ADMET has many years of experience in the material testing industry and this has shown the significance of equipping test machines with the exact grips and fixtures.
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Image Credit: Admet Inc.
A machine can only be exploited to its full capacity if the right fixtures or grips are used. With all the available options, selecting the correct accessories for a testing application can be more complicated than one thinks.
Grips and fixtures are mainly categorized by two key factors: the kind of testing that they will be used for and their capacity. Overloading the grips may damage not only the grips but also the machine frame and the load cell, so it is very important to avoid overloading. This article will focus on grips employed for tensile testing and guide customers through the steps involved in determining the appropriate tensile grips for their testing.
Specimen slippage from the grip faces may occur not only due the material characteristics of samples, but also due to several reasons associated with the grips selected:
Instead of slipping from the grips, certain specimens may break right at the grip faces. It is necessary to monitor the behavior of the sample during the tests and observe how the specimen breaks. The recorded breaking strength will not accurately represent the actual breaking strength if the break is at the line of the jaw faces. There are a few ways to handle specimen breakage:
What if the samples are too small or too large and have a non-standard shape that it is almost impossible to find the right grips? This might also be an issue if customers are interested in testing the end product, not just the material with which the end product is made. Very often, the solution is to have a custom grip engineered to suit the customers’ testing requirements or look into non-standard grips which are not always listed in product catalogs.
One example is a fixture that is used for holding needles. The ADMET’s Engineers have developed the Luer lock to adapter fixture, as shown in the picture below, for a quick solution.
Custom Luer Lock test fixture. Image Credit: Admet Inc.
Keeping those items in mind, users can avoid the most common issues associated with tensile grips by being conscious of five key factors in choosing the correct grips for their application.
Tensile testing grips include self-tightening grips, pinching, webbing grips, rope and thread grips, hydraulic grips, wedge grips, pneumatic grips and manual vise grips. The selection of the most suitable tensile grips to effectively secure the samples is essential in obtaining accurate measurements of tensile properties.
Vise grips are the most common tensile grips and ADMET offers these grips with one or two t-handles.
Figure 1. Manual Vise Grip diagram. Image Credit: Admet Inc.
Particular tensile grips may be limited to the opening width of the jaws or limited to a specific capacity due to their design specifications. For instance, manual vise grips can test samples up to 50 kN. Pneumatic grips can go up to 30 kN, but when the capacity increases, the opening width of the grip jaws decreases.
Wedge grips are often used to test higher capacity samples such as metals. They are also used with ASTM E8 metals testing and supplied with optional alignment tools in order to ensure axiality of the applied loads.
Figure 2. Specimen centering with wedge grips. Image Credit: Admet Inc.
Rope, thread, capstan and webbing grips come with custom designs to specifically test specific materials such as yarns, ribbons, wires and cords.
Figure 3. Webbing grip diagram. Image Credit: Admet Inc.
Figure 4. Rope tensile grips.Image Credit: Admet Inc.
Figure 5. Pneumatic capstan thread grips for tensile testing. Image Credit: Admet Inc.
Scissor grips provide a large opening width together with wide jaws, and hence they can be used with samples with non-standard shapes, such as plastic belts.
Figure 6. Scissor grips. Image Credit: Admet Inc.
O-ring tensile testing fixture, loop testing grips and hook grips are examples of non-standard solutions that can be a better choice for customers’ materials.
Figure 7. Hook grips. Image Credit: Admet Inc.
Figure 8. O-Ring tensile grips. Image Credit: Admet Inc.
The same grip can be employed for testing several samples just by changing the grip face type. Without knowing the specifications of the sample material, it would be difficult to recommend a grip face. Certain ASTM standards will contain a recommended grip face, but most will leave it to the user to decide based on the dimensions and characteristics of the specimen material.
Grip Face Description
In addition, ADMET provides a quick change system for all types of jaw surface mentioned above. Users who are interested in quickly changing from one jaw type to another can use the jaws with quick change carriers.
Figure 9. Quick change grip faces. Image Credit: Admet Inc.
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Tensile grips are employed to achieve results on the tensile properties of customers’ samples such as yield, tensile modulus, elongation, peak load and tensile strength.
Different materials demonstrate different material characteristics. Before selecting grips, customers must be confident of the maximum force that will be needed to test their samples.
The end product and its internal component materials with varying features can be tested for tensile properties using a universal testing machine.
Common materials tested in tension include textiles, paper, metals, plastics and elastomers, composites, biomaterials and adhesives. At first, each material is prepared for testing in a particular geometry that is typically defined in the testing standards. Common specimen geometries include cylindrical or flat dog-bone geometries such as bars and tubes.
Sample preparation may be performed by die cutting or machining. ADMET provides dies conforming to particular testing standards. Sample preparation is essential and usually specific. One example is ASTM D638, which explains five different specimen dimensions that have to be selected based on the characteristics of the material that needs to be tested.
Figure 10. ASTM D638 die specifications. Image Credit: Admet Inc.
Very often, hard specimens such as composites, metals and certain plastics are difficult to hold properly as slippage and premature breakage can be common. Therefore, grips with high clamping forces, such as wedge grips and hydraulic grips are recommended.
On the contrary, elastomers and rubbers are more easily held in a range of grip designs such as wedge grips, pneumatic grips, manual vise grips or eccentric roller designs. The easy-to-use and most common grips are pneumatic or manual vise grips with rubber coated or serrated jaw faces.
In addition to recommending the test method, particular testing standards indicate a fixture design to be made specifically for testing in accordance with that standard. Examples of tensile fixtures that are designed to specific standards include ASTM D3039, ASTM D1414 and ASTM C297.
Figure 11. ASTM C297 custom test fixture. Image Credit: Admet Inc.
The final item on the list is attaching the grips on the testing machine. Since grips are not linked to the electronics of customers’ universal testing machine, they can be used together with any make and model. Usually, ADMET tensile testing grips are mounted on Tinius Olsen, MTS and Instron frames using adapters.
Adapters can be provided with customers’ grips of choice of if customers would like to machine them in-house, the company’s Sales Engineers can provide drawings to match the precise dimensions required.
Figure 12. Male end adapter for mounting grips. Image Credit: Admet Inc.
To determine the best suited grips for tests, customers can let ADMET’s Sales Engineers know the maximum force capacities required to test their samples, shapes, dimensions, sample material and elongation properties. The Engineers will then discuss the options with the customers, and, if required, the team can even test their samples to select the right grips for their testing requirements.
This information has been sourced, reviewed and adapted from materials provided by Admet, Inc. - Materials Testing Equipment.
For more information on this source, please visit Admet, Inc. - Materials Testing Equipment.
Pressure testing systems and equipment are critical tools used in various industries to assess the integrity and safety of pipelines, vessels, and other components by subjecting them to controlled pressure levels. Understanding their principles and applications is essential for maintaining the reliability and safety of infrastructure and machinery.
Pressure testing is crucial to ensure a pressure vessel's proper operation and safety. A pressure testing system is a process of testing the reliability of a vessel to specific laid out pressure ratings, and it is used to test parts of the equipment of a vessel for strength and leaks before their use. There are a variety of pressure test processes, each of which provides a different, specific check on the pressure vessel.
At Tikweld.com, we have over twenty years of experience distributing, designing, and building pressure testing equipment. We also have expertise in pressure test applications that utilize pneumatic, hydrostatic, hydraulic, and proof testing methods. With our experience and knowledge, you can be confident that your test performance will be optimized with safety in mind.
Hydraulic power control systems such as pressure test benches are essential to the mechanical systems applicable in every automotive and mechanical field to test a vessel's reliability and ascertain pressure ratings. Hydrostatic testing is a great way to test for leaks and the structural strength in a container or cavity. This method is also an excellent way to test the integrity of your components. By designing and building low and high-pressure hydrostatic testing instruments, you can conduct burst-test, leak-test, flow-test, or calibrate your parts with ease.
Hydrostatic pressure testing units are designed to test the strength and durability of materials. They can include manual or automatic testing capabilities and automatic part load/unload features and are designed to collect detailed data for test evaluation.
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Pressure gauges come in all shapes and sizes, but for the most part, they are relatively inexpensive and are read manually. One of the most popular types is the Bourdon gauge, patented by Eugene Bourdon in France in 1849.
Bourdon gauges contain a thin-walled metal tube typically threaded into the compartment where pressure is measured. As pressure increases in the tube, the tube begins to straighten. On the other end of the tube is a lever system that contains a pointer. As the tube straightens, the pointer moves around a dial, indicating pressure in pounds per square inch (PSI). Common tube shapes include curved or C-shaped, spiral, and helical. This is a mechanical device that is manually read. Another type of mechanical gauge that operates similarly and contains a pointer is called a diaphragm gauge.
There are many different pressure gauges, each with its advantages and disadvantages. Traditional gauges, such as the Bourdon and diaphragm gauges, are sensitive to vibration and condensation. Another type is called a "filled" pressure gauge, and it is filled with viscous oil. This design has fewer moving parts than the traditional pressure gauges and is more reliable. This design dampens pointer vibration and is not susceptible to condensation.
The temperature and pressure recorder receiver is an instrument that records controlled temperature and pressure on a graph. It can be used for various applications and is designed to be easy to use.
The static pressure system consists of a helical bourdon tube connected to a piping system and measures the static pressure. The thermal system consists of a spiral bourdon tube, a capillary, and a bulb. Usually, all parts are made of stainless steel.
The recording mechanism often is a pen system that continuously records data. It converts the mechanical input of the pressure and temperature into lines on a rotating chart.
A Hydrostatic Test Pump is a pump used to test equipment by filling it up with an incompressible liquid, usually water. The pump is connected to the equipment being tested by a high-pressure hose. The pump is self-contained, portable, and can be powered by hand, air, electric, or gas engines.
The pressure of the test component is slowly increased with the help of a pump with appropriate safety relief and controls. The pressure is held at a predetermined set point for a predetermined time, and then a visual inspection is done to see if there is any leakage or if the pressure has reduced from the set point.
This hydrostatic pressure test equipment is compact, efficient, and cost-effective, available in different pressure and flow combinations (pressures to 1000 bar (14,500 psi) are possible). Though theoretically, water is considered a non-compressible fluid, it requires multiple feeding to raise the pressure.
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The safe operation, service, and maintenance of any pressure equipment, pressure vessel, or pressure control system are essential to the efficient running of any organization. In turn, it forms the basis of compliance with the Pressure Systems Safety Regulations 2000 (PSSR) and the Provision and Use of Work Equipment Regulations (PUWER) 1992.
Generally, the following pressure system service and maintenance activities are performed:
Further guidance on regulation 11 (Operation) and regulation 12 (Maintenance) of the Pressure Systems Safety Regulations 2000 is given in the Approved Code of Practice Safety of pressure systems.
The Pressure test equipment is essential for firms that have pressure equipment and wants to test the integrity of their vessel before use constantly. Pressure testing equipment is used to test parts of the equipment vessel for strength and leaks before use. It can also help your company test new components and sub-assemblies before installation, thus shortening the troubleshooting time and taking the guesswork out of the diagnoses. Contact Tikweld welding supplies and services in Nigeria for further inquiries on pressure testing equipment.
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