1.

If running dyes or colorants, the system should be easily changeable between colors.

2.

The prepolymer and the curative require a constant blanket of nitrogen or –40 dewpoint dry air.

3.

It is a real advantage, and often a necessity to have the ability to vacuum de-gas material.

4.

Filters should be installed on the tank side of the pumping system. Avoid piston metering systems due to high maintenance.

5.

The machine should be capable of taking material at ambient temperatures from either totes or drums and delivering to the mix-head at slightly elevated temperatures. An adequate temperature is 100 F. This allows for consistent viscosities, and therefore consistent ratios, as environmental conditions vary. In some applications, heated tanks, lines and mix-head may be necessary.

6.

The mix ratio of the machine must be easily changeable. Capital expenditure considerations versus frequency of change will determine whether a gear change, the press of a button, or the dial of a number is the best design. Normally, a range of ratios from 1:5 to 5:1 is adequate.

7.

When checking the ratio in a production setting, the materials must be taken through the mix-head. A ratio check before the mix-head is not indicative of running conditions; any blockage in the head will distort the actual ratio.

8.

Unless you have 100 psi, -40 dewpoint dry air, the dynamic mix-head must be driven electrically.

9.

The mix-head should have the prepolymer (iso) stream entering above (for vertical designs), or behind (horizontal designs) the curative (poly) stream. This will lower downtime due to seal wear.

10.

All mix-head seals should be easily replaced. Use Viton seals if solvent is used for flushing.

11.

To anticipate future expansion or change of your molding layout, the mix-head should be movable. It should be mounted on the end of a scissors arm to reach as close to the mold as possible without the use of an extension hose.

12.

The manufacturer should confirm that the equipment will deliver product on ratio and well mixed instantly so there is no startup waste at the beginning of the molding process.

13.

The machine should be capable of generating an absolute minimum amount of waste during the mix-head clean-out or blow-down process. The blow-down waste should be non-hazardous.