Calibration Procedures for a Two-Stream System: Methodology, Pros, and Cons

RIM systems most commonly utilize two streams of fluid that are injected (impinged) at high pressure for effective mixing. Calibration in these systems commonly involves plugging off one stream and taking shots to evaluate expected weight verses actual delivered weight. This can be cumbersome, as removing orifice assemblies and shutting off one stream can be difficult. In some systems, the plc and hardware may not be configured to even allow single stream dispensing.

Calibrating two streams at a time offers major advantages, and many RIM manufacturers are not aware it is possible to calibrate with both streams running at the same time.

This post explores the pro's and con's of performing single stream and dual stream calibrations.

Two-Stream Calibration Methodology

The process for calibrating a system with two streams running at the same time involves taking a series of shots while changing the flow rates for each stream in between shots. The contribution to the % error in expected flow by each stream can be determined by increasing and decreasing the flow of one stream at a time and analyzing the results.

If this sounds confusing, don't worry. We have a worksheet with instructions to guide you through step by step. Keep reading to find out more...

Pro's and Con's

Single Stream Calibration:

Advantages: Straightforward, easy to calculate % error and required correction. Typically only requires 3-5 measurements.

Disadvantages: One stream needs to be blocked off, requiring valves to be closed and orifice ports to be plugged. This can occasionally lead to accidental crossover. This is also more disruptive to production as the system needs to be modified with plugs, turning off valves, etc.

Dual Stream Calibration:

Advantages: Requires no changes to the mix head or system. The procedure can be performed and the system put right back into production.

Disadvantages: Many measurements need to be taken (at least 15) in order to get an accurate picture of the system error for each stream.

Requirements

In order to properly calibrate your system using the Dual Stream method, you will need the following:

Tools:

• Sample Cups

• Measuring Scale

• Orifice Needle Adjuster Tool (hex key, screwdriver, etc.)

• Calibration Worksheet (see below)

Information:

• Desired Shot Size (typically 1-4 seconds)

• Typical Production Flow Rates

• Units of Flow (grams/sec, pounds/min, etc.)

• Flow Meter K-Factors (typically found on the HMI)

• Ability to adjust the flow rates (HMI or Pump Vernier)

Calibration Worksheet

MHR has developed a straightforward calibration worksheet that will determine the % error for each stream, and suggest a new corrective K-Factor for each flowmeter. By performing the calibration as shown you will be able to adjust your machine (if necessary) to be accurate and precise.

If you wish to receive a copy of the MHR Dual Stream Calibration Worksheet, with instructions, simply download it from our online members resource page: Members Download Page | MHR Inc

*Note, if you do not already have a login you will need to create one (it's free).