#081 Method of Using Standard Components (30) Urethane Spring
The method of using a urethane spring of providing it on the punch of a simple mold and using it as a substitute for a striper as is shown in Fig. 1 is relatively frequent. | ![]() |
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Fig. 2 is the form of using a urethane piece as a spring for the stripper. | ![]() |
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Fig. 3 is a method of use as a die cushion in drawing or bending operations. The urethane pieces used in the above forms are mainly pieces cut from a long round shaped material. | ![]() |
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Fig. 4 is a special method of use, and the urethane piece is used by gripping it between the plates. This method of use is adopted when wanting to absorb the variations of the bottom dead point. A plate shaped urethane piece is used in this method. A large amount of compression cannot be obtained. | ![]() |
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Urethane pieces can be classified broadly into two types. One type is that in the state of ordinary rubber (ordinary urethane), and the other is what is called the porous type. Porous type has the shape of a sponge.
When ordinary urethane is compressed and deformed, heat is generated due to internal friction. If this heat is accumulated inside, the pressure characteristics change, and the pressure generated decreases from the initially set pressure. This is a point that has to be paid attention to in using urethane. The amount of heat generated is proportional to the amount of compression (deflection) and the speed of compression. In the case of ordinary urethane, the limit to the deflection is about 20% of the free length of the urethane spring. At this time, the limit to the speed (spm) of the press machine is about 100spm. As the speed (spm) is increased, the amount of deflection of the urethane spring should be made smaller. For example, the limit to the amount of deflection will be about 14% at a press machine speed of 200spm.
When the porous type is compressed, the internal air bubbles get deformed and the spring gets deflected. Since the deformation of the material inside the urethane spring is small, the heat generation is small compared to ordinary urethane, and hence since even the heat accumulation is small, it is possible to increase the amount of deflection. It is possible to increase the amount of deflection to about 35% at 100spm. However, the generated pressure is small compared to ordinary urethane. This type is used when a large deflection is required.
Even when a urethane spring is being used within the specifications, it gets deteriorated and break by developing cracks. It is necessary to replace early.


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