How To Handle Seizure Issues Of Non-Standard Screws And Precautions For Material Selection Of Special Screws

Non-standard screws refer to customized screws that do not comply with national standards (such as GB), international standards (such as ISO), or industry standards, and are designed with specific specifications (e.g., special threads, irregular heads, non-standard lengths/diameters) to meet the needs of particular equipment. These screws are often adapted to special working conditions, and their quality mainly depends on core indicators such as material selection, manufacturing process, dimensional accuracy, mechanical properties, and surface quality. They are widely used in fields such as environmental protection machinery, electronic equipment, food processing machinery, and medical devices. When seizure (galling) occurs with non-standard screws, the following handling and prevention methods can be adopted:

1. Handling and Prevention Measures for Seizure of Non-Standard Screws

Accurate selection and adaptation: Before use, confirm that the screw's material, thread specifications (thread form, pitch), and accuracy grade are compatible with the connected components. Avoid seizure caused by material incompatibility (e.g., mixing stainless steel with carbon steel) or excessive thread fit tightness (interference fit). Meanwhile, select screws with corrosion-resistant or high-temperature-resistant materials according to working conditions (such as corrosive, high-temperature, or vibrating environments).

Ensure thread cleanliness and quality: Rough, burrs, damage on the screw thread, or contaminants such as welding slag, metal debris, or oil trapped between threads can easily lead to seizure. Clean the thread surface before use, repair or replace screws with damaged threads; if necessary, apply lubrication to the threads (e.g., anti-seize compound, molybdenum disulfide lubricant) to reduce friction.

Control tightening parameters: Excessive tightening force can cause thread plastic deformation, and excessively fast tightening speed can generate frictional heat leading to metal adhesion (seizure). Use a torque wrench to fasten according to the design-recommended torque value, follow the "step-by-step tightening" principle (pre-tighten first, then gradually increase force), and avoid one-time brute-force tightening. Meanwhile, control the tightening speed, generally not exceeding 30r/min.

Ensure tightening coaxiality: During tightening, ensure the nut is aligned coaxially with the bolt's centerline to avoid skewing, which can cause uneven stress concentration on one side of the thread and local high-pressure adhesion. Use guiding tools or positioning fixtures to ensure installation accuracy, and prohibit inclined force application.

Reasonable selection of anti-loosening accessories: When installing screws, use flat washers matching the screw material (to increase stress-bearing area and distribute pressure), and avoid using spring washers (spring washers have limited anti-loosening effect and may exacerbate uneven thread stress). For vibrating or seizure-prone working conditions, use anti-loosening washers, disc springs, or nylon lock nuts instead of ordinary spring washers.

Post-seizure handling: If the screw has seized, do not forcefully twist it (which may cause thread breakage). First, inject rust remover or lubricant into the thread gap, let it stand for 10-30 minutes to soften the adhered part; then slowly loosen it with reverse torque. If necessary, use tools such as an angle grinder to cut the nut along the side and remove it to avoid damaging the threaded hole of the connected component.

2. Precautions for Material Selection of Special Screws

Material selection for flat washers: For ordinary flat washers without mechanical performance requirements, qualified leftover materials (such as Q235A) can be used on the premise of consistent material and no quality defects (e.g., cracks, rust). If there is a mild hardness requirement, thicker Q235A sheet metal can be used and processed by calendering and quenching to achieve the specified hardness. For scenarios with large loads or corrosion requirements, washers matching the screw material should be selected (e.g., stainless steel washers for stainless steel screws) to avoid electrochemical corrosion.

Material selection for rivets and pins: The materials of rivets and pins should be selected according to connection strength, working conditions, and assembly requirements, not necessarily the same as screws. Rivets are often made of low-carbon steel (such as 1010, 1015) due to their good plasticity and ease of deformation for riveting. Some rivets require a hardness lower than HRB60 (Rockwell Hardness B scale), while the hardness of normalized materials is usually between HRB70-80. Therefore, such rivets need to be annealed to reduce hardness and improve plasticity to meet riveting requirements. Pins need to bear shear force and are often made of medium-carbon steel (such as 45# steel) or alloy steel (such as 40Cr), which are quenched and tempered to improve strength and toughness.

Material selection for special screws used in welding: Arc welding and gas welding have no special restrictions on screw materials, but it is necessary to ensure good welding compatibility between the screw material and the connected component to avoid cracks after welding. If spot welding is used, low-carbon steel materials (such as Q235, 1010) must be selected due to their excellent weldability and stable weld joint strength. If it is necessary to improve the overall strength after welding, low-carbon high-manganese steel (such as 10Mn2, Q345B) can be used, which has good weldability and higher mechanical strength than ordinary low-carbon steel.

Standardized process for material substitution: If the material specified by the customer is not in stock or is difficult to purchase in the market, first thoroughly understand the screw's application scenario and mechanical performance requirements (such as tensile strength, corrosion resistance, temperature range) from the customer. Then, under the premise of meeting all performance indicators, propose a material substitution plan and submit a written application, attaching the performance verification report of the substitute material (such as material certificate, mechanical test data). Mass production can only be carried out after the customer's written confirmation to avoid equipment failures caused by improper material substitution.

By standardizing the handling and prevention process of seizure issues and combining scientific material selection for special screws, the reliability, stability, and service life of non-standard screws can be significantly improved. This avoids equipment malfunctions caused by seizure or improper material adaptation and ensures the safe operation of related equipment.