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„One piece doesn’t make statistics”. Rawlplug’s fixing strength tests

5 min
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“Strength” is a multifaceted concept, especially when it comes to the extensive product range offered by Rawlplug. This is why our strength tests are also multifaceted, so as to provide our customers with a product that both complies with the applicable standards and is reliable in everyday use.

Strength is a key word at Rawlplug, whether it concerns fixings, hand tools, power tools, or the respective dedicated accessories. Our experts in the areas of product management and laboratory tests will tell you all about how we check it.

Pull-out tests on strict terms

Most of the strength tests we perform at Rawlplug’s laboratories involve checking compliance of the strength parameters achieved by our products with the values declared in the relevant technical documentation, such as the National Technical Assessment (KOT) or the European Technical Assessment (ETA). We are obligated to perform such tests under the Factory Production Control (FPC) system we implemented, which is supervised and reviewed in annual audits by a Technical Assessment Body. The most common procedure in this case is the pull-out test, determining the durability of the fixing piece and the fixing connection strength.

How do we perform the tests? We install the fixing piece being tested in accordance with the installation instructions provided in the technical documentation and the anchoring parameters such as: drill bit diameter, drilling and embedment depth, and substrate type. Subsequently, we perform a pull-out test on this set-up. This is carried out using universal testing machines that pull the piece that has been fixed upwards with a predetermined speed until the maximum value for the specific fixing piece is reached. Machines of this type make it possible to test any type of our fixings, embedded in any material.

Fixings are tested in strictly defined conditions.

  1. Firstly, we always test more than one fixing piece at a time. 
One piece doesn’t make statistics. We perform at least three, and five identical tests as a standard, in the same block, with the same drill bit and to the same embedment depth.

Artur Grzesiak

Laboratory Department Leader

2. Secondly, we always assume the theoretically least favourable, i.e. the most shallow fixing depth. 

If we have a fixing piece with a length of 100 mm, and the approval indicates 70 mm as the minimum anchoring depth, we don’t anchor the fixing piece at 80 or 90 mm during the tests, but always at the minimum depth. It is for the latter that we declare the specific load capacity, and we don’t rely on the relationship in which greater embedment depth equals higher pull-out strength.

Artur Grzesiak

Laboratory Department Leader

3. Thirdly, we verify the results. 

We calculate the characteristic load capacities and work on that basis. They differ from arithmetic means in that they take into account the scatter of results – the characteristic load capacity will never be higher than the lowest result of the whole series of measurements. Taking into account the influence of the scatter of individual results on the final outcome means that we also check the repeatability of the strength parameters obtained for our products.

Artur Grzesiak

Laboratory Department Leader

Compression, bending, screwing time trials, and... freezing

In addition to pull-out tests, we perform shear strength tests: by positioning the block properly, we can achieve a force exerted at an angle of 90° to the plane of the screw head plane. For timber fasteners, in turn, we test the force at which the head is pulled through a timber beam. Our everyday practice also includes tensile strength tests focused on the material parameters of the steel from which the fixing piece is made.

We can test compressive or bending strength, as well as look for the force needed to push a nail into wood. Using a torque wrench, we carry out twist-off tests for screw heads. In specialised applications, impact strength is also checked, which is a standard test in the case of roof sleeves. 

We also have a machine to test the useful drilling effectiveness. It allows us to adjust spindle pressure and speed and, as a result, test the screwing time of a particular fixing piece.

Artur Grzesiak

Laboratory Department Leader

An unusual procedure involves strength testing on a machine that simulates the properties and behaviour of cracked concrete. Test of this type are particularly important for fixings intended for seismic applications.

Anchors are also subjected to strength tests. The test plan differs slightly depending on the type of bonded anchor, but we test every lot manufactured. As part of double verification, we also test the chemical raw materials used in the production of our bonded anchors, even though we obtain certificates from the tests carried out by the suppliers.

In the case of bonded anchors, we have an interesting group of tests that we perform in freezers. These are mainly supposed to check the anchor bond strength or the capacity of squeezing the bonding compound from the cartridge. Interestingly, in the case of bonded anchors, we also test the consistency of the resin mixture after it has mixed with the hardener. The purpose of this is to check the flow properties of the bonded anchor. This test is carried out using a specialised instrument: a rotational rheometer.

Artur Grzesiak

Laboratory Department Leader

Many of the tests performed in Rawlplug's laboratory are specialised and commissioned by customers who use our products for non-standard applications or in atypical conditions. They often provide the basis for product upgrades and the preparation of new designs that meet practical installation needs even better.

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