How much do you know about screws (2)

Screw Structure Classification

1. Slotted ordinary screws are mostly used for the connection of smaller parts. It has pan head screws, cylindrical head screws, countersunk head screws and countersunk head screws. Pan-head screws and cylindrical-head screws have high nail head strength, and they are connected to ordinary components; the head of the semi-sunk head screw is arc-shaped, and its top is slightly exposed after installation, and it is beautiful and smooth. It is generally used for instruments or precision Mechanically; countersunk screws are used where the nail head is not allowed to be exposed.

2. The head of the hexagon socket head and hexagon socket head screw can be embedded in the component, and a larger torque can be applied, and the connection strength is higher, which can replace the hexagonal bolt. It is often used in joints that require a compact structure and a smooth appearance.

3. Cross-recessed ordinary screws have similar functions to slotted ordinary screws and can be replaced with each other, but the groove shape of cross-recessed ordinary screws has higher strength, is not easy to twist and bald, and has a more beautiful appearance. When in use, it must be loaded and unloaded with the matching cross-shaped screwdriver.

4. The lifting ring screw is a kind of hardware fitting for load-bearing during installation and transportation. When in use, the screws must be screwed in to the position where the supporting surface fits closely. It is not allowed to use tools to tighten it, and no load perpendicular to the plane of the lifting ring is allowed to act on it.

5. The locking screw is used to fix the relative position of the parts. The locking screw is screwed into the screw hole of the part to be tightened, and its end is pressed against the surface of another part, that is, the former part is fixed on the latter part. Locking screws are usually made of steel or stainless steel, and their end shapes are conical, concave, flat, cylindrical, and stepped. The end of the tapered end or concave end locking screw directly tightens the parts, generally used for places that are not often disassembled after installation; the end of the flat end locking screw is smooth, does not damage the surface of the part after tightening, and is used for joints that need to be frequently adjusted , can only transmit a small load; the cylindrical end locking screw is used in the fixed position that needs to be adjusted frequently, it can withstand large loads, but the anti-loosening performance is poor, and anti-loosening measures must be taken when fixing; the stepped arbor locking screw is suitable For parts with thicker walls.

6. Self-tapping screws, when self-tapping screws are used on the connected parts, the connected parts may not be threaded in advance. When connecting, use the screw to tap the thread directly. It is often used to join thin metal plates. There are two types of self-tapping screws with tapered ends and self-tapping screws with flat ends.

7. Self-tapping locking screws Self-tapping locking screws not only have self-tapping effect, but also have low screw-in torque and high locking performance. Its thread is a triangular cross-section, and the surface of the screw is hardened to have high hardness. Its thread specifications are M2~M12.

Screw common problems and solutions

1. The head of the screw is deformed and the head is crooked. The possible reasons are poor installation of the first punch of the screw mold and improper adjustment of the machine.

2. The head of the screw is not rounded. The reason is that the choice of the first punch of the screw mold is improper or the first punch is not full enough.

3. The screws have burrs or burrs. The reason is that the first punch is poorly formed, mainly caused by the excessive gap between the punch rod and the die hole or the punch rod being too short.

4. The screw head is cracked, and the screw head has cracks. The reason may be that there is a problem with the quality of the screw wire itself, so the screw wire must be inspected by the quality department before it is headed, and it must be tapped with water. Especially for stainless steel screw wire, it is necessary to check which is stainless steel 201 and which is stainless steel 304. It is also possible that the first die is used incorrectly (such as the first die of the hexagonal silk head for the pan head), and the viscosity of the lubricating oil is invalid.