1 Design concept
1.1 Production line design requirements
1.1.1 Capacity Design Requirements
The annual production capacity of one-component polyurethane waterproof coating is 20,000 tons, and the annual production capacity of two-component polyurethane/polyurea waterproof coating is 10,000 tons, meeting the company's growing production demand.
1.1.2 Quality Design Requirements
Guarantee the production stability of polyurethane/polyurea waterproof coating, the product performance is excellent, meet the requirements of GB/T 19250-2013 "polyurethane waterproof coating" and GB/T 23446-2009 "spray polyurea waterproof coating", and provide customers with good quality Polyurethane/polyurea waterproof coating.
1.1.3 Production line operation design requirements
The equipment realizes electrical control automation, easy operation, accurate measurement, and controllability in the intermediate process; effectively reduces manual operations and reduces labor intensity of workers.
1.1.4 Environmental Design Requirements for Production Lines
By processing the gas generated by vacuum dehydration, the content of toxic substances in the gas is reduced, and environmental pollution is reduced; dust is effectively adsorbed, and a dust-free workshop is established to provide workers with a healthy working environment.
1.2 Division of Production Functions
1.2.1 Raw material storage area
The synthesis of prepolymers is the basic reaction of polyurethane waterproof coatings. Active hydrogen-containing compounds (polyether polyols or polyester polyols) and binary or multi-component organic isocyanates containing isocyanate groups (-NCO) are the main components of polyurethane waterproof coatings. Raw materials [2]. Polyether polyol type polyurethane is currently the mainstream polyurethane coating product because of its performance advantages. The single-component polyurethane waterproof coating and two-component polyurethane waterproof coating produced by the company are selected from Shandong Bluestar Dongda Chemical Co., Ltd. The produced polyether DL-2000D and EP-330N. In terms of raw material arrangement, the four 150 m3 stainless steel storage tanks in the liquid raw material tank area store polyether DL-2000D, EP-330N and two other main liquid fillers, chlorinated paraffin and aromatic oil, while the remaining two storage tanks Canisters are reserved in case of recipe adjustments. The raw materials in the 4 storage tanks can be accurately delivered to each batching tank through the central control metering pump. Powder is the secondary film-forming substance of coatings and an indispensable raw material for the preparation of polyurethane waterproof coatings. The moisture in the polyurethane production process mainly comes from the powder, and if the moisture content of the powder is too high, it will affect the storage stability of the product and make the product gradually thicken, so that it cannot be used due to its high viscosity. Therefore, the company built a 1 100 m2 powder warehouse on the second floor of the new paint workshop to prevent the powder from absorbing moisture from the ground during storage, especially in summer. At the same time, the steam return pipeline is laid to effectively use the steam heat to dry the powder.
1.2.2 Temperature control equipment area (heating, cooling)
The new polyurethane waterproof coating production line is heated by boiler steam. When selecting equipment, a new type of coal-fired steam boiler was selected for the consideration of environmental protection and energy saving. The boiler adopts an upward combustion mechanism design, which meets the smoke and dust emission requirements of coal-fired boilers, and can be used in a first-class environment-friendly area without disturbing the residents. Compared with fuel oil and electric heating steam boilers, coal-fired steam generators can reduce energy consumption by 30%, and the heating area of steam generators can reach 92%. The boiler is fully absorbed, which greatly saves the operating cost of the boiler.
The polyurethane reactor on the old production line uses cold heat transfer oil to cool down, and the efficiency is very low. Especially in summer, it takes about 150 minutes for the reactor to cool down from 115 ℃ to 80 ℃. The new polyurethane production line is equipped with a jacket and uses cold water to cool down. It only takes 70 minutes to cool down the reactor from 115 °C to 80 °C, which greatly shortens the cooling time and improves production efficiency.
1.2.3 Vacuum equipment area
Moisture content is the index that needs to be controlled most in the production process of polyurethane waterproof coatings. Since the relative molecular mass of water is only 18 and contains 2 hydroxyl groups, the amount of -NCO that can be consumed by the same mass of water and polyether DL-2000D is more than 100 times different, so when synthesizing polyurethane prepolymers, it is necessary to avoid water Engages and prevents excess water consumption—NCO, which causes polyurethane coatings to thicken and stick. This is the main reason why polyurethane raw materials need to be dehydrated.
Vacuum equipment needs stable working reliability to ensure the dehydration effect of raw materials. The new polyurethane production line adopts two water-ring Vacuum Pumps, which have uniform air suction, stable and reliable operation, and convenient maintenance; the structure is compact, the pump has a high number of revolutions, and can be directly connected to a general motor without a deceleration device, with a small structural size A large displacement can be obtained. Polyurethane raw materials may be drawn out during vacuum dehydration, so each polyurethane reaction tank is equipped with a buffer tank to check whether the material is drawn out, and it also serves as a storage function.
1.2.4 Hydraulic equipment area
When the new production line was designed, it was positioned as a polyurethane production line with domestic professional level, so most of the control points were replaced by manual operation with electrical control. Some important operating points, such as the discharge valve, retain both manual operation and pneumatic valve control to prevent effective operation when the pneumatic valve fails.
The work of the pneumatic valve needs to be driven by compressed air, and the new polyurethane production line basically uses a Diaphragm Pump to transport, so the working stability of the Air Compressor is of great importance. We chose a twin-screw Air Compressor with good dynamic balance characteristics, which directly drives the compressor by the motor to make the crankshaft rotate, drive the connecting rod to make the piston reciprocate, and cause the cylinder volume to change. Due to the change of the pressure in the cylinder, the air enters the cylinder through the air filter (muffler) through the intake valve; in the compression stroke, due to the reduction of the volume of the cylinder, the compressed air passes through the exhaust valve, and then passes through the exhaust pipe, one-way The valve (check valve) enters the gas storage tank, and when the exhaust pressure reaches the rated pressure of 0.7 MPa, it is controlled by the pressure switch to stop automatically, and when the pressure of the gas storage tank drops to 0.5-0.6 MPa, the pressure switch is automatically connected and started.
1.2.5 Production equipment area
The new polyurethane coating production line has a total of 19 enamel reactors, of which 6 6 m3 reactors (1#-6#) produce single-component polyurethane waterproof coatings, and 4 3 m3 reactors (9#-12#) are used as single-component Component polyurethane batching tanks, 7#, 8# kettles (5 m3) are used as grinding storage tanks for single-component polyurethane. 17#, 18#, 19# reactors (3 m3) produce two-component polyurethane material A, two 5 m3 reactors (15#, 16#) produce two-component polyurethane material B, and 13# reactor As the batching tank of material B of two-component polyurethane, the 14# reactor is used as the grinding storage tank of material B of two-component polyurethane. Each enamel reaction kettle is equipped with 4 pressure weighing modules, which can transmit the quality signal of the kettle body to the central controller. After calculation, the quality of the kettle body is displayed on the reactor data box and the central control LED screen .
The new polyurethane coating production line is equipped with 3 vertical sand mills. The prepared slurry enters the sand mill through a Diaphragm Pump, and then the solid materials in the slurry are ground and refined and then flow out from the sieve. The barrel of the sand mill is equipped with a cooling device to prevent the heat generated by the mutual friction of polyurethane slurry, grinding media and discs in the barrel from affecting product quality.
1.2.6 Finished product storage area
Polyurethane waterproof coatings are chemical products and should not be stored in the production workshop to avoid accidents. The new polyurethane waterproof coating workshop is equipped with a finished product warehouse of 3 000 m2, which is divided into areas according to product categories and signs are placed. Products are uniformly stacked on pallets, and forklift access is provided for easy access.
2 Improvement of key processes
2.1 Segmented production
In the old polyurethane waterproof coating production line, the batching, dehydration, and reaction processes are all carried out in a reactor. It is necessary to wait for the completion of the previous process before proceeding to the next process, and the production efficiency is low. The new production line divides the production process of polyurethane waterproof coating into three stages: batching, grinding, and reaction, so that the three stages do not affect each other and can be carried out at the same time, effectively utilizing the working time. For example, the dehydration time of polyurethane raw materials is very long, generally around 3-4 hours, which could not be used before, but now workers can carry out batching and grinding for the next shift during this time, realizing continuous production.
2.2 Improvement of detail process
The new polyurethane waterproof coating production line has been improved in many details.
After the polyurethane raw material is prepared in the batching tank, the viscosity of the formed slurry is very high. If an ordinary centrifugal pump is used, the feeding speed will be slow, because the working point of the centrifugal pump is set based on water. If the material viscosity is slightly If it is high, it needs to be equipped with a reducer or a frequency conversion speed regulator, so that the cost is greatly increased, and the same is true for the gear pump. Therefore, the new polyurethane coating production line adopts a Diaphragm Pump suitable for medium and high viscosity materials. Since the Diaphragm Pump uses air as power, the flow rate can be automatically adjusted with changes in back pressure (outlet resistance).
In view of the high viscosity of polyurethane slurry in the early stage, which is not conducive to transportation, the new polyurethane coating production line has also installed a heat exchanger to reduce the viscosity by increasing the temperature of the slurry to ensure that the viscosity of the slurry will not be too high due to heat dissipation in the pipeline .
The single-component polyurethane reaction tank (1#-6#) and the two-component polyurethane A material reaction tank (17#-19#) of the new polyurethane coating production line are equipped with dripping tanks, which can be added dropwise at a uniform speed through the mass flow meter TDI-80, control the reaction speed. Experiments have shown that controlling the dropping rate of TDI-80 can increase the tensile strength of the product by 10%.
