In the manufacturing industry, screws are crucial components that affect product quality and durability. With a wide variety of types and standards, appropriate selection can be said to be a fundamental element in product development.

However, selecting screws requires specialized knowledge, which can be difficult for beginners. This guide covers everything from the basics to advanced applications of screws, supporting the selection of optimal screws for various purposes. Through this article, readers will gain comprehensive knowledge about screws and improve the accuracy of screw selection in product development.

Screws come in a wide variety of types depending on their shape and application. Appropriate screw selection is essential for ensuring product performance and safety. Below, we explain representative screw types and their respective features and applications.

These are relatively small in diameter and often used in combination with nuts or female threads. They are suitable for fixing relatively small parts in precision equipment and furniture. Head shapes are also diverse, including flat head, round head, and truss head, allowing for selection according to application.

Characterized by their hexagonal heads, bolts are used in combination with nuts and are widely employed for fixing relatively large parts and structures in machinery and building structures. They can withstand high tightening torque, making them suitable for locations requiring strong connections.

Tapping screws can be screwed directly into material without a pilot hole, and were developed to improve work efficiency. They are effective for relatively soft materials such as wood and thin metal sheets. Since the threads cut into the material as they advance, they provide a firm fixation.

Wood screws are designed specifically for wood, with pointed tips and threads shaped to bite easily into wood. They are utilized in various woodworking situations, such as furniture assembly and DIY woodworking.

SEMS screws, which have a washer integrated, eliminate the need to prepare a washer separately, contributing to improved work efficiency. Additionally, since the washer cannot detach, they also have the effect of preventing parts from being lost.

Many screws specialized for specific applications also exist. For example, trapezoidal screws and ball screws are used in mechanisms that convert rotational motion into linear motion. These screws are selected when precise positioning or the transmission of large forces is required.

The choice of screw material is very important depending on the usage environment and required performance. Below, we explain representative screw materials and their respective characteristics and applications.

Steel materials are the most common screw material, and their greatest advantage is their high cost-performance. Hardness varies with carbon content, and high-carbon steel boasts high strength, but also has the disadvantage of being prone to rust.

Stainless steel has excellent corrosion resistance and is suitable for use in environments prone to rust, such as around water or outdoors. It is also widely adopted in fields requiring hygiene, such as medical equipment and food machinery.

Brass is an alloy of copper and zinc, possessing excellent electrical conductivity, making it used for screws in electrical components and electronic devices. It is also used for decorative purposes due to its aesthetic appeal.

Aluminum is lightweight yet strong, making it highly valued in fields requiring weight reduction, such as aircraft and automobiles. It also has environmental benefits such as being easy to recycle.

Titanium is a material with many excellent properties, including high strength, lightweight, corrosion resistance, and heat resistance. It is used in environments requiring extremely high performance, such as aerospace and medical fields.

Resin screws are lightweight and non-magnetic, making them used in specific applications such as electronic devices and medical equipment. Some types also have excellent insulation and chemical resistance.

Screw selection requires careful consideration as it directly affects product performance, safety, and durability. Below, we explain the main points when choosing screws.

The length and thickness of a screw are determined by the thickness and material of the component to be fixed. Generally, the screw length should be such that it can penetrate the component and screw in a few more millimeters. The thickness is selected based on the strength required for fixation and the material of the component. Thicker screws are suitable for hard materials, while thinner screws may be sufficient for soft materials.

The head shape of a screw is selected based on its application and design. Flat heads are designed to be flush with the component surface, suitable for areas where aesthetics are important or where protrusion would be inconvenient. Pan heads are the most common shape and can be used for a wide range of applications. Truss heads have a large head and a wide bearing surface, making them suitable for fixing thin or soft components.

Pitch refers to the coarseness of the screw threads, and there are two types: coarse pitch and fine pitch. Coarse pitch is used for general applications, while fine pitch is used when resistance to loosening is required, or for precision equipment where finer adjustments are needed.

The material of a screw is selected based on the usage environment and required performance. It is important to choose the appropriate material, such as stainless steel when corrosion resistance is required, titanium when strength and lightweight are required, or steel materials when cost performance is required.

Screw selection in mechanical design is a crucial factor that affects product performance and safety. Below, we explain the key points for screw selection in mechanical design.

In screw selection, work efficiency during the assembly process must also be considered. It is important to design the placement of screws in easily accessible positions, allowing workers to tighten them without undue effort. Especially for mass-produced products, shortening assembly time leads to cost reduction.

Screw fastening methods include through bolts and tapped bolts. Through bolts are used in combination with nuts, allowing for strong fastening. Tapped bolts are screwed directly into threaded holes, fixing components together. Each fastening method has its advantages and disadvantages, so it is necessary to select the appropriate method according to the product design and application.

When using tapped bolts, the design of clearance holes is important. A clearance hole is a hole through which a bolt passes, and it must be slightly larger than the nominal diameter of the bolt. Without an appropriate clearance hole, the bolt cannot be inserted smoothly, leading to fastening defects.

The strength class of a bolt is indicated by numbers engraved on the bolt head. These numbers represent the tensile strength and yield point of the bolt, which are crucial information for ensuring product safety. Designers must calculate the load applied to the product and select bolts with the appropriate strength class.

Screw standards include ISO (International Organization for Standardization) and JIS (Japanese Industrial Standards). These standards define the dimensions, materials, strength, etc., of screws, ensuring interchangeability and quality. Designers must select screws based on these standards and clearly specify them in the product design drawings.

Screw strength and standards are extremely important for ensuring product safety and reliability. Below, we explain the key points regarding screw strength and standards.

The strength class of a screw is determined by its material and heat treatment, and is expressed by its tensile strength and yield point. Tensile strength is the maximum tensile force a screw can withstand before breaking, and the yield point is the tensile force at which the screw begins to deform permanently. The strength class is indicated by numbers engraved on the screw head; for example, “8.8” means a tensile strength of 800 N/mm² and a yield point of 640 N/mm².

The safety factor is a coefficient in product design that indicates how much the allowable stress of the screw actually used exceeds the assumed maximum load. By appropriately setting the safety factor, product safety can be ensured, and unexpected accidents can be prevented. The safety factor is determined by considering the product’s usage conditions, material, type of load, etc.

Screw standards include ISO (International Organization for Standardization) and JIS (Japanese Industrial Standards). These standards define the dimensions, materials, strength, test methods, etc., in detail, ensuring interchangeability and quality. By selecting screws based on these standards, designers can confidently develop products, and users can safely use them.

The selection of screw material is a crucial factor affecting product performance and durability. Choosing the appropriate material can extend product life and reduce the risk of failure.

The material of a screw is selected based on the usage environment and the object. For example, if used outdoors or in humid environments, stainless steel, which has excellent corrosion resistance, is suitable. On the other hand, aluminum or titanium are options for products requiring lightweighting. Also, if electrical conductivity is required, brass is suitable. Thus, it is important to consider the usage environment and product requirements to select the optimal material.

Screw surface treatment is performed to improve corrosion resistance, wear resistance, aesthetics, etc. Electroplating is a common method that forms a thin film of metal on the screw surface to enhance corrosion resistance. Various types of electroplating exist, such as zinc plating, nickel plating, and chrome plating.

Electroless plating is a method that forms a thin film of metal through a chemical reaction without using electricity. Since a uniform film thickness can be obtained, it is suitable for screws with complex shapes. Examples include electroless nickel plating and electroless copper plating.

In addition to these surface treatments, various other surface treatments exist, such as heat treatment to improve screw strength and heat resistance, and lubrication treatment to reduce friction.

Screw selection is a crucial factor that affects product quality, safety, and durability. To choose the appropriate screw, the following points must be considered:

Beginners should refer to these points to acquire basic knowledge for screw selection. If you are unsure about screw selection, consulting an expert or manufacturer is also effective.

Conclusion

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