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Proper Torque Control for RF/COAX & SMA Connectors

SMA Torque Tools

   
Joint relaxation occurs to some extent in all fastened joints and is caused by the surfaces of the part embedding or by "soft parts", such as gaskets, collapsing under the clamping force. For correctly designed joints, relaxation is small and can be virtually ignored. However, relaxation is a particular problem on joints where gaskets, or parts such as spring washers, are present. On these joints it can take a long time before the joint settles and results in a reduction in clamping until the condition has stabilized. 
The physical phenomenon for the collapse of material is called "creep." All material creep to some extent. For example, glass is a liquid and creeps over time. That is why an old glass window may show "waves" at the bottom of the window.
The creep is most obvious and dramatic right after the force has been applied. In many tightening applications the majority of the creep, reducing the clamp load (and sometimes static torque), appears within the first 10-50 milliseconds

 

Mountz, Inc. offers a couple of torque tool options for ensuring the correct torque is applied for applications that involve RF/COAX & SMA Connectors. The correct tightening of COAX and SMA Connectors used in RF cabling applications is essential to ensure optimum performance. This is particularly important in high frequency applications using stainless steel or beryllium-copper bodies.

The general thought is that hand tightening of RF/COAX cables or SMA connectors are acceptable. It is not. Over-torque can crush the insulation, as well as the center contacts and ground mating surfaces. Any change to those can alter the impedance and VSWR signal.  Under torque can be just as bad if an air-gap is left in the insulator, or the center pin or ground-mating surface isn't fully engaged. 

If manufacturers and operators want to "do it right," then they need to find a torque tool that's designed specifically to prevent over-tightening for RF/COAX and SMA connectors.  The torque tool should be designed to limit the amount of torque applied to an assembly or fastening application and minimize the shock to assembly.

Mountz Inc. offers TB Break-Over wrenches and Hand Torque Screwdrivers that can be used for accurately tightening COAX and SMA connectors and ensuring that over tightening doesn't occur. The TB is commonly used with an open-ended spanner, while the pre-set torque screwdriver with a Crowsfoot Spanner Head enables vertical access in places where conventional torque tools cannot be used. The Spanners are available to suit the standard sizes of all the major connector manufacturers.

For applications that require a torque tool to be used for round knurled or non-knurled nuts where gripping to tighten might damage the surface, Mountz features a new wrench with a roller grip head. The head is designed with soft grip material that won't damage plastic caps, RF/COAX and SMA connectors or tubes. The spring loaded design allows the head to fit snuggly around the cap, tube or connector. A medical manufacture of syringes uses this torque wrench to tighten the end cap of their syringes to a specified torque without damaging the cap.

Mountz offers a wide range of torque wrenches. Conventional wrenches click when torque is reached, dial wrenches accurately measure torque and cam and break-over style wrenches prevent overtorquing.