Coolant emulsions play an essential role in wire drawing and other metal-forming processes. At the high drawing speeds and elongation rates used in cable and wire production, considerable friction develops between the wire and the drawing tools. Effective lubrication reduces this friction, while cooling removes the resulting heat and helps maintain stable processing conditions and consistent wire quality. For this reason, coolant concentration monitoring in wire drawing is important for maintaining the coolant emulsion within its defined operating range. Coolant emulsions typically consist primarily of water combined with lubricating oil, emulsifiers, solvents such as alcohols, defoamers, bactericides, and other additives. Depending on the application, typical concentrations in wire drawing processes are approximately 2–10%. Even relatively small deviations from the target concentration can affect lubrication performance, cooling efficiency, tool life, product quality, and operating costs. Continuous process monitoring and reliable laboratory verification therefore provide an important basis for efficient and reproducible wire production.

Why Is Coolant Concentration Important in Wire Drawing?

The coolant concentration directly influences the balance between lubrication and cooling during wire drawing. If the concentration is too low, lubrication performance may decrease, which can contribute to increased tool wear and surface defects on the manufactured wire. If the concentration is too high, more coolant concentrate may be consumed than necessary, increasing operating and production costs. Variations in coolant concentration can therefore result in:

• Reduced lubrication or cooling performance
• Increased wear of drawing tools
• Surface defects and inconsistent wire quality
• Excessive consumption of cooling lubricants
• Higher production costs
• Less stable process conditions
• Increased requirements for manual process control

Reliable coolant concentration measurement helps operators identify these changes early and adjust the emulsion accordingly.

Why Does Coolant Concentration Change During Wire Drawing?

During operation, the composition of the coolant does not remain constant. Carryover losses, water evaporation, and oil discharge can alter the concentration of the emulsion. Consequently, regular monitoring is necessary to detect deviations and restore the required process conditions.

How Is Coolant Concentration Measured with a Refractometer?

Refractometry is a widely used method for determining the concentration of coolant emulsions. The refractive index of the emulsion is measured and can be expressed as a Brix value. This value is then multiplied by a coolant-specific refractometer factor to determine the actual coolant concentration. Traditionally, this measurement is often performed using handheld refractometers. Although suitable for basic checks, manual measurements have several limitations. They require sampling and operator involvement and may be influenced by temperature variations or high turbidity of the coolant. Metal particles, abrasion products, and microbial contamination can further interfere with conventional measurements. Particularly for higher-concentration or strongly contaminated emulsions, handheld measurements may therefore provide only an approximate indication of the actual concentration.

How Do Laboratory Refractometers Measure Coolant Concentration?

Laboratory refractometers provide a precise reference method for verifying coolant concentration and supporting routine quality control. Compared with handheld measurements, stand-alone laboratory refractometers offer higher accuracy, while controlled laboratory conditions reduce influences such as temperature fluctuations and subjective scale reading. SCHMIDT + HAENSCH laboratory refractometers can be used for applications including:

• Preparation and verification of fresh coolant emulsions
• Routine concentration checks during production
• Validation of inline measurements
• Investigation of deviations in coolant concentration
• Quality assurance and process documentation

Temperature-controlled measurement is particularly useful because it allows samples to be analyzed under defined conditions. Laboratory refractometers therefore provide reliable reference data for assessing coolant condition and verifying that the required concentration range is maintained.

How Can Coolant Concentration Be Monitored Continuously During Wire Drawing?

While laboratory measurements provide accurate verification, wire drawing is a continuous process in which coolant concentration can change during operation. Inline refractometry enables these changes to be monitored directly in the circulating coolant without relying solely on periodic manual sampling. The SCHMIDT + HAENSCH iCS² CL inline concentration sensor for cooling lubricants measures the refractive index directly in the process stream and continuously provides information about coolant concentration under actual operating conditions. Designed specifically for the demanding conditions of metal processing, the iCS² CL is highly resistant to contamination. Even under heavily contaminated process conditions, its robust measurement system supports reliable concentration monitoring. The sensor is also designed for maintenance-free operation, helping to minimize maintenance requirements and support high system availability. Continuous measurement allows deviations to be detected as they occur so that the coolant composition can be corrected before concentration changes significantly affect lubrication, cooling, or wire quality. For applications requiring a wider temperature range, the iPR C² inline process refractometer can be used as an alternative inline solution.

Where Should an Inline Refractometer Be Installed in a Wire Drawing Process?

Depending on the production layout, inline refractometers can be integrated at different points in the coolant system, including:

• Directly in the coolant circulation system
• In the main process line
• In a bypass line for flexible integration
• At selected monitoring points within the coolant treatment system

A bypass installation can provide additional flexibility when integrating the measurement system into an existing production line. VARINLINE® housings with different connections and diameters allow the measuring system to be adapted to different installation conditions.

How Can Coolant Concentration Be Controlled Automatically?

SCHMIDT + HAENSCH inline refractometers can also be integrated directly into the plant control system. This allows defined upper and lower concentration limits to be monitored continuously. If the coolant concentration exceeds or falls below the specified range, the process control system can automatically initiate corrective dosing. Water or coolant concentrate can be added as required to restore the desired mixing ratio and maintain the coolant emulsion within its specified concentration range. This enables closed-loop concentration control, significantly increases automation during the process, and reduces the need for manual intervention, and helps maintain stable lubrication and cooling conditions throughout the production process.

How Does the Wire Drawing Process Work?

During wire drawing, a metallic semi-finished product is pulled through one or more drawing dies. Each drawing step reduces the cross-section of the material while increasing its length. The combination of high drawing speeds, material deformation, and contact with the drawing tools generates friction and heat that must be controlled throughout the process. The process typically involves:

• Feeding the wire or metallic semi-finished product into the drawing line
• Passing the material through one or more drawing dies to progressively reduce its cross-section
• Supplying coolant emulsion to the drawing zone for lubrication and heat removal
• Continuously circulating the coolant through the system
• Monitoring and adjusting coolant concentration to maintain stable operating conditions
• Further processing or heat treatment of the drawn wire as required

What Are the Benefits of Continuous Coolant Concentration Monitoring?

Continuous inline coolant concentration monitoring can support:

• Real-time monitoring of coolant concentration
• Immediate detection of concentration deviations
• More stable lubrication and cooling conditions
• Consistent wire and part quality
• Reduced wear of drawing tools
• Longer service life of machine tools and coolant emulsions
• Reduced manual sampling and staffing requirements
• Reduced risk of operator-dependent measurement errors
• Optimized consumption of cooling lubricants
• Reduced production costs
• More stable and reproducible production conditions