Proposal Description

During the retrofitting process, the original control system circuit remains unchanged. The contactors in the vulcanizing machine’s hydraulic station are replaced with frequency converters. The start/stop signals provided by the system’s PLC are directly connected to the frequency converters to control their start and stop operations (eliminating the need for intermediate relays). At the same time, the pressure signal from the hydraulic station is connected to the analog input port of the frequency converter, creating a closed-loop control system with pressure feedback. The frequency converter’s speed is then controlled based on this pressure signal.

After the modification is completed, once the PLC sends a start signal, the frequency converter starts up, and the hydraulic station’s pressure rapidly rises to the set value, providing hydraulic power for mold opening or closing. Once the mold-opening and closing actions are complete, the voltage (or current) output from the pressure sensor decreases, causing the frequency converter’s frequency to drop to a low-frequency state, at which point the motor runs at a low speed while the hydraulic station’s pressure remains stable at the set value. When the hydraulic device begins to operate, the hydraulic station’s flow rate increases, causing the pressure to drop; consequently, the voltage (or current) output from the pressure sensor rises, and the frequency converter’s frequency quickly increases to its rated frequency, driving the motor to run at high speed and supplying the hydraulic station with the required pressure. This process repeats cyclically. When a cycle is finished and the PLC sends a stop signal, the frequency converter shuts down and enters a standby mode, awaiting the start of the next working cycle.

Scheme Composition

Xinshida ME500-4T 0037 inverter replaces the contactor.

After the retrofit, the equipment operates stably, with precise and smooth control, and delivers significant energy-saving benefits. Maintenance costs and equipment noise levels have also been noticeably reduced. We recommend that the entire hydraulic station of this vulcanizing machine undergo a frequency conversion retrofit.

● Stable and reliable performance

Since being put into operation, the frequency converter has been functioning reliably. During summer, when the temperature in the hydraulic station of the vulcanizing machine approaches 50℃, the ME500 has successfully overcome the conventional limitation that standard frequency converters cannot operate normally in high-temperature and dusty environments—without experiencing any failures whatsoever. As a result, production has remained continuous and uninterrupted, leading to increased output.

● Reduced maintenance costs

Because the frequency converter operates with stability and reliability, there are no unplanned shutdowns or component failures during production. Therefore, there is no need to stop the machine to replace damaged contactors (or soft starters) or other spare parts. Routine maintenance—such as dust removal and tightening screws—is performed only during scheduled shutdowns for inspection and repair, which helps save on labor resources and spare parts costs while ensuring continuous production and boosting output.

● Reduce impact, extend the service life of mechanical components and motors, and lower procurement costs for spare parts and accessories.

Frequent direct starts and stops of equipment can generate powerful mechanical shocks, leading to accelerated wear and even damage of mechanical components. Moreover, the motor, subjected to inrush currents 6 to 10 times its rated current during startup, may experience coil aging, reduced service life, and even burnout. However, the soft-start and soft-stop functions of a frequency converter ensure smooth operation during equipment startup and shutdown. Additionally, when the hydraulic station is not producing hydraulic output, the motor operates at a low frequency in the frequency converter’s low-frequency mode, which further reduces mechanical wear on the equipment. As a result, these features effectively minimize mechanical shocks, extend the service life of mechanical components and motors, and reduce the costs associated with procuring spare parts.

● Energy saving

Before the equipment upgrade, an electricity meter was installed at the hydraulic station to calculate and record the electricity cost per tire. As shown by the electricity cost statistics collected via the meter, there is still considerable room for energy savings by using a variable-frequency drive.

Table 1: Comparison of Specific Energy Consumption Between Jingyuan Hydraulic Vulcanizing Machine and HF Vulcanizing Machine

Note:

① The Jingyuan vulcanizing machine F01-F05 pump stations are equipped with one 37-kW motor and one 22-kW motor each.

② The installed single-phase energy meter has an initial value of approximately 0.02 kWh, which results in a relatively large first reading.

③ Calculate the consumed electrical energy: Single-phase watt-hour meter reading × 3 × 20 (100:5 current transformer).

Based on the statistical results in Table 1, we can calculate that, before the retrofit, the average electrical energy consumption per tire for the Jingyuan hydraulic vulcanizing machines F01-F05 was:

H unit consumption = (0.364 + 0.293 + 0.293 + 0.284) ÷ 4 = 0.3085 yuan

Table 2: Comparison of Specific Energy Consumption for Jingyuan Hydraulic Vulcanizing Machines

Note:

① The Jingyuan vulcanizing machine F01-F05 pump stations are equipped with one 37-kW motor and one 22-kW motor each.

② The installed single-phase energy meter has an initial value of approximately 0.02 kWh, which results in a relatively large first reading.

③ Calculate the consumed electrical energy: Single-phase watt-hour meter reading × 3 × 20 (100:5 current transformer).

According to the statistics in Table 2, the electricity consumption per tire after the frequency conversion retrofit is:

H unit consumption = 0.19 yuan

That is: Each tire produced saves S per unit = 0.3085 – 0.19 = 0.1185 yuan.

The daily tire production is: Daily output = C production × B shifts = 300 × 3 = 900 tires.

Monthly savings = S per unit saved × daily output × number of days in the month = 0.1185 × 900 × 30 = 3,199.5 yuan

Based on 300 consecutive days of production per year, with three shifts per day and a daily output of 300 tires per shift, the cost of the retrofit can be recouped within one year simply by saving on electricity costs.