molding
processes for thermoset compounds.
– Compression molding
– Transfer molding
– Injection molding
• The process used will be determined by
which process can produce the part to
appropriate specifications at the most
economical rate

25. Production Methods and
Equipment
• The choice of methods and equipment
for use in the production of thermosetting
molding compounds is usually
determined by the type of reinforcement
being used
• Reinforcements are added to thermosets
to improve properties. Impact, flexural
strengths, shrinkage, etc.

26. Compression Molding
• Introduction
– Uses a hydraulically operated press
– Press consists of two heated mold platens, one
stationary and one movable
– Platens have either “T” slots or tapped holes to fix
the mold halves to the platens
– Tie Rods, usually 4, provide for precise alignment
as the press is opened and closed
– The press open and shut height and the platen
temperature are controlled.

28. Compression Molding
• Compression presses are rated by their
closing force capacities
• Can be manual, semiautomatic or fully
automatic
• Preform temperature, molding temperature,
molding pressure, molding time and cooling
time are the most important design
parameters
– Cavity depth is very important to achieve the proper
molded density

30. Transfer Molding
• Similar to compression molding
• Four basic types
– Pot type transfer molding – old technology
– Plunger transfer molding
– Automatic Transfer molding
– Screw transfer molding

31. Pot Type Transfer Molding
• Mold design provides a “pot” into which the
compound, heated or unheated, is placed and
the press closed
• The clamping pressure exerted by the press
also forces the compound from the pot into a
runner system, then into the cavity
• Was innovative, providing an improved means
for certain parts and producing less flash at the
parting line

33. Pot Type Transfer Molding
• Also made it possible to feed the molding
compound for a single location
• Produced a lot of waste due to pot
volume being 15% higher than the
runner and cavities volume, to overcome
the pressure needed to force material to
the runners and cavities

34. Plunger Transfer Molding
• Developed in early 1940’s to overcome
difficulties/expenses of the pot type
• A hydraulic cylinder is mounted on the top
platen of a standard compression press. It’s
the plunger
• The clamping pressure is used to keep the
mold totally closed while the top cylinder
provides the pressure required to force the
compound into the runner system and cavity

36. Automatic Transfer Molding
• An attempt to integrate perform and
preheat as a function of press operations
• An overhead performer capable of
feeding a precise weight of perform
feeds a dielectric preheater directly
below
• The preheater feeds the compound to
the plunger

37. Automatic Transfer Molding
• The plunger feeds the mold
• Completely automatic, but confined to
the use of free flowing granular materials
• They have been slightly redesigned for
other materials

38. Screw Transfer Molding
• Uses an extruder to supply a precise
weight, temperature and density, shot,
that feeds into the mold on a completely
automatic basis

39. Screw Transfer Molding