A brief discussion on spray coatings and their application in flues

 什么是喷涂料

喷涂料是以气动工具机械喷射施工的不定形耐火材料，由耐火骨料、粉料及结合剂组成，按体积密度分为轻质、中重质和重质三类。该材料广泛用于高炉、转炉、中间包等工业窑炉的内衬构筑修补及热态维护。

喷涂料骨料临界粒径为3～5nm，粉料含量达35%～45%，含烧结镁砂、速溶聚磷酸盐结合剂及羧甲基纤维素等增塑剂。

湿式碱性喷涂料通过螺旋泵喷射至永久衬上，喷涂层厚度按使用炉次分为45-60mm（20-30炉次）和60-80mm（30-40炉次） 。喷涂层具有抗渣性、抗渗透性及隔热性能，可通过垂直喷射增强与基体结合力 [5-6]。施工需控制喷嘴距离、风压及一次喷涂厚度，冬季作业需避免水分冻结，烘烤工艺需防止涂料层剥落。

喷涂料在烟道中的应用

烧结机大烟道温度高、冲刷侵蚀严重。用一般的FN-130喷涂料，根本不能满足大烟道苛刻条件的使用。

那么，烧结机大烟道到底用什么类型的耐火喷涂料好呢？
其实大烟道条件严峻，必须得用耐磨耐火喷涂料才行，如果选择重质喷涂料或是选用轻质喷涂料，根据使用经验，两者结合才是最好的选择。

原因是把轻质隔热喷涂料喷涂在烟道壁做隔热保温作用，还能防止管道受热变形，然后在隔热轻质喷涂料的上面再喷涂一层，耐磨耐火喷涂料，这样两者结合，即烟道内衬使用喷涂料寿命长，耐磨耐侵蚀。还起到保温隔热使用，还防止大烟道变形。
那么轻质隔热喷涂料一定要注意导热系数，要≦0.020+0.0001T（W/M.K）。体积密度控制在1.3以下。这样重量不大，还起到相应的作用。
工作层的耐磨耐火喷涂料一定要注意耐磨、抗侵蚀。体积密度不能低2.3，而且耐压强度要大于50Mpa,要经受得住1350℃的温度疲劳。这种耐磨耐火喷涂料不要求铝含量有多高，但必须线变化率小，强度高。耐高温侵蚀。
当然，也有用户厂家选用只用耐磨耐火喷涂料，这种选用也可以，不做隔热层。内衬工作层只用重质耐火喷涂料。但是如果轻质隔热喷涂料做隔热层，重质耐磨耐火喷涂料做工作层，则是最好的选用方式 。
这样，既耐磨喷涂料使用寿命长，隔热层的轻质耐火喷涂料还能防止管道变形。但是只选用轻质耐火喷涂料是不行， 需要搭配重质的而且得是耐磨的喷涂料才是最好的选用。

What is hot repair mass?

Hot repair mass is a monolithic refractory material applied mechanically by pneumatic spraying. It consists of refractory aggregate, powder, and binder and is categorized by bulk density into three types: light, medium, heavy, and heavy. This material is widely used for lining repair and hot maintenance in industrial furnaces such as blast furnaces, converters, and tundishes.

The critical particle size of the hot repair mass aggregate is 3–5 mm, and the powder content is 35–45%. It contains sintered magnesia, a quick-dissolving polyphosphate binder, and plasticizers such as carboxymethyl cellulose.

Wet alkaline spray coating is applied to the permanent lining via a screw pump. Hot repair mass is categorized by the number of heats used, ranging from 45–60 mm (20–30 heats) and 60–80 mm (30–40 heats). The hot repair mass exhibits slag resistance, permeability resistance, and thermal insulation properties, and can be enhanced through vertical spraying to enhance adhesion to the substrate . During construction, nozzle distance, wind pressure, and spray thickness must be controlled. Winter operations must prevent freezing of moisture, and the baking process must prevent paint flaking.

Application of hot repair mass in Flue Ducts

Sintering machine flues experience high temperatures and severe erosion and erosion. Conventional FN-130 spray coatings simply cannot meet the demanding conditions of large flues.

So, what type of hot repair mass is best for sintering machine flues?

The harsh conditions of large flues necessitate the use of wear-resistant and hot repair mass . Whether to choose heavy-duty or lightweight spray coatings, experience suggests that a combination of both is the best option.

The reason for this is that lightweight thermal insulation hot repair mass  are applied to the flue walls to provide insulation and prevent heat-induced deformation. Then, a layer of wear-resistant and refractory hot repair mass is applied over the insulating lightweight spray coating. This combination ensures that the hot repair mass used in the flue lining is long-lasting, wear-resistant, and erosion-resistant. It also provides thermal insulation and prevents deformation of the flue. For lightweight thermal insulation hot repair mass, the thermal conductivity must be ≤ 0.020 + 0.0001T (W/M.K). The bulk density must be kept below 1.3. This ensures low weight while still providing the desired effect.

The wear-resistant and refractory hot repair mass for the working layer must also be wear-resistant and erosion-resistant. The bulk density must not be lower than 2.3, and the compressive strength must be greater than 50 MPa, capable of withstanding thermal fatigue at temperatures up to 1350°C. This type of wear-resistant and refractory hot repair mass does not require a high aluminum content, but must have a low linear gradient, high strength, and resistance to high-temperature erosion.

Of course, some manufacturers choose to use only wear-resistant and refractory hot repair mass, which is acceptable, without the thermal insulation layer. Heavy-duty refractory hot repair mass  are used for the inner lining working layer. However, the optimal approach is to use lightweight thermal insulation hot repair mass for the thermal insulation layer and heavy-duty wear-resistant and refractory spray coatings for the working layer.

This approach not only prolongs the service life of the wear-resistant   hot repair mass, but also prevents pipe deformation with the lightweight refractory  hot repair mass for the thermal insulation layer. However, it is not enough to use only light-weight refractory  hot repair mass. It is best to combine heavy-weight and wear-resistant hot repair mass.