- Process flow chart of resin abrasive tool mixing
Powdered resin abrasive molding material, wetting agent needs to be added during the mixing process. Generally speaking, it is liquid phenolic resin and liquid epoxy resin. After they are hardened, they become part of the bonding agent. The mixed molding material has good looseness and plasticity, which is convenient for spreading and realizing the automation of molding. The structure is more uniform, and the green strength of the green body is also higher.
The surface of the abrasive is first coated with a layer of low-viscosity liquid. After the filler and powdered resin are added, the liquid resin will bond them to the outer surface of the abrasive grains. When the mixing ratio of the liquid resin and the powdered resin is appropriate, The molding has good looseness, and there is a layer of dry resin powder film on the outer surface of each abrasive particle, so that the particles can be separated from each other.
If the amount of liquid resin is small or the amount of powdered resin is too large, the material will be dry and powdery. Excessive powdered resin that does not adhere to the abrasive particles will be free in the mixture and will easily deposit on the bottom surface of the abrasive tool during feeding, resulting in blank volume. Powder phenomenon, resulting in uneven hardness of the product after hardening.
When the amount of liquid resin is too large or the amount of powdered resin is small, the resin powder film cannot be formed on the surface of the abrasive particles, and the molding material is wet and agglomerated, which affects the molding operation and the uniformity of the parts. For this reason, the ratio of liquid resin and powdered resin must be adjusted well when mixing, in order to mix molding materials with good properties.
- Factors affecting uniform mixing of molding materials
- The influence of feeding order
Abrasive—wetting agent—mixing—powder resin + filler—mixing
First, the wetting agent wets the surface of the abrasive grains, and then the powdered resin and filler are added to make the bonding agent evenly adhere to the abrasive grains. The molding material has both plasticity and a certain degree of looseness. At the same time, the powdered resin and filler The agent is evenly distributed on the surface of the abrasive, and the filler can play the expected role during the cutting process. Therefore, this order of feeding is more reasonable. If there are abrasive grains that are not wetted, the abrasive grains are surrounded by powdery materials and are not easily wetted by the wetting agent. The wetting agent binds the resin powder into small binder clusters and affects the uniform distribution of the binder.
- The effect of mixing time
The length of the mixing time is related to the state of the molding material, the viscosity of the resin liquid, the thickness of the abrasive particle size, the structure of the mixer and the level of room temperature. Generally speaking, if the mixing time is too short, the mixing will be uneven. If the mixing time is longer, the mixing will be more uniform. But too long mixing time is also harmful. If the mixing time is too long, the number of friction between the particles of the mixture will increase and heat will be generated, which will easily dissolve the resin powder film on the surface of the abrasive, and the molding material will lose its looseness and cause agglomeration. Therefore, after adding the powdered resin, the stirring should be stopped immediately when the dispersion is uniform. Generally, the mixing time of fine-grained molding materials is longer than that of coarse-grained molding materials. Because the total surface area of fine-grained molding materials is large, it must have a longer time for the wetting agent to fully wet the abrasive particles and uniform distribution of the bonding agent.
- The influence of resin liquid viscosity
High viscosity liquid resin has poor wettability and long mixing time. It is difficult to mix evenly if used for fine-grained materials. From the point of uniform mixing, low-viscosity resins are easy to disperse, which is conducive to the uniformity of mixing. Because low-viscosity liquid resins can dissolve more resin powder, the molding materials will agglomerate and lose looseness.
For coarse-grained abrasives, choose a higher resin liquid;
For fine-grained abrasives, resin liquid with lower viscosity can be selected.
With the current situation of resin grinding wheel production, in order to solve the problem of product decline, strength and other aspects, fine-grained abrasives are also using high-viscosity, high-solid content liquid resin.
- The influence of the particle size and softening point of powdered resin
Under the same condition of the resin powder, the total area of coated abrasive particles is small when the particle size of the powdered resin is coarse, and the molding material is easy to become wet; while the total surface area of the coated abrasive particles is large when the particle size is fine, and the material is easy to dry .
The powdery resin has a low softening point and tends to agglomerate, but the opposite is true when the softening point is high. Therefore, the mixing ratio should be determined according to the particle size and softening point of the powdered resin.
- The influence of resin powder and resin liquid ratio
The quality of the molding material has a lot to do with the ratio of the resin liquid to the resin powder, that is, the dry humidity.
If it is too wet, that is, the proportion of resin liquid is too large, the molding material is easy to agglomerate, it is difficult to spread the material, and it is difficult to ensure the uniformity of the abrasive tool.
If it is too dry, that is, if the proportion of the resin solution is too small, the resin powder will not be able to fully adhere to the surface of the abrasive particles, and will be in a free state in the molding material, which will easily cause defects such as uneven hardness.
The ratio of resin powder to the amount of resin liquid is related to the viscosity of the resin liquid, ambient temperature, humidity, the softening point of the resin powder, the particle size of the abrasive, and the amount of filler added.
For powdered materials, the ratio of resin powder to resin liquid volume should generally be about 2 or so.
- The effect of room temperature
The room temperature is too high or too low to affect the viscosity, and the viscosity affects the uniformity of the molding material. In order to stabilize production, foreign resin abrasive tools workshops require the room temperature to be kept at about 25°C. If the constant temperature cannot be maintained, it should be adjusted according to the season.
- The effect of sieving
For coarse-grained materials, agglomeration can be eliminated, the materials are loosened, and the materials are easy to spread.
For fine-grained materials, it not only has a loosening effect, but the selection of a suitable mesh number can make the molding material achieve the goal of uniformity.
- Other influences
The effect of mixing speed, generally speaking, the faster the speed, the worse the mixing effect;
The influence of the depth of the mixing pot, the deeper the pot is, the more difficult it is for the molding material to be uniformly mixed in the upper and lower layers of the molding material in the pot;
The influence of the mixing amount, the mixing amount is too much and it cannot be stirred evenly, and the mixing amount is too small and it is inefficient;
The influence of the design of the mixing fork is that the mixing force of the designed material fork increases, and the molding material is easy to heat. The unreasonable angle of the design material fork makes the molding material unable to mix the upper and lower molding materials in the pot easily.
It is not only the above reasons that affect the mixing process, such as the cleanliness of the abrasive and the specific gravity and particle size of the auxiliary materials. Therefore, the quality of the mixing is often affected by many factors, and the specific conditions can be adjusted when necessary.
Third, the adjustment of the dry humidity of the molding material
- The molding material is too wet:
a) Switch to resin liquid with higher viscosity and low water ratio.
b) Increase the amount of powdered resin and reduce the amount of liquid resin under the condition that the total binding amount remains unchanged.
c) Add a certain amount of dry molding materials of the same specification and the same formula for secondary mixing.
d) Increase the amount of filler used or increase the amount of inert filler used;
e) Add a certain amount of dry molding materials with the same specifications and the same formula for secondary mixing.
- The adjustment method of the molding material is too dry
a) Switch to liquid resin with lower viscosity;
b) Add an appropriate amount of auxiliary wetting agent (such as furfural, motor oil, dibutyl ester, cresol, etc.);
c) Increase the amount of liquid resin and reduce the amount of powdered resin under the condition that the total binding amount remains unchanged;
d) Reduce the amount of filler used or reduce the amount of inert filler used;
e) Add a certain amount of wet molding materials with the same specifications and the same formula for secondary mixing.
Fourth, the inspection of the uniformity of the molding material
- Visual inspection method
The color of the material is consistent, without binding agent clusters and filler clusters, which can be regarded as uniform. This method is simple but not accurate.
Use the glass inspection method to spread the material between two glass plates for observation.
- Solvent inspection method
Take samples from different material boxes in the same pot, dissolve the resin with a solvent and dry them. When the difference between the quality of the sample and the sample does not exceed 0.1% of the content, it means that the material has been mixed evenly. This method is more accurate, but it takes longer.
- Detection method of sand ratio
Samples are taken from different material boxes in the same pot to test the sand binding ratio. When the difference between the sand binding ratios of the samples does not exceed 1%, it means that the material has been mixed evenly. This method is relatively accurate, but it takes a long time to detect
Five, common problems in the mixing process of molding materials
- Mismatched materials:
The main reason is carelessness (misreading, no calibration, etc.).
- Uneven mixing
The lumps of auxiliary materials, dry masses, liquid resin spots on the surface of the green body, and powdery resin deposition patterns are all non-uniform mixing.
The main reason is that the mixing time is short, the feeding sequence is incorrect, the resin liquid viscosity is high, and some parts of the mixing equipment are severely worn.
- Judgment and treatment of deterioration of raw and auxiliary materials
Resin powder: it absorbs moisture and agglomerates. After opening the bag, you can see spherical lumps of varying sizes. It can be broken with light touch. When it is not serious, use it directly, when it is serious, it can only be scrapped.
Resin liquid: The properties change, the viscosity increases, and it can still flow. It can be mixed with an appropriate amount of low-viscosity resin liquid. If it becomes a solid, it can only be scrapped.
Other auxiliary materials: mainly inorganic materials, and the deterioration is mainly caused by moisture absorption and agglomeration. It can be used continuously after drying and crushing through the corresponding sieve.