The cement compression and flexural testing machine is an indispensable piece of equipment for the mechanical performance testing of cement and cementitious materials. This article provides a systematic introduction to the cement compression and flexural testing machine, covering its structural principles, installation and commissioning methods, operating instructions, routine maintenance procedures, and product calibration. It aims to help users gain a comprehensive understanding of the equipment’s working mechanism and key operational points, thereby improving the accuracy of test data and extending the service life of the equipment.

I. Structural Principle

The testing machine mainly consists of a frame, hydraulic control unit, force measurement display system, and electrical system.

1. Machine Body

The machine body is composed of a crossbeam, columns, upper and lower flexure testing assemblies, hydraulic cylinder, frame, and base plate. The measuring instrument is installed at the upper right side of the frame, while the hydraulic control system is located at the lower right side.

The lower flexure assembly is mounted on top of the piston and equipped with guide plates to ensure stable vertical movement of the flexure platform. A scale is installed on the flexure table, and adjustable limit devices on both sides allow flexible adjustment of the span. The rollers can move vertically to maintain force balance during testing.

The upper flexure assembly is installed beneath the crossbeam and fixed by turning bolts and positioning columns. It includes a ball head, ball seat, and spring mechanism to balance the loading process. The rollers can automatically adjust according to the specimen surface condition, ensuring that the curved pressing surface maintains proper contact with the specimen, thereby improving test accuracy.

A dust-proof seal is installed between the cylinder and piston to prevent dust ingress and reduce wear. A sealing ring is also used to prevent hydraulic oil leakage. An annular groove and oil return channel are designed at the top of the cylinder, allowing excess oil to flow back to the oil tank through a plastic pipe.

For compression testing, the flexure assembly can be removed, and a compression pad and lower platen can be placed on the flexure table to perform the test.

2. Hydraulic Control System

The control unit of the testing machine mainly consists of an oil tank, hydraulic oil filter, motor, speed regulating valve, and oil return valve. When the oil supply valve is opened, the piston rises slowly and smoothly.

3. Force Measurement System

Please refer to the instrument manual for detailed information on the force measuring display system.

4. Electrical System

The electrical system consists of a control unit, motor, start button, stop button, and AC contactor.

II. Installation and Commissioning

The testing machine should be installed on a solid and reliable foundation to ensure proper operation and accurate readings. The foundation may be raised appropriately above ground level depending on site conditions. A clearance of no less than 0.7 m should be reserved around the machine for operation and maintenance.

Anchor bolts (M12×300 mm) should be fixed using a secondary grouting method to ensure correct positioning and stability. During installation, the machine must be leveled with a tolerance not greater than 0.1/1000. A 0.1/1000 precision frame level should be used to check the flatness of the flexure table. If deviation is found in the longitudinal or transverse direction, shims may be placed under the base plate for adjustment before tightening the anchor bolts.

After installation, connect the power supply. The electrical system must be properly grounded to ensure safe operation. The power supply voltage fluctuation should not exceed ±10% of the rated value.

III. Operating Instructions

1. Preparation and Pre-Operation Inspection

Before operation, open the rear door and check whether the hydraulic oil in the oil tank is sufficient. If the oil level is low, refill it to the specified level.

Inspect all hydraulic pipe joints and fasteners to ensure they are not loose. If any loosening is found, tighten them immediately to prevent oil leakage, component damage, or test errors. Check whether the dust-proof seals are intact, and confirm that the electrical grounding and safety protection systems are functioning properly.

Also inspect the specimens for visible defects. Any damaged specimens should be replaced. Before testing, the specimen surface should be cleaned to ensure accurate test results.

2. Operating Procedure, Method and Precautions

At the beginning of operation, set the left oil return valve to the open position and adjust the right oil supply valve to the slow position. Press the start button to power on the system and start the motor.

Then close the oil return valve clockwise and slowly open the oil supply valve to raise the piston slightly. Check for any abnormal conditions such as jamming. If any fault is found, stop the machine immediately for inspection and troubleshooting.

After confirming normal operation, check whether the instrument display is at zero. If not, press the reset button to return it to zero. Then open the oil return valve to bring the piston back to its initial position.

(1) Flexural Test Operation

According to the scale markings and specimen size, place the specimen horizontally on the lower flexure support rollers. Close the oil return valve and slowly adjust the oil supply valve to raise the piston rapidly until it approaches the upper flexure assembly.

Once contact is made, switch to slow loading until the specimen breaks. Then close the oil supply valve and open the oil return valve, allowing the piston to return to its original position under its own weight.

Record the displayed value as the flexural strength. Remove debris and press the reset button to prepare for the next test.

(2) Compression Test Operation

Place the specimen at the center of the lower platen. Adjust the oil supply valve to raise the piston quickly before contact with the upper platen, then switch to slow loading until the specimen is crushed.

After the test, close the oil supply valve, open the oil return valve, and record the force value. Clean the broken specimen and press the reset button for the next test.

(3) Precautions

During operation, it is strictly forbidden to place hands or any part of the body between the upper and lower platens to avoid injury.

Specimen fracture may cause debris to fly; proper protective measures should be taken. After specimen failure, the oil return valve should be opened promptly, but not too quickly, to avoid equipment damage or hydraulic shock.

IV. Maintenance and Care

1. The testing machine should be installed in a clean, dry environment with uniform temperature, free from vibration and corrosive gases.

2. The testing machine should be kept clean. Parts without protective coatings should be regularly lubricated to prevent rust.

3. Maintenance

The hydraulic oil should be replaced every 6 to 12 months of use. During oil replacement, the oil tank and oil filter must be thoroughly cleaned. For cleaning, kerosene can be poured into the tank for repeated flushing until completely clean. After cleaning, wipe the bottom of the tank and refill with clean hydraulic oil.

If the hydraulic oil is found to be severely contaminated or cloudy, it should be replaced immediately. Otherwise, it may accelerate wear of hydraulic components and affect the accuracy of test results.

Recommended hydraulic oil grades based on ambient temperature:

(1) 10–20°C: GB443-84 N46#

(2) 20–30°C: GB443-84 N48#

4. Storage When Not in Use

When the machine is not in use for a long period, it should be covered with a plastic protective cover to prevent dust contamination.

V. Product Calibration

1. This testing machine shall be calibrated annually.

2. Calibration shall be performed under the following conditions:

(1) Room temperature 20±10°C;

(2) Relative humidity ≤80%;

(3) Vibration-free environment;

(4) Power supply voltage fluctuation not exceeding ±10% of the rated voltage, and the voltage is stable.

3. After starting the motor, repeat the loading and unloading process three times to the rated load. Then press the instrument reset button; the display will return to zero, and the formal calibration will begin.

4. Calibration items include relative error and relative variability of the indicated value. The calibration results should meet the following requirements:

Relative error of indicated value: ≤1%

Relative variability of indicated value: ≤±1%