Dispensing/Mixing of Polyurethanes
Presented at the PMA Meeting in Atlanta May 2, 2004
by
James B. Knizley Dr. Jens A. John
A. Survey of Dispensing/mixing options 1. Hand batching
a. Buckets/hand mixing b. Hand batch stations c. Centrifugal mixers
2. “Dead End” Machines a. Piston pump machines b. Gear pump machines
3. Re-circulating machines
B. How to select the appropriate machine
C. Scenarios
Prepolymer Curative
Polyurethane Prepolymer Processing
Dispensing
Demold
Curing
Finishing
Post-Cure
(Melting),Warming &Degassing
Melting orWarming
(Degassing)
Metering
Molding
Mixing
Hand Batch Equipment 1. Oven/Microwave Oven 2. Scale 3. Hand mixer with high shear attachment 4. Vacuum chamber/pump 5. Buckets 6. Thermometer
Hand Batching
Hand Batch Station
Hand Batch
Station
Control Panel
Hand Batch Station Dispenser
1. Needed Equipment
a. Oven b. Scale c. Cups/containers d. Disposable syringes e. Thermometer
2. Properties a. Degassing while mixing b. Variable time/speed option c. Narrow batch sizes dependent on make and model
Centrifugal Mixers
Small Centrifugal Mixer
Large Centrifugal Mixer
Piston Pump Machines 1. Properties
a. Cylinder loads material, which is delivered when piston compresses
b. Fluctuating Stream of material c. Ratio set by piston size and stroke length d. Dynamic Mix head
2. Possible Uses a. Parts that can be filled by a single piston stroke b. Room temperature systems c. Large, non-dynamic parts with longer gel times
Gear Pump Machines
1. Properties a. Pumps driven by a common shaft b. Ratio set by changing gears and pump sizes c. Multi component set-up possible d. Lines and tank heat electronically controlled
2. Possible Uses a. Variable part sizes b. Multiple part geometries with the same material c. Continuous and shot pours
Re-circulating Machine
1. Properties a. Pumps driven by individual DC Motors b. Material Ratio
i. Set by calibrating pump and flow meter c. Flow Meters
i. Piston ii. Gear iii. Mass
d. Continuous or shot pours e. Multi component available f. Heating systems dependent on machine manufacturer g. Production aids include:
i. Slinger degasser ii. MBCA melter iii. MBCA transfer device iv. Automatic tank refill v. Computer controls available
Re-circulating Machines
1. Possible Uses a. High volume production b. Parts demanding precise ratio control c. Multiple Materials d. Short gel times
Re-Circulating Machines
Re-circulating Machine Multiple Components
Re-Circulating Machine
Two
Components
How to select the appropriate machine Basic Information
a. Polyurethane machines must operate every day b. Decide how many materials need to be run on the machine c. How many molds are needed for efficient operation? d. Additional ovens may be necessary e. Can Machine Operators/Maintenance personnel be trained
adequately? f. How much maintenance is required?
This information can be classified into three main areas: 1. Volume 2. Quality 3. Processing
Volume
1. The amount of parts outstrips the hand batch
production capacity
2. The size of each part is too large to be handled through hand batching
3. Production efficiency will increase.
Quality
1. Hand batching can be inconsistent.
2. Ratio control is repeatable with a machine.
3. Temperature control is improved with a machine.
4. Mixing is consistent with a machine.
Processing 1. Does the application demand a unique material with
outstanding properties?
2. How many parts need to be made to be economically viable?
3. How much mold turn over can be achieved with and without a machine?
4. How fast is the gel time?
5. How can the appropriate cosmetics and performance characteristics be achieved?
Scenario I Press on Tires
a. Simple Part open pour. b. Variable size c. Continuous process possibly with tunnel ovens d. Good cut and tear, and good dynamics needed e. Average pot life, no unusual viscosity, good de-mold. f. Increase product line to cover a larger durometer range. g. Modest budget
A “dead end” gear pump machine will fit this situation
Scenario II Skate Wheels
a. More complex geometry b. Same size c. Higher production rate d. Excellent cut and tear, excellent dynamics e. Fast gel time f. Higher budget
A re-circulating machine with flow meter control will fit this situation
Thank you to the following people: Mr. James Knizley
Ms. Donna Day Dr. George Nybakken
Thank you to all the machine suppliers for sending me information about their products.
Thank you to all of
you for your time and attention!