Comparative analysis of selection
In the mechanical properties testing of plastic films, the tensile testing machine is the core equipment to evaluate parameters such as tensile strength, elongation at break, and modulus of materials. Single-column and double-column structures are two mainstream designs, and their selection directly affects the accuracy and ease of operation of the test results. Based on domestic and foreign standards, this paper compares the structural principle, force value range, application scenarios and cost control.
Structure and principle
The single-column tensile testing machine adopts a single column to support the beam and sensor, and the whole is a C-shaped open frame. Its compact loading chain is suitable for small force testing, usually with a maximum force value of less than 5 kN. The double-column tensile testing machine uses two columns to symmetrically support the beam to form a closed frame, which can withstand large bending moments, and the force value range is commonly from 1kN to 50kN. The beam deflection is small when the load is applied in the double-column structure, which is due to the lateral force shared by the columns on both sides.
For plastic films, most standards (such as ISO 527-3, GB/T 1040.3) require longitudinal and transverse tensile tests of the specimen, usually between 200N and 2000N. The single-column model has met the accuracy requirements in this range, but the double-column structure can reduce the system error introduced by the clamping deflection of the specimen due to the higher parallelism of the upper and lower beams.
Quantitative comparison of force accuracy and stiffness
Suppose the same high-precision sensor (level 0.5) is installed on two racks and measures a 200N load. Due to the cantilever structure, the deflection of the beam end can be expressed as:
δ = (F * L^3) / (3 * E * I)
where F is the load, L is the height of the free end of the column (about 0.6m), E is the elastic modulus of the material (about 210GPa for steel), and I is the moment of inertia of the section. Substituting typical parameters, δ a single column is about 0.15mm. Due to the symmetry of the columns on both sides, the deflection of the double-column frame is only about 1/8 of that of a single column, about 0.02mm. This means that at fast stretching (500mm/min), the dual-column rack reduces data runout due to deformation and provides better repeatability.
The following table lists the main comparisons:
| Compare items | Single column machine / Twin column machine |
| Limit force value range | Usually ≤ 5kN / Usually up to 50kN |
| Beam parallelism deviation | 0.1~0.3mm/m /<0.05mm/m |
| Stability of tensile speed | Good / High grade |
| Applicable film thickness | 0.01~0.3mm / 0.05~1.0mm or higher |
| Fixture proximity | Excellent (open on three sides) / Medium (limited anterior) |
| Standard compliance | Meets GB/T 1040.3 / ISO 527-3 and ASTM D882 at the same time |
| Typical procurement costs | Low/Medium to High |
Differences in application scenarios
For thin blown films with a thickness of less than 0.1mm, the breaking force is often less than 100N. Due to the wide operating space, the single-column machine is suitable for frequent replacement of fixtures (such as pneumatic flat fixtures for thin films), which is suitable for rapid screening of multiple batches of specimens in the R&D stage. For multi-layer composite film, heavy-duty packaging film or metallized film (thickness above 0.2mm), its tensile breaking force can reach more than 800N, and the specimen is prone to necking during the stretching process. Due to its excellent rigidity, the dual-column machine can reduce the interference of the elastic deformation of the frame to the detection of fracture points, ensuring data consistency.
In addition, when multiple cycles of loading need to be performed, such as creep or elastic recovery tests of films, the dual column machine has an advantage in maintaining constant strain for a long time. However, if the laboratory is mainly focused on quality inspection and compact space, a single-column machine is a more economical choice.
Key points of selection suggestions
Based on the above analysis, users can make decisions based on the following principles:
1. Force value conditions: The normal measured force value is less than 1000N, and the thickness of the specimen is less than 0.2mm, single-column machine is preferred. Beyond this range, the twin column machine offers a higher safety margin.
2. Detection frequency: high-frequency, multi-variety switching single-column machine; High-precision, single-batch large number of specimens are selected by dual-column machine.
3. Standard requirements: If only the conventional stretching of plastic film in GB/T 1040.3 needs to be performed, a single column machine is sufficient. If rubber elastomer tests such as ISO 37 and ISO 34-1 are involved at the same time (which may require a larger stroke), the double column machine is more secure.
4. Budget and site: The single-column machine covers an area of about 0.2m², which is suitable for countertop operation; the double-column machine needs to be placed on the ground, occupying about 0.5m² and considering the floor load-bearing.
Epilogue
Single-column and double-column tensile testing machines have their own applicable boundaries in plastic film inspection. When selecting the actual type, it is recommended to consider the typical force value range, standard requirements and laboratory resource balance of the membrane material to be tested. Choose a rack structure that matches your testing needs to get reliable data support.
References
1. GB/T 1040.3-2006 Plastics - Determination of tensile properties - Part 3: Test conditions for films and flakes
2. ISO 527-3:2018 Plastics — Determination of tensile properties — Part 3: Test conditions for films and sheets
3. ASTM D882-18 Standard Test Method for Tensile Properties of Thin Plastic Sheeting
4. Principles of Structural Design of Material Testing Machines (Machinery Industry Press, 2015)