1, raw materials for the reason: domestic or foreign because of poor polyurethane raw materials, a large number of broken bottom caused returns. Not only to pay the bottom also to pay shoes, and caused millions of of dollars in losses, in the 80 's Shanghai had banned the use of polyurethane soles due to broken bottom. After these years of continuous improvement and practice, the current domestic raw material technology has been completely cleared, due to raw materials caused by the broken bottom events have rarely occurred. such as raw material selection is not correct, hardness is excellent, the use of low temperature and so on. The adjustable range of the Wakahara solution is too wide or too narrow to find a central formula (the best formula) and is easy to break the bottom.
2, mold reasons: such as sharp angle or along the bend direction pattern too deep and so on.
3, equipment or operation reasons:
(1) Mold temperature: preheating and ripening when the mold temperature to 35~40℃ is appropriate, too high reaction is too fast, easy to overflow, the bottom surface is easy to produce cracks, molding will produce "nest", mold temperature is too low, poor reaction, can not be fully foaming, the epidermis thickened.
(2) The total pouring amount is not suitable, the general raw material milky white period of about 8-10 seconds, pouring time to no more than 5 seconds, otherwise affect the mixture in the mold cavity filling and reaction.
(3) Mixing ratio error: not tuned to the center formula of the best position, when metering pump delivery or mixing device transformation caused by measurement errors, may be beyond the allowable range of the central formula.
(4) The change of material temperature is too large: especially when the two groups are different when the feeding, the new raw liquid temperature is higher, due to the difference in material temperature is too large, resulting in the ratio error.
(5) The demoulding time is premature or the C material (catalyst) is insufficient: the mixture has not been fully reacted and initially cured in the mold, at this time the demoulding may produce cracks or broken bottom.
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