Strength Test
Green strength and dry strength is the holding power of the various bonding materials. Generally green compression strength test is performed on the specimen of green sand (wet condition). The sample specimen may of green sand or dry sand which is placed in lugs and compressive force is applied slowly by hand wheel until the specimen breaks. The reading of the needle of high pressure and low pressure manometer indicates the compressive strength of the specimen in kgf/cm2. The most commonly test performed is compression test which is carried out in a compression sand testing machine. Tensile, shear and transverse tests are also sometimes performed. Such tests are performed in strength tester using hydraulic press. The monometers are graduated in different scales. Generally sand mixtures are tested for their compressive strength, shear strength, tensile strength and bending strength. For carrying out these tests on green sand sufficient rammed samples are prepared to use. Although the shape of the test specimen differs a lot according to the nature of the test for all types of the strength tests can be prepared with the of a typical rammer and its accessories. To prepare cylindrical specimen bearing 50.8 mm diameter with for testing green sand, a defined amount of sand is weighed which will be compressed to height of 50.8 mm. by three repeated rammings. The predetermined amount of weighed molding sand is poured into the ram tube mounted on the bottom. Weight is lifted by means of the hand 1ever and the tube filled with sand is placed on the apparatus and the ramming unit is allowed to come down slowly to its original position. Three blows are given on the sample by allowing the rammer weight to fall by turning the lever. After the three blows the mark on the ram rod should lie between the markings on the stand. The rammed specimen is removed from the tube by means a pusher rod. The process of preparing sand specimen for testing dry sand is similar to the process as prepared before, with the difference that a split ram tube is used. The specimen for testing bending strength is of a square cross section. The various tests can be performed on strength tester. The apparatus can be compared with horizontal hydraulic press.
Oil pressure is created by the hand-wheel and the pressure developed can be measured by two pressure manometers. The hydraulic pressure pushes the plunger. The adjusting cock serves to connect the two manometers. Deformation can be measured on the dial.
The compression strength of the molding sand is determined by placing standard specimen at specified location and the load is applied on the standard sand specimen to compress it by uniform increasing load using rotating the hand wheel of compression strength testing setup. As soon as the sand specimen fractures for break, the compression strength is measured by the manometer. Also, other strength tests can be conducted by adopting special types of specimen holding accessories. Copied from A Textbook of a Basic Manufacturing Processes and Workshop Technology by Rajender Singh.
