Views:6 Author:Site Editor Publish Time: 2021-02-18 Origin:Site
Because foaming relies on heat, if there is no heat, the foaming agent in the system cannot evaporate and foam plastic cannot be formed. The heat comes from two aspects, one is the heat produced by the chemical reaction, and the other is the heat provided by the environment. The heat of chemical reaction is a fixed value, without the influence of external factors, but the heat provided by the environment changes with the change of the ambient temperature.
When the ambient temperature is high, the environment can provide heat to the reaction system, which can increase the reaction speed and shorten the reaction time. It is manifested as the foam is fully foamed, and the density of the foam surface and core is close. When the ambient temperature is low, part of the reaction heat is dissipated to the environment The heat loss, on the one hand, causes the foam maturation period to be prolonged and increases the foam molding shrinkage rate; tests show that the same foam material, the foaming volume at an ambient temperature of 15 ℃ is 25% smaller than that at 25 ℃. On the other hand, a hard skin that is not fully foamed or even hugged will be formed on the surface of the foam, which increases the amount of foam infusion and increases the cost of foam production.
At present, the most common type of cement foaming machine on the market is the third-generation cement foaming machine (the first and second generations have been basically eliminated). Its structure can be roughly divided into several parts: feeding system, mixing system, foaming system, and conveying system. Then we use this to make a simple analysis of various cement foaming machines:
1. Feeding system
At present, the main feeding devices of cement foaming machines in China are screw propellers and belt conveyors. Screw propellers used to have small size, low cost, good sealing performance, less environmental staining, and beautiful appearance, but after several years of practice However, several shortcomings were discovered, 1. High failure rate and frequent crashes; 2. Small feed volume, which could not meet the construction needs; 3. Short life span and troublesome maintenance, gradually eliminated by consumers. The belt conveyor with good sealing performance has been recognized by consumers because of its large feed volume, low failure rate and simple maintenance.
2. Mixing device
When other conditions are the same, the strength of foamed concrete with uniform mixing and non-uniform mixing can differ by 3%-10%, and sometimes by 20%. The third-generation cement foaming machines all use horizontal horizontal shafts, similar to horizontal mortar-type concrete mixers, mixing with high-speed blades installed on the horizontal shaft to achieve uniform mixing of cement and water. The main components of the mixing system are the barrel, the horizontal shaft, the mixing blade and the motor.
1. The twisted blades should be designed reasonably, and it is best to avoid uneven materials accumulated in dead corners during mixing. All parts of the twisted leaves should be stirred, so the best gap between the twisted leaves and the barrel is 10-20mm. Buyers can use tools to measure the distance between the hinge leaf and the four walls for inspection.
2, The connection between the horizontal shaft and the hinge blades is best to use mechanical connection. If the horizontal shaft and the hinge blades are fixed by welding, the horizontal shaft will inevitably be deformed and bent when heated, and cannot be parallel to the axis. When the machine is running, it must be twisted. It is also the main reason that the horizontal shaft seal is prone to material leakage. The mechanical connection will not cause deformation of the horizontal axis during installation and is convenient for disassembly.