[Technical class] Points for attention in the Makeup function and structure design of the BB cream base
Ordinary bb cream base is usually assembled from several parts: cover, bottom, rear button + pin, powder tray, and front button snap.
The design of the front button structure: the basic type adopts the cover and bottom buckle design, and there are also designs that use the front button piece (the front button piece with different structures and actions).
The design of the rear button + pin structure: The rear button structure can be roughly divided into metal pins, plastic pins, one-piece plastic pins, and pin-free designs.
There are many types of metal pins, such as solid nails, hollow coil nails, and tooth nails. Different types of pins can be selected according to different material and functional requirements to reduce cost and achieve the most suitable function.
The opening and positioning angle of the cover is mainly based on the consumer's usage habits. The pinhole needs to be a guide section to prevent the pinhole from breaking during nailing. In order to avoid misplacement of the nails as much as possible, all compacts should be double nailed.
(1) Fitting clearance
The gap between the rear button of the cover (A in the figure below) is 0.15mm for the unpainted side, and 0.25mm if it is to be painted.
After the cover is opened and closed, the rotation gap at the button (B and C in the figure below) should not be less than 0.3mm
At the hook of the front button of the cover opening and closing (D and E in the figure below), the gap between the front button and the inner seat or bottom during rotation should not be less than 0.3mm.
The gap between the bottom surface and the bottom of the button before turning over should not be less than 0.35mm.
The matching gap between the inner seat and the bottom, whether it is snap-fit or supersonic, both sides need to retain the gap.
(2) Component strength
Back button strength: the thickness of the back button pinhole wall of the cover/bottom, for materials with good impact (such as ABS, PCTA, etc.), the material thickness is not less than 1.5mm; for brittle materials (ABS, PS, PMMA, etc.), not less than 1.8 mm. If the product is to be electroplated or masked, the thickness of the pinhole needs to be reserved.
Front button strength: For materials with good impact, the thickness of the front button should not be less than 0.8mm; if it is a brittle material, it should not be less than 1mm. In addition to the parting surface and the splicing surface, the product should be rounded as much as possible, which will not only improve the strength of the parts but also facilitate filling.
(3) Plate hole design
The shape and depth of the pan hole must be larger than the nominal size of the powder pan. Generally, the size of the pan hole is about 0.5mm larger than that of the pan, and the rounded corners of the powder pan hole must be smaller than that of the powder pan.
This is because the powder pan will expand after being pressed, so the hole of the pan is larger than the size of the powder pan.
The dimensional tolerance of the powder tray hole is generally 0.13mm.
(4) Lens design
All lenses must be lower than the edge of the cover. Use hot-melt adhesive to glue the mirror, and the depth of the frame should be at least 0.5mm deeper than the thickness of the mirror; if you use double-sided tape, it should be at least 0.2mm deep; if the frame needs to be painted, it needs to be added 0.2mm.
There is a gap of about 0.2mm between the mirror and the mirror frame. The size of the mirror is rounded up.
The gap between the frame surface and the inner seat surface should be at least 0.4mm.
(5) Gate location of injection molded parts
The gate of the compact part is generally at the back button or the center gate.
The back button gate is generally a side gate and a latent gate. The latent gate has the advantages of not affecting the appearance of the product and no post-processing, but it is not suitable for strong and tough materials (such as PCTA, etc.).
The center gate needs to make a pit at the gate, the size and depth are generally 0.5mm~0.7mm (depending on the wall thickness of the gate), and the diameter is generally 3mm~5mm (try to take the largest value). This has two advantages: one is that there is no need to cut the gate burr, and the other is that it can buffer the injection pressure, and will not cause stress concentration at the gate to affect the quality of the finished product.
