Steel head protective shoes soles how to prevent "separation"

1, raw materials reasons: domestic or foreign due to poor polyurethane raw materials, large quantities of broken bottom caused return. Not only did you have to pay for shoes at the bottom, but it caused a loss of several million yuan. In the 1980s, Shanghai prohibited the use of polyurethane soles because of the bottom. After years of continuous improvement and practice, the domestic raw material technology has completely passed through, and the bottom-cutting incidents due to raw materials have rarely occurred. If raw materials are not selected properly, the hardness is too high and the temperature is too low. If the adjustable range of the liquid is too wide or too narrow, it is not easy to find the center formula (best formula) and it is easy to break the bottom.
2, mold aspects: such as sharp corners or patterns along the bending direction too deep.
3, equipment or operation reasons:
(1) Mold temperature: The mold temperature should be 35~40°C for preheating and maturing. If the temperature is too high, the reaction is too quick and easy to overflow. The bottom surface is prone to cracks. When the mold is formed, “stove” is produced; if the mold temperature is too low, then Poor reaction, insufficient foaming, and thick epidermis.
(2) The total amount of pouring is not suitable. Generally, the milky white period of the raw material is about 8 to 10 seconds, and the pouring time does not exceed 5 seconds. Otherwise, the filling and reaction of the mixture in the cavity are affected.
(3) Insufficient supply and affecting the change of mixing ratio: The sufficient supply of material is a prerequisite for accurate measurement. The reason for the lack of supply: the original liquid viscosity is too high, affect the metering pump suction, by increasing the material temperature to reduce the viscosity or dry compressed air (0.5kgcm2) in the tank to facilitate the metering pump suction; the inlet pipe of the metering pump is not Unobstructed, due to the slower flow rate of the original liquid in the inlet tube v = 0.5 ~ 1ms, it is easier to wall, should be cleaned in due time; filter clogging, reducing the filter area, should be cleaned frequently (required daily or once per shift).
(4) Mixing ratio error: It is not adjusted to the optimal position of the center formula. When the metering error is caused by the delivery of the metering pump or the change of the mixing device, it may exceed the allowable range of the center formula.
(5) Material temperature change is too large: especially when the two components are not fed at the same time, the temperature of the new additive liquid is relatively high, resulting in a large difference in material temperature, resulting in a mismatching error.
(6) The demoulding time is too early or the C material (catalyst) is insufficient: the mixture has not been fully reacted and initial curing in the mold, and at this time, the mold may crack or break.
(7) The instantaneous ratio and the required ratio do not match: Since the viscosity and flow rate of the two groups of liquids in the A and B groups are not the same, when the flow rate changes from reflow to pouring (or from pouring to reflow), the flow rates are different. To make the ratio change, commonly used to change the size of the injection orifice different throttle, making instant ratio and the required ratio is basically the same.
(8) In order to prevent the bottom of the steel head protective shoes, attention must be paid to the operation: Record and observe the changes in parameters (such as pressure, temperature, and speed) on each meter; analyze the causes of the changes and possible consequences; always check the soles The intensity of the flash, such as changing the crisp may be wrong ratio, should stop the inspection reasons; regular pouring test cup, "long cup" pouring 3 seconds, (see the total ratio and mixing conditions), "short cup" Pouring 0.3 seconds (see instant mix and mix).

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