Testing with SATRA lastometers
An overview of SATRA’s range of lastometer test equipment.
Most footwear construction requires the upper material to be stretched in the process of forming the footwear shape. In the lasting process, upper material is rapidly pulled over a last. As the grain surface of leather is stretched, there is a risk that it can crack. This can be, for example, as a result of the leather being of poor quality or if it is too dry. The ‘lastometer’ test (sometimes referred to as a ‘ball burst’ test) assesses the ability of an upper material to withstand the process of lasting.
It does this by measuring how much a material can be stretched simultaneously (‘distended’) in two directions without sustaining physical damage, such as from grain cracking. In addition to assessing leathers, a lastometer can be used to test woven materials. It is not typically used to assess nonwoven materials.
SATRA has been supplying lastometers since at least 1940, having developed the method some years previously, and significant advances have been introduced since those early devices were produced. Nevertheless, the principle of a lastometer test has stood the test of time, and it is used today both in laboratories and as a quality inspection method within the footwear industry around the world.
In a lastometer test, a circular specimen of the material to be tested is clamped around its edge and is gradually distended by forcing a small metal ball attached to a plunger through the specimen at a controlled speed. As the test proceeds, the displacement of the ball plunger is accurately recorded, along with the force on the plunger. In this article, we will now highlight SATRA’s range of lastometers.
SATRA STD 104 lastometer
Specimens cut from the material are placed in this mechanical unit and a ball-ended rod is raised by turning a handle. The load, measured by a sealed hydraulic system, is displayed on an analogue dial by means of a ‘maximum’ pointer. A mechanical counter geared to the movement of the ball-ended rod records distension. This equipment provides all the necessary information that is required to determine the suitability of the specimen material for lasting.
SATRA STD 190 instant lastometer
The SATRA STD 190 instant lastometer is a simplified form of the STD 104 unit. Intended as a simple pass/fail gauge, it can be used in an incoming goods area for testing leather hides or sheet materials. Utilised in conjunction with normal laboratory tests, STD 190 can provide a valuable quality control check, allowing unsuitable materials to be rejected before production begins, and testing is non-destructive.
The instant lastometer is pneumatically operated via a push button mounted on the frame, and the user can select one of three pre-set distensions – 6, 7 or 8 mm. When operated, the device clamps the material and pushes a ball-ended rod into the specimen. If the surface of the material cracks or tears, the material is unlikely to be suitable for lasting. The chosen pre-set distension value should be established by carrying out full laboratory tests. A filtered and lubricated air supply is recommended for instant lastometers to prevent damage to the internal mechanisms.
SATRA STD 190L instant lastometer (extended throat)
Another simplified form of the STD 104 with the same testing specification as the SATRA STD 190 instant lastometer, this equipment has an extended throat which allows tests to be carried out anywhere on the incoming material. The STD 190L device, which is intended to be used as a bench-top unit, is provided with a foot-operated treadle to conduct the tests. This leaves the operator with both hands free to move the material being evaluated.
SATRA STM 463 digital lastometer
The two-dimensional stretch of footwear materials can be tested faster and more accurately using SATRA’s digital lastometer. Specimens cut from the material are placed in the machine, and the results are displayed on an LCD panel as well as on a print-out provided at the end of the test.
Designed to measure the tendency of an upper material to crack or burst during the lasting process, this lastometer is ideal for multiple tests conducted in a modern laboratory. It incorporates a series of features not available on other models, including an electronic menu-driven system displaying continuously updated test information on an LCD panel, load and distension data which may be downloaded via a USB output, and the testing of several samples to calculate average load, distension and standard deviation.
The SATRA STM 463 digital lastometer can be set to provide load results in kilogrammes or newtons, while distension is displayed in millimetres. An optional graph of the test is also available. STM 463 allows for the testing of single test pieces or batches of three, four, six, eight or specimens.
How can we help?
Email email@example.com for further information on SATRA lastometers and to purchase these items, and visit www.satra.com/test_equipment for an overview of SATRA’s extensive range of test equipment.
This article was originally published on page 10 of the December 2022 issue of SATRA Bulletin.