Download Dow Blow Molding Guide PDF

TitleDow Blow Molding Guide
TagsExtrusion Polyethylene Materials Industries Building Engineering
File Size255.0 KB
Total Pages51
Table of Contents
                            Front cover
Introduction
Table of contents
	Parison problems
		Air Bubbles (See Bubbles)
		Blow-out
		Bubbles
		Clear (See Shiny or Clear)
		Cuffing (See Curling/Rolling)
		Curling/Rolling
		Curtaining
		Die Lines
		Drawdown (See Sag)
		Flash - Excessive
		Flash - Tail
		Flash - Top
		Holes
		Hooking
		Melt Fracture
		Melt Stretching (tubular)
		Melt Surface Appearance
		Needle Penetration
		Non-uniform Parison
		Output Fluctuations
		Parison Length - Head-to-head (multiple heads)
		Parison Length - Shot-to-shot (See Output Fluctuations)
		Pinch-off Thickness
		Rings - Horizontal
		Rolling (See Curling/Rolling)
		Sag
		Shiny or Clear
		Smoking
		Stretch (See Sag)
		Stringing
		Swell - High
		Swell - Low
		Tail Lengths (See Parison Length - Head-to-head)
		Webbing
	Container problems
		Alligatoring (See Melt Fracture)
		Blowing Incomplete
		Blow-outs or Holes
		Bubbles
		Cap Leakage (See Neck Finish)
		Cold Spots (See Surface Appearance)
		Container Temperature
		Definition of Detail
		Delamination
		Detail - Poor (See Definition of Detail)
		Die Lines
		Dirt or Streaks
		Drawdown (See Sag)
		Environmental Stress Crack Resistance (ESCR) - Low
		Fish Scales (See Melt Fracture)
		Flash - Excessive
		Flash - Tail
		Flash - Top
		Folds (See Curtaining)
		Gloss - Poor
		Handles - Lost
		Herringbone (See Melt Fracture)
		Holes (See Blow-outs or Holes)
		Impact Strength
		Melt Fracture
		Mold Bottom - Thick
		Mold Bottom - Thin
		Neck Finish
		Orange Peel (See Surface Appearance)
		Parting Line - Hole or slit
		Parting Line - Thinning or stretching
		Part Volume - High
		Part Volume - Low
		Part Weight
		Pinch-off
		Pits (See Surface Appearance)
		Roughness (See Surface Appearance)
		Scales (See Surface Appearance)
		Seal (See Pinch-off)
		Sharkskin (See Melt Fracture)
		Shrinkage
		Specks
		Sticking
		Streaking (See Dirt or Streaks)
		Streaking (See Die Lines)
		Striations (See Die Lines)
		Surface Appearance
		Tail Lengths
		Temperature (See Container Temperature)
		Top Load Strength
		Toughness (See Impact Strength)
		Trimming
		Unmelts
		Wall Thickness - Thin in general
		Wall Thickness - Thin at die orifice end (See Sag)
		Wall Thickness - Uneven
		Warpage
		Webbing (See Curtaining)
		Weld - Poor (See Pinch-off)
Back cover
Legal notices
                        
Document Text Contents
Page 1

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Blow molding
troubleshooting guide

1 of 51

Page 2

Blow molding troubleshooting guide

Introduction
This guide indicates possible causes and
corrective actions for problems typically
encountered in the blow molding process.
It is not, however, intended to provide a com-
plete listing of all blow molding challenges
and problems.

For additional troubleshooting information,
contact your Dow representative. In the
United States, you can also call The Dow
Customer Information Group (CIG) at
1-800-441-4369 or 989-832-1426. For
contact information in other global regions,
please refer to the back cover.

Plastics covering the extremes
and everything in between
To meet and exceed the incredible demands
placed on today’s blow molded applications,
Dow offers a product portfolio comprising
everything from industry essential resins to
innovative high performance materials.

Industry Essential Resins

UNIVAL™ High Density
Polyethylene Resins

Developed for blow molded bottles, drums,
and other industrial containers, UNIVAL™
High Density Polyethylene (HDPE) Resins
provide excellent rigidity/top-load strength,
superior environmental stress crack resistance
(ESCR), high impact and melt strength, and
moderate swell. UNIVAL resins are used to
produce containers up to 20 gallons in size
for the Dairy, Water, and Juice; Household
and Industrial Chemical (HIC); Pharmaceutical,
Cosmetic, and Toiletry; and Industrial Drum
and Container markets.

DOW™ Polypropylene Resins

DOW™ Polypropylene Resins offer an optimal
balance of price and performance, making
them an outstanding choice for inter-material
substitution in blow molding applications that
have historically used metal, glass, or other
polymers. DOW Polypropylene Resins offer
consistent processability, high heat resistance,
good clarity and gloss, low water absorption,
high stiffness/hardness, excellent moisture
barrier and chemical resistance, enhanced
mold filling and release ability, and excellent
fatigue resistance.

DOW High Density Polyethylene Resins

DOW HDPE Resins provide the toughness,
rigidity, and strength required by today’s blow
molding operations. In fact, their excellent
combination of stiffness and ESCR makes
them the materials of choice for many
personal care, HIC, and other blow molded
applications.

®™ Trademark of The Dow Chemical Company (“Dow”) or an affiliated
company of Dow

Continued on next page

2 of 51

Page 25

PROBLEM: Swell — Low swell

CAUSE(S) ACTION(S)
Low extrusion pressure/rate.

High melt temperature.

Wide die gap.

Low pre-blow air pressure or
time.

Parison diameter too small.

Insufficient resin die swell.

• Increase extrusion pressure or rate.

• Decrease melt temperature.

• Decrease container weight.

• Increase pre-blow air pressure or time.

• Change tooling to a larger die and
mandrel set.

• Modify tooling design.

PROBLEM: Swell — High swell

CAUSE(S) ACTION(S)
High extrusion pressure/rate.

Low melt temperature.

Narrow die gap.

Excessive pre-blow air
pressure or time.

Parison diameter too large.

Excessive resin die swell.

• Decrease extrusion pressure or rate.

• Increase melt temperature.

• Increase container weight.

• Decrease pre-blow air pressure or time.

• Change tooling to a smaller die and
mandrel set.

• Modify tooling design.

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Page 26

PROBLEM: Webbing

CAUSE(S) ACTION(S)
Folds in parison.

Insufficient swell.

• See Curtaining, page 11.

• See Swell – Low, page 25.

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Page 50

PROBLEM: Warpage – Warpage of container

CAUSE(S) ACTION(S)
Parison temperature too high.

Mold temperature too high.

Wall of container too thick.

Blowing air pressure too low.

Material density too low.

Poorly designed part.

Cycle time too short.

• Reduce melt temperature.

• Check mold for proper cooling.
• Increase cycle time to obtain proper mold

cooling.

• Check for proper resin distribution.
• Check tooling design.
• Center mandrel.

• Check blowing air pressure.

• Consult your Dow representative. In the U.S.,
you can also call The Dow Customer
Information Group (CIG) at 1-800-441-4369
or 989-832-1426. For contact information in
other global regions, please refer to the
back cover.

• Check material distribution in part for
unnecessarily thick or thin sections.

• Increase cycle time.

50 of 51

Page 51

Printed in U.S.A.

®™ Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
® Registered trademark of American Chemistry Council
Dow is a partner in the American Chemistry Council Responsible Care initiative.

Form No. 305-02982-0706X SMG
SMG 10968

51 of 51

For more information on the products, innovations, expertise, and other services
available from Dow’s Plastics business group in your region, please visit our web site
at www.dowplastics.com or contact us as indicated below.

Europe/Middle East +800-3694-6367

+32-3-450-2240

South Africa +800-99-5078

Asia Pacific +800-7776-7776

+60-3-7958-3392

North America

U.S. & Canada 1-800-441-4369

1-989-832-1426

Mexico +1-800-441-4369

Latin America

Argentina +54-11-4319-0100

Brazil +55-11-5188-9000

Colombia +57-1-319-2100

Mexico +52-55-5201-4700

Our belief in the principles of Responsible Care® and Sustainable Development influenced the production of this literature. To
help protect our environment, this document was printed in small quantities on paper containing recovered/post-con-
sumer fiber and using 100 percent soy-based ink whenever possible.

NOTE: The photographs of end-use applications in this document represent potential end-use applications but do not nec-
essarily represent current commercial applications, nor do they represent an endorsement by The Dow Chemical Company
of the actual products. Further, these photographs are for illustration purposes only and do not reflect either an endorse-
ment or sponsorship of any other manufacturer for a specific potential end-use product or application, or for The Dow
Chemical Company, or specific products manufactured by The Dow Chemical Company.

NOTICE: No freedom from infringement of any patent owned by Dow or others is to be inferred. Because use conditions
and applicable laws may differ from one location to another and may change with time, the Customer is responsible for
determining whether products and the information in this document are appropriate for the Customer’s use and for ensuring
that the Customer’s workplace and disposal practices are in compliance with applicable laws and other governmental
enactments. Dow assumes no obligation or liability for the information in this document. NO WARRANTIES ARE GIVEN;
ALL IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESS-
LY EXCLUDED.

NOTICE: If products are described as “experimental” or “developmental”: (1) product specifications may not be fully deter-
mined; (2) analysis of hazards and caution in handling and use are required; and (3) there is greater potential for Dow to
change specifications and/or discontinue production.

DOW MEDICAL APPLICATION POLICY: Dow will not knowingly sell or sample any product or service (“Product”) into any
commercial or developmental application that is intended for:
a. permanent (Long term) contact with internal body fluids or internal body tissues. Long term is a use which exceeds 72

continuous hours (except 30 days for PELLETHANE™ polyurethane elastomers);
b. use in cardiac prosthetic devices regardless of the length of time involved; (Cardiac prosthetic devices include, but are not

limited to, pacemaker leads and devices, artificial hearts, heart valves, intra-aortic balloons and control systems, and ven-
tricular bypass assisted devices);

c. use as a critical component in medical devices that support or sustain human life; or
d. use specifically by pregnant women or in applications designed specifically to promote or interfere with

human reproduction.

Additionally, all Products intended for use in pharmaceutical applications, other than pharmaceutical packaging, must pass
the current Pharmaceutical Liability Guidelines.

• For the products sold by the Plastics Portfolio, new business opportunities require a business assessment prior to
sale or sampling of Dow products.

• Authorized distributors and resellers will adhere to this medical policy.
• The Dow Chemical Company does not endorse or claim suitability of their products for specific medical applications. It is

the responsibility of the medical device or pharmaceutical manufacturer to determine that the Dow product is safe, law-
ful, and technically suitable for the intended use. DOW MAKES NO WARRANTIES, EXPRESS OR IMPLIED, CONCERNING
THE SUITABILITY OF ANY DOW PRODUCT FOR USE IN MEDICAL APPLICATIONS.

Published July 2006

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