The day shift adds a strong mix because the reading is low. The night shift adds water because it is high. Both believe they are protecting the process, but neither knows how much fluid the other added or whether the readings were taken before the sump had mixed.
Control concentration drift with three connected records: verified concentration, usable fluid level and measured additions. Assign one approved response plan across shifts. The objective is a stable application window, not a series of large corrections around an unexplained average.
Define the operating window before choosing the top-off
The correct concentration depends on the exact product, material and operation. The initial charge, ongoing replenishment mixture and corrective mixture may have different concentrations. They serve different purposes and should not share one unlabeled mixer setting.
Use the supplier-approved application window and document the measurement method. For selecting that window, see Tech Tool's concentration guide by material and operation. This article addresses how to hold the agreed condition through daily production.
Oemeta's technical FAQ explains why maintaining the required application concentration matters to fluid performance. That does not mean stronger is always better. Repeated overcorrection can increase consumption and introduce other operating problems.
Why the concentration rises or falls
Evaporation primarily removes water, leaving the nonvolatile concentrate components behind. Mixed-fluid carryoff on chips or parts removes both water and concentrate. A leak can also remove mixed fluid. The replenishment needed depends on the combination of losses, not just the number of gallons missing.
The following simplified examples assume a uniform fluid and additive volumes. Actual systems also have retained liquid, contamination and measurement uncertainty.
| Starting condition | Loss | Result before replenishment |
|---|---|---|
| 100 gallons at 6% | 10 gallons of water evaporates | 6 gallons concentrate in 90 gallons: about 6.67% |
| 100 gallons at 6% | 10 gallons of uniform mixed fluid leaves | 5.4 gallons concentrate in 90 gallons: still about 6% |
The same falling level can therefore accompany different concentration trends. Blindly replacing every lost gallon with the original charge mixture may gradually overconcentrate an evaporation-dominated system. Adding only water when mixed-fluid losses dominate can progressively dilute it.
Measure reliably before correcting
A refractometer reading is not automatically coolant percentage. Use the exact product's correction factor or approved calibration method. Zero and maintain the instrument according to its instructions, take a representative sample and allow the system to mix before judging an addition.
Tech Tool carries the Coolant Refractometer. It supports a measurement routine; it does not identify contamination or choose the right concentration for the application. A blurred boundary or implausible result needs verification, not a larger corrective dose.
For multi-component fluids, follow the supplier's specified component-control method. One optical reading may not establish that every component remains in the correct proportion.
Build a shift handoff with six useful fields
- Machine and exact product: include the approved operating range and measurement factor in the controlled instruction.
- Before-addition condition: time, representative concentration reading and usable liquid level.
- Addition: volume, mixture concentration, water source and mixer or container identification.
- After-mixing result: measured concentration and level after the prescribed circulation period.
- Exceptions: new job, long idle period, leak, unusual carryoff, contamination or questionable measurement.
- Owner and next check: the person responsible and the response required if the condition remains outside limits.
Keep the log short enough to use at the machine. “Added coolant” is not an adequate entry; it does not tell the next shift whether the addition was water, dilute premix or concentrate.
Use a response sequence instead of competing shift habits
- Confirm the reading. Recheck the method and sample if the value differs sharply from the previous result or does not fit the recorded additions.
- Check the available volume. Determine how much liquid can be added without exceeding the machine's permitted level, including fluid that will return after stopping.
- Review the recent balance. Look for evaporation, carryoff, leaks or unrecorded additions that explain the direction of change.
- Apply the approved correction. Use a planned mixture and measured volume. Do not pour neat concentrate into a working emulsion unless the supplier explicitly specifies that method.
- Circulate and verify. Wait for the system-specific mixing interval, then record the result. Avoid stacking corrections before the first one can be evaluated.
- Investigate recurrence. If the same adjustment is needed repeatedly, review replenishment settings and the underlying loss pattern with the supplier.
A top-off calculation that exposes an impossible plan
Assume 80 gallons of working fluid is measured at 5%. The desired final volume is 100 gallons at 6%. In this simplified balance, the sump contains 4 gallons of concentrate and needs 6 gallons in the final charge. The 20-gallon addition must therefore contain 2 gallons of concentrate: a 10% premix.
Required addition concentration = (target final concentrate − existing concentrate) ÷ addition volume. Use consistent units and the concentration convention specified for the product.
This is an illustrative calculation, not approval to use a 10% corrective mixture with every product. The supplier must confirm the mixing and correction procedure. If the result exceeds a permitted mixture, if there is insufficient headspace or if the existing volume is uncertain, stop and obtain a different correction plan. The arithmetic cannot make an incompatible or physically impossible addition appropriate.
Why a mixer setting still needs verification
A proportioning device controls incoming mixture under its specified conditions. It does not automatically know the concentration already in a sump. Supply conditions, installation, maintenance and the actual device configuration also matter.
Verify the delivered mixture using the approved method, then separately verify the working sump after mixing. Do not treat “the mixer says 5%” as evidence that every connected machine is at 5%. A machine with different evaporation or carryoff can need a different replenishment strategy.
Set the check frequency around the process
Use the supplier's recommendations, the site's fluid-management plan and observed variability. A heavily used machine with frequent top-offs may need checks at shift handoff and after significant additions. A stable low-use system may have a different approved routine. Increase attention when water source, product, job mix or operating temperature changes.
Separate the action limits from statistical control limits. A manufacturer's permitted range is a process requirement; it is not a statistical chart calculated from your data. Do not manufacture precision by plotting uncertain readings to unnecessary decimal places.
Measure the cost of drift
If a 100-gallon uniform charge is held at 8% instead of an intended 6%, it contains approximately 2 extra gallons of concentrate. That is inventory in the system, not automatically two gallons wasted. The cost becomes more consequential when excess concentration repeatedly leaves on chips, parts or disposal.
Track concentrate consumption per comparable output along with correction labor and quality results. Do not lower concentration below the approved operating window to improve a chemical-use metric; apparent savings can be offset by machining or corrosion failures.
Frequently asked questions
Should every top-off use the same concentration?
Not necessarily. Use the agreed replenishment plan and current condition. Evaporation-dominated and mixed-fluid-loss-dominated systems have different balances.
Is an in-range average enough?
No. Large swings can be hidden by an average. Review the individual readings, additions and exceptions so each shift understands the condition it inherits.
Make the next shift's decision easier. Ask Tech Tool to review your Oemeta concentration and replenishment plan. Send the exact product, operating range, recent readings, additions and machine volume so the recommendation addresses the actual drift.
