 |
|||||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
Estimating Pressure Drop
There are times when you may want to estimate the pressure required to fill a part, or the pressure drop associated with a nozzle, sprue, runner, gate, and/or part geometry section. It is important to maintain dimensional consistency when using the following method.
Step 1: Determine the Volumetric Flow Rate (Q)
Q = Volumetric Flow Rate of the Geometry Section (cu in/sec),
V = Geometry Section Volume (cu in),
t = Injection Time (sec) (usually the actual 1st stage time),
Q = V/t .
Step 2: Determine the Shear Rate (g )
Use the appropriate shear rate formula for the type of section being considered.
Plate Section:
g = Shear Rate of the Geometry Section (1/sec),
Q = Volumetric Flow Rate of the Geometry Section (cu in/sec),
w = Plate Section Width Perpendicular to flow (in) ,
H = Plate Section Thickness (in),
g (plate) = (6Q)/(wH2) .
Cylinder Section:
g = Shear Rate of the Geometry Section (1/sec),
Q = Volumetric Flow Rate of the Geometry Section (cu in/sec),
p = Numeric Constant,
R = Cylinder Radius of the Geometry Section (in),
g (cylinder) = (4Q)/(p R3) .
Step 3: Determine the Resin Viscosity (h )
A viscosity vs. shear rate graph for the resin at the correct processing stock or melt temperature is needed. Match the shear rate from Step 2 with the correct temperature curve, then read the corresponding viscosity from the graph.
h = Viscosity of the Resin.
The viscosity units will be kept in "psi-sec", however, if the graph units are listed in "Pa-sec" then use the following conversion:
h (psi-sec) = h (Pa-sec) /6897
Step 4: Determine the Pressure Drop (D P)
Use the appropriate pressure drop formula for the type of section being considered.
Plate Section:
D P= Pressure Drop of the Geometry Section (psi),
Q = Volumetric Flow Rate of the Geometry Section (cu in/sec),
h = Viscosity of the Resin (psi-sec),
L = Plate Section Length (in),
w = Plate Section Width Perpendicular to flow (in),
H = Plate Section Thickness (in),
D P(plate) = (12Qh L)/(wH3) .
Cylinder Section:
D P = Pressure Drop of the Geometry Section (psi),
Q = Volumetric Flow Rate of the Geometry Section (cu in/sec),
h = Viscosity of the Resin (psi-sec),
L = Plate Section Length (in),
p = Numeric Constant,
R = Cylinder Radius of the Geometry Section (in),
D P(cylinder) = (8Qh L)/(p R4) .
After considering all the section pressure drops, they may be added together to estimate the total pressure drop:
D P(total) = D P(plate1) + … + D P(cylinder1) + …
DISCLAIMER: THE MATERIALS AND PRODUCTS OF THE BUSINESSES MAKING UP THE GE PLASTICS UNIT OF GENERAL ELECTRIC COMPANY, ITS SUBSIDIARIES AND AFFILIATES ("GEP"), ARE SOLD SUBJECT TO GE POLYMERLAND'S STANDARD CONDITIONS OF SALE, WHICH ARE INCLUDED IN THE APPLICABLE DISTRIBUTOR OR OTHER SALES AGREEMENT, PRINTED ON THE BACK OF ORDER ACKNOWLEDGMENTS AND INVOICES, AND AVAILABLE UPON REQUEST. ALTHOUGH ANY INFORMATION, RECOMMENDATIONS, OR ADVICE CONTAINED HEREIN IS GIVEN IN GOOD FAITH, GE POLYMERLAND MAKES NO WARRANTY OR GUARANTEE, EXPRESS OR IMPLIED, (I) THAT RESULTS DESCRIBED HEREIN WILL BE OBTAINED UNDER END-USE CONDITIONS, OR (II) AS TO THE EFFECTIVENESS OR SAFETY OF ANY DESIGN INCORPORATING GE POLYMERLAND MATERIALS, PRODUCTS, RECOMMENDATIONS OR ADVICE. EXCEPT AS PROVIDED IN GE POLYMERLAND'S STANDARD CONDITIONS OF SALE, GE POLYMERLAND AND ITS REPRESENTATIVES SHALL IN NO EVENT BE RESPONSIBLE FOR ANY LOSS RESULTING FROM ANY USE OF ITS MATERIALS OR PRODUCTS DESCRIBED HEREIN. Each user bears full responsibility for making its own determination as to the suitability of GE Polymerland's materials, products, recommendations, or advice for its own particular use. Each user must identify and perform all tests and analyses necessary to assure that its finished parts incorporating GE Polymerland materials or products will be safe and suitable for use under end-use conditions. Nothing in this or any other document, nor any oral recommendation or advice, shall be deemed to alter, vary, supersede, or waive any provision of GE Polymerland's Standard Conditions of Sale or this Disclaimer, unless any such modification is specially agreed to in a writing signed by GE Polymerland. No statement contained herein concerning a possible or suggested use of any material, product or design is intended or should be construed, to grant any license under any patent or other intellectual property right of General Electric Company or any of its subsidiaries or affiliates covering such use or design, or as a recommendation for the use of such material, product or design in the infringement of any patent or other intellectual property right.
For more information on GE Polymerland, please refer to our Contact Information Page.
