A great rubber product often requires both effective design and an innovative material. RL Hudson has remarkable capabilities in both areas. Our award-wining design engineers continue year-after-year to create new products that solve customers’ problems and save them money. And now, we have a material development laboratory that allows us to be equally innovative with materials. Here is a rundown of the equipment and capabilities of our in-house lab.
MIXING Designed to facilitate research and development in a lab setting, our Farrel Banbury® BR1600 mixer is smaller than a production mixer. It is, however, the finest 1.5-liter (3-pound) mixer on the market, incorporating many advanced features typically found only on larger machines. These features include a programmable logic controller (PLC). The PLC allows operating parameters — such as temperature and speed of the mixer’s internal rotors — to be closely controlled, stored in memory, and easily retrieved, thus facilitating repeatability and batch-to-batch consistency.
MILLING Once a batch of rubber is mixed, it goes to our rubber mill, which, like the mixer, was made by Farrel and customized to our specifications. It is a variable speed, variable friction, cabinet- style lab mill. The mill serves two main functions. First, it gives the batch a chance to cool (mixing generates a great deal of heat). Second, the mill facilitates sheeting (flattening) of the rubber to a specified thickness. Once this thickness is achieved and the rubber comes off the mill, samples are taken for testing
RHEOMETRIC TESTS After mixing a batch of rubber, we determine its processing characteristics by performing tests on our moving die rheometer (MDR). Manufactured by TECH/PRO, our MDR is designed in accordance with the American Society for Testing and Materials (ASTM) D 5289 standard, as well as the ISO 6502 standard. The MDR holds a rubber sample firmly between a pair of heated dies. As one of the dies rotates across a small arc, the other die gauges the reaction torque generated in the sample. The machine calculates a “cure curve” showing a number of processing characteristics, including optimum cure time for the sample.
VISCOSITY TESTS We can also gauge the viscosity (resistance to flow) of a rubber batch. This is important because a compound’s viscosity determines its ability to fill a mold properly. Different molding methods — compression, transfer, and injection molding are the big three — require different material viscosities in order to work well. We use a Mooney Viscometer (MV) to gauge viscosity of both raw rubber stock and compounded rubber. Our MV was designed in accordance with the ASTM D 1676 and ISO 289 standards. Our MV can also conduct stress relaxation and pre-vulcanization tests.
PRESS CURING The tests outlined thus far are all performed on uncured compound, but there is also much to be learned by testing cured rubber. Curing (also known as vulcanization) is the heatinduced process whereby the long chains of the rubber molecules become cross-linked by a vulcanizing agent to form microscopic three-dimensional elastic structures. This reaction transforms soft, non-cross-linked materials into strong elastic products. We cure rubber samples in a compression molding hydraulic press with a clamping force of 65 tons. Though our press can mold prototypes, we primarily use it to prepare cured slabs and buttons. These slabs and buttons are used for testing of original physical properties, low and high temperature resistance, compression set resistance, and fluid resistance.
ORIGINAL PHYSICAL PROPERTIES TESTS Original physical properties include hardness, tensile strength, modulus, and ultimate elongation. We check hardness using a Shore® durometer tester conforming to the ASTM D 2240 standard. Though Shore readings are the preference for most domestic companies, we can also generate readings in International Rubber Hardness Degrees (IRHD) per ASTM D 1415. Our Instron® model 5567 tensometer allows us to conduct tensile tests on dumbbells stamped from the molded slabs. The dumbbell is clamped between a pair of grips and pulled steadily until it breaks. The force being exerted on the dumbbell at the point of rupture is that sample’s tensile strength. Tensile tests also allow us to determine other characteristics of a sample, including modulus (the force required to produce a certain elongation, such as 100% elongation) and ultimate elongation (elongation when the dumbbell breaks). These characteristics are plotted into a tensile curve. Studying tensile test data gives us insight into how a material will perform when molded into finished parts. We can also conduct tear resistance, compression, and deflection tests using the Instron.
LOWTEMPERATURE TESTS We conduct low temperature tests using a Thermotron® environmental test chamber. Our Thermotron also allows us to conduct low-to-high cycling tests from -73° to 177° C (-100° to 350° F) at a rate of 3° C per minute.
HIGH TEMPERATURE TESTS We conduct heat aging tests of non-volatiles using five Blue M® horizontal airflow convection ovens. Air is heated to a precisely controlled temperature, then passed over rubber samples inside a specially designed chamber. These tests are important because most of the physical and chemical properties of rubber are impacted when it meets high temperatures, especially for prolonged periods. Studying whether a sample hardens, cracks, or undergoes other changes after being in a heated test environment gives valuable clues as to how that material will perform in high temperature service conditions. We can also conduct life cycling tests ranging from room temperature to 180° C.
COMPRESSION SET TESTS Cured rubber buttons are used to gauge compression set, which is the result of progressive stress relaxation. We place the buttons between the steel plates of a test fixture, then force the plates together using a bolt-tightening device and steel spacers. The buttons are compressed a particular amount (typically 25% of original thickness) for a specific time (such as 22 hours) at a given temperature (such as 100° C). These time and temperature variables are based on anticipated service conditions.We control the temperature by conducting our compression tests inside the same Blue M ovens used for high temperature tests. Once the compression is released, we measure the button. This measurement reveals to what extent the rubber has “set”; that is, not returned to its original thickness.
FLUID RESISTANCE TESTS We conduct fluid resistance tests using an aluminum heat block made by the Akron Rubber Development Laboratory (ARDL). Our heat block has a digital temperature controller (up to 400° C maximum operating temperature) and holds ten test tubes. We use the block to study elevated temperature aging of dumbbell samples in high flash point or non-volatile fluids.
RL Hudson designs and supplies a broad range of molded rubber and plastic products to many of the most respected manufacturing companies in the world.