When manufacturing lifting slings or lashing straps, tensile testing is one of the most important quality control procedures. However, a common question is:
Can the same testing machine be used for both lifting slings and lashing straps?
The short answer is: sometimes, but the testing setup is not the same.
A hydraulic tensile testing machine may look similar when testing different textile products, but the fixture, sample arrangement, loading speed, test method, capacity and applicable standard can be completely different.
For manufacturers and buyers of lifting and cargo securing products, understanding these differences is important when selecting a testing machine and interpreting test results.
The Main Difference Between the Two Testing Machines.
The biggest difference is not necessarily the hydraulic frame itself.
The more important difference is:
How the product is mounted and how the load is applied.
| Item | Lashing Strap | Lifting Sling |
| Main application | Cargo securing | Lifting |
| Typical standards | EN 12195-2, WSTDA-T-1 | EN 1492-2, EN 1492-1 |
| Typical test arrangement | Straight-line pull | Vertical, choker or basket depending on test |
| Main fixture | Hooks/fittings / suitable attachments | Test pins / suitable radius / fittings |
| Hardware | Often tested as part of complete assembly | Tested with fittings when applicable |
| Test speed | Controlled according to applicable method | Controlled according to applicable standard |
| Elongation | Important | Important |
| Breaking test | Yes | Yes |
| Proof testing | Depends on applicable standard | Depends on applicable standard |
| Safety | High-force failure | High stored energy during sling failure |
The same basic tensile frame may therefore be used for different products, but the fixtures and test procedures should be designed for the specific product being tested.
Why the Test Fixture Is So Important?
One of the most frequently overlooked factors in sling testing is the fixture.
A testing machine can have a very high capacity, but if the fixture is not suitable, the test result may not accurately represent the actual product performance.
For lashing straps
The fixture normally needs to connect securely with the hooks, fittings or tensioning device.
For a complete ratchet tie down, the test should consider the actual load-bearing assembly rather than testing only the webbing.
For lifting slings
The situation is different.
The test pin needs to have an appropriate diameter and sufficient strength.
The purpose is to allow the load-bearing fibers to distribute the force properly.
If the pin is too small or the contact geometry is inappropriate, excessive local pressure may be introduced into the sling.
This can result in:
- Local fiber damage
- Uneven load distribution
- Premature failure
- Lower-than-expected breaking strength
- Poor repeatability between tests
Test Speed Matters
Another important factor is the loading speed.
It is tempting to think:
The faster the machine pulls, the faster we can finish the test.
However, tensile testing should be performed according to the applicable test method.
For example, EN 1492-2 specifies a maximum elongation rate for the specimen during load testing.
For web tie downs, WSTDA-T-1 specifies a controlled ram speed for destructive testing.
Therefore, when selecting a testing machine, ask:
Can the machine accurately control and maintain the required test speed?
A high-capacity machine with poor speed control is not necessarily a good testing machine.
Test Capacity Is Not the Only Specification
When buying a tensile testing machine, many customers focus on one number:
“How many tons can it test?”
Capacity is important, but it is not the only factor.
A suitable machine should also be evaluated based on:
1. Maximum Test Capacity
The machine should cover the strength range of the products being tested.
For example, a manufacturer producing both flat webbing slings and round slings may need a considerably higher capacity than a manufacturer producing cargo straps.
2. Load Cell Accuracy
The load cell determines how accurately the machine measures force.
A test result is only meaningful when the measuring system is properly calibrated and sufficiently accurate.
3. Test Speed Control
The machine should be capable of maintaining the required loading speed throughout the test.
4. Effective Test Stroke
This is particularly important for long slings.
A sling may elongate considerably before reaching its maximum load.
If the machine has insufficient stroke, the machine may reach its travel limit before the specimen reaches its actual failure point.
Therefore:
Do not select a machine based only on tonnage. Check the effective testing distance as well.
5. Fixture Compatibility
The machine should be equipped with suitable fixtures for the products you actually manufacture.
For round slings, this may include suitable test pins.
For lashing straps, suitable hooks, fittings or assembly fixtures may be required.
6. Data Recording
A modern testing machine should ideally record:
- Test force
- Maximum force
- Displacement
- Elongation
- Test time
- Load curve
- Failure load
This information makes it easier to prepare professional test reports and investigate abnormal results.
Why Can the Same Product Get Different Test Results?
It is possible for two factories to test similar products and obtain different breaking loads.
This does not automatically mean that one testing machine is wrong.
Several factors can influence the result.
Fixture Design
Different pins, hooks or attachment methods can change the stress distribution.
Test Speed
Different loading rates can affect the measured result.
Test Length
The specimen length and effective test distance can affect elongation and the overall test behavior.
Product Construction
Different yarns, weaving methods, core construction, stitching and manufacturing processes can produce different results.
Pre-Loading
The treatment of the sample before the destructive test can influence the result. Applicable standards should be followed carefully.
Test Configuration
A round sling tested in a vertical configuration is not necessarily equivalent to a choker or basket configuration.
Machine Calibration
An incorrectly calibrated load cell can produce unreliable results.
This is why two factories should not simply compare the final breaking-load number without first comparing the complete testing procedure.
Calibration Is Essential
A tensile testing machine is a measuring device, not simply a piece of production equipment.
Regular calibration is therefore essential.
For manufacturers, the following records should be maintained:
Calibration certificate
Calibration date
Next calibration date
Load cell identification
Testing machine identification
Maintenance records
Test reports
A high-capacity testing machine without proper calibration cannot provide reliable quality evidence.
Frequently Asked Questions
Can one testing machine test both round slings and ratchet straps?
Yes. A suitable tensile test frame may be configured for both applications, but the fixtures, test setup, test speed and applicable testing procedures may need to be different.
What is more important, testing capacity or accuracy?
Both are important. The machine must have sufficient capacity for the product, but accurate and traceable force measurement is essential for reliable test results.
Can I test only the webbing of a ratchet strap?
You can test webbing strength separately when required, but this does not necessarily represent the strength of the complete ratchet tie-down assembly.
Do lifting slings need special test pins?
In many standardized testing procedures, yes. The pin diameter and geometry should be suitable for the sling and allow the load-bearing fibers to distribute the load properly.
How often should the testing machine be calibrated?
The frequency should follow the applicable standard and your quality system.
Is a bigger testing machine always better?
No. Capacity is only one factor. Accuracy, speed control, test stroke, fixtures, data recording, and safety are equally important.
The right testing machine is not simply the machine with the highest capacity. It is the machine that can accurately reproduce the required testing method for the product and standard being evaluated.
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