Most of the original production of ceramic wheels, ceramic bonding wheel advantages of its natural porous and chemical stability, and therefore suitable for dry and wet grinding, especially the use of water-based and oil-based grinding fluid conditions However, Ceramic wheel has poor elasticity and high sintering temperature, which limits its development.The phenolic resin bonded grinding wheel has the advantages of good elasticity, little sensitivity to shock, impact and lateral pressure.The high stability makes it The ability to adapt to higher speeds and improve grinding performance makes it particularly suitable for grinding and cutting wheels, and its good elasticity makes it suitable for ultra-precision grinding and surface finishing.
Phenolic resin bond wheel production process are mainly cold-pressed, semi-hot-pressed and hot-pressed three.
1. Cold pressing process:
Cold pressure bonding process using a combination of wetting agents and powdered resin, commonly used as a wetting agent with liquid phenolic resin, furfural, furfuryl alcohol, cresol, etc., the most used liquid phenolic resin. Determination of liquid resin and powder The proportion of resin-like (usually called liquid to powder ratio) factors are:
Abrasive particle size distribution, type of filler, amount of filler, viscosity of the liquid resin, nature of the powdered resin, etc. If the viscosity of the liquid resin is greater, more liquid resin is required to completely coat the abrasive surface; the smaller the particle size of the abrasive and filler , The greater the specific surface area, the greater the amount of liquid; the higher the molecular weight of powdered resin, the lower the free phenol, the worse its adhesion to the liquid resin, the more the amount of liquid required. Kind of situation need to improve the ratio of liquid to powder.Common liquid resin as a wetting agent, liquid ratio than the selection of 1: 2-1: 4, and furfural or furfuryl alcohol and anthracene oil mixture as a wetting agent, liquid powder ratio of 1 : 6-1: 8.
Mixer to go through process validation, to achieve the desired mixing effect and does not damage the abrasive is better.Add the fine powder mixing time is generally 2-5 minutes, too short to ensure uniform mixing, the resin film is too long Off, and lead to material temperature rise, the resin to be cured.
Mixing procedures are as follows:
First, the abrasive, usually mixed particle size, to be pre-mixed, then add wetting agent, even after wetting the abrasive, powdery resin that has been mixed well with other powdery fillers is added, and the mixing is continued until uniform. Abrasive material should have good plasticity and fluidity, the material can not be too wet, otherwise easy to caking, but can not have dough, while ensuring good fluidity, in order to ensure adequate injection, the general method of sieving to remove caking .
The method to determine the plasticity of the material is:
Grasping a good mix of materials, hand gently pinch will be better for the group.Generally the powder material will join the wetting of the abrasive easy to form dough, has been gradually eliminated, and now more is Two-pot mixing method, that is, the first abrasive and wetting agent mixed in a blender, while another blender powdery resin and other powdery filler mix, then the wetting good abrasive into Powder, mixing evenly. The advantage of the double-pan mixture is not only can not produce dough, but also to avoid contamination, easy to clean the material pan. The mixed material after sifting, you can use for pressing.
Suppression procedures are as follows:
The mold is installed, weighing the required amount of abrasive added to the mold cavity, flattened after pressing. Need to place glass fiber reinforced mesh placed on demand. And then pressurized at room temperature, the pressure range of the general cold pressure of 15-30N / mm2, preferably 15-25N / mm2. The choice of pressure depends on the plasticity of the material and the required density of the wheel. Excessive pressure should not be used, otherwise the abrasive will be crushed. The pressing time is generally 5-50 seconds, preferably 5-30 seconds, the length of time depends on the required density and shape of the wheel and the plasticity of the material, then you can remove the grinding wheel for the next step - curing.
Curing procedures are as follows:
Curing operation can be placed in a fixed curing oven can also be in the flow of tunnel curing kiln cured with a curing oven, the placement of grinding wheel is particularly important, the wheel is generally fixed with steel or ceramic discs, To ensure that the grinding wheel is not deformed during the curing process, uniformly placed in the furnace, the air circulation inside the furnace to make all parts heated evenly, and then start the heating process for curing; curing with a tunnel curing kiln, the first wheel with steel or Ceramic disc fixed, and then placed in the car, pushed into the tunnel, according to the set speed. General initial temperature of 60-80 ℃, the final temperature of 160-190 ℃, the entire curing process takes 20-25 hours , Finally cooled to 40-60 ℃, open the oven door, you can remove the wheel.
The physical and chemical changes occur during the whole heating process. The following reactions occur mainly in each temperature stage: the resin begins to melt at 80 ° C, the water evaporates, and the curing reaction begins. At 110 ° C, the resin is decomposed six times and the molten resin is caused to crosslink , While releasing ammonia, water and other gases; 110-180 ℃ resin cross-linked until fully cured, a large number of ammonia release.High temperature zone for too long will lead to resin over-solidification, the wheel hardness increases at the same time, resulting in The strength of the wheel decreases, generally according to the different requirements of the wheel to choose a different curing curve and curing the final temperature of the final temperature of 165-170 ° C, the wheel hard and toughness; final temperature of 175-180 ° C, the wheel hard; 190 ℃, wheel hard and brittle.
2. Semi-hot pressing process:
The pressing temperature in the semi-hot pressing process is generally 50-65 ° C. The rest of the process is exactly the same as the cold pressing process, the viscosity of the liquid resin becomes smaller at this pressing temperature, the powdery resin can be well integrated, The fluidity of the resin system is improved and it is easier to penetrate all the spaces. Even if the pressure of the press is not too high, it can be well shaped and the dwell time does not need to be too long, which is especially suitable for an automated press line for continuous operation.
3 hot pressing process:
Hot pressing process is generally used to produce larger density grinding wheel, the average density of ordinary grinding wheel 2.4-2.7g / cm3, the highest 2.9g / cm3, while the density of high density grinding wheel up to 3.1-3.5g / cm3, so to achieve High density, hot pressing process is the most suitable. Hot pressing process of mixing requirements and cold pressing process is different, commonly used dry mixing method, or less than 1% of the weight of the abrasive furfural wetting agent wetting abrasive, and then Mix well with powdered resin. Powdered resin generally use low mobility, the appropriate range is 15-20mm or less, can not use liquid resin and fluidity of the powdery resin is easy to grease when hot.
suppress:
The pressing temperature is in the range of 160-170 ° C and the pressing time is 30-60 seconds / mm Grinding wheel thickness, for example pressing a 60 mm thick grinder Refer to the following requirements: Pressure: 20-40N / mm2; Pressing temperature: 150-170 ° C .; Pressing time : 30-60 minutes During the pressing process, one to several times of deflation within 4-8 minutes after pre-pressing Curing: The hot-pressed grinding wheel already has considerable strength, but the best performance is still to be done Curing treatment Curing temperature of 160-180 ℃, curing time 8-12 hours.