{"id":197,"date":"2026-07-09T08:51:57","date_gmt":"2026-07-09T08:51:57","guid":{"rendered":"https:\/\/industrialelectricmotor.net\/?p=197"},"modified":"2026-07-09T08:51:57","modified_gmt":"2026-07-09T08:51:57","slug":"vfd-motor-for-ball-mill-and-grinding-mill","status":"publish","type":"post","link":"https:\/\/industrialelectricmotor.net\/el\/vfd-motor-for-ball-mill-and-grinding-mill\/","title":{"rendered":"VFD Motor for Ball Mill and Grinding Mill"},"content":{"rendered":"
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Korea Ever-Power \u00b7 YVF2 Series \u00b7 Ball Mill and Grinding Mill Drive Guide<\/span><\/p>\n

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VFD Motor for Ball Mill and Grinding Mill:
\nCritical Speed, Starting Torque and Mill Drive Selection<\/span><\/h1>\n

Ball mills, rod mills, SAG mills, and laboratory grinding mills impose some of the most demanding motor requirements in industrial processing: very high starting torque to overcome the inertia of a fully charged mill, a defined critical speed that must never be exceeded, VFD speed control to optimise grinding efficiency for different feed materials and product specifications, and continuous S1 duty for 24-hour-per-day operation in cement, mining, and mineral processing plants. Korea Ever-Power YVF2 inverter-duty motors with IC416 forced cooling are the correct motor specification for VFD-driven ball mill and grinding mill applications requiring variable speed control and full torque from zero to rated speed.<\/p>\n

High Starting Torque<\/span>
\nCritical Speed Control<\/span>
\nIC416 S1 Continuous<\/span>
\nClass H Insulation<\/span>
\n0.75\u2013200 kW<\/span><\/div>\n<\/div>\n<\/div>\n

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2.5\u00d7 T<\/div>\n
Starting torque requirement<\/div>\n<\/div>\n
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65\u201380%<\/div>\n
Critical speed operating range<\/div>\n<\/div>\n
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IC416<\/div>\n
Full torque at any speed<\/div>\n<\/div>\n
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S1 24hr<\/div>\n
Continuous mill operation<\/div>\n<\/div>\n
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0\u2013120 Hz<\/div>\n
Speed optimisation range<\/div>\n<\/div>\n<\/div>\n

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\"YVF2<\/p>\n
Korea Ever-Power YVF2 inverter-duty motor for ball mill and grinding mill drives \u2014 the IC416 forced cooling blower maintains full rated torque from zero to rated speed, enabling the high starting torque required to rotate a fully charged ball mill from rest and the variable speed control needed to operate at the optimum percentage of critical speed for different ore types and grinding targets.<\/div>\n<\/div>\n

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Contents<\/div>\n
1. Ball Mill Critical Speed<\/a>
\n2. Starting Torque Requirement<\/a>
\n3. Why VFD Speed Control Improves Grinding<\/a>
\n4. Mill Motor Power Calculation<\/a>
\n5. S1 Continuous Duty and Thermal Derating<\/a>
\n6. YVF2 Specifications for Mill Drives<\/a>
\n7. Ball Mill and Grinding Mill Applications<\/a>
\n8. Frequently Asked Questions<\/a><\/div>\n<\/div>\n

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1. Ball Mill Critical Speed and Operating Speed<\/h2>\n

The critical speed of a ball mill is the rotational speed at which the centrifugal force acting on the grinding media (balls) equals the gravitational force, causing the balls to rotate with the mill shell rather than cascading and tumbling across the charge. At the critical speed there is no grinding action \u2014 the balls are pinned to the shell and the charge rotates as a solid body. All ball mills must operate below the critical speed.<\/p>\n

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Critical Speed Formula and Operating Range<\/div>\n
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Critical speed formula:<\/div>\n
Nc = (42.3 \/ \u221aD) rpm
\nwhere D = mill internal diameter in metres<\/p>\n

Example \u2014 1.2 m diameter ball mill:
\nNc = 42.3 \/ \u221a1.2 = 42.3 \/ 1.095 = 38.6 rpm<\/p>\n

Example \u2014 3.0 m diameter ball mill:
\nNc = 42.3 \/ \u221a3.0 = 42.3 \/ 1.732 = 24.4 rpm<\/p><\/div>\n<\/div>\n

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Operating speed selection:<\/div>\n
Wet grinding ball mills: 65\u201375% of Nc
\nDry grinding ball mills: 70\u201380% of Nc
\nSAG mills: 75\u201385% of Nc<\/p>\n

1.2 m mill at 70% Nc: 38.6 \u00d7 0.70 = 27.0 rpm
\n3.0 m mill at 72% Nc: 24.4 \u00d7 0.72 = 17.6 rpm<\/p>\n

VFD allows operating speed to be adjusted in real time from 60% to 80% Nc to optimise for changing ore hardness or product target.<\/span><\/div>\n<\/div>\n<\/div>\n<\/div>\n

The output shaft speed from the mill drive motor and gearbox must match the required mill operating rpm. With a VFD, the motor frequency (and therefore the mill speed) is continuously adjustable, allowing the operator to optimise the percentage of critical speed for the actual ore being ground. Without VFD, the mill runs at a fixed fraction of critical speed determined by the fixed gear ratio \u2014 acceptable for single-ore operations but inflexible for variable-ore mineral processing plants.<\/p>\n<\/div>\n

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2. Starting Torque Requirement for Ball Mill Drives<\/h2>\n
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Dead Start Torque Problem<\/div>\n

When a ball mill is stopped with a full charge of grinding balls and ore, the balls settle and pack at the lowest point of the mill shell. The static friction between the balls and the mill lining, combined with the gravitational load of the settled charge, creates a very high starting torque requirement \u2014 typically 2.0 to 2.5 times the rated running torque. This starting torque must be provided without damaging the motor winding through excessive starting current.<\/p>\n<\/div>\n

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VFD Torque-Boost for Ball Mill Starting<\/div>\n

When the YVF2 motor is driven by a VFD with torque-boost or vector control, the VFD can deliver motor starting torque of 1.5 to 2.0 times rated torque at zero speed without exceeding the rated motor current. This is achieved by the VFD increasing the motor flux (through higher V\/Hz ratio at low frequency) to produce additional torque during the start sequence. The YVF2 Class H winding handles this elevated magnetic flux at low speed without insulation stress. Sensorless vector VFD control provides the most accurate starting torque control for ball mill applications.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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3. Why VFD Speed Control Improves Grinding Efficiency<\/h2>\n
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Optimise for Ore Hardness<\/div>\n

Harder ores require the ball charge to drop from a higher angle, which means running at a higher percentage of critical speed (72 to 78% Nc for hard ore). Softer ores grind more efficiently at lower speed (62 to 68% Nc). A fixed-speed mill set for hard ore runs at excess speed (and excess energy consumption) when processing softer ore. VFD allows the operator to reduce mill speed for softer ore periods, saving 10 to 20% of mill drive energy.<\/p>\n<\/div>\n

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Reduce Ball and Liner Wear<\/div>\n

Running at above-optimal speed for the ore type causes balls and liners to impact harder than necessary, accelerating wear. A 5% reduction in mill speed from the optimum for a given ore can reduce ball consumption by 8 to 12% and liner wear by 5 to 8%, extending maintenance intervals and reducing consumable costs. VFD adjustment to the optimum speed provides this wear reduction without sacrificing throughput.<\/p>\n<\/div>\n

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Soft Start Reduces Mechanical Stress<\/div>\n

Direct-on-line starting of large ball mill motors produces high current inrush (5 to 7 times rated) and high mechanical shock to the gearbox and mill shell as the motor comes up to speed. VFD starting ramps the motor from zero to operating speed over 5 to 15 seconds, eliminating current inrush and reducing the torque shock on the gearbox by 60 to 80%. This extends gearbox service life and reduces the frequency of gearbox gear tooth and bearing damage from heavy starts.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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4. Ball Mill Motor Power Calculation<\/h2>\n
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Bond Formula \u2014 1.2 m Diameter \u00d7 1.5 m Length Ball Mill<\/div>\n
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Given:<\/div>\n
Mill diameter D = 1.2 m
\nMill length L = 1.5 m
\nBall charge: 30% of mill volume
\nBall density: 7,800 kg\/m\u00b3 (steel)
\nFeed F80 = 6,000 \u03bcm; Product P80 = 150 \u03bcm
\nBond Work Index Wi = 14 kWh\/t (medium hardness)
\nFeed rate: 2.0 t\/h<\/div>\n<\/div>\n
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Power calculation:<\/div>\n
Bond W = 10\u00d7Wi\u00d7(P80\u207b\u00bd \u2212 F80\u207b\u00bd) = 10\u00d714\u00d7(0.00816\u22120.00041)
\nW = 140 \u00d7 0.00775 = 1.085 kWh\/t
\nMill power = 1.085 \u00d7 2.0 t\/h = 2.17 kW at mill shell
\nWith drive efficiency 0.92: motor power = 2.17 \u00f7 0.92 = 2.36 kW
\nWith starting torque factor 2.5: peak motor = 5.9 kW
\n\u2192 Select YVF2 4-pole 3.0 kW IC416 (running) with VFD torque boost to 2.5\u00d7 for starting<\/strong><\/div>\n<\/div>\n<\/div>\n<\/div>\n

The Bond formula provides an estimate of specific grinding energy for mill sizing. For accurate motor selection on large industrial ball mills above 30 kW, use the full Bond calculation with correction factors for mill diameter, feed size, product size, and ore work index. Korea Ever-Power recommends applying a 1.25 service factor to the calculated motor power for VFD mill drives to account for model uncertainty and process variability.<\/p>\n<\/div>\n

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5. S1 Continuous Duty and Thermal Considerations<\/h2>\n
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S1 Duty for Continuous Mill Operation<\/div>\n

Industrial ball mills in cement, mining, and mineral processing typically run S1 continuous duty for 20 to 24 hours per day, stopping only for planned maintenance intervals (typically weekly or bi-weekly) and liner change shutdowns. The YVF2 motor must be rated for S1 continuous at the operating point \u2014 the mill running power at the chosen percentage of critical speed. The IC416 blower ensures this S1 rating is maintained at any speed from 40% to 100% of rated.<\/p>\n<\/div>\n

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Altitude Derating Above 1,000 m<\/div>\n

Mining applications at high altitude (many South American and African mining operations are at 2,000 to 4,500 m) require motor power derating for the reduced cooling air density. At 2,500 m altitude, air density is approximately 74% of sea level, reducing motor cooling capacity. Standard IEC derating: apply a power factor of 0.92 per 1,000 m above 1,000 m. At 3,000 m: derate by 1 \u2212 (2 \u00d7 0.08) = 0.84 of rated power. Specify a larger YVF2 frame to compensate for altitude derating, or specify the motor at the derated power as the S1 continuous rating for the installation altitude.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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6. Korea Ever-Power YVF2 Specifications for Mill Drives<\/h2>\n
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The Korea Ever-Power YVF2 series provides the complete inverter-duty motor specification for ball mill, rod mill, and grinding mill VFD drives from small laboratory mills at 0.75 kW through to medium-scale cement and mineral processing mills at 200 kW. The IC416 forced cooling system, Class H VFD-duty winding, sensorless vector control compatibility, PTC thermistor protection, and IEC 72-1 metric frame make the YVF2 the correct replacement for existing fixed-speed mill motors being retrofitted with VFD drive systems. The full range is in the VFD motor section<\/a>. For large mill drive specifications above 200 kW or synchronous motor requirements, contact Korea Ever-Power<\/a>.<\/p>\n<\/div>\n

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YVF2 \u2014 Ball Mill Drive Data<\/div>\n\n\n\n\n\n\n\n\n\n\n
Power range<\/td>\n0.75\u2013200 kW<\/td>\n<\/tr>\n
Speed range<\/td>\n0\u2013120 Hz<\/td>\n<\/tr>\n
Cooling<\/td>\nIC416 forced blower<\/td>\n<\/tr>\n
Starting torque<\/td>\n2.5\u00d7 with VFD boost<\/td>\n<\/tr>\n
Insulation<\/td>\nClass H VFD-duty<\/td>\n<\/tr>\n
Duty<\/td>\nS1 continuous<\/td>\n<\/tr>\n
Protection<\/td>\nPTC thermistors standard<\/td>\n<\/tr>\n
Altitude<\/td>\nDerate above 1,000 m<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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7. Ball Mill and Grinding Mill Applications<\/h2>\n\n\n\n
\"YVF2<\/p>\n
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Mineral Processing Ball Mill<\/div>\n

Gold, copper, and iron ore processing ball mills from 0.9 m to 3.0 m diameter. YVF2 4-pole 7.5 to 132 kW IC416 with gear drive at 10:1 to 30:1. Operating at 65 to 75% of critical speed via VFD adjustment. S1 continuous operation 20 to 24 hours per day. PTC thermistors mandatory for 24-hour unattended operation. Altitude derating applied for high-elevation mine sites above 2,000 m.<\/p>\n<\/div>\n<\/td>\n

\"YVF2<\/p>\n
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Cement Ball Mill Retrofit VFD<\/div>\n

Cement grinding mills retrofitting existing fixed-speed drives with VFD for speed optimisation and soft starting. YVF2 4-pole 45 to 200 kW IC416 replacing existing standard motors. VFD enables 5 to 12% energy saving by optimising mill speed for different cement blends. Existing gear and pinion drive maintained; only motor and control panel changed. Sensorless vector VFD tuned to mill inertia for optimal starting torque.<\/p>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

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Pharmaceutical Laboratory Ball Mill<\/div>\n

Small pharmaceutical and research ball mills for API particle size reduction. YVF2 4-pole 0.75 to 3.0 kW IC416. Tight speed control \u00b1 0.5 rpm for reproducible particle size distribution. Clean room compatible motor if required (BXG SS316L for pharmaceutical GMP area installation).<\/p>\n<\/div>\n

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Ceramic and Tile Grinding Mill<\/div>\n

Porcelain, alumina, and ceramic raw material wet grinding mills for tile and sanitary ware production. YVF2 4-pole 5.5 to 55 kW. Wet grinding at 68 to 72% Nc. Speed control for different ceramic body formulations requiring different grinding fineness targets. IP55 for wet grinding building environment.<\/p>\n<\/div>\n

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Pigment Grinding Mill<\/div>\n

Ceramic pigment, titanium dioxide, and iron oxide pigment grinding for paint and ink manufacturing. YVF2 4-pole 2.2 to 22 kW. Precise speed control for particle size target. If grinding solvent-based pigments, specify YB2 Ex d IIB T4 for Zone 2 classification in solvent pigment areas.<\/p>\n<\/div>\n

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Rod Mill for Coarse Grinding<\/div>\n

Rod mills for coarse grinding in mineral processing circuits before ball mill secondary grinding. Similar drive requirements to ball mills: YVF2 4-pole 15 to 132 kW IC416, VFD control at 60 to 70% Nc. Rod mills typically have lower operating speed than ball mills of the same diameter due to the risk of rod tangling at high speed.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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\"Korea<\/p>\n

Motor Production<\/div>\n<\/div>\n
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\"Korea<\/p>\n

High Torque Test<\/div>\n<\/div>\n
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\"Korea<\/p>\n

Engineering Support<\/div>\n<\/div>\n
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\"Korea<\/p>\n

Global Export<\/div>\n<\/div>\n<\/div>\n

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8. Frequently Asked Questions<\/h2>\n
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What happens if a ball mill exceeds its critical speed?<\/div>\n<\/div>\n
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If a ball mill speed is increased above its critical speed, the balls are centrifuged to the mill shell and rotate with the shell rather than cascading. Grinding ceases completely because there is no relative motion between the balls and the ore charge \u2014 the balls are simply rotating at the same speed as the shell surface, generating no impact or abrasion forces. Additionally, running above critical speed causes the ball charge to become unbalanced as balls distribute unevenly at the shell surface, creating vibration that can damage mill bearings and shell welds. In practice, the centrifugal effect begins to reduce grinding efficiency significantly above about 85% of critical speed before the complete pinning effect at 100% Nc \u2014 this is why the standard operating range of 65 to 80% Nc provides the optimum grinding efficiency with adequate margin below the critical speed at which grinding would cease. The VFD speed limit must be set in the VFD programming to prevent the motor from driving the mill above the maximum safe speed corresponding to approximately 85% Nc.<\/p>\n<\/div>\n<\/div>\n

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Can I retrofit an existing ball mill fixed-speed motor with a YVF2 VFD drive system?<\/div>\n<\/div>\n
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Yes, retrofitting an existing ball mill with a VFD and YVF2 motor is a common energy-saving project in cement and mineral processing plants. The key steps are: (1) verify the existing gearbox and pinion can handle the increased torque from the VFD-boosted starting sequence \u2014 sometimes the gearbox must be upgraded when removing the existing fluid coupling that previously limited starting torque to the fixed-speed motor; (2) replace the existing standard motor with the YVF2 IC416 of the same rated power and frame size \u2014 the IEC frame dimensions are identical, so the motor mounts directly on the existing base plate; (3) install the VFD in a motor control cabinet adjacent to the mill \u2014 size the VFD for the motor rated current with a 10 to 15% current margin for starting torque boost; (4) commission the VFD with the mill parameters \u2014 set the maximum frequency limit, the torque boost for starting, and the ramp rate. Korea Ever-Power can supply the YVF2 motor with a pre-commissioning data sheet documenting the motor parameters required for VFD programming.<\/p>\n<\/div>\n<\/div>\n

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How long does a YVF2 IC416 motor last in continuous ball mill service?<\/div>\n<\/div>\n
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With proper maintenance and correct application, a YVF2 IC416 motor in S1 continuous ball mill service should achieve 80,000 to 100,000 hours (approximately 10 to 12 years) of service life before winding insulation ageing requires replacement or rewind. The critical maintenance tasks that extend motor service life in ball mill applications are: bearing replacement every 20,000 to 30,000 hours (2.5 to 3.5 years) based on bearing manufacturer recommendations for continuous duty at rated load; IC416 blower filter cleaning every 3 to 6 months to ensure cooling airflow is not reduced by dust accumulation in the blower air intake; annual insulation resistance measurement to detect early moisture or contamination ingress; and periodic connection check on terminal box to prevent connection overheating from vibration loosening of terminals in the high-vibration mill environment. Grease replenishment every 6 to 12 months for the main motor bearings depending on bearing size and ambient temperature. Korea Ever-Power provides a maintenance schedule specific to the YVF2 frame size and power rating on request.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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Korea Ever-Power \u00b7 YVF2 Series \u00b7 Ball Mill and Grinding Mill VFD Motors<\/div>\n

Need VFD Motors for Your Ball Mill or Grinding Mill Drive?<\/h2>\n

Korea Ever-Power YVF2: IC416, Class H, 2.5\u00d7 starting torque, 0\u2013120 Hz, S1 continuous, 0.75\u2013200 kW, PTC thermistors. Retrofit data sheets available for VFD commissioning.<\/p>\n

View YVF2 Motor Range<\/a><\/p>\n<\/div>\n<\/div>\n

Edited by Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Korea Ever-Power \u00b7 YVF2 Series \u00b7 Ball Mill and Grinding Mill Drive Guide VFD Motor for Ball Mill and Grinding Mill: Critical Speed, Starting Torque and Mill Drive Selection Ball mills, rod mills, SAG mills, and laboratory grinding mills impose some of the most demanding motor requirements in industrial processing: very high starting torque to […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[28],"tags":[],"class_list":["post-197","post","type-post","status-publish","format-standard","hentry","category-industrial-electric-motor"],"_links":{"self":[{"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/posts\/197","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/comments?post=197"}],"version-history":[{"count":3,"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/posts\/197\/revisions"}],"predecessor-version":[{"id":201,"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/posts\/197\/revisions\/201"}],"wp:attachment":[{"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/media?parent=197"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/categories?post=197"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/el\/wp-json\/wp\/v2\/tags?post=197"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}