Rubber deflashing

In most cases deflashing is a necessary step in the manufacture of molded rubber, whether by:
Injection
Compression
Transfer

1. Rubber Deflashing -What It Is and
Why It's Applied
Luis Tormento
LT Quimicos
09/10/2012

2. What is Flash?
Flash is the result of the overflow of rubber
compounds out of the molding area.
This overflow is undesirable and should be
removed

3. Deflashing
In most cases deflashing is a necessary step
in the manufacture of molded rubber, whether
by:
Injection
Compression
Transfer

4. Deflashing

5. Deflashing
Ifoverflowiscontrolled/plannedornot,itis
undesirableandshouldberemoved.
Themanualwithdrawalistimeconsumingand
tedious.
Machiningprocesses,despitebeingautomated,
areloadedmanuallyandaretimeconsuming.

6. Flashes
In order to obtain better appearance and
technical quality, we must use appropriate
techniques to:
Decrease flash generation
Decrease size and thickness of flashes

7. Flashes
Techniques to reduce flash
generation

8. How to reduce flash -Process
In molding we must control four basic
categories:
Temperature
Pressure
Time
Distance
Temperature
Pressure
Time
Distance

9. How to reduce flash -Process
Temperature
Melt point control
The flow of material in the mold includes its path
from the feeder to the mold cavity.
Generally the material is heated and then flows
into the molding cavities
Mold temperature control
Variations in mold temperature are responsible for
greater or lesser contraction

10. How to reduce flash -Process
Pressure
Initial pressure
Applied to the fused compound, it is responsible for
filling the cavity and forms the artifact
Final pressure (lift)
Used to fill the final mold and maintain the shape until
the final solidification (vulcanization) of the artifact.
Return pressure

11. How to reduce flash -Process
Time
The time required to cast an artifact is the sum
total of:
Mold closure
Flow of the compound into the cavity
Opening to eliminate voids and occluded air
Vulcanization until reaching T90
Opening
Demoulding

12. How to reduce flash -Process
Distance
Importance
Distance control is critical in the production of high
quality products because long distances mean long
cycles of curing (curing)
Mold closure distance
The initial closing speed is very fast.
The final closing speed (1 cm) is very slow
Mold opening distance
The mold opens slowly (1/4 ") to break the vacuum
formed in the molding.

13. How to reduce flash
Molding

14. How to reduce flash –Molding
The molding step has a great influence on
the generation of flashes.
Molds that do not follow an RMA molding pattern
tend to generate a greater amount of flassh.
Equipment with pressure and temperature
deficiencies also tend to generate more flashes.

15. How to reduce flash -Molding
Molding Processes
Compression Molding
Transfer Molding
Injection Molding

16. How to reduce flash -Molding
Compression Molding
Most of the presses used in compression molding are hydraulic presses of
ascending lower plateau;
In these, a hydraulic cylinder is housed in a bench or in the lower part of the
press;
The piston, by means of hydraulic pressure, rises until it is compressed on
the upper plateau, fixed in the upper part of the press.
To open the press simply close the inlet of hydraulic fluid and open the
outlet, this fact that dislodges the liquid of the cylinder for the descent by
gravity of the piston and lower plateau;
Auxiliary systems, mechanical or hydraulic, are often used to accelerate the
opening and improve the productivity of the installation.

17. How to reduce flash -Molding
Compression Molding
Presses used in compression molding

18. How to reduce flash -Molding
We highlight the different heating systems of
the plateaus:
Steam -the plates have zig-zag channels for steam circulation; The system has a
set of traps for the elimination of condensed steam. To regulate the volume of
steam it is recommended to use pressure switches, which ensure the consistency
and precision required to maintain the vulcanization temperature.
Thermofluids -fluids are liquids that withstand temperatures of up to 200 °C or
more, without boiling or suffering appreciable thermal degradation, for prolonged
periods; Circulate on the plateaus instead of the steam; The capacitors are
removed and work at low pressures, which simplifies the sealing problem. As the
thermofluid is kept in circulation in a closed circuit, generally of little extent,
temperature control is easier.

19. How to reduce flash -Molding
We highlight the different heating systems of
the plateaus:
Electrical -the system is clean and simple, but usually presents problems of
temperature uniformity over the surface of the plateau and oscillations over time;
with electronic pulse control systems, frequency and duration between the actual
and theoretical temperature, it is possible to reduce these oscillations. Recently a
heating system was started by heating plateaus by induction, obtaining a faster
heating and better regulation and uniformity of the temperature.

20. How to reduce flash -Molding
Compression molding is not very different from the
manufacture of a cookie or waffle. A given quantity of
material must be placed in a cavity, ensuring that it is
filled. Heat and pressure are applied by taking the
compound to flow, filling the cavity and shaping the part;
The surplus material flows out through flow channels
(burrs).
Compression molding is generally chosen for medium
hardness compounds in high volume applications or
applications that particularly use very expensive
materials.

21. How to reduce flash -Molding
The excess, or flash, created by pieces of large
diameter, is of particular interest when using more
expensive compounds. Compression molding helps to
reduce this excess.
The range of application ranges from simple O-rings to
belts and complex diaphragms with a diameter greater
than 254.0 mm.
The flash in a typical compression molded part has a
maximum of 0.102 x 0.254 mm at 0.127 x 0.813 mm,
depending on the deflashing method.

22. How to reduce flash -Molding
CompressionMolding

23. How to reduce flash -Molding
Transfer Molding
Transfer molding differs from compression molding; In the latter,
the material is placed in a receptacle, located between the upper
part of the mold and a piston. The material slides into the cavity
through one or more holes called "door" or "passageway".
The flash in a small mold or O-ring will be at most 0.127 mm
thick, extending to approximately 0.076 mm on the surface of the
part.

24. How to reduce flash -Molding
Transfer Molding

25. How to reduce flash -Molding
Injection Molding
Injection molding is the most automated of the molding
processes. The material is heated to an easy flow
state; is injected under pressure from the heated
chamber through a series of holes or "ports" in the
mold.
Injection molding is ideal for high production volumes
of relatively simple configuration rubber parts.

26. How to reduce flash -Molding
Injection Molding
There are two types of injection presses:
Plastification and injection by spindle, and
Plastification by spindle and injection by piston.

27. How to reduce flash -Molding
Injection Molding

28. How to reduce flash -Molding
Degassing
The removal of gases (air entrapped) generates
flashes that are removed by various methods:
manual extraction, cryogenic grinding or sanding.
It is advisable to maintain a good tolerance in
mold closure to reduce your losses to a minimum.

29. How to reduce flash -Mold
Desgassing
As tolerance for these degassers it is suggested:
Material hardness Depression or typical projection
from the surface
Lessthan50 0.381mm
50 ormore 0.178mm

30. How to reduce flash -Mold
Feeding
Thenumber,sizeandlocationoffeederholes
varygreatly,dependingonthemoldingprocess,
materialhardness,dimensionaltolerances,
cosmeticconsiderationsandothercustomer
requirements.
Thecorrectmaterialentrydesignisadecisive
factorinthereductionofscrapintheprocess

31. How to reduce flash -Mold
Feeding
Here are the five most common mold feeding
processes:

32. How to reduce flash -Mold
Corners
Twokeypointsshouldbeconsideredwhen
designingcorners:
Thecornershouldberoundedtofacilitateremovalofthe
tooling
Wheneverpossible,themoldshouldopenboth
horizontallyandvertically.
Thus,whentheoperatorremovesthepartfrom
themold,itwillseparatethecentralpartandthe
piecewillslipaway,thusavoidingtearinglosses.

33. How to reduce flash -Mold
Corners
The figure below shows an example of this type of
mold.

34. How to reduce flash -Mold
Holes
Alwaystrytousethebasicruleof2:1,ie:the
heightoftheholeshouldnotbemorethantwice
thediameter,thusreducingthepressurerequired
toremovethematerialfromthemold.

35. How to reduce flash -Mold
Durability of molds / dies
As far as possible, we must always use "clean" or
low dirt materials on the mold; this is relevant
because in the injection molding processes the
cleaning of the molds is very complicated and
may require hours for its completion.
As far as possible, use polymers of controlled
viscosity, avoiding the use of process aids or even
release agents (a mold surface finish is
necessary).

36. How to reduce flash -Mold
Durability of molds / dies
Additionalcareshouldbetakenwiththeuseofperoxides,as
theyreleaseproductsthatcauseoxidationofthemolds;forthese
applicationsitisrecommendedtousechromedorstainlesssteel
finish.
Takecareofthecleaningofthemolds:veryabrasivecleaners
willwearoutthemoldanddeformthedimensionsgenerating
moreflashes.
Sandblastingwasbannedin1999,asitcausessilicosis.
Currentlyplasticmediaareusedforthisprocess.Ideally,the
moldwilllastfor100,000times.

37. How to remove flashes
After we have taken all the care in process
control, compounds and molds to reduce
flashes, we will now explain the processes of
removal of them:

38. How to remove flashes
Deflashing

39. Deflashing
Several processes and methods are used in
the deflashing of rubber artifacts:
Manually
Drilling
Cutting
Milling
Cryogenics

40. How to remove flashes
ManualDeflashing-Deflashingwasinitiallya
manualoperation.Dozensofworkers,seated
intinyworkstations,pickedupthepiecesone
byoneandremovedtheexcessrubber(burr)
withknives,scissorsandspecialdevices.
Eventoday,someartifactsneedtobe
deflashedinthisway,duetotheircomplexity
andsize.

41. How to remove flashes

42. How to remove flashes
We can say that manual deflashing has
several drawbacks:
The quality of manual finishing is unstable
Manual deflashing is a slow and time-consuming
process,
Due to the extensive use of labor it is gradually
becoming a costly process.

43. How to remove flashes
Other manual deburring processes include:
Drilling
Machining
Sanding
Cleaning

44. How to remove flashes

45. How to remove flashes
Manual Process uses a series of techniques
and instruments:

46. How to remove flashes
Vibrators and Rotating Chambers
The first cryogenic machines were vibrators and
rotating chambers. (Model 300)
In these machines, the artifact is frozen by means of
liquid nitrogen until reaching its glass transition
temperature. The machine has the internal hexagonal
shape and the hardened flash is removed by impact
between the frozen parts or by means of some type of
media.
Plastic or ceramic media are generally used to assist in
impact and break flash.

47. How to remove flashes
Vibrators and Rotating Chambers
Theyarelimited:theyareefficientwhentheartifactmust
bedeflashedexternally;areoflowefficiencyforinternal
deflashing.
Currentlythevibratorsandrotatingchambersare
efficientinthedeflashingofseveralartifacts;inother
artifacts,serveasapre-treatmentforfinishingthemost
efficientcryogenicequipment-oneoftheseequipment
istherotatingblastingbasket(Polyblaster2.0).

48. How to remove flashes
Polyblast modelo 300

49. How to remove flashes
Shotblasting Equipment (Polyblaster 2.0)
A large increase in the productivity of the
deflashing came with the development of basket-
type equipment by blasting media.
In this equipment the artifacts are frozen in a
basket with a volume of 28 to 112 liters. This
basket is positioned in a thermally insulated
chamber after reaching the desired temperature
(according to the type of elastomer).

50. How to remove flashes
Shotblasting Equipment (Polyblaster 2.0)
The basket rotates and on the artifact is injected
plastic media to break the flash; This flash falls
along with the media to a set of sieves that makes
removal of the flash and broken media.
The media returns to a container and, via
compressed air, returns to the deflashing
chamber.
After the preset time the artifact is free of flashes
and ready for use.

51. How to remove flashes
Polyblaster 2.0

52. How to remove flashes

53. How to remove flashes

54. How to remove flashes
There are only four basic controls on these
machines:
Temperature
Injection Wheel Speed
Basket speed
Cycle time

55. How to remove flashes
Thesemediaarepolycarbonate,especially
compositetowithstandimpactat-184°C.
(Forexample,siliconedeflashing)
Thesepolycarbonatemediaarecylindricalin
shape.
Ithasalreadybeenproventhattheshapeof
themediahaslittleeffectonthedeflashing
process,butthecylindricalshapeisthe
easiesttohandle.

56. How to remove flashes
The temperature needed to crystallize the
flash varies from compound to compound.
Important factor in the productivity of this
process is to determine the ideal temperature
(Tg) for each compound; With this it is
possible to better deflashing and saving of
nitrogen.

57. How to remove flashes
Reference Temperatures:
Denominação Temperatura do Ponto
de Rigidez ºC
Faixa de
Temperatura de
Rebarbação ºC
Etileno-Propileno (EPDM, EPT, EPR) -68 -70 a -96
Borracha de Cloropreno (Neoprene) -46 -60 a -70
Butadieno Acrilonitrila (Buna -NBR) -46 -50 a -70
Epicloridrina (Hydrin, ECO) -34 -43
Poliuretano (Millathane) -29 -45
Fluopolímero (FPM) -37 -51
Poliacrilato (Vamac) -51 -60 a -80
Polietileno Clorosulfonado (Hypalon) -51 -62 a -70
Silicone -85 -87 a -118
Fluorsilicone -68 -68
Fluorelastômero -29 -29
Borracha de polibutadieno -73 -80 a -100
Borracha Natural -60 -70 a -100
Borracha de Isopreno (Poliisopreno) -59 -70 a -90
Borracha butílica (IIR) -59 -70 a -90
Borracha de Estireno Butadieno (Buna-S, SBR) -59 -80 a -100

58. Thank you
Luis A. Tormento
LT Químicos
[email protected]
Tel: [phone]