In this article, we will discuss a case for door handle casting parts finishing. These door handle parts are made from zinc alloy which is the common material for casting parts. Zinc material is a lightweight material with specific gravity 1.73.
1. Parts condition before finishing
Material: Zinc alloy
Appearance: The parts surface is dark and dull before tumbling. The surface seems covered with an oxidation layer which generates from the casting process. No big burr or scale is observed with the naked eye.
Shape: The door handle parts have a simple geometry. So we can choose the smaller size media that able to enter the edge.
Process before finishing: Die Casting
Process after finishing: Electro Plating
2. Parts Surface requirement
- Smoothing parts surface without damage parts
- Remove the black layer generate from the die casting process
- Reduce surface roughness prepare for plating process
3. How we process the parts
|Machine||Vibratory Finishing Machine (without separation)||Vibratory dryer|
|Tumbling Speed||50/60HZ (full speed)||50/60HZ (full speed)|
|Chip Type||Plastic Media TET/Cone Light cutting||Corn Cob tumbling media|
|Media to Parts Ratio||4:1||8:1|
|Compound Type||LC-13, PH 8 (mild grinding compound)|
|Water Level||Just cover the mass|
|Tumble Time||1 Hour||30 Mins|
|Notes—||Manually take the parts out of the machine, and rinse them||Absorb water content and clean part surface|
4. Parts condition before and after polishing
After vibratory tumbling process, you can see black layer removed. The zinc handle surface formed a matte texture.
You can see in detail that the oxidation layer at edge and step is removed. This is because we choose a mixture of cone shape and Tetrahedron shape plastic media.
Since zinc is a softer metal, and we did not see big burr and scale, therefore light cutting plastic media is used for the process.
5. Other considerations
Zinc is very easy to corrosion when exposed to water and air at the same time. Therefore we need to clean and dry the parts as soon as the wet tumbling process finished.
During the separation step, manually take out the parts can prevent parts on parts impingement. Especially the zinc parts are softer and delicate.
We can also use barrel tumbling machine process, but that takes a longer time. Generally, the barrel tumbling process creates a smoother surface with the same media.
Some manufacturers developed a dry tumbling media to eliminate water process. So there will be no corrosion problem. This process is carried out with a specially designed vibratory finishing machine and a dust collector. However, parts surface is better with the wet process.
In this article, we show an example of zinc door handle parts smoothing with plastic media. This process can be used also for belt buckles, sliders, key chains, and souvenir that made from zinc.
Firstly, we discuss the parts condition before finishing. Secondly, we show parts surface requirement from clients. Thirdly, we show the process that we did for the zinc parts in details. Later, we compare the surface before and after mass finishing. At last, we discuss other possibilities for zinc parts deburring and polishing.