Select and compare elements
In the mechanical properties test of plastics and rubber materials, the structure of the universal testing machine directly affects the test accuracy and ease of operation. Double-column portal and single-column are two mainstream designs, which differ in frame rigidity, load range, space adaptability, etc. Based on domestic and foreign standards (such as ISO 527, ASTM D638, GB/T 528, etc.) and technical data, this paper systematically compares the two to help laboratories make reasonable choices according to testing needs.
Frame structure and rigidity
Double column portal type: the columns on both sides and the beam form a closed frame, with the internal lead screw transmission system, the overall rigidity is high. Under large tensile or compressive loads, the amount of deformation is small, which can ensure the measurement stability of the force value sensor. Suitable for large tonnage testing (typically ≥ 5 kN).
Single-column type: It adopts a single column and movable beam structure, and the frame is open, making it easy to access the specimen area. However, the rigidity is relatively low and is significantly affected by bias loads, and it is usually suitable for small load testing (≤5 kN). In the high elongation test of plastics and rubbers, improper partial load control may affect the repeatability of modulus and elongation at break.
Load capacity and test range
The double-column portal can be configured with sensors from 0.5 kN to hundreds of kN, covering the full range from lightweight plastic films to high-strength engineering plastics and rubber composites. The upper limit of the load of the single column is mostly within 5 kN, which is suitable for low-strength materials such as thin sheets, flexible PVC, thermoplastic elastomers, etc. For rubber tensile tests (e.g. dumbbell-shaped specimens in the GB/T 528 standard), the double-column portal provides a wider rate range (0.001–1000 mm/min) at the same time.
Space layout and specimen installation
The single-column working space is not blocked by columns on both sides, making it easy to install large deformation extensometers, fixtures and environmental chambers (such as high and low temperature boxes). The double-column portal requires more careful planning when installing clamps or sensors with larger lateral dimensions due to the presence of pillars on both sides, but the clear width between the two pillars is usually ≥ 400 mm and can accommodate most standard fixtures. For the folding clamping method commonly used in rubber testing, the double column provides clamping support on both sides to reduce early breakage due to clamping offset.
Test accuracy and repeatability
In constant velocity tensile and compression cycle tests, the double-column portal has a lower load eccentricity due to its good mechanical symmetry, and the repeatability standard deviation can be reduced by 0.5%–1.2%, especially when measuring the modulus of elasticity (e.g., the initial tangent modulus as defined in ISO 527). Due to the cantilever structure, the beam may have a small lateral displacement when loaded, which introduces additional errors for deformation measurements in high-elongation rubber tests (elongation at break >500%), which needs to be compensated with high-quality extensometers.
Budget and maintenance considerations
Single-column models typically cost 30%–50% of similar double-column portals, and are lightweight and have a small footprint, making them suitable for laboratories with limited budgets or small test volumes. The purchase and installation cost of the double-column portal type is high, but because of its rigid design, the wear of the lower lead screw and guide rail is more balanced in long-term use, and the calibration period can be extended to 12-18 months (depending on the frequency of use), and the comprehensive maintenance cost is lower.
Summary of selection suggestions
The following brief table summarizes the applicable scenarios of the two types of testing machines:
| Parameter dimension | Tend to choose |
| Maximum load requirement > 5 kN | Double pillar style |
| Testing of high-elongation rubber (>800%) | Double pillar style |
| Change fixtures or environmental boxes frequently | Single column |
| Limited budget and low testing volume | Single column |
| High repeatability modulus measurements are required | Double pillar style |
When selecting the model, it should also be comprehensively evaluated in combination with factors such as fixture interface size, software function and data acquisition frequency. It is recommended that laboratories conduct cross-validation tests with the same batch of specimens before procurement to confirm that standard error requirements are met.
Cited source
1. ISO 527-1:2019 Determination of tensile properties of plastics - Part 1: General principles.
2. ASTM D638-22 "Standard Test Method for Tensile Properties of Plastics".
3. GB/T 528-2009 "Determination of tensile stress and strain properties of vulcanized rubber or thermoplastic rubber".
4. "Technical Guide for Selection of Universal Material Testing Machine", Academy of Mechanical Sciences, 2021.