Cold-Box core shooting machines and plants
Since foundry cores vary in size and characteristics, we should choose the equipment that best suits our Cold-Box production needs.
The machines used to produce solid or hollow cores, of simple or complex shapes, are all poured from above and use third dimensions positioned in the lower table.
These machines can be divided into three categories:
- Machines for vertical split core boxes
- Machines for horizontal split core boxes
- Universal machines suitable for both types of core boxes
Sand can be dosed using different dosing systems. One of these consists of using a valve directly from the container above the mixer, but this system is not very precise. A screw conveyor is a more accurate system, while a weighing hopper dosing system is very precise, as well as a volumetric system.
Timed screw or weighing hopper systems are flexible because they allow for the creation of recipes with different amounts of sand, in order to create mixtures for shot machines of different volumes, avoiding waste of the mixture. The volumetric system allows for the same flexibility.
Different options are also available for dosing resins. These can be dosed with volumetric pumps directly from the ground level to the mixer, avoiding double transport.
Flow control systems can be used to obtain greater control, but the basic system is already very precise. Other resin dosing systems are weight-based or volumetric.
The optimal temperature for using resins is 20-25°C, but slightly lower temperatures can be tolerated. There are heating systems available for both sand and resins, useful for maintaining the ideal temperature during the production of the mixture. The sand-resin mixture can be produced with any type of mixer, but the best result is obtained with a helical blade mixer.
After mixing, the mixture is conveyed into a hopper on the moulding machine ready for entry into the cartridge or firing head.
Mixers for preparing the mixture can be divided into two groups and, with few exceptions, can be used for all processes that use liquid resins, both for hot and cold processes.
However, it is important to carefully evaluate the characteristics of the mixer and choose the one that is suitable for your needs, avoiding purchasing an over or under-sized mixer.
- The intensive mixer: allows to quickly mix a pre-set quantity of sand with resins dosed by volumetric dispensers, but is only suitable for feeding a single machine and the mixture has a limited lifespan
- The mixer with scraping or muller blades uses blades that scrape the bottom and walls to mix sand, resins and catalyst, which can be added manually or automatically. This system is particularly suitable for mixing high-density resins. However, when using a mixer with scraping blades, it is important to pay attention to the mixing time, especially at high temperatures, as the mixture could overheat and cause the evaporation of solvents contained in the resins, leading to a loss of product characteristics.
In colder periods, on the other hand, by prolonging the mixing time, the mixture can be brought to the right temperature, improving the coverage of the sand grains and facilitating the flowability of the mixture for the filling of the core box
The mixture can be transported to the core shooting machines in two ways: directly from the mixer through a motorized trolley or through a sliding hopper on a monorail and a motorized carriage. If the mixer feeds multiple machines, it is important that it is programmable to meet the needs of each one. These solutions require the entire plant to be positioned on a specific height mezzanine, but in some cases, this is not possible. In this case, the option is to install the preparation plant at ground level and use a lifting hopper and a trolley to distribute the mixture to the machines.
There are different types of machines available on the market, each developed based on the manufacturer’s experience. Some require the use of cartridges, which must be removed and cleaned at the end of the shift, while other manufacturers build specifically designed tubes to avoid sand build-up on the walls and without compromising shooting efficiency. The shooting or blowing is done by the impact of pressurized air on the sand, through the rapid opening of a valve of adequate size for the volume of the cartridge or tube and the shooting head.
For both core boxes and moulds with vertical or horizontal openings, the holes or slots in the shooting plate to allow the mixture to pass through must be positioned in the least wear-prone points in the core box, preferably not directly above the model shape or filters used to expel air, as this could cause their breakage or immediate closure. This requires the removal of the shooting attachment at the end of core production. However, in some cases, it is possible to use shooting bushes directly applied to the shooting plate to avoid this.
The shooting bushes, preferably of larger size, with straight internal and external diameters suitable for the core box shooting hole through a terminal conical insert and a rubber cap, can reduce the impact velocity in the core box and thus the sand grain peel-off, as well as reduce the mould’s own consumption. The shooting is usually carried out at a pressure between 2.5 and 4 bar, although in some cases, higher pressures are required to conform to the cores to be produced. A lower pressure carries a lower risk of sand grain peel-off from the resin and therefore a lower adhesion. Also, a lower shooting pressure carries less wear on the core box.
It is possible to vary the range of the shot pressure, but it is important to consider that a low shot pressure:
- Reduces the risk of sand stripping from the resin and sticking to the core box
- Reduces the wear of the core box
In the market, machines for the production of cores can be automatic, semi-automatic or manual and suitable for different types of core boxes. In addition, to complete the core forming process, a gassing system, called a Gas Generator, must be matched to the machine, which varies depending on the type of Cold Box process used and the components used, such as catalysts.
The Gas Generator is equipped with equipment to transform the catalysts into steam and, if necessary, to heat the wash air, as well as tools to control the quantities of catalyst and wash air used. During the gassing process, an initial pressure of about 1 bar is used to avoid sand collapse, followed by a pressure of 2-6 bar to complete the operation.
Equipment cleaning and maintenance
Risk of contamination
To keep Cold-Box equipment in good condition, it is important to pay attention to maintenance and cleaning to avoid the risk of contamination.
It is not advisable to come into contact with the liquid components of the Cold-Box process with:
- Cleaners containing water or alcohol
- Containers contaminated with incompatible substances such as water, alcohol, lubricants, liquid detergents, resins, or oil
- Containers not approved for use with flammable materials, as in the case of amine catalysts
Instead, it is recommended to use cleaners that soften resin build-up to facilitate removal.
However, such cleaners should not be used on rubber or plastic, especially on the coating of electrical cables.
Pumps, tanks, and lines
Regarding pumps, tanks, and lines, it is important to take the same precautions described earlier for cleaning.
In case of shutdowns exceeding one week, it is necessary to discharge part A and part B resins to avoid prolonged contact with air and solvent evaporation.
This will prevent contamination of the components and ensure proper functioning of the equipment.
- Remove any build-up when necessary (at least daily).
- Do not use water
- Use appropriate cleaning products and, if they are not sufficient, remove mechanically
Core shooting machine
- The mixture hopper and discharge valve
- The shooting head
- The parts in contact with the mixture (if necessary, coat the hoppers with Teflon)
Gas equipment (gas generators and lines)
- Check the catalyst gasification pumps and make sure there are no leaks
- Check the catalyst nozzles and the feed line for leaks (if necessary, install new shut-off valves)
- Clean or replace the washing air filter and the condensate separator if necessary