What is sand casting
Below we describe how to make a Søe-Jensen door handle using the casting process called sand casting. And why it matters to you when you need to select your new door lever.
Why do we sand cast our door handles and fittings?
Brass is a mixture (an alloy) consisting primarily of copper and zinc . You might say that the alloy is the recipe the manufacturer uses to achieve the desired qualities. For rod brass, it is primarily dictated by the continued production method using CNC machines, including a need for precision as well as hardness, which also influences machining and volume.
At Søe-Jensen, we use the same alloy (recipe) that was used when the company started in 1862. It’s an allot with a higher copper level. Today, Søe-Jensen uses recycled materials to the greatest possible extent, after which we adjust the alloy by adding gun metal. This allows us to keep the old alloy recipes. Gun metal is made from a copper alloy with tin, lead, zinc, and castings, and it is also used for assembling pipes approved for potable water.
This alloy impacts the finished product, e.g., making it more resistant to dirt and the surrounding air. The visible difference, however, only becomes greater with time.
Brass patinates, which means that the surface reacts with the surrounding air (a chemical reaction, also known as oxidation), which means that the surface changes over time. The castings keep their inner glow, and they have a slightly yellowish-green marbling unlike rod and plate brass that enclose the material with a brownish surface.
For illustration, look below at the two production methods side by side after being exposed to oxidation. This door lever is sand cast in high-quality brass, whereas the escutcheon plate is machine-generated from industrial sheet brass.
The first difference is visible immediately after production. If the door lever is made from rod material, has a yellowish sheen, while the door lever made from brass of the best quality has a reddish sheen. Furthermore, the surface here has great depth and a look that is somewhat reminiscent of marbling. The visible difference, however, only becomes greater with time.
Brass patinates, which means that the surface reacts to the surrounding air (a chemical reaction also known as oxidation), which essentially means that surface changes over time.
For illustration, look below at the two production methods side by side after being exposed to oxidation. This door handle is sand cast in high-quality brass, whereas the escutcheon plate is machine-generated from sheet brass.
Materials for sand casting
Let’s start by looking at the materials used in the process.
- A precise shape of the product we will be casting, which, in this case, is the door handle. In this example, it’s the Weingarden lever you can see in the illustration here on the right.
- Wet quartz sand This is special sand with properties that allow it to be compacted tightly around a mould, and where it can hold its shape (as you know it from wet sand in a sandbox). Another essential property is that sand can withstand extremely high temperatures, up to several thousand degrees, which is necessary as brass reaches over 700 degrees Celsius.
- Two frames (an upper frame and a lower frame) like you see here on the right. These are the frames for holding the sand and the item being cast.
- There must be an entry pipe allowing liquid brass to enter the mould, and there must be an exit pipe for excess brass.
- And finally, we obviously need the raw material, which is the liquid brass alloy.
Above: Weingarden door handle
Including: The frame for sand casting
This is how we sand cast
To explain the individual steps in the production method, we refer to the illustration below. When we sand cast, we typically make 6 door handle in the same mould Here, we describe it for a single door lever only. When you look at the illustration below, imagine that we have cut the form and you are looking at it from the front, allowing us look inside the mould, where we can see the shape of a Weingarden door handle).
- The lower frame is placed on a platform and filled with compacted sand. The frame without the sand is shown by itself in the illustration above.
- Now, half of the mold is pressed into the sand (illustrated here with a mold for Weingarden).
- Next, the upper frame is placed on top of the first one, and the two frames are fixed to sit precisely on top of each other.
- Afterwards, sand is pressed into the upper frame, both around and above the door lever, until both frames are 100% filled with compacted sand. hen, the caster creates an inlet pipe and an outlet pipe in the sand so that the molten brass alloy can reach the mold and flow out, as indicated by the two arrows. The mold is left to rest for 24 hours.
- After this, the two frames are unfixed and separated. Now, the mould must be removed carefully, leaving a precise outline of the door lever in the sand, and this must be done without disturbing the sand. At the same time, the caster ensures that the entry and exit pipes have free access to the moulding area itself, so the liquid brass can flow freely into and out of the mould.
- After this, the two frames are put together again and fixed into the exact same place. Now, the mould is ready for use.
The caster then works to create the correct alloy, mixing copper, bronze, and zinc based on our own recipe The actual mixing is done in a so-called “Dille”, which is a container that can withstand extremely high temperatures and where the brass alloy can be liquefied. This manual process is crucial for the finished product, as it ensures that the caster can also remove any waste products that could reduce quality. Along the way, old bottles are placed in the “Dille” to help maintain the correct temperature.
8. Now, the allot is poured into the entry pipe until it flows out of the exit pipes. This will ensure that the entire mould is filled 100% and that there are no air pockets in the moulded door handle.
9. After this, the mould is left to cool for about 5 hours.
10. After cooling, the rough door lever is ready, it is gently knocked out of the mould to be ready for the next step in the process. The mould cannot be reused.
Ready to be grinded and polished
When the door lever is removed from the mould, it is completely rough, and now starts the huge task of creating the final product. This part of the process can only be done by an artisan who is extremely experienced with sand casting. Part of the reason is, that after burnishing the product must remain consistent within very small tolerances, and part of it is the fact that this process obviously determines how the finished product will look.
- Runners from the entry and exit pipes are cut off mechanically.
- Subsequently, the product is sanded to perfection, ensuring that the door lever maintains its correct shape and remains within the indicated tolerances (length, width, and diameter). This process is illustrated on the right.
- Now, it’s time to cut holes for the “torque blade”. This is the iron spindle that connects two door handles. And finally, a hole and threading are created for the screw that will keep the lever and torque blade in place. Now, the door lever is finished in terms of form and function.
- The final process is polishing. This is the process that makes the door handle shiny and mirror-like, ensuring that the deep glow is expressed clearly.
- Are there errors in the door lever, and does it have the correct shape?
- Do the dimensions fit within the set tolerances (size of door handle, size of holes and any screw holes)
- Is the sheen as it should be?