Before we understand how stainless steel sinks are made, let’s take a brief look at stainless steel sinks.
Stainless steel sinks first appeared in Europe and the United States. China’s stainless steel sinks first appeared in Taiwan. In the early 1990s, Taiwanese merchants brought in stainless steel sinks when they invested in the China’s mainland. In the early days, there were brand like “Mantangchun” and later “Molin”.
The stainless steel sinks is used in the modern kitchen as one of the indispensable part for washing vegetables or dishes.
What equipment will be required for making stainless steel sinks?
Let me show you.
The production of stainless steel sinks need:
- 2 sets of hydraulic drawing press (400T&500T)
- 1 set of hydraulic press (200T)
- 1 set of power press
- 4 sets of mold
Among them, the drawing machine needs one 400T and one 500T drawing press machine. The 400T drawing press machine is used for drawing and the 500T press is used for forming.
One 200T hydraulic press will be needed for edge trimming.
The power press is mainly used for hole punching.
The 4 sets of the mold are respectively a drawing die, a forming die, a trimming die and a punching die.
Now we have a brief understanding of stainless steel sinks and it’s making equipment.
How is it been made?
Let’s dive into the production process of stainless steel sinks.
#1. Purchasing of Raw Material (0.8-1.5mm sheet metal)
The sink factory purchases steel plates of different widths and thicknesses according to the different requirements of the production of the sink.
The thickness of the sheet metal commonly used in the manufacturing of stainless steel sinks is between 0.8mm and 1.5mm.
And the sheet metal will be delivered to the sink factory in coil by weight.
Usually the maximum width of the uncut steel sheet is 1220mm, and the length is almost unlimited.
The ductility of the steel sheet is limited. In order to avoid cracking and damage of the steel sheet during the drawing process, it is necessary to coat laminating film on the steel sheet at the initial stage.
The coating covers only one side of the steel sheet, and the side with the coating film will face the mold in the subsequent drawing step.
The film coating can be applied after cutting or before cutting.
#3. Sheet Metal Cutting
From the picture as shown below, you can see that the workers complete the film coating by control the roller switch to pass the protective film and the steel sheet through the rolling zone at the same time.
When the coated steel sheet passes through the guillotine, the worker presses the guillotine switch as needed to cut off the steel sheet to obtain a required length.
#4. Corner Notching
The sheet after cutting is now in a regular rectangle shape. In order to roughly conform to the shape of the sink, it is also necessary to feed the sheet into the shearing machine for corner notching.
The sheet metal after corner notching are generally polygonal and sometimes have arc edges.
Smear the drawing oil evenly to both sides of the sheet metal after coating and cutting.
The drawing oil will help the sheet to be evenly stressed, reduce the chance of tensile cracking, and extend the life of the mold and press machine.
#6. First-time Drawing
Put the metal sheet on the worktable of the drawing press machine.
There are openings on the upper and lower laminated plates on the workbench. The product mold is located in the opening of the lower plate of the workbench (red-shaded on the following picture).
After pressing the motor switch, the upper plate of the hydraulic press worktable is lowered and the entire worktable is sunk.
During the sinking process, the horizontal position of the mold remains unchanged, so that the steel plate is forced upwards to complete the shape drawing. The first drawing depth must be 80% or more of the total design depth.
Take down the initially formed basin and clean the workbench contaminated with the drawing oil.
The water sink after first drawing process will be sent to the cleaning station to peel off the film, and the residual drawing oil will be washed away to prepare for the annealing process.
Why annealing is necessary?
In the case of the drawing process, if the design depth of the sink is less than 160 mm, the desired depth can be achieved in one drawing.
When the depth of the water sink reaches 180mm-250mm, the probability of rupture of the stainless steel sheet by one drawing is greatly improved.
In order to meet the deep demand, annealing treatment and secondary drawing are required at this time.
The annealing treatment restores the activity of the stainless steel sheet which is highly strained by first-time drawing.
The annealing line itself is a high temperature line of about 20 meters long, and the temperature in the furnace is about 1150℃. The entrances and exits are on both sides, and the water sink is transported by a cable type crane lock or a conveyor belt. 30 pieces of water sinks can be processed at the same time in the line.
The annealed companion also includes demagnetizing. That is, eliminate the magnetic properties of stainless steel due to drawing.
Many sink plants do not have an annealing line themselves, but are outsourced to a third-party annealing shop for annealing.
Sometimes the sink plant uses an annealing furnace to achieve the replacement function according to its own needs.
#9. Second-time Drawing
The annealed water sink was through the drawing process a second time using a mold and a hydraulic press.
The second drawing must be fully stretched to the design depth.
After the second-time drawing of the water sink, there is no longer a shrinkage in the edge of the steel sheet. At this time, it is necessary to remove the excess trim from the finished product.
When cutting the edge, it is necessary to reserve the installation position of the stiffener rib above counter basin.
#11. Hole Punching
The drainage holes and the overflow holes are successively punched on the special mold by the punching machine.
Depending on the actual conditions of the sheet and punching equipment, it may be necessary to remove the burrs at the cut-off plane.
If it is a twin-tank roll welding basin/bottom welding basin, it needs to be welded to the upper plate of the watering plate after hole punching.
Roll welding is usually done by CNC welding, but it is also hand soldered by workers.
If it is a butt welding basin, it is necessary to perform butt welding of the basins on both sides.
A distinguishing feature of the butt welding basin is that there is a weld line between the two sides of the basin.
#13. Spot Welding
Welding of the ribs/hooks using a laser spot welder.
Depending on the device settings, each spot weld produces about three solder joints. Strip stiffener ribs require spot welding multiple times at different locations.
Glue is also used to bond the ribs/hooks depending on the requirements of the ordering party.
#14. Surface Treatment
- sanding (drawing)
- sandblasting (electrolysis)
- polishing (mirror)
Here, the sanding (drawing) process is specifically introduced.
Grinding is divided into three or four steps depending on the difference between the basin and the equipment.
The first part need to be polished is the bottom of the sink.
The grinding of the sink wall is then carried out.
Depending on the degree of automation of the sink plant, this following process sometimes exists to alleviate the requirement for the worker’s grinding skills.
Since the two adjacent faces are polished in different directions, chaotic lines are likely to occur at the edges where the textures meet.
A grinding wheel will be used to remove disorderly lines between the two vertical faces.
The upper plate is grind at the end of the grinding process to remove the welding spot, weld lines and surface flaws visible in the basin.
#15. Hole Opening
Excavation of the hole of the water faucet at the position according to the requirements of the order.
This process has a high degree of freedom, may be skipped directly according to the order requirements, or may occur before any process after welding.
The marking of the stainless steel sink mainly includes the following two methods: laser mark and embossing mark.
Push the sink completely into the bayonet position to ensure consistent print position.
Laser etching is used for marking.
In addition to fully automated laser marking, there is also a lower cost manual positioning laser marking (as shown on the following picture).
Place the semi-permeable membrane with the brand logo on the designated position of the marking and use a handheld laser emitter to illuminate at zero distance.
The laser passes through the light transmissive portion of the semipermeable membrane to achieve cauterization on the stainless steel surface.
The minor damage that occurs at each production stage, which still has commercial value, is sent to the repair site by hand before the spraying process.
#18. Spray Coating
Perform a bottom spray treatment.
There are three purposes for spraying:
- To make the thin and light sink gain weight;
- Cover the burning traces caused by annealing;
- To prevent condensation in the kitchen environment.
Actually, the spraying carried out by most sink manufacturers is only painting. In fact, it does not have anti-condensation function.
In addition to spraying, pickling can also remove burning spots caused by annealing.
#19. Cleaning & Packing
The cleaning work includes removing the residual drawing oil, removing the dirt and the spray in the front of the sink, removing the scraps of grinding wheel and stainless steel, removing fingerprints and other dust.
The sink can be packaged in brackets, large boxes, or even retail packaging according to the requirement of different customers.
Finally, put the product in the warehouse and wait for the delivered location specified by the buyer.