2.1. Phosphoric acid and copper oxide adhesive
The glue consists of a solution of phosphoric acid and alumina in combination with copper oxide. Room temperature curing, excellent high and low temperature resistance. The compression shear strength of the carbon steel socket joint is ≥ 90 MPa, and the bond strength is constant at -180°C, and the high temperature resistance is 600°C. The coefficient of linear expansion is smaller than that of metal, is <1×10-6/°C, and the thermal conductivity is 1.1W/(m·k). It is suitable for bonding of tools, gauges, fracture shafts, repairs of shell cracks, castings, etc. And sticky plugging. Developed in the early 60s in China, it is used for cemented carbide turning tools and reamers. It has the advantages of simplicity and economical efficiency. It has been exploited for metal parts and other leaks and seals, becoming inorganic.
A major variety of adhesives.
(1) Preparation method
1 copper oxide. The industrial method is to roast the copper slag and oxidize it to remove water and organic impurities. After cooling, the resulting primary copper oxide was crushed and then re-oxidized to obtain crude copper oxide. It is dissolved in sulfuric acid under heating to produce a copper sulfate solution. After being clarified, under the conditions of heating and stirring, iron shavings are reduced to produce pure copper, and washed with hot water until no sulfate or iron is found. dry. Re-grade over 450 °C oxidation roasting 8 hours, after cooling, pulverization, oxidation roasting in the oxidation furnace, sieving, in order to obtain copper oxide. The reaction formula is as follows:
Copper oxide can also be made from copper sulphate. The method of preparation is to heat and dissolve copper sulfate and water in a three-necked flask first. After clarification, control the reaction temperature at 70-80° C. and add 10% sodium hydroxide under stirring. The solution was controlled at a pH of 9 to 10 and refluxed for 20 minutes to stop the reaction. The precipitated copper hydroxide was taken out, washed with boiling water until neutral, and dried at 150°C. After drying, it was crushed and put in a muffle furnace and calcined at 900±15°C for 4 hours to give a lump. After cooling, it is crushed with a ball mill, sieved (200 mesh), and baked at 110-140°C for 1-2 hours. The reaction formula is as follows:
Commercially available reagent grade or industrial product copper oxide, its content is ≥98%, fineness (100 mesh over) is less than 1.0%. However, it is directly used for rubber gluing, and it is easily gelled and cured. The pot life is extremely short, resulting in a low bonding strength. Generally after 150 ~ 200 °C baking can improve the bonding strength, but the best by 900 ± 15 °C calcined for 4 hours of treatment, is conducive to extending the pot life, and to obtain a higher bonding strength.
2 phosphoric acid solution preparation. In each 100ml of phosphoric acid, 5g of reagent-grade aluminum hydroxide powder is slowly added, stirred into a milky white liquid, heated to 220-260°C for 1 to 2 hours to dissolve the aluminum hydroxide and evaporate the water in the solution. Share, naturally cool to room temperature. The product is mainly aluminum dihydrogen phosphate, containing some pyrophosphate, and its relative density is 1.85-1.9. The main reaction is as follows:
The combination of aluminum hydroxide can prolong the gelling time of the compound, and also allows the compound to have a relatively long pot life so as to obtain a higher bonding strength. Phosphoric acid solution will crystallize at low temperature for a long time and affect the use. It can be heated to 50-60°C until it is completely melted into a clear solution. It can be used as it is after cooling. It is still difficult to melt or absorb the solution. It is placed in a beaker and heated to 220-260°C for cooling.
(2) Application process. Adhesives should be sleeved and spudded, with a gap of 0.1 to 0.3 mm. Adhesive surface finish is as low as possible, generally â–½1 ~ â–½3 is appropriate, the surface must be rust, degreasing and clean.
1 with plastic. The proportion (K) of grams of copper oxide (A) to the number of milliliters of phosphoric acid solution (B) can be tiled as follows:
K=A/B=3~5
With a large K value, the solidification rate of the rubber material is accelerated, and the K value is more than 5, the solidification of the rubber material is extremely fast, and it is difficult to adjust the adhesive, and the adhesive strength does not increase significantly. The temperature also affects the K value, so it should be adjusted according to the temperature. In general, the room temperature in winter is low, and K takes a large value. In the summer, on the contrary, a small value of K is used. Usually, the value of K is 4 to 4.3. For example, if the ambient temperature is about 25°C, and the relative humidity is less than 80%, the pot life is limited. About 10 minutes or so.
Adjust the glue: According to the determined K value, mix one, place the weighed A component on the copper plate or the glass plate, make it be concave in the middle. Extract the solution B component with a syringe or a dropper, place it in a pit, and reconcile evenly with a piece of bamboo, about 1 to 2 minutes. The rubber material is in a paste form, and can be pulled into a piece of silk more than 1 cm with a piece of bamboo. Basically no bubbles can be used. The exothermic reaction occurs when the gum is adjusted, and it is easy to condense and solidify the rubber. Therefore, it is necessary to use a good heat-conducting copper plate to easily dissipate the heat and prevent the rubber from condensing faster. It is advisable to adjust the amount of rubber to 10 grams or less per time, and use it with adjustment. If the amount of glue used is large, multiple people can be adjusted at the same time.
When preparing adhesives such as thermal conductivity and conductivity, the A and B rubber materials should be firstly blended and homogenized, and then heat conductive or conductive materials should be added and mixed.
2 coating process. Use bamboo sticks or rods, scrapers or brushes to evenly apply adhesive on the two adhesive surfaces. The grooved joints must be pushed and pulled several times. The joints should be slowly screwed in and out several times to make the glue. The liquid is evenly distributed on the adhesive surface, and the excess glue squeezed out is scraped off, and it can also be wiped with a wet cotton yarn.
3 glued conditions. The glued joints were first baked at 40-50°C for 2 hours and then heated to 100-120°C for 2 hours. It can also be cured at 60-80°C for 4-6 hours or at room temperature (25°C) for 2-3 angels. The curing temperature is high, the reaction speed is fast, and the time required is short. The glue liquid is easy to absorb moisture, so the glued joints are not placed in a damp place before being solidified, otherwise the adhesive strength will be reduced.