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!