- Embedding method of nuts in Plastic parts
Hot melt nut
Hot melt embedding is the most common and common way of embedding. Generally, hot melt machines and manual soldering irons are used to embed nails.
Injection molded nut
Injection molding embedding generally has strict requirements on the hole diameter of the nut, and the hole diameter is controlled within 0.05mm. Because the product is fixed with a Molding Pin and placed in the injection molding mold, the nut hole diameter must be controlled by the size of the PIN pin of the injection molding machine.
Ultrasonic nut
Ultrasonic embedding is a method that uses ultrasonic vibration to cause friction between the nut and the surface of the workpiece and the internal molecules, thereby increasing the temperature transmitted to the interface. When the temperature reaches the softening temperature of the workpiece itself, the nut is embedded in the rubber piece. When the vibration stops, the workpiece is cooled and shaped under a certain pressure. (We recommend you to follow the “Mechanical Engineer” official account to grasp practical knowledge and industry information as soon as possible)
- Plastic hole design and nut selection
Figure 1 Basic dimensions of nuts
Figure 2 Basic plastic dimensions
Note: D: Nut outer diameter L: Nut length d: Nut base C: Plastic hole diameter W: Plastic hole wall thickness Y: Plastic hole depth
- Selection parameters of plastic holes and nuts
- Dimension d is the nut base, also known as the guide positioning part, which matches the plastic part C before being embedded. Therefore, part d at the bottom of the nut is smaller than the inner diameter C of the plastic BOSS to facilitate positioning; 2. Dimension D is the outer diameter of the nut, which matches the inner diameter C of the plastic BOSS. Generally, the inner diameter of the mobile phone nut plastic is about 0.25-0.3mm smaller than the outer diameter of the nut;
- The influence of the opening size the plastic BOSS hole size
If there is no problem with the selection of plastic and nut, the standard state of the nut after being embedded in the plastic is as shown in Figure (1)
If: the nut size is too small and the plastic BOSS hole is too large, the nut cannot absorb the glue after being embedded in the plastic, resulting in insufficient torsional force.
If: the nut size is too large and the BOSS hole is too small, glue overflow or bursting will occur as shown in Figure (3)
If there are no problems with the nut size and plastic size, but there are still abnormal phenomena, we usually consider improving it through some optimization designs;
Since the depth of the BOSS hole is shallow, for example, if you choose a nut with double twill, the embossing step will be shorter when the nut size ratio is adjusted, especially the embossing. After such a nut is embedded in plastic, there will be too little plastic on the embossing surface, which will cause insufficient torsional tension. Therefore, it is generally recommended that the BOSS hole depth be set to more than 2.5mm, and the nut size and length is generally recommended to be more than 2.0mm.
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