Dynamic efficiency testing service for screws

Dynamic Efficiency Testing Service for Screws – Accredited ISO/IEC 17025 Mechanical Performance Assessment for the Croatian Market

The dynamic efficiency of screws, including power screws, ball screws, lead screws, and threaded fasteners, is a critical performance parameter that determines the energy consumption, heat generation, positioning accuracy, and overall mechanical reliability of actuation and power transmission systems in industrial machinery, automotive systems, aerospace applications, medical devices, and precision equipment. In the Croatian manufacturing and engineering sector, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, and the Carinska uprava enforce strict quality, energy efficiency, and safety standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of dynamic screw efficiency is essential for product certification, supplier qualification, design optimization, quality control in manufacturing, and import-export processes. Our laboratory offers a comprehensive dynamic efficiency testing service for screws and threaded components, applying standardized methods that measure torque, axial force, friction coefficient, and mechanical efficiency under controlled operating conditions, including varying speeds, loads, and lubrication states. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, product validation, and market access in Croatia and the European Union.

Screw Samples and Components We Regularly Test

Our laboratory receives a wide variety of screws and threaded components for dynamic efficiency testing. Typical samples include:

• Power screws and lead screws – for linear actuators, machine tools, and material handling equipment.
• Ball screws and roller screws – for high-precision positioning systems, robotics, and CNC machinery.
• Threaded fasteners and bolts – for structural connections, automotive assemblies, and heavy machinery.
• Custom-designed screws and threaded components – submitted by manufacturers for validation of efficiency and performance before series production.
• Lubricated and dry screws – for evaluating the effect of lubrication on dynamic efficiency.
• Field-retrieved screws – for failure analysis and remaining life assessment.

Dynamic Efficiency Measurement – Torque, Force, and Power Loss Evaluation

The dynamic efficiency of a screw is defined as the ratio of the useful mechanical power output (axial force × linear velocity) to the input mechanical power (torque × angular velocity). Our tests measure the input torque, the axial force, the rotational speed, and the linear speed under controlled conditions, and we calculate the efficiency and the power losses due to friction.

• Torque and axial force measurement (ISO 16047 / DIN 946 / NTC 5900 – for screw and bolt assemblies) – we mount the screw assembly in a test rig equipped with a torque transducer (range 0‑5000 N·m, accuracy ±0.1 %) and a load cell (range 0‑500 kN, accuracy ±0.1 %). The screw is rotated at a specified speed (e.g., 10 RPM, 100 RPM, 500 RPM) while the axial force is measured. The torque and the axial force are recorded continuously. We report the torque (in N·m), the axial force (in kN), and the torque‑force relationship.
• Efficiency calculation (NTC 5901 – for the dynamic efficiency determination) – we calculate the dynamic efficiency (η) using the formula: η = (F × v) / (T × ω) × 100 %, where F is the axial force (in N), v is the linear speed (in m/s), T is the input torque (in N·m), and ω is the angular velocity (in rad/s). We report the dynamic efficiency (in %) at different loads and speeds.
• Efficiency at different loads (NTC 5902 – for the load‑efficiency curve) – we vary the axial load from 10 % to 100 % of the rated load and measure the torque and the speed at each load level. The efficiency vs. load curve is plotted. We report the efficiency at each load level and the maximum efficiency point.
• Efficiency at different speeds (NTC 5903 – for the speed‑efficiency curve) – we vary the rotational speed from 1 RPM to 1000 RPM (or the maximum speed) at a constant load and measure the torque and the efficiency. The efficiency vs. speed curve is plotted. We report the efficiency at each speed and the optimum speed range.
• Efficiency under different lubrication conditions (NTC 5904 – for the effect of lubrication) – we test the screw with different lubricants (e.g., oil, grease, dry coating) and with different lubrication amounts (e.g., fully lubricated, partially lubricated, and dry). We report the efficiency for each lubrication condition and the best-performing lubricant.

Friction Coefficient Measurement – Evaluating the Source of Energy Loss

Friction is the primary cause of energy loss in screw mechanisms. Our tests measure the coefficient of friction (both static and dynamic) between the screw thread and the nut (or the mating component), providing a direct indication of the mechanical efficiency and the potential for wear.

• Thread friction coefficient measurement (ISO 16047 / DIN 946 / NTC 5910 – for screw thread friction) – using the torque and axial force data, we calculate the thread friction coefficient (μ_th) using the standard formula: μ_th = (F × P) / (2π × T – F × μ_h × r_h), where P is the thread pitch, μ_h is the head friction coefficient, and r_h is the effective radius of the head. We report the thread friction coefficient (dimensionless).
• Head friction coefficient measurement (NTC 5911 – for the bearing friction of the screw head) – we measure the friction coefficient between the screw head and the bearing surface (e.g., the washer or the clamping plate) using a separate test fixture. We report the head friction coefficient (dimensionless).
• Static friction coefficient measurement (NTC 5912 – for the break‑away friction) – we measure the torque required to start the rotation of the screw (the static break‑away torque) at different axial loads. The static friction coefficient is calculated. We report the static friction coefficient and the break‑away torque.
• Dynamic friction coefficient measurement (NTC 5913 – for the running friction) – we measure the torque required to maintain the rotation of the screw at a constant speed, and we calculate the dynamic friction coefficient. We report the dynamic friction coefficient and the running torque.
• Friction coefficient at different temperatures (NTC 5914 – for the temperature effect) – we perform the friction measurements at different temperatures (e.g., 20 °C, 60 °C, 100 °C) to evaluate the effect of temperature on the friction and the efficiency. We report the friction coefficient at each temperature.

Backlash and Axial Play Measurement – Evaluating the Positioning Accuracy

Backlash and axial play are critical parameters for precision positioning systems. Our tests measure the lost motion, the backlash, and the axial play of the screw assembly, and we evaluate the effect of these parameters on the dynamic performance and the efficiency.

• Backlash measurement (NTC 5920 – for the angular and linear backlash) – we rotate the screw in one direction, measure the position, and then reverse the direction. The angular backlash (in arc‑minutes) and the linear backlash (in mm) are measured. We report the backlash values and the effect on the positioning accuracy.
• Axial play measurement (NTC 5921 – for the end‑float measurement) – we apply an axial force in both directions (push‑pull) to the screw and measure the displacement. The axial play (in mm) is reported. We report the axial play and the effect on the stiffness.
• Backlash under load (NTC 5922 – for the load‑dependent backlash) – we measure the backlash under different axial loads (e.g., 10 %, 50 %, 100 % of the rated load) to evaluate the effect of the load on the positioning accuracy. We report the backlash at each load level.
• Backlash and efficiency correlation (NTC 5923 – for the trade‑off analysis) – we correlate the measured backlash with the dynamic efficiency to evaluate the trade‑off between the positioning accuracy and the mechanical efficiency. We report the correlation and the recommendations.
• Stiffness measurement (NTC 5924 – for the axial and torsional stiffness) – we measure the axial stiffness (the axial force per unit displacement) and the torsional stiffness (the torque per unit angular displacement) of the screw assembly. We report the stiffness values and their effect on the dynamic response.

Temperature Rise and Thermal Behavior – Evaluating the Heat Generation and Dissipation

Friction in the screw mechanism generates heat, which can cause thermal expansion, changes in the lubrication properties, and a reduction in the efficiency. Our tests measure the temperature rise of the screw and the nut during operation, and we evaluate the effect of the temperature on the efficiency and the service life.

• Temperature rise measurement (NTC 5930 – for the temperature monitoring) – we place thermocouples on the screw, the nut, and the housing, and we measure the temperature during the efficiency test. The temperature rise (in °C) and the rate of temperature increase are recorded. We report the temperature rise and the temperature profile.
• Thermal expansion measurement (NTC 5931 – for the effect of temperature on the dimensions) – we measure the change in the length and the diameter of the screw during the temperature rise. The thermal expansion coefficient (in μm/m·°C) is calculated. We report the thermal expansion and the effect on the clearance.
• Thermal time constant measurement (NTC 5932 – for the thermal response) – we record the temperature rise and the cooling curves to determine the thermal time constant (τ) of the screw assembly. The time constant is used to predict the steady‑state temperature. We report the thermal time constant and the thermal response.
• Effect of temperature on efficiency (NTC 5933 – for the thermal degradation of efficiency) – we measure the efficiency at different steady‑state temperatures (e.g., 25 °C, 50 °C, 75 °C) to evaluate the reduction in efficiency due to the temperature. We report the efficiency at each temperature and the temperature derating factor.
• Thermal imaging (NTC 5934 – for the hot‑spot detection) – we use an infrared camera to capture the thermal image of the screw and the nut during the operation. The hot‑spots and the temperature gradients are identified. We report the thermal images and the hot‑spot locations.

Durability and Life Testing – Evaluating the Efficiency Degradation over Time

The dynamic efficiency of a screw can degrade over time due to wear, lubricant degradation, and surface damage. Our durability and life tests simulate the long‑term operation of the screw and evaluate the change in the efficiency and the friction over the service life.

• Life test under constant load (NTC 5940 – for the endurance evaluation) – we operate the screw under a constant load (e.g., 50 % of the rated load) and a constant speed (e.g., 100 RPM) for a specified number of cycles (e.g., 10⁶ cycles). The torque and the efficiency are measured at regular intervals (e.g., every 10,000 cycles). We report the efficiency degradation and the life to a specified efficiency loss (e.g., a 5 % loss).
• Life test under variable load (NTC 5941 – for the realistic duty cycle) – we operate the screw under a variable load profile that simulates the actual duty cycle of the application. The efficiency is monitored continuously. We report the efficiency degradation and the predicted service life.
• Wear measurement (NTC 5942 – for the wear depth and the surface roughness) – after the life test, we measure the wear depth on the thread surface and the surface roughness (Ra, Rz) using a profilometer. We report the wear depth and the change in the roughness.
• Lubricant analysis (NTC 5943 – for the degradation of the lubricant) – we take a sample of the lubricant before and after the life test and analyze its viscosity, the acid number, and the particle content. The degradation of the lubricant is correlated with the efficiency loss. We report the lubricant condition and the contamination level.
• Fractographic analysis of worn threads (SEM – ASTM E1508 / NTC 5944 – for the failure analysis) – we use scanning electron microscopy (SEM) to examine the worn thread surface to identify the wear mechanisms (e.g., adhesive wear, abrasive wear, or fatigue). We report the SEM images and the wear mechanism.

Complementary Tests – Surface Finish, Hardness, and Material Verification

To fully understand the efficiency performance and the factors that influence it, we perform complementary tests, including surface finish measurement, hardness testing, and material verification. These tests help explain the efficiency results and are essential for the quality control and the material selection.

• Surface finish measurement (ASTM D7127 / NTC 5950 – for the thread surface and the bearing surfaces) – we measure the surface roughness (Ra, Rz) of the thread profile and the bearing surfaces using a contact profilometer. The surface finish is correlated with the friction and the efficiency. We report the roughness values and the surface condition.
• Hardness testing (ASTM E18 / NTC 5951 – Rockwell, Brinell, or Vickers) – we measure the hardness of the screw material (the thread surface and the core) to verify the heat treatment condition and to detect any localized hardening or softening. We report the hardness values and the uniformity.
• Metallographic examination (ASTM E3 / NTC 5952 – for the grain size and the microstructure) – we examine the microstructure of the screw material (the grain size, the phase distribution, and the inclusion content) using optical microscopy and SEM. The microstructure is correlated with the wear resistance and the friction. We report the grain size, the phase distribution, and the inclusion rating.
• Chemical composition analysis (ASTM E415 / NTC 5953 – for the alloy composition) – we use X‑ray fluorescence (XRF) or optical emission spectroscopy (OES) to determine the chemical composition of the screw material. We report the composition and the compliance with the specified grade.
• Lubricant compatibility test (NTC 5954 – for the effect of the lubricant on the efficiency) – we test the screw with different lubricants and evaluate the efficiency, the friction, and the wear. The compatibility of the lubricant with the screw material is assessed. We report the lubricant compatibility and the performance ranking.

Test Report and Recognition in the Croatian Mechanical and Industrial Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (torque transducers, load cells, speed sensors, temperature sensors, etc.) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the screw (manufacturer, type, size, material, thread geometry, and heat treatment).
• Detailed description of the test methods applied (ISO/HRN EN/NTC standards, test conditions, speed, load, temperature, and lubrication).
• Numerical results: dynamic efficiency (%), torque (N·m), axial force (kN), friction coefficient (μ), backlash (mm), temperature rise (°C), wear depth (μm), and life (cycles).
• Graphical data: efficiency vs. load curves, efficiency vs. speed curves, torque vs. force curves, and temperature vs. time curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ISO 16047, DIN 946, HRN EN 13832, and the requirements of the HZN, Ministarstvo gospodarstva, and Državni inspektorat).
• Photographs and micrographs (SEM) of the screw threads before and after the test, showing the wear and the surface condition.
• Recommendations for design optimization, lubricant selection, and quality control measures to achieve the required efficiency and service life.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98‑3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo gospodarstva i održivog razvoja for energy efficiency compliance, by the Državni inspektorat for market surveillance, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of screws and mechanical components. Additionally, we offer consulting services for the selection of high‑efficiency screw designs, the optimization of lubrication strategies, and the implementation of quality control programs for dynamic efficiency, contributing to the energy efficiency, reliability, and competitiveness of mechanical systems in the diverse and growing Croatian industrial market, from the automotive and aerospace sectors to the manufacturing and renewable energy industries.