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Dry filtration pressing method
Slurry preparation: The cellulose raw material (such as wood pulp paper) is completely crushed, and mixed and stirred with nitrocellulose (an energetic material), resin (as a binder), and stabilizers in a reactor to form a uniform slurry.
Dry pressing molding: The prepared slurry is poured into a container with a porous filter plate, and the liquid is filtered out through the filter plate under vacuum, thus a circular wet green body with a certain size and thickness on the filter plate. This process is completed under specific pressure and time.
Press molding and drying: The obtained wet preform is placed in a hot-press molding mold, and then thermopressed at the set temperature, pressure, and time to solidify and shape. Finally, the molded specimen is placed in a vacuum oven to dry, and then the final combustible cartridge is obtained.
The specific process of suction filtration and pressure molding
1. Suction filtration preforming
Nitrocellulose paste is poured into a cylindrical mold with filtration holes (the inner wall of the mold matches the outer diameter of the ammunition bucket and a mandrel can be set in the center), and the bottom/side wall filtration system of the mold is turned on at the same time (negative pressure 0.5-0.08 MPa). Filtration will quickly filter out the solvent (acetone) in the paste, allowing the fibers to preliminarily accumulate into semi-dry cylindrical blank (water content reduced to 30-40%) in the mold, avoiding deformation or safety risks caused by excessive solvent during subsequent molding.
2. Pressure molding compaction
After suction filtration, the semi-dry green body (still in the mold) is transferred to the explosion-proof mold pressing machine for molding under pressure of 15-25 MPa and a temperature of 40-50℃:
- The pressure further compacts the fibers, eliminating the residual pores by suction filtration and ensuring uniform density of the barrel wall;
- The low temperature promotes the curing of the binder, while avoiding the decomposition of the nitrocellose due to high temperature.
3. Demold
After pressing and cooling, the mandrel and the finished barrel blank are taken out, and then enter the trimming and drying process.
In actual production, it is usually achieved through mechanical assistance, rather than relying entirely on manual handling, because:
A， The transfer process requires maintaining the overall stability of the mold and the billet to prevent cracking and deformation of the semi dry billet due to vibration or tilting.
B ，Production efficiency and safety requirements, especially in explosion-proof environments.
1. Quality：avoids secondary damage, deformation, or contamination of the billet during the transfer process.
2. Efficiency：Seamless automation connection between processes has been achieved, and the pace is controllable.
3. Explosion proof safety: The entire transfer process is carried out in a closed or controllable environment, reducing exposure to dust and solvent vapors.
4. Flexibility: By replacing the mold sleeve or base, different specifications of products can be produced on the same line.
Transfer method：
1. * * Integrated transfer system with mold**
-After the filtration is completed, the mold (using a movable tray or combination mold) along with the blank enters the conveyor belt or slide rail and is sent to the molding machine station.
-The mold has * * positioning holes/slots * * for precise alignment inside the molding machine.
2. **Integrated design of molds and filtration/molding equipment**
-The production line will directly connect the filtration unit with the molding machine, and push the entire mold to the lower mold of the molding machine (or directly include the mold when the molding machine is closed) through hydraulic or pneumatic push rods.
-The mold may be designed to be vertically separable: the lower half mold (with a filter screen) is used for filtration, and the upper half mold is provided by the press during molding, while the lower half mold still carries the blank into the press.
3. **Mechanical arm handling**
-Using customized grippers or vacuum suction cups, the entire mold (including the blank) is smoothly clamped and transferred to the molding machine table.
-Suitable for multi specification molds or flexible production.
